Educational Resource
Understanding the precision joining technology that powers the electric vehicle revolution — from battery cells to power electronics.
Explore the TechnologyLaser beam welding (LBW) is a high-energy fusion welding process that uses a focused laser beam as the heat source to join materials with exceptional precision and speed.
A laser beam concentrates energy into an extremely small spot — often less than 0.5 mm in diameter — producing intense, localized heat that melts and fuses metal.
The process is computer-controlled and repeatable to micrometer accuracy, making it ideal for complex geometries and sensitive components.
LBW can achieve welding speeds of several meters per minute, enabling high-throughput industrial production at scale.
A high-power laser — typically a fiber laser, disk laser, or diode laser — generates a coherent beam of light. Fiber lasers are most common in e-mobility due to their efficiency and beam quality.
The beam is guided via optical fiber to a scan head or welding optic, where lenses focus it to a small spot on the workpiece surface. The spot size and focal position are precisely controlled.
At high intensities, the laser creates a keyhole — a vapor capillary surrounded by molten metal — enabling deep, narrow welds. At lower intensities, conduction mode produces shallow, smooth welds ideal for thin materials like battery foils.
As the laser moves on, the molten pool rapidly solidifies to form a strong, dense weld seam. The surrounding material is barely affected, preserving component integrity.
The interaction between the laser beam and the material changes fundamentally depending on the power density at the focal spot. This gives rise to three distinct welding regimes, each with different weld geometry, stability, and application range.
At low power densities, the laser energy is absorbed at the material surface and conducted inward as heat — no vaporization occurs. The melt pool is wide and shallow, producing a smooth, rounded weld bead with a low aspect ratio (width greater than depth).
Conduction mode is inherently stable and spatter-free, making it ideal for applications where surface quality matters and weld depth requirements are modest. It is the preferred mode for welding thin battery foils, current collector tabs, and cosmetic seams on battery housings.
In the transition regime, the power density is sufficient to cause partial vaporization, but the keyhole cannot be sustained stably. The weld alternates between conduction and keyhole behavior, resulting in a characteristic "nail-head" cross-section — wide at the top (conduction zone) with a narrow penetration spike below.
This mode is generally avoided in precision manufacturing because the instability leads to inconsistent weld depth, porosity, and unpredictable mechanical properties. Process windows in this regime are narrow and difficult to control. Most production processes are deliberately tuned to operate clearly in either conduction or keyhole mode.
Above a critical power density, the laser vaporizes the material faster than it can flow back, forming a vapor capillary — the keyhole — that penetrates deep into the workpiece. This keyhole is surrounded by a molten pool and acts as a blackbody absorber, capturing the laser energy with very high efficiency regardless of material reflectivity.
Keyhole mode produces deep, narrow welds with high aspect ratios — enabling full-penetration joints in thick sections that would require multiple passes with other processes. In e-mobility, it is used for battery housing seams, thick busbar joints, and motor components. The main challenges are keyhole collapse (leading to porosity) and spatter — both of which technologies like BrightLine Weld and beam oscillation aim to mitigate.
The spatial intensity distribution of a laser beam — its mode — fundamentally determines what kind of weld it produces. Understanding beam modes is key to selecting the right laser for each e-mobility application.
A Gaussian intensity profile with the highest possible beam quality (M² ≈ 1). Energy is concentrated at the beam center, enabling the smallest focus spot and highest intensity. Ideal for fine, deep-penetration welds and highly reflective materials like copper.
Multiple transverse modes superimposed, resulting in a broader, more uniform intensity profile and higher M² values. Enables higher average power delivery over a larger spot — suited for wider weld seams and thicker materials at high throughput.
M² (M-squared) describes how close a beam is to a perfect Gaussian (M²=1). BPP (Beam Parameter Product) is the product of beam waist radius and divergence angle — lower is better. These values determine how tightly a beam can be focused and how far from the optic it remains usable.
