Extrusion of delrin

[kjoiner]

Hello,

We currently use some machined blocks of delrin to guide a door bar up and down some rods in a machine we produce. The blocks are currently machined and are quite expensive. Right now, we don't make high volumes of parts, but even then, we use outside vendors and pay accordingly. The blocks are around $14 each. The blocks have helicoils in them, but I am considering removing them and just using screws & nuts to retain the part. Now for the question:

This part is 1.50"L x 1.00"w and 1/4" thick. The part has four clearance holes for #6 screws near the corners, and a Ø.656 hole in the middle for the rod. Can delrin be extruded into bars which would allow us to simply cut the blocks to the 1/4" thickness using something as simple as a miter saw?

I plan to contact some vendors but thouht I would have some information ahead of time.

Thanks

Kyle

 

[patprimmer]

It can be done, but it won't be easy. Distortion and stress cracks after cooling and settling for a day or two will be an issue. It would be a lot easier to injection mould the finished parts. Threaded inserts can be moulded in to replace the helicois if necessary. Threaded inserts will be a LOT stronger than a thread cut into plastic.

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.

 

[Pud]

If your dimensions are correct (small part), why not use the money you will have to pay for an extrusion die towards the cost of an alloy tool and injection mould them?

At $14 each at the moment, you would soon get the money back. (Finished part out of the tool.)

You would also have a choice of many more materials...and it would look like a "proper" job! - get your company name and part no. engraved on the tool!


Cheers

Harry

 

[dgowans]

Your part is obviously a small part that would be a simple open-and-shut injection mold. In low volume you could use a service like Protomold to tool up quickly and still probably save money. You'd probably need to install threaded inserts yourself; I don't know if they offer that service. The downside of Protomold is that they won't guarantee they can hold any needed tolerances - they simply shoot parts, albeit quickly.

Where are you located? I've used a local shop (Cleveland, OH area) that does low-volume production and is pretty price-comparable with Protomold on tooling. I know they will install threaded inserts as I've got a product with them that requires inserts.

You can probably find a shop local to you that will do the same thing if geography is an issue.

 

[MikeHalloran]

It's a natural for a simple injection mold. Some guys do it in aluminum for surprisingly small tooling costs.

Inserts can be problematic in Delrin. It's cheaper, faster, and stronger to just mold the part with hex recesses for nuts.



Mike Halloran
Pembroke Pines, FL, USA

 

[kjoiner]

Hello,

Thanks for all of the feedback and suggestions. I agree with the use of injection molding as a better process to make the parts but thought I would explore an option that popped into my head yesterday. I figured there were some limitations to extrusions. Also I would lose material due to the saw kerf and that would add up over time. I have a molder that is just up the road from me and have had excellent results from his work. Either way, the threaded inserts- helicoil or other, will probably have to go due to cost. The other benefit of injection molding for these parts is that I will be able to keep the rounded edges on the center hole. Another item to mention is that I have a similar block on the other side of the bar that has obround holes to allow for tolerances in the machines. I'm thinking that a 2 cavity tool would be a good choice and could shoot both parts at once. Thanks again and I'll let you know how it turns out.

Kyle

 

[MikeHalloran]

So- called 'family' molds, with multiple similar cavities, rarely work as well as one might hope.

But talk to your molder. If the parts are similar, a single cavity with interchangeable inserts might be able to make both parts, one at a time.



Mike Halloran
Pembroke Pines, FL, USA