What Is Projection Welding and When Is It Used?

Projection welding is a resistance welding process that concentrates current and force at raised features on one part. Those projections heat and collapse to form one or more welds. The process is widely used for weld nuts, studs, brackets, crossed wires, and repeatable sheet-metal assemblies, but dependable results require controlled part geometry, tooling, machine settings, and inspection.

What Is Projection Welding?

Projection welding is a specialized resistance welding process. Small raised features on one component create the first contact points between the parts. When the electrodes clamp the assembly and current flows, the projections create high local current density and heat. The heated projections deform under force, and a weld forms at each planned location.

The process is used in automotive, appliance, electrical, hardware, and wire-product manufacturing. Common parts include weld nuts, studs, bosses, clips, brackets, reinforcements, crossed wires, wire mesh, and sealed electronic packages. The American Welding Society’s projection welding handbook chapter covers its equipment, materials, variables, schedules, quality, applications, limitations, economics, and safety.

Projection welding is not an arc process. It does not create an open welding arc, and it normally does not use filler wire or shielding gas. The joint forms from resistance heating at the part interface while the electrodes apply force and carry current.

How Projection Welding Works

A projection weld is made through a short, controlled sequence. Exact timing and control names vary by machine, but the basic cycle is the same:

1. Load and locate the parts. The fixture or locating pin positions the components and supports them against movement.
2. Apply squeeze force. The electrodes close and reach a stable force before current starts.
3. Pass welding current. Current follows the restricted path through the projections, producing concentrated heat at the interface.
4. Allow controlled collapse. The heated projections soften and shorten while the welding head follows their movement and maintains force.
5. Form the weld nugget or fused zone. Heat and pressure create the joint at each projection.
6. Hold under force. Current stops, but electrode force remains while the weld cools and solidifies.
7. Release and inspect. The electrodes open, the part is unloaded, and required visual or production checks are completed.

Why the Projection Heats First

Resistance heating is often described with the relationship heat is proportional to current squared × resistance × time. In a real weld, resistance changes rapidly as coatings break down, surfaces heat, and the projection collapses. That is why a projection weld cannot be controlled by current alone.

Control	What It Changes	Typical Risk When Incorrect
Projection geometry	Initial contact area, heat location, and collapse behavior	Uneven heating, premature collapse, or an undersized weld
Electrode force	Contact resistance, containment, and projection collapse	Expulsion at low force or flattened projections at excessive force
Current and weld time	Rate and amount of heat input	Weak bonding, excessive indentation, thread damage, or expulsion
Squeeze time	How long the machine stabilizes force before current	Arcing, splash, or inconsistent contact
Hold time	Cooling under force	Movement, cracking, or loss of joint consistency
Mechanical follow-up	How well the head maintains force as the projection shortens	Force loss and expulsion during rapid collapse

Projection Collapse and Weld Solidification

The projection should collapse in a controlled way while the weld forms. The machine frame, ram, tooling, and electrodes must remain aligned and maintain force as the joint thickness changes. After current stops, hold time keeps the assembly under pressure while the fused zone cools.

A visually flattened projection does not prove that a sound weld formed. Production settings should be established with test parts and verified by the required torque, push-out, peel, sectioning, or other acceptance test.

A repeatable projection weld is a system result: part geometry, material condition, tooling, force response, power delivery, cooling, and inspection must work together.

Projection Welding Projections and Joint Design

The projection is not merely a bump in the metal. It is a designed current and force concentrator. Its shape, height, base width, position, spacing, material hardness, and manufacturing tolerance affect how the joint heats and collapses.

Common projection types include:

• Embossed projections: formed in sheet by stamping, pressing, or coining.
• Machined or coined projections: made on thicker or solid components where tighter control is needed.
• Ring or annular projections: used around an opening or package perimeter when a circular or continuous weld path is required.
• Fastener projections: nibs, bosses, or rings built into weld nuts, studs, and threaded fittings.
• Natural projections: existing geometry, such as two wires crossing at a point.

