Electric mobility - new challenges, new solutions
21.05.2019
For some time now, the automotive industry has been intensively occupied with the construction of components for electrified vehicles. The newly designed parts and their serial production within narrow tolerances are often a challenge and require the know-how of machining specialists.
As a long-standing partner and supplier of cutting tools for the automotive industry, MAPAL also took on electric mobility at an early stage. Their expertise in machining the conventional powertrain is transferred to the components in electrically driven vehicles. MAPAL has developed suitable solutions for these new challenges.
For example, for machining they designed the so-called central housings. These housings often contain not only the electric motor, but also the power electronics and the transmission. The contours are therefore quite complex. The fact that cooling channels are often integrated into the housing makes machining even more difficult.
For instance, the main bore for the rotor in these housings must be machined to an accuracy of a few µm. These bores have diameters of up to 300 mm. That is why large tool diameters are in demand that can handle this task.
Lightweight tools ensue high precision for large diameters
MAPAL recommends machining in three steps - pre-machining, semi-finishing and fine machining. For the latter, MAPAL relies in many cases on tools in a welded construction. These tools are ideally suited for processing the mostly thin-walled and unstable central housings.
In the case of "welded constructions", a pipe construction serves as the tool body. Compared to a conventional boring bar, the tools weigh only half as much and are still very stable. The carriers of the inserts and the guide pads are welded on and support one another by means of connecting ribs. This minimizes the risk of chatter. In addition, the support in case of cut interruptions is ensured. The bending resistance moment is very good due to the tube construction and the stabilizing ribs. To keep the cutting forces acting on the component as low as possible, MAPAL individually designs the machining process and the tools - for pre- and semi-finish machining as well - depending on the stock removal situation, machine and clamping system.
Highly complex, thin-walled battery housings can be machined chatter-free
MAPAL also offers the appropriate tools with the optimum strategy for the various variants of battery housings. PCD is used as the material for the inserts and MMS technology ensures maximum economy. Depending on the stock removal, machining task and component, different milling technologies are used, which guarantee for reduced cutting forces. Certain contours, for example, are best milled by cutters for high-volume machining. The SPM milling cutter from MAPAL is ideally suited for this task. Thanks to its highly positive cutting geometry and optimally designed chip spaces, the effective cutting force is reduced by up to 15 percent compared to conventional milling cutters. When deep pockets are machined, for example, MAPAL relies on special PCD milling cutters whose inserts are arranged with both positive and negative axis angles. In conjunction with the trochoidal milling strategy, the cutting force is also kept very low during this machining process - despite the stock removal over the entire depth of the pocket.
Spiral forming with tolerances in the µm range
Not only the drive and energy storage systems are affected by the electrification of the vehicles, but also some ancillary units. An example of this is the electric refrigerant compressor. At the heart of this compressor are two interlocking spirals made of aluminum - a scroll stator and a scroll rotor. The efficiency of the compressor depends in particular on how precisely these components are manufactured. The requirements for shape and position tolerances are in the range of a few µm. A particular challenge, for example, is the machining of the "screw". A defined rectangularity of less than 0.04 mm and a surface roughness (Rz) in the single-digit µm range must be ensured. Despite these requirements, the thin wall and the depth of the part, finishing has to be carried out in one go. MAPAL has developed an SPM milling cutter with finishing geometry and a highly positive rake angle for this purpose. It ensures a low-vibration cutting and is equipped with an additional chamfer on the diameter. Thus, machining of the base, wall and chamfer on the front face can be carried out in one step. As a result, the narrow tolerances with regard to rectangularity and surface finish are reliably achieved.
The tools for machining stator housings, battery housings and electric refrigerant compressors are used successfully in practice. They illustrate the multitude of processes and solutions that MAPAL offers for machining components in electrically driven vehicles.