To the Graduate Council: I am submitting herewith a thesis written by Bennett S. Fowler entitled “Process Development for Aluminum 6061 RAM2 for Wire Arc Additive Manufacturing.” I have examined the final paper copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Mechanical Engineering. Dr. Jared, Major Professor We have read this thesis and recommend its acceptance: Dr. Bradley Jared Dr. Chad Duty Dr. Brett Compton Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School To the Graduate Council: I am submitting herewith a thesis written by Bennett S. Fowler entitled “Process Development for Aluminum 6061 RAM2 for Wire Arc Additive Manufacturing.” I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Mechanical Engineering. Dr. Jared, Major Professor We have read this thesis and recommend its acceptance: Dr. Bradley Jared Dr. Chad Duty Dr. Brett Compton Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official student records.) Process Development for Aluminum 6061 RAM2 for Wire Arc Additive Manufacturing A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Bennett S. Fowler August 2025 © by Bennett S. Fowler, 2025 All Rights Reserved. ii Acknowledgements I would like to thank my wife and mother for their love and support over the last 5 years of my schooling. Along with being there for me over the last couple of busy months of working and writing. I would like to thank Dr.Jared for offering me the opportunity to work as an undergrad in the MAPL lab and then offering me this role as a graduate researcher. Also for the guidance and support when I needed assistance. I have gained a lot of knowledge and real experience in my time working in the lab. I would also like to thank all of the other graduate students who have assisted me along the way. Thank you to Devon Goodspeed for helping me learn the ins and outs of welding and talking parameters when I was not sure what to try next. I would also like to thank Hannah Sims and Jonathan Pegues for thier technical support throughout this project along with Sandia National Laboratories for their financial sponsorship of my research. I would also like to thank Fortius Metals and Nick Squanda for their quick response when we needed assistnace and initial help when starting the project. Thank you to my committee members Dr. Compton and Dr. Duty for taking time to review and advise on this thesis. iii ”You can’t wake up if you don’t fall asleep” - Wes Anderson, Asteroid City iv Abstract Wire arc additive manufacturing (WAAM) is an advanced manufacturing alternative to subtractive manufacturing techniques which allows companies to save time, money, and material. Aluminum 6061 is a widely used engineering material due to its strength and corrosion resistance. It is prone to hot cracking, however, when deposited through a WAAM process. Fortius Metals developed a 6061 reactive additive manufacturing (RAM) 2 wire that provides an inoculant-based solution to mitigate hot cracking and material deposition. Work will be described which has explored the WAAM processes for Al 6061 RAM2 wire. Deposition was tested with different weave types, heat inputs, and travel speeds. One hundred percent argon was used for shielding gas. Then those materials were compared to as-printed material tensile values provided by Fortius Metals. Tensile testing was completed and used ASTM E8 standards for samples. The process started with base layer testing, then moved to build layers. The build layers were used to create single-pass walls and a diamond geometry to gather material for testing. Brief multi-pass experimentation was completed successfully with a proposed larger geometry to be built in the future. Mechanical properties testing proved the material had a ultimate tensile strength of 145.4 MPa and a yield strength of 79.7 MPa. Both values are within 10 MPa of the values provided by Fortius. Porosity was a prevalent issue in the resulting deposits and tested pieces. Different steps were taken to mitigate the issues. Parameter changes, trailing gas and baking the wire were all tested but proved to make no difference in the porosity levels. New wire provided by Fortius eliminated most of the porosity. Final parameters chosen for the v base layer was a wire feed speed of 350 in/min, a 10 in/min travel speed, a two mm triangle weave and a pulse welding process. The build layer parameters were a wire feed speed of 260 in/min, a travel speed of 12 in/min, a 2.5 mm triangle weave using a CMT process. These parameters allowed for successful wall and part printing. Future work is to complete a large multi-pass geometry of a power-T and to extract more tensile bars and samples for mechanical and microstructural testing. vi Table of Contents 1 Introduction 1 2 Background 3 2.1 Wire Arc Additive Manufacturing (WAAM) . . . . . . . . . . . . . . 3 2.2 Aluminum 6061 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Previous Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Experimental Methods 9 3.1 WAAM Development Cell . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1.1 KUKA KR-6 Robotic Manipulator . . . . . . . . . . . . . . . 9 3.1.2 Fronius Welding Torch . . . . . . . . . . . . . . . . . . . . . . 12 3.1.3 Path Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.4 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2 Process Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2.1 Wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2.2 Build Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2.3 Heat Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2.4 Weaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2.5 Contact-Tip-to-Workpiece Distance . . . . . . . . . . . . . . . 25 3.2.6 Shielding Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.2.7 Interpass Temperature . . . . . . . . . . . . . . . . . . . . . . 27 3.3 Process Development . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 vii 3.3.1 Base Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.3.2 Build Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 3.3.3 Single-Pass Walls . . . . . . . . . . . . . . . . . . . . . . . . . 32 3.3.4 Multi-Pass Walls . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.4 Material Characterization . . . . . . . . . . . . . . . . . . . . . . . . 37 3.4.1 Material Porosity . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.4.2 Tensile Testing . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4 Experimental Results 45 4.1 Base Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.2 Build Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 4.3 Single-Pass Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 4.3.1 Diamond Builds . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.3.2 Tensile Testing . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.4 Porosity Reduction Methods . . . . . . . . . . . . . . . . . . . . . . . 70 4.4.1 Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.4.2 Parameter Experimentation . . . . . . . . . . . . . . . . . . . 78 4.5 Multi-Pass Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 5 Conclusions 107 Bibliography 109 Appendix 114 A All Completed Experiments 114 B EDS Results 116 B.1 EDS Results - WE25060401 Samples . . . . . . . . . . . . . . . . . . 116 B.2 EDS Results - WE25060501 Samples . . . . . . . . . . . . . . . . . . 119 Vita 122 viii List of Tables 3.1 Al 6061 RAM2 wire composition before and after deposition compared to Al 6061. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.1 WAAM Process Parameters . . . . . . . . . . . . . . . . . . . . . . . 51 4.2 Tested bead parameters for experiments and dimensions with Al 6061 RAM2 wire, WE24071801. . . . . . . . . . . . . . . . . . . . . . . . . 52 4.3 Trial Results for Weave Dimensions . . . . . . . . . . . . . . . . . . . 55 4.4 Successful diamond process parameters and CTWD measurements per layer, WE24101001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.5 Tensile strength results from successful flat dog bone testing. . . . . . 73 4.6 WE24101001 Reduced Composition - High Magnification . . . . . . . 80 4.7 Parameters for all porosity reduction tests. . . . . . . . . . . . . . . . 100 A.1 All experiments conducted in this research labeled by experiment number, material, diameters, step of process, and purpose. . . . . . . 115 B.1 Elemental composition from EDS analysis, WE25060401 . . . . . . . 116 B.2 Elemental composition from EDS analysis, WE25060501. . . . . . . . 119 ix List of Figures 2.1 As built, large scale WAAM part (Simunovic et al., 2020). . . . . . . 4 3.1 WAAM development cell. . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2 KUKA KR-6 Robot . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3 Kuka robot controller pendant . . . . . . . . . . . . . . . . . . . . . . 13 3.4 Fronius welding torch head . . . . . . . . . . . . . . . . . . . . . . . . 14 3.5 Fronius pendant interface. . . . . . . . . . . . . . . . . . . . . . . . . 15 3.6 Fronius wire roller and housing. . . . . . . . . . . . . . . . . . . . . . 17 3.7 Wire cleaner and silica in housing to reduce contamination. . . . . . . 18 3.8 Octopuz software interface. . . . . . . . . . . . . . . . . . . . . . . . . 18 3.9 Miller Lem Box for data acquisition. . . . . . . . . . . . . . . . . . . 20 3.10 Aluminum 6061 RAM2 roll of wire from Fortius. . . . . . . . . . . . . 20 3.11 Build plate preparation station with the angle grinder and wire brush. 22 3.12 KUKA robot pre-configured weave types, KUKA Roboter GmbH (2015) 24 3.13 Definition of the contact tip to workpiece distance (CTWD) for deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.14 Gas nozzle on torch head. . . . . . . . . . . . . . . . . . . . . . . . . 28 3.15 Dual laser temperature gun being pointed at base of wall to check interpass temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.16 The 2 beads on the left show a dull color and poor chevron definition while the third bead on the right has a shiny sheen and consistent chevron definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 x 3.17 Base layer experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.18 Build layer experiments. . . . . . . . . . . . . . . . . . . . . . . . . . 34 3.19 Single-pass wall experiments. . . . . . . . . . . . . . . . . . . . . . . 36 3.20 Diamond model showing measurements. . . . . . . . . . . . . . . . . 36 3.21 Overlapping bead schematic. Müller and Hensel (2023). . . . . . . . 38 3.22 Drawing showing calculation for bead overlap for beads with width = 9.5mm and height = 2.6 mm. . . . . . . . . . . . . . . . . . . . . . . 38 3.23 Bandsaw utilized for sample cross-sectioning. . . . . . . . . . . . . . . 39 3.24 Keyence VR-5200 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.25 Tensile Testing Components . . . . . . . . . . . . . . . . . . . . . . . 42 3.26 ASTM E8 round tensile bar drawing (ASTM International, 2021). . . 43 3.27 Diamond geometry layout for round tensile bars. . . . . . . . . . . . . 43 3.28 ASTM E8 subsize specimen flat bar (ASTM International, 2021). . . 44 4.1 Al 5356 base layer parameter trials with bead 10 highlighted as the chosen parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 4.2 Al 6061 RAM2 base layer parameter trials. . . . . . . . . . . . . . . . 48 4.3 Chosen base layer bead. . . . . . . . . . . . . . . . . . . . . . . . . . 48 4.4 3D base layer bead scan. . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.5 Tie in of base layer bead, both left and right are base parameters. . . 