Overmold/Substrate Shutoff Area

[miuraj10]

Hey Guys,

Looking to gain an understanding on what is a better design for an overmold (TPE) shutoff area. Is it better to have the TPE butt right up against the substrate, or would it be easier to control with an intentional reveal line that is a 1mm x 1mm groove?

Below are the two options, both are just general ideas (ie no draft, radii, etc. Just a made up block so i can convey my idea)



Thanks!

[rickbatey]

It depends on the parting line and shape of the part. We have parts with over mold is finished at a radius at the end of the substrate. We fight the shut off for flashing and end up shimming or welding the tool. The stationary half has spring loaded cavity blocks due to part shape. Again NOT what you want.
Also how do you plan to over mold the substrate? That too is very important to your success!
Rick

[joeprocess]

We prefer Option 1 especially with the over-molds we do whereas the substrate is usually a textured housing. This raised rib provides a good shutoff and looks like a style line. So instead of crushing the texture to get a good seal which shows up as a shiny spot, the crush look like it's supposed to be there. As Rick mentions, it's not exciting to use the rib when wrapping down over a radius, unless it is straight up and down. You will have some funky transitions that would look pretty bad. If you are wrapping then it is a challenge. Attached is a picture of an overmold we helped develop. The original was bridge tooling with two separate molds(transfer molding) to get it to market quickly. Now it is two-shot. This part has ribs on some of the part, but the scalp areas on the back housing(by the buttons) needed to be as your option 2 shows. On the front housing where the label comes out we were able to build a rib because there was proper draft to allow for it. This was a fun one. Everything you see in black except the display and the buttons are all over mold material including the thin rib of material between the display and the Brady name and the flow channels on the back of the part feeding the logo

[miuraj10]

Thanks for the replies! And sorry for the delayed response i got roped into another project. Going to be posting a question on that in a second too haha!

Looks like we have buy in to go with option 1. My hope is that if the tool does flash, we can hide it down in the reveal which is much less of a concern for me cosmetically.