Ultraprecision micromachining of hardened steel by applying ultrasonic elliptical vibration cutting

Ultraprecision micromachining of hardened steel with a single point diamond tool, which is practically impossible due to rapid tool wear, is realized by applying elliptical vibration cutting technology which has been developed by the authors. A practical ultrasonic elliptical vibration cutting system is developed in the present research, which consists of a practical vibration control system and an ultraprecision planning machine. The control system is fabricated to keep the elliptical vibration to have a desired locus, where the amplitudes of the two directional vibrations and their phase shift are kept to be desired values, and the vibration frequency is locked to an average value of their resonant frequencies. The vibration control system is mounted on the on the ultraprecision planning machine, which consists of three feed tables with double hydrostatic oil guideways in XYZ axes, two rotary index tables in BC axes and a five axis control system. The developed elliptical vibration cutting system is applied to ultraprecision diamond planning of hardened die steel, and a high quality mirror surface is obtained over a large area of the whole finished surface. Maximum roughness of the finished surface is less than 0.04 μm Ry, although the cutting distance reaches 1110 m. On the other hand, the surface finished by ordinary cutting without the vibration, is cloudy with maximum roughness of more than 0.52 μm Ry, within a cutting distance of 1 m. Based on this advantage, the elliptical vibration cutting system is successfully applied to ultraprecision micromachining of dies for a front light panel of LCD. An optical quality surface with fine microgrooves over a large area of 122 × 91 mm² and with surface roughness of less than 0.04 μm Ry is obtained by the developed system, which is difficult for any conventional machining methods including grinding, polishing and ordinary cutting.