DIY Injection moulding or short run moulds/sprues

Colin

We are attempting to make 1/4 and 1/2 scale car bodies.

Looking at foam to carve and shape like they do for movie props.

First foams are Woodland Scenics sheet foam and then

3M Great Stuff sprayable expanding foam.

We would make a 'buck' first and then take molds off of it.

As backup I am going to look into clay over foam, it's kind

of messy though.

Model Maker

I was looking at foam as well for carving as the buck or master.

Also looking around and saw this stuff Mold Max 60, the site shows them pouring pewter into it, so I figured, heck if it can do pewter it should be good for plastic right?
https://www.smooth-on.com/tutorials/casting-pewter-mold-max-60/

Then yesterday in Canadian Tire I saw RTV gasket silicone, just happend to randomly walk down that isle and past silicone stating "High Temp" on it, it caught my eye. It's good to 600 deg, so well within the range of molten plastic in an injector and that tube just went right in the basket.

Tomorrow I've got the day to myself, so I'm going to make a box and put a random plastic and foam object in there and see if I can make a mould of it. If it works, it might just be a really cheap good way to make my own injection parts. Even if the mould is good for say 10-20 uses it's still a really cheap way to make some high temp moulds.
It might be a terrible idea, if so then I've got some gasket sealant for my 61' Alpine mk2 I'm restoring, if it does work then welcome to cheap high temp silicone moulds :)

My impression is that injection molding takes a pretty expensive setup.  In addition to the molding machine, the dies are usually metal, and a reverse of the part.

The high capital costs of injection molding is why so many small firms go for resin casting.  For the individual, or for a low capital startup, this seems to be the way to go.  You use RTV to encase your pattern and create a mold.  In addition to the standard urethane resins for casting the parts, the RTV molds will stand up to a limited number of casts of low temperature metals like those Micro Mark sells.  Micro Mark also sells a kit to get started in urethane plastic- the kit includes RTV for molds, the urethane casting resin, and some mixing supplies.  Such a kit is a good way to get started, and you can then buy the resins and rtv individually once you have caught on to the process.

http://hfmodeling.kitmaker.net/modules.php?op=modload&name=SquawkBox&file=index&req=viewtopic&topic_id=170700#1432685

Above is alink to a piece I did on using sprue and silicone. I've been doing this sort of stuff for twenty plus years and if you don't mind a little clean up time it works great and is very cheap.

As Don Says It will be expensive, if at all possible.

I question why you want or need to do injection moulding?

I work for a University & we did have the IM machines, but the dies are always metal to contain the pressure.

Nowadays all the rapid prototyping is CNC cut/lathed, or LASER cut, or 3D printed, but knowledge of 3D design is needed, as is access to printers, but there are companies like Shapeways if you don't have the printers etc.

If you can produce masters, then you can produce sillicon/RTV/Vulcanising rubber moulds and produce your parts in resin, plaster, etc.

Let us know how you get on...