Meaning
Application of compression force using compressed air cylinders is a standard method for holding assemblies together and driving weld penetration in plastic joining. Adjusting the pneumatic clamp force is a critical step in establishing the process window for ultrasonic welding, where it controls the rate of energy transfer into the joint. If the force is too low, the horn will lose contact with the part, causing surface burning and poor energy transmission.
Conversely, excessive force can stall the horn or crush the molded energy directors before they can melt.
Force Control
Delivery of consistent pressure to the actuator ensures that the tool descends and compresses the workpiece with repeatable force. Through pneumatic clamp force, the system holds the two plastic halves in alignment during the weld and hold cycles. This pressure must be adjusted based on the surface area of the joint and the stiffness of the polymer.
Melt Interaction
Energy directors on the molded parts must melt and flow across the joint line to form a strong, hermetic seal. If the pneumatic clamp force is too high during this phase, it will squeeze the molten polymer out of the joint, creating flash and a weak, hollow bond. Maintaining a lower initial force during melt initiation and increasing it during solidification helps in producing a high-strength weld.
Process Limit
Variations in factory air pressure can cause the force to fluctuate from cycle to cycle, leading to inconsistent weld strength. Using a dedicated pressure regulator and surge tank is required to stabilize the pneumatic clamp force during high-volume production.
