Battery busbar welding station (cell-to-busbar laser welding in module and pack lines)

01

Control the busbar-to-terminal fit-up and clamping

A Sanyo Electric patent on busbar welding explains why fit-up drives this station: when a gap opens between the busbar and the electrode terminals to be laser-welded, reliable and stable welding cannot be carried out, and in a battery system with a plurality of cells such gaps are very difficult to eliminate because of dimensional error in the cells and the busbar. [2]

The patented design guides each terminal's protruding portion into a cut-away in the busbar and leaves an exposure gap — preferably more than 1 mm, more preferably 2 mm or more — so that the inner edge is fillet-welded to the terminal face. It gives the welding width as, for example, 0.8 mm or more (preferably 1 mm or more, further preferably 1.2 mm or more) and 5 mm or less, and the welding-plate thickness as, for example, 0.3 mm or more and 2 mm or less, preferably up to 1.6 mm. [2]

Laserax's battery pack laser welding machine clamps each cell-to-busbar connection with 4 to 8 SCARA robots while the laser welds in parallel; the clamping tools give pressure feedback and motorised angle adjustment, and the clamping position is corrected from 3D-vision feedback. Laserax lists a typical weld-to-cell accuracy of ±100 µm with vision. [1]

Give the supplier the cell format and terminal geometry, busbar material, thickness and coating, the joint design (lap, fillet, through-hole), cell count and layout per module or pack, the cell-height and position tolerances you can hold, the line cycle time, how parts arrive (conveyor, AGV, pallet), and the weld acceptance tests you will run.

02

Size the laser source, optics and in-cycle weld monitoring

Laserax's product sheet lists a 2000 W single-mode continuous-wave ytterbium fiber laser at 1070 nm, described as typical for busbars under 2 mm, with 1000–6000 W single-mode, multi-mode and ring-core sources available. It welds nickel-plated steel, aluminium, copper and stainless steel; scanning-optics and 3D-vision fields of view are 400 × 400 mm or 650 × 650 mm, and typical welding speeds are 100 ms per cell (2 welds, 21xxx series), 150 ms per cell (46xx series) and 300 ms per prismatic pole. [1]

The same sheet states a typical power consumption of 27 kW with a 2000 W source and 40 kW with a 6000 W source, an operating range of 15–35 °C at under 70% humidity, and weld monitoring that analyses photodiode emissions and HD images to identify the defect type and trigger rework in the same station and cycle. [1] Editorial calculation: at the typical 100 ms per cylindrical cell, 1,000 cells take 1,000 × 0.1 s = 100 s of welding time, before clamping moves, part transfer and rework are added. [1]

Choi and co-authors' open-access review of tab-to-busbar welding in EV packs describes a laser welding set-up as a laser device, a welding head and a clamping fixture with shielding gas, and reports work on copper with multi-mode fiber lasers at 3–8 kW in which raising power beyond 4 kW altered the process limit, and helium shielding gave on average about 15% lower penetration depth and about 25% larger bead width than welding without shielding gas. [3] The review calls for closed-loop in-process control that compensates for variation in surface quality and gap fit-up. [3]

03

Parts of a cell-to-busbar laser welding station

04

Values to fix before quoting a busbar welding station

Current, voltage and electrode force in this list apply when the station uses resistance welding; for laser stations ask for laser power, clamp pressure and monitoring instead.

05

Describe the cells, busbars and line rate

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Cells: [format; terminal geometry; count and layout]
Busbar: [material; thickness; coating; joint design]
Process: [laser or resistance; weld width; acceptance tests]
Fit-up: [clamping concept; tolerances]
Line: [cycle time; part transport; MES]
Monitoring: [signals; rework; data retention]

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