Plastic Molding DIY??

[Anarx]

Hey guys i think i might of allready figured out how to do this but i'm not sure.. i figure someone here might be able to know the awnser..

me and a friend are trying to do nylon plastic molding.. we have no real idea where to start.. we have been making a prototype out of wood to be used in the mold..

right now where thinking of using plaster to make the mold then pour it with the polymer i have no idea where to get the raw polymer to use for this or even if polymer is the right word for it..

vac forming is not going to work with this project.

any help would be greatly appresated.

Jess

[mc_n_g]

I do not think pouring into the mould will work unless it is flat. Even with that you will have problems with air bubbles.
Nylon is not nice to work with. For the most part nylon is hydrous (it holds water). When you heat it it gives off water as steam and causes bubbling. This can be minimized by preheating the nylon prior to moulding.
Depending upon what you are moulding you will probably need to perform this as a injection mould, not a pour mould. Pouring is more for resins and liquid metal. You can not make plastic flow that easy without it cooling too fast and skinning over.
You need to review your design and determine what you need to do and what material you need.
Thermoplastics will flow around 320-375 degrees. Thermoset polymers (resin type, 2+ materials poured together) are a one shot deal that hardens/sets with time.

mc_n_g

[Anarx]

thanks for the info.. how hard is it to do injection molding? is this something a DIY homebrew type operation can do?

i was told on a differnt forum that i might want to use a urathane to make the mold and pour a epoxy glass plastic for it..

i am a totally newbie to this stuff as you can probably tell...

*bout to say screw it and make it out of alluminium*

[ViperTX]

Home Shop Machinist had a series on a small injection mold machine that someone described how they built it. If budget is a concern and you're not going to mass produce and sell the items then this might be interesting.

If you intend to mass produce, sell and quality is of importance then I would investigate having a professional injection molding company make the molds (estimated cost is probably around $3K for something the size of a cell phone case) for one of the commonly used injection molding machines. Once you own the molds you can job shop the work overseas....you can also have the molds made off-shore.

You also need to know what material, shot size, etc.

[miljnor]

Once you own the molds you can job shop the work overseas....you can also have the molds made off-shore.

Och! A nife right thru the heart! ...... stager ...... stager...... fall......

I know the molds may be cheaper elsewhere but is the cost of injection molding driving it offshore as well. I always thought the the local injection molders were alright in the price range... The last thing I had quoted was about 10 cents a part for 100,000/3 month (which as I understand it is a small run for an injection molder). hard to compete with only a 10cent part. Isnt it?

[ViperTX]

What I've encountered in dealing with offshore vendors is that they will generally amortize the cost of the mold over a set number of parts over some period of time, so you can keep up-front costs low. They will also make you a mold for about 1/2 of what you would get stateside......

[TinkerDJ]

Check out lindsay books, theres a how to on an plastic injection molder setup, one of Vince Gingery's books. Dave Gingery's books are excellent even if your not going to build the lathe or machine shop stuff some of the detail and casting ideas are worth the purchase. You can easily cast low density and high density plastics, the easiest to get is plastic milk cartons. Its all in the book. Last i looked it was only $9.99us.

[darrell]

Some information on what you want to make would be helpful. It is possible that vacuum forming could be the answer to your question. (not with nylon of course, but many other plastics vacuum form well)

Vacuum forming is relatively easy and inexpensive to do compared to injection molding.

Darrell Hall
Deco Plastics, Inc.
Houston, Texas

[ynneb]

It would help to know what you wanted to cast and what its use would be. This way we can determin the most suitable material and also the best moulding method. There are DIY injection moulding plans availiable on the net, but these plungers are slow to use.
I guess it all comes down to how many of the parts you need per day.

I recently finished reading a book on plastic forming methods and was very surprized at how many methods and variable there was in casting items.

When you mention vacuum forming, this method usually referes to shaping a flat sheet of plastic. The finished item will be hollow and not solid. Casting nylons usually requires a mould that will cast the entire object instead of just one side like vacuum forming. To cast an item in nylon will produce a solid item.
Then there is rotational moulding where beads of plastic are put into the mould and the mould is rotated in all directions while been heated. The easter egg principle. This will produce fully skinned item that is hollow.

Dont ever think " bout to say screw it " It may take some research but in the end you will get what you want and at the price you want it.

[trubleshtr]

I run Nylon 66 at work, 500 +degrees Farnh. to keep things flowing, You could build a small hyd operated machine with heaters. but as Mc N G say's you will also have to dry the nylon and vent the gases/steam or you could potentially explode what you are trying to mold.
I have been wanting to build my own also, I would go hydraulic if it were me....
just my 2 cents.

[damae]

Can you post some pictures of the part you want to mold, or a sketch? I design injection molded parts all day long! I'd be happy to look at it for you and see if I can offer any advice.

But you also need to tell us how many parts you want to make, and what kind of application it is -- do you want it to be plastic because of the impact, electrical, strength, or appearance properties?

[damae]

....I have been wanting to build my own also, I would go hydraulic if it were me....

All the big commercial presses are hydraulic.... except for the very latest injection mold machines, which are totally electric, servo driven! And considering the expertise in the CNC community here, a servo driven injection molder would seem to actually be easier to do and more garage compatible -- no messy hydraulic fluid.

If you go the hydraulic route, www.surpluscenter.com seems to have a TON of hydraulic components (pumps, valves, tubing, actuators, etc.) for cheap. If you go the servo route, that same website has an unreal deal on 1kw servos right now -- $40. And they work with Rutex drives!

Surplus motors
http://www.surpluscenter.com/item.as...1&item=10-2210

For a DIY injection mold machine, you'd probably need three servos. One to drive the platten (via a simple 4-bar linkage), one to drive the injection screw to push the plastic shot, and the third motor to rotate the screw. No matter if you do hydraulic or electric, I would think that software would be a problem. I don't know if there's any equivalent to Mach2 for injection molds. Anyone else heard of such a thing?

Servo driven injeciton molds are truly top-dollar, expen$ive machines that when purchased, are usually touted on the top of a molder's line card, or when you talk to them. The reason is that the motion profile can be tuned VERY precicely. A vendor visited my office recently and said that if you place a piece of paper between the platens, the machine can detect the difference in displacement and back the platen off, or compensate for the clamping force! Hydraulic machines don't usually have such finesse and I've been told they usually only detect something's wrong if a part gets stuck or crushed in the mold (or an arm). Here's a writeup, that explains why servo driven presses are better for commercial use:

http://www.4spe.org/training/products/0192sampbk4.pdf

It's no big deal to run hydraulic lines and air compressors in a commercial molding shop. They switch to servos because it's better. But for us DIY'ers it seems that the servo route would be easier too!

Actually, I've been thinking a lot about what it would take to build an injection mold, DIY style. I know there are kits to convert your drill press (temporarily) into an injection mold:

http://cgi.ebay.com/BUILD-A-PLASTIC-...QQcmdZViewItem

But I have seen pictures of the results and haven't seen any that can do any real work yet. If I didn't already have so many projects, I'd attempt to build my own. Maybe someday. On the other hand, you could just go to ebay and buy something like this:

http://cgi.ebay.com/Injection-Molder...QQcmdZViewItem

or this if you are more serious:

http://cgi.ebay.com/TRUEBLOOD-50-Ton...QQcmdZViewItem