Quality 101

Quality

Quality, as in “the quality of a product”, is the degree of excellence against an expectation (typically that of the customer). In the manufacturing world, we say that quality is what the customer says it is. As far as we are concerned, the standard of quality of the AR platform is still largely driven by the original customer: the U.S. Military.

Quality can be divided into two halves: proactive quality and reactive quality. These would be Quality Assurance and Quality Control, respectively.

Quality Assurance (QA) is comprised of systems of control that prevent defects from occurring and set the standards against which product is judged. They include the process design, procedures, training, specifications, and calibration/validation.

Quality Control (QC) includes the systems of inspection and defect repair that ensure a product meets the defined specifications before being released to a customer. QC can be performed in the middle of a process (in line or in process QC) or at the end of a process or series of processes.

The following diagram illustrates the tree of Quality that concerns us.

Specifications

Specifications represent the expected attribute performance of a product. For physical products, these include materials, treatments, dimensions, finishes, and performance testing. A manufacturer will use specifications to design a manufacturing process and the associated quality control activities.

All specifications are prospective, meaning that they describe what is expected of a product. We verify that a product conforms to specifications via our Quality Control activities.

With physical products, a common tool for communicating physical dimensions is Geometric Dimensioning and Tolerancing (GD&T). We will discuss this in a subsequent article.

Inspection and Testing

Inspection is the systematic evaluation of an object. It is a component of Quality Control. Inspection can be quantitative (e.g. dimensions) or qualitative (e.g. visual appearance). Inspection can utilize instruments, equipment, or tools, or it can be based on human perception.

Testing evaluates the function of a product. It can be destructive (e.g. ultimate strength) or non-destructive (e.g. function check).

Metrology

Metrology is the science of measurement. In an applied definition, it represents the collective effort to ensure standardization of equipment and products. Metrology is used in both Quality Assurance and Quality Control. In Quality Assurance, metrology is used to ensure calibration of instruments. In Quality Control, we then use those instruments to measure and evaluate product conformance to a standard (specification) as part of the inspection processes.

Measuring and Gauging

Measuring and gauging are subsets of metrology. They both evaluate a product against a standard or specification but do so in different ways. We will examine each of these separately.