What Is Micro Welding? Definition, Processes, and Applications 

1. Percussion Welding (Capacitor Discharge)

Percussion welding stores electrical energy in a capacitor bank, then releases it as a brief arc across a gap between two workpieces. The arc melts both surfaces in 1-5 milliseconds, and the pieces are driven together in a percussive impact that forges the molten surfaces into a molecular bond.

• Heat-affected zone: Near zero — measured in microns, not millimeters
• Cycle time: Under 3 milliseconds for most materials
• Wire range: 0.001" to 0.040" diameter
• Key advantage: Joins dissimilar metals (copper to tungsten, nickel to tantalum, aluminum to steel) that cannot be fusion-welded by other processes
• No consumables: No filler wire, no flux, no shielding gas
• Typical applications: Thermocouple junctions, battery tabs, medical device leads, aerospace sensor assemblies, heater element terminations

2. Laser Micro Welding

A focused laser beam (typically Nd:YAG or fiber laser) delivers energy to melt a small area of the workpiece. The beam can be pulsed or continuous, and the spot size can be as small as 50 microns.

• Heat-affected zone: Small but present — typically 0.1-0.5 mm depending on power and pulse duration
• Key advantage: Non-contact process, highly automatable, works on thin sheet and foil
• Limitation: Reflective metals (copper, gold, aluminum) require specialized wavelengths. Dissimilar metals are difficult due to different melting points and absorption rates
• Typical applications: Hermetic sealing, battery can welding, implantable medical device enclosures

3. Resistance Micro Welding (Micro Spot Welding)

Current passes through the workpieces between two electrodes. Resistance at the interface generates heat, creating a weld nugget. Micro resistance welding uses lower currents and shorter weld times than standard spot welding.

• Heat-affected zone: Moderate — the area around the nugget is thermally affected
• Key advantage: Fast cycle time, easily automated, well-established process
• Limitation: Requires materials with sufficient electrical resistance. Electrode wear affects consistency. Difficult with dissimilar metals of very different resistivities
• Typical applications: Battery tab attachment, wire mesh, orthodontic brackets

4. Micro TIG (GTAW) Welding

A miniaturized version of gas tungsten arc welding that uses low amperage (often under 5 amps) to produce a small, controllable arc for precision joining.

• Heat-affected zone: Larger than other micro processes — the sustained arc transfers more heat
• Key advantage: Highly skilled operators can achieve excellent results on complex geometries. Familiar to most welding shops
• Limitation: Requires shielding gas, more operator skill than automated processes, slower cycle time
• Typical applications: Medical tubing, surgical instruments, thin-wall stainless steel assemblies

5. Ultrasonic Welding

High-frequency mechanical vibrations (20-40 kHz) create friction between two surfaces pressed together, generating enough heat at the interface to form a solid-state bond without melting the base material.

• Heat-affected zone: Minimal — the process operates below the melting point
• Key advantage: Works well on plastics, thin foils, and aluminum. No electrical arc or external heat source
• Limitation: Limited to lap joints and relatively thin materials. Not suitable for wire-to-wire or pin-to-plate configurations
• Typical applications: Plastic medical device assemblies, aluminum foil battery connections, automotive wire harnesses

6. Electron Beam Micro Welding

A focused beam of high-velocity electrons delivers concentrated energy to the joint in a vacuum chamber. The energy density is extremely high, allowing deep, narrow welds.

• Heat-affected zone: Very small relative to weld depth
• Key advantage: Deepest penetration of any micro welding process. Works on refractory metals
• Limitation: Requires vacuum chamber. High equipment cost. Not practical for production-floor use
• Typical applications: Aerospace turbine components, nuclear fuel assemblies, high-value hermetic seals

No single micro welding process is best for all applications. The decision depends on:

• Material pair: Dissimilar metals favor percussion welding. Similar metals with good thermal properties work well with laser or resistance welding.
• Joint geometry: Wire-to-wire and wire-to-pin joints favor percussion welding. Sheet-to-sheet lap joints favor resistance or ultrasonic welding. Complex 3D paths favor laser welding.
• HAZ tolerance: If the surrounding material cannot accept any thermal damage (e.g., thermocouple wire, heat-sensitive electronics), percussion welding's sub-3ms cycle is the safest option.
• Production volume: All processes can be automated. Resistance and ultrasonic welding typically have the fastest cycle times for high-volume production.
• Budget: Percussion and resistance welders have lower capital costs than laser or electron beam systems.

The term "micro welding" generally refers to welds where the joint cross-section, wire diameter, or sheet thickness is below approximately 1 mm. At this scale:

• Conventional welding heat input would destroy or distort the workpiece
• Standard fixturing cannot hold parts with the required precision
• Visual inspection requires magnification
• Process parameters must be controlled to single-digit volts and millisecond timing

Common materials at this scale include fine thermocouple wire (Type K, J, T pairs as small as 0.001" diameter), medical device sensor leads, electronic assembly wire, battery interconnects, and aerospace strain gauge connections.

Most micro welding processes work best when joining the same metal to itself. The challenge comes when you need to join two different metals — copper to tungsten, nickel to tantalum, aluminum to steel — where different melting points, thermal conductivities, and coefficients of thermal expansion make fusion welding unreliable.

Percussion welding solves this by completing the entire melt-and-forge cycle in under 3 milliseconds. The arc melts a thin layer on both surfaces simultaneously, and the percussive impact forges them together before the heat can conduct into the base material. The result is a molecular bond with full electrical conductivity and near-zero heat-affected zone.

MTI Micro Welding has published verified weld schedules for over 60 dissimilar metal combinations, including specific voltage, timing, capacitance, and pulse settings for each pair. View the complete weld schedule database.