Dimension control on injection molding parts

Jafri

Starting to get Involved
#1
Hello,

This is about one of our suppliers who will be sending us injection molding parts.
They are going to do First Article Inspection on all dimensions in 3 samples initially. Some of these dimensions are difficult to check without CMM, which they don't possess. Nor do they have any checking fixture.

I am thinking what should I ask them to ensure that these dimensions stay in tolerance after some passage of time?

Should I ask them for yearly CMM check, even if from outside? Or do customers usually just don't ask for such verification?
*confused*.

Thanks. :)
 

Ninja

Looking for Reality
Trusted
#2
Do you have a CMM?

If you are specifically concerned with tool wear and dimensional creepage...can they send ahead first and last article for you to verify?

Just thinking out loud...
 

Jafri

Starting to get Involved
#4
Do you have a CMM?

If you are specifically concerned with tool wear and dimensional creepage...can they send ahead first and last article for you to verify?

Just thinking out loud...
No, we don't have CMM either.
Yes, I'm concerned about too wear, and how the supplier will be able to find out about it before it starts making bad parts.

The supplier will do FAI 100% once, but I don't understand what is last article?!
 

Jafri

Starting to get Involved
#5
I think you both need to sit down and develop and agreed checking methodology. Gauging and fixturing may help.
Checking fixture might be too expensive, but seems like this is the only option besides CMM. I will try to convince our guys to pay for it.

If it doesn't work then probably ask the supplier to check critical dimensions from outside source?
 
#6
This appears to me to be a case where a supplier has agreed to make a part without properly assessing how they are going to satisfy the customer (you) and ensure that they supply defect-free parts.

To be blunt, it is THEIR responsibility to determine their measurement strategy, which includes frequency and method of measurement. YOUR responsibility as the customer, is to review their proposal and identify any concerns you may have.

One of the things to be considered is the rate of wear - if the die feature in question is (as a general rule) expected to stay within spec for 100,000 cycles, and the annual volume of the part is 75,000 pcs, then tool wear should be caught in the annual part layout (presuming you have this as a part of your requirements).

Please keep us informed on how this progresses - I for one would love to hear the final resolution, and I am sure there are others as well who are taking an interest.

:popcorn:
 
#7
This appears to me to be a case where a supplier has agreed to make a part without properly assessing how they are going to satisfy the customer (you) and ensure that they supply defect-free parts.

To be blunt, it is THEIR responsibility to determine their measurement strategy, which includes frequency and method of measurement. YOUR responsibility as the customer, is to review their proposal and identify any concerns you may have.

One of the things to be considered is the rate of wear - if the die feature in question is (as a general rule) expected to stay within spec for 100,000 cycles, and the annual volume of the part is 75,000 pcs, then tool wear should be caught in the annual part layout (presuming you have this as a part of your requirements).

Please keep us informed on how this progresses - I for one would love to hear the final resolution, and I am sure there are others as well who are taking an interest.

:popcorn:
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.
 

AgnieszkaSz

Involved In Discussions
#8
Perhaps it is possible to damage (cut) some samples from each production order or work shift so that these dimensions that are hard to access could be measured in some easier way? Depends on part shape an size, of course.
 
#9
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.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#10
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.
 

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