One of the common problems of die castings: the dangers of burrs and their removal methods
⚡ People who are engaged in quality work in the die-casting industry probably have the same experience or troubles. One of the issues that is often complained about by customers is the problem of burr residue. Many times I am still unconvinced, thinking that it is just a small burr. How can a die-casting part be completely free of burrs? Why don’t the engine parts of fuel vehicles have such high requirements?
This article briefly summarizes the risks of these problems in new energy die castings in terms of burrs, flash, casting spots, cracks and other issues.
🔍 First of all, what are the dangers of problems such as sharp edges and burrs on the new energy electric casing?
1. Affect assembly accuracy: The electric drive assembly has many components that are press-fitted. For example, when the conductive rings, oil seals or bearings are press-fitted inside the electric drive housing, if sharp edge burrs remain in the chamfered parts of the mounting holes, it may cause abnormal press-fit assembly or cut the oil seal. Sharp-edged burrs may cause poor fit of components. For example, burrs remaining in the water channel sealing groove of the motor housing will destroy the integrity of the sealing ring and cause the risk of leakage.
The integration level of EDM products is high, and the space provided is limited. The spacing between internal assembly components is often small. For example, the height of casting points such as traditional gearboxes is generally not more than 0.5. However, if the height of protrusions such as cast points and cracks in the new energy shell is controlled within 0.5 as a rule, it may cause interference with the assembly of rival parts. Especially when the rival parts are electrical components, problems such as creepage safety distances may occur and may lead to failure.
2. Electrical function failure: Electric drives, electronic controls or chargers have many internal electrical components, and burrs on the inner wall of the electronic control system casing may scratch the insulation layer of the wiring harness, causing short circuit or leakage (such as an internal short circuit in the motor controller). If metal burrs fall off and enter the connector inside the electric drive housing, it will also cause short circuit failure.
Burrs inside the electronic control case or charging case fall off or scratch the PCB board, causing a short circuit and functional failure. Functional failure of parts often leads to assembly failure, with great impact and losses.
3. Reduce fatigue life: The bearings of new energy Sanden are basically open bearings, and the rotational speed is relatively high. At the same time, compared with fuel vehicles, there is less engine sound, and the requirements for noise control are higher. The remaining burrs fall off due to vibration or the erosion of the cooling oil inside the motor, and enter the inside of the bearing, causing abnormal wear of the bearing. This will not only lead to premature bearing failure, but also cause excessive noise.
The diameter of the oil passage inside some motor housings is only 1.5mm. When aluminum chips and burrs remain and block the oil passage, the bearings or other lubrication systems will fail, causing the assembly to malfunction.
4. Test equipment failure: If there are burrs and aluminum chips remaining in the water channels of the electric drive, electronic control and charger, during the assembly aging test, the burrs will block the filter screen of the test equipment, causing abnormal equipment temperature and equipment failure. Once the equipment loses temperature and is damaged, huge losses will occur.
🛠 So, what are the main sources of burrs on die-casting shells?
From my perspective, common burr problems in die-casting parts can be mainly divided into two categories: burrs on the blank body, burrs generated by machining, and burrs on post-process assembly products.
1. Source of burrs on die casting blank body: The flash and skin of the die-casting blank isn't completely removed or the residue isn't removed; the burrs on the edge of the ejection pin aren't removed cleanly and the remaining burrs are removed; the surface of the blank shell is shot and peeled, and there are mold cracks, burrs and casting points.
2. Machining burrs: Common burrs after machining of the casing include: sharp edge burrs on the edge of the machined surface, especially at sharp edges; secondly, the electric drive casing often has many oil passage holes, and the bottom of the oil passage hole and the intersection of the two oil passage holes are also prone to flanging burrs on the product; there are also some bottoms or ends of the through holes, which are easily affected by the infeed direction of the processing tool, causing extrusion burrs.
3. Post-process: Currently, new energy electric drive housings, electronic control housings, and charging housings will require press-fitting or assembly accessories. If the installation hole chamfering tool isn't designed properly, burrs that squeeze and trim the edges may easily occur during the press-fitting process. In addition, if the material of the tooling positioning pin is unqualified, the positioning hole will be easily scratched and produce burrs.
⚙️ Commonly used deburring methods in the Die Casting Industry:
1. Manual operation and efficiency bottleneck: Traditional deburring processes mostly rely on manual operations and have a low degree of automation. Manual deburring relies on manual grinding of files, sandpaper and other tools one by one, which is inefficient and easily affected by worker fatigue or skill level. The quality is greatly affected by the experience of workers. Cross holes or special-shaped structures are difficult to remove from the base, and problems of uneven surface or leakage may easily occur.
