In the wonderful world of desktop manufacturing there are more ways to work with plastic than just heating it up and extruding it; you can cut it, mill it, and one of my favorites: vacuum form it. While the others are certainly interesting to watch and exciting to set up, none can go from raw material to finished product as fast as a vacuum forming can. Once you’re taken your time on the setup stage, you can breeze through a dozen successful cycles in an hour. 

Before you get started you need to determine if vacuum forming is the method of manufacturing for you. There are more ways to utilize it than I could list out here, but some real world examples of vacuum forming include:

  • RC car bodies
    • Cheap, light, and thin enough to be flexible and avoid shattering in a crash.
  • Plastic packaging
    • Toy packages with a clear plastic bubble adhered to a cardboard backing, or with two halves that cradle the toy in a cardboard box. You can also find takeout containers that were vacuum formed as well, usually with a black plastic bottom and a clear top that presses together to keep your food sealed inside.
  • Food molds
    • Vacuum formed molds are used often in the food and chocolatier world for shapes too complex to make by hand. 
  • Hollywood Prop Making and Cosplay
    • All Storm Trooper costumes from the original Star Wars trilogy were vacuum formed, from the armor to the eye lenses. Cosplayers most often use vacuum forming for custom visors in complex shapes.

 alt="Food packaging commonly uses vacuum forming to rapidly produce storage solutions for a variety of food shapes and sizes." title="Food packaging commonly uses vacuum forming to rapidly produce storage solutions for a variety of food shapes and sizes."
Food packaging commonly uses vacuum forming to rapidly produce storage solutions for a variety of food shapes and sizes.

The big thing to consider when creating an object for vacuum forming is that objects cannot have overhangs whatsoever. With 3D printing, 45 degree overhangs are often the limit of unsupported structures, but with vacuum forming, any overhang will become a key that “locks” the original within the vacuum formed plastic shell. In fact, to aid in the release of the original buck, an ideally shaped buck would flare out 5 degrees. There are other considerations that can be thought of to help designs be more accurately replicated, but that’s for more advanced lessons, not the first.

 alt="The very slight 5 degree draft angle is enough to prevent the 3D print from being suctioned into the finished vacuum form, allowing for a clean and easy removal." title="The very slight 5 degree draft angle is enough to prevent the 3D print from being suctioned into the finished vacuum form, allowing for a clean and easy removal."
The very slight 5 degree draft angle is enough to prevent the 3D print from being suctioned into the finished vacuum form, allowing for a clean and easy removal.

Because it’s a simple idea to work with, my goal today is to create a custom ice tray using the Makyu Formbox. To really showcase the need to consider the limitations of the forming buck, I will create one from scratch and create one using a 3D model that already exists and modify it for the medium. In both cases, using a 3D print is the logical choice for me.

When selecting a material for your forming buck, you need to consider one that can handle the heat from the hot plastic sheet and the heater above it. You can use a 3D print as your forming buck, but you need to make sure it has the thermal properties to hold up. In my experience I have gotten lucky with plain PLA by using enough top layers to protect the top from collapsing into the infill. Using PRO Series Tough PLA or Proto Pasta HTPLA is a promising alternative due to their inherent thermal resistance, otherwise you can move up to PETG or ABS if you intend to use this buck heavily. If you aren’t using a 3D print, you can use something carved out of wood, a plaster casting, metal, or even a potato if you’re creative. Keep in mind that the hot plastic sheet will capture all the details of the original, from layer lines to wood grain, so if it is a concern, sand or coat your buck to make it as smooth as you need.

 alt="PRO Series Tough PLA finds a perfect use case as vacuum forming bucks; easy to print and can stand up to the heat." title="PRO Series Tough PLA finds a perfect use case as vacuum forming bucks; easy to print and can stand up to the heat."
PRO Series Tough PLA finds a perfect use case as vacuum forming bucks; easy to print and can stand up to the heat.

My model of choice to modify will be our mascot Phil; when laying face up, there are a number of features that would lock the 3D print into the vacuum formed plastic. Modification will be relatively simple as you could spend a lot of time getting it just right or you could start from scratch to ensure that it’s not a solution held together with duct tape. Simply enough, I just laid Phil back and started changing the support settings to fill in the gaps. I turned off any air gaps or Z distance, enabled perimeters, no X/Y distance, and set the resolution of the supports to be incredibly fine so it closely contours around the model and doesn’t seriously change Phil’s shape.

 alt="This array of Phils uses some unorthodox support settings to convert them into less-than-ideal but still usable forming bucks." title="This array of Phils uses some unorthodox support settings to convert them into less-than-ideal but still usable forming bucks."
This array of Phils uses some unorthodox support settings to convert them into less-than-ideal but still usable forming bucks.

