1 Forklift panel stamping and forming simulation
The mold is designed and manufactured according to the shape of the forklift panel, and due to the springback problem of the part stamping, the size of the cover exceeds the tolerance requirements and needs to be corrected and repaired. The size of the forklift fender after stamping and forming is collected with a coordinate measuring instrument, and the three-dimensional structure of the fender is drawn according to the measured size, as shown in Figure 1.
The finite element analysis of the forklift fender stamping process was carried out, the thickness of the fender was 14mm, and the Q345 material was formed, the yield strength was 345MPa, the tensile strength was 530MPa, the elastic modulus was 2.1×105MPa, the Poisson's ratio was 0.3, and the fender was stamped and formed at one time. The graphic of the mudguards in iges format was imported into AutoForm, and the imported fenders were automatically meshed according to the default accuracy, and then the finite element numerical simulation of the fender stamping process was carried out, as shown in Figure 2. Export and import the AutoForm calculation results into the CAD software, as shown in Figure 3, with the leftmost fender shape mesh as the finite element calculation result. A comparison of the results of the finite element numerical simulation and the measurement is shown in Figure 4. The finite element calculation results of fenders are consistent with the actual sheet metal stamping forming, and the following fenite element model of fender is used to analyze the factors affecting its stamping forming.
2 Rebound analysis of fender stamping
(1) The influence of friction coefficient on the rebound of stamping forming. By adding different lubricating oils to the mold parts to change the friction coefficient between the mold parts and the sheet, the influence of the friction coefficient between the mold parts and the fender on the springback of stamping forming was analyzed. For this reason, the coefficient of friction is set to be 0.1, 0.15, 0.2 respectively, and the numerical simulation result is shown in Figure 5, when the coefficient of friction is 0.1, there is a large error between the fender and the actual measurement result after stamping and forming, when the friction coefficient is 0.15, it is close to the actual measurement result, and when the friction coefficient is 0.2, the error between the fender and the actual measurement result after stamping and forming is small. In order to further confirm the influence of the friction coefficient on the simulation results, the die friction coefficient was set to 0.15 unchanged, and the punch friction coefficient was changed to 0.11, 0.15 and 0.2, respectively, and the numerical simulation results are shown in Figure 6. The results show that changing the friction coefficient of the punch alone has a certain effect on the fender stamping and forming results. The friction coefficient of the die and punch is 0.15, which is in line with the actual measurement results.
(2) The influence of fender positioning on the rebound of stamping forming. In the fender forming process design, the mold is provided with 5 positioning pins, as shown in Figure 7, but in the actual production process, in order to facilitate and improve efficiency, the fender adopts the underpositioning mode such as 3 positioning pins. In order to discuss the influence of the positioning mode on the rebound of the fender stamping forming, the simulated fender adopts the full positioning mode of 5 positioning pins, the positioning mode of 3 positioning pins and the positioning mode without positioning pins, and the calculation shows that the positioning mode of the fender has no obvious effect on the forming result of the part during the stamping process.
(3) The influence of the processing process of the fender on the rebound of stamping forming. The simulation results show that the two situations have no effect on the stamping and forming of the fender, and the punching and forming of the fender plate is conducive to the positioning and processing of the punching process, and the simulation is formed in the order of the fender punching first and then stamping.
(4) The influence of fender material on stamping forming. Considering the fluctuation of the quality of the steel plate material, the yield strength of the material was simulated at 300, 345 and 400MPa, and the influence of the yield strength of the steel plate material on the fender stamping was analyzed, and the results are shown in Figure 8. The yield strength of the fender material is 400, 345 and 300MPa, and the rebound changes from large to small, indicating that the greater the yield strength of the material, the more obvious the rebound. The yield strength of the material is 345MPa, and the tensile strength of the material is 470, 530 and 630MPa respectively for numerical simulation of fender stamping and forming, and the results are shown in Figure 9. The results show that the greater the tensile strength, the greater the rebound of the fender, and the material quality has an impact on the consistency of the fender stamping form, and the material quality needs to be stable. Through the above simulation calculation and analysis, under the premise of stable material quality, it is explored to compensate and control the fender stamping by modifying the die structure, so as to achieve the accuracy requirements of its one-time stamping.
3. Mould structure parameters and fender stamping and forming
The punch is designed and manufactured according to the size of the fender, without considering the influence of the rebound of the steel plate, and the influence of the mold structure size on the fender stamping and forming is analyzed, wherein the punch size is shown in Figure 10, the clamping state of the convex and concave die is shown in Figure 11, and the punch profile is composed of straight line section ED, circular arc section DB, straight line section BC and CA.
In Fig. 10, the arc radius of the punch is designed to be R396mm, and the radius of the punch is set to R426, R416, R406, R396, R386, R376, R326mm respectively, and the radius of the corresponding arc of the die is changed simultaneously, and the simulation results are shown in Figure 12. The punch radius takes R326mm, the fender stamping deformation exceeds the size requirement, the smaller the punch radius R value, the greater the rebound after the fender stamping and forming, when the punch radius takes R396mm, the fender stamping forming shape is close to the requirement, but still does not meet the requirements, take R406mm or more, the rebound deformation is no longer significant, indicating that the arc radius size of the punch has a significant impact on the fender stamping forming.
The punch AC, CB, ED is a straight line section (see Figure 10), and the length of AC and CB is 234mm. Under the condition that point A remains unchanged, change the position of points B and C, take the length of AC and CB to 214, 224, 234, 244 and 254mm respectively, keep the gap between the convex and concave die to 14mm, modify the corresponding size of the die for stamping and forming numerical simulation, and the result is shown in Figure 13.
Fig. 13 shows that modifying the position of die points B and C has a significant impact on the fender stamping forming, indicating that the position size design of punch points B and C is the key parameter of fender stamping and forming. The coordinates of the position of the punch structure parameters B and C, and the arc radius R significantly affect the stamping and forming of the fender. Because there are many structural parameters affecting fender die parts, the orthogonal test design method is adopted, the structural parameters of die parts are selected as test factors, and a total of 7 dimensions of punch B(Xb,Yb), C(Xc,Yc), D(Xd,Yd) horizontal and vertical 2 direction positions and radius R in Figure 14 are taken as test factors, each test factor takes 5 levels, and the corresponding structural dimensions of the die and punch are changed synchronously, and the numerical simulation test scheme of 7 factors and 5 levels is generated according to the orthogonal test design method, AutoForm was used to simulate each group of schemes one by one, and the optimal structural scheme of punch and die was determined to be able to compensate for stamping, so that the shape of the fender after forming and rebounding could meet the requirements. The optimal structural optimization test design scheme of punch compensation stamping rebound is shown in Figure 14.
The finite element calculation of stamping and forming was carried out according to the optimal die structure, and the results are shown in Figure 15, and the size of the fender meets the requirements.
The mold is redesigned and manufactured according to the optimal mold structure, and the fender stamping and forming process is shown in Figure 16, and the dimensions of the fender after one stamping and forming are within the tolerance requirements.
▍Original authors: Qi Haiyong1, Mei Lei1, Su Jingming1, Wang Zhenghao2, Hong Yihao2, Liu Mingqiao2, Ning Xiaobin2
▍Author Affilications:1.Hangcha Group Co., Ltd.;2.Zhejiang University of Technology