50 4.6 5356 Base layer deposits ranging from 200 J/mm to 300 J/mm. . . . 52 4.7 Experiment WE24071801, 2 layer trials testing build layer parameters. 53 4.8 Chosen build layer parameters beads 1 and 2. . . . . . . . . . . . . . 53 4.9 Top view of single wall trials with different weave widths from 4.3 showing skinniest width. . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.10 Keyence scan of 2 mm sing-pass wall. . . . . . . . . . . . . . . . . . . 56 4.11 Failed diamond build due to incorrect CTWD, WE24100701. . . . . . 58 4.12 Successful build after corrections were made to CTWD, WE24101001. 60 4.13 Successful corners completed in Experiment WE24101001. . . . . . . 61 xi 4.14 Experiment WE24101601, 2nd successful diamond build. . . . . . . . 61 4.15 Experiment WE24101801, 3rd successful diamond build. . . . . . . . 62 4.16 Current and Voltage plots for layer 21 before and after CTWD adjustment from 3mm to 2mm. . . . . . . . . . . . . . . . . . . . . . 63 4.17 Average heat input per layer for the diamond builds. . . . . . . . . . 64 4.18 Round tensile testing sample from diamond WE24101001. 1.6 inches tall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4.19 Round tensile bar from diamond WE24101001 in clamp in MTS load frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 4.20 Round tensile bar broken after testing. . . . . . . . . . . . . . . . . . 68 4.21 Diamond build, WE24101001 wall 2 stress strain curves. . . . . . . . 69 4.22 Diamond build, WE24101001 Wall 1 stress strain curves. . . . . . . . 69 4.23 New flat dog bone beside the round tensile bar. . . . . . . . . . . . . 71 4.24 New flat dog bone inside the load frame grips. . . . . . . . . . . . . . 72 4.25 Stress strain curves, flat dog bones from WE24101601 wall 3. . . . . . 73 4.26 Stress concentrations on dog bone because of water jet, WE24101601. 74 4.27 Stress strain curves, flat dog bones from WE24101801 wall 1. . . . . . 75 4.28 Stress strain curves, flat dog bones from WE24101801 wall 3. . . . . . 75 4.29 Stress strain curves, flat dog bones from WE24101801 wall 4. . . . . . 76 4.30 Helios 5 Hydra CX scanning electron microscope. . . . . . . . . . . . 77 4.31 High magnification scan of porosity in diamond build sample, WE24101001. 79 4.32 Silicon overlay, diamond build, WE24101001 high magnification. . . . 79 4.33 Low magnification scan WE24101001. . . . . . . . . . . . . . . . . . . 81 4.34 Silicon overlay, diamond build, WE24101001 low magnification. . . . 81 4.35 Example of porosity experiment walls with cut out portions where samples were extracted for sanding and imaging. . . . . . . . . . . . . 82 4.36 Exploration of weave impact on deposited porosity. . . . . . . . . . . 84 4.37 Pulsed differing weave experiment porosity images, WE25052901 . . . 85 xii 4.38 Diamond shown with travel direction when torch was pushing (clean, right side) and pulling (sooty, left side) the melt pool. . . . . . . . . . 86 4.39 Tilted torch head in pushing direction. . . . . . . . . . . . . . . . . . 87 4.40 Shiny, clean sheen of bead deposited with pushing torch angle. . . . . 88 4.41 Porosity images for travel speed experiment, all pulse and 2.5 mm triangle weave, WE25060401. . . . . . . . . . . . . . . . . . . . . . . 89 4.42 Synergic line change experiment porosity images, WE25061201. . . . 91 4.43 Taller and skinnier bead geometry. . . . . . . . . . . . . . . . . . . . 92 4.44 Trailing gas setup utilizing old torch nozzles. . . . . . . . . . . . . . . 93 4.45 Porosity images, wire modification tests. All completed with WFS = 260 in/min, TS = 10 in/min, 2.5 mm triangle weave, WE25062301. . 94 4.46 New wire experiments porosity scans. . . . . . . . . . . . . . . . . . . 96 4.47 Dull colored deposits most likely because of too high of a heat input. 97 4.48 New wire test with with limited porosity with parameters of WFS = 360 in/min and TS = 12 in/min, CMT, 2.5 mm weave, WE25070702. 98 4.49 Successful wall build with desirable deposit color and chevron definition. 99 4.50 3 bead wide multi-pass wall experiment, showing limited voids and porosity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.51 Sketch of 30% bead overlap with chosen parameters. . . . . . . . . . . 102 4.52 Multi-pass wall flat top, layer 9. . . . . . . . . . . . . . . . . . . . . . 103 4.53 Multi-pass wall fusion between beads, top view. . . . . . . . . . . . . 104 4.54 Power T top view. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 4.55 Power T isometric view. . . . . . . . . . . . . . . . . . . . . . . . . . 106 B.1 SEM image WE25060401. . . . . . . . . . . . . . . . . . . . . . . . . 117 B.2 Aluminum EDS results, WE25060401. . . . . . . . . . . . . . . . . . 117 B.3 Magnesium EDS results, WE25060401. . . . . . . . . . . . . . . . . . 118 B.4 Silicon EDS results, WE25060401. . . . . . . . . . . . . . . . . . . . . 118 B.5 SEM image WE25060501. . . . . . . . . . . . . . . . . . . . . . . . . 120 xiii B.6 Aluminum EDS results, WE25060501. . . . . . . . . . . . . . . . . . 120 B.7 Magnesium EDS results, WE25060501. . . . . . . . . . . . . . . . . . 121 B.8 Silicon EDS results, WE25060501. . . . . . . . . . . . . . . . . . . . . 121 xiv Nomenclature η Process Efficiency I Welding current (A) Q Heat Input (J/mm) TS Travel Speed (in/min) V Arc Voltage (V) xv Chapter 1 Introduction Additive manufacturing (AM) is an alternative to traditional subtractive manufac- turing, allowing for less wasted material, complex geometries, and faster production times. Metal AM is completed layer-by layer using wire or powder, Herzog et al. (2016), Çam (2022). One form of additive manufacturing is wire arc additive manufacturing (WAAM). WAAM is a form of directed energy deposition (DED) additive manufacturing. Gas Metal Arc Welding (GMAW), also known as metal inert gas welding (MIG), is used to deposit layers of a metal onto a substrate. WAAM has revolutionized part manufacturing and has in turn led to a significant amount of research to be attempted in the space of materials, monitoring, and design for WAAM. A variety of materials have been shown to be useful in this type of additive process, including stainless steel alloys, some aluminum series, and different bi-metallic materials Singh and Khanna (2021). WAAM is a lower-cost option and a simpler process compared to other metal AM technologies. The process utilizes a robotic manipulator, a welding torch, and a wire feedstock. WAAM allows for fast prints that can be printed to near-net shape. These parts can then be quickly machined to final specifications. WAAM allows for larger geometries and offers a higher deposition rate. That is one reason companies are so interested in what WAAM has to offer. Manufacturers already rely heavily 1 on robots, and welding is also widely used in these facilities. So, they have the capability to adopt WAAM as a process if they can prove that it works for their parts and materials. Their lead times for the production of parts can be dropped, resulting in cost savings and higher profits. A goal of this research is to prove that WAAM can be effectively applied to Aluminum 6061 (Al 6061). 6061 is never used as a filler material due to hot cracking. Other aluminum filler wires such as 5356 or 4043 alloys have to be used to join 6061 together Armao (2015). 6061 is a widely used material though in automotive, aerospace, and structural applications. This makes it a desirable material to be additively manufactured. To achieve this, Fortius Metals has created a new wire to combat the issues when welding the material. The new aluminum 6061 Reactive Additive Manufacturing (RAM) 2 wire is enhanced with inoculant-based solutions to mitigate the thermal issues. The goal of this work is to develop parameters when printing with this 6061 RAM2 wire and compare mechanical properties of the resulting prints to the expected as-printed values from Fortius. Another key goal is microstructural characterization to understand the resulting material. Experiments were completed in a way to build the process from the bottom up. Starting with the base layer of the bead and extending to multi-pass walls. 2 Chapter 2 Background 2.1 Wire Arc Additive Manufacturing (WAAM) WAAM is an additive manufacturing process that enables the rapid production of near-net shape parts, Rodrigues et al. (2019). It is a layer-by-layer process that involves a substrate material and a welding wire feedstock. A six-degree-of-freedom robotic manipulator is commonly used, equipped with a GMAW or MIG welding torch as the end effector. MIG welding works by creating an electric arc between a wire electrode and a substrate, the wire feedstock then melts to form the deposit. The robot provides the movement to create the path. The process is repeated until the near-net shape is completed. The robotic manipulator allows for complex shapes to be made and for path planning to be created. Additional components in a typical WAAM setup are the weld power supply, air ventilation, and gas lines that provide the shielding gas. Figure 2.1 shows an example of a large WAAM part printed by Oak Ridge National Laboratory that took 70 hours. The large part demonstrates the capabilities of WAAM, which have been made possible through extensive process development. 3 Figure 2.1: As built, large scale WAAM part (Simunovic et al., 2020). 4 2.2 Aluminum 6061 Aluminum 6061 is part of the 6000 series of aluminum alloys and contains magnesium and silicon as its primary alloying elements. The material is known for its excellent corrosion resistance and strength, Torbati-Sarraf et al. (2020). These factors make it a strong candidate for use in automotive and aerospace applications. Both need the corrosion resistance that the material provides. Aluminum 6061 is commonly heat treated using a T6 tempering process to enhance its tensile and yield strengths, and hardness. Normal Al 6061 is typically forged and wrought then tempered with a T6 treatment. However, the material used in this research will remain in the as printed state after the WAAM process. Fortius Metals supplied the wire for this project, and the AL 6061 reactive additive manufacturing (RAM) wire is one of multiple specialty materials that Fortius have developed for AM processes Fortius Metals, Inc. (2024). The Al 6061 RAM2 wire differs in composition from Al 6061 which will be detailed in section 3.2.1. There are added elements in the RAM2 wire to help mitigate hot cracking and solidification issues when welding wrought 6061, Redstone Manufacturing (2023). Another common issue restricting the welding of 6061 aluminum alloys is its reactivity with oxygen which produces porosity during deposition, Thapliyal (2019), Herzog et al. (2016). Other filler wires such as 4043 and 5356 typically must be used when welding, 6061 Redstone Manufacturing (2023). In contrast, the 6061 RAM2 wire used in this study can be welded directly onto a 6061 substrate without the need for dissimilar filler materials. 2.3 Previous Research Several researchers have explored the development of weldable or printable aluminum 6061 feedstocks. Most approaches rely on modified versions of 6061 or the additions of alloying elements. Research completed by (Doumenc et al., 2022) shows their success with WAAM with an aluminum 6061 alloy with iron-rich intermetallic compounds. 