Case Study

"We ultimately chose FDM because the cost and time to make all the parts was drastically lower than the conventional sheet metal forming processes."

First, students conducted market analysis and generated three personas to represent the consumers who would buy a transformative vehicle from BMW. Using the personas, they formed use-case scenarios to define interactions the target market would have with the vehicle.

After the persona analysis, the team defined two main design goals:

• Compact crossover with pickup capabilities – To fit the urban lifestyle of the personas, the vehicle would need to be compact and have decent fuel economy as well as capacity for hauling-a unique solution in the current small crossover SUV market.
• Versatility – To obtain the utility of a pickup truck in a compact vehicle, the design had to include functionality to easily transform and generate more space when applicable.

The resulting design had many compelling features, distinct from the BMW X3, including:

• Sliding roof – The sliding glass roof transforms the trunk compartment from an enclosed area into an open-bed configuration with the utility of a pickup cab.
• Rear window – The rear window mechanism is located behind the rear seats to seal the cabin and protect passengers when the vehicle is in truck mode. It also folds down to allow for additional cargo space.
• Rear seats – The rear seats can be adjusted to lie flat for the load floor.
• Rear doors – To enable access to the open trunk space like a truck tailgate, the more common rear hatch trunk was replaced with two doors which open on a hinge.

After landing on a design concept, the CU-ICAR team began working on a prototyping strategy and manufacturing plan. Since they were engineering a variation of the BMW X3, they didn’t have to start from scratch, but to accommodate the transformative design, the vehicle needed a new tailgate, roof, panels, side frames, guide rail and windows.

The team originally designed the transformative parts to be manufactured with steel stamping, in which pieces of flat sheet metal are formed between a tool and die. But when the design files were quoted by a metal forming shop, the Deep Orange budget ultimately couldn’t support the high costs of building these large parts in steel. Moreover, the metal shop’s lead times did not meet project deadlines.

“Even with the excellent relationships we have with manufacturing suppliers, it didn’t make sense to steel stamp these large parts,” said Bill Sowerby, Deep Orange program director. “Once the students realized traditional manufacturing was out of the question, they had to go back and rethink how to design and build the prototype.”

That’s when a student suggested using an additive manufacturing process (3D printing) to rapid prototype the parts. The parts didn’t need to be built in steel, but needed to be strong enough to support the weight of the vehicle and a heavy, structural foam that would be applied to the interior. The students decided to build the parts using the Stratasys Fused Deposition Modeling (FDM) process because of its strong engineering-grade thermoplastics and the ability to produce large parts by building separate sections and bonding them together with the same thermoplastic. The students sent the design files to Stratasys Direct Manufacturing to quote FDM services and discovered the parts would be 75 percent cheaper and ready 3-4 months faster compared to steel stamping.

“My team and I were facing the challenge of getting the parts built in the shortest possible time within budget constraints. We investigated alternate options and talked with various body shops. But we ultimately chose FDM because the cost and time to make all the parts was drastically lower than the conventional sheet metal forming processes” commented Ashish Dubey, project manager for Deep Orange 4.

By switching to additive manufacturing, the team had to consider factors unique to the alternate process. Stratasys Direct Manufacturing recommended adjusting the part design for the FDM process to ensure they met tolerances, lined up with the original BMW X3 parts on the bottom half of the vehicle and were properly configured for secondary operations.

“We were dealing with extremely tight dimensional tolerances and even a few millimeters of deviation from the CAD models would have resulted in either the parts would not align correctly or would leave with big gaps,” said Dubey.

To help create a strong, smooth surface finish, ready for sanding, priming and painting, the team changed the orientation or the angle at which the layers of material would be extruded onto the build platform to reduce layer lines. The team also slightly increased wall thicknesses in various areas of the part to increase strength and to compensate for material that would be removed while sanding and smoothing the surface. Lastly, the parts larger than 36 x 24 x 36 in. (the size of the largest FDM machine) had to be split into separate pieces with dovetail joints in design to increase tensile strength between sections that would later be hot-air welded together.

“FDM is a very different process than steel stamping so the redesign was important. I helped the Clemson students determine the best orientation and placement for the bonding joint to ensure we would accurately build and weld the parts together to meet dimensional accuracy,” said Eric Quittem, senior project engineer at Stratasys Direct Manufacturing. “With thicker walls, we also knew there would be some slight stair stepping on the surface of the parts which is inherent with the layering process. This was new to the Clemson team and we reassured them that the layer lines could be removed with secondary operations.”

Stratasys Direct Manufacturing built 14 parts for Deep Orange in ABS-M30 on Stratasys FDM 900mc platforms, including: four pieces of the tailgate, four pieces for the side frames, four pieces for the roof and rear window and two side panels. Stratasys Direct Manufacturing's finishing department sanded the parts smooth to prepare the parts for automotive primer and paint. Finishers also hot-air welded sections of the tailgate, side frames and side panels at the dovetail joints.

“The final parts were as good as it can get in terms of geometric dimensioning and tolerances (GD&T). Overall it was great working with the Stratasys Direct Manufacturing team and at the end of the day we got a chance to learn about a new technology which could very well be the future of low volume production parts.” – Ashish Dubey, project manager, Deep Orange 4.

The students successfully integrated and assembled the functional prototype vehicle in time for its debut at the Center for Automotive Research Management Briefing Seminar in August 2014. BMW Manufacturing was impressed with not only the Deep Orange 4 design, but also the manufacturing plan.

“The ability to integrate more low-volume models without incurring capital- intensive retooling costs and efficiency losses will be key to success in the future as we strive to respond to changes in market needs faster and with more flexibility,” said Rich Morris, vice president of assembly, BMW Manufacturing. “The students working on this phase of the project did an excellent job of keeping costs down while finding optimal integration opportunities.” Quote from Clemson University media release.

Stratasys Direct Manufacturing and 3D printing helped keep Deep Orange 4 on track and within budget. “Vehicle prototyping is just one of many 3D printing applications creating efficiencies and producing better parts in the automotive industry. It’s important for future automotive engineers to learn how to design for and use the technology because it’s becoming more and more of an integral process in automotive manufacturing,” said Mick Schrempp, Stratasys Direct Manufacturing account manager who worked with Clemson University.