As can be seen from the above picture:
(1) With the improvement of product qualification rate, the defect cost is decreasing. When the product qualification rate is 100%, the defect cost is zero.
(2) With the improvement of product qualification rate, "prevention cost and identification cost" are on the rise.
(3) The total quality cost is parabolic, and it is the lowest at the intersection of "prevention cost and identification cost" and defect cost.
2. The relationship between the parts of quality cost.
(1) The relationship between prevention cost and identification cost;
① The prevention cost is inversely proportional to the assessment cost, as shown in the following figure:
With the increase of prevention cost, the identification cost can be greatly reduced. This is because of the role of "quality lever", the prevention cost is 1 yuan, which is equivalent to the identification cost of 100 yuan, which is equivalent to the defect cost of 100 yuan, that is, the rate of return on resources at different stages is very different. The figure below is a quality lever, which vividly illustrates the role of various costs in improving product quality.
② Prevention cost cannot replace identification cost. Although the investment return of the prevention cost is much higher than the appraisal cost, in practice, the prevention cost cannot completely replace the appraisal cost. Of course, through continuous efforts, the evaluation cost can tend to zero.
(2) The relationship between prevention cost and defect cost.
The cost of prevention is inversely proportional to the cost of defects, as shown in the following figure:
Increasing the cost of prevention can greatly reduce the cost of defects. According to the principle of quality lever, the product quality can be greatly improved and the defect cost can be greatly reduced by investing a small amount of prevention cost. When the cost of prevention increases to a certain extent, the number of defects will tend to zero. This is also one of the theoretical foundations of six-horse management.
(3) The relationship between appraisal cost and defect cost.
The relationship between evaluation cost and defect cost is shown in the following figure:
As can be seen from the above figure, the appraisal cost is inversely proportional to the defect cost. Increasing the appraisal cost can reduce the flow of defective products to customers, thus reducing the total defect cost.