雙軸液車床之精度與加工特性

Accuracy and Machining Performance of a Biaxial Hydrostatic Lathe

本文探討自製雙軸液靜壓車床之運動精度與加工特性，並與 Moore 超精密車床之加工結果比較。此車床之機座是以花崗岩製作，導軌使用對稱封閉式液靜壓滑軌，油壓供應系統使用伺服馬達泵浦附蓄壓器以穩定供油壓力，並以線性馬達驅動平台。由精度量測結果顯示X 軸雙向定位精度為1.391 ìm、重複精度為1.28 ìm、水平直度為19.81 ìm、垂直直度為4.5 ìm；Z軸雙向定位精度為1.345 ìm、重複精度為1.016 ìm、水平直度為5.26 ìm、垂直直度為6.18ìm。另外，切削試驗是針對鋁合金試件，以主軸轉速2000 rpm、進給速率5mm/min、切削深度5 ìm、刀鼻半徑1.002 mm進行加工。可得平面試件之輪廓精度 （PV） 為0.283 ìm/42.6 mm、表面粗糙度為Ra 0.0281 ìm；球面試件之輪廓精度為0.178 ìm/10.8 mm、表面粗糙度為 Ra 0.0255 ìm，由此可知，此自製雙軸液靜壓車床可達到次微米的加工精度。

In this study a biaxial hydrostatic lathe was designed and fabricated,and the moving precision and the machining characteristics of the machinewere investigated; the results were compared with the data for Moore'sultra-precision lathe. The base of the machine was made of granite andthe frame was composed of closed-loop hydrostatic slideways; a servomotor pump with accumulator was used to supply steady hydraulicpressure and the carriage was driven by a linear motor. Results ofaccuracy measurements indicated that in X-direction the bidirectionalpositioning accuracy was 1.391 ìm, repeatability was 1.28 ìm, horizontalstraightness was 19.81 ìm and vertical straightness was 4.5 ìm; in Z-direction the bidirectional positioning accuracy was 1.345 ìm, repeatabilitywas 1.016 ìm, horizontal straightness was 5.26 ìm and verticalstraightness was 6.18 ìm. A machining test for aluminum alloy sampleswas performed using a diamond tool with a nose radius of 1.002 mm, at aspindle speed of 2000 rpm, a feeding rate of 5 mm/min, and a cutting depthof 5 ìm. For planar samples the form error (PV) was 0.283 ìm/42.6 mmand the surface roughness was Ra 0.0281 μm; for spherical samples theform error (PV) was 0.178 ìm/10.8 mm, the surface roughness was Ra0.0255 ìm. The results indicate that the biaxial hydrostatic lathe fabricatedby the authors can produce samples with sub-micron machiningaccuracy.