Metal Stamping Process Audit / Knowledge required!

CarolX

Super Moderator
Super Moderator
#11
OK - your torquing a plastic screw into 18 gauge material - frankly, I am not surprised that you are having problems.

I know very little about screws made from plastic, but I am sure that it is much softer than your metal part - btw - what type of material are you using?

Could you have some burring on the threads of the metal part that is cuting into the plastic part?

Could the screws be cross threaded when inserted?

Have you checked both components with go/no-go gages? I would highly reccommend doing this, especially on a defective part.

You stated that you measured the screw - what did you measure? Major diameter, pitch diameter?

Have you considered replacing the threads in the metal part with a threaded insert such as a PEM type nut?
 
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Golfman25

Trusted Information Resource
#12
Certainly seems like a design issue to me. The plastic screw is going to loose vs. the metal every time. And plastic threads aren't really the same as metal threads (been down that road). Sounds like you need more holding power. Good luck.
 
T

terranceyu

#13
Certainly seems like a design issue to me. The plastic screw is going to loose vs. the metal every time. And plastic threads aren't really the same as metal threads (been down that road). Sounds like you need more holding power. Good luck.
OK - your torquing a plastic screw into 18 gauge material - frankly, I am not surprised that you are having problems.

I know very little about screws made from plastic, but I am sure that it is much softer than your metal part - btw - what type of material are you using?

Could you have some burring on the threads of the metal part that is cuting into the plastic part?

Could the screws be cross threaded when inserted?

Have you checked both components with go/no-go gages? I would highly reccommend doing this, especially on a defective part.

You stated that you measured the screw - what did you measure? Major diameter, pitch diameter?

Have you considered replacing the threads in the metal part with a threaded insert such as a PEM type nut?
Thanks for the swift response. Please see my reply.

Plastic screw outer diameter tooling insert and actual part was measured by Quick Vision : 2.76 ~2.85 mm. Spec: 2.85 ±0.10 mm. Material : PC Lexan.

The Metal part hole was confirmed with Go-Nogo jig with M3 thread attached to drill press m/c. Metal part attached to the jig for thread checking. All pass.

I do not want to go back to R&D yet, until I confirmed the findings, which is related to weakness of design. FYI, we have been running fine for past several months, and this is the only first issue encountered.

Currently, we have sent the plastic screw for measurement, it is within spec as above said. For metal part with M3 hole threaded as spec, still waiting supplier to actually come back with investigation report.

Any comments?
 

CarolX

Super Moderator
Super Moderator
#14
The Metal part hole was confirmed with Go-Nogo jig with M3 thread attached to drill press m/c. Metal part attached to the jig for thread checking. All pass.
What does "m/c" stand for? Are you checking the threads with a tap or a gage?

I am not familiar with "Quick Vision". Does it check all the thread attributes?

Have you check a "failed" part?

Thread tapping on sheet metal is normally done as a "hand" operation", not in an automated machine. There are a lot of opportunities for mistakes to be made.
 
A

alspread

#16
confirmed with Go-Nogo jig with M3 thread attached to drill press m/c.
What does this mean? I don't understand the reference to a drill press when checking a thread with a Go-NoGo gage.

Look very closely (10x magnification) at the condition of the hole of a bad part, and a hole before and after threading. The design does not leave you with much material to create a thread (3-5 turns maybe). There could be something left over from the punch press causing an irregular shaped hole (i.e tapered). because the material thickness is so thin it may be difficult to determine how much of the hole many acceptable and how much is questionable.

You mentioned that things were working okay for some period. Maybe another way to attack this is to evaluate any changes during the time the failures occurred.

I'm with CarolX on a couple of ppoints
 

somashekar

Staff member
Super Moderator
#17
Thanks for the swift response. Please see my reply.

Plastic screw outer diameter tooling insert and actual part was measured by Quick Vision : 2.76 ~2.85 mm. Spec: 2.85 ±0.10 mm. Material : PC Lexan.

The Metal part hole was confirmed with Go-Nogo jig with M3 thread attached to drill press m/c. Metal part attached to the jig for thread checking. All pass.

I do not want to go back to R&D yet, until I confirmed the findings, which is related to weakness of design. FYI, we have been running fine for past several months, and this is the only first issue encountered.

Currently, we have sent the plastic screw for measurement, it is within spec as above said. For metal part with M3 hole threaded as spec, still waiting supplier to actually come back with investigation report.

Any comments?
Is the 1.2 thick sheet embossed and then tapped ? This will get you more depth of the hole to have sufficient threads. How does a standard metal screw M3 work in the tapped location ?
Another thought ... Can you use a standard clinch nut of M3 in the 1.2 mm sheet by pressing it into an accurately punched hole in the sheet ?
 
T

terranceyu

#18
What does "m/c" stand for? Are you checking the threads with a tap or a gage?

I am not familiar with "Quick Vision". Does it check all the thread attributes?

Have you check a "failed" part?

Thread tapping on sheet metal is normally done as a "hand" operation", not in an automated machine. There are a lot of opportunities for mistakes to be made.
What does this mean? I don't understand the reference to a drill press when checking a thread with a Go-NoGo gage.

Look very closely (10x magnification) at the condition of the hole of a bad part, and a hole before and after threading. The design does not leave you with much material to create a thread (3-5 turns maybe). There could be something left over from the punch press causing an irregular shaped hole (i.e tapered). because the material thickness is so thin it may be difficult to determine how much of the hole many acceptable and how much is questionable.

You mentioned that things were working okay for some period. Maybe another way to attack this is to evaluate any changes during the time the failures occurred.

I'm with CarolX on a couple of ppoints
Quick vision stand for Smart scope, which is non-touch-part approach, different from CMM machine (touch probe concept).

Thanks for your recommendation. I will actually arrange a trip to go to supplier to verify the Go-NoGo-jig condition. It is a good approach to see whether any changes made during the time the failures occured, as this is first time encountered, and the quantity is very less, 1 in 100 pcs.

Any other items I need to watch this?
 
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