A non-contact technique for the on-site inspection of molds and dies polishing

Polishing is important to the manufacture of molds and dies. Rather than changing the geometric shape of the surface, the purpose is to reduce the surface roughness to the required condition. The process is multi-stage. The surface roughness to be achieved at each stage depends mainly on the choice of abrasives and in particular on the grain size. Polishing for molds and dies can be expensive, time consuming, labor intensive, and error prone. Mistakes committed by a human operator at a later stage may result in expensive re-working. This paper investigates a non-contact approach suitable for on-site polishing inspection. The technique is based on computer vision and image analysis. Rather than direct measurement of the surface roughness which could be costly, it relies on analyzing the texture of the surface being polished to determine when the current stage of polishing is completed. Grooves are developed on the surface during polishing and their direction follow the direction of the rubbing of abrasive particles. Suppose polishing is planned such that the direction of rubbing is distinct for each location of the surface between the current stage and the previous stage of polishing. The change of the direction of the grooves may then be used to flag the completion of the current stage. Preliminary experiments have been conducted to validate the proposed polishing inspection technique in which the surface roughness was reduced from 0.9 to 0.02 μm. The results are promising and show that the proposed approach could be practical and robust.