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dimensions, injection molding, plastic injection molding
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  Post Number #9  
Old 13th April 2018, 08:57 AM
rbriggs5145

 
 
Total Posts: 9
Re: Dimension control on injection molding parts

First I would assess if these are really critical dimensions and if there are other dimensions on the print that they can check that will give you indication of tool wear. You could also look to see if there are dimensions that are not on the print that can be added in lieu of these dimensions that will indicate tool wear. If neither of these is an option then you can sit down and work out whether you can measure or another solution that works for both of you. Pushing your supplier to do costly checks that may not be necessary will only push the total cost of the program up. Whether you pay for it now or later.

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  Post Number #10  
Old 13th April 2018, 10:49 AM
Bev D's Avatar
Bev D

 
 
Total Posts: 3,630
Re: Dimension control on injection molding parts

This appears to be a real quality system gap.

Your quality system should require that the drawings be well specified. The drawing should denote the critical characteristics and these should be engineered. in other words the design is characterized such that the tolerances are KNOWN to guarantee that the final part meets YOUR Customer requirements for appearance, fit, function and reliability.

Your system should require that you select suppliers who are capable of building the parts to your specification: they have the appropriate technology, measurement systems, and quality system to support providing you with parts that meet specification.

Your quality system should require that during contract review the drawing is reviewed, the suppliers agrees to meet the requirements and you both agree on the quality plan that will monitor ongoing quality. measurement systems analysis, first articles, incoming inspection, their final inspection, SPC, when and how changes to their process will be validated, etc.
Thank You to Bev D for your informative Post and/or Attachment!
  Post Number #11  
Old 16th April 2018, 08:00 PM
Jafri

 
 
Total Posts: 20
Re: Dimension control on injection molding parts

Hello,
So in the last few days, what I did was to contact the design group. They agreed to put critical dimensions on the print.
Plan is that once these do it then Quality will have a ground to require Cp done on those dimensions. I will give them no other option.
How they do it will be their concern. The only need to tell us their method. CMM or conventional inspection equipment.

If they disagree them I will simply refuse to approve their PPAP.

But hopefully, things won't get to that point. They will listen to us. Because I have asked designers to be on the meeting with suppliers as third party (they are consultants).

Currently, I am waiting for the marked print from the design team.
  Post Number #12  
Old 16th April 2018, 08:20 PM
Golfman25

 
 
Total Posts: 1,463
Re: Dimension control on injection molding parts

Quote:
In Reply to Parent Post by Jafri View Post

Hello,
So in the last few days, what I did was to contact the design group. They agreed to put critical dimensions on the print.
Plan is that once these do it then Quality will have a ground to require Cp done on those dimensions. I will give them no other option.
How they do it will be their concern. The only need to tell us their method. CMM or conventional inspection equipment.

If they disagree them I will simply refuse to approve their PPAP.

But hopefully, things won't get to that point. They will listen to us. Because I have asked designers to be on the meeting with suppliers as third party (they are consultants).

Currently, I am waiting for the marked print from the design team.
So you're asking them to prove capability on critical dimensions after the fact and taking a hard line by not approving their PPAP?

Last edited by Marc; 18th April 2018 at 12:33 PM. Reason: Remove unnecessary comment.
  Post Number #13  
Old 16th April 2018, 08:24 PM
Jafri

 
 
Total Posts: 20
Re: Dimension control on injection molding parts

So what are you suggesting? That we should accept FAI only and forget about any process capability, no matter how important the dimension?

What are our options?

Quote:
you'll get much further working together.
Of course. The way I'm saying here will not be the way I will be talking to them.
This PPAP signing thing was just frustration. Probably.
I can't stop a supplier selected by the company and who has spent a lot of money developing the tool.

Last edited by Jafri; 16th April 2018 at 08:29 PM. Reason: you'll get much further working together.[/QUOTE]
  Post Number #14  
Old 18th April 2018, 12:46 PM
Marc's Avatar
Marc

 
 
Total Posts: 26,666
Re: Dimension control on injection molding parts

Quote:
In Reply to Parent Post by Golfman25 View Post

I disagree. There are too many drawings these days drawn with zero thought on how to check the part in the real world. Everytime we ask the designer "how are we going to check that" we get a blank stare. They'll defer to their quality people who will respond "good question." Both sides need to be on the same page regarding measurement.
The problem is a very old one. I've had clients where I had to bring in a GD&T expert (who specialized in both making and marking prints correctly, and in "how to best measure") to guide the supplier in producing prints and the customer in reading them (as "best" measurement equipment / techniques. Essentially I set up meetings where the expert, the supplier and the customer were all in a meeting room and we went over prints and how to measure the various dimensions (as well as potential measurement fixtures).

There are many companies who have no GD&T and/or measurement techniques experts. I mention this because sometimes it takes more than simply supplier and customer "working together".
  Post Number #15  
Old 18th April 2018, 01:42 PM
Wes Bucey's Avatar
Wes Bucey

 
 
Total Posts: 11,169
Re: Dimension control on injection molding parts

Quote:
In Reply to Parent Post by Marc View Post

The problem is a very old one. I've had clients where I had to bring in a GD&T expert (who specialized in both making and marking prints correctly, and in "how to best measure") to guide the supplier in producing prints and the customer in reading them (as "best" measurement equipment / techniques. Essentially I set up meetings where the expert, the supplier and the customer were all in a meeting room and we went over prints and how to measure the various dimensions (as well as potential measurement fixtures).

There are many companies who have no GD&T and/or measurement techniques experts. I mention this because sometimes it takes more than simply supplier and customer "working together".
I wrote about our process a long time ago here in the Cove. If I have time, I'll research for the exact post, but, essentially, in our high tech precision machining business, we used a process similar to what Marc describes on EVERY product we made for customers as part of Contract Review. BEFORE we ever cut a chip off metal, we had the inspection plan agreed with all parties, assuring the proper instrumentation was available to check, with operators and inspectors trained and confirmed proficient on ability to deploy such instrumentation. It sure saved a lot of grief other machining companies had when customers rejected parts because of misunderstandings on critical dimensions and methods of inspection, including sampling plans.
  Post Number #16  
Old 18th April 2018, 04:49 PM
Golfman25

 
 
Total Posts: 1,463
Re: Dimension control on injection molding parts

Quote:
In Reply to Parent Post by Wes Bucey View Post

I wrote about our process a long time ago here in the Cove. If I have time, I'll research for the exact post, but, essentially, in our high tech precision machining business, we used a process similar to what Marc describes on EVERY product we made for customers as part of Contract Review. BEFORE we ever cut a chip off metal, we had the inspection plan agreed with all parties, assuring the proper instrumentation was available to check, with operators and inspectors trained and confirmed proficient on ability to deploy such instrumentation. It sure saved a lot of grief other machining companies had when customers rejected parts because of misunderstandings on critical dimensions and methods of inspection, including sampling plans.
That's where it kind of is these days. But it is still a chore. You just pull the "grief" up to the beginning of the the process. Too many designers don't want to listen to what the process is capable of. Plus, you're usually in a rush to get things going -- somebody has sucked up all the lead time.
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