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Polishing method and internal crack detection method of die casting

2020-08-12 14:17:29

Die casting is a popular and popular process. Due to the metal copper, zinc, aluminum and aluminum alloy fittings, now people like to have a little sense of metal, and the die casting has the characteristics of metal, but the process is relatively simple, the die casting has good fluidity and plasticity, and the casting process is cast in the pressure die casting machine, so the aluminum die casting can make various complex shapes, and also can make higher precision and finish, so as to improve the accuracy and smoothness To a great extent, the machining capacity of castings and the casting allowance of copper, zinc, aluminum or aluminum alloy are greatly reduced, which not only saves power, metal materials, but also greatly saves labor costs; while copper, zinc, aluminum and aluminum alloys have excellent thermal conductivity, small proportion and high machinability; therefore, die castings are widely used in automobile manufacturing, internal combustion engine production, motorcycle manufacturing Motor manufacturing, oil pump manufacturing, transmission machinery manufacturing, precision instruments, landscaping, power construction, architectural decoration and other industries.


At present, there are several common polishing methods

1) Mechanical polishing

Mechanical polishing is a polishing method which can remove the micro convex part of the product surface and make the surface smooth. Mechanical polishing generally uses polishing wheel, vibration grinder or other grinding equipment.


The polishing wheel is usually composed of multi-layer canvas, felt or leather, clamped by metal circular plate on both sides, and the wheel rim is coated with polishing agent composed of fine powder abrasive and grease. Polishing is to press the die-casting products manually to the high-speed rotating polishing wheel, so that the abrasive can roll and micro cut the surface of the workpiece, so as to obtain a smooth surface. When a non greasy matting polishing agent is used, it can dull the bright surface for appearance.


At present, most factories have used vibration grinder to polish zinc alloy die-casting products, which can be polished in batches. The polished products have high surface smoothness and save manpower, material and financial resources.


2) Chemical polishing

Chemical polishing is to use chemical medium to dissolve the micro protruding part of die casting surface, so as to obtain smooth product surface. The main advantages of this method are that it does not need complex equipment, the investment of polishing equipment is small, the operation is convenient, the workpiece with complex shape can be polished, and the polishing efficiency can be improved by batch polishing. The use of chemical polishing zinc alloy products, can quickly get bright outside, at the same time with good performance, and easy to electroplating, spraying and other processes.


3) Electropolishing

The basic principle of electropolishing is the same as that of chemical polishing. However, compared with chemical polishing, electrolytic polishing can eliminate the influence of cathode reaction and get good results.


4) Ultrasonic polishing

Ultrasonic polishing is the use of ultrasonic vibration, so that placed in the ultrasonic field of zinc alloy products and mold material suspension vibration, so that abrasive die cutting product surface, achieve polishing effect. And the ultrasonic polishing will not produce product deformation due to polishing, resulting in scrapping. But ultrasonic polishing equipment investment is more, installation is more troublesome, not suitable for separate use. Combined with chemical polishing and point solution polishing, it can improve the ability of products.


5) Magnetic abrasive polishing

Magnetic abrasive polishing is the use of magnetic abrasive under the action of magnetic field to form abrasive brush to grind the surface of die casting parts. The efficiency of magnetic abrasive polishing is relatively high, and the quality of zinc alloy die casting products is good, and the working environment is excellent.


Detection method for internal crack of die casting parts:

1. Ultrasonic testing

Ultrasonic testing and thickness measurement of various metal pipes, plates, castings, forgings and welds. When ultrasonic waves encounter cracks, cavities, segregation and other defects, the acoustic parameters such as ultrasonic velocity, amplitude and frequency will change accordingly. According to these changes measured by instruments, the existence of defects can be judged and their specific positions can be determined.

The ultrasonic pulse (usually 1.5MHz) shoots the detected object from the probe. If there is a defect in its interior, there will be an interface between the defect and the material, then a part of the ultrasonic emitted by human will be reflected or refracted at the defect, and part of the ultrasonic energy transmitted in one direction will be reflected, and the energy passing through the interface will be reduced accordingly. At this time, the reflected wave of the defect can be received in the reflection direction; the ultrasonic energy received in the propagation direction will be less than the normal value, which can prove the existence of defects. In flaw detection, the position and size of the defect can also be detected by the performance of the probe receiving pulse signal. The former is called reflection method, and the latter is called penetration method.

2. Magnetic particle inspection

It is suitable for nondestructive testing of ferromagnetic materials such as casting, forging and other machined parts.

3. Ultraviolet lamp

It is cheap, high and easy to operate. It can detect the leakage of all kinds of pipes, check whether the coating is uniform or not, detect the impurities or stains, semiconductor and biological fields, stage special artistic effect.

4. Radiographic inspection

X-ray inspection can be divided into X-ray, gamma ray and high-energy ray detection.

X-ray photography is based on the attenuation law of rays in materials and the photochemical and fluorescent effects on some substances. From the point of view of ray intensity, when the ray intensity on the workpiece is J0, the ray passing through the workpiece will be weakened to JC due to the attenuation of ray by the workpiece material. If there are defects in the workpiece, the actual thickness of the workpiece through which the ray passes through is reduced, then the ray intensity JA and JB passing through the point is larger than that of the point without defect. From the point of view of the photochemical effect of the ray on the negative, the part with strong ray has a strong photochemical effect on the negative film, that is, it has a large amount of light. A negative with a high sensitivity becomes darker after being treated in a dark room. Therefore, the defects in the workpiece produce black shadow on the negative film by ray, which is the principle of radiographic inspection.

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