Projection Design Factors

• Equal height: Multiple projections should contact the mating part as evenly as practical so one point does not take most of the current and force.
• Stable base: The surrounding sheet or fastener body must support the projection without buckling or distorting before the weld forms.
• Adequate spacing: Projections placed too close together can divide current and force unevenly.
• Edge distance: Projections near an unsupported edge may distort the part or produce an incomplete weld.
• Collapse allowance: Tooling and locators must allow the moving electrode to follow the shortening joint without binding.
• Thread protection: Weld-nut and stud tooling should prevent misalignment and keep weld splash away from usable threads.

Materials, Coatings, and Surface Condition

Projection welding is most straightforward when the parts are electrically conductive, compatible with resistance welding, and consistent in thickness and surface condition. Low-carbon steel and coated low-carbon steel are common production materials. Stainless steel, aluminum, copper alloys, high-strength steel, and dissimilar combinations may also be possible, but they can require different electrodes, power supplies, force response, and acceptance testing.

Coatings change contact resistance and heat balance. Zinc, galvanneal, aluminum-silicon, paint, primer, oil, scale, and plating should not be treated as interchangeable. ISO 16432:2006 covers embossed projection welding for specified uncoated and metallic-coated low-carbon steels, but it does not cover organic-coated or primer-coated steels. Always confirm the material and coating in the drawing, supplier data, and qualified procedure.

Projection Welding Equipment and Setup

A projection-welding system normally includes a power supply and control, transformer or stored-energy circuit, welding head or press, electrodes, fixture, part locators, cooling system, and safety controls. The machine must provide enough current and force without operating at the edge of its capacity.

Power Supply Options

Power Type	General Characteristic	Where It May Fit
AC	Line-frequency current controlled by cycles or portions of cycles	Many conventional steel projection-welding applications with suitable current and force capacity
MFDC or inverter DC	Faster electronic control and feedback than conventional line-frequency AC	Automated applications that benefit from precise current control and process monitoring
Capacitor discharge or stored energy	Stores energy and releases it in a short pulse	Applications needing rapid localized heating, provided the frame and follow-up system can maintain force during fast collapse

No power-supply type is automatically best for every part. Material resistance, coating, projection mass, required pulse shape, machine stiffness, available force, follow-up speed, electrical service, and production rate all affect the choice.

Electrodes, Fixtures, and Cooling

Projection welding commonly uses broad, flat electrode faces because the part geometry defines the weld location. The electrode material and face design must carry current, resist deformation, support the work, and remove heat without damaging the part. Weld-nut tooling often uses an insulated locating pin so current does not bypass the intended projections.

Fixtures should locate the part without rocking, support thin sheet around the weld, and keep the load centered under the ram. Water-cooled electrodes and tooling must have adequate flow, and leaks or blocked passages should be corrected before production continues.

When to Use Projection Welding

Use projection welding when the part can include a reliable projection and the process benefits from fast, repeatable joining. It is especially useful when fixtures can control alignment and when one machine stroke can make several welds.

Best Applications

1. Weld nuts and studs: attaching threaded hardware to sheet metal for later assembly.
2. Brackets, clips, and reinforcements: making localized joints without a long arc-weld bead.
3. Cross-wire products: joining racks, baskets, screens, and mesh where wire crossings act as natural projections.
4. Multi-point assemblies: making several welds in one cycle when projection height and force distribution are controlled.
5. Ring-welded components: joining circular or perimeter features in selected sealed or structural assemblies.
6. Mixed-thickness stacks: joining compatible conductive parts after testing confirms heat balance and strength.

When Not to Use Projection Welding

Projection welding may be a poor choice when the part cannot hold a repeatable projection, the joint cannot be reached by opposed electrodes, the assembly cannot be clamped and supported, or production volume does not justify the tooling and process development.

Choose another process when the joint needs a long continuous structural bead, field-repair flexibility, one-sided access without specialized equipment, or a material combination that cannot be qualified with available power, force, tooling, and inspection methods.

Process Advantages

• Fast cycle time: Multiple projections can be welded in one cycle when current and force divide evenly.
• No added filler: The joint normally forms from the base materials alone.
• Defined weld location: Part geometry establishes the planned weld points.
• Localized heating: Focused heat can limit overall distortion when the schedule is correct.
• Broad electrode faces: Larger supporting electrodes can reduce visible marking and may improve electrode life in suitable applications.
• Automation potential: Feeders, fixtures, sensors, and weld controls can support high-volume production.

The tradeoff is tighter control of part design, tooling, projection tolerance, machine response, and preventive maintenance. A small error can repeat across an entire production batch.

