1. Finite element analysis and computer simulation
Computer simulation and finite element analysis of cold forming are hotspots of theoretical research, and many papers and research results have been published at home and abroad. How to carry out computer simulation for actual production problems and solve specific problems should become the research goal and the basis for inspection results. According to actual problems, we have made simulation research on double hemming with zero inner radius, bag wave defect analysis of wide plate, and distortion of pre-punched hole, and carried out relevant experimental verification.
1. Double folding simulation with zero inner radius
In cold-formed components, double folding is a common form. In the design of double folding, solving the calculation of the plate width and determining the reasonable forming process steps are the key issues. The conclusions obtained by using MSC Marc for finite element simulation are as follows:
(1) Through the equivalent strain analysis of the deformation zone, it is verified that during the deformation process, with the further bending of the sheet, the neutral layer deviates from the central layer and moves to the inside of the bend. The simulation gives the specific offset process and value.
(2) Through the comparison of the units before and after the deformation, it is found that during the bending, the outer peripheral unit shrinks, the inner peripheral unit stretches, the plate thickness in the middle of the bend increases, and the material flows.
(3) Through the analysis of stress and strain, it is found that the deformation of the bending section is relatively close to the characteristics of plane strain, so it is determined that the bending of sheet metal can be simplified to a plane strain problem.
(4) Through the analysis of the bending stress concentration, it is determined that there is a large tensile stress concentration on the outer periphery of the bending, a large compressive stress concentration inside the bending, and there is a transition zone between the bending area and the non-bending area (or smaller bending area). Larger shear stress concentration.
2. Analysis of Defects in the Forming of Wide Sheets
The generation of pocket waves is a common problem in the forming of wide plates. In the process of cold bending of sections such as carriage panels, profiled panels, and wide-width rolling doors, pocket wave defects often occur.
In the experiment, 18 combinations of experiments were carried out according to different plate thickness and roll configuration, and the three kinds of obvious defects such as bag wave, edge wave and longitudinal bending were analyzed and studied from the generation mechanism and experimental results. And put forward corresponding measures to eliminate the defects. The main conclusions are as follows:
(1) The generation of the bag wave is mainly due to the occurrence of the de-line phenomenon of the plate during the bending process, and the transverse tensile stress and transverse strain are generated in the bending part. According to the Poisson relationship of sheet material deformation, shrinkage deformation occurs in the longitudinal direction, and the longitudinally contracted part exerts pressure on the unshrinked part of the middle part, and the middle part of the sheet material loses stability and a bag wave appears. The bag wave is mainly elastic deformation.
(2) When a bag wave appears, some passes can be added appropriately. The width of the section edge has a certain influence on the pocket wave, and the thin plate is more prone to the pocket wave than the thick plate. The bag wave can be slowed down by applying tension to the sheet.
(3) The generation of edge waves is a combination of two effects. The first is the same as the generation of bag waves. The second is that the material at the edge of the section is first stretched and sheared under the action of external force, and then again Compression and shear produce plastic deformation and cause edge waves. These two effects are superimposed on each other, causing side waves. Edge waves may occur in each pass, and the previous pass has a greater impact on the appearance of edge waves. Thin plates are more prone to edge waves than thick plates, and wide edges are more prone to edge waves than narrow edges.
3. Simulation Research on the Distortion of Pre-punched Hole
One of the development directions of cold-formed products is to continuously meet the needs of various applications and realize multiple functions on the products. Electric control cabinet column profiles, shelf profiles, etc. need to be pre-punched before forming. Because the hole pitch and hole geometry are required to be high, and large deformation is not allowed during the bending process, the simulation research and control measures of the pre-punched hole shape distortion are very important.
Taking the pre-punched sheet as an example, a new method to control the hole shape distortion in the cold bending process of the pre-punched sheet is obtained through field experiments, the mechanism of hole shape distortion is analyzed, and the experimental results are summarized. At the same time, computer simulation software was used to simulate the machining process, and the field experiment results were compared with the computer simulation results.
According to the process drawing, the simulation results are shown, and the deformation degree of the cross section of the material is displayed by means of cloud diagrams and curves, which lays the foundation for further understanding of the deformation laws during the rolling process.
