People who work in die casting industry and are engaged in quality work probably have same experience or troubles. One of problems that customers often complain about is problem of burr residue. Many times, they are still very unconvinced, thinking that it is just a small burr, how can a die casting be completely burr-free? Isn't this deliberately embarrassing people? Why are there no such high requirements for fuel vehicle engine parts?
This article will sort out risks of new energy die castings based on my personal experience, such as burrs, flash insulation, casting points, cracks, etc.

There are many parts of electric drive assembly that are pressed, such as when conductive ring, oil seal or bearing is pressed inside electric drive housing. If sharp edge burrs remain in chamfered part of mounting hole, it may cause abnormal press assembly or cut oil seal. Sharp edge burrs may cause poor matching of parts. For example, burr residue in water channel seal groove of motor housing will destroy integrity of the seal ring and cause leakage risk.
Integration of three-electric products is high, and space is limited. Spacing between internal assembly parts is often small. For example, height of casting point of traditional gearboxes is generally not more than 0.5. However, if height of protrusions such as casting point and cracks inside new energy housing is controlled within conventional 0.5, it may cause interference with assembly of opponent, especially when opponent is an electrical device, there may be problems such as creepage safety distance, which may lead to failure.

There are many internal electrical components of electric drive, electric control or charger. Burrs on inner wall of electric control system housing may scratch insulation layer of wiring harness, causing short circuit or leakage (such as short circuit inside motor controller). If metal burrs fall off and enter internal connector of electric drive housing, it will also cause short circuit failure.
Burrs inside electric control housing or charging housing fall off or scratch PCB board, causing short circuit and functional failure. Functional failure of parts often leads to assembly failure, which has great impact and loss.

Bearings of new energy vehicles are basically open bearings, and speed is relatively high. At the same time, compared with fuel vehicles, there is less engine noise, noise control requirements are higher. Burrs are left in vibration or cooling oil inside motor falls off and enters bearing, causing abnormal wear of bearing, which will not only cause premature failure of bearing, but also cause excessive noise.
Diameter of oil channel inside some motor housings is only 1.5mm. When aluminum chips and burrs remain and block oil channel, bearing or other lubrication system fails, resulting in failure of assembly function.

If there are burrs and aluminum chips left in water channel of electric drive, electronic control and charger, burrs will block filter of test equipment during aging test of assembly, resulting in abnormal equipment temperature and equipment failure. Once equipment loses temperature and is damaged, loss will be huge.

From my point of view, common burr problems of die-casting parts can be divided into two categories: burrs on blank body, burrs caused by machining, and burrs on products assembled in post-process.

Flash of die-casting parts is not removed cleanly or is left out; burrs on the edge of ejector are not removed cleanly and burrs are left; surface of blank shell is peeled by shot blasting, and there are also mold cracks, burrs and casting points.
Air tightness requirements of new energy electric drive shell are high, and product has many integrated parts, resulting in more ribs or mounting columns on shell surface. In order to ensure structural strength and density of these parts, 3D printed contoured cooling inserts are sometimes set. After mold is produced for a long time, joints of these parts are prone to flash, they are also easily ignored and missed.

Common burrs after shell machining include: sharp edge burrs on the edge of machined surface, especially sharp corners of edges; secondly, electric drive shell often has many oil channel holes, bottom of oil channel hole and intersection of two oil channel holes are also prone to product flanging burrs; some through-hole bottoms or ends are easily affected by feed direction of machining tool, resulting in extrusion burrs.

 

At present, new energy electric drive housings, electric control housings and charging housings will involve requirements of pressing or assembling accessories. If chamfering tool for installation hole is not designed properly, it is easy to produce burrs of extruded cutting edges during pressing process.
In addition, if material of tooling positioning pin is unqualified, positioning hole is also easy to be scratched and produce burrs.

Traditional deburring processes mostly rely on manual operation, with a low degree of automation. Manual deburring relies on manual use of files, sandpaper and other tools to polish each piece, which is inefficient and easily affected by worker fatigue or skill level. Quality is greatly affected by experience of workers. Cross-hole or special-shaped structure is difficult to remove, and it is easy to have uneven or missing surface problems.
Poor processing quality and consistency, difficulty in recruiting workers, and occupational health risks. In addition, many die-casting companies now outsource this process to a third party.

