Quality Control

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What is Quality Control

A state of control is not a natural state for any process. Left unattended most processes will eventually produce outside of permissible limits.

Data must be consistently collected to understand and monitor how any process is truly performing. Process adjustments must be made when data indicates that they are necessary.

Quality Control Definition

QC is simply the observational techniques and activities used to verify that requirements have been fulfilled.

It's a regulatory process that gathers measurements, compares those measurements to a standard, and determines whether or not the requirements for quality have been met. This data acquisition and analysis also facilitates quality improvement.

When requirements are met the product or service moves forward to the next step in the process. When requirements are not met, the material or service is identified as nonconforming and appropriate action is taken, usually rework.

Simply put, Quality Control (QC) is InspectionIts emphasis is to uncover defects and report them.

Alternatively, Quality Assurance (QA) attempts to improve and stabilize processes to avoid defects in the first place.

QA is before and QC is after! Applying QC is intended to prevent defect escapes to the customer either internal or external.

QC is used to understand and maintain the acceptable state.

It's executed upon the product or service and is implemented through a Quality Control Plan. Quality Audits are also a form Quality Control.

QC Inspection should be performed on:

  • Incoming goods and services, 
  • Internal work-in-process (WIP) and, 
  • End item products prior to shipping them to the customer.

The amount of inspection to apply depends upon the capability of the process.

From Statistical QC, SPC and Process Capability, to Total Quality Control and Six Sigma, QC methods and techniques continue to evolve.

Quality Assurance Planning leads to putting processes in place to meet requirements. QC Planning uses measurements that determine if these processes are functioning as intended.

Implementing Quality Control

In order to implement Quality Control you first must decide what specific requirement(s) and standards the product or service must meet.

There's good news here though. Almost anything that you need at the process level can be purchased for a lot less than it will cost you to create it from scratch.  

Next you'll need to determine an acceptable quality level (for example, the percentage of units that pass end-item inspection and testing).

Lastly, you must collect data and review the results to determine if the target standard for quality is being achieved. 

When standards for quality are not met both short-term and long-term corrective action should be taken to resolve the gap between needed performance and actual performance.

  • Short-term corrective action could include sorting and reworking the material or service. Putting a quick fix in place at the point of defect generation to minimize the impact of the issue.
  • Long-term corrective identifies the root-cause of the problem and puts permanent counter-measures in place to prevent problem recurrence.

To be effective Quality Control efforts must be consistent and ongoing to ensure satisfactory process output and to immediately detect problem recurrence or identify any new instances of problems.


Inspection is “an appraisal activity that compares the product or service to applicable requirements”. Inspections that must be performed are documented in the QC Plan.

Quality Control

Inspection Examples

  • Workmanship
  • Counts
  • Appearance
  • Size and Location
  • Function
  • Marking and Labeling
  • Documentation Correctness
  • Packaging
  • Any “important requirement” especially those that exhibit poor performance or process capability.

Inspection Choices

100% inspection is costly and not very practical especially for high volume producers. However, 100% inspection may be appropriate for critical items or to shield internal or external customers from problems.

Sampling inspection involves drawing a sample quantity of “the item of interest”” from a larger population. The samples are inspected and a disposition, usually pass or fail, about the entire population is made.

No inspection allows problems to go undetected. Problems are passed to the next work station or end-item customer. No inspection is very risky. However, no inspection is possible with completely error-proofed processes.

Basic practice is concerned with QC Planning in the following areas;

  • The inspection of incoming goods. This is known as Incoming Inspection.
  • The inspection of one’s own value-add, or in-process materials. This is known as In-process Inspection. Here things are inspected along the way to realization.
  • The inspection of the final product or service end-item. This is known as Final Inspection.

From QC to Free-Six-Sigma

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