保(bao)證機(ji)床床身鑄(zhu)件精度需注意(yi)哪幾(ji)個方(fang)面

　　為了保證(zheng)機(ji)床鑄件的加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)精(jing)(jing)(jing)度(du)(du)，粗、精(jing)(jing)(jing)加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)好分開進行。因為粗加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)時(shi)，切削量(liang)大(da)，工(gong)(gong)(gong)(gong)(gong)件(jian)所受(shou)切削力、夾緊(jin)力大(da)，發熱量(liang)多，以及加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)表面有較 的加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)硬化現象，工(gong)(gong)(gong)(gong)(gong)件(jian)內(nei)部存在(zai)著較大(da)的內(nei)應(ying)(ying)(ying)力，如果粗、精(jing)(jing)(jing)加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)連續進行，則精(jing)(jing)(jing)加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)后(hou)的零(ling)件(jian)精(jing)(jing)(jing)度(du)(du)會因為應(ying)(ying)(ying)力的重新(xin)分布而很快喪失。對于機床床身鑄(zhu)件(jian)加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)精(jing)(jing)(jing)度(du)(du)要求高的零(ling)件(jian)。在(zai)粗加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)之后(hou)和精(jing)(jing)(jing)加(jia)(jia)工(gong)(gong)(gong)(gong)(gong)之前，還應(ying)(ying)(ying)安排低(di)溫退火或時(shi)效處(chu)理(li)工(gong)(gong)(gong)(gong)(gong)序來消除內(nei)應(ying)(ying)(ying)力。

　　合理地選用設備。粗加工主要是切掉大部分加工余量，并不要求有較高的加工精度，所以粗加工應在功率較大、精度不太高的機床上進行，精加工工序則要求用較高精度的機床加工。機床鑄件粗、精加工分別在不同的機床上加工，既能充分發揮設備能力，又能延長機床的使用壽命。在機械加工工藝中常安排有熱處理工序。熱處理工序位置的安排如下：為改善金屬的切削加工性能，如退火、正火、調質等，一般安排在機械加工前進行。為消除內應力，如時效處理、調質處理等，一般安排在粗加工之后，精加工之前進行。為了提高零件的機械性能，如滲碳、淬火、回火等，一般安排在機械加工之后進行，如熱處理后有較大的變形，還須安排終加工工序。