BrightLine Weld is TRUMPF's proprietary beam shaping technology that uses a specially designed fiber — with a central core and a surrounding ring fiber — to produce a composite beam with two independently controllable intensity zones: a focused central spot and a surrounding ring of lower intensity.
This dual-zone beam fundamentally changes the welding dynamics. The central core drives deep penetration, while the ring component acts as a preheating and post-heating zone around the melt pool. This stabilizes the keyhole, reduces spatter ejection, and suppresses pore formation — problems that are especially severe when welding copper.
Core + Ring beam profile
The optic is the interface between the laser source and the workpiece. Choosing the right optic determines spot size, working distance, flexibility, and process stability.
A collimating lens captures the diverging beam from the fiber and converts it to parallel light; a focusing lens then converges it to the required spot size at the focal plane. Fixed optics are robust, compact, and suited for high-power continuous welding. Focal length and working distance are set at design time. Common in battery housing sealing and busbar welding.
Galvanometer-driven mirrors deflect the beam rapidly across a working field without moving the workpiece or robot. Scan speeds of several meters per second enable oscillation welding, remote welding, and complex weld patterns. Scanlab, TRUMPF, and Precitec are leading suppliers of industrial scan heads used in e-mobility production.
Focal length sets the spot size and working distance. The collimation ratio (collimator focal length / focusing focal length) scales the fiber core image onto the workpiece. Protective glass shields expensive optics from spatter. Crossjet air curtains and spatter shields are standard in production environments.
The PFO (Programmable Focusing Optic) is TRUMPF's 3D remote laser welding scanner. Unlike standard 2D galvo scanners that only deflect the beam laterally, the PFO adds a dynamic focusing element that adjusts the focal position along the Z-axis in real time — enabling the laser to follow complex 3D component geometries at full scan speed.
In e-mobility, PFO systems are used for welding stator hairpins, battery contact elements, and 3D busbar geometries where a fixed focal plane would be insufficient. The system can be programmed to execute hundreds of individual weld spots or seams per second across a large working field, making it highly suited for high-volume EV production.
On-the-fly welding refers to laser welding performed while the workpiece is in continuous motion — the laser tracks and welds without stopping, eliminating idle time and dramatically increasing throughput.
In conventional laser welding, a robot or positioning system moves the part to the weld position, stops, welds, then moves on. Each stop-and-start cycle consumes time that does not add value. On-the-fly welding eliminates this entirely: the workpiece moves continuously — on a conveyor, rotary table, or along a robot path — while the laser (or a scanner) synchronizes with the motion and welds at the correct position and speed in real time.
The motion controller and laser controller must be tightly synchronized. The scanner or robot receives position data from the conveyor or motion system and compensates in real time, keeping the laser spot locked to the target joint even as it moves.
Robot-on-the-fly: The robot arm holding the welding optic moves simultaneously with the workpiece conveyor, welding while both are in motion. Requires coordinated motion planning between robot and conveyor controller.
Scanner-on-the-fly: A fixed galvo scanner tracks the moving workpiece within its working field. As the part passes through, the scanner deflects the beam to compensate for conveyor movement and executes the weld pattern. Much faster than robot motion, enabling very high cycle rates.
On-the-fly welding is used in battery cell contact welding on moving assembly lines, busbar joining on rotating battery module carriers, and stator hairpin welding where the stator indexes continuously through a scanner station.
Successful on-the-fly welding requires a real-time motion interface between conveyor and laser/scanner, precise encoder feedback, and a laser with fast power modulation response. Vision systems are often added for seam finding and position correction.
Synchronization errors cause weld position offset. At high speeds, the effective interaction time per spot is reduced, requiring higher peak power or optimized scan patterns. Joint gap variation on a moving part is harder to compensate than in a stopped fixture.
Electric vehicles demand joints that are electrically conductive, mechanically robust, hermetically sealed, and produced at scale. No other joining technology matches LBW across all these requirements.
