A modified six sigma approach to improving the quality of hardwood flooring

Total quality or continuous improvement is a consensus theme used by many industries for improving product quality and service. In the last decade a newer quality philosophy known as "Six Sigma" has become well established in many companies, e.g., Motorola, General Electric, Ford, Honda, Sony, Hitachi, Texas Instruments, American Express, etc. Some have suggested that the "Six Sigma" quality improvement philosophy is not only impacting the global business sector, but will also re-shape the discipline of statistics. The "Six Sigma" philosophy for improving product and service quality is based upon existing principles established by other well-recognized quality experts, e.g., Deming, Juran, and Ishikawa. The significant departure of the "Six Sigma" philosophy from existing quality philosophies is that it promotes a stronger emphasis on monitoring production yield and manufacturing costs associated with any quality improvement effort. The other significant contribution that "Six Sigma" makes to the quality movement is the detailed structure for continuous improvement and the step-by-step statistical methodology. The goal of any "Six Sigma" improvement effort is to obtain a long-term defect rate of only 3.4 defective parts-per-million manufactured. The problem definition of the thesis was to determine if a modified "Six Sigma" philosophy for continuous improvement would improve the quality of hardwood flooring. The study was conducted over a six-month time period at a hardwood-flooring manufacturer located in Tennessee. There were six research objectives: 1) Define the current-state of product variability for hardwood "flooring-veneer" and the specific attributes of "finished blank" length, width, and "veneer-slat" thickness; 2) Determine the capability of the product attributes defined in objective one relative to specification limits; 3) Determine the current production yield and manufacturing costs associated with the manufacture of "veneer-slats;" 4) Define the sources of variability that influence the product attributes "finished blank" length, width, and thickness, and "veneer-slat" thickness (This involved a detailed understanding of the relationships that existed between key process variables that influenced "finished blank" length, width, and thickness and "veneer-slat" thickness); 5) Recommend to senior management the improvements necessary to enhance the overall quality of "veneer-slats;" 6) If any of the recommendations are adopted from objective five, the first four objectives would be repeated to determine if quality has improved. There were four major findings resulting from this work. First, there was statistical evidence (at α = 0.05) that top (p-value = 0.0007) and bottom (p-value = 0.0167) "veneer-slat" thickness increased as "finished blank" thickness increased. There was no significant statistical evidence (p-value = 0.3904) that indicated the thickness of the three middle "veneer slats" was affected by "finished blank" thickness. Second, 20% of rejected "veneer-slats" were good and 10% were down-gradable. Third, there was statistical evidence (p-value = 0.1126) that indicated "rip-saw" width was in control and the natural tolerance was 0.428 mm, which was within engineering tolerance. Target sizes of "rip-saw" width should be reduced to improve yield. Fourth, drying stresses and honeycomb were present in dried lumber. Drying schedules and proper conditioning of kiln loads were not appropriately executed. There was statistical evidence (p-value = 0.0001) that indicated top and bottom "veneer-slat" width was greater than the middle "veneer-slats" given the drying stresses. Four recommendations made to senior management were: 1) If "finished blank" thickness variation could be reduced by improving blank molder setup there would be a cost savings of $520,000 dollars per year; 2) A conservative estimate of the cost savings associated with the recovery of the 20% misdiagnosed "veneer-slats" would be $500,000 dollars per year; 3) Analysis of the "rip-saw" indicated an 8% yield increase if "rip-saw" target sizes and saw kerf were reduced and; 4) Appropriate drying and conditioning schedules should be followed to reduce "veneer-slat" width stresses and moisture content variation (eliminating top and bottom "veneer-slat" width variation would result in cost savings of $10,000 dollars per year). None of the previously mentioned recommendations would require capital investment by the company.