5 Their study demonstrated the ability to produce defect free thin-walled WAAM prints in two orientations. Their two print orientations were alternating travel direction for each layer while depositing. The other was repeating the same travel direction for each layer. They reported tensile stresses up to 130 MPa in the as-built sections. While they noted slight difference in the microstructure between the two building strategies, hardness values remained similar. A similar study by Chi (Chi et al., 2023) achieved high-quality printing of Al 6061 with nanotreated wires. The added TiC nanoparticles were there “to enhance the alloy’s manufacturability and resultant properties.” (Chi et al., 2023). Porosity levels were low in the resulting materials and crack free. Yield stresses from 89-94 MPa were achieved with ultimate tensile strengths up to 190 MPA. The aluminum alloy 5356 has been shown to have better mechanical and microstructure properties, than conventional 5356 casting alloys, after being deposited using WAAM cold metal transfer (CMT) process Su et al. (2019a), Gierth et al. (2020). The research was completed by testing different parameter sets and then doing tensile and hardness testing. Su et al. (2019a) reports ultimate tensile strength values of 255+5 MPa and yield strength of 128+10 MPa. Gierth et al. (2020) reports ultimate tensile strength values of 294.5 MPa horizontally and 292.3 MPa vertically. These results are compared to the conventional 5356 casting alloys that have ultimate tensile strength of 202 MPa and a yield strength of 87 MPa, Su et al. (2019b). To determine the microstructure details Su utilized optical micro-graphs, X- ray diffraction, and scanning electron microscopy (SEM). The microstructure results showed pores and cracks in the inter layer boundary with pores < 33.5 µm. Another study Wieczorowski et al. (2023) with 5356 wire showed that quicker deposition travel speeds and longer cooling times reduce the diameter of internal pores, specifically the total pore volume. But then in testing they proved that there was no relation between the measured ultimate tensile strength and yield strength to the measured porosity. Most of these studies have been completed using a (CMT) welding process for the aluminum alloys. Cong et al. (2015) claims though that CMT is not suitable for 6 AM processes with Al-6.3% Cu alloy due to the large amount of gas pores that build up. They claim that CMT pulse advanced (CMT-PADV) is the only way the gas pores can be eliminated. He shows this tested with many varying travel speeds in CMT where porosity was prevalent and CPT-PADV. CMT-PADV proved to be the most suitable process eliminating porosity because of its low heat input, fine equiaxed grains, and effective oxide cleaning of the wire. Hauser et al. (2021) has shown that porosity in Al 4043 increases with increasing gas flow velocity. Forced convection causes rapid solidification which is not ideal for the process. Allowing the melt pool to remain liquid for a longer period allows for gaseous pores to escape before solidification. Fu et al. (2021) showed that hot-wire arc additive manufacturing processes can allow for less porosity in the resulting material. The research was completed with Al 2024 wire, a gas tungsten arc welding (GTAW) system, and a hot-wire auxiliary device. Hydrogen contaminants on the wire surface are believed to be a main cause of porosity in WAAM aluminum alloys. Hydrogen contaminants entering the liquid environment of the weld causes porosity because the the hydrogen exceeds the solubility of the solid aluminum alloy. Heat resistance allowed for the hydrogen contaminants on the wire to be removed to decrease the porosity amount. Laser Powder Bed Fusion (L-PBF) is another metal AM process but it utilizes a powder feedstock instead of wire. Mehta et al. (2021) showed that there were issues printing unmodified Al 6061 due to excessive porosity and solidification cracking in L- PBF. They tested a 6061 alloy with 1% wt addition of zirconium (Zr) which produced as-deposited material with nearly full density and without solidification cracking. Resulting mechanical properties where improved over as-cast Al 6061. L-PBF was used in another study using Al 6061 without any additions and showed that print bed heating up to 500◦ can reduce solidification cracking to create crack free components. Uddin et al. (2018). They also reported ultimate tensile strength and yield strength results of 130 MPa and 60 MPa with this material which is comparable to wrought 7 AA6061 values. They did report a decrease in the elongation at the breaking point though compared to the wrought material. 8 Chapter 3 Experimental Methods 3.1 WAAM Development Cell The research described in this thesis was performed on the WAAM development cell in the Manufacturing Automation and Processes Lab (MAPL) at the University of Tennessee. The cell utilizes a KUKA KR-6 robotic manipulator and a Fronius welding torch to perform wire-arc based deposition. Octopuz software is used for robot path planning and torch control. Data acquisition is available on the cell to monitor and record robot motion, welding torch performance and various process conditions. Figure 3.1 shows the robot, torch head, and the welding table where all experiments take place. The Lincoln Electric air ventilation fume extractor system is also visible which extracts welding fumes and helps ensure a safe operating environment for users. 3.1.1 KUKA KR-6 Robotic Manipulator The KUKA KR-6 is a six degree of freedom robotic manipulator that allows WAAM processes to be completed with precision and repeatability. The robot provides a 6 kg load capacity and a 1.6 m maximum reach. A final goal of this research is to produce a part on the order of 0.5 m3 which is well within the range. The robot can be seen in figure 3.2. The KUKA smartPAD pendant provides the operator 9 Figure 3.1: WAAM development cell. 10 Figure 3.2: KUKA KR-6 Robot 11 interface for controlling the robot and for manual programming of simple, point-to- point trajectory paths, figure 3.3. On the pendant there is a 6-D mouse and buttons enabling manual control of the robot’s motion in all six axes. The KUKA utilizes KUKA robot language (KRL) code to program its movements. KUKA Arctech is a software package that allows for WAAM control to be added to the KRL. It facilitates communication between the robot and the Fronius welding system, allowing programming of welding jobs and weave patterns in the same code KUKA Roboter GmbH (2015). 3.1.2 Fronius Welding Torch Metal deposition was performed using a Fronius cold metal transfer (CMT) 4000 Advanced series torch head and power supply, figure 3.4. It can operate in modes using standard MIG, CMT, pulse, or some combination of the three. Fronius invented the CMT process which coordinates controlled transfer of molten metal droplets with wire feeding. CMT leads to less spatter and lower heat inputs during deposition, Lekkala and Prasad (2025), (Ain et al., 2025). CMT is desirable for aluminum alloys because of the decreased amount of heat input which allows for less thermal distortion, Ain et al. (2025). The Fronius pendant, figure 3.5, enables selection of the wire feed speed (WFS) which determines the resultant current and voltage values based on the chosen synergic lines. Raising the WFS increases the current and voltage for a higher heat input and a lower WFS decreases the heat input. Synergic lines are pre- programmed settings of welding parameters that are stored on the Fronius pendant. Synergic lines are selected based on what filler wire is being used, type of shielding gas, wire diameter, and what welding mode is selected. Since 6061 is traditionally not a filler wire there are no synergic lines for 6000 series aluminum on this Fronius torch so deposition was explored with synergic lines for Al 5356 and Al 5183 wire. If the synergic line does not fit the material well, the resulting deposit could be much 12 Figure 3.3: Kuka robot controller pendant 13 Figure 3.4: Fronius welding torch head 14 Figure 3.5: Fronius pendant interface. 15 colder or hotter than expected or desired. During operation, the pendant shows torch current and voltage in real time. The Fronius wire roller is seen in figure 3.6. Due to tendency for porosity to form during arc welding, a silica gel packet was added inside the wire roller housing to reduce moisture collection on the wire. Similarly, an abrasive cleaning pad was wrapped around the wire, figure 3.7, was added to remove contaminants and oxides prior to wire entering the wire delivery of the torch. 3.1.3 Path Planning Path planning can be accomplished manually on the Kuka pendant for quick deposit tests. But for builds with many layers or complex geometries the path planning is performed using Octopuz software (OCTOPUZ Inc., 2025). Octopuz allows for WAAM robot paths to be made by programming points and combining control of the robot movements and control of the arc. Weave options, subsection 3.2.4 are available as is the ability to choose what Fronius job number is called when depositing. The software also automatically programs the lead-in and approach movements for the robot before the arc is started and after it ends. Base coordinate frames are created by users with the KUKA pendant and then related to Octopuz by entering the robot’s parent position values at the origin of the base which are given to the user on the pendant when creating their new base frame. Using the set origin from the base frame, precise robot positions can be programmed in x,y,z coordinates in millimeters. These steps allow for the user to visualize in the software and know where the movements will occur in the WAAM cell. A screenshot of the Octopuz interface and controls is shown in figure 3.8. The screenshot shows the paths on the left hand side and the points and speeds in the bottom left for the selected path 21. The right side of the screen shows the position of the torch and the orientation. 16 Figure 3.6: Fronius wire roller and housing. 17 Figure 3.7: Wire cleaner and silica in housing to reduce contamination. Figure 3.8: Octopuz software interface. 18 3.1.4 Data Acquisition The last element of the WAAM development cell is its data acquisition and process monitoring capabilities. In the cell, there are multiple systems that all run together through a custom-made Python script. These items include a Miller LEM box, figure 3.9, which is used to collect real-time welding parameters such as current and voltage. These values can then be used to calculate deposition heat inputs and to monitor arc stability. 3.2 Process Parameters 3.2.1 Wire Developing parameters for the aluminum 6061 RAM2 wire produced by Fortius Metals is the main goal of this research. The wire diameter for the wire used in the majority of the depositions is 0.035 inch, figure 3.10. As mentioned before conventional Al 6061, is difficult to deposit and Fortius’ wire addresses these issues. Alloy inoculants that have been added to the wire allow the material to have improved thermal stability, high thermal conductivity, and increased strength at low and high temperatures Fedotowsky and Williams (2023). These changes allows for the material to not suffer from hot cracking. Table 3.1 shows the elemental composition of the wire. These results are from NSL Analytical and were found by utilizing inductively coupled plasma mass spectrometry (ICP-MS) and inductively couple plasma (ICP) testing. Magnesium and silicon are the highest alloy elements present in Al 6061. The table also shows there is a slight decrease in oxygen in the deposited material. The deposited material sample was from a single pass wall, section 4.3. Briefly for the first base layer test a 0.035 in Al 5356 wire was ran as the Fortius 6061 RAM2 wire was not available. Fortius deemed the material processed in a similar way. 19 Figure 3.9: Miller Lem Box for data acquisition. Figure 3.10: Aluminum 6061 RAM2 roll of wire from Fortius. 