QC stands for Quality Control, which is the package of activities that ensure quality on product level, by finding and identifying defects and failure sources with using
various quality tools and methods.
Quality control is emphasizing testing and validation, so it is more reactive, less proactive, but the outputs (data, information) of quality control can also lead to
preventive measures, which help later the preventive Quality Assurance (QA)
of product realization.
Typical examples for quality control are testing, product validation, inspection, when the controlled product is measured, compared against a defined requirement or
specification. Based on Juran’s methodology, the key deliverables and inputs / outputs of Quality Control (QC) are the following:
Quality Control Process (input-output diagram) (Source: Joseph M. Juran - Juran's Quality Handbook)
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
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
- 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)
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).
"Quality control has as its primary purpose to maintain control. Performance is evaluated during operations, and performance is compared to goals during operations. The
resulting information is received and used by the operating forces. Quality assurance’s main purpose is to verify that control is being maintained. Performance is evaluated after operations, and the resulting
information is provided to both the operating forces and others who have a need to know." - Joseph M. Juran
Source: qMindset.com; Joseph M. Juran - Juran's Quality Handbook