What is Statistical Quality Control?

As consumers, we always expect products to function properly and work according to how it is designed for. Have you ever tried buying a DVD player and finding out that it only chooses the discs that it plays? Moreover, what about bringing home a newly purchased bag and discovering that the zipper is not functioning? These situations can be very depressing and disappointing. While it is true that manufacturers have full responsibility over their products; it cannot be assumed that these discrepancies are done intentionally. In as much as manufacturers aim for their products to be functional and defect-free, defects are inevitable.

Product defects are most observable for products that are mass-produced. In addition, product defects are more significant in manufacturing companies that are not so keen in controlling the quality of their products. If manufacturers want top quality products, measures should be taken in ensuring that product quality is maintained from the beginning of the production process until the end of the production line. Other manufacturing companies even guarantee the quality of their products way beyond after the products are purchased. As such, these companies offer warranties for their products because these companies are confident that their products are of excellent quality.

One way of ensuring quality control is integrating quality into the process. Every process should be critically considered and guarded against errors that lead to product defects. However, in reality it is difficult to impose product inspection along every process- so much more if the production is quite large. This is why the task of maximizing the ability to control the quality of the products has become a challenge for most manufacturing companies.

Fortunately though, this dilemma is addressed by the application of Statistical Quality Control in measuring and evaluating the quality of the products. One of the identified factors that contribute to product defects is variation in the production process. Thus with statistical quality control, variations are measured, analyzed, and rectified. There are three categories in statistical quality control, and each of these categories is effectively used in product quality evaluation.

Descriptive Statistics. In this SQC category, quality characteristics and relationships are described. In order to achieve these, it is important to find out the mean, range, standard deviation, and measure of the distribution of data of the sample.

Statistical Process Control. This category verifies if a process is functioning properly or not. A random sample of the products is taken, inspected, and decided if these manifest characteristics that fall into a predetermined range. The predetermined range determines if the process is functioning or not.

Acceptance Sampling. Acceptance sampling determines if a whole lot of products is acceptable based on the results of random inspection. In other words, acceptance sampling determines if a product batch is acceptable or not. If the products are not acceptable, then the whole batch is rejected.

Each of these categories employs statistical tools which are used in analyzing the quality of the products. While all of these categories are helpful in quality analysis, the most frequently used is the Statistical Process Control practically because quality control is integrated into every process resulting into the identification of quality problems in the production process.

Fig.1. Statistical Quality Control Diagram

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Fig.2. Microsoft Excel Generated SQC Chart

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