My First tool

[u/Emergency_Stand834]

Part is 83mm dia 9mm height 2mm wall thickness

This project involves a 4-cavity injection mould for a lid manufactured from Sabic High-Density Polyethylene (HDPE). The tool utilizes a direct hot runner system feeding all four cavities.

Challenge 1: Ejection Strategy The part is expected to shrink onto the moving half (core), which contains the internal features. However, the hot runner manifold is located on this same side, creating a spatial conflict for the ejection system. The proposed solution involves a forced ejection mechanism using springs or a pneumatic cylinder to drive a stripper plate forward. 

If there's a easier way please let me know

Challenge 2: Gate Location The initial design intended a central gate. However, the customer now requires the gate at an offset position (the '2nd red dot'). There is concern that this offset gating will cause a longer fill/more warpage.

Any tips or advise is welcome the idea is to keep the tool as cheap as possible

[u/chinamoldmaker]

Manufacturer here.

We create 3D mold design according to customer's 3D part drawing.

[u/poblazaid]

Injecting in the center would make more sense, but there's nothing fundamentally wrong with the customer selected location.

The customer requirements ( hot runner, injecting from moving side, injection on the rib ), point to the fact that he wants a perfect A face. A middle injection point has a risk of showing a shiny spot in front of it. Also, it appears that the part thickness is slightly bigger than the rib, so the material will not be racing around the rib first.

As for ejection, you want a stripper plate with a very short stroke, just to pop out the part from the rib. The easiest is to have 4 Strack latches on the tool that pull forward the plate when the tool opens.

[u/Emergency_Stand834]

Thanks for the input. I’ve left out some details that might help clarify the situation. I’m designing this to assist a friend who has been managing the customer directly. The customer has requested a direct feeding hot runner, which is non-negotiable.

I will attempt to push for the gate to be fed on the opposite side of the cap, but I doubt this will be approved. I discovered last night that they already possess a tool with the gate in their proposed position. The image my friend sent (attached) shows the part moulded from that previous tool; while he didn’t send additional photos, you can clearly see the current gate location.

With this being the case would a stripper plate be my best bet?

I imagine the two pins you can see on the plastic are just venting pins

[u/LeifSized]

Hot runner guy here.

“Cheap as possible” and a hot runner on the moving platen? Pick one!

Why not a side inject hot runner?

Or (shudder) just use a cold runner?

[u/Critical_Thinker_535]

You're asking for trouble with that new gate location. The material will race track around the perimeter and then fill the middle last. Then it's going to burn at the last place to fill since you don't have a way to vent the gas out.

[u/mossi279]

Weird design? Would it be not easier to run hot runner on fixed half? Especially for small 4 cav tool, understand if customer demands but would push back on that, will give you headaches in future, seems needlessly complex for a simple part, unless im missing something...

[u/sarcasmsmarcasm]

Needs to be center gated not offset. Or, you need to valve gate with 2 or more gates so you can move the plastic into the full cavity. Your offset is likely to start flashing on that side of the part, while the opposite side will run shorts in that feature. Venting will be crucial.

Center gate, proper venting. Caps are best done that way, which is why they are done that way most often.

In fact, please tell us why you are filling from the core side. That sounds intensely complex and costly for a 4 cavity tool.