A Study on Machining Texture Applied to Machine Tool Hard Rail

Abstract

Hard rails are usually employed for feeding system of heavy load and heavy-duty machine tools. While hard rail requires lubrication on the contact surfaces scraping is applied to allow lubricant flow into the interface. However, the characteristics of such feeding system is hard to control because of the quality of manual scraping varies depending on the craftsmen's skill as the technique is inherited between masters and apprentices. Previous studies have revealed that friction characteristics are can be improved micro-structure textures fabricated on the friction surfaces by computer numerical controlled machining. However, the friction characteristics of such texture are not consistent, found from characteristic tests. This study is to design and to fabricate a new texture to improve the stability of friction characteristics in the reciprocating motions of feeding system. The major results achieved in this study can be summarized as follows. (1) Results of pilot experiments showed that the friction coefficient, based on previously designed textures, of forward and backward strokes are different in the reciprocating motion. (2) The friction characteristics of three types of manually scrapped blocks are close to that of manually scraped hard rail of a machine tool. The result showed that the friction coefficients of forward and backward strokes are stable, unless under the condition of low velocity and low pressure. (3) A new texture with new configuration of grooves is designed and tested. The results showed that the friction coefficient of the new texture is about the same as that of manual scrapping, in both value and stability. The results of this study revealed that, by comparison with manual scraping, the friction properties of the sliding blocks with new texture are on the same level. While the texture is machined by CNC machining, the quality and repeatability can be well controlled that overcomes the major drawback of manual scraping. This study also reveals that current manual scraping of hard rails can be replaced by this technology with better quality.

硬軌為重負載與重切削的工具機常採用之進給系統軌道，故需在接觸面鏟花以便運動時使潤滑油進入接觸面以改善摩擦特性，但長期以來鏟花技術為師徒相傳之技藝，使得鏟花品質因人而異，無法有效掌控進給系統之性能。本研究根據文獻在摩擦面以CNC加工滑塊紋理之研究成果，因不同紋理之滑塊其往返運動之摩擦特性不一致，故在滑動面設計新型微結構紋理，並實際加工後架設於進給平台量測其摩擦性能，驗證其改善效果。 本研究之主要結果整理如下：(1)先導實驗顯示，文獻所設計之硬軌紋理在進給平台運動去回程的摩擦係數表現不一致；(2)本研究加工三種不同的手工鏟花滑塊並架設於進給平台所測得之摩擦性質與直接手工於工具機硬軌鏟花之結果相近，但手工鏟花滑塊除在低面壓且低速的運動狀況下之外，其去回程的摩擦係數表現具一致性；(3)本研究進一步改良滑動面紋理之溝槽之配置，並利用油溝連接相鄰之油袋，所改良之綜合型紋理滑塊經測試顯示其摩擦係數與手工鏟花滑塊相近，且在不同測試條件下去回程運動的摩擦係數大致相同，也顯示新型紋理具穩定性與重現性。 本研究之結果顯示所改良之綜合型紋理滑塊所表現之摩擦性能已與目前工具機產業手工鏟花後之硬軌相同甚至較佳，顯示本研究之成果可取代機械產業之手工鏟花硬軌，以提升硬軌之品質穩定性。