Cpk Calculation - I analyse a double seam cans

#1
I need help in setting up my process CPk. I analyse a double seam cans and data taken using a software KUHNKE is been used to set-up my CPK which gives negative value after inputing my USL,LSL AND AVERAGE.Kindly advise me on how best to get my CPK with the data( eight seaming heads,generating different data on a particular machine)
Thanks in anticipation.
Uwalasky
 
Elsmar Forum Sponsor

Jim Wynne

Staff member
Admin
#2
What is being measured? Are you trying to combine data from multiple sources? Have you verified that the process is statistically stable for each data source? A description of the process would also be helpful.
 

Bill Levinson

Industrial Statistician and Trainer
#3
The only way to get a negative Cpk is to have the process mean outside the specification limits. Also, if the heads generate different data while doing similar jobs (correlated) we could conceivably be looking at a multivariate situation, but I don't know enough to say.
 
#4
Thanks @Jim Wynne & @ Bill Levinson. The process as i earlier said is a can making factory, i need formula on how to calculate the CPK because what am using is not correct. Clue on the data i have: Average value, LSL & USL.
Thanks
 
#5
Thanks @Jim Wynne & @ Bill Levinson. The process as i earlier said is a can making factory, i need formula on how to calculate the CPK because what am using is not correct. Clue on the data i have: Average value, LSL & USL.
Thanks
As @Jim Wynne pointed out, have you verified that the data is statistically stable?

Also, if you use any statistical software package, for example: Minitab or JMP, it can help you calculate the Cpk, if that is what you are asking.
 

Jim Wynne

Staff member
Admin
#8
There are variation in data,Kindly see the manual calculation in excel. sheet as attached
It would be good if you could answer the questions I asked earlier. I suspect that there are few people here who are familiar with the machinery and details of your process.
 
#9
The machine in question is a canopy seaming machine, with 8 seaming heads ported producing cans at a speed of 800 cans per mins. Am trying to monitor the effectiveness of the machine using one of its critical parameters seam thickness with Lower limit of 0.90 and upper limit of 1.03
The cans in question are used for the production of evaporator milk, meaning there is no room for micro leakage.
Thanks for all the contributions
 

Welshwizard

Involved In Discussions
#10
Without knowing your machine and process its impossible to make a judgement about how to organise the data in context. Whether you can isolate the data from each head or group the data some other way is a rational decision that you have to make based upon your process knowledge, the steps below are the bare essentials and fundamentals of what you seem to be asking, apologies if you already know this.


Crucial - Demonstrate homogeneity of the process data stream by plotting the data in time series order on an individual moving range chart. If the data demonstrates a lack of stability then the process is unpredictable and any characterisation is wishful thinking.

If the data demonstrates predictability from the past then you can predict in to the future with reasonable confidence.

The best description of Cpk for me is; effective space available/ one-half of the space required = Distance to the nearer spec/ Average - Lower Natural Process Limit.

Worked Example:

Process demonstrates stability/predictability

Process Average = 0.14063"
Design specs on a fictitious dimension are an upper limit of 0.155" and Lower limit of 0.125"
Distance between the natural process limits is 0.1517 - 0.1296 = 0.0221"

Calculate Cpk
- Distance to the nearer spec = 0.155 - 0.1406 = 0.01437"

- One half of space required = Half the distance between the natural process limits 0.0221/2 = 0.01105"

