Vacuum Thermoformer
Retrieved from Get Up! And DIY (http://gdiy.com)

This project is an example of a Vacuum Thermoform Machine.  This machine takes a plastic sheet (specifically: High Impact Polystyrene), heats it, and then applies a vacuum over a positive mold to replicate parts.

Vacuum Thermoforming as a means of forming plastic has many applications for industrial and commercial products that we use every day.  For example, it is used for creating things like hot-tubs, food trays and product packaging.  It is pretty likely that you have had some interaction with a vacuum thermoform product at some point today.
 

Examples of Thermoform products

  

The project costs under $200, and is moderately difficult and time consuming.

 

Properly heating the plastic takes practice (which I have not yet mastered, I will provide better instruction in the near future). The hardest part of this project was designing/constructing the oven.

Notes: 

  • I have attempted to remain consistent when naming parts throughout this document.  All part names are underlined to help.
  • Sometimes I have deviated from the CAD design (or otherwise).  Design deviations are explicitly called out in this report.
  • YOU are responsible to ensure that your electrical circuit can handle the power loads required by this oven.  Using properly rated generator is suggested.  We are not liable for any damage you cause.

 

Bill of Materials:
[ edit this section ]

Material

Quantity

Source

Screws

 

Home Depot

Washers

 

Home Depot

MDF

 

Home Depot

Hardibacker 500 (3’ x 4’ sheet) [G1] 

1

Home Depot

Ceramic Insulators

 

 

Fire-blocking Caulk (tube)

1

Home Depot

Liquid Nails™ Adhesive Caulk (tube)

1

Home Depot

Vacuum adapter

1

Home Depot

Nichrome Wire

 

 

Box Steel tube

 

Home Depot

L-channel steel

 

Home Depot

Eye bolts

4

Home Depot

Wing nuts

4

Home Depot

Fender washers

4

Home Depot

Hot glue

 

 

Wire

 

Home Depot[G2] 

End plug

 

 

Vacuum

 

 

Silicone Caulk (tube)

1

Home Depot

0.030” HIPS (24” x 24”)

10 or more

Indplastic.com

JB Weld

 

 

Paint

 

 

Sand

 

 


 [G1]Check this

 [G2]Specify gauge

 

The frame/clamp is basically welded steel tube, with dimensions given in the following drawings[G1] .  Tabs were welded onto the tube, and bolts are attached to use as a clamping mechanism. 

 

JB weld was applied to the frame, and sprinkled with fine sand before curing, to improve gripping the plastic.   I then painted the frame with heat-resistant paint to prevent corrosion.  The hinge was created by drilling a bolt-hole at the hinge-point[G2] .


 [G1]Insert drawings

 [G2]Insert pictures of frame

 

Vacuum Platen
[ edit this section ]

 

 

The vacuum platen consists of 3 parts:

  • Platen Table
  • Platen support
  • Platen top

 

Platen Table:

Simple, just a 2 x 3 foot [G1] sheet of MDF. 

Platen Support:

Cut a sheet of 1/2” x 22” x 22” MDF.  Then cut a large hole into it, so only about 1” of framing remains.  Also, cut a hole in the Platen Table to accept the Vacuum Adapter.  Use the Liquid Nails™ to mount the platen support onto the platen table. Clamp, and allow to cure:

 

 

Platen Top:

The platen top is a ¾” x 22” x 22” melamine-coated MDF sheet.  Drill a grid of 200 holes into the platen top.  After the platen support has cured onto the platen table, mount the platen top to the platen support, using silicone caulk and clamping like above. 

 

Design deviation:  I also inserted a couple of spacers to help support the middle of the platen top.  The spacers are 1” strips of ½” MDF, about 10” long or so.  I mounted these just to the platen table (not the platen top).

 

 


 [G1]check

 

The oven was the most difficult part of the project, but hopefully the cutting angles and information I provide will alleviate all of the problems I had.

 

 

 

Parts:

Hardibacker 500

Nichrome Wire

Ceramic posts

Washers[G1] 

Screws

Some [G2] gauge wire

 

Oven Shell

To create the oven shell, cut out the walls and floor according to the following drawings[G3] :

 

Note that the walls draft inward, this is to help distribute heat to the edges.  If the walls are straight up (I did this before), the edges aren’t heated as well.

Wiring

To ensure that the edges are heated evenly, use a spiral pattern while wiring. Make sure lots of the wiring is around the edges, because the center heats easily.  Here are the approximate dimensions of my oven’s wiring[G4] :

 

Drill holes


 [G1]what kind?

 [G2]

 [G3]Get dimensions from oven, replicate here.

 [G4]Insert picture

 

 

Here are some examples of the results when we tried out the vacuum thermoform machine.  You can see the finished machine in the two pictures below.  The frame is holding a 2 foot by 2 foot sheet of Vivak PETG plastic.  This is a food-grade plastic common for making food molds for chocolates.  It is probably available from your local plastics distributor.  In the picture on the left the frame is holding the plastic sheet over the heating coils.  By lifting the lid off a little bit you can check to see if the plastic is ready to flip onto the object you are molding.  As it heats it will start bowing down closer to the coils.  After the whole sheet is visibly melted it's time to flip it onto the object.  We found that the heating coils were too hot for the specific plastic we were using so we just disconnected one of the segments in the middle to compensate.  They still created more than enough heat for the job.

In the middle image the frame holding the hot plastic is flipped onto the object to be molded.  In this case the object is a Venus de Milo statue.  The image was taken just before the vacuum pulled the plastic over the shape of the statue. 

In the image on the right you can see the statue with the plastic pulled over it.  Since there were a lot of contours on the statue the plastic was pulled under and this made it really difficult to remove.  If I did this again I would put some styrofoam or cloth around the base to bisect the statue so there were no undercuts...or maybe just choose an object that was easier to mold with this process.

 

 One of the better results of the thermoform machine was the bike seat cover as seen in the images below.  The purpose of this was to have a seat cover for the bike in the case that it rains.  Assuming the rain has stopped and you want to bike home or somewhere you put on the seat cover and then you don't end up all wet from sitting on a squishy seat.  As you can see we have stacked up some cloth below the bike seat.  That is there so we can make sure we get a little bit of an undercut in this case.  When we cut the plastic shape out this will prevent us from ending up with a sharp edge.

After the plastic is hard and cooled (this takes only a few seconds) you can go over any edges you don't like with a small propane torch like in the images below.  Just keep the vacuum pump going.  Anywhere you apply heat will be sucked against the contours of the object being molded.  Make sure you apply heat to a large area or you'll end up with a hole where the vacuum has pulled too hard on teh soft plastic.  You can see where this happened on the far-right image.  A hole developed so I had to patch the vacuum leak with my finger while we kept applying heat to the rest of it.

 

The process takes some getting used to.  After some trial and error you can pretty easily get the hang of it.  It definitely helps to have a second person around on certain parts but it's not absolutely necessary.  The easiest thing to mold would be something that is flat on one side and doesn't have any odd or protruding shapes to get stuck in the hard plastic that results.  I guess I'll have to try finding something like that next.

 

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