Injection Molded Parts -- Drawings and QC
Hey y'all!
I have several questions regarding the drawings of Injection Molded parts and Quality Control of them as well.
Context:
We have received T0 samples of our parts already. Our supplier is Chinese.
- DIMENSIONING:
Our supplier wanted almost every feature to be dimensioned.
But the QC team then complains that we cannot measure every dimension.
The straightforward way would be to make another set of drawings only for QC.
However, according to some reddit posts, dimensions that are critical and I want measured by QC should be highlighted separately on the same drawings. Maintaining another set of drawings for QC is of course going to be inefficient as there will be more work; possibility of some drawings not updated to the latest etc.
While I will follow the latter approach but I still am a bit confused.
There are 3 kinds of dimensions:
- critical and measurable
- non-critical and measurable (I cannot trust the supplier; so I would want to know he did not off something by say 20 mm; they even made a critical boss length that had a -0.3mm tolerance 10mm longer)
- critical and non-measurable (like say there is a hole for sleeve bearing deep inside the part) What does one do about these dimension, just hope they will be okay? Like I cannot ask QC to measure these.
So confusion is about the third type of dimension. Also, do you guys mention the 2nd kind of dimension? Cause if we don't, the supplier can easily say these were not mentioned.
Supplier drawings: Mention almost all dimensions. Critical/non-critical. Measurable/non-measurable.
For QC: Highlight critical, non critical only measurable dimensions on the same supplier drawings.
2. SYMMETRY:
Should not the QC measure all features symmetric about some centre line?
If I have 8 pins and I mentioned diameter only on 1, my assumption was that if I am mentioning TYP with that dimension, QC will measure all, at least for the very initial samples. But what I have noticed is that they don't.
If some boss is dimensioned 50mm from the central symmetry line, they only mention that boss dimension on the QC inspection report. And not the other (symmetric) one. There is no guarantee that the supplier has gotten the other boss right by checking only 1.
What do I need to do in this scenario? Do I need to mention each feature even if it's symmetric or part of a pattern?
I need tips on how to dimension features for QC such that they do their work properly.
3. DATUM PLANES:
The part I am dealing with is sized at 500*300 mm2. I dimensioned features from the central imaginary longitudinal and lateral planes. Cause every thing is drafted, I could not take outer walls as reference cause what if they themselves are off from the centre? So what do you guys think I should have done? The central portion too had a feature that was tapered. I could only think about imaginary longitudinal and lateral planes to dimension features.
Any design engineer who can guide me? Like yes, we are done with T0 but I still have so many questions. I am not satisfied with the QC. And I need to also lay out a plan for QC of parts once production starts.