Chapter 1 - Heated Tool Welding

Abstract

This chapter describes the process of hot plate or hot tool welding. In hot tool or hot plate welding, a heated platen is used to melt the joining surfaces of two thermoplastic parts. After the interfaces of the plastic parts have melted, the heated platen is removed, and the parts are held together under low pressure to form a molecular, permanent, and hermetic seal. A hot plate is used for flat joining surfaces; for curved or irregular joining surfaces, complex tools that allow the hot surfaces to match the contours of the joint interface are required. For accurate mating and alignment, holding fixtures (collets, gripping fingers, mechanical devices, vacuum cups) must support the parts to be joined. The chapter suggests that the joint surfaces should be clean and relatively smooth to the surface of the heated tool; weld quality is affected if the surfaces are contaminated by mold release agent or grease. Surfaces can be treated mechanically or chemically. In hot plate welding, the parts to be joined are pressed against the hot platen; platens can be coated with polytetrafluoroethylene (PTFE) to inhibit melt sticking. This chapter also describes two ways that are commonly used to perform welding: “welding by pressure” and “welding by distance”. Both processes consist of four phases, shown in the pressure vs. time diagram in the chapter.