On product quality control

Before explaining the product manufacturing process, let's first understand what a product is.

I. What is a product

To understand a product, you should know what an enterprise is.

An enterprise generally refers to a legal person or other that uses various factors of production (land, labor, capital, technology, and entrepreneurial talents, etc.) to provide goods or services to the market for the purpose of profitability, and implements independent operation, self-financing, and independent accounting. It is a pure socioeconomic organization.

An enterprise is a product of social development, and it has grown and expanded due to the development of social division of labor. Enterprises are the main participants in market economic activities; under the socialist economic system, the coexistence of various enterprises together constitute the micro-foundation of the socialist market economy.

There are two forms of enterprises: one is to provide goods, and the other is to provide services.

The company that provides goods depends on the product. If there is no product, the company cannot exist.

So what is a product?

Product refers to anything that can be supplied to the market, used and consumed by people, and can meet certain needs of people, including tangible goods, intangible services, organizations, concepts, etc. Products can generally be divided into five levels, namely core products, basic products, desired products, accessory products and potential products.

The core product refers to the direct benefits and utility provided to buyers by the overall product;

The basic product is the macroscopicalization of the core product;

Expected product refers to a set of characteristics or conditions that customers generally expect to obtain when purchasing a product;

Accessory products refer to products that exceed customer expectations;

Potential products refer to the improvements and changes that a product or development may produce in the future.

The realization of any product must have a process, so the International Committee for Standardization ISO defines a product as "the product is the result of the process".

II. what is the process

Above we talked about "the product is the result of the process", so what is the process next?

Process, in layman's terms, is the process of doing something. After we do anything, no matter whether it is successful or not, there will always be a result, and this result is the output of the whole process of doing this thing. When this process is over, people will often continue this process, and another process will occur. At this time, you will notice that the premise of continuing is to start on the basis of the previous process. Therefore, we call the result of the previous process the input of the continuation of the latter process. At the same time, the input of one process becomes the output of other processes. Therefore, the process is a set of interrelated or interacting activities that transform a set of inputs into outputs.

Taking the bearing processing industry as an example, the formation of a finished bearing ring is roughly produced by multiple processing links such as forging → turning → heat treatment → grinding → superfinishing. Each link is a complete process, and each process It also contains many small links. For example, the grinding process of the outer ring of a bearing includes grinding end face → grinding outer diameter → grinding channel → channel superfinishing process, and each process can be subdivided into rough grinding, fine grinding, and fine grinding (finishing).

III. The nature of product

Since the product is the result of the processing, the result may have two phenomena: ideal and undesirable. In terms of products, an ideal product is a qualified product, and an undesirable product is a substandard product (also called a defective product). So what kind of product is an ideal product (qualified product), and what kind of product is an undesirable product (substandard product)? In layman's terms, it is:

1. Qualified product (conformity)-meet the requirements.

2. Non-conforming product (non-conforming)-not meeting the requirements.

IV. Product requirements

Qualified products and unqualified products are the difference between meeting and dissatisfying requirements. It is easy to understand, but what does "requirements" mean?

In the work practice of a company, everyone will think that products that are qualified by the company's authorized and qualified inspectors. The basis of the inspector's request is the product processing technology documents used by the company to guide the production site.

In addition to the relevant provisions of the relevant standards, the process documents also imply the conventions or general practices of enterprises, customers and other related parties, that is, requirements or expectations outside the standards.

V. About unqualified product

Everyone understands the meaning of qualified. Next, we will focus on unqualified.

1. Unqualified product

What is a substandard product? All products that have not passed the inspection are substandard products. So the question we are discussing now is: Do substandard products lose their meaning? The answer is no.

Product quality inspection involves two judgments: one is to determine whether the product meets the standard, which is called conformity judgment; the other is to determine whether the product is suitable for certain user requirements or certain specific purposes, which is called applicability judgment. Applicability judgment is essentially a way to deal with non-conforming products after conformity judgment, that is, recycling, repairing, and scrapping of defective products.

In general, in addition to a small amount of waste, most of the non-conforming products have certain expected value, such as repaired products.

Below we will further explain the substandard products:

(1) Reworked products-measures taken to make non-conforming products meet the requirements.

(2) Repaired product—Measures taken to make the nonconforming product meet its intended use.

(3) Waste products-products that have completely lost their original intended use. The usual measure taken for its products is scrapping.

In addition, companies will encounter the following degraded products and concessions to receive products in actual work:

(4) Degraded products—changes to the grades of nonconforming products to meet requirements different from the original ones.

(5) Concession (acceptance) of products-the license to use or release products that do not meet the specified requirements. (Generally, concessions are limited to the delivery of products with unqualified characteristics within the time or quantity agreed by the supplier and the buyer).