During casting process, workpiece deformation is inevitable, especially in thin-walled parts or products such as controller/charger housings, where deformation difference is large, which increases difficulty of deburring. Using CNC programming automation operation, robot arm or tool path is controlled by preset parameters to achieve high-precision deburring. It supports continuous high-intensity operation and can handle multiple processes at a time, with an efficiency several times that of manual work. Parametric control ensures uniform processing results and is suitable for complex geometric shapes and high-precision surface treatment.
CNC deburring has obvious advantages in efficiency, quality and large-scale generation. With strengthening of automation trend in manufacturing industry, CNC equipment is gradually replacing traditional manual processes. At present, customized development services of many domestic deburring supporting manufacturers have become relatively mature. In the past two years, they have also been constantly innovating and developing multi-axis processing equipment, multi-station deburring equipment and other deburring equipment.

Use a high-pressure cleaner (cleaning water pressure of 28~35Mpa) to clean processing surface, holes, oil channels, remove burrs and sharp edges generated by processing. Use high-pressure flushing fluid to flush the parts and wash away burrs. This method is suitable for removing some loose burrs, but it is not effective for firmly attached burrs, special flushing equipment and flushing fluid may be required.
Different suppliers choose slightly different high-pressure flushing equipment. Some use independent high-pressure cleaning equipment to remove burrs, some use tunnel-type equipment that integrates ultrasonic, spraying, drying, etc. At present, six-axis high-pressure water deburring equipment developed by domestic high-pressure water deburring equipment manufacturers can achieve complex structures and parts coverage, and efficiency has been greatly improved. In the end, it is also necessary to evaluate, select a more efficient and economical deburring method based on product structure requirements and production efficiency.

 

Six-axis high-pressure water deburring equipment

Intersecting oil channels or special-shaped structure positions are suitable for brush deburring, or ball milling cutter removal, or high-pressure cleaning spray gun deburring. Which method is more suitable should be confirmed based on product structure and removal effect.

 

Ultrasonic waves generate instantaneous high pressure to remove burrs, mainly for some microscopic burrs. Generally, if burrs need to be observed with a microscope, they can be removed by ultrasonic methods.

Fiber brush or abrasive brush deburring is a method of removing burrs on the surface of a workpiece using a fiber brush. Fiber of fiber brush has a certain hardness and toughness. When it contacts surface of workpiece and performs friction, scraping and other operations, fiber can cut and scrape burrs, so that burrs are gradually removed. At the same time, softness of fiber also allows it to adapt to complex shapes and different angles of workpiece surface, can penetrate into some difficult-to-reach areas for deburring operations.

 

Fiber internal control brush deburring
Compared with some traditional deburring methods, fiber brush deburring will not generate new burrs during deburring process, can ensure smoothness and quality of workpiece surface. Wide range of applications: It can be used for workpieces of various materials, such as metal, plastic, ceramic, etc. It can also adapt well to workpieces of different shapes and sizes, especially suitable for removing burrs on some small and complex structure workpieces. Flexible operation: Fiber brushes are usually light and flexible to operate. They can be operated manually according to specific situation of workpiece, or they can be used with some electric tools or automation equipment to meet different production needs.

 

Magnetic grinding and deburring: Put workpiece into magnetic field formed by two magnetic poles, put magnetic abrasive in gap between workpiece and magnetic poles, and abrasive is arranged along direction of magnetic line of force under action of magnetic field force to form a magnetic grinding brush. When workpiece rotates and vibrates axially, abrasive brush grinds and deburrs surface of 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 inner and outer surfaces of rotating bodies, flat parts, gear teeth, complex surfaces, etc. It can also remove oxide scale on wire and clean printed circuit board, etc.
At present, I know that the first six methods are the most commonly used for die castings. It is often difficult to completely avoid burrs during machining. We still need to solve it as much as possible through technology and try to reduce manual intervention. Although burrs are small, they are very harmful. Don't let small burrs cause electric drive or electronic control machine to be scrapped.