Prototyping Shows 3DP’s Value as a Metalcasting Tool

Sept. 1, 2018
Follow the development process for an aluminum motor housing to see how functional design shapes the production process.

The role of 3D printing in metalcasting operations remains somewhat undefined: there are excellent applications for printing sand as molds or cores, and there are practical uses of additive processes like laser-sintering to form or repair detailed molds used in diecasting or permanent mold casting.

And then there is prototyping, the practical but somewhat esoteric process for developing parts or molds before series production begins. Prototyping presents an opportunity for metalcasters to adopt 3D printing capabilities beyond the parameters of sand or specialty metal alloys, and when 3DP prototyping succeeds it serves as a bridge to adopting newer processes like rapid casting, as well as to winning new orders by developing designs for cast parts.

The experience of CRP Group is proof. In recent years the Italian industrial group has evolved from a provider of contract machining services to the performance motorsports sector into a specialist in additive manufacturing and precision machining. Together with Windform, a supplier of composite materials for additive manufacturing, CRP established the Energica Motor Co. to design and produce electric motorcycles. The first model, the Energica Ego, introduced commercially in 2015, is said by its developers to be the world’s first street-legal electric motorcycle. It is comprised of multiple component parts, many of these produced by 3D printing. The prototyping and development of the Energica Ego motor housing — produced finally by rapid casting — is an instructive study for metalcasters.

The motor housing is an important component of an electric motorcycles, with highly complex features. Energica engineers and CRP Group staff started by working together to redesign an existing component to accommodate the rotor, stator, and the speed reducer. The propulsion unit to be supported is so flexible and compact that the Energica motor housing can be adapted to any vehicle.

The Energica Ego reducer consists of a straight-cut gear train that adds structural strength but also design simplicity and low noise emission, which is important to riders of electric motorcycles. The structure holds the shaft and pinion, and the final drive to the wheel with a standard motorcycle chain.

The Energica and CRP designers had to consider several different requirements, namely lightness (because the electric motor is heavy, the housing had to be light); high resistance (because the motor generates a lot of torque); correct sizing for the gears; and appropriate choice of materials and heat-treating process. Support for the frame is partially provided by the motor housing itself.

Creating the prototype — CRP Technology, the group’s 3D-printing business unit, built a functional prototype using selective laser printing (SLS) with Windform® LX 3.0, a new composite polyamide-based material reinforced with glass fiber. The part allowed the technicians to validate the 3D CAD drawing and helped Energica mechanics to work on the development of the motorcycle.

The 3D-printed functional prototype was mounted directly on the motorcycle, enabling a full check of potential major issues related to the assembly of each part (machining tolerances, frame connection joints, assembly of the gears and their proper functioning, and the placement and function of cables.) Thus, it provided the vehicle mechanics with the functionality needed to manage critical issues that occur while working on a prototype motorcycle.

“Being able to touch the 3D-printed prototype of the motor housing was very important for us, as we are the ones who manage fit and assembly,” according to one Energica Motor technician.

“For example, we have been able to study directly if the component can be assembled and disassembled easily, if all the parts can be reached, if it is possible to use standard wrenches ... We must put ourselves in the shoes of those who will handle the motorcycle in the market: customers, dealers, and mechanics.”

The Energica Ego developers maintained that in coordinating the objectives of technology/engineering, design, and function, they must accommodate the input of each one. The prototypes 3D-printed in Windform3D made it possible to study the various elements, “and to improve them where required by shortening development time and reducing costs.”

The combination of SLS and Windform composite materials made it possible to ensure ongoing study of the motorcycle’s components. The prototypes are fully functional, and can mounted on a motorcycle and road- or track-tested.

Creating the component — Once the CAD file of the design was validated in its composite form, the next phase was to choose materials for an aluminum prototype. The requirements were similar to those set for similar parts used in motorsports and F1 racing, namely performance, lightweight, and temperature-resistance. The designers settled on aluminum 6082 and 7075 alloys. CRP Meccanica (the group’s precision machining arm) milled the part from billet via five-axis CNC machines.

The central and largest part of the housing structure had a pass-through window in its original design, to allow the motor to be positioned within. Each side of the housing was a half shell of the whole, and one of the two halves was to receive the gear housing, with a cover to seal it all in. The pinion and oil pan are housed in the lower half of the motor housing.

The original design for the oil pan was SLS-printed in Windform GT polyamide-based glass fiber-reinforced composite material. It is waterproof and oil-resistant and (importantly) not electrically conductive. By using advanced 3DP processes and composite materials, CRP Group was able to settle on the preferred materials for the product to take into series production — aluminum 6082 for the large motor housing and aluminum 7075 for lids.

“This phase was completed in a short time,” according to the Energica technician. “CRP assisted us, and we did not have any problem with the component during the bench tests nor in the assembly on the motorcycle: the tolerances required were very complicated and precise, as the project included two rows of bearings (on the motor, plus the outer ones to support the output shaft.) Finally, we were able to validate the road-going prototype.”

With the design proven in road tests, the prototyping process proceeded to pre-series production of component models. These were first produced by sand casting, drawing on the established understanding of that process.

The following phase involved the realization of models for pre-series testing. 3D printed sand molds were produced for the design, and the same aluminum alloys were used to produce the design as rapid-cast parts.