The processing quality and consistency are poor, it is difficult to recruit workers, and there are occupational health risks. Moreover, many die-casting companies now outsource this process to third parties.
2. CNC deburring: During the casting process, workpiece deformation is inevitable, especially in thin-walled parts or products such as controller/charger casings, where the deformation differences are large, which increases the difficulty of deburring. CNC programming is used to automate the operation, and the mechanical arm or tool path is controlled through preset parameters to achieve high-precision deburring. It supports continuous high-intensity operations, can handle multiple processes at a time, and the efficiency is several times that of manual work. Parametric control ensures uniform processing results and is suitable for complex geometries and high-precision surface treatment.
CNC deburring has obvious advantages in efficiency, quality and large-scale production. As the trend of manufacturing automation increases, CNC equipment is gradually replacing traditional manual processes. At present, the customized development services of many domestic deburring supporting manufacturers have become relatively mature. In the past two years, they have continued to innovate and developed multi-axis processing equipment, multi-station and other deburring equipment.
3. High-pressure water gun: Use a high-pressure cleaner (cleaning water pressure of 28~35Mpa) to clean the processed surface, holes, and oil passages, and remove burrs and sharp edges caused by processing. Use high-pressure cleaning fluid to flush the parts and flush away the burrs. This method is suitable for removing some loose burrs, but isn't effective for firmly attached burrs, and may require special flushing equipment and flushing fluid.
Different suppliers choose slightly different high-pressure cleaning equipment. Some use independent high-pressure cleaning equipment to remove burrs, and some are tunnel-type equipment that integrates ultrasonic, spray, drying, etc. At present, the six-axis high-pressure water deburring equipment developed by domestic high-pressure water deburring equipment manufacturers can achieve coverage of complex structures and parts, and the efficiency has also been greatly improved. Ultimately, it is necessary to evaluate and select a more efficient and economical deburring method based on product structure requirements and production capacity efficiency.
4. Brush or special tool: Intersecting oil passages or special-shaped structures can be deburred with a brush or ball milling cutter. You can also use a high-pressure cleaning spray gun to deburr. Which method is more appropriate should be confirmed based on the product structure and removal effect.
5. Ultrasonic deburring: Ultrasonic waves generate instant high pressure to remove burrs, mainly targeting microscopic burrs. Generally, if the burrs need to be observed with a microscope, you can try to use ultrasonic waves to remove them.
6. Deburring with fiber brush: Fiber brush or abrasive brush deburring is a method that uses fiber brushes to remove burrs from the surface of the workpiece. The fiber of the fiber brush has a certain hardness and toughness. When it comes into contact with the surface of the workpiece and performs friction, scraping and other operations, the fiber can cut and scrape the burrs, so that the burrs are gradually removed. At the same time, the softness of the fiber also allows it to adapt to the complex shapes and different angles of the workpiece surface, and can penetrate into some hard-to-reach parts for deburring operations.
Compared with some traditional deburring methods, fiber brush deburring doesn't produce new burrs during the burr removal process, and can ensure the smoothness and quality of the workpiece surface. Wide range of application: It can be used on workpieces made of various materials, such as metals, plastics, ceramics, etc. It can also be well adapted to workpieces of different shapes and sizes, and is especially suitable for removing burrs on some small and complex structural workpieces. Flexible operation: Fiber brushes are usually lighter and more flexible to operate. They can be operated manually according to the specific conditions of the workpiece, or can be used with some power tools or automated equipment to meet different production needs.
7. Magnetic grinding and deburring: Place the workpiece into the magnetic field formed by two magnetic poles, and place magnetic abrasives in the gap between the workpiece and the magnetic poles. The abrasives are arranged into magnetic grinding brushes along the direction of the magnetic lines under the action of the magnetic field. When the workpiece rotates and vibrates axially, the abrasive brushes grind and remove burrs on the surface of the workpiece. This method is suitable for parts of various materials, sizes and structures. It can grind and deburr efficiently and quickly. It can be used for grinding and deburring the internal and external surfaces of rotating bodies, flat parts, gear teeth, complex profiles, etc. It can also remove oxide scale on wires and clean printed circuit boards, etc.
At present, the first six methods are mostly commonly used for die-casting parts. It is often difficult to completely avoid burrs during the machining process. We still need to solve them through processes and try to reduce manual intervention. Although burrs are small, they are extremely harmful. Do not cause the electric drive or electronic control machine to be scrapped because of small burrs.