# Capability Study for a Specific Thickness of Rubber Sheeting

#### PABSR

##### Inactive Registered Visitor
Hello to all and thanks for your valuable help!
I work in a rubber roll manufacturing company. One of our customers is asking a Process Capability study performed on a certain quantity of rolls, and for a specific thickness. I understand that Process Capability is used to demonstrate whether a Process is capable, and not to demonstrate the capability to manufacture a determined specific thickness rubber roll. In other words, the process and its several steps can produce rolls to any thickness. If I demonstrate the process is capable at .125" thickness, could it be assumed the process is also capable for let's say 1/16" thickness? I think that yes it could be assumed the process is capable for 1/16" as long as the same steps are taken to produce a .125" and a 1/16" roll. The only thing that changes is the machine set up to a different thickness.
Thank you.

#### Miner

##### Forum Moderator
Staff member
Re: Capability study for a specific thickness

This will heavily depend on the process. Certain types of processes may have constant variation regardless of nominal dimension. Other types of processes will have increased variation at larger nominal dimensions. I recommend that you perform a capability study at at least three different dimensions (i.e., bottom, middle, top) of your ranges.

Perform a test for equal variances. If the variances are equal, you are in luck and you can use one capability for all dimensions. If the variances are not equal, plot the variances versus the dimension. If the plot appears linear, perform a linear regression and use the model to predict capability at a given dimension. You may also try using the coefficient of variation (CV = SD / mean) in a similar manner.

If it is not linear, perform two more studies at the quartiles of the range, and perform a curvilinear or nonlinear regression to predict capability at a given dimension.

1

#### 12stones

Re: Capability study for a specific thickness

The only way to ensure that the process would be capable at 1/16" would be to perform the same study you did at 0.125" to ensure that it is capable. Depending on your machines, is there any other variability that could come into play with a different machine setup? As Minor stated, it depends on your process, and you can't assume that because they're virtually the same, that they'll produce the same results.

A

#### Al Dyer

Another thing to consider might be the R&R of your measurement system as the Shore Duro reading on the material could show significant variation.

Al...

#### PABSR

##### Inactive Registered Visitor
Re: Capability study for a specific thickness

To All...my sincere thanks for your help.
Miner, when you say: 'If it is not linear, perform two more studies at the quartiles of the range, and perform a curvilinear or nonlinear regression to predict capability at a given dimension'. Why would it have to be at the quartiles? Would you recommend any book or site where I could learn more about curvilinear regression, variance analysis and related stuff?

12 stones, thank you. I just wanted to know a good way, and economical to alternatively demonstrate capabilty. I think that if the customer wants a study like this, he should pay the cost to perform it. As he is not doing that, then I had thought that we could show them capability for other thicknesses.

Al, the main characteristic is hardness but not measured in oo Duro, but in Compression Deflection. Thickness is the second characteristic. I've performed R&R studies on both but in different thicknesses.

#### Miner

##### Forum Moderator
Staff member
Re: Capability study for a specific thickness

Miner, when you say: 'If it is not linear, perform two more studies at the quartiles of the range, and perform a curvilinear or nonlinear regression to predict capability at a given dimension'. Why would it have to be at the quartiles? Would you recommend any book or site where I could learn more about curvilinear regression, variance analysis and related stuff?

Al, the main characteristic is hardness but not measured in oo Duro, but in Compression Deflection. Thickness is the second characteristic. I've performed R&R studies on both but in different thicknesses.
It does not have to be precisely at the quartiles. Doing so gives you five evenly spaced data points with which to estimate the relationship.

Here are some online resources:
Curvilinear regression refers to the fitting of polynomials (i.e., y = B0 + B1X^2 and B2X^3). Most statistics software packages perform this type. Nonlinear regression is more complex (e.g., y = e^(B0/x), and fewer packages will do this. Minitab 16 is the first version of Minitab to do so.

Since your characteristic of interest is compression deflection, I suspect that you will find that it is not a linear relationship.

#### bobdoering

Trusted Information Resource
Remember this - you have two variations in converting type processes - left to right across the web and over time down the web. The variation is different, but needs to be considered in overall variation for capability. To sort it out, you need to do capability at separate locations across the width of the sheet. You also have lot to lot variation, depending on raw material variation, and vulcanizing oven variation, etc.

Always cosndier the total variance equation when developing a plan to evaluate capability.

