Patent-pending manufacturing process for electric motor housings offers new opportunities

The process is the perfect combination of two established production methods. A roll-bonded core (RoBoC) is inflated on one or both sides with approx. 100 bar compressed air to create cooling channels of the usual dimensions. This core is placed in a permanent mold and aluminum is cast around it. During the casting process, temperature is controlled from the inside through the existing channels so that deformation or melting is prevented. The result is a metal sheet integrated into the housing with the structures required for cooling the E-machine.

The cooling channel layout can be represented in a helical shape. Thus, the hottest channel section is embedded between the coldest and second coldest channel sections. The result is a homogeneous temperature distribution without a hot spot during engine operation. This design cannot be represented in the classic 2-shell design (e.g. in die casting), since there would be a thermal short circuit due to overflow from one channel section to the other. Depending on the customer’s requirements, however, meander-shaped or flat duct layouts can also be realized. Sealing against cooling water leakage is ensured by means of the self-contained roll bond core and is therefore no longer dependent on the casting quality. An expensive helium leakage test on the finished part, which can result in a very high loss of added value, is no longer necessary. Assembly, as required with the 2-shell design, is completely eliminated.

AionaCast has provided proof of concept by means of “proof of concept”. Little attention was paid to the cross-sections for the cooling medium and weight reduction. Now the team is working on Generation 2, where the inserted and inflated sheet is in direct contact with the stator, which again increases efficiency and reduces weight.

This concept makes it possible to reduce the wall thickness between the stator and the water-bearing channel from about 5 to as little as 1.5 mm. This reduction in wall thickness is also reflected in the overall weight of the electric motor housing for a typical BEV traction motor, which is reduced by approximately 1 kg.

Furthermore, the response time from the interaction of the optimizations is significantly reduced. To present the performance of the system, a CFD simulation of an existing traction motor from a major OEM was compared to the RoBoC Gen2 development. The time for the temperature reduction from 60° to 40°C in the stator could be reduced by about 70%. A pleasant side effect is also the significantly reduced casting process time, where the time to component removal from the casting mold can be significantly reduced due to direct cooling of the aluminum casting from the inside.

• The helix design and the smaller distance between stator and cooling medium results in higher thermal efficiency.
• The tightness of the cooling water channel is independent of the casting quality. Due to the concept, seals are completely eliminated and there is no residual dirt problem due to the absence of core sand. This makes this innovation more reliable than conventional systems.
• To list just a few cost advantages, such as the elimination of assembly (2-shell design), the lack of a sand core eliminates the need for reworking and capping of the core marks, several quality tests are no longer required, and the non-negligible shorter casting cycle makes the invention competitive.

For further development (prototypes), the patent holder AionaCast, which is also responsible for project management, was able to win well-known partners for the modification of a Bosch series housing:

• Kupral S.p.A. (Italy) / casting technology
• voxeljet AG (Germany) / 3D-printed molds for core package
• LPM S.p.A. (Italy): Foundry equipment
• Peter Prinzing GmbH (Germany): Roll-bond bending

In view of approximately 75 million traction electric motors to be produced from 2030, Jürgen Pohl sees further business development for this new manufacturing process as extremely positive. Furthermore, the same manufacturing concept with modified cooling channel layout (e.g. meander-shaped, flat or parallel channels) also offers potential for the production of battery and power electronics housings, he said.