20 Table 3.1: Al 6061 RAM2 wire composition before and after deposition compared to Al 6061. Element Wire Deposited Material 6061 Standard Ag 0.001% 0.001% - Al 95.2% 95.7% 95.8–98.6% C 0.20% 0.17% - Cr 0.11% 0.11% 0.04–0.35% Cu 0.24% 0.25% 0.15–0.40% Fe 0.13% 0.14% ≤ 0.70% Mg 0.92% 0.90% 0.80–1.2% Mn 0.003% 0.004% ≤ 0.15% O 0.055% 0.041% - Si 0.58% 0.61% 0.40–0.80% Zn 0.004% 0.011% ≤ 0.25% Zr 0.001% 0.001% ≤ 0.15% 3.2.2 Build Plates The build plates used in development were all 6 in by 12 in and half an inch thick Al 6061 T6 tempered plates. A critical preparation step for the WAAM process is to ensure that the build plate is clean and properly prepared for welding, figure 3.11. Wire brushing with an angle grinder removes oxides, oils and other contaminants from the initial deposition surface. The surface is then wiped down with acetone to remove any other contaminants. Such preparation is necessary to ensure proper adhesion and prevent the introduction of impurities into the deposited material. 3.2.3 Heat Input Heat input is a key parameter in WAAM that affects the quality, penetration, and microstructure of a deposit. Too much heat can cause for a dull sheen on the deposit surface, and bead shapes that are too flat with ill-defined edges and chevron patterns. Not enough heat input can lead to a deposit that suffers from a lack of penetration or tie-in, and beads that are inconsistent or too narrow. Heat input is primarily determined based on the chosen wire feed speed. Wire feed speed is a measurement of how fast the weld system is feeding the wire into the substrate. Wire feed speed along with travel speed (TS), how fast the robot moves, are the two main factors that 21 Figure 3.11: Build plate preparation station with the angle grinder and wire brush. 22 are varied to increase or decrease heat input (Q) overall, per equation 3.1. The Fronius pendant displays the current (C) and voltage (V ) for a defined wire feed speed. This equation can then be used to find the expected heat input (Q). The efficiency (η) value accounts for the fact that not all of the energy created is transferred to the workpiece or assists in the melting of the wire. The efficiency value is a percentage of how much of the energy is used in the process and it depends on the material deposited. Since this is a new material being used a true efficiency value has not been determined yet, so a value of 1 was used when calculating heat input. Q = V × I × 60× η TS × 25.4 (3.1) The same equation can be used when analyzing the arc voltage and current recorded from the data acquisition system after deposition, mentioned in subsection 3.1.4. 3.2.4 Weaves Weaving is common practice in both manual welding and WAAM to control the melt pool to produce consistency in melt pool shape and manage heat input producing better fusion. The weave length also allows fir different widths of deposits. Manual welders use a wide range of weaving techniques according to their experience and preference to produces the best weld for their material and joint configuration. For this research, the Kuka KR-6 robot and KUKA ArcTech software allows a set of different weaves to be programmed. These choices are triangle, figure 3.12b, trapezoid, figure 3.12c, and spiral, figure 3.12d. Figure 3.12a shows how the weave amplitude and length parameters are defined, KUKA Roboter GmbH (2015), as the length represents the distance of one complete weave cycle and the amplitude represents the deflection from the straight travel centerline. These definitions apply for each type of 23 (a) Length (1) and Amplitude (2) definitions shown on triangle weave (b) Triangle Weave (c) Trapezoidal Weave (d) Spiral Weave Figure 3.12: KUKA robot pre-configured weave types, KUKA Roboter GmbH (2015) 24 weave, but is shown on a triangular weave. Due to prior research projects a triangle weave was chosen to begin and worked well so it was then used for the majority of this research. The triangle weave produced the required bead widths and the consistency. It has also been observed that weaves fend off issues from wire cast or wire bending from the robot or wire feeder rollers. One important detail about weaving is that while the straight-line travel speed remains constant along the deposit length, the torch, melt pool and arc are moving faster than the programmed robot travel speed. When referring to triangular and trapezoidal weave lengths for the rest of this thesis a 2.5 mm weave will represent a 2.5 mm length and a 2.5 mm amplitude. These values are not required to be the same, but in the work performed the length and amplitude were kept the same. Spiral weaves, however, have a restriction that requires the weave length to be double the amplitude. 3.2.5 Contact-Tip-to-Workpiece Distance Contact-tip-to-workpiece distance (CTWD) is an important parameter when deposit- ing metal material in arc-based processes. CTWD is the length from the contact tip of the welding torch to the substrate, figure 3.13 and needs to be established accurately as it is critical to stable material deposition. Layer height also plays a role in this as the CTWD must increase the same as layer height to keep a consistent distance over a build with multiple layers. If the torch contact tip is too close to the substrate and resultant melt pool, then the risk of overheating increases and the contact tip can weld itself to the substrate. If the CTWD is too large, the longer wire length increases the arc resistance resulting in current losses and an inconsistent melt pool and bead deposit. Poor shielding gas coverage also occurs when the torch is further away from the melt pool increasing dispersion of the gas away from the deposition zone where it is desired. There is evidence of both these issues later in figure 4.11. 25 Figure 3.13: Definition of the contact tip to workpiece distance (CTWD) for deposition. 26 For the experiments completed a CTWD of 15 mm was tested to start and eventually moved down to 12 mm. 3.2.6 Shielding Gas Shielding gas is important in wire-arc AM because it allows the melt pool to solidify in an inert atmosphere, eliminating the presence of reactive gases like oxygen and nitrogen. These gases can react with molten elements in the alloys and cause porosity or material contaminants within or onto the deposit. The shielding gas utilized to deposit the aluminum alloys studied here was 100% argon. The gas had a volumetric flow rate of 30 cubic feet per hour. For most of the material deposited there was only one gas nozzle present, figure 3.14. In section 4.4, however, trailing gas was implemented to explore the impact of increasing the dwell time of the solidifying material region under the shielding gas. 3.2.7 Interpass Temperature Interpass temperature is a designated temperature that the deposited material or substrate are allowed to cool to before depositing more material. When work began, Fortius Metals recommended a 200 ◦C interpass temperature with their 0.045” wire, but noted that 80 ◦C was sufficient for a single-wall build. So, the interpass used for this research was 80 ◦C. Interpass temperature was measured using a Southwire 31040S Non-Contact Digital Infrared Thermometer dual laser temperature gun, figure 3.15. Due to emissivity issues on the shiny surfaces of the bead, the temperature was measured at the base of the bead or wall where the soot had made the build plate darker and a more reliable reading could be recorded. Temperatures of 200 ◦C were never reached when measuring interpass during any experiments. 27 Figure 3.14: Gas nozzle on torch head. 28 Figure 3.15: Dual laser temperature gun being pointed at base of wall to check interpass temperature. 29 3.3 Process Development Work is presented and organized around the steps that were taken when developing process parameters for the wire. First, the base layer parameters were developed. Then build layer settings were examined to build ten layer walls and see how the deposits interacted. Next, parameters were tested on a diamond geometry. The next development step was to create parameters for multi-pass builds. The final stage was to build a multi-pass Power T to show the successful parameters. A table showing all of the experiments done and their intent can be found in appendix A. 3.3.1 Base Layer The first building block to a good WAAM part is a solid base layer, i.e., the first layer deposited onto the initial substrate. To begin developing parameters, it is important to find a base layer deposit that introduces enough heat into the build plate or initial substrate that is ”cold”, i.e., near room temperature. The base bead ensures the rest of the material will stay connected to the plate. If these parameters are incorrect this could result in parts that are not stable on the plate. The first step was to test different wire feed speeds and travel speeds to see what parameters gave a result that was able to be built upon. Due to a limited amount of the Al 6061 RAM2 wire, first experiments were tested with Aluminum 5356 and were accomplished with help from classmates∗. According to Fortius Metals this material mimicked the expected behavior of the Al 6061 RAM2 material. The bead’s color, uniform chevron definition, uniform bead shape and consistent tie-in. All of these results will be examined about a deposit when doing these bead test experiments. A good bead will have a shiny sheen for color, too much heat causes a dull sheen. Chevrons are formed by the melt pool movement and show that the arc is stable, bead shape stays consistent, and that the material is not solidifying too fast or slow. These differences can be seen in figure 3.16. Bead width is determined by the chosen weave ∗Steven Willams, Matthew Roach, Caleb Campbell, Dylan Lewis, and Grant Wilmoth 30 Figure 3.16: The 2 beads on the left show a dull color and poor chevron definition while the third bead on the right has a shiny sheen and consistent chevron definition. 31 but the height needs to be fairly consistent over the width to ensure even stacking when more layers are added. A bead that has a considerable peak or tented look is not an ideal top surface, rather a flat top surface is desired. Good tie-in is represented by crisp, straight bead edges that do not spread or bulge along the substrate. Minimal spatter is also a desirable result when looking at deposits. An example of a base layer tests is shown in figure 3.17. These results will be discussed in section 4.1 3.3.2 Build Layer The next step was to develop the parameters to be used in all subsequent layers of the part, i.e., the build layers. These parameters operate at a lower heat input than the base layer since it it will retain its heat from deposition. Once again the second layer needs to have a bead shape where the top is consistent enough for another layer to rest on top. The second layer must also have good tie in with the base layer. With good tie-in, subsequent beads successfully build on top of one another. A potential issue would be running too hot, which can be noticed by inconsistent layer heights or widening bead profiles over time. The goal is to replicate beads on top of one another and preserve a constant width and layer height ensuring the user can replicate layers and builds and be able to control what will be put down and predict deposits for future geometries. The first experiments were simple two layer builds where one layer deposited on the previously selected base layer deposit. Additional layers were then explored to determine parameters that created consistent weaves and preserved the desired part shape. Another aspect of these parameters is how wide and long the weave would be for the deposits. An example of a build layer test is shown in figure 3.18. These results will be discussed in section 4.2. 