Abstract Magnesium alloy castings and forgings have residual stress and deformation more or less after forming and solution treatment-quenching. The dimensional and shape accuracy may not meet the standard requirements, and the surface will also leave lubricant and ash. Oxidation, gates, flash, burrs, etc., should be finished. Cast...
Magnesium alloy castings and forgings have residual stress and deformation more or less after forming and solution treatment-quenching. The dimensional and shape accuracy may not meet the standard requirements, and the surface will also leave lubricant, ash and oxidation. Leather, gates, flash, burrs, etc., should be finished. Excess metal, such as process residuals, flash, leaky agglomerates, spills, vents and non-metallic slag, are always left on the castings of the finished magnesium alloy die castings and castings. Trimming is often combined with drilling, trimming and other processes, and there is a certain corrective effect. Generally, the precision of the trimming mold determines the quality and size of the finished product. If the workpiece is deformed during heat treatment at T4 and T6, straightening or machining correction is also required.
Some die-cast parts are net-formed, no further processing is required after trimming, and some require mechanical processing such as vibration, ultrasonic, or shot peening to improve surface quality. For some castings that require strict and repeatable deviations, high-precision secondary machining is required.
Surface treatment of magnesium alloys is poor in corrosion resistance, and the surface treatment of castings and die castings should be carried out, such as anodizing, passivation, spraying or shot peening. Grinding, polishing and other finishing processes can also be used to improve surface quality and condition and improve corrosion resistance.
Finishing and trimming of forgings is an indispensable process for trimming and shaping in the production of magnesium alloy forgings. Cracks should be carefully controlled when trimming. Magnesium alloys have low plasticity at temperatures below 220 ° C, are sensitive to tensile stress, are weak at high temperatures, are highly viscous and easily strained, so cracks are prone to occur when trimming. It is usually cold cut with a band saw, or it can be cold milled or cut with a trimming die.
The use of band saw trimming or cold milling trimming is suitable for the production of forgings of small batch size, simple shape or large size, without cracking, and the trimming die can be omitted.
When the burr is hot-cut by the press, the bite type die can be used to minimize the gap or the gap of the convex and concave molds, and avoid the occurrence of trimming cracks, and the cutting edge temperature is 200 ° C ~ 300 ° C. Advantages of die cutting: low labor intensity, safe work, high quality of trimming, high production efficiency, but high mold price, special use, a forging, and easy to produce burrs.
Straightening and precision due to the complex shape of the forging, uneven organization during forging, improper placement during quenching, uneven quenching temperature and water temperature, uneven cooling shrinkage, etc., internal stress will occur, causing forging deformation, and forging The forging will also warp the forgings, so the shape of the forging will be distorted, the size will change greatly, and it must be straightened to be aging.
Straightening and coining are carried out in a final pressure mold at a temperature of 200 ° C to 300 ° C. Advantages of die cutting: low labor intensity, safe work, high quality of cutting edge and high production efficiency. However, the price of the mold is high and the use is specific. A forging piece is also easy to produce burrs.
Straightening and precision due to the complex shape of the forging, uneven organization during forging, improper placement during quenching, uneven quenching temperature and water temperature, uneven cooling shrinkage, etc., internal stress will occur, causing forging deformation, and forging The forging will also warp the forgings, so the shape of the forging will be distorted, the size will change greatly, and it must be straightened to be aging.
Straightening and coining are carried out in a final pressure mold at a temperature of 200 ° C to 300 ° C to obtain semi-thermal cold hardening with a degree of deformation of 10% to 15%.
Surface treatment All magnesium alloy forgings are etched regardless of the intermediate process or the final forging process. The intermediate process etch is to visualize the surface defects of the forging and intermediate blanks for repair. In addition to surface defects, the purpose of the finished product erosion treatment is to determine the repair or scrapping, but also to make the surface smooth and easy to apply oil coating. The specifications for the erosion of magnesium alloy forgings are shown in the table below.
When eroding, pay attention to the position of the forging in the material frame, which is convenient for the trough to flow out and not accumulate in the forgings. Otherwise, the forgings will be corroded.
After repairing the forgings, it is advisable to repair them immediately. It can be repaired with pneumatic grinder, electric soft grinder, air shovel and flat shovel. Before repairing, carefully check the location and state of defects such as folding, cracking, pressing, peeling, etc., and determine the repair order. The transition of the repair site should be smooth and the width is 8~10 times of the depth. The process protrusions in the intermediate process should be repaired. For the forged parts after repair, it is necessary to re-clean and check whether the repair is thorough. If it is not completely repaired, it should be repaired twice. The qualified finished forgings are packaged and put into storage after being oiled.
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