The non-conforming product is easy to understand, so what is the non-conforming item? Non-conformity refers to the problem that does not conform to the stipulations (or norms, procedures, standards, systems, etc.). For example, if an operator produces a non-conforming product during the processing phase, the company's first thought is to take certain measures against the non-conforming product, but in order to avoid the recurrence of the non-conforming product, while taking measures against the non-conforming product, it also should focus on the analysis of the causes of non-conforming products. There are many reasons for this, such as: operating machine tools;

A1. Although there are machine operation regulations, they are not formulated in detail and should be supplemented and perfected;

A2. The machine tool operating rules have been formulated in detail, but the operators have not implemented them, or have not implemented them carefully.

Product inspection:

B1. The first product processed by the operator has not been self-inspected, and it has not been inspected by the inspector at the same time? It is because the company has no express regulations on self-inspection and first article inspection;

B2. The company has clear regulations on self-inspection and first inspection, and neither operators nor inspectors have implemented them seriously.

Process discipline:

C1. The processing technology regulations are not clear, or the process schematic diagram is not standardized;

C2. The on-site process documents are standardized and clear, and the operators do not carefully check and understand, and blind or reckless work appears.

In the above example, we can see that A1, B1, and C1 are companies that have no corresponding regulations, or have regulations but are not in place; A2, B2, and C2 problems are entirely caused by individual operators, including inspectors. We say that whether it is A1, B1, C1, or A2, B2, C2, the final result is the unqualified product. And we call A, B, and C collectively as unqualified items. Therefore, it can be understood that the term refers to the software, and the product refers to the physical object, which is the hardware. Items are causes, products are effects, and they are causality.

We know that when a company is engaged in the ISO9000 quality management system standard certification review, the non-conformity issued by the certification body after the company's audit is a non-conformity (there are two types of general non-conformities and serious non-conformities), and will not target products.

VI. Disposal of substandard products

We mentioned above that the purpose of an enterprise is to make a profit. To make a profit, there must be products. All the activities of an enterprise are based on the production of qualified products. However, due to human, machine, material, method, environment, measurement and other factors in the production process, the appearance of substandard products is also inevitable. The question is, what should be done after the non-conforming product appears, and what measures should be taken to deal with it?

First of all, we have to decide based on the specific circumstances of the non-conforming product. In production practice, companies usually adopt the following six methods:

1. Rework: This is the first consideration when possible. Qualified rework can reduce the loss of the company and help reduce production costs;

2. Downgrade: What is downgrade? Downgrading means that the quality index of the unqualified product has not reached the original product grade requirements of the enterprise, and its grade must be changed. This change can only be low, never high. Downgrading will reduce the price, and the price reduction will increase the production cost of the enterprise accordingly;

3. Concession (acceptance): It is a concession (acceptance) permission for products that do not meet the specified requirements. The situation of concession (acceptance) generally means that the product has a specific user, and after negotiation, the other party agrees to implement it. Therefore, such products are generally limited to the delivery of products with unqualified characteristics within an agreed time or quantity.

4. Repair: measures taken to make the non-conforming product meet its intended use.

There is a noun mentioned here: "expected". What is "anticipation"? It is the anticipation in advance. Advance means advance, purposeful meaning. Therefore, rework is different from rework. The measures taken to make the non-conforming product meet the requirements are called rework (commonly speaking: "rework" means that the non-conforming product is reprocessed and inspected to meet the specified requirements and become a qualified product); After the qualified product is processed again, the degree of non-conformity may be reduced and can be reused, but it still does not meet the specified requirements and still belongs to the non-conforming product. Therefore, repairing may change some parts of the unqualified product to achieve the desired purpose. Therefore, repairing is sometimes not only for non-conforming products, but also for qualified products to achieve the expected purpose if necessary.

We might as well give two simple examples to deepen our understanding of the meaning of rework:

1) A lady bought a very valuable coat, with all the trademarks, certificates, etc. After I bought it, I haven't worn it after the season, and when I took it out for the next year, I found it was no longer suitable. What should I do? She remodeled (reworked) this coat, and her daughter would wear it after remodeling. In this example, we have noticed two points: first, this jacket is a qualified genuine product; second, Ms. Zhang has already had the idea of the intended use before the restructuring, that is, she wants her daughter to wear it after the restructuring and cannot be wasted.

2) We know that the inner hole of the bearing is matched with the journal of the shaft. Bearings are standard parts of mechanical parts. Therefore, the manufacturing tolerances of shafts should be determined based on the standard tolerances of the inner bore of the bearing. Now there is a manufacturer that processes 200 shafts with non-standard tolerances. The diameter of the shaft is 0.05mm larger than the standard tolerance of the bearing hole, so a corresponding number of bearings are needed to match. The factory producing shafts put forward a request to a bearing factory. A bearing factory happened to have 150 parts with unqualified inner diameters (out of tolerance). In order to meet the needs of customers, 50 qualified parts were put forward from the semi-finished product library, and the inner bore of the bearing was repaired according to the tolerance required by the customer. The expected use of the bearing parts is realized.

