Projection welding

Six complete mains cycles take 0.120 s at 50 Hz or 0.100 s at 60 Hz. Verify the actual controller's timing convention. In a separate example, a projection falls from 1.20 to 0.30 mm above the same reference, a 0.90 mm or 75% reduction. Qualify joint quality independently of projection collapse and electrode travel.

Embossments, solid projections, rails or rings concentrate resistance-welding current and force. Identify the process even when equipment shares capacitor-discharge power with arc stud welding. AMADA WELD TECH: projection welders

The process is used for applications as different as weld nuts on sheet and sealed electronic packages. Those joints do not share one geometry, power schedule or acceptance test. A fastener that remains attached is not automatically qualified for its service load, and a continuous-looking ring is not automatically leak tight.

Define the projection and joint together

AMADA explains that projections focus current and increase interface resistance while helping balance heating between unequal parts. Because the workpiece feature concentrates the current, larger electrode contact faces can be used, potentially reducing electrode wear. This is a design opportunity rather than a guarantee of electrode life or a universal solution for dissimilar materials. AMADA: projection-welding glossary

Its design guidance distinguishes round, rail and ring projections and notes that dimensions and shape depend on the materials and part sizes. A projection that is too large may not collapse appropriately; one that is too small can melt too quickly. Do not copy one projection height or collapse percentage into every application. AMADA: heat balance and projection design

For annular projections, TWI stresses uniformity of shape and height because force and current initially concentrate in a small contact area. Its dimensional and electrical examples are guidance for the described arrangements, not defaults for every ring or threaded boss. Agree the drawing with the welding supplier before releasing machining or forming tools. TWI: annular projection recommendations

Force, current and motion are coupled

For weld nuts, TWI calls for a sufficiently rigid machine and electrode assembly, aligned flat electrode faces, and a freely moving head with low enough inertia to follow the collapsing projections. Its guidance also identifies an insulated locating pin. A nominal force setting does not demonstrate that the moving assembly maintains the required contact during the weld. TWI: projection welding weld nuts

Define squeeze, electrical pulse and hold portions of the approved cycle together with the current waveform and mechanical setup. Record the power-source type, electrode/tool identity, cooling arrangement, force control and any displacement monitoring used. A schedule expressed only as current and time omits the geometry and contact conditions that make it applicable.

Avoid treating more force as an unrestricted correction. For its electronic-package ring application, AMADA warns that excessive force can flatten a projection prematurely or drive it into the mating part, while increased force changes contact resistance. Its discussion shows why electrical and mechanical adjustments must be evaluated together. AMADA: designing ring projections

Inspect incoming projections, mating surfaces and location features. Burrs, damaged projections or misalignment should be dispositioned through the approved process rather than concealed by increasing the machine setting. Establish how tooling wear and part variation will be detected before production drifts outside the qualified arrangement.

Original timing and collapse examples

Timing convention. Convert complete mains cycles using time = cycles / frequency. Six cycles are 20% longer at 50 Hz than at 60 Hz. Follow the controller’s convention for milliseconds, half-cycles or inverter pulses.

Geometric collapse. The example gives 1.20 − 0.30 = 0.90 mm, or 75% of initial height. Electrode travel can include seating, component deformation and machine compliance. Verify actual fusion area and strength separately.

Material and application evidence

A named research example is Luo and colleagues' resistance projection welding of zinc-coated Q235A T-shaped nuts to 1.5 mm Al–Si-coated Usibor1500 hot-stamped steel using capacitor-discharge equipment. The study found a fusion zone, heat-affected regions and sheet-side softening, and examined interfacial, pullout and projection failure modes. These observations belong to the tested material pair and conditions; they demonstrate why a general “nut welded to high-strength steel” description is inadequate. Luo et al., ISIJ International 59 (2019), 305–311

For ring-sealed electronics, AMADA discusses both trapped expelled particles and glass-feedthrough cracking as postweld concerns. Current, resistance and displacement monitors can aid development and production control, but appearance and collapse monitoring do not replace the ordered leak or reliability requirements. AMADA: ring-seal monitoring and postweld defects

Qualification and release

ISO 15614-12:2021, edition 3, October 2021, specifies procedure-qualification tests for resistance spot, seam and projection welding. Its procedures are written for embossed projections and can be adapted for solid projections such as nut, stud and cross-wire welding. That scope distinction matters when selecting a qualification route; the standard number does not by itself approve a production schedule. ISO 15614-12:2021

TWI's weld-nut guidance describes destructive torque testing supported by peel or push-off examination of the individual projection attachments. Its table applies to identified square nuts and sheet conditions; adopt neither its settings nor failure torques as universal acceptance values. Specify the actual test method, requirement, sampling and failure interpretation for the component. TWI: weld-nut testing

For delivery, distinguish attachment strength, thread/hole usability, component position, surface condition and any sealing requirement. Agree permitted repairs and the final inspection stage after coating or other downstream processing. Preserve material/projection traceability, tooling and machine setup, approved cycle and production-test records. Evaluate changes in coating, projection manufacture, electrode geometry or power source against the qualified route.

Source versions

Reviewed 2026-11-01. ISO identifies edition 3, October 2021. The research publisher gives 15 February 2019 as publication date and 23 February 2019 as J-STAGE release date. No separately verified technical issue date is assigned to the cited AMADA and TWI live guidance; website copyright years are not editions. The timing/collapse examples and handoff recommendations are original.

Related reference

Welding methods