Abstract
Ultrasonic Machining (USM) applies slurry between workpiece and vibrating tool subject to a static load, and the material removal is the result of a series of material fracture. CAD/CAM/CAE has been introduced to automated mold production, while the polishing is a vital technology in mold manufacturing process. However, the molds are often polished by skillful handwork and take up 13%-23% of total mold processing time. As a result, the process is time-consuming and not well accepted concerning the reliability of the polished surface. The hardness and the brittleness of the mold surface increase due to the carbon permeating and quenching during electrical discharge machining. Therefore, the following polishing is difficult to apply. The objective of this research is to remove the damaged layer of the mold surface after EDM and to achieve the mold polishing by the removal mechanism of the hard and brittle material associated with USM. The automated ultrasonic mold polisher with three degrees of freedom controlled by PC is designed. The polishing loop can be worked out to substitute for the conventional hand polishing.From the experimental results, two major phenomena can be observed during polishing as the formation mechanisms of the polished surface: (1) Microcutting and plowing effects exist. These cutting traces of the abrasives are the main mechanism of ultrasonic polishing. (2) The local microscopic plastic deformation occurs because the abrasives directly press on the mold surface. This study also shows that the abrasive size should be determined by the amplitude of the tool and the surface roughness before polishing. The optimal choice lies between the vibration amplitude and three to four times the maximum surface roughness. As to the static load, whether the different abrasive sizes are changed or not, the higher the static load, the smoother the surface. For a certain abrasive size, there is a polishing limit. Multi-pass polishing continuously improves the surface quality up to the limit.