16 - Wildcard

This week we will take advantage of our 'Wildcard Week' to work with the thermoformer and create a mold based on the head of the animatronic we want to build.

BASIC CONCEPTS

The thermoforming machine is a device used in the industry to shape plastic sheets through the thermoforming process. This process involves heating the sheet until it becomes malleable, then adapting it to the shape of a mold. Once cooled, the plastic permanently retains the shape of the mold used.
The most commonly used materials for thermoforming are:

Material	Properties	Common Applications
PET (Polyethylene Terephthalate)	Transparent, strong, recyclable	Food and beverage packaging
PVC (Polyvinyl Chloride)	Chemical and mechanical resistance	Blister packs, cards, medical uses
PS (Polystyrene)	Rigid, low cost	Trays, disposable cups, packaging
HIPS (High Impact Polystyrene)	Impact-resistant, easy to form	Signage, toys, electronics
ABS (Acrylonitrile Butadiene Styrene)	High impact resistance, thermal stability	Automotive parts, appliance housings
PP (Polypropylene)	Flexible, heat and chemical resistant	Reusable containers, medical products
PETG (Polyethylene Terephthalate Glycol)	Easy to form, transparent, food-safe	Food packaging, displays
PLA (Polylactic Acid)	Biodegradable, renewable source	Eco-friendly packaging, disposables

"The above table was generated by 'Copilot' using the following prompt: 'Most commonly used materials in thermoforming'."

PREPARING THE MOLD

Before carrying out the thermoforming process, it is essential to have a mold that will serve as a base for the copy. In our case, we decided to use the 3D model of the animatronic face that we scanned during the " Week 5 - 3D Scanning and printing ". Later, in Blender software, we added a matrix of holes distributed across the entire surface of the face. This modification aims to ensure that, when applying suction from the thermoformer, all the details of the mold are captured more precisely. Each hole has a diameter of 1.5 mm and is spaced 10 mm apart.

Below is an image of the mold with all the holes; this face was printed in PLA.

The following link shows the PLA datasheet.

PLA.

Although PLA is a material sensitive to high temperatures, the datasheets indicate that the temperature it will be exposed to during the thermoforming process falls within its safe operating range. Therefore, there is no risk of the mold deforming during the process.

MY FIRST STEPS WITH THE THERMOFORMER

Before getting started, it is essential to understand the material that will be used for thermoforming. In our case, we will use styrene sheets. You can find more information about this material at the following link.

stylene sheet

PARTS OF THE THERMOFORMER

The first step is to connect the air supply for the vacuum valve and the piston operation.

The next step would be to stretch the sheet inside the frame; for that, it is important to know the parts of the frame.

The frame is lifted and the sheet is placed, trying to make it as tight as possible. Once it is tight, the frame is lowered and the locks are secured.

It is important that the sheet to be placed has larger dimensions than the thermoformer's frame (75 x 56.5 cm).

Once everything is in place, the machine can be turned on and the temperatures can be set.

Due to the high temperatures, it is necessary to wear a lab coat, boots, and leather gloves.

The following image shows all the parts that make up the thermoformer.

Vacuum pump timer. It is important to have the pump turned on in order to perform the suction
Machine power switch. Rotary knob that turns on the equipment.
Temperature control. There are two zones; the temperature of each zone is controlled using the buttons.
Vacuum valve. When the sheet is lowered and covers the piece to be formed, it is important to activate the vacuum valve so the suction can occur.
Piston actuator. Responsible for raising or lowering the frame where the sheet is placed.

Once the machine is turned on, it is important to check the temperature of the heating elements using an infrared thermometer to ensure they are within the proper operating range.

Once the appropriate temperature has been reached, the heating elements must be slid along the rails using the handle. Next, the piston is activated to raise the frame, allowing the heating elements to directly heat the plastic sheet.

During the heating of the sheet by the heating elements, it is crucial to constantly monitor the temperature. To achieve optimal thermoforming, it must remain within the range specified in the material's datasheet.

Once the sheet reaches the ideal temperature, it begins to sag, which indicates that it is ready for thermoforming. At that moment, the piston should be activated to lower the frame and position the sheet over the mold. It is essential to activate the vacuum valve just as the sheet covers the mold, as the suction will allow for a more precise replication of all the model’s details.

RESULTS

As can be seen in the images, the holes distributed across the mask allowed the thermoforming to faithfully reproduce the details of the mold. However, these same holes also appeared in the resulting surface. This presents an important trade-off: the better distributed and more numerous the holes are, the greater the fidelity of the replica; however, if the hole diameter is too large, they will also be visibly reflected on the molded surface.

Taking advantage of the new mold, it was decided to make the skin of our animatronic using 'Dragon Skin'. The results are shown below.

Learning outcome

During this week we learned to use the thermoformer, an extremely useful tool for mass-producing parts from a mold. This process not only allows for precise shape replication, but is also very practical for creating molds that can be used in other manufacturing methods.