Aluminum castings are prone to internal porosity, shrinkage, porosity, sand holes, and other defects in aluminum die casting. After machining these defective castings, the surface dense layer composition is removed, but the internal organization defects are easily exposed.
Die-casting surface cracks are linear or irregular, with the external force having a tendency to expand. Cracks include cold cracks (unoxidized material at the crack) and hot cracks (oxidized material at the crack). The defect can be recognized by visual inspection.
There are two types of visual defects:
Casting cracks are cracks formed at relatively high temperatures. They are prone to occur when the casting shrinks in volume and has a high coefficient of thermal expansion.
Heat treatment cracks: Cracks caused by overheating or heat treatment, often showing cracks through the crystal.
Reasons and suggestions for cracks:
1, the casting structure is not reasonably designed, resulting in uneven shrinkage, sharp corners, and too large a change in wall thickness. If cracks occur in this case, the structural design of the casting should be improved to avoid sharp corners, and efforts should be made to strengthen the wall thickness and smooth transition.
2, poor yield properties of the sand mold (core) will also appear cracks. Measures should be taken to increase the yield of the sand mold (core).
3. Mold local overheating will produce cracks. We should ensure that all parts of the casting are solidified simultaneously or sequentially and improve the design of the pouring system.
4. A pouring temperature that is too high will also produce cracks. It should be appropriate to reduce the pouring temperature.
5. Too early opening of the mold leads to insufficient rigidity of the casting; when the casting is taken out too early, the casting will be deformed, and thermal correction methods should be used. The cooling time of the mold should be controlled.
6. The heat treatment is too hot, and cracks are produced after the cooling rate is too aggressive. When the casting is deformed, use the thermal correction method. Correctly control the heat treatment temperature and reduce the quenching and cooling speed.
7. The ejector mechanism is not reasonably designed, resulting in unbalanced ejection of castings; it may also be caused by the local surface roughness, product ejection deformation, and casting ejection resistance; ejection force is large, resulting in product deformation. The local temperature of the mold is too high, and the products are not solidified sufficiently.
8. Improper method of removing the gate: the gate is too thick and easily deformed when cut off.
Solution:
1. Material selection: aluminum die-casting manufacturers are in the process of manufacturing to ensure that the melting process of the alloying element content is correct; choosing the right material is an important consideration. The material should be suitable for the application and have the proper mechanical and physical properties to withstand the operating conditions. The material should also be free of impurities that can weaken the casting and increase the risk of cracking, such as inclusions, pores, and voids.
2. Aluminum die casting services require proper design considerations: optimization of the die casting structure, avoiding uneven wall thicknesses, and designing the die casting to minimize stress concentrations that can lead to cracking. This includes avoiding sharp corners, creating transition radii, and ensuring uniform wall thicknesses, smooth surface finishes, and appropriate fillet radii.
3, control casting temperature and cooling rate: control of the casting process temperature and cooling rate is critical to prevent cracks. Cooling rates should be optimized to achieve uniform solidification and avoid sudden thermal gradients that may cause high stress.
4. Optimized gate and riser design: Proper gate and riser design helps prevent casting defects and reduces the potential for cracking. It also ensures that the molten metal flows uniformly into the mold cavity and that any excess material is efficiently discharged.
5. Inspection and quality control: Regular inspection and quality control practices should be followed to detect any early signs of cracks or other defects in the casting. This includes visual inspection, non-destructive testing, and other methods to ensure the quality of the finished product.
