Capability Study on Continual Arbitrary Dimension

[Ospif1]

Hi,

I am new to performing this kind of analysis so a little confused as to what my options are. We currently produce a heat shield and need to perform a capability study on the critical aspects of the shield, which are the diameters and locations of the fastening holes situation on the shield and the form of the shield.

The hole diameters and locations I have no issues with performing the capability however i am confused as to how i can perform one for the form since the form is not a set dimension, it's continual.

What we do have, is the ability to check whether or not the form is within a specified tolerance, but unless you measure the exact point of the form on ever shield tested, the co-ordinates of the form area tested will never be the same.

So I suppose my question is whether or not there is a method of performing a capability study for something which does not have an exact single dimension and location such as a hole does and all you have available to you is a CMM machine which can tell you if the form at any point on the shield is in or out of spec.

Appreciate any help, Cheers.

 

[Bev D]

depending on why you are performing a capability study, a simple approach is to use a categorical (aka attributes or pass/fail) data approach. Thsi gets you to how many bad parts you are making. If you are looking for margin to the limits or slow drifts towards the specification limits, you will need to fixture the parts and measure in specific locations...

 

[Ospif1]

So does having a simple pass or fail option give you the requirement to perform a capability study? Would be great if that can be done because I can then perform a proper dimensional study on diameters and locations and then another for a pass/fail approach for the form and edge.

Thanks for your answer!

 

[Bev D]

So does having a simple pass or fail option give you the requirement to perform a capability study?

Depends on where your requirement for a capability study comes from. If you are doing it because your customer requires it, then they may have specific requirements and constraints about what they want. (I always advocate for simply asking them) If the requirement comes from your organization, determine the true intent. Is it margin, trending, or yield prediction?

 

[roland_lu]

The hole diameters and locations I have no issues with performing the capability

It will be very interesting to know how you do the capability study for hole locations.

Thanks.

 

[Ospif1]

It will be very interesting to know how you do the capability study for hole locations.

Thanks.

We use a CMM machine to locate all the holes in relation to a single specific hole on the part.

So for example the x,y,z coordinates from hole A to hole B, A to C, A to D etc. We have columns for x,y and z, calculate the capability for each of those coordinates then determine an overall capability result from that.

It's bloody tiresome when you have to do 125 parts for a PPAP though

Thanks for the help guys, I will get back to the customer regarding their exact requirements for the special characteristics in question.

 

[Stijloor]

We use a CMM machine to locate all the holes in relation to a single specific hole on the part.

So for example the x,y,z coordinates from hole A to hole B, A to C, A to D etc. We have columns for x,y and z, calculate the capability for each of those coordinates then determine an overall capability result from that.

It's bloody tiresome when you have to do 125 parts for a PPAP though

Thanks for the help guys, I will get back to the customer regarding their exact requirements for the special characteristics in question.

How are the hole locations toleranced? Any positional tolerances used; with or without modifiers? "M" for example?

Stijloor.

 

[Ospif1]

How are the hole locations toleranced? Any positional tolerances used; with or without modifiers? "M" for example?

Stijloor.

Yeah the customer placed positional tolerances on the holes in all directions. I simply CMM the physical part to the CAD of the part and determine if the physical part follows the CAD within the supplied tolerances.

 

[Stijloor]

Yeah the customer placed positional tolerances on the holes in all directions. I simply CMM the physical part to the CAD of the part and determine if the physical part follows the CAD within the supplied tolerances.

Did the customer accept this practice? If the MMC principle is specified, then it would possibly provide you with an additional (bonus) location tolerance. I am just guessing here because I have not seen the print.

Stijloor.

 

[Ospif1]

Did the customer accept this practice? If the MMC principle is specified, then it would possibly provide you with an additional (bonus) location tolerance. I am just guessing here because I have not seen the print.

Stijloor.

To be completely honest with you, I am not sure how MMC works, the customer was also very vague as to their requirements with the capability, it was simply "we need it performed on 125 parts and for all special characteristics as shown on the FMEA" and the special characteristics were outlined as hole diameters and locations plus the form of the shield.

My own experience is also limited as this is the first time I have ever performed a PPAP and everything that goes with it (I didn't even know what a capability study was a month ago ). So it's very much a learning experience for me.