Product quality control is a necessary link in the production process of all products, especially in the production process of precision parts, quality control is particularly important. In this article, we categorize quality inspections in several ways to give you an idea of their importance.
1 – Classification according to the order of production process
1.1 – Incoming goods inspection
Incoming inspection is the inspection of the purchased raw materials, purchased parts, outsourcing parts, accessories, auxiliary materials, supporting products and semi-finished products before entering the warehouse.
The purpose of incoming goods inspection is to prevent unqualified products from entering the warehouse, to prevent the use of unqualified products from affecting product quality, affecting enterprise reputation or disrupting normal production order. This is essential for good quality control and reduce unnecessary economic losses for enterprises.
The incoming inspection should be carefully inspected by the full-time inspector of the enterprise in strict accordance with the technical documents.
Incoming inspection includes two types: first (piece) batch sample inspection and batch purchase inspection.
1.2 – Process inspection
Process inspection, also known as process inspection, is an inspection between various processing operations in the process of product formation. Its purpose is to ensure that the unqualified semi-finished products of each process shall not flow into the next process, prevent the continued processing of unqualified semi-finished products and the unqualified batches of semi-finished products, and ensure the normal production order. Since the process inspection is carried out according to the production process and operating procedures, it plays the role of verifying the process and ensuring the implementation of the process regulations.
There are usually three main forms of process inspection: first article inspection; roving inspections; Completion inspection.
1.3 – Final inspection
Final inspection, also known as finished product inspection, aims to ensure that non-conforming products do not leave the factory. Finished product inspection is a comprehensive inspection of the product after the end of production, before the product is put into storage.
The finished product inspection is responsible for the quality inspection agency of the enterprise, and the inspection should be carried out in accordance with the provisions of the finished product inspection instructions, and the inspection of large-scale finished products is generally carried out by statistical sampling inspection.
Products that pass the inspection of finished products should be issued by the inspector before the workshop can handle the warehousing procedures. All finished products that fail to pass the inspection shall be returned to the workshop for rework, repair, downgrading or scrapping. After rework and repair, the product must be inspected again for the whole project, and the inspector should make an inspection record of the reworked and repaired product to ensure that the product quality is traceable.
2 – Classification by inspection site
2.1 – Centralized inspection
The inspected products are concentrated in a fixed place for inspection, such as inspection stations. Generally, the final inspection adopts the method of centralized inspection.
2.2 – On-site inspection
On-site inspection, also known as on-site inspection, refers to the inspection at the production site or where the product is stored. General process inspection or final inspection of large products adopts the method of on-site inspection.
2.3 – Mobile inspection (circuit inspection)
Inspectors should conduct roving quality inspections of the manufacturing process at the production site. The inspector shall conduct the inspection in accordance with the inspection frequency and quantity specified in the inspection instruction and make a record. The process quality control point should be the focus of the circuit inspection. The inspector should mark the inspection results on the process control chart. When the patrol inspection finds that there is a problem with the quality of the process, on the one hand, it is necessary to find out the cause of the process abnormality with the operators, take effective corrective measures, and restore the controlled state of the process; On the other hand, all the processed workpieces after the last inspection to before this inspection must be re-inspected or screened to prevent unqualified products from flowing into the next process or users.
3 – Classification by test method
3.1 – Physical and chemical testing
Physical and chemical inspection refers to the method of mainly relying on measuring instruments, instruments, meters, measuring devices or chemical methods to test products and obtain inspection results. Physical and chemical tests are used as much as possible when possible.
3.2 – Microbiological testing
Microbiological testing mainly relies on microscopy, staining technology, culture medium preparation technology, inoculation, separation and purification and culture technology to judge the freshness and contamination of the product as a means.
3.3 – Sensory examination
Sensory testing, also known as functional testing, relies on human sensory organs to evaluate or judge the quality of products. For example, the shape, color, smell, scars, aging degree of the product, etc., usually rely on human vision, hearing, touch or smell and other sensory organs to test, and judge the quality of the product or whether it is qualified.
