Simulation and Optimization of Automobile Steering Arm Forming Process (Part I)

The steering arm of the car is an important part in the steering system of the car. It plays the role of connecting the wheel and the body. During the running of the car, the turning arm is subjected to frequent and complicated multi-variable stress. Once the parts are damaged, it may cause a major accident. , is an important safety component, for which the process performance and use requirements are relatively high. The parts are mainly obtained by forging, and the domestic production of such forgings still has problems such as large machining allowance, difficult forming and mold design difficulties. The finite element numerical simulation technology is used to explore the reasonable forging method of the forgings for China's automobile industry. Development is of great significance.

1. Research status of steering arm

The steering arm is an important part of the steering system of a light truck. Since the turning arm is a variable-section curved-axis forging, the forming process requires a blanking process such as rolling, drawing, bending, etc., and the force is also complicated during the working process, and the quality is relatively high. This type of forgings usually use the hammer forging process, but the quality is difficult to guarantee. In recent years, with the rapid development of the automobile industry, the requirements for dimensional accuracy, internal and surface quality of forgings with complex shapes of light-duty steering arms are becoming more and more strict, and reasonable design turns to the bending arm forming process and mold. Structure is the key to solving such problems. Combining with the production needs of Hefei Auto Forging Co., Ltd., we have developed a composite process of roll forging blank-fray press die forging. The whole process is: blanking → medium frequency induction heating → roll forging blank → bending → forging → cutting Edge → correction → heat treatment, reasonable roll forging process and final forging die are designed for different turning arms.

2. Structural characteristics of light cargo turning to curved arm

The light-duty truck turning arm parts (see Figure 1) belong to the long-axis bending parts. The characteristic is that the axis is spatially curved and multi-directionally curved. The interface difference and the drop along the length direction vary greatly, and the shape is more complicated.

Figure 2 is a forging diagram of a light-duty truck turning arm. The material is 40Cr. The cross-section is composed of a circle and a rectangle. The maximum diameter of the circle is 51mm, the minimum diameter is 32mm, and the rectangular section in the bending zone is 60mm×27mm. Gradient to 39mm x 26mm.

3. Rolling forging numerical simulation

The DEFORM simulation software was used to simulate the roll forging process, and the metal flow law, stress field, strain field, temperature field and mold load distribution during the roll forging process were analyzed to investigate the influence of the design parameters of the roll forging process on the metal deformation law. And provide the basis for optimizing mold design parameters.

(1) Simulation problems and solutions DEFORM-3D software operating environment is relatively simple, the contact between the mold and the blank at the beginning of the pre-processing simulation does not provide the design function of the geometric model parameters, and the parameter modeling needs to be completed by other general CAD software. . The DEFORM pre-processing model input is implemented by using IGES, STL and other data interfaces. In DEFORM, only the mold and the blank can be simply rotated and moved, and the mold and the blank cannot be accurately positioned. For such a situation, the UG assembly system can be used to find the contact position between the mold and the blank in the UG development environment, and then respectively export them as STL files, and then respectively import them into DEFORM, so as to avoid cumbersome trials. By looking for contact points, it is also possible to avoid excessive contact or intersection of the mold and the workpiece, so that the simulation process can proceed smoothly.

(2) Bending problem during billet forging Due to the uneven deformation of the billet during the roll forging process, the billet is bent along the lower die of the roll forging during the simulation process, and the bending of the billet will seriously affect the billet entering the next roll forging. . Misalignment during deformation causes the blank to fail to meet the specified shape requirements and uneven deformation occurs. For this phenomenon, a method of restricting the movement state of the blank can generally be employed.

(3) Reasonable selection of the gap of the roll forging die The die gap is an important factor affecting the quality of the blank, which also causes the blank to bend. If the gap of the mold is too large, the blank can not get better limit. During the roll forging process, the blank and the mold will not contact, which will affect the forming quality of the blank. If the gap of the mold is too small, the unevenness of the deformation force of the blank will increase. Large, so that the billet metal deformation when flowing unevenly, which will lead to the occurrence of bending phenomenon during roll forging, the smaller the gap of the roll forging die, the greater the degree of bending of the billet.

Therefore, choosing a reasonable mold gap is an important guarantee for obtaining the roll forgings whose cross section meets the production requirements, and also an important factor to prevent the bending phenomenon of the blank during the roll forging process. In this paper, the turning of the bending arm roll forging is repeated and repeated. After the test, a reasonable mold gap of 4 mm was finally determined.