Through the comparison of the simulation results of different dies, the influence of different dies on the stress and strain of the pre-punched area of the material was discussed, and the optimal model scheme suitable for the experiment was obtained.
Through the analysis of the stress and strain conditions of the cross-section of the processed sheet material, the main reason for the hole shape distortion defect is found: the reason for the hole shape distortion of the sheet material is: the edge of the punching area of the material will appear during the forming process With a large stress increase, the equivalent stress in the punching area gradually increases during the machining process, and the strain also accumulates. The plate on the outside of the forming corner of the pre-punched part produces lateral displacement. It is manifested in the pre-punched hole edge that produces a large displacement strain, and then produces hole shape distortion. When the degree of strain accumulation exceeds the strength limit of the material, tearing will occur.
According to the obtained optimal simulation plan, the roll shape process drawing was modified, and field experiments were carried out. Experiments show that the simulation results can be used as a basis for mold design, and it is very effective to avoid hole distortion.
2. Production line of high-precision complex profiles
Cold roll forming is particularly suitable for mass production. Compared with the bending process, the production efficiency of roll-type cold bending is high, and the product size is consistent, and it can realize complex sections that cannot be produced by bending. With the rapid development of my country’s car industry, there is an increasing demand for cold-formed production lines for high-precision and complex profiles.
For car doors and windows, cold forming is often the first and key process. After cold bending, several layers of metal need to be seam welded at some spaced points. Therefore, the production line also needs to include online seam welding equipment, tracking and cutting equipment, etc.
For the cold bending forming production line of car doors and windows, not only does it have many forming passes but also requires high precision. We summarized and put forward more than ten indicators for controlling and inspecting the accuracy of rolling mills, focusing on controlling the axial movement of the rolling mill and the accuracy of the axial positioning datum on all units.
Reasonably formulate the molding process, and determine the optimal molding step through simulation with COPRA software. Using CAD/CAM technology to manufacture high-precision rolls, a number of high-precision complex profiles were successfully rolled.
The COPRA software of German data M company is a professional software for cold-formed forming design, and it has been most widely used internationally. The leading enterprises in the domestic industry use it as a means of developing new products. We have successfully designed and manufactured hundreds of cold-formed products by applying this software.
3. On-line bending of cold-formed profiles
Many profiles require a 2-dimensional arc in the length direction, and online bending after the cross-section is formed is a better method. In the past, the commonly used method was to bend through a mold on a press. The mold needs to be repeatedly adjusted. When the properties of the material change, the mold needs to be modified frequently. Press bending needs to install specific tooling cores one by one to avoid defects such as wrinkles during the bending process. These inner cores are removed after completion, which requires a lot of work, low efficiency and poor safety.
Online bending only needs to install a set of online bending device at the exit of the cold-formed profile to make the profile reach the required arc size. The device can be adjusted to solve the effects of different material properties and material rebound. As long as it is a 2-dimensional arc, it can be bent on-line no matter in the horizontal plane or in the vertical plane.
Theoretically, 3 points determine an arc. But in order to obtain better bending quality, we believe through experiments that the forming trajectory should be determined by a specific deformation trajectory curve.
The specific deformation curve of the curved circle trajectory should be determined by the equation: ρ=ρ0 + αθ
Or from the equation:
Fourth, CAD/CAM integrated technology to manufacture high-precision rolls
In order to transform our years of scientific research achievements into productivity, and provide high-quality technical services and technical support for domestic and foreign users, RlollForming Machinery Co., Ltd. was established in Shanghai. Adopting CAD/CAM integration technology to provide a full range of services for domestic and foreign customers. Liju has multiple CNC machine tools and a complete set of processing equipment, successfully providing users with various specifications of high-precision rolls and online bending and other related equipment.
Relying on the advantages of the Shanghai Industrial Base and the Yangtze River Delta, extensive domestic and foreign cooperation is carried out to gather and train high-quality, high-quality talents, and scientific modern management can provide customers with high-quality products and technical services. Liju takes this as the goal to develop and progress together with my country’s cold-formed forming industry.
Post time: Apr-25-2021