Sensory tests can be divided into:
(1) Hobby sensory testing, such as wine tasting, tea tasting and product appearance and style identification. It is necessary to rely on the rich practical experience of the inspectors in order to make correct and effective judgments.
(2) Analytical sensory inspection, such as train spot check and equipment spot check, rely on the feeling of hands, eyes and ears to judge temperature, speed, noise, etc.
3.4 – Experimental use identification
Experimental use identification refers to the actual use effect of the product is tested. Through the actual use or trial of the product, observe the applicability of the product use characteristics.
4 – Cssification according to the quantity of the product being inspected
4.1 – Full number test
Full inspection, also known as 100% inspection, is a full inspection of all products submitted for inspection piece by piece according to the specified standards.
It should be noted that even if the full test is due to errors and omissions, it is not guaranteed to be 100% qualified. If the desired product is 100% qualified, it is necessary to repeat the full inspection several times to approach 100% qualified.
4.2 – Sampling inspection
Sampling inspection is to take a specified number of samples from the submitted batch to form a sample according to the predetermined sampling scheme, and infer that the batch is qualified or the batch is unqualified through the inspection of the sample.
4.3 – Exemption from inspection
Exemption from inspection, also known as no test inspection, is mainly for products that have passed the product quality certification of the national authority or trusted products at the time of purchase, and the receipt or not can be based on the supplier’s certificate or inspection data.
When implementing inspections, customers often have to supervise the production process on the supply side. The supervision method can be carried out by sending personnel to station or requesting control charts of the production process.
5 – Categorized by the nature of the data by quality characteristics
5.1 – Measurement value inspection
Measurement value inspection needs to measure and record the specific value of quality characteristics, obtain measurement value data, and judge whether the product is qualified according to the comparison of data value and standard.
The quality data obtained by the measurement value inspection can be analyzed by statistical methods such as histograms and control charts, and more quality information can be obtained.
5.2 – Count value test
In order to improve production efficiency in industrial production, limit gauges (such as plug gauges, card gauges, etc.) are often used for inspection. The quality data obtained is the count value data such as the number of qualified products and the number of unqualified products, but the specific value of the quality characteristics cannot be obtained.
6 – Classified according to the condition of the sample after inspection
6.1 – Destructive testing
Destructive testing means that the test results can only be obtained after the sample to be tested is destroyed (such as the bursting ability of shells, the strength of metal materials, etc.). After destructive testing, the sample being tested completely loses its original use value, so the sample size is small and the risk of testing is large.
6.2 – Non-destructive testing
Non-destructive inspection refers to the inspection that the product is not damaged during the inspection process and the product quality does not change substantially. Most inspections, such as the measurement of part dimensions, are non-destructive. Now due to the development of non-destructive testing technology, the scope of non-destructive testing is gradually expanding.
7 – Classified by inspection purpose
7.1 – Production inspection
Production inspection refers to the inspection carried out by the production enterprise at all stages of the entire production process of product formation, in order to ensure the quality of the product produced by the production enterprise. Production inspection implements internal control standards.
7.2 – Acceptance inspection
Acceptance inspection is the inspection carried out by the customer (demander) in the acceptance of the products provided by the manufacturer (supplier). The purpose of acceptance inspection is for customers to ensure the quality of accepted products. Acceptance inspection implements acceptance criteria.
7.3 – Supervision and inspection
Supervision and inspection refers to the market spot inspection supervision and inspection carried out by independent inspection institutions authorized by government departments at all levels, according to the plan formulated by the quality supervision and management department, to extract commodities from the market or directly from production enterprises. The purpose of supervision and inspection is to carry out macro control over the quality of products put into the market.
7.4 – Verification inspection
Verification inspection refers to the inspection of independent inspection institutions authorized by government departments at all levels to take samples from the products produced by the enterprise and verify whether the products produced by the enterprise meet the requirements of the quality standards implemented through inspection. For example, the type test in product quality certification is a verification inspection.