Capability study with a minimum spec Statistical Analysis Tools, Techniques and SPC 8
Capability or Gage R&R Study for Leak Tester? Reliability Analysis - Predictions, Testing and Standards 15
Machine Setup for a CNC Machine Capability Study Capability, Accuracy and Stability - Processes, Machines, etc. 1
Capability Study for Tapped Hole Reliability Analysis - Predictions, Testing and Standards 3
Plotting capability study data - I have a bimodular data distribution Capability, Accuracy and Stability - Processes, Machines, etc. 4
Generic requirements regarding capability study in automotive Capability, Accuracy and Stability - Processes, Machines, etc. 1
Capability or Gage R&R Study for Leak Tester Reliability Analysis - Predictions, Testing and Standards 11
IATF 16949 - Capability study on non critical dimensions? Statistical Analysis Tools, Techniques and SPC 4
Excel Template for Cgk Study wanted (Capability Gauges Study) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
Process Capability Study - Aggregate vs. Individual Processes Statistical Analysis Tools, Techniques and SPC 24
Capability Study and Qualifying a Supplier Capability, Accuracy and Stability - Processes, Machines, etc. 5
B Capability Study => Check %Study Variance and NDC? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
B Conflict between department of MSA and Capability Study Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
J How to determine a Capability Study for Low-Volume Suppliers Capability, Accuracy and Stability - Processes, Machines, etc. 3
S What is Cc? Capability Study on Key Critical Dimensions Capability, Accuracy and Stability - Processes, Machines, etc. 9
L Capability Study for a Honing Machine Statistical Analysis Tools, Techniques and SPC 3
Inspection Capability Study (Kappa Analysis / Attribute R&R) as Certification Req't Training - Internal, External, Online and Distance Learning 7
C Subgroup Size in Minitab for Capability Study Statistical Analysis Tools, Techniques and SPC 4
O One Cavity Mold Prototype Capability Study and PPAP Approval APQP and PPAP 1
G How to calculate Subgroup Size for Machine Capability Study Statistical Analysis Tools, Techniques and SPC 4
V How to calculate Machine Capability Study using Minitab Using Minitab Software 4
V JCI standard numbers of pieces required for Capability Study? APQP and PPAP 2
T Industry Standards for # of parts for Capability Study and Layout FAI's? APQP and PPAP 4
D AIAG 4th Edition Capability Study and Gage R&R Requirements Document Control Systems, Procedures, Forms and Templates 8
Q When to use Cpk or Ppk for a Process Capability Study? Capability, Accuracy and Stability - Processes, Machines, etc. 14
O Capability Study on Continual Arbitrary Dimension Capability, Accuracy and Stability - Processes, Machines, etc. 11
Attribute Data and Capability Study of Holes in Parts Capability, Accuracy and Stability - Processes, Machines, etc. 11
D Process Capability Study which involves MMC (Maximum Material Condition) Capability, Accuracy and Stability - Processes, Machines, etc. 8
A Yearly MSA (Measurement System Analysis) & Capability Study - TS 16949 Requirements Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
Process Capability - Interview Case Study Capability, Accuracy and Stability - Processes, Machines, etc. 1
A Process Capability Study using Variables Data (weight of the product) Statistical Analysis Tools, Techniques and SPC 9
M Capability Study on a New Machining Process - Issues Capability, Accuracy and Stability - Processes, Machines, etc. 40
S Does anyone know what is involved in a HiPot capability study? Capability, Accuracy and Stability - Processes, Machines, etc. 2
A Process Capability study of CNC Machining Process Capability, Accuracy and Stability - Processes, Machines, etc. 3
Q Machine Capability Study - Cpk (Cmk) of an R/F testing machine Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
B MSA (Gage R&R) vs. Capability Cpk Study - Helium Leak Check Station Statistical Analysis Tools, Techniques and SPC 2
T Machine GR&R (Gage R&R) - Capability Study Capability, Accuracy and Stability - Processes, Machines, etc. 5
M Cmk (Machine Capability) - Case study Capability, Accuracy and Stability - Processes, Machines, etc. 5
Visual Inspection - Capability Study on Attribute Data Capability, Accuracy and Stability - Processes, Machines, etc. 13
Capability Study on Extruded Alumin(i)um - How would one define a "batch"? Capability, Accuracy and Stability - Processes, Machines, etc. 4
A Capability Study Template Capability, Accuracy and Stability - Processes, Machines, etc. 1
Capability Study Required as a Condition to Adopt a Sampling Plan? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 6
Process Capability Study for Electrostatic Powder Coating Statistical Analysis Tools, Techniques and SPC 6
Process Capability Sheet for a short term 30 piece study needed Statistical Analysis Tools, Techniques and SPC 1
B Capability Study for Radii of laser cut pockets - 0.030" radius Capability, Accuracy and Stability - Processes, Machines, etc. 15
V Machine short term capability study with Cmk index in automotive industry Capability, Accuracy and Stability - Processes, Machines, etc. 3
How do you identify your heat treat capability study samples? Capability, Accuracy and Stability - Processes, Machines, etc. 3
E Capability study on true position callout. What would be the upper and lower spec? Statistical Analysis Tools, Techniques and SPC 7
K Format for presenting capability study results? Statistical Analysis Tools, Techniques and SPC 7
Initial Capability study on N50 parts - Subgroup Size? Statistical Analysis Tools, Techniques and SPC 5