推荐回答(1个)
钛合金以其比强度高、机械性能及抗蚀性良好而成为飞机及发动机理想的制造材料,但由于其切削性差,长期以来在很大程度上制约了它的使用。随着工艺技术的发展,钛合金已广泛用于飞机发动机的压气机段、发动机罩、排气装置等零件的制造以及飞机的大梁隔框等结构框架件的制造。但是钛合金导热性差致使切削温度很高,在切削过程中的这些特点使其变得十分困难。
一、钛合金工艺的特性分析
(1)钛合金导热系数低
因切削区散热慢不利于热平衡,在切削过程中散热和冷却效果很差,易于在切削区形成高温,零件变形回弹大,造成切削刀具扭矩增大、刃口磨损快耐用度降低。
(2)钛合金的导热系数低
使切削热积于切削刀附近的小面积区域内不易散发,前刀面摩擦力加大,不易排屑,切削热不易散发,加速刀具磨损。
(3)钛合金化学活性高
在高温下易与刀具材料起反应,形成溶敷、扩散,造成粘刀、烧刀、断刀等现象。
二、钛合金切削的工艺措施
(1)钛合金车削工艺
钛合金车削易获得较好的表面粗糙度,硬化不严重,但切削温度高刀具磨损快。针对这些特点主要在刀具、切削参数方面采取合适的刀具前后角、刀尖磨圆;较低的切削速度;适中的进给量;较深的切削深度;较大的刀具主偏角等。
(2)钛合金铣削工艺
钛合金铣削比车削困难,因为铣削是断续切削,并且切屑易与刀刃发生粘结形成崩刃,极大地降低了刀具的耐用度。因此对钛合金铣削一般采用高速高刀具顺铣;刀具前角应减小,后角应加大;铣削速度宜低;从工件装夹及设备方面提高工艺系统刚性。
(3)钛合金磨削工艺
磨削钛合金零件常见的问题是粘屑造成砂轮堵塞以及零件表面烧伤。其原因是钛合金的导热性差,使磨削区产生高温,从而使钛合金与磨料发生粘结以及强烈的化学反应。为解决磨削钛合金采取的措施是选用合适的砂轮材料;稍低的砂轮硬度;较粗的砂轮粒度;稍低的砂轮速度;稍小的进给量。
(4)钛合金钻削工艺
钛合金钻削比较困难,常在过程中出现烧刀和断钻现象。这主要是由于钻头刃磨不良、排屑不及时、冷却不佳以及工艺刚性差等几方面原因造成的。因此在钛合金钻削时选用硬质合金刀具;加大刀具顶角、减少外缘前角、增大外缘后角;勤退刀并及时清除切屑。
(5)钛合金铰削工艺
钛合金铰削时刀具磨损不严重,使用硬质合金和高速钢铰刀均可。使用硬质合金铰刀时,要采取类似钻削的工艺系统刚度防止铰刀崩刃。钛合金铰孔时出现的主要问题是铰孔不光,可采用油石修窄铰刀刃带宽度,以免刃带与孔壁粘结;切削刃与校准部分转接处应为光滑圆弧,磨损后要及时修磨,并要求各齿圆弧大小一致。
(6)钛合金攻丝工艺
钛合金攻丝因为切屑细小,易与刀刃及工件粘结,造成表面粗糙度值大,扭矩大。攻丝时丝锥选用不当及操作不当极易造成硬化,效率极低并时有丝锥折断现象。因此要优先选用跳牙丝锥;切削锥角宜大;为便于排屑还可在切削锥部分磨出负倾角;尽量选用短丝锥以增加丝锥刚性。
三、钛合金切削油的选用
(1)如果使用含氢的切削油,切削过程中在高温下将分解释放出氢气,被钛吸收引起氢脆;也可能引起钛合金高温应力腐蚀开裂。
(2)部分以氯系添加剂为主要成分的切削油中在使用时还可能分解或挥发有毒气体,使用时宜采取安全防护措施;切削后应及时用清洗剂彻底清洗零件,清除含氯残留物。
(3)使用以硫化脂肪酸酯为主剂的钛合金切削油能很好的解决刀具磨损的问题,同时有利于排屑,避免积屑瘤的产生。
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