# Resistance seam welding

Wheel-electrode resistance welding: current paths, nugget overlap, material and access limits, process controls, and seal acceptance.

Reviewed: 2026-11-01

Tags: processes, welding, resistance-welding, sheet-metal

At an assumed **25 mm/s** and **20 pulses/s**, one nugget per pulse gives **1.25 mm pitch**. With a **3.00 mm** longitudinal nugget, modeled longitudinal overlap is **58.3%**. At **40 mm/s** it falls to **33.3%**, with **2.00 mm pitch**, if nugget size stays constant. Test continuity and seal performance on representative joints.

Wheel electrodes apply force and current along a path. A continuous seam depends on a succession of sound, sufficiently overlapping resistance welds. [TWI, What is Resistance Welding?, undated](https://www.twi-global.com/technical-knowledge/faqs/what-is-resistance-welding)

Specify the intended result: an intermittent structural connection, a continuous welded region, or a qualified gas/liquid seal. A continuous-looking wheel track is not a leak-test result, and electrical continuity is not evidence of mechanical strength or hermeticity.

## Identify the electrode arrangement and joint

Conventional opposed-wheel seam welding commonly uses a lap joint with access for electrodes on both sides. Wheel profile, reach, drive, force application, and the part's shape limit the accessible path. Internal corners or nearby features can obstruct the wheels. TWI distinguishes continuous-motion and intermittent-motion operation and also describes a consumable copper-wire variant that presents a renewed electrode contact surface. Those are distinct equipment/process choices, not interchangeable settings on every machine. [TWI, What is Seam Welding?, undated](https://www.twi-global.com/technical-knowledge/faqs/what-is-seam-welding)

Parallel-gap seam sealing of microelectronic packages is another arrangement. AMADA MIYACHI's **©2019** hermetic-sealing presentation describes rolling electrodes sealing a lid/package system and contrasts that with opposed-electrode projection sealing. Do not transfer a thin electronic-lid schedule to a sheet-metal tank simply because both processes are called seam welding. [AMADA, Hermetic Seam Sealing Microelectronic Devices](https://amadaweldtech.com/wp-content/uploads/2020/03/Hermetic-Seam-Sealing-Microelectronic-Devices-_customer-reference-copy.pdf)

A useful enquiry includes material grades, coatings/platings, each component thickness, overlap or seal-ring geometry, tolerances, path/corner geometry, available electrode access, and required production rate. Confirm the completed assembly can travel through the machine without losing alignment or force.

## Materials and standards have bounded scope

Resistivity, thermal conductivity, surface films, coating behavior, thickness, and joint contact affect where heat develops. A weld schedule for clean uncoated steel does not establish capability on zinc-coated sheet, stainless steel, aluminium, or dissimilar thicknesses. Select electrode material and geometry together with the work materials and equipment.

Taylor-Winfield's *Copper Products for Resistance Welding* catalogue offers several seam-wheel alloys and distinguishes recommendations for aluminium, coated steels, and stainless/high-temperature alloys. This producer evidence is also a reason to avoid reading broad statements that seam welding is unsuitable for aluminium as an absolute prohibition: specialised material/electrode routes exist. The catalogue's retrieved text has no verified issue date; no 2020 edition is inferred from its upload directory. [Taylor-Winfield, seam welding wheels, printed page 40](https://taylor-winfield.com/wp-content/uploads/2020/11/CopperProductsforResistanceWelding.pdf)

**ISO 16433:2006, edition 1, April 2006**, concerns resistance seam welding of specified uncoated and metallic-coated low-carbon steels in two-sheet assemblies, with maximum individual sheet thickness within **0.4–3 mm**. The official record notes confirmation in 2021 and a further review stage in 2026. That scope is not a general material/thickness limit for all seam welders, nor an automatic procedure qualification for another alloy or electrode arrangement. [ISO 16433 official scope and lifecycle](https://www.iso.org/standard/30976.html)

## Develop and control the weld schedule

Control electrode force, current waveform, pulse duration and spacing, travel speed, wheel alignment/profile, contact condition, cooling, and the start/finish sequence. Force influences electrical contact as well as mechanical containment; increasing current cannot reliably compensate for an uncontrolled contact or badly fitting joint.

