The Enlighten Award recognizes achievements in weight reduction across the automotive industry in full vehicle and module categories.
The General Motors team took top honors in the OEM-focused full vehicle category with its 2016 Cadillac CT6, which is 157 lbs (71 kg) lighter than the body-frame integral (BFI) construction. Fernando Krambeck, program engineering manager, Cadillac CT6, says, “It was a true honor for the CT6 team to be recognized for the efforts we put into developing this car.”
ContiTech, with its unique polyamide cross beam developed for the 2016 Mercedes S-Class,was the winner in the module category. The front cross member of the rear suspension is 30%lighter compared to the previous aluminum component. “It’s really the first time we’ve been recognized for one of our advanced products in the North American market, and winning the Enlighten Award has been a great honor for us,” according to Scott Bykowski, manager R&D,ContiTech North America.
Through innovative design techniques, materials technology and manufacturing processes, these companies are developing lighter-weight vehicles that help meet fuel economy targets and government regulations.
Design Direction
The Cadillac CT6 is unique in that its weight is equal to or less than vehicles a full class size below its dimensions. Sixty-four percent of the body structure is aluminum, with strategic use of high-strength steel(HSS) to aid in passenger safety, NVH and overall weight savings.
GM explains that rather than optimizing different metals to gain weight savings, the vehicle was designed using computer-aided engineering (CAE)technology that allowed the team to “self-select” the material based on the intended use, such as crash safety, stiffness, NVH, etc.
Innovative proprietary joining methods for vehicle construction allowed different metals – steel and aluminum, for example – to be joined together. In addition, parts content and complexity were reduced.
HSS was used strategically to reinforce the body structure – and in conjunction with high-strength aluminum to create a safety cage surrounding the occupants. The structural portion of the B-pillar,or center pillar, was constructed completely of HSS,which was chosen to aid vehicle ingress, egress and visibility. The use of HSS also contributed to mass savings and cabin quietness.
A high-strength aluminum impact bar was added to the rear of the vehicle. 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.
Simulation, including topology and multi-disciplinary optimization, was used extensively throughout the vehicle’s development to ensure an efficient use of material. In addition, an innovative use of mixed materials was employed across the CT6 to further minimize weight without compromising performance.
Like the GM sport utility vehicle, the full-size Mercedes S-Class luxury car had some interesting design challenges. Rear suspensions a re typically built from steel or aluminum materials. In this instance, it was the first time a rear suspension cross member had been designed and produced in polyamide material for production. According to ContiTech, it took a great engineering effort to break through traditional paradigms and change the typical way of designing. Cont iTech explains that it relied on its Integrative Design Process to move the rear suspension cross member project forward. That process focuses not only on the shape of the product but also uses mold flow analysis and glass fiber alignment (anisotropic modeling) to achieve the design. As a result of this simulation, the polyamide design was 30% lighter than the aluminum version.
“It’s really the first time we’ve been recognized for one of our advanced products in the North American market, and winning the Enlighten Award has been a great honor for us.”
– Scott Bykowski, manager R&D, ContiTech North America
Manufacturing Processes
When there are significant changes to a design process, companies often alter their production processes. Such was the case with GM.
GM invested $300 million in its Detroit-Hamtramck Assembly plant, and part of the investment was used to configure a separate space to create the body structure. The specialized area includes a large robotic arm that lifts the entire vehicle from one part of the assembly line to an upper level conveyor – something unheard of for a vehicle the size of the CT6.
In addition, several new manufacturing processes were employed including patented aluminum spot welding technology; aluminum laser welding, used to create 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 join different types of materials and are used in conjunction with adhesive.
Engineers faced a new challenge in manufacturing the advanced mixed material vehicle structure for the sport utility vehicle. Combining different types of joining methods, the team overcame previous manufacturing difficulties involving the joining of traditionally dissimilar materials while still allowing the team to optimize every panel for its desired purpose.
ContiTech, on the other hand, did not implement any vehicle assembly changes. The part was staged in the same work cell as its aluminum version.
In terms of manufacturing challenges, the front cross member of the rear suspension was the largest product ContiTech has produced from polyamide materials. It was a great effort to understand and calculate the shrinkage and warping characteristics of the product,according to the company.
Making a Difference
The accomplishments of these engineering teams from GM and ContiTech are applicable to other applications and programs. For example, GM points out that “material self-selection” – in which the use of simulation allows for part of a structure to be optimized for intended use first, and for material selection second – will lend itself to future efficiencies on later vehicle structures, and so will the groundbreaking construction methods of combining different metals.
What’s more, the mixed material body construction allows for a more rigid structure, enhancing vehicle driving performance and driver confidence. The weight savings also allow for fuel economy savings – up to 31 mpg highway with the 2.0L turbocharged four cylinder engine.
In addition, there is a decrease in part complexity. The body structure allows for a reduced number of parts for the vehicle structure. GM cites the example of the reduction from 35 parts in a traditional stamped approach to just two parts on the CT6’s front fender assembly.
ContiTech notes that its polyamide component is applicable to other rear wheel drive vehicles and the part offers damping benefits, especially the reduction of noise transferred through the suspension.
A Word from the Innovators
Simulation has played an important role in the development efforts of the recent Altair Enlighten Award winners.
Fernando Krambeck, program engineering manager, Cadillac CT6,says, “We used multiple types of analysis to try to develop this vehicle. We used about 13 high-pressure die casts. We used certain types of analysis just to develop the overall optimum pattern in the casting – defining where the ribs need to be, how to define the structure and how to best utilize that technology, geometrically, to meet all the attributes that we were looking for…We used all different types of analysis,depending on the application and the location on the car.”
Scott Bykowsky, manager R&D, ContiTech North America, reports that the company employed a very detailed, integrated simulation process. “What that means,” he explains, “is that we incorporated all facets of the manufacturing process early on in the development phase, using glass fiber analysis,mold flow simulation, etc. Everything has to be set from the beginning.”
Where do these companies think lightweighting is headed in the future? Krambeck says, “As we continue to lightweight vehicles, we’re going to use two approaches. First, we’re going to use lightweight materials anywhere and everywhere we can. Second, we’re going to look at where we can minimize the use of material…As we go forward, it’s going to be a balance between both – eliminating material where we don’t need it, and then using the right material where we can to get the best mass.”
Bykowsky remarks, “You are going to see new classifications of not only polyamide or polymer materials but also steel and aluminum. You will see thinning gauges that are actually stronger in steel now. There’s going to be a place for all of this technology in vehicles to come. But the polyamide or polymer materials are really going to take offin the near future.”
For more information about the 2017 Altair EnlightenAward, visit www.altairenlighten.com.
Beverly A. Beckert is Editorial Director of Concept To Reality.