Precise wall thickness control in liquid-cooled motor housing is crucial for mitigating the risk of thermal stress concentration. This requires coordinated management across multiple dimensions, including material selection, process optimization, thermal stress relief, and quality inspection. In material selection, priority should be given to matching coefficients of thermal expansion. For example, aluminum alloys, due to their low coefficient of thermal expansion and high thermal conductivity, are commonly used as the base material for liquid-cooled housings. However, composition optimization (such as adding silicon and magnesium) is necessary to further enhance their resistance to thermal fatigue. In the base material pretreatment stage, normalizing or annealing processes should be used to eliminate initial internal stress, preventing wall thickness fluctuations caused by stress release during subsequent processing. For example, steel housings require controlled annealing temperatures of 550-600℃ and slow cooling to reduce internal stress below 200MPa.
The precision control of the processing technology directly affects wall thickness uniformity. During the precision steel tube blanking stage, laser cutting or CNC sawing should be used instead of traditional abrasive wheel cutting to reduce elliptical deformation of the tube end. After cutting, a surface grinder should be used to flatten the end face, ensuring that the perpendicularity of the end face to the axis is ≤0.02mm/m, providing a precise reference for subsequent clamping. In machining, high-precision CNC lathes or vertical machining centers are crucial. Their spindle runout must be ≤0.003mm and guideway straightness ≤0.005mm/m to effectively suppress vibration deviations during machining. Tool selection must match material properties. For example, when machining aluminum alloys, YW2 carbide-coated tools with a rake angle of 15°-20° and a clearance angle of 5°-8° are recommended to reduce cutting resistance and tool sticking. Simultaneously, the cutting fluid flow rate should be controlled at 15-20L/min to prevent localized overheating that could cause material expansion and affect wall thickness.
The clamping method is critical to the machining accuracy of thin-walled shells. Soft jaw clamping requires grinding to match the outer diameter of the steel pipe, ensuring a fit ≥90% to avoid roundness deviations caused by clamping stress. For ultra-long steel pipes exceeding 1000mm in length, a clamping method with end supports and a central follower post should be used to control deflection during cutting and ensure straightness meets specifications. Clamping force needs to be controlled differently based on material properties. For example, the clamping force for aluminum alloy shells should be controlled at 5-8 MPa to prevent deformation due to insufficient material rigidity. For thin-walled shells with a wall thickness ≤4mm, a layered cutting process should be adopted, with each cutting depth ≤0.1mm, to reduce vibration caused by insufficient rigidity by reducing the cutting force.
The heat treatment process is crucial for balancing mechanical properties and precision stability. After finishing, steel shells require tempering. The quenching temperature should be controlled at 850-880℃, and the holding time should be adjusted according to the wall thickness (1-1.5 minutes per millimeter). Oil cooling or air cooling should be used, with a cooling rate ≤10℃/min to prevent quenching deformation. The tempering temperature should be 500-550℃, and the holding time 2 hours, to achieve a surface hardness of HRC28-32, balancing rigidity and toughness. After heat treatment, a dial indicator should be used to check the deformation. Parts exceeding tolerances should be straightened, and after straightening, a low-temperature annealing process (450-500℃, holding for 1 hour) should be performed to eliminate straightening stress. The aluminum alloy casing does not require heat treatment, but it must undergo degreasing and pickling before anodizing to control the oxide film thickness to 8-12μm to avoid affecting the fit accuracy.
The impact of flow channel design and sealing process on wall thickness accuracy is often overlooked. The U-shaped cooling flow channel of the liquid-cooled casing needs to be formed into a continuous channel through cross-grooving. Rounded corners (radius ≥2mm) are required at flow channel corners to avoid stress concentration caused by sharp corners. The welding of the sealing block and the annular blocking protrusion requires a sealed welding process to ensure weld strength and coolant compatibility, preventing excessive local temperature differences caused by coolant leakage due to seal failure, which would exacerbate thermal stress concentration.
A quality inspection system must be implemented throughout the entire process. Sampling inspection is required after each processing step. For example, after cutting, a coordinate measuring machine is used to check the wall thickness uniformity, with a sampling rate of no less than 5%; after heat treatment, hardness and deformation are checked; after deburring, surface roughness and burr residue are checked. A full-dimensional inspection is required before assembly; defective products are immediately reworked to prevent them from entering the assembly stage. During mass production, a first-piece inspection and last-piece verification system must be implemented. Mass production can only begin after the first piece passes inspection, and the last piece is compared with the first piece to check for accuracy deviations caused by equipment drift.
Through coordinated control of the entire process—from material selection and processing technology to heat treatment, flow channel design, and quality inspection—the wall thickness deviation of the liquid-cooled motor housing can be effectively reduced, keeping the risk of thermal stress concentration within a reasonable range. This systematic management not only improves the reliability of the housing but also ensures the stable operation of the motor under high-temperature and high-load conditions.
