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毕业论文题目对螺纹的车削与常见的故障分析专业数控加工与维护工程1摘要在机械制造业中，用车削的方法加工螺纹是目前常用的加工方法。在普通车床上车削标准螺纹，车床主轴与刀具之间必须保持严格的运动关系：即主轴每转一转，刀具应均匀地移动一个导程的距离。它们的运动关系是这样保证的：主轴带着工件一起转动，主轴的运动经交换齿轮传到进给箱；由进给箱变速后再传给丝杠；由丝杠和溜板箱上的开合螺母配合带动刀架作直线移动，这样工件的转动和刀具的移动都是通过主轴的带动来实现的，从而保证了刀具和工件之间严格的运动关系。在实际车削螺纹时，由于各种原因，造成主轴到刀具之间的运动在某一环节出现问题，引起车削螺纹时产生故障，影响正常生产，这时应及时加以解决。多线螺纹的各螺旋线是等距分布的，从他们的端面上可以看出，各螺旋线的起始点，在圆周上相距的角度是相等的，在车削过程中，解决螺旋线的等距分布问题叫分线，如果等距误差过大、会影响内、外螺纹的配合精度和蜗杆蜗轮的啮合精度，降低使用寿命.削多线螺纹在机器制造业中应用广泛，因而螺纹的车削是技工学校车工专业必修的一个实习课题，如何搞好螺纹车削这门技术的教学，笔者从螺纹车刀的准备、车削方法的选择、合理的切削用量的选择及如何处理故障等方面进行阐述刃磨车刀时刀尖角不正确，即车刀两切削刃在基面上投影之间的夹角与加工螺纹的牙型角不一致，导致加工出的螺纹角度不正确。解决方法：刃磨车刀时必须使用角度尺或样板来检测，得到正确的牙型角。与普通车削相比，螺纹车削的进给速度要高出10倍，螺纹刀片刀尖处的作用力要高100～1000倍，切削速度较快，切削力较大和作用力聚集范围较窄导致螺纹的加工难度高。笔者通过大量的实验认为要从刀具的几何参数、切屑液和程序的编辑3个方面来提高数控车削螺纹的精度。关键词：螺纹车削方法故障解决1目录第一章三角形螺纹的车削方法1.1车削螺纹工件的螺纹参数和工艺要求································································31.2车刀的选择、刃磨和安装···············································································41.3检测螺纹参数······························································································5第二章多线螺纹的分线方法和分线精度2.1轴向分线法·································································································62.2圆周分线法·································································································82.3用卡盘卡爪分线···························································································82.4用分度盘分线······························································································9第三章车削中出现的问题及解决方法3.1刃磨车刀时刀尖角不正确···············································································103.2车刀安装不正确···························································································103.3刀具磨损····································································································103.4螺距（或导程）不正确··················································································113.5表面粗糙度值大···························································································113.6解决方法····································································································123.7乱牙··········································································································123.8中径不正确·································································································123.9扎刀或顶弯工件···························································································12第四章故障分析及解决方法4.1啃刀与乱扣·································