Stability and flatness of platic injection molding parts

[SoilentG]

We have a flat rectangle, 30mm W x 96mm L x 4 mm H that we need to manufacture in high production quantities, ~100k/year that needs to have a flatness on the 30x96 face of 0.005mm.

Chemical resistance is not a high requirement.

Operating temperatures are in the 25dC +/- 5dC range with a controlled temperature change of no more than 2dC/hour.

Non-flourescence is a high requirement.

Any recommendations on what plastics families we should be looking at are?

 

[Pud]

Have you thought about the tooling to make this part? I would assume that tooling has be made to closer tolerances to give some tolerance for process variation. You are dealing here in the almost impossibly practicable.

Otherwise, I would suggest a non-crystalline material - e.g. styrenics, acrylics etc. Not PP, PA, etc.

You might make them by casting PMMA onto an optically flat glass surface, but I have no idea of the feasibility of this

Incidentally, 100K per annum would be considered low volume for injection moulding...

Cheers

Harry

http://www.tynevalleyplastics.co.uk

 

[HDS]

I disagree that 100K a year is low volume for injection molding. Many tools are only rated for 100K parts.

I agree that the flatness requirement is extreme.

Instead of plastic try optical glass parts or metal gauge blocks.

 

[Pud]

Many tools are only rated for 100K parts.

I assume these are aluminium?

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

Even mild steel moulds can go well over 100,000 parts.

100,000 parts per year is considered high volume but not very high volume here.

Noryl would be a good material choice to optimise flatness. Gate position and size and very uniform surface temperature of the mould also is essential.

Cast acrylic would certainly work. They make Perspex brand acrylic sheet by casting between glass plates. I am not aware of their normal flatness specs, but I expect it is quite tight, but then again 5 micron is also very tight. A few degrees temperature difference accross the part from body heat as you hold it in your hand could distortit that much

Regards
Pat
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