7.5 – Arbitration Inspection
Arbitration inspection means that when there is a dispute between the supply and demand parties due to product quality, the independent inspection agency authorized by the competent government department at all levels will take samples for inspection, and provide the arbitration institution as the technical basis for the award.
8 – Classified by supply and demand
8.1 – First-party inspection
The producer (supplier) is called the first party. First-party inspection refers to the inspection of the products produced by the manufacturer itself. First-party inspection is actually production inspection.
8.2 – Second-party inspection
The user (customer, demander) is called the second party. The inspection carried out by the demander on the purchased products or raw materials, purchased parts, outsourcing parts and supporting products is called second-party inspection. The second-party inspection is actually the purchase inspection (purchase inspection) and acceptance inspection.
8.3 – Third-party inspection
Independent inspection bodies authorized by government authorities at all levels are called impartial third parties. Third-party inspection includes supervision inspection, verification inspection, arbitration inspection, etc.
9 – Classified by inspector
9.1 – Self-test
Self-inspection refers to the inspection of the products or parts processed by the operators themselves. The purpose of self-inspection is for the operator to understand the quality status of the processed product or parts through inspection, so as to continuously adjust the production process to produce products or parts that fully meet the quality requirements.
9.2 – Mutual inspection
Mutual inspection is the mutual inspection of processed products by operators of the same type of work or upstream and downstream processes. The purpose of mutual inspection is to timely discover quality problems that do not meet the requirements of the process regulations through inspection, so as to take corrective measures in time, so as to ensure the quality of processed products
9.3 – Special inspection
Special inspection refers to the inspection carried out by personnel directly led by the quality inspection agency of the enterprise and engaged in quality inspection full-time.
10 – Classified by inspection system components
10.1 – Batch by batch inspection
Batch-by-batch inspection refers to the inspection of each batch of products produced in the production process, batch by batch. The purpose of batch-by-batch inspection is to determine whether the batch of products is qualified or not.
10.2 – Cycle inspection
Cycle refers to time, and cycle inspection is an inspection carried out at a determined time interval (quarter or month) from a batch or batches that pass the batch or batches one by one. The purpose of cycle inspection is to determine whether the production process is stable during the cycle.
Periodic inspection and batch by batch inspection constitute a complete inspection system of the enterprise. The cycle test is a test to determine the effect of system factors in the production process, while the batch test is a test to determine the effect of random factors. The two are a complete inspection system for putting into production and maintaining production. Cycle inspection is the premise of batch inspection, and there is no batch inspection in the production system without cycle inspection or unqualified cycle inspection. Batch-by-batch inspection is a supplement to the periodic test, and the batch-by-batch test is a test to control the role of random factors on the basis of eliminating the role of system factors through periodic testing.
In general, batch-by-batch inspection only tests the key quality characteristics of the product, while the cycle inspection tests all the quality characteristics of the product and the influence of the environment (temperature, humidity, time, air pressure, external force, load, radiation, mildew, moth, etc.) on the quality characteristics, and even includes accelerated aging and life tests. Therefore, the equipment required for cycle inspection is complex, long and expensive, but it must not be necessary to eliminate cycle inspection. When the enterprise does not have the conditions to carry out the cycle inspection, it can entrust the inspection agencies at all levels to do the cycle inspection on its behalf.
11 – Categorized by the effect of the test
11.1 – Verdictive test
Deterministic inspection is the conformity judgment of whether the product is qualified or not through inspection according to the quality standards of the product. The main function of the judgmental test is gatekeeping, and its preventive function is very weak.
11.2 – Informative inspection
Informational inspection is a modern inspection method that uses the information obtained from inspection for quality control. Because informational inspection is both inspection and quality control, it has a strong preventive function.
11.3 – Cause-finding test
Cause-finding inspection is in the design stage of the product, through full prediction, to find the possible cause of non-conformity (cause), targeted design and manufacture of error-proof devices, used in the production and manufacturing process of the product, to eliminate the generation of unqualified products. Therefore, causal testing has a strong preventive function.