SPC in Injection Moulding and Metal Pressing/Stamping

[Howard Atkins]

You have got me on my high horse now.
IMHO the demands for SPC in QS are antedeluvian and refer to process that are controllable and are given to immediate detection.
Most SPC is on the part and not on the process. I experimented with finding parameters of injection molding that can be charted but in most cases this was not possible.
If you are using closed loop machines then they corrct themselves. The only real parameters that are worth checking are total cycle time and plastification time.
As plastic shrinks to measure dimensions immediatley means extrapolation of the shrink and thus measurement of the "wrong" dimension.
I have persuaded customers that this is irrelevant to the spirit of the Standard.
Weight is a parameter that could be used but it needs to be changed according to the density of each lot of material.
For PPAP I submit a PPK number based on the measurements of samples 24 hours after production. This is acceptable.
I hope that this helps you for further information please return.

We are an injection moulding and metal pressing company supplying 1st automotive suppliers. As a result of a recent QS9000 audit i have been asked to re-look at the entire SPC strategy as to its applicability in supporting process controls (mainly process parameter control, First off, patrol inspection etc) and reviewing what is sensible industry practice. I am currently concentrating mainly on new product introduction - What are other similar organisations doing ?

[Sam]

I agree with Howard. I have tried several different methods for applying SPC to the injection molding process. For the same reasons Howard cited I too have reverted to dimensional measurement and/or testing to satisfy the requirement.

"For PPAP I submit a PPK number based on the measurements of samples 24 hours after production. This is acceptable."

This is the same criteria that I have used and have found it to be adequate, in that most materials haved "cured" within this time frame.

Ford requires on-going SPC to monitor the dimensional and test results and this method satisfys them when noted in the control plan.

[Don_Amaru_Sarma]

Thanks Howard. I did read it. By the way guys can anyone guide me on doing SPC for Plastic Injection moulding?

[Howard Atkins]

Originally Posted by Don_Amaru_Sarma

Thanks Howard. I did read it. By the way guys can anyone guide me on doing SPC for Plastic Injection moulding?

First what and why do you want to do?

As we say SPC on dimensions is not useful.

Please give more info

Thanks

[Don_Amaru_Sarma]

Well Howard,

I'm thinking of doing it on moulding defects. We are currently using a material called Bakelite. And there are some defects such as excessive flashing, short shot, burnt part etc. These defects appear at the moulding stage itself.

Further down the line, there are secondary processes such as deflashing/deburring, screw hole taping, clip hole drilling, etc. Now I would like to apply the SPC on this line of processes. Lets say:-
1. Molding
2. Runner cut
3. Deflashing
4. Screw Hole tapping
5. Packaging

I'm also not looking at the dimensions. Right now its more focused at the appearance of the part itself. Dimensions are usually ok. The Outgoing QC in my company confirms that dimensions are ok (except in the case of short shot of course).But usually what fails is the appearance. Eg. The part may have flow marks, Deflashing notdone properly(i.e flashing still visible) etc.

I'm sorry I didn't explain further in detail in my original thread. As I am new to this field. .
I hope this provides further explanation. Thanks

[bobdoering]

Originally Posted by Don_Amaru_Sarma

Now I would like to apply the SPC on this line of processes. Lets say:-
1. Molding
2. Runner cut
3. Deflashing
4. Screw Hole tapping
5. Packaging

Nice list. They are all dependent variables. Now, find the independent variables that control these variables. Perhaps a fishbone diagram with each of these items as an output would be a good start.

[Don_Amaru_Sarma]

Well I will begin the fishbone diagram ASAP. The problem is that currently all the processes are already in the Masspro stage. I would have to start with a current running one. I was actually thinking for a new product. That was what I thought will be easier. But will try to fit in the analysis into my work. Unfortunately I'm the only engineer in the whole company, so right now I'm overloaded with work. But will try to do it ASAP.