Specification: USL is 85, LSL 84.5
Xbar Chart UCL is 84.80, LCL is 84.70
Some of the points are within the Specification limits but out of the Control limits
2007-12-10 14:31:56 · 2 answers · asked by rrdizon 1 in Science & Mathematics ➔ Engineering
The control limits are based on statistical analysis of process capability data. The specification limits are not used in their determination.
Xbar Chart UCL is 84.80, LCL is 84.70 means that when your process is well managed all or very nearly all of the product will fall within this range. This is due to the normal variation inherent in your process and its inputs. That is entirely independent of how well or poorly the process satisfies the specification limits.
2007-12-10 14:52:14 · answer #1 · answered by Tim C 7 · 0⤊ 0⤋
Most likely, your control limits are not set at +/- 3 sigma values. Assuming your process is centered in your control charts (i.e. mean is 84.75) and Cpl=Cpu, a rough back calc of your 3 sigma limits would put them at ~+/- 0.12. Another possibility is that your process is not centered in your limits, which result in even more OOC points in one direction.
2007-12-10 15:00:13 · answer #2 · answered by machupi1 3 · 0⤊ 0⤋