Hot-plate welding can produce strong, leak-tight plastic assemblies with complex geometries. It is a robust, viable and technically sound joining process that is used to assemble batteries, fuel tanks, fluid reservoirs, taillight lenses and other applications where strong seals are critical.
Traditionally, hot-plate welding offered limited process control, minimal data acquisition capabilities and slow cycle times. But, that’s not the case anymore. Today’s welders allow engineers to precisely control the motion of the platen, the temperature of the heating surfaces and the force applied to parts.
Hot-plate welding involves a heated platen with heated tool inserts and two opposing press platens comprised of nonheated tooling. The heated platen accepts interchangeable tooling inserts to accommodate the specific welding configuration of the parts being assembled.
The temperature of the heated tooling is adjustable. It can range from 350 to 900 F.
Press tools are also interchangeable. They precisely align and support the parts being welded. Welders can be configured to function either horizontally or vertically.
Hot-plate welding involves seven phases:
1. Load. Components are placed in nonheated locating fixtures that ensure adequate support and accurate alignment.
2. Melt. Components are automatically positioned to make contact against the heated tooling. The melt displacement is controlled.
3. Heat. Components are held at this position, which is called melt time. This allows heat to conduct into the material, even though displacement has stopped.
4. Open. During this phase, the components are removed from the heated tooling and the heated platen is retracted.
5. Seal. Components are positioned to bring the semimolten joint surfaces together to form a welded interface.
6. Cool. Components are held in position, allowing the welded joint to cool and the plastic to resolidify.
7. Unload. A welded assembly is removed from the tooling.
Making high-speed hot-plate welding a reality requires more than just the addition of servo-driven platens to achieve both precision and speed. Control of the key parameters of force, velocity, distance and heat requires advanced hardware and software.
The ability to precisely control the key variables allows for true process optimization and verification, cycle time reduction, and considerable machine set-up simplification. Features such as heated-platen stir and stutter offer additional control for difficult applications.
True control of the force exerted on the components during the heating and sealing phases of the weld process is critical. To optimize weld strength, precise force control is necessary.