How do they do that?

hey, there was a big article on just this thing in scale auto a couple of years ago. it went into the full depth of the model making prosess, from making molds , to showing how the injection machines work, and the final product. it was a very eye opening story, i dont remember the issue though, but i'm sure someone in here will. back issues are always on sale at scale the auto web site, so if someone gives you an idea what issue it was in try to get the back issue.hope this helps.

i did a bit of plastic moulding at college, a ashtray with the college logo, and sprue parts which resulted in a little kit!!! it was a rubics cube or something.
the molds were initialy curved in wood, still the process for limited run vacs, then through CNC to metal moulds (last more). The moulds have litlle holes where the liquid plastic is injected. Often the mould has heating elements too. Plastic can be in grain powder form to for faster and uniform melt. Apply pressure for some molds. in this case there was a plastic sheet put on the mold a bit like coin making. (vacforms are more or less the same thing only that plastic is sucked into place. .After a while cool and pop out using ejector pins the marks of which have ben seen by all...lol what strikes me is why they dont vaccum out the kit or just place the ejectors at selected location outside of the pieces. There is enough plastic wasted on sprues anyway....so dont buy the economy on plastic thing.

Not long ago I had the "fortune" to work at a facility that produced CD cases. All was done robotically with 2 piece injection molds. The mold closes, Poly was injected into the stainless steel molds and a second or two later the finished product was ejected via pins and a bit of air. Lots of Hydraulics and large heavy cumbersome equipment. The whole process was delicate and any bit of mis-synchronization could result in disaster. I know its not exactly supercool models and stuff but i couldnt picture the process being any different.

Injection molding is an automated process and, yes, the process is the same as making cd-casings and similar plastic parts.
Making/designing metal molds is a fairly expensive process.

If you want to make your own kits at home your route most likely will be Silicone molds and Resin cast parts.

Steps for doing so:
1.) Sculpt your master from appropriate material or scratchbuild if applicable.
2.) Make your 2-part mold from Silicone(2 day process)
3.) Cast your parts in Resin and clean them up after casting.
4.) Trouble shoot why your parts didn't come out ok
5.) Fix molds and repeat process from step 2 or 3.

If you are into pirated and recasting kits simply skip step 1.

QUOTE: [i] If you are into pirated and recasting kits simply skip step 1.

And, unless you are replacing parts for your own use, pay the fine and do the time as this is illegal and unethical.

QUOTE: Originally posted by bdelov Has anyone wondered how the injection molded kits are manifactured? I imagine that you have to have some fancy machinery. And what about the plastic? And what is a person to do if he wants to make a kit in his garage? Thanks, Borislav

I've read that cost of a single mold for one kit in in the neigborhood of $10,000. That does not include the rest of the injection molding machinery.

A few years ago FSM did an indepth article on the making of injection mould kits. I still may have it my collection.

A couple of years ago an article in Time (or Newsweek) caught my attention because it was about a company which did injection molding (they didn't do models though). The thing that has remained with me is that the company didn't use two piece molds, but molds that were made of 3 or more pieces. And those molds could run as much as 7 figures new.

QUOTE: Originally posted by qmiester The thing that has remained with me is that the company didn't use two piece molds, but molds that were made of 3 or more pieces. And those molds could run as much as 7 figures new.

Yup , 3+ piece molds are used for complex shapes or parts that have a heavy undercut.

Haven't see one of those for injection molding, but have seen 4 & 5 piece molds for Resin Kits.