3.3.3 Single-Pass Walls The next phase involved applying build layer parameters to single-pass wall builds. These builds use a single bead layered multiple times to create the desired geometry. 32 Figure 3.17: Base layer experiments. 33 Figure 3.18: Build layer experiments. 34 The motivation behind these tests is to demonstrate the ability to build to a certain height, complete corners, and see how start and stops affect the build over time. The first single-pass experiments tested in this research will be straight walls, alternating travel direction each layer. Single pass walls allows the build to reach the desired height and see how the beads develop over time. Because of the height gained, the contact-tip-to-workpiece distance, section 3.2.5, can be monitored and refined as the number of layers increases. These tests are also where monitoring the interpass temperature becomes very important, section 3.2.7. Being consistent with interpass is important because welding when too hot or cold will cause shape inconsistencies. A single-pass wall experiment is shown in figure 3.19. After straight walls are completed, single-pass diamond builds were printed. Each wall was 139 mm long with a height goal of 45 mm. Too fit on a build plate the acute angle ends were 250 mm apart and the obtuse angle corners were 120 mm apart. The acute angles were 50 degrees and the obtuse angles were 130 degrees. A modeled diamond with measurements is shown in figure 3.20. A diamond geometry allows for acute and obtuse corners to be tested with the chosen weave and deposition parameters. Material can be built up in these spots because of the extra time spent in the corners when weaving, especially the acute corners. Height build-up in these spots must be monitored and ideally eliminated. Details like corner rounding and speed control can help keep the corners to the correct height to avoid overbuilding and the CTWD becoming too small. The diamond builds also provide enough material to extract tensile bars for mechanical testing and samples for metallography. These results will be discussed in section 4.3. 3.3.4 Multi-Pass Walls The final step in developing parameters to build real parts is multi-pass wall testing. Most large metal structures have features more than a single WAAM bead width and require multiple passes to achieve their desired thickness. Multi-pass development 35 Figure 3.19: Single-pass wall experiments. Figure 3.20: Diamond model showing measurements. 36 is completed by using the bead parameters from single-pass builds and measuring the bead width. That bead width can then be drawn in 2D in a CAD software to determine the required overlap percentage. Overlap needs to be calculated and tested to make sure no voids are formed from being too far apart or build up does not occur from being compressed together. The percentage is representative of the amount by which each successive bead overlaps the previous one. Figure 3.21 shows the overlap distance. Using the CAD sketch in figure 3.22 the area of the beads overlapping at the bottom and the valley area above can be compared. To conserve mass transfer and create a flat surface between beads, these areas should be equal, as a first order estimation, and provide an initial overlap distance to explore. The final overlap is then adjusted and determined by characterizing layer heights and intra-bead porosity. These results will be discussed in section 4.5. 3.4 Material Characterization 3.4.1 Material Porosity One critical issue when welding aluminum is porosity. Porosity was checked quickly by cutting samples, sanding down the surface and then imaging them. A band saw, figure 3.23, was used to quickly cut beads or walls into cross-section samples. The cut face was perpendicular to the print direction of the beads and were sanded and polished to rapidly reveal the absence or presence of large material pores. Sample imaging was performed using a Keyence VR-5200 fringe projection microscope, figure 3.24. While it is primarily used to create precise 3D surface measurements of parts, it was used to stitched 160x magnification images of sample cross-sections. Parameter adjustments were then performed based on the observed level of porosity. The entire process was quick and responsive, able to be create sample images roughly two hours after a print has completed and cooled to a safe handling temperature. 37 Figure 3.21: Overlapping bead schematic. Müller and Hensel (2023). Figure 3.22: Drawing showing calculation for bead overlap for beads with width = 9.5mm and height = 2.6 mm. 38 (a) Bandsaw Side View (b) Bandsaw Front View Figure 3.23: Bandsaw utilized for sample cross-sectioning. 39 Figure 3.24: Keyence VR-5200 40 3.4.2 Tensile Testing WAAM parameters are not productive if they do not provide mechanical properties that meet or exceed mechanical tensile strength values that are expected of the material. Fortius Metals provided as printed values from their work of an ultimate tensile strength of 155 MPa and a yield strength of 75 MPa. For reference 6061-O has values of ultimate tensile strength of 124 MPa and a yield strength of 55 MPa. Thus, material testing was performed on a Material Testing System (MTS) Criterion Model 45 load frame. The load frame is capable of applying 100 kN of force. MTS Vee Wedge grips were specifically bought for these samples with their geometry in mind. The load frame and the grips can be seen in figure 3.25. Initial material testing was performed using the American Society for Testing and Materials (ASTM) E8 round bar specimen 4 specification (ASTM International, 2021), figure 3.26. E8 samples were explored at the request of the project sponsor. Samples were extracted from the completed diamond print, subsection 4.3.1 using a wire electrical discharge machining (EDM) tool. Round bar specimens were then machined to shape in the Manufacturing Core at University of Tennessee’s (MCUT) lab using a CNC lathe. A diagram showing how the samples were cut out of the diamond can be seen in figure 3.27. Seven total samples, four vertical and three horizontal, could be extracted from a five inch long wall from the diamond builds. Section 4.3.2 discusses the results from the round bar tensile testing. There were slipping and end crushing issues with the smaller samples, so the decision was made to change to larger flat, dogbone-shaped tensile bars, figure 3.28. The shape of the dog bone was cut from the wall vertically using an EDM and then sliced horizontally into layers which allowed for 8 samples to be extracted from a single wall. The larger flat geometry allows for a larger gripping space to relieve slipping. 41 (a) MTS Load Frame (b) Vee Wedge Grips for Load Frame Figure 3.25: Tensile Testing Components 42 Figure 3.26: ASTM E8 round tensile bar drawing (ASTM International, 2021). Figure 3.27: Diamond geometry layout for round tensile bars. 43 Figure 3.28: ASTM E8 subsize specimen flat bar (ASTM International, 2021). 44 Chapter 4 Experimental Results 4.1 Base Layer Developing parameters for a quality base layer starts with ensuring that the bead achieves a strong interface, or tie-in, with the substrate. The bead must also have a consistent shape where the sides stay straight and the top does not slope too far side-to-side or from start-to-stop. A good base also must be wide enough to contain the first build layer. Bead color is important as it allows the user to notice if too much heat is being input into the deposit. Another consideration in bead evaluation is uniform chevrons. First experiments were completed using 0.035 in Al 5356 wire since the Fortius material was not originally available, and 5356 was identified by Fortius to process in a similar manner. A 5356 synergic line for 0.045 in wire was used on the Fronius with a pulse process. Figure 4.1 shows the resulting beads from this initial Al 5356 exploration. The beads were all 127 mm long deposits and they started on the right side of the plate. The first bead was based on previous aluminum work with a heat input of 400 J/mm but proved to not have enough heat input shown by the lack of tie-in and the inconsistent shape of the sides of the bead. Changes were then made to increase the 45 Figure 4.1: Al 5356 base layer parameter trials with bead 10 highlighted as the chosen parameters. 46 heat input to create the desired result of a consistent shape with a good color and chevron definition. As the deposits go from bead 1 to 10 they improve with each one with better consistency, shape, and chevron definition. The heat inputs from these beads range from 400-930 J/mm. Bead 10 represents the final parameters chosen because of the sheen of the deposit and the consistent bead width and height. The tie-in was better than the others also. The parameters used for the bead was a wire feed speed of 580 in/min, a travel speed of 10 in/min, and a 2 mm triangle weave length and amplitude resulting of a heat input of 800 J/mm. These parameters were tested from prior aluminum 2319 research. As Fortius reported, Al 5356 material did process like the 6061 RAM2 wire, described below. The base layer experiment for the Al 6061 RAM2 wire was completed next and the resulting bead deposits can be seen in figure 4.2. The experiment started by testing out the parameters previously chosen from bead 10 from the 5356 experiment, figure 4.1. The pulse 5356 synergic line for 0.045 in wire was also used in this experiments. The resulting beads are represented by deposits 1 and 2 on the plate and was deposited with the wire feed speed of 580 in/min, travel speed of 10 in/min, and a 2 mm triangle weave, figure 4.3. When the parameters are selected on the Fronius pendant a current of 180 amps and a voltage of 22.75 V are reported for the pulse process mode. The resulting heat input is around 800 J/mm. The consistent shape and width of bead 1 in figure 4.4 was a factor in these parameters being chosen. The bead had a constant height from front to back also. Figure 4.5 shows the quality tie in of the base parameters. More parameters with similar heat inputs were tested by changing the wire feed speed and travel speed along with no weaves, table 4.1. There were some quality deposits, but their shapes were not as consistent as bead 1. This experiment allowed for these parameters to be selected to be utilized in the build layer step next. These parameters were adjusted later when the diamond builds were completed. The first test was run and the wire liner melted as a result of too much heat being input into the base. The wire feed speed was adjusted to 475 in/min, but the travel speed of 10 in/min and the 2 mm triangle weave remained the same. 47 Figure 4.2: Al 6061 RAM2 base layer parameter trials. Figure 4.3: Chosen base layer bead. 48 Figure 4.4: 3D base layer bead scan. 49 Figure 4.5: Tie in of base layer bead, both left and right are base parameters. 