5. Scrap: For products that can neither be reworked or downgraded, nor can they be repaired or requested to be accepted by the user, and completely lose their use value, they will be scrapped directly.

6. The company formulates "Technical Conditions for By-products" to make full use of some unqualified products. Some companies, based on the characteristics of the products, limit the tolerances of non-conforming products that exceed the national or industry standards to a certain extent, and formulate the corporate standard "Technical Conditions for Secondary Products". To some extent, such byproducts can basically guarantee the normal use of the product in terms of performance and life. In the "Technical Conditions for Sub-Products", the company has also made clear labeling regulations on the products and packaging, and the "Sub-Products Qualification Certificate" is attached when leaving the factory to show that it is different from qualified products. However, this approach is unlikely to be administratively recognized by the technical quality supervision departments of the state and local governments.

VII. The general steps of non-conformity disposal

In conclusion, there are two types of unqualified products: unqualified products and unqualified items. Therefore, different situations should be handled in different ways. For the unqualified products, we should find the reasons technically, and for the non-conforming items, we should focus on finding the reasons from the management aspect. Although the ways of finding the reasons are different, the basic steps are roughly the same. The idea is as follows:

1. Description of unqualified facts

2. Correct

3. Analysis of unqualified reasons

4. Corrective actions

5. Trial

6. Implementation of corrective actions

7. Verification

8. Preventive measures

In work practice, there are many factors that produce unqualified products. Technical and management problems are often mixed together. It is difficult to distinguish which are technical problems and which are management problems. Therefore, when dealing with non-conforming products or non-conforming items, we must not only follow the principle of "simplification of complex issues", but also strive to clarify the facts, the purpose of which is to avoid the possibility of similar situations recurring. For important products, once there is a quality problem, it is necessary not only to find out the cause and implement corrective measures, but also to draw inferences from one another. When necessary, sufficient verification shall be carried out through the method of "fault reappearance". If the "fault recurrence" fails to show the cause, it means that the cause analysis and corrective measures are not in place. Reanalyze the cause, formulate corrective measures, and test repeatedly until the correct result is obtained, so as to achieve the dual return of technology and management. Zero consistency.

VIII. The relationship between correction and corrective measures

From the steps of disposing of non-conforming products, we see two words: correction and corrective measures. Let's explore the relationship between the two below.

A Correction: Measures taken to eliminate the non-conformities that have been found.

B Corrective measures: measures taken to eliminate the causes of unqualified or other undesirable conditions that have been discovered.

1) Correction is "just the matter". The measures (methods) taken to solve (eliminate) one (or one, batch) of non-conformities do not consider any other circumstances, and this is only a "corrective" action, not a corrective measure.

2) The corrective measures are that after discovering the non-conformity, you can't simply discuss the matter. Once a hundred times, it is necessary to conduct an in-depth analysis of the cause of the non-conformity, and then take measures to prevent the recurrence of similar incidents according to the cause.

Example 1: Existing a small batch of bearing inner rings, after inspection, it is found that the inner hole size is generally smaller than the lower limit size specified by the process, and the consistency is very good.

1) Correction: all rework, re-grind the inner diameter size, and re-inspect after re-grinding;

2) Reason analysis: The measurement size of the standard parts used by the operator does not match the size used by the inspector. After the two standard parts are measured again, the size used by the operator is small;

3) Corrective measures: A. Before using the standard parts, first determine whether the appraisal date of the standard parts is within the validity period; B. During the measurement and use, the standard parts of the operator and the inspector should be calibrated with each other in time, and any inconsistencies should be resolved immediately .

Example 1 shows that the work of re-grinding the unqualified inner ring is to correct, and the formulation of corrective measures depends on the cause analysis. In other words, through analysis, it is known that the reason for this batch of unqualified inner holes is due to the standards used by the operators.

The size of the piece does not match the inspector’s. The size of the standard part used by the inspector is correct. Through the implementation of corrective measures, similar situations will not happen again in the future.

Example 2: During a production site audit in a workshop of an enterprise, it was found that the first product processed by the operator did not undergo self-inspection, nor did it undergo the first inspection by the inspector. During the inspection, the inspector found that the products processed by the operator had a small batch of unqualified products. Case.

1) Correction: 100% self-inspection of the processed products by the operator, and the qualified products are handed over to the inspector for acceptance;

2) Cause analysis: The workshop has no express requirements for the self-inspection of the operators and the first inspection of the inspectors;

3) Corrective measures: The workshop clearly stipulates that the operator must perform self-inspection on the processed products. After the self-inspection is passed, the inspector will be notified for the first inspection and the first inspection record shall be made. The operator will mark and save the first-inspected qualified products, and then carry out mass production.

