Making bolts

[graemeian]

I want injection mold bolts using A glass filled PPS. To avoid a seam in the bolt, I want to inject the resin into a threaded die and unscrew the bolt when the resin cools. Will the resin shrink or relax enough to be able to unscrew the part from a threaded barrel die? Thank you.

[Suhas]

Hi Graemeian,,
You should be able to get it out of the mold, I do not see a problem - just make sure that the threads are polished. However, what is the length and dia of these screws and where are you planing to gate them?
Suhas

[tfrounfe]

I have overmolded plastic heads to bolts but I have not molded an entire bolt out of plastic before. Depending on the size and thickness of the bolt, I would worry about sink, and how you would get the bolts out if you break the head off without damaging the high polished threads. I made different tooling inserts for a MUD to fit various lengths of bolts and to make it easier for the operator to put in and take out the bolts. The downside to this is we did not have cooling in the inserts.

[brentb]

Might want to lay it down in the mold if cost and complexity are a concern!

Keep on Molding!
brent

[graemeian]

I want to make 10-32 screws. The length of the screw will be .6" long. I planned to use a three piece die. The sprue end at the bottom of the screw to be trimmed. The 0.6" threaded barrel. And the screw head at the top. After the resin is introduced into the die, the resin will cool and the screw head die component will back away from the barrel. A motorized "wrench" will swing into position and back out the screw. The process will be automated.

It may be easier to lay down the screw in the mold and make several screws per shot. I could still use a two piece die to hold the screw to trim the excess and then chase the threads if necessary. My concern with the sandwich method is the wear on the threads where the die goes together This material can be abrasive. Replacing a barrel would be easy. The barrel could be an insert in the mold. Making two molds and grinding them to get a round screw with matching threads would be difficult. Any thoughts?