Cadillac will use an advanced mixed-material approach for the lightweight body structure of the upcoming CT6 range-topping full-size sedan, which will debut 31 March at the New York International Auto Show. The structure is aluminum-intensive, but the new Cadillac also includes 13 different materials customized for each area of the car to advance driving dynamics, fuel economy and cabin quietness; the mixed material approach saved 90 kg (198 pounds) compared to a predominately steel construction.
Sixty-four percent of the CT6 body structure is aluminum, including all exterior body panels. Thirteen complex high-pressure die cast components make up the lower structure of the CT6 body, along with aluminum sheets and extrusions. The vehicle underbody uses steel close-out panels on the lower structure to create a bank vault-quiet cabin without the added weight of extensive sound-deadening material, often used to compensate for aluminum panels in the occupant compartment.
High-strength steel is used strategically to reinforce the body structure, and is also used in conjunction with high-strength aluminum to create a safety cage surrounding the occupants. The structural portion of the B-pillar is constructed completely of high-strength steel, which was chosen to aid vehicle ingress, egress and visibility, in addition to mass savings and added cabin quietness.
A high-strength aluminum impact bar was added to the rear of the vehicle, and a combination of high-strength aluminum and steel was used for front and side impact zones to further increase passenger safety in the event of collisions.
The structure of the CT6 is one of the most-advanced body systems we’ve ever produced. The innovation surrounding our joining techniques have enabled us to create a vehicle structure with the highest torsional rigidity of any Cadillac while achieving one of the most mass-efficient vehicles in the segment.—Travis Hester, Cadillac CT6 executive chief engineer
Cadillac in January revealed a series of high-technology material joining techniques that create a new methodology for assembling the CT6. These enabled engineers to design a completely new structure for which 21 patents are pending. Material joining techniques prominent in the body construction of the CT6 include:
Patented aluminum spot welding technology (earlier post);
Aluminum Laser Welding, which creates a seamless joining of exterior panels;
Self-Piercing Rivets, which are able to join different types of materials together with a clean appearance; and
Flow Drill Screws, which are able to join different types or materials and used in conjunction with adhesive. (Earlier post.)
Aluminum arc welding and structural adhesive are also separately used for CT6 body assembly.
Among the five techniques, the CT6’s engineers were able to select the best joining method depending on material combination and body location (for machine equipment access).
To weld both the inner and outer vehicle frames, 28 robots descend on the vehicle body in two separate framing stations, joining the body-in-white together from all angles. The robots are mounted above and beside the vehicle and can also reach beneath it. The two framing processes were choreographed to compensate for different microscopic vibrations.
Once the body construction is complete, a large robotic arm lifts the entire vehicle from one part of the assembly line to an upper-level conveyer—a first for a vehicle the size of CT6—to be transferred across the Detroit-Hamtramck plant.
The CT6 marks the return of a full-size luxury sedan to Detroit-Hamtramck. The plant also builds the Cadillac ELR electrified luxury coupe, among other products.