Views: 153 Author: Site Editor Publish Time: 2023-11-28 Origin: Site
Bending tooings are the main parts for sheet metal processing and forming. With the development of construction machinery, automobiles, aerospace, electrical instruments and construction and decoration industries, the precision and shape of sheet metal products formed by press brake machine and its requirements are getting higher and higher, and the surface quality of sheet metal parts is more strickly. Especially for the bending processing of stainless steel plates and aluminum plates, it is required that there are no scratches. In order to avoid indentation on the surface of the workpiece during bending process, the surface of the sheet metal part during bending is analyzed from the four aspects of the bending method for the sheet metal part: the material hardness, the lower die structure, the choice of the machine and its mold accuracy ,the cause of indentation.
The figure below shows the structure of the lower die under the traditional bending method. This structure usually has V-shaped grooves with different openings, which are used to bend plates of different thicknesses. The points A and B in the figure below are the stress points of the plate, and the creases usually appear at points A and B. When bending, the upper die falls, and the sheet slides along two points, A and B, L is the sliding range, and it is also the place where the indentation is most likely to occur. If the manufacturer adopts the coating method to avoid indentation, the protection film is easy to break by the change of bending pressure. Once the protective film is broken, indentation will occur.
During bending process, under the action of bending force, the sheet moves along the edge of the V-shaped notch of the lower die and is pressed and sliding friction by the bending force, so that the surface of the formed sheet metal part forms obvious indentation and scratches. The width of the defective band is about 0.414 times that of the V-shaped notch, which seriously affects the appearance quality of the product. To solve the above-mentioned defects in traditional bending, it is necessary to overcome the friction and squeezing force caused by the movement of the plate and the V-shaped groove of the lower die on the plate during the bending process.
⒈Non-indentation mold structure
Based on the above principles, according to the current processing capacity of CNC bending machines in the market, a mold for indentation free is coming into the market.
⑴ According to the plate type, the minimum bending material thickness of the mold is designed to be 0.6mm, the maximum bending material thickness is 2mm for steel plates and 2.5mm for aluminum plates.
⑵ In the design of the bending length, the combination of the characteristics of the lower die of the CNC bending machine is used to complete the combination. Considering the difficulty of the mold processing, the length is designed to be 200mm. Multiple sets of spares can be produced in the work, according to the different bending lengths of the parts requirement for a combination.
⑶ In order to maintain the stability of the mold performance and reduce the deformation during the mold processing, the materials of the die base and the rotating lower die are all used for the cold die special material Cr12 with stable performance, and it must be kneaded and forged, and the carbide segregation is 1 ~2 (fine pearlite tissue).
⑷ A specially designed special tension spring is used to meet the needs of the mold.
⑸ The mold meets the requirements of our company's existing CNC bending machine, and is convenient, safe and reliable to use.
⒉The design principle of non-indentation bending process
Aiming at the defects of traditional bending, engineers used the principle of seesaw to design the bending lower die into one piece for each of the left and right that can rotate around the axis. When the mold is not working, the working surfaces of the left and right lower molds are on the same horizontal plane. When the bending upper mold moves downward to perform the bending process, the left and right lower molds respectively perform a flipping movement around their respective rotation centers, forcing the material to rotate around the apex of the upper mold while being close to the working surface of the lower mold, thereby Bending deformation occurs, and finally the bending process of the material is completed. Since the working surface of the lower die rotates, the force uniformly acting on the surface of the material through the working surface of the lower die will not squeeze the local parts of the material, avoiding the crushing defects caused by the extrusion on the surface of the parts. At the same time, because the material rotates and bends around the apex of the upper mold, the material does not slide on the working surface of the lower mold, thereby avoiding the scratches on the surface of the parts.
The structure of the roller-type non-indentation mold is shown in the following figure. During the bending process of the metal plate, the workpiece contacts the hard alloy core rod on the lower mold during the bending process, and the core rod will follow the plate Rotation in the direction of movement makes the workpiece change from traditional sliding friction to rolling friction after contact with the lower die, which greatly reduces the pressure marks and scratches on the surface of the workpiece due to compression, and effectively improves the appearance quality of the workpiece And precision. However, during the bending process, there is still squeezing force between the lower die roller and the plate, and bending indentation cannot be completely avoided, especially when bending a soft material plate.
The structure of the Non-indentation mold with double semicircle rollers is shown in the following figure. During the process of pressing the workpiece into the lower mold channel by the upper mold, the semicircle roller rotates in the lower mold body because the workpiece is in contact with the plane of the rotary roller. During the bending process, there is no relative sliding with the rotating flap. At the same time, the workpiece and the rotating flap are in surface contact, eliminating the indentation and scratches caused by the extrusion on the surface of the workpiece, and effectively improving the appearance quality and accuracy of the workpiece.
In addition to the above two non-indentation molds, which can solve the indentation of the workpiece surface during bending, it can also be used by using an indentation-proof rubber pad, a single V lower mold anti-indentation rubber sleeve, block superior glue +AT cushion, hard Quality rubber lower die and other methods to solve the indentation of the workpiece surface during bending to meet product quality requirements, as shown in the following figure. However, rubber pads, rubber sleeves, non-indentation molds, block superior glue and hard rubber are easily deformed during the bending process and have a short lifespan, which affects the dimensional accuracy of the bent workpiece. It is only suitable for workpieces with low dimensional accuracy requirements.
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