Success Strategies for Laser Welding Copper to Aluminum Tabs

A Tier-1 supplier of electric vehicle battery packs in Michigan was producing 25,000 battery modules per month for an electric SUV. Each module required 24 welds joining 0.3 mm thick copper tabs to 0.4 mm thick aluminum busbars—a total of 600,000 welds per month. The company’s existing 3 kW multi-mode fiber laser produced inconsistent welds plagued by two defects: incomplete fusion due to copper’s high reflectivity at 1,070 nm, and centerline cracks in the weld nugget caused by brittle copper-aluminum intermetallic compounds (IMCs). The scrap rate for cracked or porous welds was 18%, costing $216,000 annually in scrapped material and rework.

The solution was a YIHAI LASER welding cell integrating a 4 kW single-mode fiber laser, a galvo scanner head with beam oscillation capability, and the HypWelding control system preloaded with a copper-to-aluminum parameter library. The single-mode beam’s high power density overcame copper’s reflectivity and reliably initiated a stable keyhole. The beam oscillation technique—wobbling the laser spot at 300 Hz in a 0.4 mm circle—stirred the molten pool, disrupted IMC growth, and prevented cracking. Scrap fell to 0.3%, cycle time per weld dropped from 1.5 seconds to 0.8 seconds, and the total annual cost of welding was reduced by $312,000. The $110,000 machine investment was recovered in 3.5 months.

The Pre-Upgrade Baseline: Cracking and Reflectivity Failures

The battery pack consisted of 96 lithium-ion pouch cells per module, with each cell’s 0.3 mm thick, 15 mm wide copper tab laser-welded to a 0.4 mm thick, 30 mm wide aluminum busbar. The weld was a lap joint, 10 mm long, requiring full penetration into the aluminum with a minimum nugget width of 1.5 mm and a shear strength exceeding 80 N. The copper and aluminum surfaces were bare (no plating), with a joint gap of less than 0.1 mm.

The existing process used a 3 kW multi-mode fiber laser (BPP ~2 mm·mrad) with a fixed focus head, argon shield gas, and a constant-power continuous-wave (CW) profile. The parameters were: power 2.8 kW, welding speed 600 mm/min, spot diameter 0.15 mm. The multi-mode beam’s lower power density (approximately 4 × 10⁶ W/cm²) struggled to couple into the highly reflective copper surface. The coupling was inconsistent, leading to intermittent melting and partial penetration. When the keyhole did form, the direct fusion of copper and aluminum generated a thick layer of brittle IMCs (CuAl₂ and Cu₉Al₄) along the weld centerline. The IMC layer, measured at 5–15 µm in cross-section, cracked under the thermal stress of solidification and during the module’s subsequent vibration testing. Electrical resistance across the cracked joints was elevated by 20–50%, causing hot spots during battery cycling and posing a fire risk.

Every weld was visually inspected and pull-tested on a sampling basis. Failed welds required the entire module to be scrapped, as re-welding was not permitted by the customer’s specification. The monthly scrap rate of 18% (108,000 bad welds, affecting 4,500 modules) translated to $18,000 per month in scrapped materials and labor. The constant threat of field failures also delayed the customer’s vehicle launch.

Monthly operating cost of the pre-upgrade process (600,000 welds):

Cost Element	Monthly Total
Welding machine operator labor (2 operators × $26/hr × 160 hrs)	$8,320
Scrap material cost (4,500 modules/month, $42/module)	$189,000
Rework/disposal labor (for scrapped modules)	$7,200
Argon shield gas (cylinders)	$1,800
Laser consumables (protective windows, nozzles)	$650
Total Monthly Cost	$206,970

The scrap cost alone was $2.27 million annually. The problem was clear: the multi-mode laser and the static welding parameters were incapable of reliably welding copper to aluminum.

---

Selection Criteria

The company evaluated three laser-based solutions: a green-wavelength (532 nm) laser to increase copper absorption, a dual-beam system that preheated the copper, and a single-mode fiber laser with beam oscillation. The selection criteria were:

1. Weld consistency (>99.5% first-pass yield) on 0.3 mm Cu to 0.4 mm Al without cracking.
2. Cycle time <1 second per weld to meet the production takt time of 600,000 welds per month on two shifts.
3. Intermetallic layer thickness <3 µm, as per the customer’s fracture toughness specification.
4. Minimal reflectivity-related instability, even with slight variations in copper surface oxidation.
5. Preloaded welding parameters to eliminate lengthy process development.