4. Rolling forging simulation results and analysis

(1) Analysis of stress and strain of billet blanks in each pass. As shown in FIG. 3 and FIG. 4, since the first pass roll forging model groove is elliptical, the deformation of the blank contacted with the two roll forging die in the radial (height) direction is an upset deformation during the roll forging process. It is elongated in the axial direction and widened in the lateral direction. In the process of roll forging deformation, due to the change of the section, that is, the circular to elliptical transition, the blank has a certain back slip phenomenon, which should be noticed during the design of the roll forging die, and effectively controlled and compensated.

Stress and strain analysis of the second pass roll forging. As shown in Fig. 5 and Fig. 6, the second pass roll forging model groove is circular, and the metal blank in the deformation zone is in a three-direction compressive stress state throughout the roll forging process, and the blank is flattened in the radial direction, in the axial direction. It is elongated and has a small spread in the lateral direction.

During the two-pass roll forging process, the internal stress and strain of the blank in the deformation zone are unevenly distributed in the three-dimensional direction. The internal equivalent strain distribution of the blank in the deformation zone during the first pass rolling process is shown in Fig. 7a. It can be seen from the figure that due to the influence of the friction between the blank and the forging die, the blank in contact with the tool is affected by the mold due to the flow. The degree of deformation is small, and the deformation of the middle portion of the blank is the largest, and the degree of deformation of the side drum portion is between the two. Fig. 7b shows that the equivalent internal stress value of the blank in the contact portion with the roll forging die is large, and the equivalent stress value of the side of the blank which is not in contact with the roll forged model groove is small. As can be seen from Fig. 8, on the surface of the blank, the equivalent stress value of the portion in contact with the roll forging die is the largest, and the further the distance from the contact point in the axial direction and the circumferential direction of the blank, the smaller the equivalent stress value.

After the billet is turned over 90°, the second pass roll forging is performed, and the internal equivalent strain field of the blank in the deformation zone is as shown in Fig. 8a. It can be seen that after the second roll forging, the internal equivalent strain value of the blank is relatively large, especially the cross-shaped area of ​​the core of the blank, and the strain value of the region is the result of the superposition of two major deformations, and the side of the blank and The strain value at the contact between the blank and the roll forging die is small. It can be seen from the equivalent stress field of the blank section of Fig. 8b that, compared with the first roll forging, the internal stress field of the blank is relatively uniform, and only the surface of the blank has a large stress.

(2) Simulation results and analysis of the billet velocity field of each pass The circular billet is rolled into a circular roll forging by two passes of elliptical-circular groove. In actual production, the deformation process has undergone biting, stable roll forging and Three stages of throwing steel. Figure 9 and Figure 10 show the velocity field of the billet in the roll forging direction in the two-roll roll forging zone. In the initial biting stage, the roll forging process is in an unstable state, and the blank is bitten by the roll forging die. As the amount of pressing increases, the metal extends longitudinally and laterally widens. At the initial stage of roll forging, as shown in Fig. 9a, there is a big difference in the velocity distribution gradient at the ends of the blank forging of the roll forging. This is because the deformation of the two ends of the blank is different, and the force of the roll forging on the surface metal of the blank is also Different. The reduction amount of the roll forging die of the deformation section is gradually increased, and the initial reduction amount is small, so that the flow speed of each node on the blank is not much different. In the front sliding zone, the metal near the roll forging die has a high deformation speed, gradually decreases inward, and the center portion in contact with the roll forging die has the lowest speed. In the rear sliding zone, the opposite is true. As shown in Fig. 9b, as the steady-state roll forging process progresses, the amount of reduction increases continuously, and the difference in flow velocity on the cross section of the blank increases continuously. The final reduction does not increase any more, and the velocity field on the blank also tends to be stable.

The two-stage roll forging makes the cross section of the billet change from circular to elliptical, and then rolled into a circular shape to compare the deformation process of two passes, and the first pass has a large deformation amount. It can be seen from the flow velocity field of the two-roll roll forging process in Fig. 9 and Fig. 10 that in the sliding zone after the second pass rolling, the difference in the flow velocity between the middle and the ends of the blank is relatively large, but the blank and the roller The difference in speed over most of the forging die contact is small and almost equal. The metal in the contact area between the front sliding zone and the roll forging die has a slower flow rate, and the metal flow speed on both sides is very fast. (to be continued)

About the author: Xiao Laibin, Tao Shanhu, Hefei Auto Forging Co., Ltd.; Chen Guoqiang, Chen Wenlin, School of Materials Science and Engineering, Hefei University of Technology.