What is Micro Welding? A Plain-English Guide

Micro welding is the branch of welding that operates at a scale where ordinary MIG and TIG lose control. This page walks through what defines the category, the four processes buyers pick between, and the physics that decides which one fits a given part.

Micro welding, defined

The scale that matters

Micro welding is defined by three numbers rather than by any single machine. Heat input is measured in joules, sometimes fractions of a joule, rather than the kilojoules that keep an ordinary TIG puddle open. Spot geometry is measured in fractions of a millimeter: a laser focus can sit under 0.3 mm across, and a resistance spot electrode tip is often a millimeter or two. Cycle time is measured in milliseconds — a resistance spot pulse can be over in under 20 ms. Those three numbers together are what people mean by "micro."

Why "micro" is a real category

Ordinary welding assumes there is enough mass around the joint to absorb heat. Micro welding assumes the opposite: the parts near the joint are thin, delicate, or heat-sensitive, so the heat has to be small, fast, and placed within tenths of a millimeter of the target. Below a certain scale, ordinary equipment cannot hold arcs stably or pull heat back in time. Micro welding is a different tool class built around those constraints.

How micro welding differs from ordinary welding

Heat input: two orders of magnitude smaller

An ordinary TIG weld on a 3 mm structural plate might deliver several kilojoules per centimeter of joint. A micro laser pulse on a 0.2 mm thin-wall might deliver under 10 joules total. That is roughly two orders of magnitude less energy dumped into the part, and the heat-affected zone shrinks from millimeters to fractions of a millimeter.

Consequences of that gap

Thin walls survive: a 0.15 mm stainless tube can be sealed without slumping. Heat-treated features stay heat-treated even a few millimeters from the joint. Near-joint components (sensors, plastics, wire insulation, adhesive) do not have to be masked or removed before welding. Assemblies once joined last, after every other operation, can be welded mid-process without cooking earlier work.

When you're forced into it

Some parts cannot be welded any other way. A pacemaker case, a battery tab onto a live cell, a hairspring in a mechanical watch, a fine-mesh medical filter: the neighbors of the joint would not survive ordinary heat. Those parts drive the whole category.

The four micro-welding processes

Laser micro welding

A focused laser beam delivers energy directly into the joint through the surface. Beam waist can be tuned under half a millimeter, and pulse duration ranges from milliseconds to microseconds. The joint is autogenous: the two parent materials fuse into each other without added filler. That yields the smallest heat-affected zone in the field, the cleanest weld surface, and the best fit for hermetic seals on thin walls. The honest weak point is that laser welding needs the joint fit together already; it cannot fill a visible gap or add material to a worn surface. For the machine family that produces these welds, see laser micro welders.

Pulse arc (micro TIG)

Pulse arc uses a tungsten electrode and a rapidly pulsed low-current arc, with fine filler wire fed by hand or through a controller. Because filler wire is part of the process, you can bridge gaps, build up worn edges, and repair molds or dies where base metal has been ground away. That flexibility is why pulse arc lives in jewelry, dental lab, and mold-repair shops. The heat-affected zone is measurably wider than a laser weld, and the process carries ongoing consumables in tungsten electrodes and argon shielding gas. For the machine family, see pulse arc / micro TIG welders.

Resistance spot welding

Resistance spot fuses two overlapped parts by pushing a current pulse through the joint. Heat is generated inside the metal itself, at the interface between the two parts, by the metal's own electrical resistance. Because fusion happens inside the sandwich, the process is fast (under 20 ms per weld is common) and highly repeatable across a shift. The weak points are structural: current has to pass through both sides; the weld leaves a visible mark on both surfaces; and electrode dressing is a real ongoing workflow. Highly reflective, oxide-prone metals like aluminum are marginal for the same conductivity reasons. For the machine family, see resistance spot welders.

Laser marking (adjacent, not a joining process)

Laser marking uses lasers from the same wavelength family as fiber laser welding, but it is not a welding process. The beam is set to remove or oxidize a thin surface layer, leaving a permanent mark: a serial number, a logo, a data-matrix code. No metal is fused. Marking is included here only because buyers routinely confuse it with laser welding — the machines look alike, and both often share a production cell. A marking machine cannot weld; a laser welder can mark but with reduced quality. For the machine family, see laser marking machines.

Key concepts you need to understand the field

Heat-affected zone (HAZ)

The heat-affected zone is the ring of parent metal around the weld that got hot enough to change but not hot enough to melt. Grain structure shifts there and residual stress builds up. On thick structural steel the HAZ is a design consideration; on a micro part it is the difference between success and a ruined component, because it can extend into a bearing surface, a sensor housing, or a heat-treated zone.

Nugget formation

On resistance spot welds, the joint is called a nugget: a small lens of molten and then solidified material at the interface between the two sheets. A good nugget is symmetric, sits at the interface, and reaches the design diameter without breaking the outer surfaces. A bad nugget is off-center, expulsed (splashed sideways under too much current or too little force), or undersized. Quality is checked destructively by tearing the weld apart, or non-destructively by cross-section.

