I have been amused reading reviews of kits lately featuring the "new" slide mold technology. Foundries have been doing this with various types molds for at least 50 years.
I thought some of you might want a quick explanation of how it works. Well, sort of quick...



Okay, say you want to make a 50 cal machine gun tube you don't have to drill out. At the top of the picture is the "old" method, looking down on the mold. The plastic, light blue, fills the whole mold and you get a solid muzzle. With the new method, you put a slide in the side wall of the mold, the red in the bottom part of the picture, and draw it out after the plastic (or whatever) is injected into the mold. That way you get a round gun barrel with a nice round hole in it.

Here are two pictures of a cast iron box we inject resin coated sand into to make cores.
The first picture shows the slide in, the way it is when the sand is blown into the mold. The dark areas at the bottom of the photo will be filled with sand...
The second shows the slide out. You have to pull the slide out to get whatever you are making out of the mold. The slide moves in the direction of the arrow.





This is what we get:



A round hole and a post. For comparison, this is what our mold would look like compared the gun barrel mold in the first picture:



If our mold did not have a slide we would have to glue several cores together to do the same thing.

Relatively quick explanation, I guess.

Shaun

Very interesting stuff, molding technology. I'd absolutley love to see what the molds look like for a contemporary plastice injection molded kit. Thanks for the info Shaun.

There was a good article in FSM some years ago about how models are made. They had pictures of the tooling at the Testors plant IIRC. I will see if I can find it. Injection molding tooling is bigger than what we use here and much more expensive. Tooling for a job here may cost about $25,000. Tooling for a model runs about $150,000-200,000 from what I hear. It is machined from special alloy stainless steel..

Shaun

Shaun, thanks for that - very informative. The difference (to my eyes a least) is that DML (who are the only ones using it at the moment) are working on some pretty innovative stuff - the latest use is for MG barrels....Jim

Jim,

The principle is exactly the same. I am suprised someone hasn't dome this a while ago. However, the tolerances they hold at DML are obviously much tighter than we hold blowing sand into gas fired cast iron boxes.
The tooling I would like to get a look at, from a professional point of view, is for the Fruil track links with holes for the wire cast into them. As near as I can tell just looking at the final product they must use the same "slide mold" concept with a wire they pull out of the mold after the metal is poured.

But, I digress..

Shaun

hehe, Keenan, you the man!

In my line of work (I am in product development for electronics), I work extensively with plastic injection. I actually took one of the Armorama member to a plastic injection factory, and gave him a little tour, from Pro-E till Injection.

Next time I am near a tooling factoy, I will take some pics too, and show you guys, It's fun.

That picture you showed of that brown sand item, looks like what we used for cores to make hollow places in the iron when we poured it.

The regular mold was black sand, then they would place them brown real hard sand plugs in the molds before they went together to form hollow spots like you say, one of our parts were the opening to the bearing to the Ford spindle that used to go on the front wheels.

They had many others, but I just can't think of them, cause we had a whole department that made nothing but them brown plugs in all different sizes and shapes, depending on what they needed, then they would ship them to what ever line was using them.

The Beura line used them everyday, and they had 8 to 12 women that done nothing but put them plugs in the molds, to form something the mold itself couldn't.

Kerry

Kerry,

That is exactly what that is, a shell core. We have probably 600 different cores that we make for various castings. You can see some of the things we make at the link below.

Aren't foundries fun? :-) :-) :-)

Shaun

http://www.atlasfdry.com/products.htm

Like you say, I can't quite understand what's "revolutionary" about this method. Perhaps I'm being thick? Surely there must be many moulds/dies made that have several parts to them, particularly in the automotive industry? If you want to see a convoluted casting, look at a Norton twin cylinder head - it's all one piece with the (hollow) rocker boxes all cast in. It's sand cast of course, Triumph ones were die cast but were a lot simpler.
In fact, come to think of it, when I worked for Charles Stadden Studios, we had several rubber moulds with seperate parts inside them (eg to fit between horses legs). We also had a contract we did for Franklin Mint , where the castings radiated out from the sprue like the spokes of a wheel, the figures were all one piece except for a hand/weapon (reduces assembly costs!), so the mould had to be made in several interlocking pieces (it was silicon rubber, the castings were of course white metal).
Most casting requires that one part of the process, either the mould (with metal in silicon rubber or sand), or the mouldings (plastic pieces in metal dies) are resilient to some extent to allow the pieces to be extracted. I'm not quite sure how Dinky used to work, with Mazac into a metal die - presumably the mould split in more than one plane? Or were they casting in rubber?
The main problem with any complicated die is that as it ages, there will be more & more flash as the pieces work loose.

I think the "innovative" comes from nobody in the injection molded model companies has done this before. Thanks loads Shaun for explaining what the process is all about.

I thought that some manufactures use copper or brass in their molds. I remember Academy claiming this on some of their kits about 10 years ago.

Scott,

I don't know for sure. Never heard of the copper or brass. I know brass or copper would be much easier to machine to make the molds because it is so much softer but I think the tool life would be greatly reduced because they are softer. I don't know if tool wear is a big issue in injection molding though...

Shaun

Lord Blast not really. We in plastic does it all the times. I was scratching my head hard when I see DML claim it's as innovative.

Wait till they did something in overmolding, they will calim it's a revolutionizing idea in modling.

I am still a DML fan, just wanna set the record straight.

Stainless Steel for sure, copper or brass may not even be able to withstand the heated plastic, and not deformed.

Lord Keenan, next time if I have a metal question I will ask ya, and if you have anything to do with plastic, I am here all the times.