Thermoforming Research

Owned by Javier Sosa
Last updated: Dec 04, 2024
3 min read

An easier and faster method to making the windshield.

Guide to Thermoforming (Guide to Thermoforming )

Another Guide (https://www.weetect.com/thermoforming-polycarbonate/ )

Material (LEXAN 12 in. x 24 in. x 0.093 in. Clear UV Stable Polycarbonate Sheet GE-33 )

Custom PC Parts Company (Custom Plastic PC (Polycarbonate) Thermoforming service - China MDE plastics Company )

Thermoforming Processes

  1. Vacuum Forming: This thermoforming process makes use of a vacuum to shape the sheet. First, the plastic sheet is heated to ensure it is flexible. The vacuum forming machine then pulls the air out, forcing the sheet against a mold. The vacuum process is known for its cost-effectiveness and the speed of the manufacturing process.

  2. Pressure Forming: The pressure forming process similarly involves the heating of the plastic sheet and utilizing a vacuum to pull air away to force the sheet against a mold. But there’s an extra step. A pressing tool applies pressure once the air is removed to ensure the shaped plastic better maintains its final shape. Pressure forming is used when higher levels of details are required from the thermoforming process.

  3. Drape Forming: In drape forming, the heated plastic sheet is draped onto a mandrel designed with specific patterns. The mandrel’s pattern is pressed onto the plastic sheet to form the finished part. The drape forming process is one of the most-affordable thermoforming techniques because limited tooling is required. As the thickness of the material can be maintained, the process doesn’t result in weaknesses in the parts.

    1. https://www.youtube.com/watch?v=6xwp48M2v-8

    2. https://www.youtube.com/watch?v=K8UmJnaWO2s

 

Drape Forming Procedure

  • Materials Needed:

    • Polycarbonate Sheet: Choose a sheet with the desired thickness (refer to regs)

    • Mold: positive or negative mold (positive would most likely be best for the shape of the final canopy) made from aluminum or fiberglass is ideal for drape forming due to its durability and heat tolerance

    • Oven: Large enough to accommodate the polycarbonate sheet; it must have accurate temperature control up to at least 320°F (160°C).

    • Heat-Resistant Gloves: Necessary when handling the polycarbonate after removing from the oven and placing on the mold

 

  1. Prepare the Mold

    1. Clean the Mold: Make sure there is no dust, dirt, or debris on the mold that could mar the surface of the polycarbonate. Apply Mold Release Agent: Use a suitable mold release agent to prevent the polycarbonate from sticking. Make sure to apply it evenly

  2. Prepare Polycarbonate Sheet

    1. Trim the polycarbonate sheet to fit over the mold with some extra margin. The extra material will make it easier to handle and trim later.

    2. Secure the polycarbonate in a holding frame. The frame should be large enough to support the sheet’s edges without interfering with the forming process

  3. Preheat Oven

    1. Preheat to around 300°F (150°C) (softening temperature for polycarbonate) but avoid exceeding 320°F (160°C) (polycarbonate can bubble or degrade)

  4. Heat Polycarbonate

    1. Once oven is at a stable temperature, place the framed polycarbonate sheet in the oven. Heat the sheet for 5–10 minutes, depending on the thickness. Watch for the polycarbonate to sag slightly in the frame, indicating it has softened adequately for forming.

    2. A little trick is to put a small piece of the sheet on a block in the corner and wait to see sagging of the corners, then you know the sheet is ready to take out.

  5. Forming Process

    1. Remove the Polycarbonate Sheet: Using heat-resistant gloves

    2. Drape over the Mold: Quickly place the softened sheet over the mold, positioning it to align with any design features or critical areas on the mold surface. (need multiple people for this step)

    3. Apply Pressure: Gently press the sheet against the mold to shape it. Weights can be used to hold the polycarbonate against the mold

    4. Use a Heat Gun (Optional): For areas that need further detailing or adjustments, apply a heat gun carefully to achieve precise form-fitting.

  6. Cooling

    1. Polycarbonate generally cools to safe handling temperatures in around 10 - 15 minutes

  7. Finishing the Part/Inspection

    1. Trim Excess Material: Once fully cooled, remove any excess polycarbonate around the edges

    2. Polish Edges (Optional): Sand and polish the edges for a clean, finished look

    3. Check for Surface Imperfections: Inspect for bubbles, warping, or surface marks that may have occurred during heating or forming

 

Testing Process

  1. We will buy a 1x2ft sheet of polycarbonate (PC) from Home Depot and cut into test sheets.

  2. Create a positive mold through 3D printing

  3. Create a negative mold utilizing fiberglass and gelcoat

    1. We want to see if the gelcoat is smooth enough and can handle the heat emitted from the PC

    2. Also we want to see if using gelcoat or not is needed, we do not want smudges or scrateches on the final part

  4. Put the PC sheet in the oven preheated to 300 F for 10-15 minutes (until sagging)

  5. Take it out and drape it over the mold

  6. Second mold test will be using an overfit and underfit (positive and negative mold) then squishing the PC sheet

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