Quality inspection

Quality inspection are measures aimed at checking, measuring, or testing of one or more product characteristics and to relate the results to the requirements to confirm compliance. This task is usually performed by specialized personnel and does not fall within the responsibility of production workers. Products that don't comply with the specifications are rejected or returned to improve.

Origins of quality inspection

Quality inspection is the first stage of evolution of quality approach (see figure 1). The origins of the quality inspection back to the late nineteenth and early twentieth century. In days of fast-growing industry, Frederick Winslow Taylor developed the rules of scientific management. Quality wasn't up to speed with rapidly increasing labour productivity. Often, the customer had to reckon with defective products. To alleviate customer frustration, this problem was solved by replacing the defective product with a new one. Conducting this type of procedure entailed generating considerable cost. To reduce the excessive cost escalation manufacturers introduced controller position, unknown to craft. The designated employee, through carried out inspections, made sure that the greatest possible number of good products leave the gate of the factory. This initial form of quality inspection based on the principle of quality by sorting.

The scope of quality inspection

Organization which uses quality inspection, treats inspector as if he was a customer. The optimum form of quality inspection is the man who's aim is the best customer satisfaction. Quality inspection serves three main purposes:

1. Identification of the quality problem
2. Provision of information to managers
3. Elimination of the problem by managers

Quality inspection can be performed at the end of production process (final inspection) or at several stages of the production (intermediate inspection).

Quality inspection vs. quality control

Development of quality approach

Quality inspection is concerned on postoperative or post-production check of products. It doesn't have direct impact on production process. Quality inspector only sorts products, and he doesn't let poor quality products to leave the factory. Quality inspection has no feedback loop. That means that information about failures and their causes is not passed to workers or managers. Therefore, this system cannot improve itself.

Quality control is the next stage of quality approach evolution. In that approach there is a direct connection between quality inspector and workers. Tests should not only distinguish bad products from good, but also find the cause of problems. This information should be sent to managers, as well as workers, who can then improve the process. The sub-stage of quality control is statistical quality control, known also as statistical process control. Quality control is a one feedback loop system. Information is passed to workers, who can try to improve their work, but not to change system or product.

See comparison between quality control and quality assurance in article about Quality control.

Sample size

See: sampling for more information. Due to improvement of statistical methods 100% sample is not necessary, and it never have been efficient. In practice errors made by quality inspectors lead to sending low quality products to customers. The most efficient way is quality self-assessment and protective actions. In fact, many scholars and managers point that quality inspection does not create value to the customer (e.g. Genichi Taguchi).

• Inspection one hundred percent - consists of subjecting the inspection of all units produced. Due to time-consuming, this method is applied only to products manufactured individually or in small series. It was typical for phase of quality inspection
• Statistical inspection - a lot of statistical inspection is assessed on the basis taken in a random sample. Therefore, this form of control is called a sample inspection. Depending on the size and frequency of sampling and the use of audit information to reverse effects on the production process, inspection may be statistical in nature. This method was typical in early phase of quality control.
• Statistical process control (SPC) is an idea created by Walter A. Shewhart who created methodology for using statistics to detect potential errors before they happen. Thanks to Shewhart's control charts managers can predict errors based on information about production process malfunctions. This method was popularized in phase of quality control and is used in quality assurance and quality management approaches.

Examples of Quality inspection

• Visual Inspection: Visual inspection is the most common type of quality inspection. In this type of inspection, the inspector looks at the product to ensure that it meets all of the required specifications. This may include examining the product for flaws, defects, or other issues.
• Functional Testing: Functional testing is also a common type of quality inspection. In this type of inspection, the inspector tests the product to make sure that it is functioning as expected. This may include testing the product in different conditions, such as checking the power consumption, speed, or other performance criteria.
• Statistical Process Control (SPC): Statistical process control is a type of quality inspection that uses statistical analysis to evaluate the performance of the product. This may include analyzing the data from production to determine whether the product is meeting the desired specifications.
• Dimensional Measurement: Dimensional measurement is a type of quality inspection that involves measuring the size and shape of the product to make sure it meets the required specifications. This may include measuring the length, width, height, and other dimensions of the product.
• Sampling: Sampling is another type of quality inspection that involves testing a sample of the product to make sure it meets the required specifications. This may involve taking a sample of the product and performing tests on it to determine if it meets the specifications.

