Ultrasonic Welding

Ultrasonic welding joins parts using high-frequency vibration and pressure, creating fast, low-heat solid-state bonds in plastics and thin metals.

Overview

Ultrasonic welding uses a vibrating sonotrode (typically 20–40 kHz) and clamping force to generate frictional/viscoelastic heating at the interface, forming a solid-state joint. It’s widely used for thermoplastics (energy directors, hermetic seams) and for thin, ductile metals like aluminum and copper (often for electrical interconnects). Cycle times are usually sub-second to a few seconds, with no filler, flux, or open flame.

Choose ultrasonic welding for high-volume assemblies needing consistent joints, low part distortion, and clean manufacturing (minimal fumes and consumables). It excels when you can control joint geometry and fixturing and when parts tolerate localized pressure.

Tradeoffs: joint design is not optional—features like energy directors and weld lands drive success. Tooling/fixtures are specialized, cosmetic marking is common at the horn contact, and thick/hard metals and large weld areas can be impractical. Validation often focuses on weld strength, peel/shear testing, and process windows rather than dimensional tolerance alone.

Common Materials

  • ABS
  • Polycarbonate (PC)
  • Polypropylene (PP)
  • Nylon 6/6 (PA66)
  • Aluminum 1100
  • Copper C110

Tolerances

±0.005 in

Applications

  • Battery tab to busbar welds
  • Wire harness splices and terminals
  • Medical device housings (sealed plastic enclosures)
  • Automotive sensor housings
  • Plastic packaging seals (blister packs)
  • Nonwoven fabric bonding (filters, masks)

When to Choose Ultrasonic Welding

Pick ultrasonic welding for repeatable, high-throughput joining where you want minimal heat-affected zone, no filler materials, and low cycle time. It fits best when the joint can be designed for vibration coupling (energy director/weld land) and parts can be rigidly fixtured. It’s strongest for thermoplastic assemblies and for thin, conductive metal stacks used in electrical connections.

vs MIG (GMAW)

Choose ultrasonic welding when you need a low-heat, filler-free joint on thermoplastics or on thin aluminum/copper where arc heat would distort parts or damage nearby insulation. It’s better for fast, repeatable production joints that don’t require a molten weld pool or shielding gas.

vs TIG (GTAW)

Choose ultrasonic welding when joint speed, low thermal input, and minimal post-processing matter more than cosmetic fusion weld appearance. It works well for thin foils/stacked tabs and plastic housings where TIG heat input and access requirements would be limiting.

vs Stick (SMAW)

Choose ultrasonic welding for controlled, clean joining in production environments where you need consistent joints without slag, spatter, and high operator variability. It also enables joining plastics and thin conductive metals that are poor fits for high-heat, consumable-electrode welding.

vs Resistance Welding

Choose ultrasonic welding when you need to weld highly conductive stacks (copper/aluminum) at low temperature without expulsion and with good electrical performance. It can be easier on thin foils and mixed stacks where resistance welding struggles with current shunting or electrode wear.

vs Adhesive Bonding

Choose ultrasonic welding when you need short cycle times, immediate handling strength, and no cure time or surface-prep sensitivity. It’s also preferred when outgassing, contamination, or long-term adhesive aging are risks and the joint can be designed for a welded interface.

Design Considerations

  • Add energy directors or defined weld lands on thermoplastic parts to concentrate melt and reduce required amplitude/force
  • Design for robust fixturing: include datum surfaces and anti-slip features so parts can’t move under vibration
  • Keep joint interfaces clean and consistent; specify allowable mold release, oils, and particulate contamination
  • Avoid large unsupported thin walls near the weld line; add ribs or local thickness to prevent collapse and cosmetic sink
  • Specify horn contact areas and cosmetic expectations (witness marks, texture changes) early to prevent rework
  • For metal welding, control stack-up thickness and include strain relief so the joint isn’t carrying bending loads