生产过程能力控制

,单击此处编辑母版标题样式,*,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,一、公司应用Cpk的必要性：,1、,Cpk数据能够直接反映过程控制的好坏、过程控制是否,取得持续进步，这方面我们做得很不够，很少应用Cpk,2、,越来越多的大客户都十分注重Cpk，他们对供应商的第,一个要求是：提供Cpk数据。,因此我们有必要对所有的在职员工进行一次全面Cpk知识培训，同时把它纳入新员工入厂培训资料中,二，与CPK有关的一些基本定义,Cpk：适用于统计稳定过程的能力指数，,这个能力指数将考虑到过程有无,偏移。,在大规模生产时，常用Cpk表达生产线能力指数。（如每天抽取5个数据，统计连续一个月的数据来计算Cpk）,二，与CPK有关的一些基本定义,Ppk,：过程的性能指数，此过程不一定,稳定，会由于特殊原因的发生而,受影响，此能力指数将考虑到过,程有无偏移。,在样品制作时，常用Ppk表达生产线能力指数（如连续生产200个样品，依此200个数据来计算Ppk）,二，与CPK有关的一些基本定义,Cp,：适用于统计稳定过程的能力指数，,这个能力指数,不考虑过程有无偏移,。,Pp,：过程的性能指数，此过程不一定稳,定，会由于特殊原因的发生而受影,响，这个能力指数,不考虑过程有无,偏移,。,二，与CPK有关的一些基本定义,Cpu,：上限能力指数，值越大，表明过程,的特性超出上限的可能性越小。,Cpl:,下限能力指数，值越大，表明过,程的特性超出下限的可能性越小。,三、Cpk计算实例：,选定30pcs样品，测其盒厚数据如下,：,序号,盒厚,序号,盒厚,序号,盒厚,序号,盒厚,序号,盒厚,1,5.94,7,5.94,13,6.01,19,5.96,25,5.94,2,5.95,8,5.91,14,5.92,20,5.96,26,5.96,3,5.92,9,5.9,15,5.9,21,5.97,27,5.96,4,5.99,10,5.92,16,5.92,22,6.01,28,5.94,5,5.91,11,5.92,17,5.97,23,5.97,29,5.99,6,5.92,12,5.99,18,5.94,24,5.99,30,5.95,平均值：5.949 目标值:5.95,+,0.05 平均偏差:0.001,方 差:0.03177 工程能力指数(CPK)=0.514,计算CPK值的几个步骤：,1、,先确定一规格值（目标值）.,如此例中我们定义目标值（最佳值）为5.95，允许,正负偏差0.05，即数值在5.906.00之间的我们都,认为是OK的。必须注意!,这个值是我们定义出来的，而非计算出来的.,UCL=6.00,LCL=5.90,允许偏差T=UCL-LCL=6.00-5.90=0.1,计算CPK值的几个步骤：,2、,计算平均值：上述30个数值的平均值 X=（5.94+5.95+5.92,5.99+5.95）/30=5.949,3、,平均偏差，即实际算出的平均值与目标值之偏差的绝对值：,=|5.95-5.949|=0.001,4、,均方差的计算：,s,=,(,（5.94,2,+5.95,2,+5.92,2,5.99,2,+5.95,2,）-30*5.949,2,),=0.03177,30-1,1/2,计算CPK值的几个步骤：,5、,工序能力指数的计算：,Cpu=(UCL-X)/3/s=(6.0-5.949)/3/0.03177=0.5351,Cpl=(X-LCL)/3/s=(5.949-5.90)/3/0.03177=0.5141,Cpk=(T-2*,)/6/s=(0.1-2*0.001)/6/0.03177=0.5141,从此可看出Cpk考虑到了过程偏差,或 Cpk=MIN（Cpu，Cpl）=MIN（0.5351,0.5141）=0.5141,Cp=T/6/s =0.1/6/0.03177=0.5347,从此可看出Cp不考虑过程偏差,四、得到Cpk后我们的处置对策：,我们 将Cpk值分成5个等级做为评价的基准。对CPK值予以评价的主要目的在能够确切地来区分制程精密度的好坏，并依据制程精密度的好坏对制程有所处置。以下处置原则仅供参考。,A+,级：Cpk=1.67 产品变异如大些也不要紧，,考虑管理的简单化或降低成本,。,A,级：1.33,Cpk1.67,理想状态，故维持现状,。,B,级：1.00,Cpk1.33 Cpk接近于时，恐怕会,产生不良品，故尽可能改善为A级。,C,级：0.67,Cpk1.00 过程状态不足，须探求,原因，进行品质的改善。或须采取紧急对,策，并重新检讨规格。,*,五、实例练习：,（一）（二）,平均偏差:,均 方 差=,序号,厚,度,序号,厚,度,序,号,厚,度,序,号,厚,度,序,号,厚,度,序号,厚,度,1,0.075,11,0.080,21,0.090,1,0.079,11,0.076,21,0.084,2,0.077,12,0.080,22,0.086,2,0.076,12,0.078,22,0.089,3,0.079,13,0.081,23,0.083,3,0.081,13,0.082,23,0.083,4,0.080,14,0.073,24,0.091,4,0.082,14,0.087,24,0.077,5,0.086,15,0.077,25,0.091,5,0.085,15,0.085,25,0.089,6,0.081,16,0.082,26,0.085,6,0.084,16,0.085,26,0.081,7,0.085,17,0.086,27,0.076,7,0.079,17,0.079,27,0.079,8,0.084,18,0.085,28,0.079,8,0.086,18,0.083,28,0.083,9,0.082,19,0.080,29,0.079,9,0.078,19,0.087,29,0.093,10,0.076,20,0.080,30,0.080,10,0.074,20,0.091,30,0.091,平均值：,目标值:0.08,+,0.02,平均值：,目标值:0.08,+,0.02,平均偏差:,均 方 差：,工程能力指数(CPK)=,工程能力指数(CPK)=,CP=？，Cpu，Cpl,CP=？，Cpu，Cpl,此练习要求所有QC人员能单独完成。,