Overmoulding a part

[dolaol]

I have to design an injection mould which moulds over a steel part. This is no problem except for the tolerance of the steel part. It is +.5, -.5. Any ideas how to soak up the tolerance in the tool?

 

[patprimmer]

+ or - .5 what? inches, thou, metres microns?

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[patprimmer]

What material.
Is the gap the furthest point from the gate.
Can you tolerate a little flash.
How good will the ring check valve be.
How good will the injection control device be.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dolaol]

the tolerance is in mm,

the steel part will be overmoulded in nylon,

no flash allowed

the whole steel part is covered in plastic (top, bot & sides) except for some pads on the top & bot face of the steel part which need to s/o in the tool.

There is a hole up the centre of the part which is not
overmoulded , this is where the feed will be, so steel on the tool needs to stand up & s/o in this hole.

The finished part has a tolerance of +/- 0.1mm (plastic to plastic). This is where the problems are

 

[patprimmer]

As I read this, the worst case scenario will give 1.0mm clearance if the biggest steel part will also fit in the mould. This is an impossible situation.

You will need much tighter tolerances for the steel, or you will need to sort the steel by size and have a number of inserts for the mould so that the gap is never over about 0.05mm.

Another option is to have a hydraulic core that closes against the steel in the critical area and seals off.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.