Inspection and Quality control, 4 types of inspection, Statistical Quality Control.

In a manufacturing plant, Inspection, and quality control are the most important process in order to make a high-quality product. Inspection and quality control ensures the standard quality by checking the product during manufacturing at different stages.

If the product is not able to meet the desired quality, the product will reject and there will no further process on that unit. It saves unnecessary processing costs on rejected parts.

Let’s have a look on-

What are Inspection and quality control in manufacturing?

Inspection is important to maintain a certain quality during the manufacturing of a product. Quality control is a process by which customer ensures receive product free from defects.

Let me explain both the term separately-

Definition of Inspection:

After manufacturing, the product is required to perform certain functions. The process of checking whether the product does so or not is called Inspection.
Inspection compares the qualities of the product with a standard product during manufacturing. In other words, Inspection is a process of checking the acceptability of a manufactured product.
what is inspection
Inspection (Photo by Andrea Piacquadio from Pexels)

Objectives of Inspection:

  • Inspection separates defective components from the non-defective component so that adequate quality can be maintained.
  • Inspection locates defects in process or raw material which otherwise causes problems at the final stage.
  • It prevents further working on spoiled semifinished products. It helps the product to be more economical.
  • Inspection detects the weak position and trouble in the weak position by checking the design.

Types of Inspection methods:

  1. Revolving process, patrolling or floor inspection,
  2. Fixed inspection,
  3. Key-point inspection,
  4. Final inspection.

1. Revolving Inspection:

In this type of inspection, the inspector walks around the workplace floor and checks machine to machine, samples of the work of various workers, and machines.
The revolving inspection helps to find errors during the process and before the final product is ready. It is more effective and not need to move the product to another department for checking.

2. Fixed Inspection:

Fixed Inspection finds defects after the job has been completed.
Fixed inspection is used when inspection equipment and tools can not be brought on the workplace. In this case, workers brought the sample to a centralized position of the workplace, at the interval to check the quality.
Advantages of fixed inspection are the number of inspectors needed is less and workers and inspectors do not come in contact with each other, thus it eliminates the chance of approving the doubtful products.

3. Key-point inspection:

A key point is a stage of production beyond which it requires an expensive operation or it may not rework. Every product has a key point in its process of manufacturing.
Inspection at key point separates faulty products and reject them from going to further processing. Thus avoid unnecessary further expenditure on those poor and substandard products. It reduces the cost of production.

4. Final Inspection:

In the final inspection, the inspector checks the performance and appearance of the product before delivery.
These types of checking include destructive and non-destructive testing such as tensile testing, impact testing, fatigue testing, etc. The final stage of inspection ensures that the product should pass the X-ray radiography, ultrasonic inspection, etc.

quality control

What is Quality control?

Quality control in manufacturing is a process through which a production system ensures that standard product quality is maintained or improved according to customers’ needs.
In other words, it incorporates the testing of units and determines if the product is within the specification for the final production. The role of testing is to determine there is any need for correction in the process, so that product can meet the customer’s desire.
If I explain “quality” and “control” separately, Quality is a relative term, and it is explained by comparing it with a standard product. For example, gear used in sugarcane juice extracting machine isn’t as correct, finished as gear used in an engine transmission system. So, a component is said to be good quality if the component works well for which it is meant.
On the other hand, control is a system for determining – what to inspect, how to inspect, how often to inspect. It also finds out the causes for producing a poor product, and suggest the corrective action.
An important aspect of quality control is the establishment of well defines controls. Limiting the chances of error and reduce the manufacturing cost will generate more profit.

Basic fundamentals of Statistical Quality Control

It called statistical quality control (S.Q.C.) if statistical techniques are applied to control the quality or to solve quality control problems. Statistical quality control makes inspection less costly and more reliable than other techniques. It controls the quality of outgoing products to conclude whether the quality of each product is as per laid quality standard or not.
The S.Q.C. technique collects, analyses the data, and permits more fundamental control over the product quality. It scientifically fixes the process tolerance.
The fundamental of statistical quality control is based on the probability theory.
The chance of the sample to represent the entire batch is developed from the theory of probability.

Statistical Quality Control uses 3 scientific techniques, namely,

  1. Sampling Inspection,
  2. Analysis of the data,
  3. Control charting.
Inspecting all components is a very tiring and costly process. Instead of inspecting all components, some sample of the component can be inspected. This process is call sampling inspection. Chances of error in sampling inspection are high. On the other hand, if a random sample is selected from a lot and relying on the probability theory is assumed to represent the lot. So, there are much savings in the cost of the inspection.
In certain cases (example: tensile and fatigue testing, the chemical composition of an alloy, etc.) sampling inspection is the only method of inspection.
The results of the inspection are then analysed by determining by mean, range, standard division and the control limits for predetermine level of confidence. Statistical Quality Control (S.Q.C.) also decides the size of the sample and describe the sample reliability.
As control limits are plotted, and individual observations marked on a graph paper it takes the shape of a control chart. The jig-jag line present on a control chart represents whether the quality of the product is improving or going down. Control charting continuously monitors processes and machines and immediately tells if any process or machine is getting out of adjustment.

Thus, Inspection and quality control are the most important department in any Production unit.

What is the role of inspection in quality control?

It’s very important for every organization that the quality of the products is maintained when they are delivered to the consumers since the product quality is the topmost parameter for the success of any organization. However, during the production employees do mistakes some time, machine and equipment have breakdowns. This leads to destabilization of the process and results of that low-quality product can be produced.

Hence inspection and quality checking become mandatory to ensure customer satisfaction. Inspection and testing are the processes of controlling products quality by comparing it with the standards and specifications. During the inspection process, they focus on appearance, construction, and working of the product. Inspection is one of the operational parts of quality control.

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