Battery cells, busbars, hairpin windings, and power electronics involve materials like copper, aluminum, and nickel — often in very thin gauges and dissimilar combinations. These materials are notoriously difficult to weld with conventional methods.
Traditional resistance welding generates excessive heat and spatter. Ultrasonic welding is limited in joint geometry. Laser beam welding overcomes both — delivering clean, controlled joints with minimal heat input and no consumables.
A single EV battery pack may contain thousands of individual cell connections. LBW systems integrated with robotics and vision systems can produce and verify these connections at production rates impossible with manual or semi-automatic methods.
The concentrated energy input keeps the heat-affected zone (HAZ) extremely small, protecting thermally sensitive components like battery cells and electronics.
The laser never touches the workpiece, eliminating tool wear, contamination, and mechanical stress — critical for delicate EV components.
LBW can join copper to aluminum, nickel to steel, and other material combinations that are problematic for conventional processes — common requirements in battery and power electronics assemblies.
Laser welds can be made fully leak-tight, essential for sealing battery housings, cooling channels, and electrolyte-containing components.
LBW integrates naturally with robotic systems, vision-based seam tracking, and inline quality monitoring — enabling fully automated, high-volume production lines.
Unlike MIG/MAG or TIG welding, LBW requires no filler wire or electrodes, reducing material costs and eliminating contamination risks inside battery systems.
Connecting the positive and negative tabs of cylindrical, prismatic, or pouch cells to busbars or current collectors. Requires precise energy control to avoid damaging cell internals.
Welding copper and aluminum busbars that distribute current within battery modules. LBW achieves low electrical resistance joints with minimal cross-sectional distortion.
Hermetically sealing aluminum battery enclosures and cooling plates. A leak-tight weld is critical for safety and longevity of the battery system.
Joining the copper hairpin conductors in electric motor stators. The weld must be electrically sound and mechanically robust under thermal cycling.
Welding components in inverters, DC/DC converters, and onboard chargers, where precision and low thermal load are essential to protect sensitive semiconductors.
Joining small, precision components such as temperature sensors, current sensors, and high-voltage connectors used throughout the EV powertrain.
Reliable, defect-free welds in e-mobility production require more than good process parameters — they require real-time sensing. Sensors monitor the weld process, detect anomalies, and enable inline quality assurance at production speed.
Fast photodiodes measure optical emissions from the process zone — plasma plume radiation, back-reflected laser light, and thermal emission from the melt pool. Signal deviations indicate keyhole instability, pore formation, or surface contamination. Low cost and high speed make photodiodes the most common inline sensor in production LBW systems.
Pyrometers and IR cameras measure the temperature distribution of the melt pool and surrounding heat-affected zone. This gives insight into energy input consistency and can detect changes in material properties or fit-up. Camera-based pyrometry enables spatial temperature mapping rather than a single-point measurement.
Microphones (airborne) and accelerometers (structure-borne) detect the characteristic sounds of the welding process. Keyhole collapse, spattering, and crack formation each produce distinct acoustic signatures. Acoustic monitoring is particularly useful for detecting process instabilities that optical sensors may miss.
Coaxial or off-axis high-speed cameras (10,000–1,000,000 fps) capture the melt pool geometry, keyhole behavior, and spatter ejection in real time. Used primarily for process development and root cause analysis rather than inline production monitoring, due to the high data volumes involved.
Laser triangulation sensors and structured-light cameras scan the joint ahead of the welding spot to detect its exact position, gap width, and misalignment. This allows real-time correction of beam position — critical when welding long seams on battery housings or busbars where fixturing tolerances are limited.
Post-weld camera systems with machine learning classifiers inspect weld surface appearance — detecting cracks, undercut, excessive spatter, or missing welds. Combined with process sensor data, AI models can correlate surface appearance with internal weld quality, reducing the need for destructive cross-section testing.