Existing welds and other conductive paths can divert current from the intended region. AMADA's **2024 technical brief 991-488, Cascading**, explains shunting in closely spaced resistance spot applications. Its particular control solution concerns multiple weld circuits; it is not a seam-welding schedule. The relevant circuit principle is to identify bypass paths rather than equating total measured current with current through the new weld region. [AMADA WELD TECH, Cascading](https://amadaweldtech.com/wp-content/uploads/2023/04/Cascading.pdf)

Inspect and maintain wheel contact geometry. Wear, pickup, dressing, and wheel diameter can alter contact and motion, so preserve the qualified effective speed and pulse placement after maintenance. Specify cooling and equipment duty requirements for the actual production cycle rather than selecting a transformer from peak current alone. These are process-development checks, not a universal current, force, or dressing interval.

## Worked example: pulse pitch and overlap

Use the hypothetical **25 mm/s**, **20 pulses/s** and **3.00 mm** longitudinal nugget length, assuming one nugget per pulse and steady travel:

- Nugget pitch = speed / pulse frequency = 25 / 20 = **1.25 mm**.
- Longitudinal overlap fraction = (3.00 − 1.25) / 3.00 = **58.3%**.
- At **40 mm/s**, with pulse frequency and assumed nugget length unchanged, pitch becomes **2.00 mm** and calculated overlap **33.3%**.

The overlap is longitudinal. Nugget size can change with speed or thermal conditions. Demonstrate continuity and sealing on representative joints.

AMADA's 2019 package-sealing presentation treats spot spacing, speed, force, current, overtravel, and lid dimensions as linked controls. It illustrates inadequate overlap and insufficient corner travel as potential leak sources. Its numerical examples concern microelectronic packages, not a universal minimum overlap for sheet-metal seams. [AMADA hermetic-sealing presentation, process and failure examples](https://amadaweldtech.com/wp-content/uploads/2020/03/Hermetic-Seam-Sealing-Microelectronic-Devices-_customer-reference-copy.pdf)

## Starts, corners, and closure deserve inspection

Qualify more than a straight mid-seam coupon. Evaluate entry, exit, corners, path transitions, and closure over an existing seam. Motion changes can change pulse spacing and heat accumulation. For the electronic-package arrangement, AMADA discusses corner radii, electrode coverage, and travel beyond the lid dimensions; these are geometry-specific design lessons rather than instructions to overrun every production seam. [AMADA hermetic-sealing presentation](https://amadaweldtech.com/wp-content/uploads/2020/03/Hermetic-Seam-Sealing-Microelectronic-Devices-_customer-reference-copy.pdf)

Define surface preparation, fixture insulation where needed, alignment, and disposition of interruptions or expulsion. Suspect regions need an approved repair and reinspection route, not an undocumented extra pass.

## Finished-joint acceptance and handoff

Separate the evidence needed for different requirements:

- **Geometry and condition:** seam location, indentation, distortion, edge condition, expulsion, and surface damage.
- **Weld formation and strength:** suitable sections or destructive coupons, with sampling that represents the relevant materials and path features.
- **Sealing:** agreed leak-test method, medium, pressure differential, duration, detection sensitivity, and reject criterion.

A gross-leak test, fine-leak measurement, and strength test answer different questions. State units and test conditions rather than writing only “hermetic.” A production current monitor can support process control, but does not directly prove every specified joint property.

Record the drawing and material/coating identities, machine/electrode configuration, qualified schedule, wheel maintenance state, fixture, monitoring limits, sampling plan, and finished-joint results. Follow the installed machine's electrical, pinch-point, cooling, and maintenance instructions. Release against the agreed specification, with supplier examples retained as development guidance rather than universal recipes.

## Related reference

[Welding methods](index.md)