ABSTRACT
Thermoforming is a low pressure process of converting single plastic sheets or continuous roll stock. In this process, materials are classified into two categories based on thickness. Materials thicker than 0.010˝ (0.254 mm) are referred to as sheets while materials thinner than 0.010˝ (0.254 mm) are called films. This chapter focuses on sheet processing since it is the more common of the two material categories. The material is clamped into a rigid frame and moved to the heating stage where it is heated until it becomes semi-pliable. It is then drawn onto a mold form using one of the following processes: vacuum pressure, forced air (pressure), or mechanical assisted plugs. The part cools very quickly and excess material is trimmed. Finally, the formed part is stacked or, in food packaging applications, the parts may be sent through an auto-fill station. Figure 4.1 shows continuous feed and individual sheet systems.
