请大虾帮忙解惑，关于进行Cpk计算前的正态性检验问题

问题的背景是这样的，我想算一个实心塑料棒的长度的Cpk,取样方法是在同一产线上每半小时取3根，数据如下。计算Cpk前我按书上说的进行正态性检验，但是居然不正态，一般情况下，长度不是正态数据么？接下来我怎么办啊？
长度mm
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