Masters Theses

Date of Award

8-2004

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

Narendra B. Dahotre

Committee Members

Hahn Choo, Craig A. Blue

Abstract

Higher the number of effective cutting edges on the surface of a grinding wheel, the higher is the grinding efficiency. However due to continuous grinding, efficiency is reduced as the effective cutting edges on wheel surface get worn out and blunt. Moreover, the wheel also gets loaded with metal chips during machining. Both geometric and functional characteristics of the grinding wheel have to be restored periodically. Dressing is a sharpening operation designed to generate a particular surface topography on the cutting face of the wheel. The conventional processes, like diamond dressing, do not produce consistent grinding results due to dresser wear which affects the wheel surface topography and its performance in grinding.

High power Nd:YAG laser is being explored in the present study as a non-contact type dressing tool for alumina grinding wheels. Surface processing of ceramic grinding wheels by laser irradiation offers potential advantages such as: precise control over high input of thermal energy at spatial levels, rapid processing speed and unique modification of microstructure due to rapid heating, remelting, solidification and cooling. Within the range of laser power employed, the alumina grinding wheel sample surface underwent a transformation ranging from solid-solid to liquid-solid, forming a modified layer on the surface. Refinement of the grain size took place. After laser-dressing, the individual particles on the surface evolved into defined faceted structures. Microcutting edges are generated on the individual grains and particles, which can act as cutting edges for improved grinding. The altered grain structure on the surface of the wheel gives laser-dressing advantage over conventional mechanical methods. The surface roughness of the dressed wheel is a manifestation of the new morphologically laser modified surface and is measured using a stylus-based surface profilometric technique.

Morphological modification during laser-dressing is strongly influenced by the microstructure formed during the rapid solidification process. Microstructure in turn depends mainly on the cooling rates amongst many other factors related to the laser processing conditions. Using a two-color based optical pyrometer temperature measurement setup the cooling rates were estimated during the laser-dressing process. Orientation imaging microscopy (OIM) was used to determine the grain orientations in the resolidified layer on the dressed surface. Post laser-dressing x-ray and pole-figure analysis indicated evolution of planar crystallographic textures in the particles of the resolidified surface layer. Cooling rates and the OIM combined, indicate a preferred orientation of grains along the {110} planes. This preferred orientation can be a reason for the formation of grains with multi-faceted surfaces having cutting edges and vertices, for grinding operation. OIM and cooling results also show existence of a competitive growth mechanism for the grains in the dressed layer. Laser treatment modified the morphological features on the surface of alumina grinding wheel to achieve efficient dressing.

The performance of the laser-dressed grinding wheel was evaluated in comparison to the undressed wheel for a plain carbon steel pin using a high-speed grinding apparatus (Pin-on-disc type). The modification in morphological features on surface after laser-dressing helps maintain a very high grinding efficiency. Laser-dressed grinding wheels are best suited for efficient high-speed microscale grinding to produce smooth surface finish on the workpiece material.

There are several inherent advantages associated with the use of laser for dressing applications. Laser-dressing is a very fast process and it can be easily automated. Also, selective removal of the clogged material alone is possible and desired surface structure (roughness, grain morphology and porosity) can be generated. Furthermore, consistent dressing conditions can be produced by the use of laser and this can help achieve grinding reproducibility. As the laser beam can be delivered using a fiber optic cable, remote dressing operation without discontinuation of the grinding process, during laser-dressing is possible. Thus, the downtime in the grinding operation associated with conventional methods, can either be eliminated or substantially reduced in laser-dressing. Overall, laser-dressing can be used as an effective dressing technique.

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