50 Table 4.1: WAAM Process Parameters No. WFS (in/mim) TS (in/min) Weave 1 580 10 2 mm 2 580 10 2 mm 3 580 8 None 4 580 9 None 5 590 10 None 6 600 10 None 7 580 9 None 4.2 Build Layer Build layer parameters are critical to part fabrication since they are used for all subsequent layers after the initial base layer. Thus, depositions were explored to find parameters producing beads that were wide and flat enough to layer on top of one another and yet stably fit on top of the base layer. Once again initial testing was completed with 5356 wire. The tests were not weaved, but heat inputs ranging from 200 J/mm to 300 J/mm were tested in figure 4.6 and a heat input of 250 J/mm proved to be the best deposit. This was chosen because of the shiny sheen of the deposit while the 300 J/mm tests looked dull and too hot. Based on results from the Al 5356 there was a goal of achieving 250 J/mm as the resulting heat input value with the RAM2 wire. So, the first experiment was performed with parameters selected based on a 250 J/mm heat input but a weave was added. A wire feed speed of 240 in/min and a travel speed of 10 in/min with a two mm weave was tested. The other parameters and measurements can be seen in table 4.2 and the resulting beads deposited onto the plate can be seen in figure 4.7. Beads 1 and 2 were the beads with the goals of 250 J/mm and they can be seen in figure 4.8. These beads were successful, displaying acceptable bead geometry and a shiny sheen that was desired. The chevron pattern and shape were consistent which both are needed for repeatability and layers. Beads 3-5 in this experiment included 51 Figure 4.6: 5356 Base layer deposits ranging from 200 J/mm to 300 J/mm. Table 4.2: Tested bead parameters for experiments and dimensions with Al 6061 RAM2 wire, WE24071801. Trial WFS (ipm) Travel Speed (in/min) Heat Input (J/mm) Width (mm) Height of Build Layer (mm) 1 240 10 252 7.0 3.5 2 240 10 252 7.0 3 3 220 8 275 6.75 4 4 220 8 275 10.0 – 5 250 10 270 9.5 – 52 Figure 4.7: Experiment WE24071801, 2 layer trials testing build layer parameters. Figure 4.8: Chosen build layer parameters beads 1 and 2. 53 varying wire feed speeds, travel speeds of 8 in/min, and longer weaves. These beads were also quality deposits, but the sheen was not as good. Beads number 4 and 5 were deposited and then were built upon to test the repeatability of the the 250 J/mm heat input value and to test how different weaves affected bead widths and heights. This included weaves with 4 mm weave length and amplitude along with a deposit that had a 4 mm amplitude and a 2 mm weave length. The longer four mm weave showed a less consistent geometry. 4.3 Single-Pass Walls Demonstrating the fabrication of single-pass walls was the next development step. Using the 250 J/mm heat input goal that was discussed in section 4.2 the goal was to develop the weave parameters and layer height necessary to fabricate walls wide and tall enough to extract 40.6 mm tall round tensile bars. Layer height determines how high the CTWD needs to increase for each layer to remain constant for the entire build. The straight single wall experiment was a eleven layer test that included a base layer that measured 127 mm in length. The experiments allows for layer heights and width to be measured for a taller geometry build after layers have stacked on top of one another. Three walls builds were created in the experiment, one with a triangle two mm weave, length and amplitude. One had a three mm triangle weave and the other tested a four mm weave. Table 4.3 shows the resulting wall widths, wall heights, and layer heights which were measured with calipers. The resulting walls can be seen in figure 4.9. The walls were cut and sampled to check porosity, figure 4.10. The cross-section image shows a lot of porosity, an issue in these builds, discussed in section 4.4, and prevalent in each wall. Even though the tensile bar has a maximum 8 mm diameter, successful extraction required at least 8.5 mm of wall material thickness. All of the walls had an average width that would have been thick enough, but the lower build layers on the wall were 54 Table 4.3: Trial Results for Weave Dimensions Trial Weave (mm) Wall Width (mm) Wall Height (mm) Layer Height (mm) 1 2 10 25.5 2.1 2 3 11 23 1.85 3 4 12 20.75 1.63 Figure 4.9: Top view of single wall trials with different weave widths from 4.3 showing skinniest width. 55 Figure 4.10: Keyence scan of 2 mm sing-pass wall. 56 skinnier than the top shown in figure 4.9. So, to ensure the full wall would have the required thickness the chosen weave length and amplitude for the diamond builds was 2.5 mm, halfway between the 2 mm and 3 mm tests which produced similar results. 4.3.1 Diamond Builds After generating parameters for single-pass walls, a diamond geometry was explored to develop parameters and programming for a closed geometry, for both obtuse and acute corner angle features and for material characterization and tensile testing. Corners are a good test because most geometries require them and they will show issues with parameters quickly by overbuilding issues requiring adjustments to travel speed or wire feed speed. These are issues that would not arise when testing straight walls. The geometry of the diamond was specifically chosen to accommodate the chosen tensile testing geometry, figure 3.26. The target width of the diamond walls was 10 mm with a height of 43 mm. For a layer height around 2 mm, 21 layers were printed including the base. The experiment was to be completed with a CTWD of 15 mm. The first diamond build test was a failed experiment which melted the liner in the torch head during the base layer. This was believed to be a result of an arc on time of close to two minutes when prior tests lasted around 30 seconds. The base layer wire feed speed was then lowered to 475 in/min with a lower heat input of 600 J/mm. For the next experiment the base layer WFS was lowered to 475 in/min to limit the amount of heat that was added into the base plate and the torch. The build experiment, WE24100701, produced a completed diamond geometry, figure 4.11, but part quality was poor due to excessive soot and oxidation of the bead surfaces. After investigation, it was discovered that the torch contact tip to workpiece distance increased with each layer of the build. The layer height was the expected 2 mm but there was an error when programming the path and the layer height was set for 3 mm. Meaning that the CTWD was increasing an extra millimeter each layer 57 Figure 4.11: Failed diamond build due to incorrect CTWD, WE24100701. 58 leading to poor results. Increasing the CTWD increases the arc resistance during deposition, producing arc settings that are no longer optimized from the nominal conditions. Thus, material deposition and melt pool behavior change with each layer, moving further and further away from optimal parameters. Increasing the CTWD also increases the distance from the torch end to the deposition zone, creating a reduction in shielding gas as it disperses away from the torch nozzle outlet. A successful build was achieved after the path plan was remade in Octopuz and the CTWD was reduced to 12 mm from 15 mm and changed the step up after each layer to 2 mm to match the layer height. These changes led to a successful print seen in figure 4.12. The WE24101001 build looked as expected and had the desired geometry showing a good sheen over the layers. It also had the required amount of material in thickness and height for the tensile samples. Figure 4.13 shows the obtuse and acute angles deposited successfully and did not need to be adjusted further. Table 4.4 shows the current, voltage, CTWD, and temperature that were recorded for each layer of the printing process. For this build the CTWD distance was consistent for the layers where the issues began on the first attempt. Once a successful process was demonstrated, two additional diamond builds were printed to provide material for tensile testing, figures 4.14 and 4.15. The successful diamonds had a consistent height of 42.5 mm. Using the data acquisition system in the WAAM cell, section 3.1.4, arc voltage and current were recorded for each of the diamond builds. Figures 4.16a and 4.16b compare simple arc current verses voltage plots on the final, 21st layer for the ”bad” and ”good” quality diamond builds discussed previously, builds WE24100701 and WE24101001 respectively. While work is needed to define evaluation metrics for comparisons, the variation in the poor build quality part is evident due to issues from changes in CTWD across print layers. The results representing the successful experiment look much more defined than the failed experiment. Based on average layer-wise arc voltage and current, average heat inputs were calculated for each layer of the four diamond builds, figure 4.17. While some data was lost during acquisition, 59 Figure 4.12: Successful build after corrections were made to CTWD, WE24101001. 60 Figure 4.13: Successful corners completed in Experiment WE24101001. Figure 4.14: Experiment WE24101601, 2nd successful diamond build. 61 Table 4.4: Successful diamond process parameters and CTWD measurements per layer, WE24101001. Layer Current (A) Voltage (V) CTWD (mm) Temp (°F) Base 148 20.0 12 210 2 70 15.5 12 190 3 70 15.5 11.5 180 4 70 15.5 11.5 180 5 70 15.5 11.0 180 6 70 15.5 11.0 170 7 70 15.5 11.0 180 8 70 15.5 11.5 180 9 70 15.5 11.0 180 10 70 15.5 10.5 180 11 70 15.5 11.0 180 12 70 15.5 11.5 170 13 70 15.5 11.0 175 14 70 15.5 11.75 175 15 70 15.5 12.15 170 16 70 15.5 11.5 170 17 70 15.5 10.0 170 18 70 15.5 11.5 170 19 70 15.5 12.0 170 20 70 15.5 12.25 170 21 70 15.5 12.0 170 Figure 4.15: Experiment WE24101801, 3rd successful diamond build. 62 (a) Voltage and current plot for layer 21 failed build because of CTWD error, WE24100701. (b) Voltage and current plot for layer 21 successful build, WE24101001. Figure 4.16: Current and Voltage plots for layer 21 before and after CTWD adjustment from 3mm to 2mm. 63 Figure 4.17: Average heat input per layer for the diamond builds. 64 the successful prints were similar while also distinctive from the poor quality build, WE24100701. The actual arc values also deviate from the values shown on the Fronius pendant, highlighting the importance and value of capture real-time arc information. Following these experiments the base layer parameters were set at a WFS of 475 in/min, a TS of 10 in/min, and a triangular weave of 2 mm with a heat input of 600 J/mm which is a slightly lower heat input than before. The build layer parameters were set at a WFS of 240 in/min, TS of 10 in/min, and triangular weave of 2.5 mm and a heat input of 250 J/mm. 4.3.2 Tensile Testing An important step in material characterization was to quantify the tensile properties of the as-printed material. Initial testing was performed on the ASTM E8 round bar samples, figure 4.18. Figure 4.19 shows the sample clamped in the system and figure 4.20 shows the sample after it has been tested and broken. According to Fortius Metals, the wire supplier, the expected as-deposited ultimate tensile strength and yield tensile strength are 155.8 MPa and 75.2 MPa respectively Fortius Metals (2024). A total of twelve samples were tested and tensile curves were created from samples extracted from walls 2 and 1 from build WE24101001 respectively, figures 4.21 and 4.22. For example, sample V-1210 is a vertical sample from the furthest left spot on the wall (1), wall two from the diamond (2), from the first diamond WE24101001 (10). So, the first plot shown is wall 2 of the first successful diamond print, figure 4.12. Wall 2 stress-strain curves were fairly consistent with yield strengths at or exceeding the 75.2 MPa expectation. Ultimate strength results were generally also close to the 155.8 MPa expectation. The strain curves, however, are not consistent or continuous, indicative of sample slipping in the MTS wedge grips. The tensile curves for wall 1, exhibited greater scatter and inconsistency in both yield and ultimate strengths, as well as additional indications of slipping. 