The Effect of X-ray Inspection on the Defect of Castings and Development of the Foundry Industry

Aluminum castings have the advantages of accurate sizes and smooth surfaces and they can be used directly after machining, which not only improves the metal's utilization rate, but also reduces a large amount of processing equipment and man-hour casting prices. It is easy to use combined die casting materials and other metal or non-metals, which saves both assembly man-hours and metals.
 
Die casting has a wide range of applications, and aluminum casting is one of the most advanced metal forming methods. It is an effective way to achieve the purpose of fewer cuttings or no cuttings. It is widely used and is developing rapidly. At present, die-cast alloys are no longer limited to non-ferrous metals such as zinc, aluminum, magnesium and copper, and are gradually expanded to cast iron and steel castings. The size and weight of the die-cast parts depend on the power of the die casting machine. As the power of the die casting machine continues to increase, the shape and size of the die casting part can range from a few millimeters to 1 or 2 meters; the weight can range from a few grams to tens of kilograms. Foreign aluminum manufacturers can manufacture die casting parts with a diameter of 2 meters and a weight of 50kg. Die casting parts are no longer limited to the automobile and instrument industry, and gradually expanded to other dozens of industrial sectors, such as agricultural machinery, machine tool industry, electronics industry, defense industry, computers, medical equipment, clocks, cameras, daily hardware, etc. In terms of die casting technology, new processes such as vacuum die casting, oxygenation die casting, precision, fast die casting, and soluble mold cores have emerged.
 
Aluminum die castings are widely used in instrument, automobile, agriculture, medical, 5G communication, and other industries. For the growing aluminum die castings, their quality is also a concern for manufacturers.
 
The quality of aluminum castings often affects that of the entire product. For example, aluminum castings are an important part of the automotive industry. Manufacturers are investing more and more in lightweight. As lightweight materials, aluminum alloy is one of the effective ways to reduce the weight of the car.
 
The quality of die castings has a great influence on the performance of mechanical products. For example, the wear resistance and dimensional invariance of machine tool castings will indirectly affect the accuracy and service life of the machine tool. The size of the various pump's impeller, casing and hydraulic parts, accuracy and roughness of the contour indirectly affect the working efficiency of the pump and hydraulic system, increase in energy consumption and cavitation. The strength and resistance of castings such as internal combustion engine cylinder blocks, cylinder heads, cylinder liners, piston rings and exhaust pipes will indirectly affect the service life of the engine.
 
In the die casting process, casting defects have always been a major problem that plagues foundry enterprises. Poor solutions to casting defects will affect the quality of castings. Various types of defects are generated on the surface and inside of die casting parts in the manufacturing process due to various reasons. There are more than 100 kinds of common die casting defects. In China's national standard GB/T5611-1998 Casting Terminology, die casting defects are divided into the following 8 categories according to their morphological characteristics: 1. Over materials 2. Holes 3. Cracks and cold shuts 4. Surface defects 5. Incomplete defects 6. Shape and weight errors 7. Inclusions 8. Unqualified performance, composition and organization.
 
Many factors affect the quality of die castings. In the die casting process, it is essential to control and inspect the quality of the die castings. Usually, the internal defects of the die castings can be detected. Non-destructive testing is performed by ultrasonic and X-ray methods for castings to check and judge the quality of the castings.

For aluminum die castings with complex structure, check whether or not the internal structure meets the design requirements. Sometimes it is necessary to cut the casting. This will damage the aluminum castings. In order to ensure the quality of the castings, manufacturers attach great importance to the quality inspections of the castings, but most of the internal defects of the castings cannot be detected by ordinary methods. There are many quality assessment methods for castings, among which X-ray inspection is the best. It can detect information such as the internal structure and mechanical properties of the inspected object without destroying the inspected object. Many internal defects such as shrinkage cavities, slag inclusions, slag holes, shrinkage porosities, cold shuts, cracks and other internal defects of the casting can be seen well, and it is easy to perform qualitative and quantitative analysis of defects.
 
X-ray equipment can detect the relationship between the penetration ability of X-rays and density of substances, and the characteristics of differential absorption can distinguish substances of different densities. Therefore, if the inspected object is damaged, its thickness is different; the shape changes, and the X-ray absorption rate is different. The resulting image is also different, so it is possible to produce a distinctive black and white image.
 
The X-ray tube mainly supplies electrons from the hot cathode to accelerate to the anode through an electric field. When electrons are rapidly accelerated to a high-speed state under high pressure of tens of kilovolts, the kinetic energy is converted to release X-rays when they hit the anode body. The size of the collision area is that of the X-ray source. Through the principle of small hole image-forming principle, we can roughly know that the size of the X-ray source is inversely proportional to the definition, that is, the smaller the X-ray source is, the clearer the image becomes. This is the principle by which X-rays can detect defects in die castings.
 
The importance of X-ray inspection for inspecting die castings is self-evident. Quality inspection for die casting parts is not only a manifestation of high-quality production services for enterprises, but also a favorable guarantee for industrial safety production. It can be said that the development of the casting industry is inseparable from that of X-ray inspection. The X-ray inspection equipment uses X-ray imaging principles to well detect defects such as cracks, cold shuts, sand holes, gas holes, slag holes, shrinkage porosity and slag inclusions in aluminum die castings without damaging the products.