Difference Between SPC and SQC (With Table)

One of the main works is the checking and analyzing of a product in the company. This helps to identify the defects, whether it is before manufacturing or after. Two of these processes are SPC and SQC. These are similar processes but there are differences too.

SPC vs SQC

The difference between the SPC and SQC is that in the case of SPC, the quality of the product is checked before the manufacture to prevent defects in the products. But in the case of SQC, the process is done after the manufacture of the products to check the quality and eliminate the defective products from good ones.

The full form of SPC is Statistical Process Control. This is a process of checking the quality of products before manufacturing and prevents that accordingly. The best quality machines are also not able to produce the perfect products. There are some of the other errors in them. The goal of this process control is to ensure the stability of production.

The full form of SQC is Statistical Quality Control. Inspecting each product is expensive and sometimes unrealistic, but the minimization of damaged products is also a requirement. So to solve this problem, the statistical quality control selects some random samples or subsamples of products and analyzes their quality.

Comparison Table Between SPC and SQC

Parameters of ComparisonSPCSQC
MonitoringProcess inputsProcess outputs
ProcessA process to prevent defects in the real timeA process to prevent defects from reaching the end customers
Done duringBefore manufacturingAfter manufacturing
DutyTo check production flawsThis observes specific amount of samples to measure the acceptability of product
Charts preparedControl charts, multivariate chartsAnalysis of means chart

What is SPC?

In the year 1920, the theory of SPC was developed by Bell Laboratories. The full form of SPC is Statistical Process Control. This is a process of checking the quality of products before manufacturing and prevents that accordingly. At that time, it was differentiated into two types random fluctuation and intermittent fluctuation.

The random fluctuations are the flaws due to the machines. The best quality machines are also not able to produce the perfect products. There are some of the other errors in them. The Intermittent fluctuations are the errors made by the manufacturer or by manual flaws, or due to the problem of calibrations. The goal of this process control is to ensure the stability of production. It also aims to control the proportion of the products that do not meet the need of specification limits.

Sometimes if only the product is under control, it does not mean that the product is always of good quality. So when it came to the observation that it has some of the other flaws. Some things are needed to be changed, like changing the process, redoing the same procedure, again analyzing the historical data, etc. The charts prepared to look after the process of SPC are control charts and multivariate charts.

What is SQC?

The full form of SQC is Statistical Quality Control. This is a process done to prevent defects from reaching the end customers. SQC ensures that the product is compliant with the customer’s requirements. This is done after the manufacturing of the products.

Inspecting each product is expensive and sometimes unrealistic, but the minimization of damaged products is also a requirement. So to solve this problem, the statistical quality control selects some random samples or subsamples of products and analyzes their quality. This ensures that the batch of the products how many damaged products are there. This is important for the assurance of the product for the customer. When the products are delivered, the customers also check the batch of products their quality. So the statistical quality control is the most important step for holding the company’s reputation and value in the market.

There are many steps for quality control. Quality control is directly related to good products production. If the SQC is high for the products, the product is considered good and high quality. The chart prepared for the statistical quality control is known as the analysis of means chart. This chart is used for making a decision regarding the quality and delivery of the products or for the reassurance and rectification of the products.

Main Differences Between SPC and SQC 

  1. SPC is the monitoring of process inputs in comparison to that the SQC is the monitoring of process outputs.
  2. SPC is a process to prevent defects in real-time, and on the other hand, SQC is a process to prevent defects from reaching the end customers.
  3. The process of SPC is done before manufacturing. On the other hand, the SQC process is done after manufacturing.
  4. SPC is done to check production flaws. In contrast, the SQC is done to observe a specific amount of samples to measure the acceptability of the product.
  5. The types of charts for SPC are control charts, multivariate charts. On the other hand, the SQC has an analysis of means charts.

Conclusion 

The companies have high respect in the market due to their products. The higher quality products make the company higher in rank in society. To maintain their reputation, these companies are very concerned about their output. There are many processes done for making a product. Some of these include the planning, raw materials, processing, etc.

The SQC is a subpart of the SPC. Statistical quality control is a part of the whole process control. These small processes are maintained very crucially for the high-quality products. These processes are done by every industry irrespective of the products they are making. These also depend on the professionalism and the skills of the manufacturers working in the industry as well as the machines used. The best machines are also not able to produce the perfect products with zero errors.

References 

  1. https://academic.oup.com/clinchem/article-abstract/64/2/289/5608851
  2. https://link.springer.com/chapter/10.1007/978-4-431-53969-8_6
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