Although many North American auto manufacturers still use steel of various grades for the majority of the automobile’s frame construction, aluminum is now the second most used material in vehicles today. This lightweight metal is being integrated into more aspects of the automobile’s construction to help reduce fuel consumption. Beyond increase in fuel efficiency, lighter vehicles are designed to be faster, safer, and potentially more duplicatable than their bulkier predecessors. Find out the challenges the industry is facing incorporating aluminum into auto design and what joining processes are trending.
Aluminum and Steel Laser Welding
Aluminum and other metal composites are the front-runners in the race for fuel efficiency materials. Joining aluminum can prove to be a challenge as its metallurgic properties are remarkably different than the traditional king of automotive materials, steel. Steel’s melting point is approximately 1,500 degrees (Fahrenheit) higher than aluminum and the conductivity of each varies as well. This material migration is causing joining issues for both aluminum to aluminum joints as well as aluminum to steel.
Even though aluminum isn’t new to the automotive game, Ford pushed this lightweight metal into the spotlight. The 2015 Ford F150 was the first large-scale vehicle to use an all-aluminum body. Ford’s solution to this joining challenge was self-piercing rivets, adhesives, flow-drill screws, and laser welding. Their assembly line went through a massive retooling phase that included a switch from applying approximately 5,000 spot welds on the 2014 steel model, to 2,000 rivets on the 2015 truck.
These new aluminum bodies are lighter than their steel predecessors, but the joining rivets weigh more than welds. As auto manufacturing goes, there is a constant push for improved weight, strength, and safety.
GM spent two years developing a resistance spot welding technique to joining aluminum to steel. The Cadillac CT6 incorporated 11 materials to make the lightest vehicle in its class back in 2016. GM implemented a spot welding process that joined steel to aluminum. This production advancement allowed GM to avoid riveting, in turn reducing weight, cost, and parts. This was all done with minimal machinery changes.
Most recently BMW is testing counter-stand element welding for attaching aluminum to steel.
As the industry continues to explore joining processes, laser welding seems to be the prevalent technology. The AWS Welding Journal and this Fraunhofer USA study sites reasons laser is rising.
- Overcomes the thermal conductivity and melting temperature differences between aluminum and steel
- No drying time as with adhesives
- Lighter than rivets
- Stronger joints than spot welds
- Reduced cracking susceptibility when laser welding with filler material
- Fast and flexible joining process
Even though great advancements have been made, there are still metallurgical issues with joining dissimilar metals. David Havrilla of TRUMPF Inc. stated, “Lasers have demonstrated successful joining of aluminum to steel, but other challenges remain such as galvanic corrosion and differences in material elongation that can lead to wrinkling of visible panels”.
4 Important Laser Welding Advances
1. Real-time seam tracking
Because laser welds are typically smaller than arc welds, vision-based sensors are used to ensure laser welding heads are accurately aligned with the joints. Welding robots using re-programmed paths don't always produce sufficient seams. All major manufacturers have integrated these processes for efficiency and accuracy in mass production.
2. Gap bridging
Remote laser welding for body-in-white joints are ideally welded with a zero-gap between parts. But often door openings, roof beans, and under-bodies are more difficult to achieve a zero-gap. For these more difficult welding locations, the gaps between sheets can vary, causing problems while welding.
One study conducted by Florian Albert found that:
Thin steel sheet gaps, nearly up to the material thickness of the upper sheet, can be bridged. The welding position PA, PF, PG has less relevance regarding the weld seam formation and quality. A different picture can be seen with Aluminum fillet welds. In PA position it’s possible to bridge gaps up to 50…60 % of the thinnest sheet thickness by the usage of a gap-dependent beam oscillation strategy for aluminum. In PF or PG position, bridging is feasible when gaps are roughly 20…30 % of the thinner sheet thickness. Possible reasons for that are the lower viscosity of the Aluminum weld pool in comparison to steel as well as the surface tension of the molten puddle. When processing at upward or falling welding positions, when gap size increases, the molten aluminum has greater tendency to drop out of the weld seam.
Remote laser welding technology has evolved and can incorporate an automated gap bridging process used by triangulated lasers. "If there is a gap between the parts, automated bridging strategies by beam oscillation/or beam defocusing will be applied."
3. Beam oscillation
When laser welding thin aluminum, hot cracks and porosity are commonly reported issues. This study, Weldability of aluminum alloys for automotive applications, finds systems using oscillating laser produce higher quality welds vs. triple-spot welding techniques.
- Possible to achieve crack-free welds with both the oscillation- and triple-spot optics
- The oscillation welds show a deeper more uniform penetration profile
- The welds produced with oscillation optics received a higher ultimate tensile strength
4. Finishing wheels
In order to achieve smooth paintable seams, finishing wheels adapted to laser welding are the way to go. Cotton Fiber Wheels can be manufactured to fit seems perfectly. In addition these durable wheel will not need to be replaced often and thus saves time, effort, and money.
Integrate these tools to optimize laser welding and see measurable improvements in product durability and quality and manufacturing efficiency.
Interested in laser brazing? Download our guide: The Future of Automotive Assembly is Laser Brazing .