Heat Staking vs Ultrasonic Welding

Both heat staking and ultrasonic welding form joints in thermoplastic parts. They are not interchangeable. This guide breaks down the real tradeoffs — cycle time, equipment cost, material compatibility, joint geometry, cosmetic outcome, and process documentation — so you can pick the right process the first time. It is written from a heat staking equipment manufacturer's perspective, but with honest comparisons in both directions: there are jobs ultrasonic does better, and we will say so.

Short version: ultrasonic wins on sub-second cycle time at very high volumes when the materials and geometry cooperate. Heat staking wins on dissimilar materials (metal-in-plastic), forgiving design rules, lower equipment cost, and cosmetic surface quality. Glass-filled and energy-absorbing resins are easier on heat staking than on ultrasonic.

Cycle Time

Ultrasonic: typically sub-second per joint, sometimes 0.1 to 0.3 seconds for an established part. Heat staking: typically 2 to 8 seconds per joint depending on boss volume and head profile, but multi-up tooling stakes up to 8 bosses in one cycle, so per-joint cycle time scales differently. For a single-stake high-volume part, ultrasonic is faster. For a multi-stake assembly, heat staking can be competitive or faster on a per-part basis.

Material Compatibility

Ultrasonic needs a resin that transmits ultrasonic energy efficiently — rigid amorphous resins (ABS, PS, acrylic, PC) work well; soft, semi-crystalline, or energy-absorbing resins (polyolefins, glass-filled grades, some nylons) work poorly or need very specific design. Heat staking is more forgiving: essentially any thermoplastic stakes acceptably, glass-filled grades stake with a slightly rougher head finish, and the host resin choice is less constrained.

Joint Geometry

Ultrasonic welds two pieces of similar plastic together at an energy director or shear joint. It cannot easily capture a non-plastic component. Heat staking forms a rivet-style head in a plastic boss that captures a clearance-holed second part — which can be metal, PCB, fabric, foam, glass, or another plastic. For metal-in-plastic, foam-in-plastic, or PCB-in-plastic, heat staking wins by default.

Cosmetic Surface Quality

Ultrasonic transmits vibration, which can mark, scuff, or stress-whiten cosmetic A-surfaces in contact with the horn. Impulse heat staking with cold-tip retract leaves no marks on the cosmetic side because the heat is contained at the boss tip and the tip cools before retract. For cosmetic-critical interior trim, consumer products, or visible electronics housings, heat staking is the safer choice.

Equipment Cost

Ultrasonic welders for high-volume production are typically more expensive per station than heat staking presses, and the tooling (horn, anvil) is more expensive and longer lead time. Heat staking benchtop presses are lower capital cost; custom automation cells scale similarly to ultrasonic automation. For low- to mid-volume programmes, heat staking is usually the lower total-cost option.

Process Documentation

Both processes can produce auditable cycle records. Modern impulse heat staking with energy-per-joint control records each cycle's delivered energy, which maps cleanly to Cpk documentation and customer audits. Ultrasonic with closed-loop energy control offers similar capability. For regulated production (medical, automotive), both processes can satisfy quality system requirements.

Which to Pick

If your part is high-volume, single-joint, similar materials, no cosmetic constraints: ultrasonic. If your part captures dissimilar materials, has cosmetic surfaces, uses glass-filled or energy-absorbing resin, or assembles multiple stakes per cycle: heat staking. If you are not sure, send the part for an honest review. We have told customers to use ultrasonic before — the right process is the one that fits the part, not the one we happen to sell.

Side-by-Side Comparison

Frequently Asked Questions

Is heat staking stronger than ultrasonic welding? Not usually, and it rarely matters. Ultrasonic fuses two like plastics into a molecular bond, which wins a pull test on a welded seam. Heat staking forms a mechanical head that clamps a captured part, and for holding a PCB, bracket, or lens inside a housing that clamp is far stronger than the joint needs to be. Strength is seldom the deciding factor — material mix and cosmetics usually are.

Is heat staking cheaper than ultrasonic welding? For low and mid volume, yes. Heat staking presses cost less per station, and heated tips are cheaper and faster to make than ultrasonic horns and anvils. At very high single-joint volumes the gap narrows. We do not publish a price list because the tooling and part drive the cost; send the part and we return real numbers within 24 hours.

Can ultrasonic welding damage electronics? It can. Ultrasonic drives high-frequency vibration through the part, which can stress solder joints and sensitive components. Impulse heat staking keeps the heat at the boss tip for a sub-second window and never vibrates the board, which is why PCB-in-housing assembly usually lands on heat staking.

When should I use ultrasonic welding instead of heat staking? When you are joining two pieces of the same rigid thermoplastic, you need a hermetic or watertight seal, and the volume justifies a custom horn. Ultrasonic also wins on sub-second single-joint cycle time. If that describes your part, we will tell you to use ultrasonic.

Can you heat stake glass-filled or nylon parts? Yes. Glass-filled grades stake with a slightly rougher head finish; nylon and polypropylene need a bit more energy because they absorb more heat before they flow. Those are the same resins ultrasonic often struggles with, so the comparison frequently tips toward heat staking.

Does heat staking leave marks on visible surfaces? Not with impulse and cold-tip retract. The tip cools under compressed air before it lifts, so there is no molten drag and no witness mark on the A-surface. Continuous hot-probe tips are the ones that string and scuff cosmetic parts.