Automatic polishing process of plastic injection molds on a 5-axis milling center

TL;DR

This paper presents an automated polishing method for plastic injection molds using a 5-axis milling center, aiming to replace manual polishing, reduce costs, and maintain high surface quality through specialized algorithms and compliance control.

Contribution

It introduces a novel automated polishing technique on a 5-axis milling center, including algorithms for tool path planning and force control to replicate skilled manual polishing.

Findings

Effective surface roughness achieved comparable to manual polishing

Method reduces production costs by integrating polishing into machining

Simple implementation demonstrated on a 5-axis machining center

Abstract

The plastic injection mold manufacturing process includes polishing operations when surface roughness is critical or mirror effect is required to produce transparent parts. This polishing operation is mainly carried out manually by skilled workers of subcontractor companies. In this paper, we propose an automatic polishing technique on a 5-axis milling center in order to use the same means of production from machining to polishing and reduce the costs. We develop special algorithms to compute 5-axis cutter locations on free-form cavities in order to imitate the skills of the workers. These are based on both filling curves and trochoidal curves. The polishing force is ensured by the compliance of the passive tool itself and set-up by calibration between displacement and force based on a force sensor. The compliance of the tool helps to avoid kinematical error effects on the part during 5-axis tool movements. The effectiveness of the method in terms of the surface roughness quality and the simplicity of implementation is shown through experiments on a 5-axis machining center with a rotary and tilt table.