How do I calculate Cpk with a single Control Limit?

B

Bob in KY

#1
Is it possible to come up with a CPK for a part with a single control limit. We take readings on the part and the minimum reading allowed (the single control limit) is 25, however it can be above 25, just not below 25. Therefore we have readings anywhere from 25 to 55. How would I go about calculating a CPK with the single Control Limit of 25? I'm sure this is very simple for most everyone, but I'm very new to the Quality Assurance program. Any help would be greatly appreciated. Thank you all.

 
Elsmar Forum Sponsor
B

Bob in KY

#3
Cpl...thank you!

Thank you Atul Khandekar, I now see that I cannot get a Cpk and must use a Cpl. Thank you again.
 
C

cleverfox

#4
Hi Bob,

I have several parts in which there is only one spec limit. CPK is calculated by "x(bar) - LSL / 3s".

Good luck,
-Fox
 
B

Bob in KY

#5
cpk

Cleverfox, pardon me for being ignorant on the subject but what is the "s" in the "3s", of x(bar) - LSL / 3s. Thanks.
 
C

cleverfox

#7
Bob,

The "s" is for standard deviation; calculated as s = R(bar)/ d2. The "d2" is a constant and its value is found on a chart in the AIAG SPC reference (or other SPC guides) manual.

-Fox
 
Y

ysdennis

#8
Your 25-55 should be the sampling amount,right?.
Actually,it would be stlll OK if over 55. The reason why we have to collect 25 above is that the sampling distribution of X-bar will be approaching to Normal distibution. This is derived from "Law of large number" in statistics.
 

Darius

Quite Involved in Discussions
#9
I still felt that cpmk could be better estimate for one sided specs. I added a spreadsheet with an example of "with larger variation on target or less variation far away from target.

by the way
This is derived from "Law of large number" in statistics.
is the central limit teorem?....
 

Attachments

L

lday38

#10
economic control limits /sample size of 2

I am switching from a sample size of 5 to 2 pcs. I have a history of spc on 5 piece chart. I had calculated economic control limits( infinity qs) on the 5 pc charts. The two pc sample size would be before the operator dumps the parts into a bin. I am usign visual spc software
I would like to hear feedback on anyone using other control limits when the CP and Cpk is large and also any feedback on the type of chart for a sample size of 2.
 
