Quality Assurance Versus Quality Control

Quality Assurance (QA)

Quality Assurance is concerned with how the product is made. It establishes and maintains systems that make it likely the product will be right first time.

Typical QA activities include:

• Developing documented procedures and work instructions

• Process validation

• Training and competence assessment

• Supplier approval and auditing

• Risk assessments (PFMEA)

• Process capability studies (Cp/Cpk)

• Internal audits

• Calibration systems

• Continuous improvement

• Compliance with standards such as ISO 9001 or ISO 13485

Engineering example:

Before introducing a new PCB assembly process, QA would:

• Validate the soldering process.

• Approve the solder paste and components.

• Produce work instructions.

• Train operators.

• Establish inspection criteria.

• Ensure equipment is calibrated.

• Conduct process capability studies.

The objective is to build quality into the process.

Quality Control (QC)

Quality Control is concerned with what has been produced. It confirms that products conform to specification.

Typical QC activities include:

• Incoming goods inspection

• First Article Inspection (FAI)

• In-process inspection

• Final inspection

• Functional testing

• Dimensional measurement

• Visual inspection

• Sampling plans

• Recording non-conformances

• Acceptance or rejection of product

Engineering example:

After PCB assembly, QC would:

• Inspect solder joints against IPC standards.

• Perform AOI or X-ray inspection.

• Carry out functional testing.

• Measure critical dimensions.

• Record any defects.

• Reject or rework assemblies that do not meet specification.

The objective is to identify non-conforming product before it reaches the customer.

A manufacturing example

Imagine manufacturing a steam locomotive fusible plug.

QA asks:

• Is the machining process validated?

• Are the drawings controlled?

• Are operators trained?

• Are gauges calibrated?

• Are approved materials being used?

• Is the brazing process qualified?

QC asks:

• Does this individual plug meet drawing dimensions?

• Has it passed pressure testing?

• Are the threads within tolerance?

• Has visual inspection passed?

• Does it comply with the acceptance criteria?

An easy analogy

Think of baking a cake.

Quality Assurance

• Uses a proven recipe.

• Calibrates the oven.

• Uses fresh ingredients.

• Trains the baker.

• Follows a documented method.

Quality Control

• Checks whether the cake is cooked.

• Measures its weight.

• Looks for cracks.

• Tastes it.

• Rejects it if it doesn't meet the required standard.

QA makes it likely the cake will be good.

QC checks whether it actually is.

The relationship

QA and QC are complementary.

A strong QA system should reduce the amount of QC failures because the process consistently produces conforming products. However, QC remains necessary to verify that the process continues to perform as intended and to detect any unexpected variation.

A concise engineering definition

Quality Assurance is the planned, systematic set of activities that provides confidence a process will consistently produce products that meet requirements. Quality Control is the operational inspection, measurement and testing of products to verify they meet those requirements before release.

In Lean manufacturing terms, QA builds quality into the process, while QC verifies the quality of the output. The highest-performing organisations focus on prevention through robust QA, using QC as confirmation rather than as the primary means of ensuring quality.