Heat staking reshapes a plastic boss with a heated tip so two parts lock without a screw. It is common in automotive interiors, appliance housings, and consumer assemblies where fasteners are costly or unwanted. The robot (or fixed press) repeats the motion reliably. The joint fails when the thermal recipe does not.
Ultrasonic metal tab welding is a different physics and a different horn life story. Adhesive dispense cells own bead volume. This note is thermoplastic heat staking.
The process in one paragraph
The tip reaches a set temperature, contacts the boss, dwells long enough to form a head, then retracts—sometimes with a cool step so the head sets before the next index. Too cold or too short: the head is incomplete and the joint pulls apart in handling. Too hot or too long: the boss sinks, cracks, or leaves cosmetic marks that QA rejects even when the joint is strong.
What to control on the cell
- Tip temperature at the working face—not only the cartridge setpoint. Dirty tips and worn coatings change contact heat.
- Dwell and force as a paired recipe per resin and boss geometry. Copying parameters across materials is a common scrap source.
- Alignment to the boss center. A beautiful robot TCP that is 1 mm off shears the boss instead of forming it.
- Cooling / release so the head does not smear on retract.
- First-article pull or torque checks after tip change, resin lot change, or weekend idle that let the tip oxidize.
Change control
A new resin grade, colorant, or boss height is a process MoC—not a silent HMI edit. Keep a small board of “last good” stake photos and pull values at the cell. Arguments from memory after a night-shift tip polish waste more time than the board costs.
If stakes fail in the field but the robot cycle time never moved, start with temperature and dwell logs before rewriting the palletizer that ships the assembly.