But "laser welding" isn't one process. It's a family of techniques, and the two most common are laser seam welding and laser spot welding. Both use focused light energy to fuse metal. Beyond that, they serve very different purposes.
Choosing between them isn't a minor engineering detail. It affects joint strength, whether a part holds a hermetic seal, how fast your line runs, and how much your tooling costs. Get it wrong, and you're looking at rework, leak failures, or a bottleneck nobody planned for.
This guide breaks down how these two processes differ and how to decide which one belongs on your production line.
TL;DR: Seam vs. Spot Welding
- Laser seam welding: continuous, often hermetic joint via overlapping pulses or a continuous beam.
- Laser spot welding: discrete single-point welds for localized attachment with minimal heat input.
- Core difference: continuous connection vs. intermittent connection.
- Best fit: seam for structural/sealing work (battery trays, implants); spot for electronics, tacking, and small assemblies.
Laser Seam Welding vs. Spot Welding: A Quick Comparison
Both processes share a laser source, but the similarities mostly end there. Here's how they stack up side by side:
| Parameter | Laser Seam Welding | Laser Spot Welding |
|---|---|---|
| Weld Type | Continuous, linear, non-porous joint | Discrete, single-point weld nuggets |
| Strength & Sealing | High structural integrity; excellent for hermetic seals | Localized strength only; not suitable for sealing |
| Speed | Fast along the full path: meters per minute | Milliseconds per spot; throughput depends on spot count |
| Heat Affected Zone (HAZ) | Continuous but narrow HAZ along the entire seam | Minimal, isolated HAZ confined to each spot |
| Gap Tolerance | Very low; requires tight fit-up or seam tracking | More forgiving for lap joints |
That last row matters more than it looks. Laser beam diameters typically run just 50 to 900 microns, so positional error needs to stay under half the beam width.
Gaps generally can't exceed 10% of the thinnest material at the joint, according to The Fabricator's guidance on laser welding fundamentals. Miss that tolerance, and the beam simply doesn't engage both sides of the joint.
What Is Laser Seam Welding?
Laser seam welding uses a focused beam to create a continuous, fused joint between two workpieces. Either the part moves under a stationary laser, or the laser head travels along the seam. Either way, the result is a single, unbroken line of fusion rather than a series of separate points.
There are two operational modes, and picking the right one depends on the material and the job.
Conduction Mode
Conduction mode is the lower-power option. Energy enters the material through heat conduction. The mating surfaces melt and merge, and the joint cools into a smooth, cosmetically clean weld. Weld depth typically runs from a few tenths of a millimeter up to about 1 mm: shallow, but wide and controlled. This makes it a natural fit for hermetic sealing on thin-walled parts like medical device housings.
Keyhole Mode
Keyhole mode is a different animal entirely. Power density climbs to roughly 1 MW/cm², high enough that the laser vaporizes material and creates a narrow vapor cavity (the "keyhole") that lets the beam penetrate deep into the joint. Depth can reach up to 10 times the weld width, with some deep-penetration processes hitting 25 mm. That's the mode structural applications need.
Core benefits of laser seam welding:
- Strong, continuous, leak-proof joints
- High welding speeds that boost throughput
- Clean, aesthetic welds with minimal spatter
Where Laser Seam Welding Gets Used
- Automotive: Gas-tight seams on EV battery trays, body-in-white components, and roof panels
- Medical: Helium-tight hermetic seals on pacemakers, defibrillators, and other implantables without harming heat-sensitive internals
- Aerospace & Industrial: Sensors, electronic packages, and heat exchangers that need continuous, defect-free joints
What Is Laser Spot Welding?
Laser spot welding is a non-contact process that fires a short, high-energy pulse to create a single weld nugget at one specific point. The pulse melts a small volume of material on both workpieces at once. That molten pool solidifies almost instantly, forming a metallurgical bond exactly where you need it and nowhere else.
A typical pulsed weld runs 0.5 to 5 joules, with pulse widths of 1 to 5 milliseconds and spot diameters around 200 to 400 microns, based on Coherent's published welding parameters. Some systems push much further: TRUMPF's TruPulse platform, for example, offers up to 120 joules per pulse. Whatever the power level, each pulse is brief, tightly focused, and finished in milliseconds.