Projection Welding vs Spot Welding

Projection welding and resistance spot welding both use current and electrode force, but they define the weld area differently. Spot welding relies mainly on electrode-tip location and face size. Projection welding relies on a raised or naturally restricted feature in the workpiece.

Factor	Projection Welding	Spot Welding
Weld location	Set by projections or natural contact points	Set mainly by electrode-tip position
Typical uses	Fasteners, bosses, brackets, crossed wires, and multi-point joints	Overlapping sheet-metal lap joints
Electrode shape	Often broad and flat to support the part	Usually has a defined tip face that helps establish weld size
Part preparation	Requires controlled projection geometry or a natural projection	Usually requires a suitable lap stack and electrode access
Multi-weld potential	Several projections can weld in one press cycle	Often one spot per gun, unless multi-spot equipment is used
Main control challenge	Equal projection contact, collapse, and force distribution	Tip condition, shunting, fit-up, and sheet-stack consistency

Use projection welding when a fastener, boss, ring, or designed contact point should define the weld. Use spot welding for simpler overlapping sheets when projections are unnecessary.

How to Develop and Control a Projection-Weld Schedule

A weld schedule is the documented combination of force, current or energy, timing, pulse shape, electrode arrangement, cooling, and part conditions used to produce an acceptable joint. Do not copy a schedule from a different fastener, coating, sheet thickness, or machine without verification.

1. Define the requirement. Record the material, coating, thickness, fastener or projection standard, joint load, appearance limits, thread requirements, and required tests.
2. Confirm machine capability. Check current, force, duty cycle, frame stiffness, ram travel, follow-up response, electrode cooling, and control resolution.
3. Inspect trial parts. Measure projection height and uniformity, fit-up, flatness, hole location, surface condition, and coating lot.
4. Establish safe starting settings. Use applicable standards, fastener data, and machine-supplier guidance as starting points.
5. Run controlled trials. Change one main variable at a time and record current, force, time, displacement, expulsion, indentation, and part condition.
6. Test the joint. Use the specified torque, push-out, peel, cross-section, leak, or load test and confirm the required failure mode.
7. Find a stable operating window. Verify that acceptable welds are produced across expected part, coating, voltage, cooling, and electrode-wear variation.
8. Document and lock the process. Record approved limits, setup checks, inspection frequency, reaction plan, and maintenance triggers.

ISO 15614-12:2021 addresses qualification testing for spot, seam, and projection welding procedures. Product drawings, customer specifications, applicable codes, and contract requirements still control the final acceptance criteria.

Key Process Variables

• Electrode force: Low force can allow expulsion; excessive force can crush the projection before enough heat develops.
• Weld current or energy: Too little produces weak bonding; too much can cause splash, indentation, overheating, or thread damage.
• Weld time and pulse shape: The current must heat the interface before the projection loses its concentrating effect.
• Squeeze time: Force should be stable before the weld pulse begins.
• Hold time: Pressure remains after current stops so the joint can solidify.
• Electrode alignment and condition: Worn, dirty, tilted, or overheated tooling changes force and current paths.
• Part fit-up: Gaps, burrs, rocking, distorted sheet, and unequal projections can make one weld form before the others.
• Cooling: Changing water temperature or flow can alter electrode condition and process stability.

Common Defects and Troubleshooting

Use troubleshooting as a structured process. Confirm the defect with the required test, then check part geometry, force, current, timing, tooling, cooling, and material condition. Do not correct every problem by simply increasing current.