Advantages of Quality inspection

Quality inspection is an important part of the manufacturing process as it allows for a certain level of control and quality assurance. It can help to reduce customer complaints, improve customer satisfaction, and increase the efficiency of the production process. The following are some of the main advantages of quality inspection:

• Improved Quality: Quality inspection ensures that the finished product meets customer specifications, as well as any other standards that may be set by the company. This helps to guarantee that customers receive a product that is of high quality and free of any defects.
• Reduced Costs: Quality inspection can help to reduce costs associated with producing a defective product. By catching any defects before they are shipped to a customer, companies can save on the cost of replacing or repairing the product.
• Improved Efficiency: Quality inspection helps to ensure that production processes are efficient and running smoothly. By catching mistakes early on, companies can reduce waste and ensure that their products are produced in a timely manner.

Limitations of Quality inspection

Although quality inspection is a common practice to ensure products meet certain standards, there are several limitations that can affect the effectiveness of the process. These limitations include:

• Time: Quality inspection can take a considerable amount of time to complete depending on the complexity of the product and the number of characteristics being tested. This can lead to delays in production and lost profits.
• Cost: Quality inspection often requires specialized personnel, equipment and materials, all of which add to the cost of production.
• Focus: Quality inspection is usually limited to testing for only a few characteristics of the product, leaving other potential issues undetected.
• Human Error: Quality inspection is often performed by human testers, which can lead to errors due to fatigue, lack of concentration, or lack of expertise.
• Subjectivity: Quality inspection can be subjective, as it relies on the opinion of the tester. This can lead to inconsistent results.

Other approaches related to Quality inspection

Quality inspection is a process of measuring and testing the characteristics of a product in order to ensure that it fulfills the requirements of the specifications. This process is usually performed by specialized personnel and doesn't fall within the responsibility of production workers. Other approaches related to Quality inspection include:

• Quality assurance - this is an approach that focuses on prevention of errors and defects in the production process. Quality assurance seeks to ensure that the product will meet its specifications and requirements, and that the production process is consistent and reliable.
• Quality control - this is an approach that focuses on the detection and removal of errors and defects that may have occurred during the production process. Quality control measures are used to identify any issues or potential problems and take corrective action to improve the process.
• Statistical process control - this is an approach that uses statistical methods to monitor and control the production process. It is used to detect any inconsistencies in the process, identify the cause of the problem, and take corrective action.

In summary, Quality inspection is a process of measuring and testing the characteristics of a product in order to ensure that it fulfills the requirements of the specifications. Other approaches related to Quality inspection include Quality assurance, Quality control and Statistical process control.

Quality inspection — recommended articles

Quality control — Line balancing — Quality assurance — Statistical process control — 5S method — Single minute exchange of die — Control plan — Zero defects — Quality control plan

References

• Boukouvalas, C., De Natale, F., De Toni, G., Kittler, J., Marik, R., Mirmehdi, M.,... & Vernazza, F. (1997, May). An integrated system for quality inspection of tiles. In Int. Conference on Quality Control by Artificial Vision, QCAV (Vol. 97, p. 49-54).
• Lieberman GJ (1965), Statistical Process Control and The Impact of Automatic Process Control, Technometrics, Volume 7, Issue 3
• Taguchi, G. (1986). Introduction to quality engineering: designing quality into products and processes
• Taylor HM, Statistical Control of a Gaussian Process, Technometrics, Volume 9, Issue 1
• Unal, R., & Dean, E. B. (1990). Taguchi approach to design optimization for quality and cost: an overview.
• Myth of added value of inspection @ wawak.pl.

Author: Slawomir Wawak