数控加工工艺路线的确定
在数控加工中,刀具刀位点相对于工件运动的轨迹称为加工路线。编程时,加工路线的确定原则主要有以下几点:
(1)应能保证零件的加工精度和
表
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面粗糙度的要求。 (2)应尽量缩短加工路线,减少刀具空程移动时间。 (3)应使数值计算简单,程序段数量少,以减少编程工作量。
对点位控制的数控机床,只要求定位精度较高,定位过程尽可能的快,而刀具相对于工件的运动路线是无关紧要的,因此这类机床应按空程最短来安排走道路线。除此之外还要确定刀具轴向的运动尺寸,其大小主要由被加工零件的孔深来决定,但也应考虑一些辅助尺寸,如刀具的引入距离和超程量。
对于位置精度要求较高的孔系加工,特别要注意孔的加工顺序的安排,安排不当时,就有可能将坐标轴的反向间隙带入,直接影响位置精度。如图2-23所示,图a为零件图,在该零件上镗六个尺寸相同的孔,有两种加工路线。当按b图所示的路线加工时,由于5、6孔与1、2、3、4孔定位方向相反,Y方向反向间隙会使定位误差增加,而影响5、6孔与其他孔的位置精度。
paper has produced remarkable results. By pay close attention to reform, all three business units exceeded annual targets on schedule task. Hotel as originally planned one month in advance to achieve the annual task of Pingliang, four months ahead of the dynamic balance of revenues and expenditures year, annual operating revenue reached 10.41 million Yuan, accounting for 114% of the annual plan, achieved a net profit
a) b) c)
图2-23 镗孔加工路线示意图
按c图所示路线,加工完4孔后往上多移动一段距离到P点,然后再折回来加工5、6孔,这样方向一致,可避免反向间隙的引入,提高5、6孔与其他孔的位置精度。
在数控机床上车螺纹时,沿螺距方向的Z向进给应和机床主轴的旋转保持严格的速比关系,因此应避免在进给机构加速或减速过程中切削。为此要有引入距离δ和超越距离δ。如图2-24所示,δ121和δ的数值与机床拖动系统的动态特性有关,与螺纹的螺距和螺纹2
的精度有关。一般δ为2,5?,对大螺距和高精度的螺纹取大值;1
δ一般取的1/4左右。若螺纹收尾处没有退刀槽时,收尾处的形状2
与数控系统有关,一般按45?退刀收尾。
paper has produced remarkable results. By pay close attention to reform, all three business units exceeded annual targets on schedule task. Hotel as originally planned one month in advance to achieve the annual task of Pingliang, four months ahead of the dynamic balance of revenues and expenditures year, annual operating revenue reached 10.41 million Yuan, accounting for 114% of the annual plan, achieved a net profit
图2-24 切削螺纹引入距离
铣削平面零件时,一般采用立铣刀侧刃进行切削。为减少接刀痕迹,保证零件表面质量,对刀具的切入和切出程序需要精心设计。如图2-25所示,铣削外表面轮廓时,铣刀的切入和切出点应沿零件轮廓曲线的延长线上切向切入和切出零件表面,而不应沿法向直接切入零件,以避免加工表面产生划痕,保证零件轮廓光滑。
铣削内轮廓表面时,切入和切出无法外延,这时铣刀可沿零件轮廓的法线方向切入和切出,并将其切入、切出点选在零件轮廓两几何元素的交点处。图2-26所示为加工凹槽的三种加工路线。
图2-25 切入切出方式
paper has produced remarkable results. By pay close attention to reform, all three business units exceeded annual targets on schedule task. Hotel as originally planned one month in advance to achieve the annual task of Pingliang, four months ahead of the dynamic balance of revenues and expenditures year, annual operating revenue reached 10.41 million Yuan, accounting for 114% of the annual plan, achieved a net profit
a) b) c)
图2-26 凹槽加工路线
图a和b分别为用行切法和环切法加工凹槽的走刀路线;图c为先用行切法最后环切一刀光整轮廓表面。三种
方案
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中,a图方案最差,C图方案最好。
在轮廓铣削过程中要避免进给停顿,否则会因铣削力的突然变化,将在停顿处轮廓表面上留下刀痕。
paper has produced remarkable results. By pay close attention to reform, all three business units exceeded annual targets on schedule task. Hotel as originally planned one month in advance to achieve the annual task of Pingliang, four months ahead of the dynamic balance of revenues and expenditures year, annual operating revenue reached 10.41 million Yuan, accounting for 114% of the annual plan, achieved a net profit