I
Introduction

Preface

Product quality is an important matter in industry. It becomes more and more important given the recent trend that customers evaluate goods critically and make complaints about any issues that arise. Managers of companies, though they did not recognize it before, will now need to appreciate the following situation. In order for companies to be successful in modern society it is of fundamental importance for them to maintain the quality of products at the highest level possible, subject to operating profitably and producing products of uniform quality with reliable methods.

To realize this it is necessary to explain concretely to the managers of companies what management needs to do. The most important management principle for maintaining a high-quality product is to establish company-wide determination to serve their customers. After this is established and a firm decision is made to endeavor to maintain a reputation for high-quality products, management should inform all the employees of this strict requirement for product quality. Managers should take the initiative in related activities. They should show with their behavior that quality is their company motto, and they also should try to ensure that the workplace environment is conducive to maintaining the highest possible product quality.

The policies for the control and management of a company should be practical and informed by progressive ideas, and they should be adhered to. Analyze the market to obtain the information on customer needs, then design and produce the products based on the result of analysis so that production is profitable. Calculate and control the costs required for planning, production, and control, and avoid waste. Whether or not it is possible to maintain high quality really depends on the design and the administrative efficiency of the company. From the above standpoint, treatment and training of the employees is very important.

It will be difficult to maintain the required level of product quality without management and employees being in perfect agreement about the meaning of quality. Employees, including those working in factories and those working in offices, should be trained so that they are willing to cooperate with management. They should be trained to contribute to producing products of high quality and to understand that their efforts will result in profit not only to the company but also to themselves.

Since such a way of thinking does not occur naturally, management should take the initiative in training activities. If good plans are incorporated into the training programs for mental activities as well as for physical labor, the effects would spread into every area of the company. The basic thinking needed to improve the quality of output is common in the divisions related to physical labor and mental activity.

So far, we have discussed the problem of quality from the standpoint of management. Now we discuss it from the standpoint of operation. A reliable consistent production process and products with uniform quality can be achieved only when the production process is planned and controlled using scientific methods for the purpose of producing products of high quality.

Design, production method, and standards for materials and process specification should be appropriate, accurate and efficient, and they should be obeyed strictly. Workers should be trained and supervised so that they can understand and carry out their jobs well. Machines, equipment, instruments, tools, and skills of workers should be suited to carrying out the required tasks within the assigned time using appropriate methods.

Even if all the above conditions are satisfied, however, it is not generally easy to maintain product quality. This is because there is a shortcoming in the control system in general management. Recently, a lot of research has been done to address this shortcoming, and as a result some tools have been developed. They are statistical methods developed for the purpose of maintaining the quality of the production process. Using these methods, we can determine product quality with pre-assigned accuracy, and in addition we can improve the efficiency of production and also reduce costs. Scientifically speaking, the main aim of these methods is to control the factors that affect the quality of the final products going out to the market.

Establishment of a system of statistical quality control provides various advantages to the company as follows.

1. Variation of quality of the continuous production process is minimized.
2. Data based on samples taken from the production process provide reliable information to judge the state of the quality of the process.
3. Inspection cost (indirectly production cost) is minimized.
4. It is possible to obtain reliable basic information to test whether the current design and control limits for quality are appropriate or not.
5. It is possible to obtain practical basic information to assess the current production capability.
6. The results of sampling inspection usually provide proof of the actual quality of the products.

There can be no doubt that quality is the most essential foundation for a company to be successful. This has been demonstrated by many substantial companies. Quality is recognized as the most important matter. Therefore, it is necessary to position quality as the sound logical foundation for management and to adopt quality control as one of the valuable control methods among the industrial factors that are vital to the prosperity of the company.

There are two fundamental tasks necessary for successful practice of quality control. They are (1) to set up a system of control, and (2) to execute the actions resulting from the system of control.

The latter requires the support of management to ensure that the newly established system of control has a chance to work successfully; while the former provides the technical means, within which statistical quality control plays the principal role. We shall discuss these matters in detail below. There are some preliminary steps required to set up the initial control system. You should perform these logical steps one by one. However, as it is not essential to complete one step before proceeding to the next, it is sometimes convenient to perform some steps in parallel.

Step 1. Establishing the Quality Standard

Product quality captures the special characteristics useful for discriminating one's products from those of rival companies, special characteristics for discriminating among the same kind of products, or special characteristics for grading the products of the same production process. There are two purposes for quality. One is to demonstrate that two or more products are in the same category, as occurs when comparing the products manufactured by rival companies. The other is as a measure of fitness for purpose.

In either case quality is not measured on an absolute scale but merely on a relative scale. One can say that something is good from a certain point of view only when it is compared with some standard on a one-dimensional scale. In such cases quality becomes a variable and the result of a comparison can be expressed as quality being higher or lower (better or worse) than the standard.

When defining the quality of a product, possible characteristics related to the goodness of quality include size, materials, shape, chemical components, function, fitness for purpose, appearance, and practicability. These characteristics depend on (a) quality of design or (b) quality compared with the standard. The former relates to technical specification for manufacturing, and the latter relates to the method for comparing with the standard and the extent of difference from the standard.

Quality of design includes the problem of the trade-off between cost and outcome. It is a commercial issue to be considered carefully by both engineers and administrators. Consider an ideal case where engineers design a product with the best quality. If nobody buys the product in the market because of high cost, the idealistic engineers are to blame. If the engineers pursue high product quality simply for the sake of quality itself without any consideration for the practical use of the product, they are not fulfilling their duties. The engineers are responsible for the commercial aspect of the product as well.

If the accuracy of size, chemical purity, or any other quality attribute improves, the value of the product increases, but so does the cost. Eventually, comparing the additional value of the product that is due to an improvement of quality and the increase in cost required for the improvement, the point at which the latter exceeds the former will be the limit for quality improvement. Therefore, it is necessary for the engineers involved in production engineering and those involved in the production process to set the quality standard so that the standard is consistent with the reason for producing the product while the cost remains commercially viable.

The problem of quality versus cost discussed above also occurs in connection with quality compared with the technical standard. For example, suppose there is a production process in which 0.1% defective items are constantly produced. That is, on average there is one unit whose quality is below the required level among 1000 units produced in a day. It is necessary to inspect 1000 units per day in order to detect one defective unit. Ordinarily the inspection cost for 1000 units is much higher than the cost of the loss or...