基于DMAIC的转向轴生产质量改进

转向轴是循环球式转向器中重要的传导部件，利用六西格玛DMAIC模式对XinH公司Z转向轴生产的高废品率问题进行了质量改进。通过SIPOC流程图和帕累托图分析找出需要改进的质量点为磨削外圆圆度超差；针对分析明确的改进质量点，在利用MSA(measurement system analysis, 测量系统分析)以及过程能力分析等方法对测量系统和工序过程能力进行判定基础上，重点结合FTA(fault tree analysis, 故障树分析)和一般线性模型方法分析，确定其关键影响因素为中心孔跳动大，并通过根源分析法找出导致中心孔跳动大的原因为液压夹紧装置夹紧压力较大；利用回归分析确定出压力值的最优区间，同时制定实施全面改进方案并对改进结果进行监控。改进结果显示，改进后的Z转向轴不合格率从改进前的8%降到了1.6%，不合格率得到有效的控制，实现了质量改进的既定目标。

Production Quality Improvement of Steering Shaft Based on DMAIC

The six sigma DMAIC model is used to improve the quality of XinH's Z steering shaft, which is an important part of the recirculating ball steering gear. Firstly, through the analysis of SIPOC flowchart and Pareto diagram, it was found that the quality point needing improvement was the out-of-tolerance of grinding outer roundness; Secondly, in view of the analysis clearly improving quality point, in the use of MSA (measurement systems analysis) and process capability analysis and other methods for measuring system based on determine process capability and process, key combination of FTA(Fault tree analysis) and method of general linear model analysis were used to determine the key influence factors for the center hole run out, with the root cause analysis to find out the cause of center hole to beat large hydraulic clamping device for clamping pressure; Finally, the optimal interval of pressure value determined by regression analysis, the comprehensive improvement scheme developed and implemented, and the improvement result monitored. The improvement results showed that the unqualified rate of the improved Z steering shaft decreased from 8% before the improvement to 1.6%, and the unqualified rate was effectively controlled, achieving the established goal of quality improvement.