...
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.
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.
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.
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
Prepare the Mold
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
Prepare Polycarbonate Sheet
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.
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
Preheat Oven
Preheat to around 300°F (150°C) (softening temperature for polycarbonate) but avoid exceeding 320°F (160°C) (polycarbonate can bubble or degrade)
Heat Polycarbonate
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.
Forming Process
Remove the Polycarbonate Sheet: Using heat-resistant gloves
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)
Apply Pressure: Gently press the sheet against the mold to shape it. Weights can be used to hold the polycarbonate against the mold
Use a Heat Gun (Optional): For areas that need further detailing or adjustments, apply a heat gun carefully to achieve precise form-fitting.
Cooling
Polycarbonate generally cools to safe handling temperatures in around 10 - 15 minutes
Finishing the Part/Inspection
Trim Excess Material: Once fully cooled, remove any excess polycarbonate around the edges
Polish Edges (Optional): Sand and polish the edges for a clean, finished look
Check for Surface Imperfections: Inspect for bubbles, warping, or surface marks that may have occurred during heating or forming