High Volume Part: Molded Plastic, Die Cast or Screw Machine??

[dapeake]

Greetings,

Below is an image of a part I am designing for manufacture.

My question for the group is, among Die cast, Injection Molding, and Screw machine, which method will yield the lowest part cost for this particular part?

Considerations:
---------------

(i) lot size: 5k to 50k

(i) The image shows a 5/16-18 threaded section which will be subject to over 100 lbs of force in both directions. (The length of the threaded area is .377)

(ii) our plan begins to fall apart as the piece price exceeds $.30 USD

(iv) there are no tight tolerances.

Thanks for your input!

Peace,

Dan

 

[tripleZ]

Plastic material? If I'm reading the drawing correctly, that little thin walled tapered area looks like a hoot. No issues with part off lines? I'll take a shot and and say injection molding followed by a secondary tapping operation. Plain vanilla machining will likely require a twin spindle setup with automation if you're going from a blank. And die casting is still going to require secondary operations.

5K-50K per year in my industry (metal injection molding and powdered metal compaction) is beans...not a lot of volume to offset the high cost of a mold and the fixturing required for machining.

I'll be interested to see the replies.

 

[MikeHalloran]

The screw machine bar stock will exceed your target cost, and if you really need to trepan that annulus, you'll go crazy getting the chips out of it.


Injection molding can probably meet your target price in glass filled nylon or something similar, if a molded plastic thread will meet your durability requirements, in which case you need some kind of hex or spline like feature to hold the part while the core that makes the thread spins out.. or remains stationary while the spline spins the part. See toothpaste tube caps and such for examples.

If you need a metal insert for thread durability, you can mold it in, or post-insert with ultrasonics or heat, but the insert and the increased time to install it may push the part over your budget.


I don't know much about die-casting.



Try putting it out for bid on mfg.com and see what you get.



Mike Halloran
Pembroke Pines, FL, USA

 

[dapeake]

Thanks for the comments!

My original image above shows a molded/cast part with attendant draft and annular shelling to reduce cycle time and to reduce sinking.

But for actual part function - we need the simple geometry shown below, which is more suitable for screw machine ops.

Volume clarification: 5k to 50k per order, with an order frequency of 5X per year.

Addressing the above comment about thin walls in the screw cylinder: Agreed. But unseen in the part shown in my original post above are internal radial braces to support the cylinder in a casting or PIM (Plastic Injection Molding) scenario.

Threads: I believe a low cost, off-the-shelf, molded in insert would be the best solution in a PIM part. However, I know of no sources or standard form factors for inserts. If you are aware of such, a referral would be greatly appreciated. Any pull strength data for tapped standard threads in the various plastic resins would also be very helpful.

If anyone out there has an educated guess as to the part costs for the following, I would be very curious to hear your guesses for US and offshore production.

15k runs
--------
PIM, 4 cavity, glass filled resin, 2nd op tap
PIM, 4 cavity, ABS, Threaded Insert molded in
Die Cast, four cavity, 2nd-op tap
Screw machine

Thanks,

Dan

 

[MikeHalloran]

I hate those internal radial braces.
Managers add them, and then blame me or the molder for the resulting polygonal parts. Shallow ribs are sufficient.





Mike Halloran
Pembroke Pines, FL, USA

 

[mcgyvr]

For molded in/ultrasonic/press in inserts for plastics look at PEM's SI catalog.

http://www.pemnet.com/fastening_products/si-inserts-for-plastic.html

They have pullout values listed in the catalog.

 

[dapeake]

Thanks for the link. Great info in Penn's pdf brochure!

Dan