injection molded part question

[JGL1980]

Hi,

I am designing an injection molded part that has a couple tricky areas. All the areas shown in green below can have no draft. All the other surfaces can have 2 degrees or more. Currently I am envision the mold opening and closing as the two arrows indicate in the first isometric view. The second isometric view shows the trickiest area, a slot that is only .06" tall and 1.25" deep and 1.6" long. My question is whether this slot can be made with zero draft with just the open-close mold or whether a side action is needed to reduce the length of the cantilevered thin piece in the mold. Is this slot going to be a problem area in the mold no matter how I do it?

 

[JGL1980]

Also, FYI, this part is still early in the design and I realize it doesn't have uniform wall thicknesses, etc. I haven't been able to core out some heavy areas since I don't know which direction to to that in

 

[Paulkuklych]

Yes it can be done with zero draft with open close mould. Zero draft will probably leave scratches in the slot though. Is it a clear part?

Paul Kuklych

http://www.improve-your-injection-molding.com

 

[JGL1980]

Thanks for your response. No, it's not clear, and I could live with scratches, since they won't be visible in such a tight slot. As long as the dimensional integrity isn't compromised (even deep scratches wouldn't hurt) it would be good. Would the slot be pulled from the right side of the view with the two arrows?

 

[Paulkuklych]

Yes that looks feasable

Paul Kuklych

http://www.improve-your-injection-molding.com

 

[Pud]

Be prepared to be replacing the blade that makes the .06" slot. At 1.25" long it's going to be very fragile and liable to breakage. Also liable to move when moulding.

Just my two pence worth..

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[JGL1980]

I was worried about that too, Pud. Would it be better for that blade to come from the left side of the picture and shut off on the round portion on the right? That way it could be a separate easier to replace piece. Or would it be better in the long run to make a side action to keep the cantilevered length shorter?

 

[Pud]

JGL1980,

I think either way will be problematic. The shut-off from the side will probably not happen as the blade will flex. The usual "rule of thumb" is thin blades/cores should be only 3x to 5x (max) thickness or diameter for reliability.

Could you have the slot much thicker (e.g. .25", tapered to the tip with say, a series of internal ribs to give the .06" between the tops of them?

Incidentally, unless this is to moulded from a zero shrinkage material, the slot will close up and be zero gap on the outer edge. Right angles are notoriously difficult and usually the tool is made so it can be adjusted after sampling to give the required 90 deg.

Have you considered making it in two parts, split along the slot and affixing together by some means?

H



www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[JGL1980]

Thanks for the tips. I'm going to have to think about this more, there has be a a creative way to avoid the slot being the way it is. Pud, your idea about the internal ribs might work, but something has to slide in there from the side without getting hung up during use, so I'll have to test it.

 

[JGL1980]

Pud, your rule of thumb for blades is that the length must be 3x - 5x the thickness of the blade? I may be able to shorten it significantly and have it still function.