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Vacuum Forming

One of the questions we get a lot is "how do you make your armor?". The process is called vacuum forming or thermoforming. Essentially, we heat up plastic to the point where it becomes soft, stretch it down over a mold, then use a high powered vacuum to pull it tight, capturing all of the details of the original.

For the impatient: Feel free to jump straight to the pictures.

Also, check out the new Mini vac-former!

The Plans

After months of research I decided to go with the Proto-Form table design and heating system. On Jan 9 2010 I ordered the 2 x 2 heating element and the plans for the table.

On Jan 13 2010 the plans arrived! I went to Kinko's for the printing... Around $40 for the assembly guide, double sided / bound with cardstock covers, the large prints, small prints, and misc other sheets. The first pull on the table was done on March 12 2010.

Major Components

There are a few major systems that make up the machine we use.

Vacuum

Many people use a shop vac for their home systems. This does work, but is not nearly as efficient as a more industrial type unit.

I found that there were three metrics I cared about when looking for the pump:

  • Inches of mercury
  • Air Flow / CFM
  • Tank Size

Mercury

Vacuum is measured in inches of mercury. I won't explain why here. If you are curious, ask Google. A shop vac does around 8" - 10", where an industrial pump can pull 29". Most recommendations I found suggested 20" - 25" to be ideal.

The downside is that a good vacuum pump can cost a lot of money. $500 - $1000 is about average to get them new, but you can often find used ones on sites like Craigslist.

Flow

The next metric that is important in selecting a pump is the CFM of the pump. If inches of mercury is the power, CFM is the speed, and more speed is good. When selecting a pump you want the highest flow you can afford.

Storage

Finally there is storage. Most pumps don't have a high enough CFM to be used directly. You need to evacuate one or more tanks first, then open a dump valve to allow the air to rush back in quickly.

The recommendations I found were for 15 - 18 gallons for a 2' x 2' platen, but as with everything here, more is better.

My System

I'm using a Gast 0083 rotary vane pump with 2 10 gallon tanks. At 10 CFM, It gets down to 26" Hg. in around a minute, which is faster than the plastic can heat.

For the plumbing, I went with black iron rather than hoses. No chance of collapsing or tearing that! Building the system was more complicated than with hose, but you really only do that once.

Platen

The platen is the forming surface. It is generally a very thin, well sealed box with one or more holes drilled into the top, and a single hole in the bottom that connects to the vacuum system.

This allows you to direct the stored vacuum to key places around your mold. Opinions vary on this, but I ended up using a plywood platen with 1/16" holes drilled every 1" across the top.

The insides of the plywood were sealed with shellac, as was the outside of the bottom layer. Sealing the side that contacts the hot plastic is a bad idea! Once the box was assembled I coated the outsides with silicone sealer.

Heater

The heating element can be one of the biggest challenges. While we all love do-it-yourself projects, we are effectively sticking the ends of a wire coil into a 220 volt, 30+ amp electrical circuit. Re-read that a few times before continuing.

Hardibacker is commonly used as a base, and nichrome wire is the norm for your actual element.

Ceramic based insulation board is better than Hardibacker, but hard to find and very expensive.

In comes Doug Walsh / http://www.build-stuff.com!

Doug sells fantastic plans for building all of this, and heating element kits. The modular panel design is flexible, easy to assemble, and includes that expensive, hard to find insulation board.

My 2' x 2' heater is connected to a 30A, 220V circuit, using an electric dryer receptacle and cord. The circuit is run to the breaker box using 1 grade higher wire than required, so that a 40A expansion could be done down the line if needed.


Plastic Carrier

Now you have the heat, the vacuum and the platen. You just need a controlled way to move the plastic from the heater to the platen.

There are two popular styles of thermoforming machine: "over/under and flip/flop".

Flip/flop has the heater and platen next to each other with a hinged carrier between them. You put the plastic over the heater then flip it to the platen. There's one BIG thing about this that I don't like. Your plastic will sag as it heats. If you overheat it, you can get hot plastic on your heating coils, ruining the system.

Over/under has a heater at the top of the system and the platen below it. The plastic is heated and then either the plastic lowered to the platen or the platen is raised to the plastic.

Protoform is an over/under, using a sturdy welded steel chassis. I had a friend do the welding for me. Let me tell you, the first time you pull down a sheet of plastic mounted to a hundred+ pound steel chassis, you know that it is Serious Business!

Table

Under all of that is a simple wooden table to support it all.

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