How are models made?

[Integra14]

Im just curious, how they are made

How do they make molds for them? by hand?

then liquid plastic is poured into the mold????

i just don't understand, will someone explain?

[fullbloodchop01]

im guessin they make designs on a P/C and they have a machine which can make molda of he design from the P/C. then i guess they do inject the molds with liquid plastic...

thats just what i think

[Jay!]

The molds are either carved by hand, cast from a master part, or cut by computer...

injection molding

edit: even more info: http://islnotes.cps.msu.edu/trp/

[tdoty]

For the plastic model industry, the molds are not cast from a master, CNC machined or cut by hand.

A combination of processes are used. The master is generally carved by hand and the pantographed into steel. This process allows the mold to be an exact reverse of the master. These masters are usually 1/10 scale models.

The details and texture are then added by hand - with air powered engraving tools and acid etching. Polishing is done by hand and machine. Some finishing and detailing is performed with Electric Discharge Machining.

CNC machining apparently doesn't transfer well to model molds - the results have been disappointing from what I've heard.

No, I don't work in the model car industry. I work in the 1:1 automotive plastic industry. The mold making process is similar - but ours are bigger! Some of our molds weigh in at over 20 tons! What do I do? My job is to repair the injection molding machines (among other equipment) and make sure they are capable of making quality parts. I also work on the molds themselves, from time to time.

HTH,

Tim D.
http://modelcartech.com

[CamaroSSBoy346]

i always thought they started with a brick of sold plastic, made a mold of a top and bottom or side and side, put the brick of plastic in the mold, melted the plasted and pushed the 2 molds together. (i though that because of the flash on certain areas. )

[tdoty]

And I forgot to answer one of your other questions.......

The molding process itself. The plastic starts out as beads or pellets of "virgin" plastic. It is mixed with color additive, if needed. The plastic is fed into the barrel of the molding press and heated (up to 500 degrees, depending on material and process variables). The mold is clamped in the machine under a lot of pressure (model machines are in the 125-500 ton range - toys compared to our 4000ton Cincinatti. That's not weight, that's clamping force!). The plastic is the forced, under pressure, into the mold cavity. The plastic fills the mold cavity to a preset limit, then stops and retracts the screw inside the barrel to prepare for the next shot.

While the screw is retracting, the part is curing in the mold. The mold opens after a preset cure time, and the part is ejected from the mold and it all starts again.

Time taken? Under 60 seconds, start to finish.

The same process is used to make 1:1 car parts.

Do you own a Chrysler minivan? Jeep Cherokee? 2000+ Chevy Extended cab pickup? Jeep Grand Cherokee? Mitsubishi Galant? Mitsubishi Eclipse? Mitsubishi.....what's the name of the new SUV? Endeavor? If you own one of these vehicles, in the US especially, it probably contains parts made in machines I work on routinely.

HTH,

Tim D.
http://modelcartech.com

[tdoty]

Ahh, yes, the glory of flash.

The flash is there because the parts of the mold weren't sealed properly. If the mold is worn, and the moving parts don't fit together tightly - or the 2 halves - plastic will leak into these gaps. If too much injection pressure is applied, the plastic will find it's way out of the cavity. If too large a volume of plastic is injected - same thing. If the plastic is too hot, sometimes it will happen then too - but usually it just warps!

These posts have just been a basic overview of injection molding - it's a bit more complicated than the explanation, but it ain't rocket science.

HTH some more,

Tim D.

[008]

Originally posted by CamaroSSBoy346
i always thought they started with a brick of sold plastic, made a mold of a top and bottom or side and side, put the brick of plastic in the mold, melted the plasted and pushed the 2 molds together. (i though that because of the flash on certain areas. )

The flash is from when the molds wear out and plastic starts to seep in between the mold parts during the injection process. It also happens with molds that are bad quality to begin with. Some companies that do low-volume production runs outsource their molds from other countries where labor is cheaper.

Warped bodies and parts trees are usually caused by the ejector pins coming out before the plastic has had a chance to cool off. Operator error, or just trying to save time? I don't know.

Scale Auto's website used to have a "how models are made" feature in their archives but it's long gone.

[rhmatt]

tdoty- you know your stuff!!! I worked for Aladin plastics for a few months back in my youth. Mostly making plastic cups, containers and jukebox fronts. I recall color changes being a pain, as the last few pellits took forever to purge from the machines!

Then I moved up to aluminum die-casting. I ran a 1200ton (clamp force) FMC machine, not sure about the weight of the mold itself, but the parts were 37lbs with the runner and biscuit attached as they were when I pulled them out of the mold by hand. Parts (timing gear covers) were for the Cummins deisel B-series engine, the ones Dodge made famous in the late 80' and early 90's.

The injection system was plunger/sleeve type, if I recall the injection force was around 2100lbs for a good "fill" rate! Fascinating work, was in it for about 4 years and NEVER EVER want to do it again! I've never looked at ejector pin marks the same way and flash takes on a whole new meaning when it's coming in the form of a "spitting" mold that is shooting out 1200 degree molten aluminum!

Ahh the good old days, it's good talking about them!

-Rick

[chipanggo]

interesting.

[Jay!]

My answer:


Tim's explanation:


Thanks, Tim!!

[rsbousquet]

aww look he's jealous man i just learned more than i needed to tonight. well good to know. thanks for the info tdoty and others!

[flyonthewall]

Originally posted by tdoty
... compared to our 4000ton Cincinatti. That's not weight, that's clamping force!)...

Don't want to get your fingers trapped in there!:22yikes: Ouch!...Squish

[daggerlee]

As part of my material science course I saw a video that went into injection molding, Tim has explained everything shown in the video and even more.

[simdel1]

fascinating stuff....the age thing explains why my tamiya lotus 7 kit (probably a re-release) has quite a few flash lines and other irregularities that will need to be sanded off.