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2.1 INTRODUCTION TO QUALITY
The quality of a product is determined by how well it suits your needs.
Where do we have to change production in an industry to improve quality?
- Design - Only design a product to meet specifications, any more is a waste of time and resources. For example, if a chemical company `tunes' their production for a certain impurity in a raw material, a sudden improvement might hurt their product quality.
- Review of Specifications - make sure the specs. describe the product well, the specs are useful to customers, etc.
Two main approaches to quality,
Typical options when products fail inspection.
- Downgrade (lower returns), e.g. try to get largest chicken eggs, but when smaller eggs are produced, sell for less.
What are some of the different ways to inspect processes?
2. Design of Experiments - Various process parameters can be varied (e.g. speeds, feeds) and the effects can be examined to determine the best settings for a process.
3. Statistical Process Control (SPC) - Various measurements may be done on a part after processing, and the process can be adjusted to keep it within spec.
Does it cost more to inspect each process instead of the final product?
- The use of statistics allow small population samples to produce enough data for a process. And, it is much cheaper to adjust a process before problems occur, than it is to fix a completed product.
- Consider the graph below, there is a basic manufacturing cost per part associated with any piece. If we consider what happens when selecting quality levels, we see that to improve quality to get 0% rejects (all parts good) our costs rise significantly. On the other hand if more rejects are produced, the economic losses rise. There is an optimal point to choose where the quality level of the product will give the optimal economic sense.
What about the cost of quality?
- All products are the results of trade-offs - the most common factor is cost, others include size weight, etc. These vary between industries and products.
- We can use (and must in many companies) money as one factor, but we must justify quality for its other benefits also.
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