Cpk = 0.0144 (rounded)/0.0115 = 1.30
 
Thread starter Similar threads Forum Replies Date
K Analysis variation among the lots during cpk calculation. Design and Development of Products and Processes 1
E Questions regarding Cpk Calculation - Should we be using LSL/USL or LCL/UCL? Capability, Accuracy and Stability - Processes, Machines, etc. 5
J Calculation of σ within subgroups for Cpk in Minitab Using Minitab Software 1
J Calculation of the Mean - Student Question about Cpk calculation Capability, Accuracy and Stability - Processes, Machines, etc. 6
K In Process Data Collection and Cpk Calculation Manufacturing and Related Processes 13
M Calculating Cp and Cpk - Is my calculation correct? Capability, Accuracy and Stability - Processes, Machines, etc. 7
K Problem with Cpk calculation of dimension with nominal at the top limit. Statistical Analysis Tools, Techniques and SPC 6
E Asymmetric Tolerance - How does an Asymmetric Tolerance affect the Cpk/Cp calculation Using Minitab Software 3
B Why 3 sigma in Cpk calculation? Six Sigma 8
T Cp and Cpk calculation for Non-normal data? Statistical Analysis Tools, Techniques and SPC 11
J Methods used to calculate Cpk value - Need help for Cpk Calculation Statistical Analysis Tools, Techniques and SPC 8
A Is the normal Cpk calculation applicable for data with positive & negative values? Capability, Accuracy and Stability - Processes, Machines, etc. 4
R Is Cpk calculation of dBA (noise level) valid? Capability, Accuracy and Stability - Processes, Machines, etc. 9
G Cpk Calculation - Tolerance to maintain 1.33 & 1.67 Cpk respectively Capability, Accuracy and Stability - Processes, Machines, etc. 17
M Calculation of Cpk and Ppk for an unstable process Statistical Analysis Tools, Techniques and SPC 7
J Calculation/math to find 1.33 Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 15
O Customer is telling me my Cpk calculation is incorrect Capability, Accuracy and Stability - Processes, Machines, etc. 13
C Software Calculation Errors for Cp and Cpk With Unilateral Tolerances Capability, Accuracy and Stability - Processes, Machines, etc. 4
R Cp, Cpk calculation for np chart - No USL or LSL - SMT Production Capability, Accuracy and Stability - Processes, Machines, etc. 16
R Cpk calculation for short runs - Manufacturing FFC (flexible flat cable) Capability, Accuracy and Stability - Processes, Machines, etc. 3
T Short Run - Low Volume Cpk Calculation Capability, Accuracy and Stability - Processes, Machines, etc. 10
D Increased positional tol. due to departure from MMC (Bonus)and calculation of Ppk/Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 9
W LTPD, AQL, Ppk and Cpk validation sampling plan table Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
M Cp and Cpk for straightness and parallelism Capability, Accuracy and Stability - Processes, Machines, etc. 8
Q Capability - CPk comparison values Capability, Accuracy and Stability - Processes, Machines, etc. 12
D Tolerance definition based on expected Cp/cpk Reliability Analysis - Predictions, Testing and Standards 14
S Recommendation for user friendly Gaga R&R and Cpk software Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 10
A How to set up Continuous CpK monitoring of an injection mold process Reliability Analysis - Predictions, Testing and Standards 7
A Interpretation with regards to Ppk > Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 14
Proud Liberal Cp / Cpk on position using multiple MMC bonuses Capability, Accuracy and Stability - Processes, Machines, etc. 2
I Can we use pin gauges to measure an accurate Cpk ? Capability, Accuracy and Stability - Processes, Machines, etc. 9
T Final process capability results - What I am supposed to present? Cp and CpK? APQP and PPAP 11
F CpK on a manufactured assembly? Reliability Analysis - Predictions, Testing and Standards 7
M How is the Cmk and Cpk calculated? Statistical Analysis Tools, Techniques and SPC 0
O Cpk for Unilateral Tolerance Capability, Accuracy and Stability - Processes, Machines, etc. 9
B How to calculate CPK with n = 1 Manufacturing and Related Processes 2
O CPK with a P value less than 0.005 Manufacturing and Related Processes 8
A Short Term vs. Long Term SPC Study - Where is Cp and Cpk Defined Statistical Analysis Tools, Techniques and SPC 8
A Cpk Formula seems off, need help!? Capability, Accuracy and Stability - Processes, Machines, etc. 11
D Cp/Cpk on Gages for MSA (vs. Cg/Cgk) Capability, Accuracy and Stability - Processes, Machines, etc. 21
B Maximum Material Condition with Bonus - Determine Cpk for this one kpc Measurement Uncertainty (MU) 2
Hami812 Cpk Setting Tolerance - Cart before the Horse? (Wifi Routers) Capability, Accuracy and Stability - Processes, Machines, etc. 3
T Calculating LCL, UCL, Cp, and Cpk in an Excel Spreadsheet Statistical Analysis Tools, Techniques and SPC 3
Proud Liberal Cpk on Position w/ MMC on Location and Size Capability, Accuracy and Stability - Processes, Machines, etc. 3
E SPC Production - Getting Cpk and Ppk Statistical Analysis Tools, Techniques and SPC 8
S Track Cpk trend Statistical Analysis Tools, Techniques and SPC 5
M Cp & Cpk about a diameter measured with min.,max. and average values. Capability, Accuracy and Stability - Processes, Machines, etc. 13
P Non-normal Data Cpk Statistical Analysis Tools, Techniques and SPC 5
alonFAI Cpk for Solder Paste Height Statistical Analysis Tools, Techniques and SPC 5
I As a part of validation, should i include the acceptance criteria of CPk index >1.33? Qualification and Validation (including 21 CFR Part 11) 4

Similar threads

Top Bottom