Precision Manufacturers employ Ron Wood, an MBA student. One of his first assign

Question

Precision Manufacturers employ Ron Wood, an MBA student. One of his first assignments is to introduce quality initiatives in the production of shafts used in engine lathes. Attached to the machine producing shafts is an X-bar chart and R chart for monitoring diameter of shafts. The present control chart has Center Line (mean X) = 2.5 inches, and three standard deviation control limits of UCL = 2.518 inches and LCL = 2.482 inches. In his enthusiasm for reducing inspection costs, he decides to reduce the current sample size of 20 units designated on the chart to 10 units. Compute the revised control limits for X-bar chart and R-chart for the new sample size.

Explanation / Answer

For sample size, n=20, Control chart constant, A2 = 0.18

We know that LCL = Xdblbar - A2*Rbar = 2.5 - 0.18*Rbar = 2.482 (given)

Solving for Rbar, we get,

Rbar = (2.5-2.482)/0.18 = 0.10

____________________________________

For revised sample size, n = 10

Control chart constant, A2 = 0.308 , D3 = 0.223, D4 = 1.777

Revised control limits are following

Control limits for X-bar chart

LCL = 2.5 - 0.308*0.1 = 2.4692

UCL = 2.5 + 0.308*0.1 = 2.5308

Control limits for R-chart

LCL = D3*Rbar = 0.223*0.1 = 0.0223

UCL = D4*Rbar = 1.777*0.1 = 0.1777

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.