impossible to mold?

[deardave]

I designed this part for a toy.

It snaps into a wooden panel and has a cross hole through which you can attach a bell.
I know this would be complicated to mold but is it impossible? That is the opinion of one of my suppliers.
Thanks.

 

[MikeHalloran]

Unless I'm missing something, or the tolerances are crazy tight, I don't think it's impossible.

The two side pulls limit you to a single cavity, which might keep the unit price too high for a high volume toy. Maybe that's what your supplier meant.

It will have flash problems, and be expensive to deburr.





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I agree with Mike.

From the drawing it looks difficult, but definitely doable.

I see four side cores with the current design, but that could easily be reduced to two if the slots are modified slightly to match line of draw of the side cores for the holes.

The tooling will be expensive.

Multiple cavities are possible, but will be very expensive.

Draft angles are not specified. Parallel pins for some long holes may be impossible.

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.

 

[ewh]

If tooling costs become prohibitive, perhaps you could look into stereolithography.

 

[bvanhiel]

Besides everything that Pat pointed out, I think I see what the supplier may think is impossible. It looks like the cross hole boss that extends into the center has a small opening to the outside and a larger opening to the inside. Not easy to get the steel out of there.

You need to talk to your supplier about your functional needs in the part and how your design can be changed to make it more manufacturable. Since this part looks like it is noncosmetic, I'm sure you can get the same function without the tooling headaches.

-b

 

[dgowans]

This part is definitely possible to injection mold, assuming sufficient draft. Proper shutoff angles (minimum of 3 degrees, 5 or more would be even better) will help to minimize flash. If you've got room you might even be able to eliminate the side pulls by getting creative with vertical shutoffs, although this probably would be of little benefit.

Could you mold the part without the cross holes and add them via a secondary drilling operation?

 

[patprimmer]

After another look and considering other comments, It can be done with 2 side cores to make the holes for the bell pivot.

Although it is not entirely clear, I see the bell pivot hole with the big boss as having the big diameter on the outside, so the side core can be extracted.

The slots can be done vertically.

The undercuts for the snap fits can be done vertically from the opposite side to the slots.

It will require a very good fit and good blank offs to prevent flash. It will be difficult to eject and will require good draft angles and line of draw polishing and stripper plate or at least sleeve ejectors to get it off the pins.

I would tend to think that the core should be the fixed half, and the cavity should consist of two blocks that split to pull the side cores and release the part from the cavity.

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.

 

[deardave]

You folks are amazing!!!
Not only do you know a lot but you share your knowledge as well. You have been a big help.
Thanks,
DD

 

[bvanhiel]

Although it is not entirely clear, I see the bell pivot hole with the big boss as having the big diameter on the outside, so the side core can be extracted.

Pat,

Take a look at the 3D view in the top right corner, and you can see that the small hole is near the surface. Either you've got thick walls or a difficult core out.

-b

 

[patprimmer]

I see it as a thick wall and therefore a sink, warpage, cycle time problem, but the core can be extracted.

As everything else looks good from section thickness point of view, I do wonder why the section is so thick there.

There is no view that shows that boss from the inside, so we are guessing.

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.

 

[deper]

Dave,

Many of the posters make valid points but your part is very mold-able. It's just a matter of how much you want to spend on your mold. If you take the time to work with your reputable mold maker or mold designer before you are under the gun, they can recommend some minor improvements to save on your tooling.

 

[smokehouse]

I agree that this is very moldable and with multiple cavities as well.
The PL will be stepped of course with 2 side slides that would be below the PL(buried).

 

[mauriciob]

The part is mouldable, but there is a lot of drafting work to be done. To mold the internal radial boss, you will need to split the draft angle so that one half is molded by the core side and the other by the cavity. Another option is to create a u-shapde boss that ends in one of the ending surfaces and core it out from the core side

Work with your mould maker to define the parting line and do the drafting in your model to ensure design functionality.

Mauricio Benavides
Injecnet Solution Inc

http://www.injecneering.com

 

[mauriciob]

For some reason the picture to my post above does not show up. The picture is in the attachment below.

Mauricio Benavides
Injecnet Solution Inc
www.injecneering.com