Core benefits of laser spot welding:
- Extremely low, localized heat input that protects nearby sensitive components
- Cycle times often measured in milliseconds
- High precision and repeatability, ideal for automated micro-manufacturing
Where Laser Spot Welding Gets Used
- Electronics and semiconductors: attaching contacts, board-level joints, and battery tabs
- Medical devices: fine-wire joints, delicate instruments, and tack welds on implant electrode leads
- Automotive: tacking parts before a seam weld, plus small brackets and fasteners
Key Factors for Choosing the Right Laser Welding Process
Once you understand what each process does, the decision usually comes down to five practical factors.
Joint Requirements: Strength vs. Sealing
Ask first whether you need a structurally sound, continuous seal or a simple, localized attachment. An EV battery tray needs a seam weld to stay gas-tight. The terminal bolted onto that same tray only needs a spot weld.
Part Geometry and Material Thickness
Thicker, structural materials generally call for keyhole seam welding to get sufficient penetration. Thin foils, fine wires, and delicate assemblies are classic spot welding territory. The process was practically built for them.
Production Volume and Speed
For one long, continuous joint, seam welding wins on throughput every time. But if your part needs dozens of scattered attachment points instead of one continuous line, a high-speed spot welding system can outperform seam welding on total cycle time.
Heat Sensitivity of Components
If the weld sits near heat-sensitive electronics, sensors, or glass-to-metal seals, spot welding's isolated heat input is often the only workable option. There's no room for a continuous heat-affected zone (HAZ) next to a component that can't take extra heat.
Part Fit-Up and Fixturing Costs
Seam welding demands tight fit-up (minimal gaps, precise alignment), which can mean more expensive fixturing or a dedicated seam tracking system. Spot welding, particularly on lap joints, tolerates more positional variance and generally costs less to fixture.
The Role of Automation Integration in Laser Welding Success
Picking the right welding process is step one. Making it work reliably at production speed is a different challenge entirely — and it's usually the harder one.
Production-ready automation has to solve several problems at once:
- Precise part fixturing that holds tolerances tight enough for the laser to hit its mark every time
- Robotic path programming that handles either a continuous seam trajectory or dozens of discrete spot locations without drift
- In-line quality control, typically vision-based, that catches a bad weld before the part moves downstream
This is where an integration partner earns its keep. GLOBAL Automation Technologies builds robotic welding cells around these requirements: custom fixture design, servo positioning, and vision systems for seam location, adaptive path correction, and weld quality verification. Each cell is engineered around the part geometry in front of it.
GLOBAL keeps that work connected after launch. The same organization that designs and commissions the cell (running on FANUC platforms as a Level 5 FANUC Authorized System Integrator) also supplies, through its technical staffing, the controls engineers, robot programmers, and technicians who run it. Staffed engineers already know the architecture of a GLOBAL-built system, which cuts ramp-up time on high-precision jobs where consistency can’t slip.
Whether the application calls for a high-speed structural seam or a high-precision spot weld near sensitive electronics, the automation strategy behind it determines whether the process delivers on the shop floor, not just on paper.
Frequently Asked Questions
What is the main difference between laser spot and seam welding?
Seam welding creates a continuous, line-based joint built for sealing and structural strength. Spot welding creates discrete, point-based connections for localized attachment.
Is laser seam welding always stronger than spot welding?
A continuous seam distributes load across a larger area, making it the stronger choice for structural parts. That said, a spot weld provides plenty of strength for its intended job: localized joining, not load-bearing structure.
How thick of a material can laser welding handle?
It depends on power and mode. Keyhole seam welding can join materials several millimeters thick, with some deep-penetration processes reaching 25 mm. Spot welding is typically reserved for thinner foils and sheets.
Which industries typically use laser spot welding?
Electronics, battery manufacturing (especially tab welding), and medical device assembly rely on it most, since these applications need precise, low-heat joins on small or sensitive components.
Can one robotic system perform both spot and seam welding?
Yes, with the right laser source, optics, and programming. A flexible automation cell can switch between continuous and pulsed modes depending on the task at hand.
Why is part fit-up so critical for laser welding?
The laser's beam is extremely narrow, often under a millimeter. For seam welding, even a small gap can cause the beam to miss the joint entirely or fail to bridge the material, resulting in a weak or incomplete weld.
