Capability for a Injection Mold Machine (35 Cavities)

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Bill McNeese

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#12
Attached are two workbooks. One shows the individuals chart for cavity 1. You can easily see the presence of chunky data in the range chart - two few values. Your measurement process appears to be masking the process variation. You probably need to start with how you do the measurement.

The second workbook contains the Cpk chart for Cavity 1 based on specs 2 to. Doesn't mean much until you fix the measurement process.
 

Attachments

F

FAndrade

#13
Attached are two workbooks. One shows the individuals chart for cavity 1. You can easily see the presence of chunky data in the range chart - two few values. Your measurement process appears to be masking the process variation. You probably need to start with how you do the measurement.

The second workbook contains the Cpk chart for Cavity 1 based on specs 2 to. Doesn't mean much until you fix the measurement process.
Thanks Bill. I now took the raw data of the measure system (Volume from Weight and Density using a software. Is the most exact system). You can find it attached on this post. On this measurement, no parameters were changed.


As I can see, the overall process capacity can be measured from 1 cavity? Is that correct having on mind that cavity 1 is obviously different from cavity 2?


Thanks in advance.
 

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Bill McNeese

Involved In Discussions
#16
When I run the numbers in Minitab, I get the results I had before. What subgroup size are you using for the capability analysis? I used n = 1 for an individuals chart. You will have values for Cp, etc. You did not have any vales for Cp, etc., just Pp, etc.
 
F

FAndrade

#17
When I run the numbers in Minitab, I get the results I had before. What subgroup size are you using for the capability analysis? I used n = 1 for an individuals chart. You will have values for Cp, etc. You did not have any vales for Cp, etc., just Pp, etc.
Using n=1 in minitab, I get the same results ;)


I need to proove that my machina is capable to fill plastic ampoules on using this specs min = 2mL max = 2.9mL


What is the best result to represent what I need to show? cpk? ppk? No parameters were changed during the data aquisition.


Thanks in advance.


EDIT: I got this cavities with ppk <1,33 but cpk > 1.33

 
Last edited by a moderator:

Bev D

Heretical Statistician
Staff member
Super Moderator
#18
Ppk (using the total variation directly calculated from all of the data) is the estimator you should use. It reflects actual performance capability

Cpk (using within subgroup variation as to estimate the total variation) is only useful as rough estimate of the 'potential' better variation if you were to eliminate the subgroup to subgroup variation....it estimates potential capability.


...of course the caveat is that you took a random sample that represents the full range of variation that the process is expected to experience...
 
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