With the rapid development of sheet metal processing industry, this industry plays an increasingly important role in industrial production. However, the increase in the number of orders has also brought some side effects, such as the increase in the error rate, the increase in the number of problem pieces, and so on. Most of these problems focus on the deformation of sheet metal processing parts and insufficient springback in the processing process.
Causes and solutions of sheet metal workpiece problems
In the forming process of sheet metal processing parts, a series of treatments are required, especially in the cooling process of parts. There are strict requirements for the type of quenching medium, cooling performance and hardenability. If it does not meet the requirements, it may cause deformation. Experience shows that the change of cooling performance of parts can be adjusted by changing the viscosity, temperature and liquid level pressure of quenching medium, using additives and stirring. The higher the viscosity and temperature of quenching oil, the smaller the elliptical deformation. The deformation of the part in the static state is small.
In the heat treatment of forgings, due to the small hardness of parts, incorrect placement may cause uneven stress, resulting in the deformation of parts. Hang the parts vertically as far as possible, or place them vertically at the bottom of the furnace, or use two fulcrums to support them horizontally. The fulcrum position should be between one quarter and one third of the total length of the parts, and the parts can also be placed flat on the heat-resistant steel tooling.
Decompression quenching of sheet metal processing is to reduce the liquid pressure of quenching medium and extend the steam film stage, so that the cooling speed of parts in the high temperature zone decreases and the cooling speed of all parts is evenly distributed. In this operation, firstly, the parts should be cooled by oil cooling from quenching temperature to slightly higher than the initial temperature of martensite transformation; Next, keep the parts in the atmosphere for a while to make the overall temperature uniform, and then conduct oil cooling to make the martensitic transformation uniform, and the irregularity of deformation is greatly improved.
Technological means to reduce sheet metal processing deformation
The processes that can effectively reduce the deformation of sheet metal processing include salt bath quenching, high temperature oil quenching, decompression quenching, one tank three-stage quenching, etc. The process of salt bath quenching is similar to that of high-temperature oil quenching. Both of them are quenched at the martensitic transformation temperature, which increases the uniformity of martensitic transformation.
For welded structures with many components, it is necessary to choose the appropriate welding sequence. First, the components should be welded and corrected respectively, and then assembled for overall welding. Using this sequence is smaller than the method of first assembling into a whole and then welding. Individual parts can also be installed and welded at the same time, which is relatively simple to operate. In order to prevent welding deformation, strip welding, back welding and symmetrical welding should be adopted in the welding sequence.
Before welding, the weldment shall be given a deformation opposite to the deformation direction after welding, and the deformation of the workpiece before welding is just offset after welding, which is called anti deformation method. Rigid fixation can also be used, which is also very effective in reducing welding deformation.
Various welding methods have different energy density and heat input when heating the weld. For thin plate welding, selecting welding methods with high energy density, such as carbon dioxide gas shielded welding and plasma arc welding to replace gas welding and manual arc welding, can reduce welding deformation. When welding aluminum and aluminum alloy structures, the deformation of gas welding is much larger than that of manual argon arc welding.
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