Feasability of This Two-Shot Mold

[CPosner]

I am considering a two-shot mold and I am curious about the feasibility of this design. The profile of the 2nd shot, the wiper, can change for manufacturability. Also, I am curious about how to detail the interface of the two materials...some kind of interlocking geometry to increase bonding? The height of the softer material is appx .1" inch.

Thanks

 

[patprimmer]

Nylon moulds over polyurethane and bonds quite well.

Bayer had a technical bulletin about it some years ago.

Main applications were shopping trolley wheels and tyres and top quality screw driver handles. Cheaper screw driver handles use PP and PP/vulcanised EDPM (like Santoprene type) elastomers.

Regards

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[CPosner]

What about the detail where the two different materials are interfaced? Anything special? also, is the sketched geometry for the softer material a feasible profile?

 

[patprimmer]

Undercuts between the elastomer and the hard polymer help, but you need some melting and welding at the interface. That is why the nylon needs to go over the PU as the nylon has the higher melting temperature.

With PP and PP/vulcanised EPDM alloys, the pp matrix and the PP will have about the same melt temperature.

Regards

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[mtpi]

Question: Is this a low or high volume part? What I would suggest is that you talk with a molder that specializes in overmolding or two shot molding as they will be able to assist in your design. Overmolding is the process of molding in most cases the harder material and then inserting it into a second tool for the overmolding of the softer material. Two shot is a process of molding both materials within the same mold on a specialized press that has two barrels for the different materials and rotating the mold within the platens. The cost difference is substantial!

Regards,

mtpi.us

 

[patprimmer]

Over moulding actually requires the higher processing temperature part to be moulded over the lower processing temperature part so as to provide enough heat at the interface for a good weld.

If both have similar processing temperatures, it then makes sense to over mould the harder part.

Regards

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[CPosner]

So you're saying that the two materials are bonded together where there is direct contact between the two materials? Like my sketch?

I am going to start talking to Mold makers/injection molders this week about the process. I think either two-shot or over molding will work in this case(?), it really comes down to mold cost and piece cost..and what my quantity... but as far as I know, two-shot is more efficient.

Thanks!

 

[patprimmer]

I am saying that there can be bonding with the correct combination of materials.

I would strongly advise talking to rawv materials suppliers ang getting their support and sample mouldings etc before proceeding.

Possible suppliers are:-
Advanced Elastomer Systems (or whatever they call themselves now) with Santoprene.

Bayer with Nylon and Polyurethane.

DuPont

DSM

BASF

Wacker with silicone Rubber compounds, including thermoplastic matrix types.

Regards

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