Problem	Likely Causes	Checks and Corrective Direction
Weak weld or loose fastener	Low heat input, poor fit-up, unequal projections, contamination, or force loss	Verify the test method, clean and measure parts, check force and follow-up, inspect electrodes, then re-establish the approved schedule
Expulsion or heavy sparks	Excessive current or energy, low force, short squeeze time, poor alignment, coating variation, or slow follow-up	Confirm stable force before current, check ram response and alignment, inspect coating and projection height, and reduce excessive heat input within the qualified window
Projection flattens before welding	Excessive force, weak or over-tall projection, soft fastener, or unsupported sheet	Run a no-current force check, review projection design and material hardness, improve support, and requalify the schedule
Nut or stud misalignment	Worn locator, bent pin, poor feeder placement, fixture movement, or off-center force	Inspect locating hardware, fixture repeatability, part feeding, ram alignment, and hole position
Thread damage or weld splash in threads	Excess heat, long weld time, inadequate locating-pin protection, or heavy expulsion	Check thread gauges, locator insulation, force, follow-up, and pulse duration; correct expulsion before resuming production
Electrode sticking or rapid wear	Overheating, wrong electrode material, poor cooling, contamination, or excessive current density	Check water flow and temperature, clean parts, verify electrode alloy and face condition, and review the schedule
Uneven multi-projection welds	Unequal height, warped parts, uneven force distribution, shunting, or fixture deflection	Measure every projection, check flatness and tool parallelism, support the sheet, and verify current and force balance
Good appearance but failed strength test	Surface collapse without adequate fusion, incorrect acceptance test, or process drift	Section a sample, review the failure mode, compare monitored data with the approved baseline, and stop relying on appearance alone

Projection Welding Pros and Cons

Projection welding can improve speed and consistency, but only when the joint and production system are designed for it.

Pros	Cons
Can form several welds in one cycle	Requires controlled projection geometry and contact
Well suited to nuts, studs, brackets, bosses, and wire products	Tooling, locating, and process development add upfront cost
Normally needs no filler metal or shielding gas	Not ideal for changing, low-volume field repair
Localized heating can limit overall distortion	Coatings, hardness, flatness, and lot variation can narrow the process window
Broad electrodes can support the part and reduce marking	Machine stiffness, follow-up, cooling, and electrode maintenance remain critical
Integrates well with automation and monitoring	Hidden welds require planned verification rather than visual inspection alone

Common Projection Welding Applications by Industry

Projection welding appears in many production settings where localized heat, short cycle time, and repeatable placement matter.

• Automotive: weld nuts, studs, fastener plates, reinforcements, brackets, filters, and selected brake or chassis-related parts.
• Appliances: brackets, tabs, mounting hardware, frames, and reinforcements.
• Wire products: racks, baskets, grilles, guards, mesh, and screens.
• Electrical and electronics: terminals, contact assemblies, enclosures, and ring-projection package seals where the design is qualified.
• General hardware: bosses, threaded fittings, clips, hinges, and stamped subassemblies.

Because several projections can be welded in one cycle, the process can reduce assembly time. The best results come when the projection, tooling, machine, inspection plan, and downstream assembly requirement are developed together.

Projection Welding Safety

Projection welding may not produce a bright open arc, but it still creates serious hazards. These include pinch and crush points, flying sparks or expelled metal, hot parts, electrical energy, stored capacitor energy, moving feeders, water leaks near electrical equipment, and fumes from coatings or contamination.

OSHA 29 CFR 1910.255 requires resistance-welding operators to be properly instructed and judged competent. It also addresses guarded controls and foot switches, point-of-operation guarding, spark shields, interlocked access panels, grounding where technically practical, emergency stops on specified multispot equipment, and periodic inspection by qualified maintenance personnel. General welding ventilation and fire-prevention requirements appear in OSHA 29 CFR 1910.252.

• Use the required eye and face protection for sparks, hot particles, and the specific operation.
• Keep hands clear of electrodes, clamps, locators, feeders, and moving fixtures.
• Do not bypass two-hand controls, light curtains, interlocks, guards, emergency stops, or grounded circuits.
• Use effective ventilation for coated, plated, oily, painted, or contaminated materials, and follow the material-specific hazard assessment.
• Keep combustible materials away from expelled metal and provide shields for nearby workers.
• Follow lockout/tagout and stored-energy discharge procedures before servicing the machine.
• Stop production for damaged cables, leaking cooling lines, overheated tooling, unusual noise, repeated expulsion, or failed safety devices.

How Projection Welds Are Inspected and Verified

The weld is hidden between the parts, so appearance alone is not enough for a critical joint. The inspection plan should match the drawing, customer requirement, load, failure consequence, and qualified weld procedure.

