Railways Technical Ability Metrology and Inspection Question Bank Metrology and Inspection

  • question_answer Quality control chart for averages was maintained for a dimension of the product. After the control was established, it was found that the standard deviation of the process was 1.00 mm. The dimension of the part is 70 \[\pm \] 2.5 mm. Parts above 725 mm can be reworked but parts below 67.5 mm have to be scrapped. What should be the setting of the process to ensure production of no scrap and to minimize the rework?

    A) 68.5 mm                      

    B) 70 mm

    C) 70.5 mm                      

    D) 725 mm

    Correct Answer: B

    Solution :

    \[\sigma =1.00\,\,mm\] Maximum size \[=72.5\,\,mm\] Minimum size \[=67.5\,\,mm\] \[UCL=70+3\sigma =73\,\,mm\] \[lCL=70-3\sigma =67\,\,mm\] The process should be set at 70 mm

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