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Written by Bill Visnic
General Motors in ready to pull the trigger on potentially game-changing manufacturing process to spot weld steel to aluminum. In a careful start for the patented process, slated for launch within months at GM"s assembly plant in Hamtramck, MI, near Detroit, the advanced spot welding eliminates rivets that join an aluminum bracket to a steel framework to form part of the seatback for the Cadillac CT6 fullsize sedan. Engineers claim GM"s steel-to-aluminum welding will be an industry first. If all goes according to plan with the seatback frame as the first production-line component joined by the new technique, GM intends to expand the process to the hood of the CT6, a car that currently represents the company"s most aggressive example of multi-material construction. A specially-designed ridged electrode for the welding-gun tip is a key component of the system, said Blair E Carlson, lightweight material processing lab group manager at GM Research & Development, but in all, there are 19 patents covering hardware and controls for the process. The advanced electrode helps to alleviate the physical-properties issues that to now have stymied steel-to-aluminum welding, including the 900 C difference in melting point of the two materials, formation of oxides on the aluminum component that compromise weld integrity and the tendency for a "glassy" layer to form between the two disparate materials, causing brittleness of the weld. Carlson said cycle time before the welding-gun tip needs to be dressed currently is about 20 welds and the goal is to move the cycle into the hundreds this as part of the GM research unit"s mandate for the new welding process to minimize added cost, enhance assembly-plant tooling flexibility for mixed-material vehicles and eventually eliminate altogether the need to rivet steel and aluminum. Once the mixed-material welding of the CT6 seatback is up to speed, engineers are eying the car"s hood with the intention of welding the pedestrian-impact steel reinforcement to the hood"s aluminum "inner," eliminating the scores of rivets currently used to join the two pieces, Carlson said. Advanced joining techniques for the CT6, which employs 11 different materials in the body structure, already have eliminated more than 1400 rivets, all of which, although individually inconsequential, add incremental weight and cost; GM estimates the new welding process could eliminate as much as ten pounds of rivets on some vehicles. Dual-beam lasers, Scotty<br /> The news of GM"s imminent deployment of the steel-to-aluminum spot-welding process came at a media event at which engineers also provided updates of other advanced-joining techniques the company currently employs, including a refinement to its aluminum-to-aluminum laser welding: a new, dual-beam laser reduces "spatter," providing a better overall surface finish and eliminating a process formerly required to clean the spatter from the surface. Another improvement: a redesigned aperture plate that controls reflection on the laser welder. The previous aperture plate had to be replaced after 30 vehicles moved through the body shop. With a more-optimized shape that came at almost no cost, the upgraded aperture plate has been used for more than 3000 vehicles and remains in service, Carlson said. Summarizing recent whole-vehicle weight reductions, GM said that for seven recently introduced models, lightweighting measures have chopped a total of 2480 lb (1125 kg), including a 700-lb (318 kg) reduction for the 2017 GMC Acadia and 400 lb (181 kg)for the 2016 Chevrolet Camaro. The aggregate savings delivers a CO2-equivalent reduction of 137,000 metric tons, GM calculated.
Date written: 19-May-2016 10:14 EDT
More of this article on the SAE International Website
ID: 3495
General Motors in ready to pull the trigger on potentially game-changing manufacturing process to spot weld steel to aluminum. In a careful start for the patented process, slated for launch within months at GM"s assembly plant in Hamtramck, MI, near Detroit, the advanced spot welding eliminates rivets that join an aluminum bracket to a steel framework to form part of the seatback for the Cadillac CT6 fullsize sedan. Engineers claim GM"s steel-to-aluminum welding will be an industry first. If all goes according to plan with the seatback frame as the first production-line component joined by the new technique, GM intends to expand the process to the hood of the CT6, a car that currently represents the company"s most aggressive example of multi-material construction. A specially-designed ridged electrode for the welding-gun tip is a key component of the system, said Blair E Carlson, lightweight material processing lab group manager at GM Research & Development, but in all, there are 19 patents covering hardware and controls for the process. The advanced electrode helps to alleviate the physical-properties issues that to now have stymied steel-to-aluminum welding, including the 900 C difference in melting point of the two materials, formation of oxides on the aluminum component that compromise weld integrity and the tendency for a "glassy" layer to form between the two disparate materials, causing brittleness of the weld. Carlson said cycle time before the welding-gun tip needs to be dressed currently is about 20 welds and the goal is to move the cycle into the hundreds this as part of the GM research unit"s mandate for the new welding process to minimize added cost, enhance assembly-plant tooling flexibility for mixed-material vehicles and eventually eliminate altogether the need to rivet steel and aluminum. Once the mixed-material welding of the CT6 seatback is up to speed, engineers are eying the car"s hood with the intention of welding the pedestrian-impact steel reinforcement to the hood"s aluminum "inner," eliminating the scores of rivets currently used to join the two pieces, Carlson said. Advanced joining techniques for the CT6, which employs 11 different materials in the body structure, already have eliminated more than 1400 rivets, all of which, although individually inconsequential, add incremental weight and cost; GM estimates the new welding process could eliminate as much as ten pounds of rivets on some vehicles. Dual-beam lasers, Scotty<br /> The news of GM"s imminent deployment of the steel-to-aluminum spot-welding process came at a media event at which engineers also provided updates of other advanced-joining techniques the company currently employs, including a refinement to its aluminum-to-aluminum laser welding: a new, dual-beam laser reduces "spatter," providing a better overall surface finish and eliminating a process formerly required to clean the spatter from the surface. Another improvement: a redesigned aperture plate that controls reflection on the laser welder. The previous aperture plate had to be replaced after 30 vehicles moved through the body shop. With a more-optimized shape that came at almost no cost, the upgraded aperture plate has been used for more than 3000 vehicles and remains in service, Carlson said. Summarizing recent whole-vehicle weight reductions, GM said that for seven recently introduced models, lightweighting measures have chopped a total of 2480 lb (1125 kg), including a 700-lb (318 kg) reduction for the 2017 GMC Acadia and 400 lb (181 kg)for the 2016 Chevrolet Camaro. The aggregate savings delivers a CO2-equivalent reduction of 137,000 metric tons, GM calculated.
Date written: 19-May-2016 10:14 EDT
More of this article on the SAE International Website
ID: 3495
