Quality Control (QC)

INTRODUCTION

What is Quality control ?

    Quality control in manufacturing is a set of systematic processes and activities implemented within the manufacturing environment to ensure that products meet specified quality standards. The ultimate goal of quality control in manufacturing is to identify and rectify defects or deviations from established quality criteria during or after the production process. This helps ensure that the final products conform to the desired level of quality and meet customer expectations.

Key aspects of quality control in manufacturing include:

1.Inspection of Raw Materials: Quality control starts with the inspection of raw materials and components to ensure they meet

the specified quality standards. This involves assessing the physical and chemical characteristics

of materials before they are used in the production process.

2.In-Process Inspection: Throughout the manufacturing process, in-process inspections are conducted to monitor the quality

of products at various stages. This helps identify and address issues early in the production cycle,

reducing the likelihood of defects in the final product.

3.Testing: Various types of testing are employed to evaluate the performance, durability, and functionality

of products. This can include mechanical testing, electrical testing, and other specialized tests

depending on the nature of the manufactured goods.

4.Dimensional Checks: Ensuring that products meet dimensional specifications is crucial, especially in industries

where precision is essential. Dimensional checks involve verifying the accuracy of measurements

against predefined standards.

5.Statistical Process Control SPC is a method used to monitor and control the manufacturing process through statistical analysis.

Control charts and other statistical tools help identify trends, variations, and potential issues in the

production process.

6.Sampling Techniques: Rather than inspecting every individual product, quality control often involves sampling techniques. A statistically representative sample is tested, and the results are extrapolated to the entire production batch.

7.Documentation: Thorough documentation of quality control activities is essential. Records of inspections, test results, and any corrective actions taken are maintained for traceability and compliance purposes.

8.Corrective Actions: If defects or deviations are identified, quality control involves implementing corrective actions to address the issues. This may include adjusting production processes, reworking defective units, or making changes to prevent similar issues in the future.

9.Quality Control Tools: Various tools and techniques are used in quality control, including visual aids, measurement devices, and specialized equipment. Statistical tools, such as histograms and Pareto charts, are also common for data analysis.

As the goal of QC is to identify and correct failures on a product, three decisions may apply after testing / measurement:

• Accept / release (OK product)

• Reject / scrap (NOK product)

• Rework / repair (NOK product that can be restored to the intended condition with 100% reliability)

In addition, it can happen that the subject of a decision is not only the product, but also the control process. For example: an SPC based control procedure starts to detect products out of the tolerance range for a given characteristic, and based on the numbers it seems, that the issue has risen due to a systematic root cause. In such a case, it is quite desirable to implement a temporary 100% testing instead of relying solely on the statistical process control. 

Quality control maintains the control of products or services, comparing measured data to references during manufacturing. Many control methods exist, based on technology, fit for purpose, frequency. In many cases companies apply only sampling tests or inspection, while some product characteristics require focused testing in 100% on all of the products. Some examples for quality control:

• Visual inspection of product with magnifier or microscope.

• 100% capacity range measurement of capacitors with a "fit-for-purpose" device.

• Measuring electrical characteristics of various semiconductor components with ICT (In-circuit test).

• Measurement of cylinder block dimensions with 3D coordinate measuring machine.

• Statistical Process Control (SPC): controlling the whole population by measuring a smaller population (samples).

Quality Improvement (QI) and Quality Planning (QP) have a huge impact on Quality Control (QC). First, planning a robust product and process design desires less quality control, as it brings decreased Cost of Poor Quality (CoPQ). On the other hand, quality improvement advances the manufacturing process (and product design as well), also decreasing the need of managing issues that already happened, with other words "fire fighting".It must be pointed out, that Quality Assurance (QA) is not equal to Quality Control (QC). While QA is the bunch of proactive and systematic activities to ensure quality during the product realization, QC is a completely reactive process that aims to identify and eliminate failures.

Simply: QA is a preventive process oriented methodology, while QC is a reactive product oriented process. Decades before, QA was mainly considered as a performance evaluation after operations, but nowadays it means much more: ensuring quality, defect prevention, verification of processes (process oriented).