Evaluation of Metallic Mold Surfaces Polished by an Industrial Robot with Stick Whetstones

Abstract

Our ultimate goal is to develop an automatic polishing system that uses an industrial robot equipped with whetstones. The robot mimics the movements skilled workers make as they polish surfaces manually. This paper, the first step in the development of our system, presents experimental results to prove that our system completely removes the marks, which is the most time-consuming and crucial process for human workers, from the flat surfaces of metallic molds produced through the Electrical Discharge Machining (EDM) process. We build a polishing system that consists of a small 6-DOF industrial robot for material handling. Attached to its wrist is a six-axis force-torque sensor and it employs a whetstone holding mechanism. Before the robot system begins its polishing work, the normal force to be applied to the flat surface can be adjusted to a target value by altering the height of the hand. We adopt two polishing paths for the whetstone, reciprocating and zigzag. We then conduct experiments using the two paths, visually inspect the surface, and measure the surface roughness and shape. Based on the experimental results, we confirm that the system has completely removed the EDM mark layer. Although we find that the zigzag path leaves striped patterns on the polished surface, we are not able to determine their cause. Finally, we test three combinations of the two paths under different conditions to find the most suitable combination.