The green laser was rejected because of its high capital cost ($300,000+) and limited power availability for high-speed welding. The dual-beam approach added complexity. The YIHAI LASER 4 kW single-mode fiber laser system with a galvo scanner and HypWelding control was selected. The single-mode beam (BPP <0.4 mm·mrad) produced a power density of over 5 × 10⁷ W/cm² at the 50 µm spot, easily overcoming copper’s reflectivity and forming a stable keyhole within 0.1 ms. The galvo scanner allowed the beam to be oscillated in a circular pattern at frequencies up to 1,000 Hz, which stirred the molten pool and inhibited the growth of continuous IMC layers. The HypWelding controller included a dedicated “Cu-Al Tab Welding” parameter set, preloaded and validated on sample parts at YIHAI LASER’s application laboratory.

---

The New Process: Single-Mode Laser with Beam Oscillation

The YIHAI LASER cell was installed in March 2026. It featured a 4 kW IPG single-mode fiber laser, a 2D galvo scanner (aperture 30 mm), an f-theta lens (focal length 250 mm, scan field 150 mm × 150 mm), and a 4-axis part fixture that presented each module to the scanner. The welding sequence was fully automated: a vision system located the tabs, the scanner positioned the beam, and the “Cu-Al Tab Weld” program executed.

Parameter comparison: old process vs. new YIHAI LASER process (lap joint, 0.3 mm Cu to 0.4 mm Al):

Parameter	Old Multi-Mode Laser (CW)	YIHAI LASER Single-Mode + Oscillation
Laser power	2.8 kW	3.5 kW
Power density at spot	~4 × 10⁶ W/cm²	~7 × 10⁷ W/cm²
Welding speed	600 mm/min (10 mm/s)	750 mm/min (12.5 mm/s) (beam travel)
Spot diameter	150 µm	50 µm
Beam oscillation	None	Circular, 0.4 mm diameter, 300 Hz
Shield gas	Argon, 15 L/min coaxial	Argon, 12 L/min cross-jet
Cycle time per weld	1.5 s (incl. positioning)	0.8 s (incl. scanner move)
IMC thickness (CuAl₂)	5–15 µm, continuous	<2 µm, fragmented
Weld shear strength (avg.)	65 N (high variability)	110 N (tight distribution)
Porosity	8–15% (keyhole collapse)	<0.5%
Scrap rate	18%	0.3%

The beam oscillation was the critical innovation. As the laser spot traced a 0.4 mm diameter circle at 300 Hz, it stirred the molten pool. This turbulence broke up the growing IMC dendrites and distributed them as fine, isolated particles within the weld nugget, rather than allowing them to form a continuous brittle layer along the centerline. The result was a ductile weld with a fracture mode that occurred in the aluminum base metal, not through the weld interface. The single-mode beam’s high power density and the scanner’s rapid beam positioning also eliminated the reflectivity problem; the keyhole initiated instantly and remained stable throughout the weld.

The galvo scanner further reduced cycle time. After each weld, the beam jumped to the next tab location in under 10 ms, eliminating the need to move the heavy workpiece or a robot arm. The 24 welds on a module were completed in 19.2 seconds of arc-on time, with the total module cycle (including loading/unloading) at 35 seconds.

---

Quantified Results: Scrap Slashed, Strength Up 69%

The YIHAI LASER cell processed the full monthly volume of 25,000 modules (600,000 welds) starting in April 2026. The results over the first quarter were definitive.

Monthly cost comparison (for 25,000 modules):

Cost Element	Old Multi-Mode Laser	YIHAI LASER Single-Mode + Oscillation	Change
Welding labor (operators)	$8,320 (2 ops)	$4,160 (1 op, automated)	–$4,160
Scrap material (modules)	$189,000 (4,500 mod.)	$3,150 (75 mod.)	–$185,850
Rework/disposal labor	$7,200	$300	–$6,900
Shield gas	$1,800 (Ar)	$1,200 (Ar, reduced flow)	–$600
Laser consumables	$650	$420	–$230
Total Monthly Cost	$206,970	$9,230	–$197,740

The annual savings of $2.37 million were dominated by the elimination of scrap. The weld strength increase to an average of 110 N provided a 38% margin over the 80 N specification, eliminating the risk of field failures and securing the customer’s approval for the vehicle launch.

