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Common processing problems and process methods of die-casting housings
2025-06-19
At present, the housing of new energy electric drive should be the die-casting with the highest processing dimensional accuracy requirements. The bearing hole of the electric drive housing is a key part in the drive system, and its processing quality directly affects the bearing assembly accuracy, transmission efficiency and equipment life. The processing accuracy of motor parts is one of the important factors affecting the performance and life of the motor. In the manufacturing process of motor parts, the control of processing accuracy is very critical to improving motor performance, reducing noise, extending service life and improving product quality. Common types, causes and measures of defects in die-cast housings are:
Poor dimensional accuracy
1. Main problems: hole diameter tolerance (too large or too small), roundness, cylindricity, position tolerance, multi-hole coaxiality deviation, and insufficient perpendicularity between hole axis and end face;
2. Possible reasons:
(1) The machining tool is worn or the parameters (such as feed rate and speed) are improperly set;
(2) Insufficient rigidity of the tool or fixture causes processing vibration;
(3) Thermal deformation caused by changes in processing temperature;
(4) The sequence is unreasonable and the processing datum is not unified (such as multiple clamping errors);
(5) Machine tool geometric accuracy (such as spindle runout) problems;
3. Conventional solutions:
(1) Tool optimization: Use coated carbide tools or CBN tools, automatically monitor tool life and regularly check tool wear.
(2) Optimize process parameters: Select reasonable cutting parameters to ensure cutting quality and processing accuracy; the process is completed in two stages: rough machining (reserving allowance) and fine machining (low-speed and high-precision cutting).
(3) Process optimization: Optimize the processing procedures and sequence, reduce the number of processes, and avoid errors caused by multiple clamping and positioning.
(4) Temperature control measures: The processing environment should be kept at a constant temperature, and the cutting fluid should be kept at a constant temperature;
(5) High-precision equipment: Use high-precision four-axis/five-axis machining centers to ensure stable accuracy; select appropriate processing tools and fixtures to improve positioning and clamping accuracy.
(6) Inspection and compensation: After processing, the three-dimensional coordinate measuring machine (CMM) is used for inspection and confirmation. If necessary, the processing path is corrected and the optimal position evaluation and calculation logic are selected.
Poor surface appearance quality
1. Problem manifestation: surface roughness does not meet the standard (Ra＞1.6μm), scratches, vibration marks, burrs, pores, and sand holes;
2. Possible reasons:
- Inappropriate cutting parameters (such as too high feed speed)
- Tool edge chipping or poor chip removal
- Uneven material hardness (such as local hard spots in castings)
- Improper casting process control
3. Common solutions:
- Parameter optimization: reduce feed rate and increase spindle speed (suitable for finishing with small cutting depth).
- Deburring: Use a profile cutter or special tool to remove burrs from the hole.
- Tool optimization: Use appropriate tools for chip breaking to avoid chip entanglement;
Preventive Measures
1. Process monitoring: The online measurement system provides real-time feedback on processing dimensions and makes timely compensation adjustments;
2. Maintenance plan: Regularly calibrate the machine tool spindle accuracy;
3. The problem of aluminum chips stuck on the spindle and tool holder is included in the daily inspection;
4. Equipped with tool breakage detection system and tool life monitoring system to realize automatic alarm;
5. The tooling is equipped with an air gap detection system to prevent abnormal clamping;
Commonly used processing technology and tools for bearing aperture
There are two common materials for the bearing holes of motor housings. One is to embed a steel sleeve in the die-cast housing (common materials are 45# steel/40Cr/stainless steel), and the other is a hole made of the aluminum die-cast housing itself. Commonly used processing tools include reamers and boring tools.
Adjustable reamers are more commonly used. Adjustable reamers can reduce a lot of tool disassembly and measurement waiting time, which greatly facilitates production efficiency and stability. Most of the bore diameters of electric drive housing bearings are within 2 wires. If a non-adjustable structure reamer is used, it is easy to cause the product size to be smaller due to slight wear.
The aluminum bearing holes of the die-cast housing itself have relatively good processing difficulty and dimensional stability in the industry, and the most problematic bearing holes are mainly the inlaid cylinder liner holes. When processing steel materials, it is very easy to cause tool wear, tool collapse, wire entanglement and other problems, resulting in unqualified bearing holes. If not discovered in time, it may lead to batch defects, so it is particularly important to choose the right tool and process.
With the technological research and development innovation of tool developers, there are now reamers suitable for processing steel sleeves on the market, and we have also verified and compared them in actual production. As shown in the figure below, this reamer is a special reamer for high-speed processing. The D80 steel sleeve bearing hole fine reaming process has a cycle of 1-3s/hole, and can stably process more than 2000~5000 φ62-120mm steel sleeve bearing holes. The adjustment is also simple. You only need to adjust the torque ≈25N/m. The hexagonal wrench can be easily adjusted, and each rotation can accurately compensate 0.005mm. The tool does not need to be disassembled, and can be adjusted directly on the machine tool.
This also solves the problem of chip breaking, and there is no need to worry about iron chips scratching the surface of parts. The roughness of the tool life range is kept below Ra1.6. It not only guarantees the processing life, but also improves the processing efficiency and ensures product quality. According to the tool manufacturer, this adjustable reamer tool can achieve the processing of holes with a diameter range of 12-120mm.
In addition, clients often have demands for extreme samples. The use of this type of tool does not require new production or disassembly of the tool for adjustment. Direct machine tool adjustment can quickly meet the production of extreme samples.
Among the three types of adjustable tools mentioned above, the single-edged adjustable boring cutter is slightly inferior to the multi-edged reamer in terms of dimensional stability, processing efficiency and inner wall roughness of the hole, especially the stability of the cylindricity and roundness of the bearing hole is relatively poor, and it may not be suitable for holes with smaller diameters.
For adjustable tools, the range of adjustable dimensions and the dimensional stability after adjustment, especially the stability of roundness and cylindricity dimensions and the roughness inside the hole are particularly important and are also the key factors we need to evaluate when selecting tools.
According to experience, when processing steel sleeve holes with single-edged tools, tool life and dimensional stability are relatively challenging. At the same time, when intermittent cutting is required for steel sleeve holes with oil groove gaps on the side walls of the bearing holes, there are higher requirements for tool structure and blade selection. It is necessary to ensure both tool life and dimensional stability and processing efficiency. Therefore, an adjustable reamer may be a better choice. Of course, the stability of machining dimensions cannot be guaranteed by tools alone. It is also necessary to control the stability of the tooling fixture, the rough machining allowance, and the rigidity of the machine tool spindle, especially the processing and control of the root groove at the bottom of the steel sleeve hole. Regardless of the type of tool used, all relevant factors affecting dimensional stability need to be comprehensively considered and monitored.
In addition, during the mass production of die-casting housings, batch failures often occur due to tool life exceeding or inadequate size detection after tool change. Therefore, in the actual production process, the 5M1E of the production process must be well monitored and managed, and accurate traceability of individual products must be achieved.
The machining accuracy of motor parts is one of the key factors to ensure motor performance and life. To ensure the machining accuracy of motor parts, it is necessary to comprehensively consider and optimize the material selection, machining technology, equipment and tools, and machining technology control methods. During the machining process, a sound quality control system should be established and strict quality inspections should be carried out to ensure that the machining accuracy meets the requirements. At the same time, the machining accuracy and stability can be improved through process improvements and the use of modern testing methods.