Designing Parts With Intentional Warp / Stress

[EricWallace]

Hello all!

I am attempting to design an injection-molded part (using Nylon 6, 15% glass infill) that will warp back on itself after being ejected from the mold, in a predictable and repeatable fashion.

I work for a company that makes holsters for concealed carry, and we utilize a variety of accessories so that people can configure how they carry based on their personal needs. One such attachment is known as the "c" or "j" clip, which attaches to the holster, curves over the belt, and wraps back onto itself below the belt. It's actually quite a common part, so I'm sure this is not that hard to accomplish, I just can't find anything online on how to achieve the effect. All I can find is guides on how to avoid warpage.

I'm thinking that a bit of extra thickness at the 180 degree turn might be all it takes, but I would really like some confirmation before we invest in a mold.

I will attach some images that illustrate how this product looks and functions below.

Forgive me if the answer is obvious! I'm new to this.

Thanks,

-Eric

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[mactec54]

Hello all!

I am attempting to design an injection-molded part (using Nylon 6, 15% glass infill) that will warp back on itself after being ejected from the mold, in a predictable and repeatable fashion.

I work for a company that makes holsters for concealed carry, and we utilize a variety of accessories so that people can configure how they carry based on their personal needs. One such attachment is known as the "c" or "j" clip, which attaches to the holster, curves over the belt, and wraps back onto itself below the belt. It's actually quite a common part, so I'm sure this is not that hard to accomplish, I just can't find anything online on how to achieve the effect. All I can find is guides on how to avoid warpage.

I'm thinking that a bit of extra thickness at the 180 degree turn might be all it takes, but I would really like some confirmation before we invest in a mold.

I will attach some images that illustrate how this product looks and functions below.

Forgive me if the answer is obvious! I'm new to this.

Thanks,

-Eric

You have to mold it just like it looks, the loop at the top tells you what's happening the thick section will shrink and close up the bottom part you want to move around, so as molded it will have a gap at the bottom separating the bottom clip part and when it cools that will close up, it may also be put in a fixture to cool to the correct shape, it is a poor molding by the shrinkage on the faces

[peteeng]

Hi Eric - Interesting problem. Many of the engineering software providers have software that will predict mould filling and warpage issues. I suggest you track down someone that can model your geometry and the moulding cycle. I use Altair FE and they have mold/part design and analysis SW. Peter

https://www.altair.com/inspire-mold

[EricWallace]

You have to mold it just like it looks, the loop at the top tells you what's happening the thick section will shrink and close up the bottom part you want to move around, so as molded it will have a gap at the bottom separating the bottom clip part and when it cools that will close up, it may also be put in a fixture to cool to the correct shape, it is a poor molding by the shrinkage on the faces

Ok, I hadn't thought of that fixturing idea. But it sounds like in your opinion that thickness towards the top is what contributes to the part closing up, confirming my initial suspicion.

Hi Eric - Interesting problem. Many of the engineering software providers have software that will predict mould filling and warpage issues. I suggest you track down someone that can model your geometry and the moulding cycle. I use Altair FE and they have mold/part design and analysis SW. Peter

https://www.altair.com/inspire-mold

Ok, good idea. I use Autodesk Fusion 360 which has some ability to simulate injection molding including warpage. I'll start there and then see if someone might be able to help confirm my results.

Thank you both for your replies! I was at a bit of a dead end.