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About one year ago, Desktop Metal, headquartered in Massachusetts, introduced its highly anticipated metal 3D printers, the Desktop Metal Studio System and the Desktop Metal Production System, to the masses. This past winter, the company began to ship Studio Systems to its first Pioneer Program customers, including Virginia startup Lumenium LLC.

Lumenium is working to develop a family of internal combustion engines, and reinvent internal combustion for a new era of engines. The startup’s novel design, the Inverse Displacement Asymmetrical Rotational (IDAR) engine, will help achieve this goal, with its unique geometry and ability to produce powerful but efficient internal combustion.

The IDAR engine parts need low thermal expansion, high dimensional accuracy, and strength under dynamic loads to stand up well under the extreme stress and heat that are part and parcel of internal combustion engines (ICE). Additionally, the parts have to be lightweight to achieve efficiency and good overall power density.

Rapid prototyping is important for any startup, and Lumenium knows that fast iterations can impact the engine’s performance and time-to-market. That’s why the company was looking for a more cost-effective, quick approach to prototyping engine assembly parts than its wire electrical discharge machining (EDM) and in-house CNC machine, and found it in the desktop DM Studio System, with its Bound Metal Deposition (BMD) technology.

While the $350 billion ICE market has three typical engine categories, the IDAR engine adds a fourth. But it’s not easy – its components have to withstand combustion temperatures of 1500°C, dynamic loading conditions, and combustion forces of 1500 psi.

According to a new case study by Desktop Metal, “Designing a complex product with extremely high performance requirements has led to multiple generations of engine designs, each with a long conceptual phase of designing, prototyping, and iterating. The ability to perform frequent design iteration has a significantly beneficial impact on final engine performance. The full engine development cycle for each generation of the IDAR engine takes between three to five years. Identifying a faster, more cost–effective approach to prototyping is critical to IDAR engine development, and the ability to lightweight parts while adhering to other mechanical property requirements directly impacts engine performance.”

Each month, Lumenium makes roughly 20 prototype parts, with 95% being built in-house with wire EDM and 5-axis CNC machining; the other 5%, which are typically round parts, are sent to an outside machine shop. But 100% of these prototype parts have long lead times of nearly a month, if not more, which hampers the startup’s ability to quickly iterate its engine designs.

Another issue with machining, in addition to high costs, is its inability to offer multiple options for making lightweight parts. This is a problem for companies like Lumenium, as a weight reduction of 50% in an engine can double its power output and RPM. Early IDAR engine versions were machined from blocks of lightweight aluminum. But this metal expands as temperatures go up, which helped lead to Lumenium’s decision to 3D print engine components out of steel, which has a thermal expansion coefficient that’s 68% less than that of aluminum.

Assembled saddle and swing arm next to an installed swing arm within the IDAR test engine.

Lumenium chose to go with Desktop Metal’s 3D printing technology to meet exacting engine requirements and achieve complex part geometries. In addition, the DM Studio System 3D prints parts with closed-cell infill, which can be adjusted to meet both weight and strength requirements.

The startup submitted three parts – a saddle carrier, a swing arm, and a connecting rod – for initial benchmarking. These parts, which fit together in an IDAR engine sub-assembly, needed to have dimensional accuracy, low heat transfer and thermal expansion, and be able to withstand both dynamic loading conditions and combustion forces of 1,500 PSI. Metal 3D printing helped achieve this for all three, at a faster, less expensive rate than machining, but the case study focuses on the saddle carrier.

Horizontal holes need internal support structures to retain the shape with most extrusion-based 3D printing methods, but Lumenium was able to modify the design and change the round holes to a teardrop shape, which did not require support structures.

Additionally, the saddle carrier has serrations along the top and bottom edges that mate with the swing arms to help the engine component withstand engine forces. These serrations can’t be made solely with 3D printing, but the startup was able to selectively adjust shell thickness for the top- and bottom-facing features to 5.2 mm, so the infill wouldn’t be exposed during machining.

Important post-processing steps, including CNC machining and wire EDM, were required for the 3D printed parts. But in comparison to parts that are only machined, the number of steps is reduced, and the steps themselves are easier to complete.

For the saddle carrier, and the other two parts as well, it was faster and less costly to use the Studio System for production, rather than machining: the cost-per-part dropped from $980 to $148 for the saddle carrier, and the part mass went down from 1,158 grams to 933.

According to the case study, “The design and function of each part within the assembly is critical, so the ability to refine and iterate quickly has a direct impact on the overall engine performance. Previous methods of machining each prototype part—either in-house or by an outside machine shop—are time–consuming and costly. The printed saddle, swing arm, and connecting rod demonstrate the time and cost savings that the system delivers.”

Lumenium will be able to reduce its product development timeline by 25% using Desktop Metal’s 3D printing solution; read the full case study here.

Discuss this and other 3D topics at 3DPrintBoard.com or share your thoughts in the Facebook comments below. 

[Images: Desktop Metal]


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