The bending process of automobile aluminum alloy profiles can be divided into tensile bending forming (two dimensional, three dimensional), roll bending forming, press bending forming and winding forming according to the different bending equipment and bending process principle. In the bending of profiles, especially in the bending of thin-walled hollow profiles, there will be various defects such as section deformation and springback, which has become an obstacle to its large-scale application.
The different shapes of industrial manufacturing workpiece can be divided into: two-dimensional bending workpiece, three-dimensional bending workpiece, bending equipment and bending process principle.
1, tensile bending forming process
1) Working principle of stretch bending forming
The stretching and bending process is basically divided into three steps:
The material is clamped by the jaws of the drawing cylinder and pre-tensile force is applied to the profile to achieve the yield strength of the material.
The rotary cylinder of the stretch bending machine is loaded with the bending rotary, and the axial tension of the stretch cylinder is set according to the program, so that the profile is fitted around the stretch bending die and the material is formed.
According to the material deformation and springback condition, additional tensile.
In the process of tensile bending, the workpiece is bent at the same time, the tensile cylinder always exerts axial tension on the workpiece, and the length of the extended part of the material is always compensated by the tensile cylinder traction, which avoids the wrinkle trend of the material and can get a good radian effect.
2) Characteristics of tensile bending forming process
Advantages of process:
① Can pull and bend the forming structure of the complex profile section.
② It can realize the stretching bending of multi-arc profile with variable curvature.
③ High arc bending precision, stable material rebound, good consistency of workpiece size.
④ can effectively eliminate the residual stress inside the material, the product dimensional stability is good.
⑤ Due to the cold hardening of metal materials, the mechanical properties of materials can be improved after tensile bending.
(1) The section size of tensile bending products is limited by the tonnage of equipment and the size of the pliers.
② The investment cost of draw-bending die is large, and the versatility of die is poor.
(3) It is difficult to control the cross-section deformation of the unsymmetrical profile.
3) Key technologies of stretch bending forming process
The camber design principle of tensile bending workpiece is not more than the elongation of the material as the limit, tensile bending forming will appear profile wall thickness thinning fracture, wrinkle, cross-section distortion and other forming defects, these forming defects and profiles mechanical properties, section shape and tensile bending process parameters and other factors are closely related.
4) Calculation of forming force of stretch-bending profiles
In the technical capability evaluation of the project, three factors need to be considered: whether the distance between the jaws of the equipment meets the tensile length of the material, whether the size of the jaws meets the clamping requirements of the section size, in addition, the most critical point of tensile bending is to calculate the maximum tensile force required by the material.
5) Structure and working principle of stretching and bending equipment:
The key technology of stretch bending is mainly mold design, stretch bending machine will not give the ideal three villa bending program, process designers need to carry out systematic analysis or CAE finite element analysis according to the properties of materials and bending forming, and through continuous workpiece trial production, so that three villa bending mold and three villa bending program to achieve the best match, and to meet the technical requirements of the workpiece, Technical personnel are required to have high product development ability.
2. Roll bending forming process
1) Working principle of roll bending forming
Roll bending machine is generally divided into vertical roll bending machine and horizontal roll bending machine. Vertical roll bending machine material operation is convenient, for large workpiece is suitable for horizontal. The process position of each shaft of roll bending machine is precisely controlled by the servo motor, the hydraulic motor system drives the linkage of each shaft, and the servo motor is controlled by the programmable controller (PLC).
2) Characteristics of roll bending forming process
Roller bending machine is generally used for the production of single arc workpiece, short mold production cycle, low input cost, simple operation.
3) Key technologies of roll bending forming process
The difficulty of the roll bending process depends on the cross-section shape of the bending material, and the design of the roll die is the key to the workpiece forming technology. Generally, the die material is made of 45 tempered steel or die steel by turning the lathe, and the hardness and surface roughness requirements of the die are obtained through the process of heat treatment and chrome plating.
4) Calculation of roll bending forming capacity
Whether the roll bending equipment meets the technological requirements of the roll bending workpiece, the following conditions should be met:
① Whether the length of the roller meets the width size of the material.
(2) Whether the minimum arc radius of the equipment roll bending is greater than the minimum arc of the workpiece.
(3) Whether the equipment pressure is greater than the material roll bending force.
3. Press bending forming process
1) Working principle of bending forming
Press bending is the use of hydraulic press to exert pressure on the material, through the press bending mold to produce bending moment, so that the material is bent to form a certain Angle and curvature
2) Characteristics and key technologies of press bending forming process
Aluminum alloy profile bending parts L shape and S shape can be used bending process, because the profile section and shape are different, all kinds of bending parts bending die rebound design is not the same, need to go through continuous bending process test to explore the rebound amount and after several times of repair mold to get a reasonable mold bending surface.
Several key technical points of bending process:
① The design of bending die should fully consider the deformation trend and rebound amount of material.
② Because aluminum alloy profiles have cavity hollow structure, reasonable filler selection is the key to bending forming.
③ Effective measures to prevent side bending should be taken into full consideration when bending profiles with asymmetric section shape.