In many industries, such as construction, railway, decoration, etc., there are all kinds of profiles that need to be bent by a profile bending machine. These profiles have different shapes from the cross-section; from the point of view of product accuracy, some Profile bending is very difficult and demanding, therefore, how to solve the problem of bending forming from the process is of great significance to profile processing and manufacturing.
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Example of bending an aluminum alloy without deformation (profile forming for side windows of subway vehicles)
The bending example of the profile is used for the side window of a subway vehicle. The shape of the profile after bending is shown in the figure above. From the cross-section of the profile used for the part, the shape is more complicated and the bending is difficult. The bending quality requirements are very high.
The original bending forming process is: make a complete set of bending dies (clamps, fixed dies, and rotary dies), use bending equipment to bend the profile, as shown in the picture above, clamp and fix the profile with the mold, and rotate the rotary die around the center of rotation to make The workpiece is bent and formed.
However, when bending, a part of the bending arc of the profile is depressed (above), which seriously affects the quality of the product. The reason is that when the outer edge of the profile is deformed because there is no filler in the groove, The turning point of the profile is subjected to force and local bending moment (below), so this part of the profile shrinks toward the bending center, causing this defect
For this reason, spring steel strips are filled in the groove (see the picture above). The bending and forming of the profile have been greatly improved, but after the profile is bent and formed, it is very difficult to take out the spring steel strip. The reason is mainly that when the spring steel strips are filled, there are gaps between the steel strips. When the profile is bent, the profile at the groove shrinks and the spring steel strips are tightly squeezed to form an “inverted trumpet” shape. , which makes it difficult to remove the spring steel strip. When other tools (such as screwdrivers, etc.) are used to forcibly remove the spring steel strip, it will cause serious damage to the profile surface and affect the product quality.
Application of low melting point alloy in the aluminum profile bending process
In order to solve this problem, it was decided to use low melting point alloy filling technology.
What is a low melting point alloy?
Low melting point alloy is a special material for making molds, and it is an alloy smelted from several non-ferrous metal materials with different melting points.
Six characteristics of low melting point alloys
Alloy materials should have the following characteristics:
- Low melting point, easy to melt, easy to mold;
- Good fluidity, and strong flow-filling ability after alloy melting;
- Has certain condensation expansion;
- No adhesion to the profile, easy to demould;
- The alloy can be reused and the cost of use is low;
- Non-toxic, harmless to the operator’s body, and does not pollute the environment
Bismuth-based multicomponent alloy
There are many materials used to make low-melting-point alloy molds, and the main applications are zinc-based alloys and bismuth-based alloys.
For the bending of aluminum profiles, when selecting the type of alloy, considering the feasibility of operation and the limitation of environmental conditions, it is decided to use the bismuth-based multi-element alloy with a melting point near 70 °C.
Design of bismuth-based multi-element alloy mold
In the past, when low-melting-point alloy molds were used as bending molds, the alloy was usually melted to make upper and lower molds, and the workpiece was bent and formed by pressure. It is made into a rectangular strip and placed at a place where the profile is easy to deform, which is equivalent to using a strip mold to cushion the profile. The low melting point alloy has a certain strength and toughness characteristics to ensure the correctness of the profile bending shape. At the same time, the low melting point of the alloy makes it easy to remove the alloy and other fillers.
Bending test of bismuth-based multi-component alloy dies for aluminum profiles
According to the formula, the alloy was prepared, melted, and cast in the groove of the section that needs to be bent, and then tried to bend. It was found that due to the wide width of the alloy strip, its toughness was not enough. Therefore, it was decided to melt the alloy and cast it into a small strip, place it in the groove, fill the gap with PV plastic strips, and dip it in boiling water after bending, the alloy can melt quickly, and other fillers can be easily taken out. In this way, which not only ensures the bending deformation of the profile but also ensures that the surface of the profile is not damaged.
Compared with no filler at all, when the filler is added, the bending stress on the profile is more evenly distributed in the entire bending surface, and there is no phenomenon of local bending moment, so the aforementioned bending defects do not occur.
PV plastic board filler strip
The PV plastic plate has a large amount of deformation, but because of its good elasticity, it does not break, thus ensuring the surface quality of the curved profile.
The inner surface of the profile in contact with the PV plastic plate is not affected by the local impact load caused by the sudden fracture of the filling strip, and the deformation is carried out under a relatively uniform load, so the profile does not break, but is uniformly bent.
After testing, small batch production, and mass production, it has been proved that this method of bending aluminum profiles is completely feasible, and the product quality and production efficiency have been greatly improved while saving a lot of manpower and material resources.
Final words
According to the above analysis and the application in actual work, flexible use of low-melting point alloy filling technology can better solve the problem of complex profile bending forming technology, and the alloy can be reused and non-toxic and pollution-free. The manufacturing cost of the product is greatly reduced, and the safety is also greatly improved, especially in the case of a large variety of products, a small quantity, and urgent supply requirements, its advantages are more obvious.