Motor Housing Machining Technology for New Energy Vehicle Motors

The explosive growth of the new energy vehicle market has created opportunities for breakthroughs in electric motor machining and related technologies.

As the central component of new energy vehicles, the quality and performance of electric motors are of paramount importance.

The motor housing and motor shaft, as core components of the motor, also play a vital role in power transmission and quality assurance.

Motor housings and shafts are prone to deformation during machining, which imposes strict operational requirements in terms of precision and other aspects.

CNC machining undoubtedly provides a superior technical solution;

Its application not only meets precision requirements but also overcomes machining challenges.

Structural Characteristics and Machining Requirements

• Motor Housings

The motor housing is a critical structural component of the electric motor—a core component of new energy vehicles.

The component features a layered connection design. It connects its open top side to the inverter and mounts its bottom end to the reduction gearbox.

Furthermore, it is fitted with embedded bearing sleeves to connect with the main shaft bearings and equipped with suspension mounts for linkage with the subframe.

The machining requirements for new energy motor housings are shown in Table 1.

Table 1 Technical Requirements for Processing of New Energy Motor Housings

• Motor Shafts

The motor shaft is also a critical component of new energy vehicle motors.

This component possesses distinct structural characteristics.

It connects the motor rotor to the transmission system. It efficiently transmits motor-generated torque to the drive wheels.

In addition, it bears alternating loads and torsional stresses during operation. It can also withstand vibration and impact forces in the rotating process.

Manufacturers typically fabricate motor shafts from 42CrMoA alloy steel or TC4 titanium alloy.

The machining process needs to satisfy multiple technical requirements.

The material requires a tensile strength of no less than 1080 MPa and a density of 4.5 g/cm³.

The surface hardness shall reach no less than 800 HV, and the hardened layer depth is controlled within 1.5–2 mm.

In terms of machining precision, the shaft diameter tolerance is limited to ±0.005 mm, and the roundness error is kept within 0.003 mm maximum.

Analysis of Challenges and Solutions for CNC Machining

• Machining New Energy Vehicle Motor Housings

1. Challenges

(1) “Deformation Control in Thin-Walled Structures”

The thin-walled structure of new energy vehicle motor housings causes machining instability.

These influencing factors make motor housing machining prone to various deformation problems.

Typical deformation types include springback deformation induced by cutting forces, thermal deformation resulting from cutting heat, and local deformation caused by clamping forces.

Improper setting of radial cutting force parameters during motor housing machining affects the sidewall springback magnitude.

This condition may cause key parameters to exceed the tolerance requirements of the bearing bore.

In addition, repeated machining passes will further accumulate and amplify springback errors.

If the temperature in the cutting zone becomes excessively high during the machining of the motor housing, it will affect the radial expansion parameters of the bearing bore;

Repeated clamping can also lead to uneven cooling.

If clamping force is overly concentrated at a single point during the machining of the motor housing, it will cause excessive indentation of the work surface within a 10-mm radius beneath the clamping plate, resulting in springback error.

(2) “Precision Control for Machining Complex Cavities”

Complex cavity structures and high machining precision requirements trigger this problem during the machining of new energy vehicle motor housings.

Inaccurate control of tool inclination angles during motor housing machining alters the distribution of cutting forces.

This defect leads to axial runout of the workpiece. It also causes deviations between the actual cutting path and the designed trajectory.

Improper aspect ratio setting of heat dissipation grooves during motor housing machining weakens sidewall rigidity.

The insufficient structural rigidity induces machining flutter.

Consequently, this condition degrades the surface roughness accuracy of the workpiece.

2. Solutions

(1) Optimizing Machining and Heat Treatment Parameters

Selecting appropriate parameters during the motor housing machining process has a significant impact on overall performance.

To determine the appropriate parameters, one should refer to the basic parameters and relevant formulas for the materials used in motor housing machining to avoid mismatches; see Table 2.

Table 2. Calculation of Motor Housing Machining and Heat Treatment Parameters

(2) Application of Five-Axis CNC Machine Tool

Engineers assemble the motor housing with other components and machine directional slots and holes on its sides, thereby imposing stringent machining accuracy requirements.

Operators can machine the part to final shape in a single setup using a five-axis CNC machine tool.

The term “five-axis” refers to the “X, Y, Z” axes and the two rotational axes, A and C.

When machining motor housings with a five-axis CNC machine tool, operators follow the operating principle of “milling mode first and turning mode second” and perform independent operations for each mode.