Thread starter Similar threads Forum Replies Date
B How to calculate CPK with n = 1 Manufacturing and Related Processes 2
A Simple 125 piece part Capabilty Excel .xls sheet to calculate Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 3
S Which one is better to calculate, Cpk or Ppk? Statistical Analysis Tools, Techniques and SPC 11
G Should I calculate both Cp and Cpk for a Unilateral Tolerance? Statistical Analysis Tools, Techniques and SPC 8
A How to calculate Cpk & Ppk if the tolerance changes during the period? Capability, Accuracy and Stability - Processes, Machines, etc. 5
F Please share an MS Excel sheet to calculate Cpk and Ppk Statistical Analysis Tools, Techniques and SPC 1
M Cpk - How to calculate when the number of samples is less than 30 pieces? Capability, Accuracy and Stability - Processes, Machines, etc. 7
D Use of Customer Specifications to calculate Cpk IATF 16949 - Automotive Quality Systems Standard 13
B How to calculate Cpk on Perpendicularity (Cyl Tol Zone at MMC) Capability, Accuracy and Stability - Processes, Machines, etc. 32
F How to Calculate Cpk with only a Minimum Tolerance Capability, Accuracy and Stability - Processes, Machines, etc. 11
C How to Calculate and Generate a Cpk Chart Statistical Analysis Tools, Techniques and SPC 4
B If I know x-bar, spec limits, and Cpk, can I calculate the control limits? Capability, Accuracy and Stability - Processes, Machines, etc. 16
J Methods used to calculate Cpk value - Need help for Cpk Calculation Statistical Analysis Tools, Techniques and SPC 8
H How can I calculate Cp & Cpk and make a control chart for maintenance activities? Capability, Accuracy and Stability - Processes, Machines, etc. 3
N Cpk vs Ppk - Which should you use and How to Calculate Cpk and Ppk Statistical Analysis Tools, Techniques and SPC 25
A Sampling Plans and Cpk - Ways to Calculate the Sample Quantity Inspection, Prints (Drawings), Testing, Sampling and Related Topics 15
N Capability study - What Values do I have to input to calculate Cp and Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 9
S Cmk and Cpk - When will we need to calculate Cmk? Machine Capability Capability, Accuracy and Stability - Processes, Machines, etc. 4
J How do I calculate the percentage of errors, when I know min, max, mean, cp and CPK Capability, Accuracy and Stability - Processes, Machines, etc. 3
D Can I calculate Cpk from Cp and Cr? Capability, Accuracy and Stability - Processes, Machines, etc. 5
P Commercial excel templates that calculate overhead, hourly rates, fee proposal Excel .xls Spreadsheet Templates and Tools 0
M How to calculate benefits? Moving some developed non controlled software/automation systems Service Industry Specific Topics 2
qualprod Calculate number of people in processes, considering cycle time/takt time = quantity of people Lean in Manufacturing and Service Industries 9
S How to calculate the maximum allowable hysteresis of a pressure gauge General Measurement Device and Calibration Topics 1
S How to Calculate the producer Risk AQL - Acceptable Quality Level 25
qualprod Methods to Calculate Available Production Rate ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 0
K Why calculate LCL in P-chart? Statistical Analysis Tools, Techniques and SPC 4
A Add-On software for VMC to calculate setting time, Idle Time, OEE etc.. Manufacturing and Related Processes 2
L How to calculate the Probability of Deficiency of the AQL of an Inspection AQL - Acceptable Quality Level 16
V How to Calculate Unbiasing Constant C4 Statistical Analysis Tools, Techniques and SPC 1
J How to Calculate OEE Indicator for a Workshop (15 Machines) Lean in Manufacturing and Service Industries 6
R How to calculate UCL (Upper COntrol Limit) and LCL (Lower Control Limit) Statistical Analysis Tools, Techniques and SPC 5
T I want to calculate reliability at 750 hours Reliability Analysis - Predictions, Testing and Standards 8
R How To Calculate & Print CDF and Lower Bound CDF value for some t(time) with Minitab? Using Minitab Software 1
N How to calculate the Premium Freight charges Service Industry Specific Topics 4
A How to calculate Mean and standard deviation without sample size in Minitab Using Minitab Software 5
R When do I need to calculate Process OEE? Manufacturing and Related Processes 12
kedarg6500 How to calculate Thread Pitch Diameter for non standard TPI like 5/8" 17.75 NF3 Manufacturing and Related Processes 3
C Definition and Way to Calculate some Metrics Lean in Manufacturing and Service Industries 6
M How calculate P value for Linearity and Bias using Excel Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
N Formula that will calculate the NoGo Major Diameter of an M20 x 1.5 6H Thread gage Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
M How to calculate Cg and Cgk for a 2-Dimensional Area Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
T Calculation Question - Calculate the runner weight for a part Manufacturing and Related Processes 2
M Spreadsheet on How to Calculate SMT Capacity wanted Manufacturing and Related Processes 2
F How to Calculate the unbiased Standard Deviation in Excel using Minitab Formula Capability, Accuracy and Stability - Processes, Machines, etc. 6
S Spreadsheet that will Calculate Audit Duration times based on IAF MD5 and MD11 Excel .xls Spreadsheet Templates and Tools 6
M Calculate PPMs by going back to Date of Production or Date Noticed Quality Tools, Improvement and Analysis 7
M How to calculate MTTF (Mean Time to Failure) Reliability Analysis - Predictions, Testing and Standards 1
H How to calculate the Lot Reject Rate Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
L How calculate the number of samples Statistical Analysis Tools, Techniques and SPC 2

Similar threads

Top Bottom