OCT is an interferometric measurement technique that uses a low-coherence light source to measure distances with micrometer precision — even inside the keyhole of an active laser weld. A secondary measurement beam is directed coaxially into the process zone, and the reflected signal is analyzed to determine the instantaneous depth of the keyhole and, by extension, the weld penetration depth.
This is the most significant advance in LBW process monitoring in recent years. Previously, weld depth could only be verified destructively after welding. OCT makes it possible to monitor and control penetration depth in real time, enabling closed-loop depth control and 100% inline verification of full-penetration welds — a critical quality requirement for battery housing sealing.
As EV production scales globally, academic and industrial research is pushing laser beam welding to new levels of capability, reliability, and intelligence.
Copper's high reflectivity at infrared wavelengths causes inconsistent energy absorption with conventional fiber lasers. Research into green (515 nm) and blue (450 nm) lasers shows dramatically improved absorption, enabling stable, spatter-free copper welding — critical for busbar and hairpin connections.
Advanced optics — including ring-shaped beams, top-hat profiles, and dual-spot configurations — are being studied to control melt pool dynamics, reduce porosity, and suppress spatter in dissimilar metal welds. Beam shaping has become a key enabler for robust copper-aluminum joining.
Machine learning models trained on photodiode signals, high-speed camera data, and plasma plume emissions are being developed to detect weld defects in real time — without interrupting production. This enables 100% inline quality assurance at the speed of the laser.
Joining copper to aluminum, or nickel-coated steel to aluminum, generates intermetallic compounds at the interface that can embrittle the joint. Research focuses on laser parameter optimization, interlayer materials, and oscillation strategies to minimize these phases and maximize joint strength.
High-fidelity numerical simulations of the laser-material interaction — including fluid dynamics of the melt pool, keyhole behavior, and thermal gradients — are used to predict weld quality and accelerate process development without costly physical trials.
Picosecond and femtosecond pulse lasers are being explored for welding extremely thin foils and glass-to-metal joints (e.g., battery window feedthroughs). The ultrashort interaction time minimizes thermal damage, opening new possibilities for next-generation cell formats.
The LBW ecosystem spans laser source manufacturers, optics and system integrators. Here are the most significant suppliers active in the e-mobility segment.
One of the world's largest laser manufacturers. Key platforms for e-mobility: TruDisk (disk laser, high power, excellent beam quality) and TruFiber (fiber laser). Home of BrightLine Weld and PFO technology.
Pioneer and market leader in high-power fiber lasers. The YLS series covers a broad power range. IPG lasers are widely used in battery tab welding and busbar joining globally.
Formed from the merger of II-VI and Coherent, incorporating former Rofin laser technology. Offers a broad portfolio of fiber, disk, and diode lasers for e-mobility manufacturing.
Known for the Corona fiber laser platform, which uses a proprietary fiber architecture to enable real-time beam parameter control — adjusting spot size and beam profile during welding without hardware changes.
Specialist in high-power diode lasers. Diode lasers offer high wall-plug efficiency and a top-hat beam profile suited for heat conduction welding of thin materials and surface treatments.
Supplies diode laser bars, stacks, and modules used as pump sources in disk and fiber lasers, as well as direct-diode solutions for industrial welding applications.
Leading manufacturer of laser welding and cutting heads. The YW series and ProFocus optics are widely deployed in automotive and e-mobility production lines. Also offers inline process monitoring solutions.
World-leading manufacturer of galvanometer scan systems. The intelliSCAN and excelliSCAN series are standard in high-precision remote laser welding applications, including hairpin stator welding.
Specializes in fiber-coupled laser processing optics. The BIMO series of modular welding heads is widely used in automotive body-in-white and increasingly in e-mobility battery manufacturing.
TRUMPF's own PFO (Programmable Focusing Optic) 3D scanner system is tightly integrated with TruDisk and TruFiber sources, offering a fully matched laser + optic solution for complex 3D remote welding.