Example 2 shows that because the workshop does not have clear requirements for self-inspection and first inspection, the products processed by the operators appear to be unqualified in small batches. The latter is a phenomenon, and the former is the cause. Through the analysis of the phenomenon, the cause was found and corrective measures were formulated.

IX. The relationship between corrective measures and preventive measures

The above mentioned the relationship between correction and corrective measures. Now let's describe the relationship between corrective measures and preventive measures.

A Corrective measures: Measures taken to eliminate the causes of unqualified or other undesirable conditions that have been discovered.

B. Preventive measures: Measures taken to eliminate the causes of potential nonconformities or other undesirable conditions.

Still we will take the above example 1 as an example

1) Corrective measures: Immediately send the standard parts used by the operator for measurement, and perform calibration with the inspector's standard parts from time to time during future use.

2) Preventive measures: The enterprise formulates the control procedure document of the measuring instrument, stipulating that all the measuring transmission standard parts used at the production site shall be measured regularly. The first product processed by the operator on duty must be inspected and qualified by the inspector in order to achieve the unity of measurement and delivery.

From this example, it can be seen that the scope of corrective measures is relatively limited. It only requires operators who have unqualified products to send the used internal hole standard parts to measure the size. During the production process, they will irregularly conduct inspections with the inspector's standard parts. Calibration, no substandard products will appear; and preventive measures should start from the overall consideration: the internal hole standard part has an error, then other standard parts also have potential risks? Therefore, the establishment of "the establishment of enterprise measurement instrument control procedures documents, stipulate that all measurement transmission standard parts used at the production site must be regularly measured. The first product processed by the operator on duty must be inspected by the inspector to achieve the unity of measurement transmission" Preventive measures, in this way, can achieve control in a more specific and comprehensive manner, achieve the effect of "inferring from one another", and achieve the purpose of "eliminating the causes of potential unqualified or other undesirable conditions" to reoccur.

Still take the above example 2 as an example

1) Corrective measures: The workshop requires operators to implement self-inspection. After passing the self-inspection, the inspector will be notified for the first inspection, and the first inspection record shall be made. The operator will mark and save the first-inspected qualified products, and then mass-produce them.

2) Preventive measures: The quality management department of the enterprise will further refine the corrective measures of the workshop and issue it as a quality control document to the entire company for implementation to avoid the recurrence of similar situations in other workshops.

The above examples can be seen: corrective measures are taken to prevent recurrence, and preventive measures are taken to prevent recurrence.

X. Summary

In conclusion, we know that product manufacturing is a complex systematic process, which is a set of interrelated or interacting activities that transform inputs into outputs. The result of the process can be ideal and unsatisfactory. The ideal result is what we expect, and the undesirable result may happen at any time. The purpose of enterprises to strengthen quality management and monitoring is to control the occurrence of unsatisfactory producnt with less occurrence, or recurrence. However, once undesirable results appear, we must have a correct and responsible attitude and deal with them in accordance with the quality management control procedures established by the company. The key is to make a careful analysis of the problems that arose, and only through thorough analysis can they be dealt with in place. Simple problems can be corrected and corrective measures can be carried out at the same time, but often a non-conforming item may be composed of multiple factors. To deal with the problem, it is necessary to investigate the source of the problem, and the analysis is correct, and the problem is accurately identified, then the problem will be correct. Those that cannot be solved at once can be implemented in stages, and eventually the problems that arise will be completely solved. It is necessary to solve one point, formulate preventive measures, and expand to the surface, so as to eliminate the potential unqualified or other undesirable causes, and finally realize the quality control of the whole production process.

In practice, it is found that what most companies lack is post-cause analysis, corrective measures and preventive measures. Once non-conforming products and non-conforming items appear, only corrections are taken, and the work is done perfunctorily, and the work is no longer carried out, lacking seriousness in dealing with things, so that the same non-conforming products and non-conforming items repeat occurrence. The head of the enterprise mistakenly believes that the cause analysis, corrective measures and preventive measures, and even verification work, are too troublesome and will affect the normal production.

At present, many companies have obtained ISO9000 and ISO16949 quality management system standards certification. In the early stage of certification, they have also compiled quality management system documents according to the requirements of the standards. I sincerely hope that companies will not put these documents on the shelf but use them fully. There is only better quality management work, not the best. The society is progressing, and the enterprise is developing. Only in the operation of the system can the quality management of the enterprise be continuously improved, and development can be achieved through continuous improvement. Problems should be treated correctly, effective corrective measures should be taken, and necessary preventive measures should be formulated. In this way, the various tasks of the enterprise will be more and more smooth, and the benefits will be better and better.