································································134.2螺距不正确·································································································144.3中径不正确·································································································144.4螺纹表面粗糙······························································································14第五章车削方法的比较5.1在机械制造业中采用数控车削的方法加工螺纹是目前常用的方法····························195.2造业中采用数控车削的方法加工螺纹是目前常用的方法········································21结束语致谢参考文献2第一章三角形螺纹的车削方法1.1车削螺纹工件的螺纹参数和工艺要求1.1.1确定螺纹大径、中径、小径外螺纹大径（公称直径d）一般应车得比基本尺寸小0.2~0.4mm（约0.13P），保证车好螺纹后牙顶处有0.125P的宽度（P是螺距）。具体数值应参照基准制来选择，基轴制的值应小些，基孔制则可大些。中径d2=d-0.6495P，在中径处螺纹牙厚和槽宽相等。小径的计算公式为：d1=d-1.3P。则在上例中的参数分别是：d=29.6~29.8，d2=28.701，d1=27.4。2、螺柱右端面要倒角至螺纹小径，左边加工退刀槽。1.1.2确定背吃刀量螺纹切削用量的选择应根据工件材料的螺距大小以及所处的加工位置等因素来决定。前几次的进给用量可大些，以后每次进给切削用量应逐渐减小。切削速度应选低些，粗车时每次切深0.3mm左右，最后留余量0.2mm；精车时每次切深0.1~0.2mm左右，粗精车的总切深为1.3P。经过总结，本人列出下表仅供参照。1.2车刀的选择、刃磨和安装螺纹车刀的选择主要考虑刀具、形状和几何角度等三个方面。高速钢车刀用于加工塑性（钢件）材料的螺纹工件；白钢刀刃磨螺的纹车刀，适用于加工大螺距的3螺纹和精密丝等工件；硬质合金螺纹车刀适用于加工脆性材料（铸铁）和高速切削塑性工件。车刀的几何角度有三个（1）刀尖角ε应等于牙型角，车削普通三角形螺纹是60°；（2）前角Υ一般为0°~15°，螺纹车刀的径向前角对牙形角有很大的影响，对精度高的螺纹径向前角可适当取小一些（约0°~5°）；（3）后角α一般为5°~10°，因螺纹升角的影响，两后角大小应该磨成不同，进刀方向一面应稍大一些。但对大直径、小螺距的三角形螺纹，这种影响可忽略不计。刃磨车刀时要根据粗、精车的要求，刃磨出合理的前、后角。粗车刀前角大，后角小，精车刀则相反。车刀的左右刀刃必须是直线，无崩刃。刀尖角的刃磨比较困难，为保证磨出准确的刀尖角，在刃磨时用螺纹角度样板测量刀尖角（见图2）。测量时，把刀尖角与样板贴合，对准光源，仔细观察两边贴合的间隙，并以此为依据进行修磨。另外车刀磨损过大时会引起切削力增大，顶弯工件，出现啃刀现象。此时应对车刀加以修磨。车削螺纹时，为了保证牙形正确，对安装螺纹车刀提出了严格的要求。安装时刀尖高度必须对准工件旋转中心（可根据尾座顶针高度检查），车刀安装得过高，则吃刀到一定深度时，车刀的后刀面顶住工件，增大摩擦力，甚至把工件顶弯，造成啃刀；过低，则切屑不易排出，车刀径向力的方向是工件中心，加上横进丝杠与螺母间隙过大，致使吃刀深度不断自动径向加深，从而把工件抬起，导致啃刀；车刀刀尖角的中心线必须与工件严格垂直，装刀时可用样板来对刀（见图3）。如果车刀装歪，就会产生牙形歪斜（见图4）；刀头伸出不能太长，一般为20~25mm（约刀杆厚度的1.5倍）1.3检测螺纹参数4检测螺纹主要测量螺距、牙型角和螺纹中径，而且这些测量要在拆卸工件、刀具前进行，发现问题才能及时补救。1.3.1测量螺距、牙型角螺距是由车床的运动关系来保证的，用钢尺测量即可。普通螺纹的螺距一般较小，在测量时，最好量10个螺距的长度，再除以10得到一个螺距的尺寸。牙型角是由车刀的刀尖以及正确安装来保证的，一般用样板测量。也可用螺距规同时测量螺距和牙型角（见图7）。1.3.2测量螺纹中径螺纹中径常用螺纹千分尺测量（见图8）。使用方法跟一般的外径千分尺相似。它有两个可以调换的测量头，在测量时，两个跟牙形相同的触头正好卡在螺纹的牙形面，所得到的千分尺读数就是该螺纹的中径实际尺寸。1.3.3综合测量用螺纹环规检查三角形外螺纹（见图9）。首先应对螺纹的直径、螺距、牙形和粗糙度进行检查，然后再用环规测量外螺纹的尺寸精度。如果环规通端正好拧进去，而止端拧不进去，说明螺纹精度符合要求。对于精度要求不高的也可用标准螺母检查（生产中常用），以拧上工件时是否顺利和松动的感觉来确定。检查有退刀槽的螺纹时，环规应通过退刀槽与阶台端面靠平。5第二章多线螺纹的分线方法和分线精度2.1轴向分线法当车好一条螺旋槽后，把车刀沿轴线方向移动一个螺距，再车第二条螺旋槽。这种方法主要是如何解决精确移动一个螺距的问题。具体方法如下：2.1.1滑板刻刻度分线法这种方法是利用小滑板刻度盘的刻线值使车刀沿轴向移动一个螺距，以达到分线的目的。这种方法简单，不需要其他附件和装置，利用车床固有的小滑板及刻度就能达到分线的目的。其分线精度处决于小滑板刻线移动的精确度和操作方法的正确性。分线时必须注意的事项：a.分线前必须保证小滑板导轨与工作轴线平行度，否则会产生误差。简单校正的方法是：在车床上车长度约150mm的外圆（100以上），量其直径，得有无锥度误差，然后将百分表安装在刀架上，使