What is a control?

In the quality profession we often hear reference to “controls”. Control Plans are created to document how a process is operated; it defines the reaction plan for a non-conformance and documents what is in place to “control the process” to defined requirements.

Often we see (today) that controls are listed as follows: control charts, checklists, audit sheets, inspection sheets, data collection forms etc.

The confusion here is that while generally referred to as “controls” these items are actually quality records. These records are “documents”; they can be audited by management or can be used as “evidence” that a quality system is in place. However, it is outdated thinking to define these documents as controls.

A true quality control is or can be error-proofed. It ensures a process can only be done the correct way and is an aide to the operator.  Controls include the process tooling, red part tests; fixtures, gages, maintenance systems etc. that ensures a robust process.

Recording results do not “control a process” any more than a control chart of temperature readings controls temperature.   A checklist does not ensure all steps were followed and does not ensure that results met requirements.  Recording results creates documentation that provides an audit trail.

In Quality Assurance the general hierarchy of a quality system begins with procedures; followed by instructions; followed by forms.  Once the forms are filled in, these documents become quality records. These records are used for traceability; to evaluate whether a quality system is in place; to evaluate if the quality system is suitable and working. Operator instructions are just that – instructions. These documents are the foundation of quality assurance not quality control.

Quality Control begins with design for manufacturability; leads to build in station and continually is improved to support the operator.  This is the only way to have less “operator dominant processes” and continually reduce defects and variation. Quality control documentation includes DFMEAs, PFMEAs, Process Flow Diagrams and Control Plans. These are the staple documents for Quality Control but are not “controls”. They document the Quality and Process Controls.

With the ever increasing demand for quality improvement it is simply no longer acceptable to mistake a quality record for a control. Documents do not control processes nor do they build in quality.

Manufacturing systems need process controls; Quality systems need documentation. Mistaking one for the other will lead to confusion and hamper any product and process improvement efforts.  It is important to document the quality system while it is equally important to control the processes that ultimately lead to value added output whether it is product or service.