Flash on plastic parts 1

[DaveE01]

I am curios if anyone has suggestion on how to quantify no flash on a part? Is it at a certain magnification or by a visual observation?

 

[ornerynorsk]

You write the spec. It can be cosmetic or physical, or both. "No flash" is an enigmatic term sorely lacking in hair-splitting detail. The one time I've had to specify, we just called out max profile dimensions of the parting line area, including a "no hand trim" instruction.

 

[Pud]

If you run a finger along it and it produces blood, it's flash.

If not it's a witness of the parting line.

It's pretty obvious what is flash - it's generally not consistent around the edges, distinguishing it from the parting line(s).

Imho, parts with "flash" are rejects and are scrap. Quantifying it should be simply "No Flash" as a moulder should know what is flash and what is not.

H

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

Harry nailed it I think.

A slight raised and uniform but not sharp shape at the parting line indicates good pack. Once it is jagged and not uniform and sharp it is flash.

Some shops specify a dimension, but that is not totally reliable as the reference point might change with even slight differences in shrinkage.

Some shops have photos on the set up sheet or QC documents. That seems to work OK mostly.

You need to be careful that "no flash" does not in fact specify by accident, not fully packed.

Regards
Pat
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[KENAT]

There are tools which simulate the 'does it cut your finger test'.

They have some kind of roll of tape and you roll it along the surface, if it cuts the tape it fails or something like that. So you could specify a requirement to pass that kind of test, I suppose.

It's come up before in relation to 'remove all burrs & sharp edges' as often specified on machining drawings.

Arguably you really should give a definite limit, but it's one of those things that it seems a lot of effort for something that you usually get any way etc.

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[dgallup]

I have used this note on surfaces that have an o-ring seal:

.002" max. MOLD MISMATCH AND FLASH COMBINED ON THIS DIAMETER.

We can quantify that by using an optical comparator at 20x magnification.

 

[loughnane]

I agree with dgallup except my phrasing goes something like... "parting line mismatch not to exceed .00X"

Chris Loughnane - Product Design

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