To keep it simple, the ice cube design I have designed from scratch doesn’t have a lot of detail. The corners are rounded and a small draft of 3 degrees is used to help aid in the buck sliding out of the finished mold, a mold wall was modeled so the mold will sit on a table without rocking, and just for fun I threw a MatterHackers logo onto the top surface.

 alt="Custom ice cubes are a great way to add some spark to an upcoming party; it makes for some cool festivities!" title="Custom ice cubes are a great way to add some spark to an upcoming party; it makes for some cool festivities!"
Custom ice cubes are a great way to add some spark to an upcoming party; it makes for some cool festivities!

Both sets of bucks were printed using PRO Series Tough PLA which has some thermal resistance already, but I made sure to cover my bases by using 8 top layers just to be sure. To keep everything spaced nicely I used a couple Design Tools in MatterControl to add some runners between the pieces so water could flow between them as it's poured and so there is a slight lip to prevent water from running over the edge. With the 3D prints prepared, it’s time to get the Makyu Formbox setup and heat the clear PETG sheet.

Vacuum Forming Procedure

  1. Plug in Makyu Formbox
  2. Plug vacuum cleaner (shop vacuum or household) into the outlet in the back of the Formbox, and the hose into the back port, using the adapter if necessary.
    1. Make sure you have the vacuum set to “on” so the Makyu can control its use.
  3. Follow the temperature directions listed on the packaging for the clear sheet (5 on the heating dial).
  4. Set the timer to the recommended time listed on the packaging (1 minute and 20 seconds.)
  5. Wait until the red light indicating the heater is not up to temperature has turned green.
  6. Remove the protective film from both sides of the plastic sheet
  7. Unclamp the plastic holder and slide the top half up toward the heater until it locks
  8. Lay the sheet down on the bottom half of the holder before bringing the top half back down and clamping it in place
    1. The lock on the holder is strong, so don’t be surprised at the force it takes to disengage it.
  9. With the sheet firmly held in place, raise the entire holder assembly up to the heat and start the timer
    1. You should hear a loud ticking from the Formbox accompanied with the indicator light flashing.
  10. Place the buck in the center of the mesh.
  11. Keep an eye on the plastic sheet. It should get wavy before it forms a big dome that will start to droop
    1. The timer should be a reliable measure, but a good rule of thumb to follow is to let the plastic droop half the height of your buck. These bucks are 1.5 inches tall so it only needs to droop ¾ of an inch.
  12. When the plastic droops enough or when the timer picks up the pace and then stops, drop the holder down onto the buck.
    1. The vacuum will engage and pull the air out from under the plastic, allowing it to fully cover the entire buck.
  13. Wait roughly 1 minute for the plastic to cool enough that you don’t distort it when removing the new form.
  14. Reverse the process of clamping the plastic sheet to remove the finished form.
  15. If you are finished vacuum forming, set the heater dial to 0 and let it cool down.
  16. To remove the 3D prints, a little flexing can be used. The hexagon shapes should pop out easily, but the Phils will present more trouble with their flat walls.
  17. Once the bucks are removed, you are free to trim excess plastic off the form and use the ice trays right away.
 alt="Watch as the hot PETG begins to droop before its ready to conform to the molding buck." title="Watch as the hot PETG begins to droop before its ready to conform to the molding buck."
Watch as the hot PETG begins to droop before its ready to conform to the molding buck.

Pour some water into the molds, let it freeze, and admire your work. If you modified an existing model you I’ll likely have discovered some parts of it that seemed taken care of in theory but in actuality may have gotten locked in the mold. Creating forming bucks that work perfectly every time takes experience, so the more you use vacuum forming the better you will understand what shapes work and which ones don’t. Hopefully you now have a better understanding of how vacuum forming works and are ready to begin experimenting with your own designs and add another tool to your arsenal. To learn more and order your own Makyu Formbox today, check out the collection here.

 alt="Ice cubes in the shape of our favorite astronaut." title="Ice cubes in the shape of our favorite astronaut."
Ice cubes in the shape of our favorite astronaut.