Method	What It Can Confirm	Important Limit
Visual and dimensional inspection	Position, seating, alignment, indentation, expulsion, distortion, and thread condition	Cannot directly prove hidden fusion or strength
Torque, push-out, or pull test	Fastener attachment strength and failure behavior	Test setup and minimum value must come from the applicable requirement
Peel, chisel, or destructive separation	Weld button or parent-metal failure at individual projections	Destroys the sample and may not suit every geometry
Macro section	Fusion-zone shape, penetration, cracks, voids, and projection collapse	Represents only the sectioned location and requires careful preparation
Leak testing	Seal performance of qualified annular or package welds	Does not replace structural acceptance tests unless the specification says so
Validated nondestructive examination	Selected internal conditions when the joint and method are suitable	Ultrasonic, radiographic, thermographic, or other methods must be proven for the actual geometry and defect types
Process monitoring	Changes in current, voltage, force, displacement, resistance, timing, or energy	Monitoring detects deviation; it does not automatically prove weld strength without correlation to tested parts

For production control, combine periodic destructive or mechanical testing with setup verification, electrode maintenance, part checks, and monitored process limits. A reaction plan should state when to stop the machine, quarantine parts, correct the cause, and revalidate the weld.

Frequently Asked Questions

What is projection welding used for?

Projection welding is used for weld nuts, studs, bosses, brackets, clips, reinforcements, crossed wires, wire grids, and selected ring-welded parts. It is most useful when parts and fixtures are repeatable and one or more welds must be made quickly in a controlled production process.

Is projection welding easy to learn?

The principle is simple, but safe production operation requires machine-specific training. Operators must understand guards, controls, fixtures, part loading, approved weld limits, quality checks, emergency stops, and the response to expulsion or failed tests.

Can projection welds be inspected?

Yes. Common methods include visual and dimensional checks, torque or push-out tests for fasteners, peel or destructive separation, macro sections, leak tests for sealed parts, and process monitoring. Specialized nondestructive methods may be used only after they are validated for the joint.

What are the different types of projection welding?

Common forms include embossed projection welding, machined or coined projection welding, annular or ring projection welding, weld-nut and weld-stud projection welding, and cross-wire welding. Each uses a restricted initial contact area to focus heat and force.

What is the difference between projection welding and resistance spot welding?

Both use resistance heat and electrode force. Spot welding mainly uses the electrode tip to define the weld area. Projection welding uses a raised or natural feature in the part, making it especially useful for fasteners, bosses, crossed wires, and multiple welds in one cycle.

Does projection welding need filler metal or shielding gas?

No. Projection welding normally forms the joint from the base materials and does not use filler metal or shielding gas. Ventilation may still be required because heated coatings, oils, plating, or contamination can produce hazardous fumes.

What causes projection-weld expulsion?

Common causes include excessive current or energy, low or unstable force, short squeeze time, poor electrode alignment, unequal projection height, coating variation, and a welding head that cannot follow rapid projection collapse. The cause should be verified before changing settings.

Can I use a generic projection-welding settings chart?

A chart can provide a starting point only when it matches the fastener, material, coating, thickness, electrode arrangement, and machine type. Final settings must be tested on real production parts and documented with the required strength and quality checks.

Conclusion

Projection welding is a fast, controlled resistance welding method for parts that include reliable raised or natural contact points. It is especially effective for weld nuts, studs, brackets, bosses, reinforcements, crossed wires, and multi-point assemblies. Compared with spot welding, the part geometry—not only the electrode tip—defines where heat and force are concentrated.

Strong, repeatable welds depend on the complete system: projection design, material and coating, part fit-up, electrode force, current or energy, timing, machine rigidity, follow-up response, cooling, inspection, and maintenance. Develop the schedule on actual parts, qualify it against the governing requirement, and keep safety devices and process controls in service throughout production.

Sources

1. American Welding Society: Projection Welding — process fundamentals, equipment, variables, applications, quality, and safety.
2. AMADA WELD TECH: Projection Welding — manufacturer explanation of projection features, current paths, heat balance, and electrode life.
3. ISO 16432:2006 — procedure requirements and material scope for embossed projection welding of specified low-carbon steels.
4. ISO 15614-12:2021 — qualification testing for spot, seam, and projection welding procedures.
5. OSHA 29 CFR 1910.255: Resistance Welding — operator competence, guarding, interlocks, shields, grounding, and inspection requirements.
6. OSHA 29 CFR 1910.252: General Welding Requirements — ventilation, fire prevention, eye protection, and general welding controls.