65 Figure 4.18: Round tensile testing sample from diamond WE24101001. 1.6 inches tall 66 Figure 4.19: Round tensile bar from diamond WE24101001 in clamp in MTS load frame. 67 Figure 4.20: Round tensile bar broken after testing. 68 Figure 4.21: Diamond build, WE24101001 wall 2 stress strain curves. Figure 4.22: Diamond build, WE24101001 Wall 1 stress strain curves. 69 So, a change was made to utilize larger, flat tensile bars which also adhere to ASTM E8 and have been tested for other materials without slipping. The geometry for this new tensile bar can be seen in figure 4.23. The flat bars gave more reliable results because there was no slipping evident in the stress strain curves. This is improved by having more material gripped firmly by the grips, figure 4.24. 30 flat samples were extracted from four walls from the diamond builds. Figure 4.25 shows results of a wall that suffered from issues with the water jet before they were cut with the EDM that caused some stress concentrations near the ends of their gauge length, figure 4.26. They were also slightly thinner than they were supposed to be. The results from this plot shows that they do not match the desired yield and ultimate tensile strengths, but because of the issues extracting the samples these results were deemed unreliable. The next three plots were all from the final diamond build, WE24101801 and they were the correct size with no issues. The plots in figures 4.27, 4.28, and 4.29 all show results that are reaching the desired property values. The yield and ultimate tensile strengths are consistent in all of the plots and there is no slipping evident. The results showed an average ultimate tensile strength of 145.4 MPa and an average yield strength of 79.65 MPa. They were comparable to the values Fortius provided for their as built material of an ultimate tensile strength of 155 MPa and a yield strength of 75.2 MPa. Table 4.5 shows the results of all of the tensile testing completed. These results were also representative of material that was suffering from severe porosity. 4.4 Porosity Reduction Methods A persistent challenge in printing the Al 6061 RAM2 material was the presence of gas porosity in bead deposits. It was observed in every sample and print, prior to and including the diamond walls. EDS was completed on three samples to test what elements could be causing any issues around the pores. Also, focused development activity explored a range of process parameters and conditions aimed at 70 Figure 4.23: New flat dog bone beside the round tensile bar. 71 Figure 4.24: New flat dog bone inside the load frame grips. 72 Figure 4.25: Stress strain curves, flat dog bones from WE24101601 wall 3. Table 4.5: Tensile strength results from successful flat dog bone testing. Sample YS 0.02% (MPa) UTS (MPa) 18101 74.10 141.92 18102 76.20 144.95 18103 84.10 147.89 18104 76.21 130.89 18105 76.64 132.66 18106 82.01 141.65 18107 74.62 146.88 18108 74.45 146.71 18301 76.76 152.25 18302 79.22 150.97 18303 83.95 151.03 18304 87.29 139.58 18305 81.40 149.67 18306 82.01 141.65 18307 84.24 149.72 18308 78.53 146.65 18401 75.21 142.6 18402 78.49 147.89 18403 83.85 150.76 18404 84.96 148.00 18405 85.03 145.80 18406 78.48 152.01 18407 77.42 137.67 18408 76.44 149.34 73 Figure 4.26: Stress concentrations on dog bone because of water jet, WE24101601. 74 Figure 4.27: Stress strain curves, flat dog bones from WE24101801 wall 1. Figure 4.28: Stress strain curves, flat dog bones from WE24101801 wall 3. 75 Figure 4.29: Stress strain curves, flat dog bones from WE24101801 wall 4. either eliminating or diminishing pores found in the as-printed material. Techniques for sample preparation and characterization are described in section 3.4.1. 4.4.1 Composition Continued issues with as-deposited material porosity prompted questions regarding its source. Thus, work was performed to search for anomalous material compositions within printed material with a goal to determine if any elements might be initiating the porosity. Work was performed on a Helios 5 Hydra CX scanning electro microscope, Figure 4.30, from Thermo Scientific located at the Institute for Advanced Materials and Manufacturing (IAMM) at the University of Tennessee. The Helios is capable of imaging metal alloys using energy dispersive spectroscopy (EDS), hence its use. EDS uses an electron beam to excite the atoms in a material, causing them to emit characteristic X-rays. By analyzing these X-rays, EDS can identify the elements present and estimate their relative abundances or weight percentages. Both SEM and EDS were completed on multiple samples to gather images and composition. Three samples were tested. One analyzed sample was extracted from the successful WE24101001 diamond wall to test what had been deposited. Two wall samples from the porosity reduction effort, section 4.4, were also scanned and their results 76 Figure 4.30: Helios 5 Hydra CX scanning electron microscope. 77 can be seen in appendix B.1 and B.2. The SEM image in figure 4.31 is from the first successful diamond build and is about 0.8 millimeters across. The process for polishing aluminum starts by potting the sample in resin. After curing, the sample is sanded on a rotating hand polisher using 400 grit to 1200 grit paper with continuous water flow. Ultrasonic baths are used to ensure grit is removed from the sample surface. Then polishing is performed with 6 µm, 3 µm and 1 µm diamond paste on a felt pad. Since as-deposited aluminum is soft, polishing is difficult and steps must be followed meticulously. Figure 4.31 shows porosity in high magnification and figure 4.32 shows the silicon overlay. Silicon was the only element that had larger clumps in the scan, but there was no elements that stood out when looking for propagation around the pores. This trend was also apparent in the other samples scanned. A low magnification scan was also completed on the same sample, figures 4.33 and 4.34 shows the silicon overlay of that scan. Once again there were no elements that showed clumps around the pores consistently. The composition results from these scans and the wire sample from section 3.2.1 are in table 4.6. 4.4.2 Parameter Experimentation The experiments done were all done by following the single wall geometry of one base layer and ten build layers. Samples were then extracted and sanded and imaged to show porosity of the deposit. An example of these tests can be seen in figure 4.35. The first set of experiments examined the effect of different weave parameters. Printing was performed using the same torch and travel parameters from the diamond builds to print a base layer and ten subsequent build layers. These parameters used CMT with the 5356 synergic line, a 260 in/min wire feed speed, a 10 in/min travel speed and a 12 mm CTWD. The resulting heat input was 285 J/mm. The control bead was deposited using the 2.5 mm triangle bead, figure 4.36a. A straight bead with no weave was created with parameters trying to replicate by Sandia National Laboratory of 360 in/min wire feed speed, 23.6 in/min travel, with no weave, figure 4.36b. A 2.5 78 Figure 4.31: High magnification scan of porosity in diamond build sample, WE24101001. Figure 4.32: Silicon overlay, diamond build, WE24101001 high magnification. 79 Table 4.6: WE24101001 Reduced Composition - High Magnification Element Reduced Composition (%) Mg 1.32 Al 94.07 Si 1.99 Cr 0.12 Mn 0.00 Fe 0.22 Cu 0.30 Zn 0.04 80 Figure 4.33: Low magnification scan WE24101001. Figure 4.34: Silicon overlay, diamond build, WE24101001 low magnification. 81 Figure 4.35: Example of porosity experiment walls with cut out portions where samples were extracted for sanding and imaging. 82 mm amplitude and 5 mm length spiral weave, figure 4.36c, and a 2.5 mm trapezoidal weave, figure 4.36d were also tested. Figure 4.36 clearly details that porosity was prevalent in each of these tests. The next set of experiments examined the use of a pulse deposition process instead of CMT. The intent was to mitigate porosity by introducing a higher, more consistent heat input into the melt pool. The same sample geometry, a base layer with ten build layers, was explored using pulse with trapezoidal, spiral, and triangular weaves. The robot travel speed was maintained at 10 in/min as before. The wire feed speed was increased to 280 in/min for one trapezoidal weave, figure 4.37c. The WFS was then dropped to 200 in/min for the trapezoidal weave, figure 4.37b, a triangle weave, figure 4.37c, and a spiral weave, figure 4.37d. As with the explorations of the weave pattern, use of pulse did not significantly impact pore formation during printing. The Fronius welding torch for some of this work had been oriented at a slight tilt relative to the build plate. As a result, the torches pushes the melt pool when it moves in the negative Y direction on the base and pulls the melt pool when moving in the positive Y direction this can be seen in one of the diamond builds from earlier in figure 4.38. It was observed during development that pushing the melt pool produced cleaner bead surfaces with no soot on them. By adjusting the torch ”push” angle to 5 degrees, as shown in figure 4.39, in each alternating travel direction it was theorized that cleaner beads in each layer could result in a reduction of porosity. While adjusting the pushing angle produced cleaner surfaces figure 4.40, there was no improvement in the material porosity as this change was part of the next set of parameters shown in figure 4.41. The next set of tests explored the impact of robot travel speed. Prior research has shown that aluminum prints better under faster travel speeds Wieczorowski et al. (2023). So, tests were performed using CMT with 10, 15, 20 and 25 in/min travel speeds. To isolate the effect to just travel speed, a consistent heat input of 250 J/mm was targeted for each deposit using the Fronius current and voltage values from the system to calculate the required WFS value. Deposited cross-sections from each test 83 (a) Triangle weave, build WE25051301. (b) Straight deposit, build WE25051401. (c) Spiral weave, build WE25051501. (d) Trapezoidal weave, build WE25051901. Figure 4.36: Exploration of weave impact on deposited porosity. 84 (a) WFS: 280 in/min, TS: 10 in/min, trapezoidal weave, WE25052901. (b) WFS: 200 in/min, TS: 10 in/min, trapezoidal weave, WE25053002. (c) WFS: 200 in/min, TS: 10 in/min, triangle weave, WE25053001. (d) WFS: 200 in/min, TS: 10 in/min, spiral weave, WE25052902. Figure 4.37: Pulsed differing weave experiment porosity images, WE25052901 85 Figure 4.38: Diamond shown with travel direction when torch was pushing (clean, right side) and pulling (sooty, left side) the melt pool. 86 Figure 4.39: Tilted torch head in pushing direction. 