用于常规粉末冶金工艺的生坯切削加工

Green machining for conventional P/M processes

生坯切削加工的好处已众所周知 ,如切削刀具的寿命较长 ,能够用可烧结硬化粉末制作形状复杂的零件等。零件生坯强度高可防止在运送过程中生坯开裂与损坏。但是 ,用常规粉末冶金工艺不易达到所要求的高生坯强度 (约大于 2 0MPa)。因此 ,生坯切削加工尚未得到广泛应用。用魁北克金属粉末公司 (QMP)新开发的高生坯强度 (highgreenstrength ,简称HGS)聚合物润滑剂 ,正在消除使用生坯切削加工的限制。这种润滑剂的一个杰出特性是其对温度的敏感性。在压制温度 5 5℃下整个坯件就能获得高生坯强度 ,这用冷压很容易达到。若将零件生坯压制到密度 6 8g/cm3 ,随后经固化处理 ,甚至可将生坯强度增高到 4 8MPa左右。这样高的生坯强度使得用常规粉末冶金工艺制造的零件都能进行生坯切削加工。本文介绍了用正时链轮进行生坯切削加工试验的一些结果。使用的材料是由QMPATOMET 4 6 0 1与HGS润滑剂组成的可烧结硬化的粉末混合料。先用冷压将链轮压制到密度约 6 8g/cm3 ,再对用压制的生坯与经固化处理的生坯进行切削加工 (在齿的中间车槽 )。结果表明 ,HGS润滑剂 ,特别是固化处理后 ,可赋予生坯足够高的强度 ,以进行装卡与切削加工作业。切削加工表面光滑且棱边完好。由可烧结硬化粉末制作的可生坯切削加工的链轮 。

The advantages of green machining have been well recognized,including longer cutting tool life and the ability to make complex parts with sinter hardenable powders The high green strength of the compacted parts also prevents green cracks and damages from handling But green machining is yet to be widely used since the required high green strength(in excess of about 20MPa)cannot be readily obtained through conventional P/M techniques The limitation of using green machining is being removed with a newly developed high green strength(HGS)polymeric lubricant at QMP One distinguished characteristic of this lubricant is its response to temperature High green strength can be obtained at a compacting temperature of 55℃,which can be easily reached throughout a green part by cold compaction Even a higher green strength up to ～48MPa can be reached by a subsequent curing process for parts pressed to density of 6 8g/cm 3 This high green strength has made green machining possible for those parts fabricated through conventional P/M processes This paper presents the results of green machining tests performed on several timing sprockets The material used was a sinter hardenable powder mix of QMP ATOMET 4601 and the HGS lubricant The sprockets were pressed to a density of ～6 8g/cm 3 by cold compaction Green machining(turning a groove along the middle of the teeth)was performed on ascompacted and cured parts Results showed that the HGS lubricant provided sufficient green strength for clamping and machinng operations,especially after curing The machined surfaces appeared to be smooth and the edges remained integrated The green machined sprockets made of sinter hardenable powder eliminated heat treatment,providing much longer tool life and improved size tolerances