I want to have a plastic clip manufactured that will slip over a piece of glass. It needs to be “springy”, thin, and clear. I’m not sure where to start. Are there any Dopers who could help me figure out what kind of plastic is appropriate and what companies I can contact to make it?
I know just the guy. I’m out of town, but if you can wait until this weekend I can PM you with his contact info.
Thanks, the SDMB comes through again!
You need one clip, or ten thousand? Unless the widget can be made by easily machining it from some ingot of plastic stock, it’s probably not worth it; while widgets made from polymers are cheap in bulk, the tooling costs for injection molding can be prohibitive (in the low thousands of dollars even for a relatively simple mold).
Without knowing anything about your application, it sounds as if the best plastics would be in the polyethylene terephthalate, polymethyl methacrylate, or polycarbonate/acrylonitrile butadiene styrene families. However, the specifics are going to depend on your application.
Stranger
There are alternatives to injection molding, depending on the complexity of the part. For instance, most of the materials metioned by Stranger can be vacuum formed, which is a process simple enough for the amateur to do at home. It really depends on the shape you want.
I want to manufacture thousands of them. If it were made from metal the pieces could be “bent”. I’m not sure if plastic sheet can be heated and bent into the relatively tight radii needed for this application. Here is a pic.
You can make formed plastic parts from thermosetting stock via roll forming or (as Q.E.D. suggests) vacuum forming, but the shapes that can be made still have limited geometry. For the clip that you sketched, injection molding is probably the way to go. This means making an injection mold, which for a part like you indicate is probably a couple thousand dollars.
A few things to consider:[ul][li]You need to flesh out your sketch to an actual engineering drawing which includes specifications on the type of plastic and processing.[]You need to consider not just whether the part is manufacturable but how long it will survive in the intended application. This will govern thickness, material selection, inside radius and other geometry, et cetera.[]While you would expect a vendor to offer you advice on the best way to make your design manufacturable, my experience has been that many vendors will take whatever you give them and try to make it regardless of difficulty or insufficient design.[/ul]What I’m leading up to is that you would be well advised–if this is something that is intended in any way to be a reliable part–to get the expert services of an experienced plastics design engineer to offer advice on the correct material selection, form, and manufacturing details so that you get what you want, rather than just taking a rough sketch to a plastics house and having them build something that may or may not be usable, especially as it is going to cost you no small amount out of pocket for molds and tooling. You may also want to check around and see whether you can find something suitable that already exists or can be adapted for this application; this type of “s-hook” is very common, and if someone is already making something suitable or that can be adapted for whatever use you plan to put it too, it may be a lot cheaper than making the part uniquely. You might look through the Grainger or McMaster-Carr catalogs and see if you can find something to suit first.[/li]
Stranger
That shape would be childs play for an extrusion, the just slice to width.
Yep, I’d go with an extrusion for that. Extrusion dies are also considerably less expensive than those for IM.
I’m not a plastics engineer by any means, but I’ll note that looking at the drawing, it doesn’t strike me as being a “clip”, but rather more just a “drape” or something.
If you want it to actually clip on, you need for the junction of the horizontal segment and the shorter vertical arm to be less than 90 degrees, such that some point between the two vertical arms is less than the thickness of the glass, and that the shorter arm then bends out or has a very rounded head so that the glass can slide under and pull it out into a pinched hold.
Not an Engineer.
Estimated part weight 9.5 grams.
Material Polyethylene
Est. Part cost (not including mold cost)
1 cavity 1.05 ea
10 cavity 0.16 ea
32 cavity 0.09 ea
60 cavity 0.076 ea
bulk pack in cartons, color = natural ( none specifed ).
Sage Rat Yes, that is more what I was thinking. Nice picture.
Robz I get the feeling you’ve done this before.
beowulf I’d still appreciate your friends contact info.