User:Lloydmichael/Evolution of Quality Engineering

Historical background In view of the emerging competitive manufacturing industry, it can be seen that quality conscious manufacturers are increasingly aware of the need to optimise products and processes. Quality achieved by means of design optimisation is found by many manufacturers to be cost effective in gaining and maintaining a competitive position in the world market. It is in this context that we try to improve product and or process quality using Taguchi methods. The use of tolerance in the specification of parameters was first initiated about 1870 with the introduction of go, no-go tolerance limits. The need came about because manufacturers found that they could not make products alike in respect to a given quality and trying to make them was costly. The go, no-go gauge provided a simple device for the technician to check his/her work quickly resulting in lowered production costs, ). Unfortunately this method led to a “do not waste time trying to be exact” approach thus compromising quality. This then led to the evolution of quality control resulting in cheaper and effective methods.

What are Taguchi Methods and how they came about? Taguchi methods are a system of cost driven quality engineering techniques that emphasize the effective application of engineering strategies rather than advanced statistical techniques. It includes both upstream and shop floor quality engineering.


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i) Upstream methods – efficiently uses small-scale experiments to reduce variability and finds cost effective, robust designs for large scale production and the market place. The basic principle applied in this concept is the reduction of variability in the performance of the end product. To accomplish this, the factors causing variability in the product (or process) must be well understood, so that design sensitivity to these causes can be minimized. The approach attempts to ensure quality through design, in this case through the identification and control of critical variables (or noises) that cause deviations to occur in process / product quality.


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ii) Shop floor techniques – provides cost based, real time methods for monitoring and maintaining quality in production. Taguchi methods also refer to techniques of quality engineering that embody both statistical process control (SPC) and new quality related techniques. Most of the attention and discussion on Taguchi methods has been focused of the statistical aspects of the procedure. It is the conceptual framework of a methodology for quality improvement and process robustness that needs to be emphasized. An important distinction must be drawn between quality engineering (Taguchi methods) and statistics. Taguchi has been confused with statistics and at times unfairly criticised by statisticians for deviating from statistical methods. A very obvious divergence is clear by contrasting the aims of the two methodologies. Statistics tells you what has happened and quality engineering tells you how to make it happen. The entire concept can be described in three basic ideas:-

Quality should be measured by deviation from a specified target value, rather than conformance to present tolerance limits. Quality cannot be ensured through inspection and rework but must be built through appropriate design of the process and the product. The cost of quality should be measured as a function of the deviation from the standard and losses should be measured system wide. In the first concept Taguchi contended that quality is directly related to deviation of a design parameter from the target value, not to conformance to some fixed specifications.
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A product can be produced with properties skewed towards one end of an acceptance range yet show a shorter life expectancy. However by specifying a target value for the critical property and developing manufacturing process to meet the target value with little deviation, the life expectancy may be much improved.

The first concept underlines the basic difference between Taguchi and Statistical Process Control methodology where as SPC methods emphasize the attainment of an attribute within a tolerance range and allows for faults and defects to be eliminated (if detected) after manufacturing. Taguchi methods emphasize the attainment of the specified target value and elimination of variation..

In conjunction with the second concept, a better way to improve quality is to design and build it into the product. Quality improvement starts at the very beginning, i.e. during the design stages of a product or process and continues through the production stage. He proposed an „off line” strategy for developing quality improvement in place of an attempt to inspect quality in to a product on the production line. He observed that poor quality cannot be improved by the process of inspection, screening and salvaging. No amount of inspection can put quality back in to a product; it merely treats a symptom. Therefore, quality concepts should be based upon, and developed around the philosophy of prevention. His third concept calls for measuring deviations from a given design parameter in terms of the overall life cycle costs of the product. These are costs of scrap, rework, inspection, returns, warranty service calls and or product replacement. These costs provide guidance regarding the major parameters to be controlled.

References 1. Ralph. Early; Guide to Quality Management Systems for the Food Industry: 1995; Blackie Academic and Professional publishers; Glasgow; U.K.2. Jesse. C. Jones; The Engineering Design Process 2nd Edition; 1996; John Wiley and Sons Inc; 10987654321; Canada.3. Keith Locker, Alan Muhlemann, John Oakland; Production and Operations management 6th Edition; 1992; ELBS with Pitman; ISBN 0-273-032364; Great Britain.4. John. S. Oakland; Total Quality Management; 1989; Heinemann Professional Publishers Ltd; Great Britain.5. Ranjit. K. Roy; A Primer on Taguchi Methods, Competitive manufacturing series; 1990; Van Nostrand Reinhold; ISBN 0-442-23729-4; New York.6. William. J. Stevenson; Production / Operations Management 3rd Edition; 1990; Richard. D. Irwin Inc; ISBN 0-256-09875; Boston.7. Total Quality Portolio Volume 3; Strategic direction Publishers; Peundt strasse 118610; Zurich; Switzerland.8. www.amsup.com9. www.spcanywhere.com