金属零件磨削加工的失效形式及原因
<h2 style=\"margin:auto 0cm\"><font face=\"宋体\">金属零件磨削加工的失效形式及原因</font></h2><p class=\"MsoNormal\" style=\"margin:0cm 0cm 0pt\"><font size=\"3\"><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span></span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><font face=\"宋体\">零件磨削加工的失效形式包括磨削表面粗糙度、磨削表面烧伤、磨削表面残余应力和磨削裂纹等。</font></span></font></p><p class=\"MsoNormal\" style=\"margin:0cm 0cm 0pt\"><font size=\"3\"><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span><strong>1</strong></span><strong><span style=\"font-family:宋体;mso-bidi-font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">、磨削表面粗糙度</span></strong><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span></span><font face=\"宋体\"><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">磨削表面粗糙度可以根据理论分析获得理论公式，但与实际相差悬殊，因此有各种实验公式：对表面粗糙度影响最大的是磨削速比</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">v</span></em><sub><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">砂轮</span></sub><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">／</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">v</span></em><sub><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">工件</span></sub><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">，砂轮速度越低，表面粗糙度越高。砂轮的工作表面修整不好或不平衡，会引起砂轮的振动，使磨削表面产生振纹，增加表面的粗糙度。</span></font></font></p><p class=\"MsoNormal\" style=\"margin:0cm 0cm 0pt\"><font size=\"3\"><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span><strong>2</strong></span><strong><span style=\"font-family:宋体;mso-bidi-font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">、磨削表面烧伤</span></strong><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span></span><font face=\"宋体\"><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">磨削钢材时，开始钢材表面呈正常的金属光泽，随后逐渐转为黄褐色甚至成为黑褐色，这就是</span><span lang=\"EN-US\" style=\"font-family:\'times new roman\';mso-bidi-font-family:宋体\"><a href=\"http://www.hj9411.com/\"><span lang=\"EN-US\" style=\"font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><span lang=\"EN-US\">磨削</span></span></a></span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">表面的烧伤现象。工件表面的各种颜色是由于在磨削高温下形成的氧化膜厚度不等，在阳光下出现干涉色不同的缘故。所以，根据表面颜色，可以推断磨削温度及烧伤程度。如淡黄色约为</span></font><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\">400~500</span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><font face=\"宋体\">℃，烧伤深度较浅；紫色为</font></span><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\">800~900</span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><font face=\"宋体\">℃，烧伤层较深。磨削表面的烧伤将使工件表面层的金相组织发生变化，烧伤严重时破坏工件表层组织，并会产生裂纹，影响工件的耐磨性和使用寿命。因此，必须避免磨削烧伤。影响磨削烧伤的因素主要如下。</font></span></font></p><p class=\"MsoNormal\" style=\"margin:0cm 0cm 0pt\"><font size=\"3\"><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span></span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><font face=\"宋体\">（</font></span><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\">1</span><font face=\"宋体\"><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">）<em><span style=\"font-family:宋体;mso-bidi-font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">磨削用量</span></em>。砂轮速度</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">v</span></em><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">及径向进给量</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">f</span></em><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">的影响较大，</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">v</span></em><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">和</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">f</span></em><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">较小时，不出现烧伤；随着</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">v</span></em><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">及</span><em><span lang=\"EN-US\" style=\"mso-bidi-font-style:normal\">f</span></em><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">的增大，烧伤逐渐严重。工件速度影响较小，只有当极小时才会出现烧伤。</span></font></font></p><p class=\"MsoNormal\" style=\"margin:0cm 0cm 0pt\"><font size=\"3\"><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span></span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><font face=\"宋体\">（</font></span><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\">2</span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><font face=\"宋体\">）<em><span style=\"font-family:宋体;mso-bidi-font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">接触长度</span></em>。砂轮与工件的接触长度大，砂轮易堵塞而不易冷却，容易出现烧伤。</font></span></font></p><p class=\"MsoNormal\" style=\"margin:0cm 0cm 0pt\"><font size=\"3\"><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span><strong>3</strong></span><strong><span style=\"font-family:宋体;mso-bidi-font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">、磨削表面残余应力</span></strong><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span></span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><font face=\"宋体\">磨削表面的残余应力是由于磨削过程中金属容积发生变化等因素造成的。其中由于磨削温度的不均匀将形成热应力，一般为拉应力；由于金属组织的变化将产生相变应力，可能为拉应力或压应力；由于磨削过程塑性变形的不均衡形成塑变应力，一般为压应力。磨削表面的残余应力应是以上三者的复合。残余压应力可提高零件疲劳强度和使用寿命。残余拉应力将使零件表面翘曲，强度下降，导致疲劳破坏。所以，磨削过程应尽量避免形成残余拉应力。</font></span></font></p><p class=\"MsoNormal\" style=\"margin:0cm 0cm 0pt\"><font size=\"3\"><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span><strong>4</strong></span><strong><span style=\"font-family:宋体;mso-bidi-font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">、磨削表面裂纹</span></strong><span lang=\"EN-US\" style=\"font-family:\'times new roman\'\"><span style=\"mso-spacerun:yes\"> </span></span><font face=\"宋体\"><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">磨削过程中，当形成的残余</span><span lang=\"EN-US\" style=\"font-family:\'times new roman\';mso-bidi-font-family:宋体\"><a href=\"http://www.hj9411.com/\"><span lang=\"EN-US\" style=\"font-family:宋体;mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\"><span lang=\"EN-US\">拉应力</span></span></a></span><span style=\"mso-ascii-font-family:\'times new roman\';mso-hansi-font-family:\'times new roman\'\">超过工件材料的强度极限时，工件表面就会出现裂纹。磨削裂纹极浅，呈网状或垂直于磨削方向。有时不在表层，而存在于表层之下。有时在研磨或使用过程中，由于去除了表面极薄金属层后，残余拉应力失去平衡，形成微细裂纹。这些微小裂纹，在交变载荷作用下，会迅速扩展，并造成零件的失效。磨削表面烧伤、残余应力及裂纹均与磨削温度有紧密联系，凡能降低磨削温度的措施，都会提高磨削表面质量。</span></font></font></p>
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