M
mike101338
Let me start by saying statistics is something fairly new to me. Let me give some background on how we inspect to make sure I am moving in the right direction.
All inspections we perform is on a pass / fail method. We track our bad product as defective, not defects. Run quantities and sample size quanities are variable.
I am using a p chart to track the data. Once graphed I can show stability. I am struggling with how I demonstrate capability. Is this where Cp and Cpk come into the equation? If so, how?
Defining what the USL and LSL is an unknown to me. I am assuming the LSL is 0, as you can not have less than 0 defects. However when I enter this into the Cpk analysis it shows that I am out of spec on the low side. Not possible as 0 defects is perfect, not out of spec. When I enter the USL, I have chosen 3 percent (not the goal, but anything lower at this time would turn people off to SPC). In order for me to attain a Cpk of 1.33 with 3 percent defect I have to attain a sigma level of greater than 4, with a DPM of 30, which is obvoisly not 3 percent. Have I not entered data correctly somewhere or have I made a mistake somewhere else?
Any advice anyone can give me is greatly appreciated.
Mike
All inspections we perform is on a pass / fail method. We track our bad product as defective, not defects. Run quantities and sample size quanities are variable.
I am using a p chart to track the data. Once graphed I can show stability. I am struggling with how I demonstrate capability. Is this where Cp and Cpk come into the equation? If so, how?
Defining what the USL and LSL is an unknown to me. I am assuming the LSL is 0, as you can not have less than 0 defects. However when I enter this into the Cpk analysis it shows that I am out of spec on the low side. Not possible as 0 defects is perfect, not out of spec. When I enter the USL, I have chosen 3 percent (not the goal, but anything lower at this time would turn people off to SPC). In order for me to attain a Cpk of 1.33 with 3 percent defect I have to attain a sigma level of greater than 4, with a DPM of 30, which is obvoisly not 3 percent. Have I not entered data correctly somewhere or have I made a mistake somewhere else?
Any advice anyone can give me is greatly appreciated.
Mike