Return on Investment:

• Capital cost (YIHAI LASER 4 kW single-mode + galvo scanner cell, installed with tooling and training): $110,000
• Monthly net savings: $197,740
• Payback period: $110,000 ÷ $197,740 = 0.56 months (approximately 17 days)

The immediate payback was a direct consequence of the 18% to 0.3% scrap reduction. The machine’s speed and quality also allowed the supplier to accept an additional 5,000 modules per month from a second customer, generating $600,000 in new monthly revenue.

---

Implementation and Operator Transition

The YIHAI LASER cell was integrated into the existing production line over a weekend. The preloaded “Cu-Al Tab Weld” parameter set required no adjustment; the first production welds passed pull and section tests. The operators, previously tending the multi-mode laser, completed a three-day training program on the galvo scanner interface and the HypWelding controller. The automated vision and positioning system eliminated the manual alignment that had been a source of variability. The machine’s built-in weld monitoring, which recorded power, position, and back-reflection for every weld, provided full traceability—a requirement for automotive PPAP documentation.

---

Conclusion

The laser welding of copper to aluminum for EV battery tabs is a microcosm of the challenges inherent in dissimilar metal joining: high reflectivity, rapid intermetallic formation, and zero tolerance for field failure. The YIHAI LASER single-mode fiber laser with beam oscillation addressed all three simultaneously. The high power density overcame copper’s reflectivity, the oscillation broke up brittle IMCs, and the galvo scanner delivered sub-second cycle times with automotive-grade traceability. The 18% scrap rate that had plagued the launch was eliminated, and the $110,000 investment was recovered in under three weeks. For any battery pack manufacturer wrestling with copper-aluminum weld cracking, the combination of single-mode fiber laser power and controlled beam oscillation is not an option—it is the production-proven path to a zero-defect process.

Read more: The Impossible Join: Laser Welding Copper to Aluminum for EV Battery Packs

Frequently Asked Questions

Why does laser welding copper to aluminum cause cracking?
Copper and aluminum form brittle intermetallic compounds (CuAl₂ and Cu₉Al₄) when directly fused. These IMCs grow as a continuous layer at the weld centerline during solidification and crack under thermal stress. Beam oscillation (wobbling the laser spot) stirs the molten pool, breaking up the IMC layer into fine, dispersed particles, preventing crack propagation.

How does a single-mode fiber laser overcome copper’s high reflectivity?
A single-mode fiber laser (BPP <0.4 mm·mrad) can focus to a spot of 50 µm or less, achieving a power density over 5 × 10⁷ W/cm². This intensity rapidly heats the copper surface, initiating a keyhole and transitioning absorption to near 100% via multiple internal reflections, regardless of the initial room-temperature reflectivity.

What is the typical payback period for a laser welding system for EV battery tabs?
In this case study, the $110,000 investment was recovered in 17 days, driven by the elimination of an 18% scrap rate. Even in applications with lower scrap, the productivity gains and quality improvements typically yield a payback of under 6 months.

Does YIHAI LASER provide specific parameters for welding copper to aluminum?
Yes. YIHAI LASER’s HypWelding controller includes a preloaded ‘Cu-Al Tab Welding’ parameter set, validated for lap joints between 0.2–0.5 mm copper and 0.3–0.8 mm aluminum. The parameters include power, speed, beam oscillation pattern, and shield gas flow, and are ready for immediate production use.

---

References

1. YIHAI LASER, Cu-Al Battery Tab Welding Parameter Library, 2026.
2. IPG Photonics, YLR-Series 4 kW Single-Mode Fiber Laser Datasheet, 2025.
3. HypWelding Control System User Manual, YIHAI LASER, 2025.
4. Braunovic, M., Konchits, V.V., Myshkin, N.K., Electrical Contacts: Fundamentals, Applications and Technology, CRC Press, 2006, Chapter 6 (Intermetallic Compounds in Aluminum-Copper Joints).
5. ISO 13919-1:2019, Electron and laser-beam welded joints — Guidance on quality levels for imperfections — Part 1: Steel (applicable joint quality metrics).
6. SAE J2464, Electric and Hybrid Electric Vehicle Rechargeable Energy Storage System (RESS) Safety and Abuse Testing.

Other Case:

How a Kitchenware Plant Replaced 5 TIG Welder Positions