Common processing problems and process methods of die-cast shells
At present, the new energy electric drive housing should be a die-casting part that requires the highest processing dimensional accuracy. The bearing hole of the electric drive housing is a key part of the drive system. Its processing quality directly affects the bearing assembly accuracy, transmission efficiency and equipment life. The machining 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, grasping the machining accuracy is critical to improving motor performance, reducing noise, extending service life and improving product quality.
Common types, causes and measures of die-cast shell defects are:
Poor dimensional accuracy
- Main problem points: excessive hole diameter (too large or too small), insufficient roundness and cylindricity, excessive positioning, deviation of porous coaxiality, and insufficient perpendicularity between the hole axis and the end face;
2. Possible reasons: wear of the processing tool or improper setting of parameters (such as feed, speed); insufficient rigidity of the tool or fixture causing processing vibration; changes in processing temperature causing thermal deformation; unreasonable sequencing, inconsistent processing standards (such as multiple clamping errors); machine tool geometric accuracy (such as spindle runout) problems.
- Conventional solutions:
- ➤ Tool optimization: Use coated carbide tools or CBN tools, automatically monitor tool life and regularly check tool wear.
- ➤ Optimize process parameters: Choose reasonable cutting parameters to ensure cutting quality and processing accuracy; it is completed in two stages: roughing (reserve allowance) and finishing (low-speed, high-precision cutting).
- ➤ Process optimization: Optimize the processing process and sequence, reduce the number of processes, and avoid errors caused by multiple clamping and positioning.
- ➤ Temperature control measures: The processing environment should be controlled at a constant temperature, and the cutting fluid should be kept at a constant temperature;
- ➤ High-precision equipment: Use high-precision four-axis/five-axis machining centers to ensure stable accuracy; select appropriate processing tooling and fixtures to improve positioning and clamping accuracy.
§ Inspection and compensation: After processing, it is inspected and confirmed by a three-dimensional coordinate measuring machine (CMM). If necessary, the processing path is corrected and the optimal position evaluation and calculation logic are selected.
Poor surface appearance quality
- Problem manifestations: Surface roughness isn’tup to standard (Ra>1.6μm), scratches, vibration lines, burrs, pores, and blisters;
- Possible reasons:
- Unreasonable cutting parameters (such as feed speed too high)
- The cutting edge of the tool is chipped or chip removal is not smooth - The hardness of the material is uneven (such as local hard spots in castings)
- Improper control of the casting process
- Common solutions:
- ✓ Parameter optimization: reduce the feed speed and increase the spindle speed (suitable for small depth of cut finishing).
- ✓ Deburring: Use a forming knife or a special tool to deburr the hole.
- ✓ Tool optimization: Use appropriate tools for chip breaking processing to avoid chip entanglement;
Preventive measures
- Process monitoring: The online measurement system provides real-time feedback on processing dimensions and makes timely compensation adjustments;
- Maintenance plan: regularly calibrate the machine tool spindle accuracy;
- The problem of aluminum chips stuck in the spindle and tool holder shall be included in the daily inspection;
- Equipped with tool breakage detection system and tool life monitoring system to realize automatic alarm;
- The tooling is equipped with an air gap detection system to prevent abnormal clamping;
Commonly used processing techniques and tools for bearing bore diameter
There are two common materials for motor housing bearing holes. One is a steel sleeve embedded in the die-cast housing (commonly used materials are 45# steel/40Cr/stainless iron), 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 commonly used. Adjustable reamers can reduce a lot of tool disassembly and measurement waiting times, which brings great convenience to production efficiency and stability. Most of the bearing holes in the electric drive housing are within 2 wires. If a non-adjustable structure reamer is used, it is easy for a slight wear and tear to make the product smaller.
The aluminum bearing holes of the die-cast housing itself are currently relatively difficult to process and have relatively good dimensional stability in the industry, but the bearing holes that are most prone to problems are mainly inlaid cylinder liner holes. The material of processed steel is very prone to problems such as tool wear, chipping, and wire wrapping, which can lead to unqualified bearing holes. If not discovered in time, it may lead to batch defects. Therefore, it is particularly important to choose appropriate tools and processes.
With the technological research and development innovation of tool developers, there are currently better reamers on the market suitable for processing steel sleeves, and we have also verified and compared them in actual production. As shown in the figure below, the reamer is a special reamer for high line speed and high-speed processing. The precision reaming cycle of D80 steel sleeve bearing holes is 1-3s/hole, and it 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, and it is easy to adjust with the hexagonal wrench. Each rotation will accurately compensate 0.005mm. The tool doesn’t need to be disassembled and can be adjusted directly on the machine tool. This also solves the problem of chip breaking. There is no need to worry about iron chips scratching the surface of parts, and the roughness during the tool life span is kept below Ra1.6. It not only ensures the processing life, but also improves the processing efficiency and ensures die casting product quality. According to the tool manufacturer, this adjustable reamer tool can process holes in the diameter range: 12-120mm.
In addition, clients often have demands for extreme prototypes. Using this kind of tool doesn’t require new production or disassembly of the tool for adjustment. Direct machine tool adjustment can quickly meet the production of extreme prototypes.
Of course, the stability of machining dimensions can’t be guaranteed by cutting tools alone. It is also necessary to control the stability of the tooling fixture, rough machining allowance, and the rigidity of the machine tool spindle. In particular, the processing and control of the root clearance groove at the bottom of the steel sleeve hole is particularly important. Regardless of the type of tool used, all relevant factors affecting dimensional stability need to be considered and monitored.
The machining accuracy of motor parts is one of the key factors to ensure the performance and life of the motor. To ensure the processing accuracy of motor parts, comprehensive consideration and optimization must be carried out from aspects such as material selection, processing technology, equipment and tools and processing technology control methods. During the processing process, a sound quality control system must be established and strict quality inspections must be conducted to ensure that the processing accuracy meets the requirements. At the same time, through process improvement and the use of modern detection methods, processing accuracy and stability can be improved.