Autogenous vs filler-added joints

An autogenous weld fuses the two parent metals into each other with no added material; laser micro welding is autogenous by default. A filler-added joint uses a wire or rod of matching alloy; pulse arc is filler-added by default. The choice is driven by fit-up: if parts sit tightly with no gap, autogenous works; if there is a gap, wear, or a missing corner, filler is needed.

Pulse shape and duration

A weld pulse is not a single number. It has a ramp (how fast the energy climbs), a peak, a tail, and sometimes secondary pulses. Ramping softens the initial thermal shock; a long tail keeps the pool liquid a bit longer for degassing. Pulse shape is where two machines with the same headline wattage produce very different welds.

Shielding gas: why and when

Molten metal reacts with atmospheric oxygen and nitrogen. On plain carbon steel and most stainless spot-weld configurations, the reaction is mild enough to ignore. On titanium, reactive stainless, and many aerospace alloys, unshielded weld metal turns brittle within seconds. Argon shielding gas pushes atmosphere away from the pool until it solidifies.

Common misconceptions

"Micro welding is just small TIG"

No. Ordinary TIG at the low end of its range still runs continuously and delivers hundreds of joules per second. Micro welding (laser, pulse arc pulsed at millisecond scale, resistance spot) delivers pulses and then stops. Heat totals sit two orders of magnitude apart. A very-low-current TIG on a thin part gives an unstable arc and burn-through.

"A laser welder can do everything"

No. Laser is the most versatile of the four processes but has hard limits. It cannot bridge a gap larger than roughly the diameter of the beam without a filler-wire attachment. It is not the fastest choice on high-volume tab-and-terminal work; resistance spot is faster per weld on those jobs. And a plain laser welder cannot rebuild worn material without added filler.

"Resistance spot works on anything conductive"

No. Reflective, high-conductivity metals like aluminum are marginal on resistance spot because the current would rather flow through the electrode than through the joint, and oxide layers on aluminum add insulation exactly where fusion is wanted. Copper-to-copper is possible with the right setup but ships far more often as copper-to-nickel or copper-to-plated-steel, where the counterpart carries more of the heat.

"You don't need shielding gas for pulse arc"

Yes you do, on any reactive alloy. Pulse arc without argon coverage on titanium leaves a straw-yellow or blue weld surface, a visible sign of atmospheric contamination and brittleness. Even on stainless in some geometries, a small argon flow through the torch is what keeps the weld from oxidizing. Shielding is not optional on reactive metals; it is what saves the weld.

"Marking and welding are the same laser process"

No. Marking removes or oxidizes a thin surface layer; welding fuses material. The wavelength range overlaps for fiber lasers, which is where the confusion comes from, but the machine settings, focus geometry, and quality checks are entirely different jobs.

Is your job in the micro welding range?

Signals it probably is

• Parts under the size of a palm.
• Wall thickness under a millimeter, often under half.
• Heat-sensitive components (sensors, plastics, adhesives, pre-hardened features) within a few millimeters of the joint.
• A precision requirement on the joint itself: cosmetic weld surface, hermetic seal, controlled penetration depth.
• Small assemblies where distortion has to stay under a few thousandths of an inch.

Signals it probably isn't

• Structural load-bearing joints on thick sections.
• Ordinary automotive body work.
• Trailer frames, pipe stands, fabrication where a MIG or ordinary TIG can lay a large fillet in a single pass.

If the part is heavy, the wall is thick, and the joint has room to breathe, ordinary welding is faster and better suited. Micro welding on such a job is overqualified equipment doing the wrong work.

The honest test

The most reliable way to know whether your job fits is a real weld on your real material. Send a representative sample, have it welded by each candidate process, and inspect the result. For a walkthrough that maps a specific part to a specific process, see How to Choose a Micro Welder.

Frequently asked questions

What's the difference between micro welding and ordinary TIG?

Heat input scale. Ordinary TIG runs a continuous arc delivering hundreds to thousands of joules per second. Micro welding delivers discrete pulses (millisecond laser pulses, millisecond resistance-spot pulses, low-current pulsed arc bursts), each carrying joules or fractions of a joule. Below that scale, ordinary TIG loses control.

Which process is best for battery tabs?

Resistance spot is the historical answer and still the volume choice for nickel and nickel-plated steel tabs onto cylindrical cells. Laser welding is the fast-growing alternative on aluminum tabs, on prismatic pack terminals, and where cosmetic weld surface matters.

Can you weld dissimilar metals with micro welding?

Yes, within limits. Copper-to-nickel, stainless-to-titanium in controlled setups, and various coated-steel pairs are routine on the right process. Mismatched melting points and thermal conductivity make the weld harder, so dissimilar-metal joints benefit strongly from a sample weld before parameters are locked.

Does micro welding need shielding gas?

Depends on the process and the material. Resistance spot generally does not, because the joint sits inside the sandwich away from atmosphere. Pulse arc almost always does on reactive metals. Laser welding on titanium or reactive stainless usually does; on plain carbon steel or common nickel alloys, often not.

Is laser marking a kind of welding?

No. Laser marking removes or discolors a thin surface layer to leave a permanent mark; no metal is fused and no joint is made. The machines share a wavelength family with fiber laser welders, which is where the confusion comes from.