If machining requires the turning-milling composite function, technicians fix the X, Y, and A axes to convert the CNC machine tool into a vertical turning center;

After the operation is complete, adjust the settings again to returning to the milling state.

Application of Turning-Milling Composite Function in Motor Housing Machining

The five-axis CNC machine tool applies the turning-milling composite function for motor housing machining.

Long-term machining with large cutting depths generates persistent friction between workpieces and cutting tools.

Such cutting friction readily induces machining deformation.

Therefore, this study fully exploits the functional advantages of five-axis CNC machine tools.

This study models various stress factors via VERICUT and generates data charts using instantaneous force sensors.

• Challenges and Solutions in the Machining of New Energy Vehicle Motor Shafts

1. Challenges

The machining of new energy vehicle motor shafts faces multiple technical challenges.

Common problems include bending vibration during turning operations, low thermal conductivity of workpiece materials, and substantial machining errors caused by standard twist drills.

These defects severely restrict the machining quality and precision of high-precision rotary surfaces.

If the aspect ratio and amplitude parameters are set improperly during motor shaft machining, it will lead to deviations in the roundness data of the shaft journal, making it prone to bending vibration during the turning process.

If the linear speed of the grinding wheel is too high during the machining of the motor shaft, the surface temperature will rise, making it prone to problems such as tempering softening or grinding cracks.

If the straightness error of the standard twist drill and the bore diameter tolerance are too large during the machining of the motor shaft, this can easily result in dynamic balance weights that do not meet requirements.

2. Solutions

Various defects including unreasonable parameter configurations and excessive machining errors commonly occur in the processing of new energy vehicle motor shafts.

To tackle these practical problems, this study integrates digital twin technology with five-axis CNC machine tools.

This integration enables the construction of a novel high-fidelity digital machining model.

The five-axis CNC machine tool serves as the core processing equipment, and the new energy vehicle motor shaft acts as the machining object.

The introduction of digital twin technology facilitates the construction of a complete technical application system.

This system consists of physical entities, virtual models, and real-time data interaction modules.

The physical entity layer takes five-axis CNC machine tools as the core platform.

It integrates cutting tools, fixtures, and multi-sensor systems to collect key operational state data.

This provides fundamental support for constructing the digital mirror of the machining model.

The virtual model layer will use the data acquired from the physical layer as a reference to construct a high-fidelity digital twin model.

The data interaction layer adopts industrial communication protocols to realize cross-module data transmission and sharing.

It supports dynamic real-time monitoring of the entire motor shaft machining process under the digital twin application scenario.

Throughout the entire process, the virtual simulation layer plays the most significant role in constructing high-fidelity digital twin models.

The high-fidelity digital twin models referred to here include geometric models, physical models, and process models.

This study adopts 3D scanning technology to build the geometric model.

It acquires point cloud data of the motor shaft component via scanning and conducts surface reconstruction to generate a standard CAD model.

Reverse engineering is further adopted to extract high-precision geometric parameters for model calibration.

The five-axis CNC machine tool will automatically import the structural model based on specific parameters and intelligently set and adjust the motion parameters for each axis.

The physical model construction follows a systematic technical principle.

First, this study constructs a physical model of the motor shaft cutting process based on finite element analysis results.

Second, this study adopts the cutting force model to calculate the magnitude and distribution of cutting forces for five-axis CNC machining under different cutting parameter schemes.

Finally, this study employs a tool wear model to quantify tool wear loss under different cutting durations and material hardness levels.

This study constructs the process model in accordance with standardized technical principles.

First, this study applies the constant residual height method based on curvature variation parameters of the motor shaft surface to automatically generate initial toolpaths.

Subsequently, this study applies a collision detection algorithm to identify interference risks between tools, fixtures, and motor shaft components.

Based on the detection results, this study intelligently adjusts the tool orientation.

Finally, this study constructs an optimization model using motor shaft surface roughness and machining error parameters to realize the logical optimization of cutting parameters.

Conclusion

The new energy vehicle industry is experiencing rapid growth, with market demand continuing to rise, thereby expanding the scope for business development among relevant companies.

To sustain competitiveness in the fierce market environment, new energy vehicle enterprises must identify core bottlenecks in vehicle manufacturing.

These manufacturing challenges can be efficiently addressed through technological innovation and engineering practice, thereby supporting long-term industrial development.

Specifically, for the technical difficulties in the CNC machining of motor housings and motor shafts, enterprises can adopt innovative combinations of five-axis CNC machining equipment and digital twin technology.

This effective technical solution breaks through manufacturing bottlenecks and resolves problems including insufficient machining accuracy.