87 Figure 4.40: Shiny, clean sheen of bead deposited with pushing torch angle. 88 (a) WFS = 450 in/min, TS = 25 in/min, WE25060401. (b) WFS = 385 in/min, TS = 20 in/min, WE25060402. (c) WFS = 315 in/min, TS = 15 in/min, WE25060403. (d) WFS = 290 in/min, TS = 10 in/min, WE25060501. Figure 4.41: Porosity images for travel speed experiment, all pulse and 2.5 mm triangle weave, WE25060401. 89 condition can be seen in figure 4.41. Once again, these results do not show any improvements in the level of deposited porosity. The next experiment aimed at testing a different synergic line on the Fronius for aluminum 5183, switching from the 5356 line. The first 3 trials were completed using a WFS of 315 in/min and a TS of 23.6 in/min for a heat input of 275 J/mm. The first three beads were run with a CMT plus pulse which combines the processes to created a process that has a balance of penetration and low heat input. The other goal of this experiment was to determine if the triangle weave amplitude or length would influence porosity. Figure 4.42a was run with the 2.5 mm weave that had been utilized previously in the diamond builds. In figure 4.42b the weave length and amplitude was reduced to 1 mm and in figure 4.42c a straight bead was deposited. The last test 4.42d in this experiment was completed with just CMT on the 5183 synergic line with a wire feed speed of 200 in/min. It produced a slightly different build shape resulting in a thinner and taller wall compared to the others it is on the far left in figure 4.43. Figure 4.42, however, again shows that the changes did not impact bead porosity. Lack of shielding gas is commonly associated with bead porosity, Jorge et al. (2023). So gas coverage was explored through the introduction of trailing gas. A control bead deposited with the nominal CMT parameters used for the diamond builds, a WFS of 260 in/min, a TS of 10 in/min, and a triangle weave of 2.5 mm with the 5356 synergic line with a goal heat input of 250 J/mm. Trailing gas was then introduced by attaching two old torch nozzles to the sides of the torch head, figure 4.44. This allowed for solidification to occur in an inert atmosphere for a longer period. Once again, however, no improvement in the bead porosity was observed, figure 4.45. Since porosity had not been improved with a change in torch parameters, robot travel or cover gas, the final factor for consideration was the condition of the Al 6061 RAM2 wire feedstock. So, experiments were performed to reduce or eliminate the source of contaminants onto the wire surface, namely moisture or oxides. 90 (a) WFS: 315 in/min, TS: 23.6 in/min, 2.5 mm trian- gle weave, CMT + pulse, WE25061201. (b) WFS: 315 in/min, TS: 23.6 in/min, 1 mm trian- gle weave, CMT + pulse, WE25061202. (c) WFS: 315 in/min, TS: 23.6 in/min, straight, CMT + pulse, WE25061203. (d) WFS: 200 in/min, TS: 23.6 in/min, straight, CMT, WE25061301. Figure 4.42: Synergic line change experiment porosity images, WE25061201. 91 Figure 4.43: Taller and skinnier bead geometry. 92 Figure 4.44: Trailing gas setup utilizing old torch nozzles. 93 (a) Control bead, WE25062301. (b) Trailing gas setup, WE25062302. (c) Unopened wire, WE25062303. (d) Baked wire, WE25062304. Figure 4.45: Porosity images, wire modification tests. All completed with WFS = 260 in/min, TS = 10 in/min, 2.5 mm triangle weave, WE25062301. 94 Wire cleaning steps were already discussed in section 3.1.2. However, additional steps were explored here, again with baseline deposition parameters WFS of 260 in/min, TS of 10 in/min, and a 2.5 mm triangle weave. The first was to deposit a new roll of wire that had not been removed from the Fortius package. Figure 4.45c illustrates no change in the porosity within the printed material. A final experiment was performed to remove moisture from the wire, from the control bead test, surface or interior by baking the wire for six hours at 100 ◦C. Once again, figure 4.45d shows no change in the porosity content for the deposited material. After exhausting all process, gas and wire options, contact was made with Fortius Metals to seek feedback on the observed porosity issues. They responded quickly and shared that changes had been made to their wire manufacturing process. A new spool of wire was delivered immediately for testing. The new wire was 0.045 in diameter, requiring adjustments to the baseline parameters. Three, ten layer walls were produced as in prior porosity explorations. The base parameters had to be changed because of the new wire and had a new wire feed speed of 350 J/mm with a travel speed of 10 in/min and the same 2 mm triangle weave as before. This resulted in a heat input of 700 J/mm. These parameters were successful and used for the next three tests. The first and second trial were completed with the CMT plus pulse 5183 synergic line. The first wall was deposited with a WFS of 270 in/min, a TS of 18 in/min, and a 2 mm length and amplitude triangle weave with a 300 J/mm heat input. The second trial was completed with a WFS of 330 in/min, a TS of 23 in/min, and a 0.5 mm length and amplitude triangle weave and a heat input of 280 J/mm. These walls showed reduced porosity compared to the previous wire, figure 4.46, but did not solve the issue completely. Both beads had a dull finish and no defined chevrons, figure 4.47, so the heat input was lowered again for the third trial. The last wall utilized a synergic line made for 5356 with 0.045 in wire. The WFS was set at 360 in/min and the TS was 12 in/min with a 2.5 length and amplitude triangle weave. The heat input for these parameters is 250 J/mm. The cross-section image 95 (a) WFS: 270 in/min, TS: 18 in/min, 2 mm triangle weave, CMT + pulse, WE25070301. (b) WFS: 330 in/min, TS: 23 in/min, 0.5 mm triangular weave, CMT + pulse, WE25070701. Figure 4.46: New wire experiments porosity scans. 96 Figure 4.47: Dull colored deposits most likely because of too high of a heat input. from this wall, figure 4.48 shows a drastic decrease in the amount of porosity. The bead also has the desired characteristics of a shiny surface and detailed chevrons, figure 4.49. The experiment was completed with a CTWD of 12 mm. These parameters were the ones selected to move onto the multi-pass portion of the development. The successful wall build had a layer height of 2.6 mm and a width of 9.5 mm. All of the parameters in this section are in table 4.7. 4.5 Multi-Pass Walls Multi-pass wall development is ongoing. The first test performed was a corner bulk wall test exploring how multi-pass beads overlap each other and turn a corner. The chosen tests showed voids or overbuilding to give insight for adjustments to print multiple layers. The experiment described has been completed with the new material and can be seen in figure 4.50. These results were determined after testing a bead overlap percentage of 30%, 40% and 50%, or 7 mm, 6 mm, and 5 mm between beads respectively. 40% and 50% both built up and resulted in a wall that was not level 97 Figure 4.48: New wire test with with limited porosity with parameters of WFS = 360 in/min and TS = 12 in/min, CMT, 2.5 mm weave, WE25070702. 98 Figure 4.49: Successful wall build with desirable deposit color and chevron definition. 99 Table 4.7: Parameters for all porosity reduction tests. 100 Figure 4.50: 3 bead wide multi-pass wall experiment, showing limited voids and porosity. 101 across the top. A bead overlap of 30%, figure 4.51 resulted with the most consistent layer height, but the beads were not tying in together on the sides. With this 7 mm overlap the layer heights were consistent and not over or under building the only issue was tie-in between the beads. To address this a wider weave of 3.5 mm was introduced for the middle bead to allow better tie-in between the beads. The parameters are still not perfected as the middle bead builds higher than the outside beads. To accommodate this, the middle layer is skipped every fifth layer of the build. Figure 4.52 shows layer nine after the middle bead had filled back in to a flat top which was successful in producing a fused result, shown in figure 4.53. These parameters and process will be used to complete the final multi-pass print. The final goal is to print a multi-pass Power T geometry to demonstrate that the chosen parameters are capable of creating a bulk part. The geometry is in figures 4.54 and 4.55. The Power T is 11 by 16 inches and will be five inches tall. The part will allow for horizontal and vertical dog bones to be extracted for mechanical testing. The material will also be used for microstructure characterization. Figure 4.51: Sketch of 30% bead overlap with chosen parameters. 102 Figure 4.52: Multi-pass wall flat top, layer 9. 103 Figure 4.53: Multi-pass wall fusion between beads, top view. 104 Figure 4.54: Power T top view. 105 Figure 4.55: Power T isometric view. 106 Chapter 5 Conclusions Aluminum 6061 is a widely used aluminum alloy that is a suitable material for many purposes because of its high specific strength and its corrosion resistance. The material has never been successfully used as a filler wire in welding though due to hot cracking. Fortius Metals developed a new wire for wire arc additive manufacturing called Al 6061 RAM2 wire. The wire has added elemental inoculants that mitigate the hot cracking issues and allow the wire to be welded. To develop parameters for the wire, first base layers were tested, them build layers, then single-pass walls, and eventually multi-pass walls. Also a diamond geometry was printed and dog bones were extracted and the material was shown to have an ultimate tensile strength of 145 MPa and a yield strength of 79.7 MPa. These are comparable to the expected as-printed values Fortius Metals provided. The results are higher than 6061-0. Most of the work described though was completed with wire that had pre-existing contamination issues so porosity was prevalent in all material. Samples were analyzed using EDS to test if any certain elements were causing issues, but none were observed. Then, experiments adjusting welding parameters and processes were completed to try and reduce the amount of porosity but to no avail. Once new wire was received, three tests were completed and by the third test in figure 4.48 porosity was almost completely eliminated. The base parameters for the new wire was a wire feed speed of 350 in/min, 107 a travel speed of 10 in/min, a 2 mm length and amplitude triangle weave, and a heat input of 700 J/mm utilizing a pulse welding mode. The build layers have a wire feed speed of 360 in/min, a travel speed of 12 in/min, a 2.5 mm length and amplitude triangle weave, and a heat input of 250 J/mm utilizing a CMT welding mode. These parameters were then used to test a multi-pass wall and was successful. Future work is to use these parameters to completes a more complex multi-pass geometry of a Power-T that will be 11 by 16 inches and 5 inches tall. This built part will then be used to do mechanical properties testing and microstructural testing. Though porosity was limited in the deposits performed, it would be beneficial to test hotter and colder heat inputs to see how the material behaves. 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