Quality assurance: proving the workpiece holds

Development of product and quality documentation is a separate competency goal on CNC technician training — and one of the things that distinguishes a professional operator from a hobbyist. In a modern company a part is not finished when it is cut but when it is measured approved and documented. The customer is not just buying the part but the proof that it meets the drawing. The person who masters quality work is indispensable in production.

§First piece must be approved

Before a series really starts, the first piece is made and thoroughly inspected — a first article inspection (FAI). All critical dimensions and tolerances are measured against the drawing, and results are documented. Once the first piece is approved, you know the setup, program, and cutting data produce a piece within requirements, and the series can run. Catching an error here costs one piece — catching it only at the end costs the entire series.

§Målerapporten dokumenterer resultatet

Scale indicates the ratio between the drawing's dimensions and reality's dimensions. A scale like 1:1 means the drawing is full size; 1:50 means a length on the drawing corresponds to 50 times as much in reality and 2:1 means the drawing is enlarged. Choose a scale that makes details readable without making the drawing unnecessarily large.

§Løbende kontrol under serien

Even with an approved first piece the process can drift: the tool wears temperature changes and dimensions slowly wander towards the tolerance limit. Therefore continuous monitoring is done during the series — at fixed intervals or using statistical process control (SPC) where you plot the dimensions and intervene before they reach the limit. If you only measure the first and last piece you discover too late that the middle of the series has drifted. Continuous monitoring is cheap insurance against expensive batch rejections.

§Traceability and quality management

In many industries — particularly in medical device, aviation and energy — traceability is required: you must be able to trace a part back to material batch, machine, programme, operator and measurement report. This is related to quality management systems such as ISO 9001, which set requirements for processes to be described and for documentation to be in order. For the CNC technician, this means that proper recording is not optional — it is part of the delivery and often a prerequisite for being allowed to produce for the customer at all.

• 01Always approve a first item before the series runs
• 02Write a measuring report on the critical measurements — not just the easy ones
• 03Check continuously so process operation is caught in time
• 04Ensure traceability from material to finished item where required
• 05See documentation as part of the product not as extra work

“A subject without documentation is a claim. With documentation it is proof.”