Rotary friction welding
Solid-state rotary joining: direct-drive and inertia routes, workholding, burn-off, flash, material compatibility and qualified acceptance.
Tags: processes, welding, solid-state-joining
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An example assembly starts with 80.0 mm and 45.0 mm components. 3.0 mm total weld shortening and 0.5 mm end finishing leave 121.5 mm. A 122.0 mm target would need 125.5 mm combined starting length under those assumptions. Use total shortening across the complete cycle and verify actual tolerance and joint quality.
Relative rotation under axial compression plasticizes the interface and expels flash. Rotation stops and axial force consolidates the solid-state joint. TWI, Rotary Friction Welding, Job Knowledge 148
This is distinct from friction stir welding, where a separate tool traverses the joint, and from linear friction welding, where the workpiece motion is translational. Specify the actual motion and equipment rather than using “friction welded” as a complete process definition.
Identify the energy-delivery route
| Arrangement | Energy delivery | Process implication |
|---|---|---|
| Direct drive | A motor continues driving the rotating component during friction heating. | Qualify speed, loading, termination and forging sequence on that system. |
| Inertia | A flywheel is accelerated, disconnected from the drive and supplies energy as rotation slows. | Flywheel inertia and initial speed belong to the qualified setup. |
These are TWI's two primary rotary arrangements. They do not describe interchangeable schedules, and the same initial rotational speed does not establish the same energy or temperature history. TWI, direct-drive and inertia descriptions
KUKA's brochure also describes a controlled-drive “virtual inertia” function without a flywheel. Such a named implementation should be identified from its actual machine/control configuration, not assumed present on every direct-drive machine. KUKA, rotary friction welding brochure, technology highlights
Workholding and component geometry
Provide the complete component envelope, joint section, grip lengths, allowable clamp marks, runout and alignment requirements. Resolve how one member rotates and how axial force and torque are reacted. The ability to grip a nominal diameter does not establish support for a thin wall, eccentric mass or adjacent finished feature.
Determine the required angular relationship between features after joining. KUKA lists defined-angle positioning as a technology feature on described equipment. That is a machine-specific capability to confirm, not an automatic result of stopping rotation. Its brochure distinguishes optional equipment from standard supply. KUKA brochure, controls and equipment scope
Burn-off, total shortening and flash
Define the stage to which each displacement value applies. TWI's length-control discussion uses burn-off for material lost during friction heating and explains that incoming lengths and clamping affect final length. A recorded heating-stage burn-off should not silently be treated as every contribution to total axial shortening. Agree how forging displacement, compliance and the finished measurement condition are handled. TWI, overall-length control
The same guidance discusses fixed and floating burn-off and forging to a stop. Its illustrative accuracy figures are not a tolerance guarantee for an arbitrary assembly. Request evidence for the proposed material, dimensions and machine rather than adopting a generic friction-welding tolerance. TWI, length-control methods
Plan the flash envelope and removal route before freezing the design. KUKA lists flash cut-off, turning and facing as equipment options. Decide which surfaces are machined after welding, how internal flash is addressed in a tubular assembly and when final dimensions are inspected. An available flash-removal option is not proof that an inaccessible internal collar can be removed or left in service. KUKA brochure, flash removal
Original assembly-length example
Use the hypothetical 80.0 mm and 45.0 mm components, 3.0 mm total assembly shortening and 0.5 mm overall end finishing:
finished length = 80.0 + 45.0 − 3.0 − 0.5 = 121.5 mm
For a 122.0 mm target, the model needs 125.5 mm total starting length. Allocate the extra 0.5 mm by the actual part requirements.
At 3.2 mm total shortening, the original parts finish at 121.3 mm. Check component variation, restraint, recovery and thermal effects. Include shortening beyond heating-stage burn-off.
Material compatibility and delivered condition
Solid-state joining can enable dissimilar combinations, but it does not eliminate interfacial metallurgy. TWI describes brittle intermetallic formation in some aluminum-to-other-metal combinations and the use of selected interlayers to limit it. An interlayer is an engineered part of the material/process system, not a universal cure or permission to combine any two grades. TWI, interlayers in dissimilar friction welds
Specify exact alloys, product forms, heat-treatment conditions and surface treatments on both sides. TWI distinguishes a weld-center region, thermo-mechanically affected zone and heat-affected zone whose extent and microstructure depend on the material/process. Do not assign parent-stock properties unchanged across every region of the finished joint. TWI, weld characteristics
Qualification, inspection and handoff
ISO 15620:2019, edition 2, May 2019, confirmed in 2024, addresses metallic friction welding, including rotary-process requirements for welding knowledge, quality, procedure specification/approval and welding personnel. Determine the governing contractual and application requirements; a machine's force range or a successful demonstration does not itself qualify production. ISO 15620:2019
Agree final dimensions, alignment/runout, flash disposition, interfacial integrity, material condition and required mechanical or functional evidence. Select examination methods and sampling for the actual geometry and failure mechanisms. A circumferential flash collar, process trace or acceptable final length alone does not establish complete joint conformance.
Provide the controlled drawing, material traceability, preparation and grip requirements, actual machine/drive route, qualified force/speed/displacement sequence, any thermal or machining operations, and final acceptance criteria. Record what changes require review, including material condition, interlayers, tooling and control configuration.
Source versions
Reviewed 2026-11-01. ISO identifies the edition and confirmation above. KUKA's brochure prints TB|Reibschweißen|EN|03|0619; that code is recorded without assigning a separately verified publication date. No technical issue date was verified for the cited TWI live guidance. The length example and handoff recommendations are original and supply no universal processing recipe or joint allowable.