Any does and don'ts when it comes to overmoulding on aluminium sheet?

[ToolEng1]

I've had a RFQ in from a customer to manufacture a 1+1 injection mould tool to overmould on to an 1mm aluminium veneer trim that fits onto an instrument panel. The substrate is in >PC-ABS<. This part is highly visual once assembled so scratches, blemishes etc are not acceptable!!

I know there are a lot of issues to look out for such as: 1. Difference in shrinkage between aluminium and plastic substrate giving a mismatch condition.
2. Aluminium trim will be damaged/scratched during moulding.
3. Flash
4. Aluminium not bonding to the PC-ABS.

The list could go on. Can anyone give me some ideas on past experiances on do's & don'ts for part and mould design?

Thanks

 

[HDS]

Is it a chemical or mechanical bond?
Is it 2D or 3D?
How will you hold the insert?
Will heat discolor it?

 

[ToolEng1]

Chemical bond during the moulding process. I'm not too sure how PC-ABS bonds to aluminium especially a smooth surface. But there is scope to change the part design to some sort of mechanical fixing i.e. rolled edge etc.
The parts are 3D, not very complicated.
The plan to hold the insert in place during tool close and injection is firstly to use vacuum to stop the part dropping of during tool close. The next fixing is mechanical by means of Ø4 pins that shut off on the 'B' surface of the aluminium veneer.
lastly I am not sure if heat will discolour it. Do you think this is possible? The finish on the aluminium veneer is supposed to be a bright brushed effect.


Thanks

 

[toolman801]

Your pinch off on the aluminium veneer will discolor. You will have to somewhat accept that. You can minimize the effect by having a knife edge for a pinch point. You can like we do for our over-molds create more or less of a "Picture Frame" with your overmold. Keep in mind with the knife edge pinch point, whoever builds the mold most be very accurate with the dimensions of the Aluminum between the pinch off areas.
When I do a knife edge I always have it on a compression slide. This takes up the small thickness difference in the sub-strate.