Thermoforming Process

Vacuum forming has established itself as a recognized plastic processing method alongside injection molding. There are two types of thermoforming: positive thermoforming and negative thermoforming.

• Positive thermoforming:
  In the positive process, the plastic sheet is placed over the tool and drawn onto it by vacuum. The outside surface is not touched, preserving the surface quality for visible parts. The inside is the tool-contact side, ensuring precise contours. Later changes in material thickness build outward and do not affect inner dimensional accuracy or assembly.
• Negative thermoforming:
  In the negative process, the heated plastic sheet is drawn into the tool by vacuum. Here, the tool-contact side is usually also the visible surface of the part. This allows coarse structures, markings, and logos to be displayed directly on the surface. Negative thermoforming is often used when the outer contour must precisely align with other components. Changes in material thickness build inward. The disadvantage lies in the higher tooling costs.

What are the advantages of thermoforming?

• Cost-effective: Low tooling costs, since usually only one mold half is required - even for very thick- or thin-walled parts.
• Wide variety of shapes: Multi-cavity molds reduce unit costs at higher volumes. Also enables the production of complex and large forms with high precision.
• Flexible for design changes: Due to the simple mold structure, modifications can be made at any time.
• Versatile materials: Broad range of thermoplastics suitable for forming. Finished parts can feature high-quality appearance with colored material, glossy or grained surfaces - no additional painting required.
• Recyclable: Thermoplastic materials used are recyclable, making the process environmentally friendly.
• Fast production: Short setup times and efficient processes allow for rapid manufacturing.

Step 1:
The plastic sheet is heated by radiant panels until the material reaches a thermoplastic state. During the heating phase, the material is continuously monitored by radiation pyrometers.

Step 2:
After heating, the panels retract. Compressed air is introduced into the sealed mold chamber, causing the softened material to stretch evenly. The aluminum mold then moves into the pre-stretched dome.

Step 3:
Once the mold is in position, vacuum removes the air between the material and the mold, so the sheet precisely reproduces the mold contour. Fans then cool the material (again monitored by radiation pyrometers). The clamping frame opens, and the molded part can be removed. At all times, the process remains visible, ensuring optimal material temperature and consistent quality.