Additive Manufacturing

JUL 2018

ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.

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JULY 2018 Additive Manufacturing FEATURE / Automotive 36 Roush Makes Fast Things, But Now It's Making Things Fast By Christina Fuges A 3D-printed cylinder head investigation reveals the possibilities of additive manufacturing. After an emisions improvement program for an off-road ve- hicle manufacturer left Roush's Advanced Engineering Group with a test engine set up in a dynometer (dyno) cell, the team saw an opportunity. The company was in the process of com- missioning one of its new metal AM machines, and it was right then that someone suggested they take a stab at growing and testing some critically stressed parts. A cylinder head sitting on a nearby workbench proved to be the perfect test piece. "And that was the start of this project," says Matt Van Benschoten, Roush's vice president of advanced engineering. "We signed an agreement with our customer, who was equally interested in seeing what we could do." After modifying the cylinder head's design, creating a support strategy and selecting a build orientation, the team also added machining stock to critical features where specific surface finishes and tight tolerancing were required. Then, they grew the cylinder head on an EOS M 290 with EOS Alumi- num AlSi10Mg material and ran it through the machine shop, treating it as a casting. The machine shop noted no noticeable difference when machining the additive part versus a tradition- al A356 or similar aluminum casting. Challenges and Successes Of course, there were a few challenges. "After the head was fully machined, our standard pressure checks on the lubrica- tion circuit and cooling jacket revealed a leak," Van Benschoten says. "Using a submersion tank, it was clear as to where the leak was coming from, just not why." The team performed a series of CT scans of the head to identify the cause: insufficient sup- port structure in the cooling jacket behind the leak location. The team saw that avoiding similar problems in the future would mean investing time up front to slice the part and en- sure sufficient support structures behind critical portions. Van Benschoten warns that in some cases this is still pretty labor-intensive. Although there are software tools that provide automatic support structure generation, they are still matur- ing. Frequently, the automatic support (or anchor) structure generation tools can apply too much support structure or support structure architectures of very high density, which are difficult to remove. Roush has developed unique support struc- ture architectures, including noncontact supports, to reduce or eliminate postprocessing requirements. The team was able to go back and hand weld the leaking portion, clean up the weld and perform a final pressure check to qualify the part for testing, cleaning and final assembly. Next, they installed the cylinder head on the development engine in the dyno test cell for a brief break-in followed by a performance evaluation at select operating conditions, includ- ing peak torque and power. Temperatures and pressures were monitored during testing to ensure the AM cylinder head was operating within typical limits and similarly to a cast cylinder head. It also withstood a 50-hour durability test running at peak power. "It performed the same as the high-volume pro- duction casting," Van Benschoten says. Then the team removed the cylinder head from the engine and disassembled it for post-cycle inspection and measurement. Roush 3D-printed this cylinder head to see whether it was possi- ble to 3D print critically stressed parts. The piece was grown with support structures holding it at a 45-degree angle from the build plate.

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