Ability of quality controllers to detect standard scratches on polished surfaces

• Perfectly polished surfaces are generated on flat stainless steel pellets.
• A nanoindenter is used for the standard scratches creation.
• The standard sample range from the invisible to the visible.
• A panel of polishing controllers participated to a defect research task.
• A visibility and acceptability thresholds have been set.

The production of polished metal surfaces addresses a large number of fields such as medical prostheses, jewellery or moulds. These surfaces are checked by people who rarely agree on the definition of the right geometry limit of scratches. The aim of this work is to study human vision of scratches. The first step was to produce calibrated scratches barely visible by the human eye on polished metal surfaces in order to define standard samples for polishing quality control. A nanoindenter with a Berkovich tip was used to produce these scratches. These standard samples were shown to polishing controllers. They were asked to perform a research task leading to the establishment of two thresholds that characterize the visualization of scratches: a visibility threshold as well as an acceptability threshold.