Recently, I have been busy analyzing and solving problems of unqualified and unstable housing dimensions. I have also published an article on GD&T geometric dimensions and annotations before. This article briefly summarizes and shares some common problems in housing machining and their analysis and solution ideas.
At present, new energy electric drive housing should be die-casting part with the highest processing dimensional accuracy requiremaents. Bearing hole of electric drive housing is a key part in drive system, its processing quality directly affects bearing assembly accuracy, transmission efficiency and equipment life. Processing accuracy of motor parts is one of important factors affecting performance and life of motor. In manufacturing process of motor parts, 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:

1. Main problem points: hole diameter tolerance (too large or too small), roundness, insufficient cylindricity, position tolerance, multi-hole coaxiality deviation, insufficient perpendicularity between hole axis and end face;
2. Possible reasons:
Machining tool wear or improper setting of parameters (such as feed rate, speed);
Insufficient rigidity of tool or fixture leads to machining vibration;
Machining temperature changes cause thermal deformation;
Unreasonable sequence, inconsistent machining datum (such as multiple clamping errors);
Machine tool geometric accuracy (such as spindle runout);
3. Conventional solutions:
Tool optimization: Use coated carbide tools or CBN tools, automatically monitor tool life and check tool wear regularly.
Optimize process parameters: Select reasonable cutting parameters to ensure cutting quality and machining accuracy; divided into two stages: rough machining (reserved allowance) and fine machining (low-speed high-precision cutting).
Process optimization: optimize processing process and sequence, reduce number of processes, avoid errors caused by multiple clamping and positioning.
Temperature control measures: keep processing environment constant temperature and cutting fluid constant temperature;
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.
Detection compensation: after processing, use three-coordinate measuring machine (CMM) to detect and confirm, correct processing path if necessary, select optimal position evaluation and calculation logic.

1. Problem manifestation: surface roughness does not meet standard (Ra＞1.6μm), scratches, vibration marks, burrs, pores, sand holes;
2. Possible reasons:
- Unreasonable 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 speed and increase spindle speed (suitable for small cutting depth finishing).
- Deburring: Use forming cutters or special tool hole burrs
- Tool optimization: Use appropriate tool chip breaking to avoid chip entanglement;

1. Process monitoring: Online measurement system provides real-time feedback on processing size and timely compensation and adjustment;
2. Maintenance plan: Regularly calibrate spindle accuracy of machine tool;
3. Problem of aluminum chips stuck in spindle and tool holder is included in daily inspection;
4. Configure tool break detection system and tool life monitoring system to realize automatic alarm;
5. Tooling is equipped with an air gap detection system to prevent abnormal clamping;

There are two common materials for bearing hole of motor housing. One is to embed a steel sleeve in die-cast housing (common materials are 45# steel/40Cr/stainless iron), and the other is hole of 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 bearing apertures of electric drive housing are within 2 wires. If a non-adjustable structure reamer is used, it is easy to make product size smaller if it is slightly worn.

 

Aluminum bearing hole of die-cast housing itself has relatively good processing difficulty and dimensional stability in industry, and the most problematic bearing hole is mainly inlaid cylinder sleeve hole. When processing material of steel, it is very easy to cause tool wear, tool collapse, wire entanglement and other problems, resulting in unqualified bearing holes. If it is not discovered in time, it may lead to batch defects. Therefore, it is particularly important to choose right tool and process.

 

With technical research and development innovation of tool developers, there are currently reamers suitable for processing steel sleeves on the market, we have also verified and compared them in actual production. As shown in figure below, this reamer is a special reamer for high-speed processing of high-speed processing. D80 steel sleeve bearing hole precision reaming processing cycle is 1-3s/hole, and it can stably process more than 2000~5000 φ62-120mm steel sleeve bearing holes. Adjustment is also simple. You only need to adjust torque ≈25N/m. Hexagonal wrench can be easily adjusted, and each rotation of one grid can accurately compensate 0.005mm. Tool does not need to be disassembled, and can be adjusted directly on machine.
This also solves problem of chip breaking, and there is no need to worry about iron chips scratching surface of parts. Roughness of tool life range is kept below Ra1.6. It not only guarantees processing life, but also improves processing efficiency and ensures product quality. According to tool manufacturer, this adjustable reamer tool can achieve processing of holes with a diameter range of 12-120mm.
In addition, client often has demand for extreme samples. Using this tool does not require new production or disassembly of tool for adjustment, but direct machine tool adjustment can quickly meet production of extreme samples.

 

Adjustable reamer

 

Adjustable boring tool
Of above three adjustable tools, single-edged adjustable boring tool has slightly worse processing size stability, processing efficiency and inner wall roughness of hole than multi-edged reamer, especially stability of cylindricity and roundness of bearing hole is relatively poor, and it may not be suitable for holes with smaller diameters.
For adjustable tools, adjustable size range and dimensional stability after adjustment, especially stability of roundness and cylindricity and roughness inside hole are particularly important, and are also key evaluation factors when we choose tools.
According to my personal experience, when single-edged tools are used to process steel sleeve holes, challenges of tool life and dimensional stability are relatively large. At the same time, when steel sleeve holes with oil groove gaps on the side walls of bearing holes need to be cut intermittently, there are higher requirements for selection of tool structure and blades. It is necessary to ensure both tool life and dimensional stability and processing efficiency. Therefore, adjustable reamer may be a better choice.
Of course, stability of machining dimensions cannot be guaranteed by tools alone. It is also necessary to control stability of tooling fixtures, rough machining allowances, and rigidity of machine tool spindles, especially processing and control of root cleaning groove at the bottom of steel sleeve hole. Regardless of type of tool used, all relevant factors affecting dimensional stability need to be comprehensively considered and monitored.
In addition, according to my personal experience, during mass production of die-casting shells, batch failures often occur due to tool life exceeding or inadequate dimensional detection after tool change. Therefore, in actual production process, 5M1E of production process must be well monitored and managed, and accurate traceability of individual products must be achieved.
Machining accuracy of motor parts is one of key factors to ensure motor performance and life. To ensure machining accuracy of motor parts, it is necessary to comprehensively consider and optimize material selection, machining technology, equipment and tools, and machining technology control methods. During machining process, a sound quality control system must be established and strict quality inspections must be carried out to ensure that machining accuracy meets requirements. At the same time, machining accuracy and stability can be improved through process improvements and use of modern testing methods.