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1、ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学第四章 表面粗糙度及检测v 表面粗糙度:旧称表面光洁度,是一种微观几何形状误差。是指加工表面所具有的较小间距和微小峰谷不平度。v 原因:机械加工过程中,由于刀痕及切削过程中切屑分离时的塑性变形,工艺系统中的高颤振动,以及被加工表面摩擦等原因,致使被加工表面产生微量高低不平的痕迹
2、。v 对零件性能的影响:不仅影响美观,而且对运动面的摩擦与磨损,贴合面的密封等都会有影响。还会影响定位精度、配合性质、疲劳强度、接触刚度 抗腐蚀性等。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学第一节 表面粗糙度一、表面粗糙度评定参数及数值1。术语及定义v取样长度l 用于判别和测量表面粗糙度时所规定的一段基准线长度,一般
3、在它的走向上量取。 规定和选取取样长度是为了限制和减弱加工表面其它形状误差,特别是表面波度对测量结果的影响。一般表面粗糙度越大,取样长度越大。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学v 评定长度ln 由于零件表面粗糙度不均匀,为了合理地反映表面粗糙度特征,就需要在表面取几个取样长度来评定表面粗糙度。 评定长度是评定轮
4、廓所必须的一段长度,可包括一个或几个取样长度。 v 轮廓中线m 是评定表面粗糙度数值的基准线。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学 最小二乘中线:在取样长度内,使轮廓上各点的轮廓偏距yi(在测量方向上轮廓上的点至基准线的距离)的平方和为最小, 这条基准线称为轮廓的最小二乘中线。ZHONG Qi-MaoZHONG
5、Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学2.评定参数评定参数 国标规定的参数有高度参数、间距参数和综合参数 高度参数高度参数 有三个有三个 v 轮廓算术平均偏差轮廓算术平均偏差R Ra a 在取样长度l内,轮廓纵坐标值的绝对值的算术平均值。Ra越大,表面越粗糙。或 ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi
6、-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学轮廓算术平均偏差ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学v 微观不平度十点高度Rz
7、在取样长度内,5个最大的轮廓峰高的平均值峰高的平均值与5个最大的轮廓谷深的平谷深的平均值均值之和。 ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学 在取样长度内,也可以从平行于轮廓中线的任意一根线算起,到被测轮廓的5个最高峰点和5个最低谷点之间的平均距离。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-M
8、aoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学v 轮廓最大高度轮廓最大高度Ry 在取样长度 l 内,轮廓最高峰顶线和轮廓最低谷底线轮廓最高峰顶线和轮廓最低谷底线之间的距离。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Tec
9、hnology , Jimei UniversityJimei University)集美大学集美大学两粗糙表面高度参数相近,但疏密不同,因此两个表面的密封性不同。两粗糙表面高度参数相近,耐磨性不同ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学v 轮廓单峰平均间距S 两相邻轮廓单峰的最高点在中线上的投影长度Si称为轮廓的单
10、峰间距。间距参数间距参数: 反映轮廓的疏密状况,即取样长度内的峰谷数量。 在取样长度内,轮廓单峰间距的平均值,就是轮廓单峰平均间距。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学v 轮廓微观不平度的平均间距Sm 在取样长度内轮廓微观不平度间距的平均值,就是轮廓微观不平度的平均间距。 含有一个轮廓峰和相邻轮廓谷(峰谷均与中线
11、有交点)的一段中线长度Smi ,称轮廓微观不平度间距。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学v 轮廓支承长度率tp综合参数:与轮廓形状特征有关的参数。(对应于不同的水平截距C给出) 轮廓支承长度:平行于中线且与轮廓峰顶线相距为C的一条直线与轮廓峰相截所得到的各段截线bi之和,称为轮廓支承长度p 。ZHONG Qi-
12、MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学3.评定参数数值 除tp外,各参数均分别由优先数系中的派生数系确定,见表4-2到4-6。 ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineer
13、ing Technology , Jimei UniversityJimei University)集美大学集美大学高度参数最大允许值高度参数最小允许值加工方法取样长度加工余量加工纹理方向间距或综合参数二、表面粗糙度 符号、代号及标注ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学标注示例:ZHONG Qi-MaoZHONG
14、 Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学第二节 零件表面粗糙度参数值的选择选择原则:首先满足零件表面功能要求,其次考虑经济性方法:参照经过验证的实例,用类比法确定。ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of
15、 Engineering Technology , Jimei UniversityJimei University)集美大学集美大学高度参数是基本参数,对表面有粗糙度要求的均需选取;当高度参数还不能满足功能要求时,可根据需要选取间距参数和综合参数;在高度参数中应优先选取Ra;当粗糙度要求特别高或特别低时选Rz ;当表面较小不足一个取样长度时选Ry ;Ra和Rz在一个表面不可同时选取;Sm、S、tp不能单独使用。另外,选取tp时应同时给出水平截距C。 ZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-MaoZHONG Qi-Mao (College of Engineering Technology College of Engineering Technology , Jimei UniversityJimei University)集美大学集美大学(2)选择原则 既要满足零件表面的功能要求,也要考虑到经济性。通常参照一些经过验证的实例,用类比法确定,见P116。