As an important part of automobile engine, pulley has high requirements for product precision and comprehensive performance. According to the characteristics of the studied pulley, a multi pass stamping forming process using circular slab to form complex pulley is proposed. The cylindrical structure of the pulley was formed by three passes of drawing, upsetting and shaping. The main technological parameters of each pass of drawing, upsetting and shaping were determined. The improved process of reverse bending stock is proposed, and the wall thickness and forming load of each process in the improved process are analyzed by numerical simulation.

Nowadays, with the development of social economy, the increasing demand for automobiles, the miniaturization of engines, the lightweight of engines and the increase of the number of accessories have become important requirements in automobile manufacturing. Therefore, the pulley becomes the key component of the engine, and is widely used in automobiles, agricultural machinery, ships and other mechanical equipment. The traditional forming process of pulley is casting, welding, deep drawing and bulging. However, the dimensional accuracy of the workpiece obtained by traditional casting is not high, which will lead to poor mechanical properties of the pulley. Although the forming precision of bulging method is high, the production cost is relatively high, resulting in expensive equipment.

Multi pass deep drawing is to distribute the total amount of deep drawing, complete part of the deformation each time, and finally realize the forming after many times of deep drawing. In multi pass deep drawing, the sheet metal is continuously deformed and the hardening effect is accumulated, which is helpful to improve the strength. At the same time, the sheet metal is directly formed, which has high material utilization rate, convenient for mass production and relatively low cost.

However, in the process of multi-step deep drawing, the material force is more complex, which involves multiple nonlinear coupling forces such as friction, contact and plasticity. The theoretical and practical problems are more complex than one-step deep drawing. At present, finite element simulation is often used to analyze the deep drawing process. Cao Jin and others calculated the drawing passes according to the drawing coefficient of the material, combined with the stamping and forging technology, and used the finite element simulation software DEFORM-3D to carry out the numerical simulation, and analyzed the stress and strain distribution in the forming process, so as to provide a reference for the actual production of forging forming multi wedge pulley. Li Xuesong and others used the finite element software DEFORM-3D to simulate the whole process. The simulation results show that the stamping forging process successfully shows the change of the bottom wall thickness of the part, and the whole process is feasible.

Forming process and parameter analysis of parts

Part analysis

Figure 1 is the part drawing of pulley, and 3.2mm thick SPHD material blank is used. The forming difficulty is that the thickness of the bottom of the pulley should be thickened to 3.27mm, and the bending angle position at the bottom of the pulley should be well filled. Considering the actual production equipment tonnage, the forming force should be controlled below 500 tons. The drawing pass times are calculated by combining the drawing coefficient of the material. The finite element simulation software DEFORM-3D is used to simulate the multi-pass drawing process of the cylinder part of the belt pulley. The load and wall thickness distribution in the forming process are analyzed, which provides a reference for the research and production of the pulley.

Figure 1 part drawing

Analysis of process parameters

The following process flow is drawn up, and the sequence of the processes is: drawing 1 → drawing 2 → drawing 3 → upsetting → shaping, as shown in Figure 2. In the numerical analysis, firstly, according to the established process route, the characteristics of the process route are summarized and the process optimization is carried out. In order to save the calculation time, the form-2d software is used in numerical analysis. The punch speed is 50mm/s, the friction type is set as Coulomb friction, the friction factor is 0.12 and the calculation step is 0.1mm.

Numerical simulation of process flow

Finite element simulation analysis

(1) draw 1. Drawing 1 is mainly for the aggregate at the fillet, and the thickness of the fillet after drawing reaches 4.01mm.

(2) deep drawing 2. The bottom thickness of drawing is 3.40mm and the thickness of outer wall is more than 3.33mm.

(3) deep drawing 3. The thickness of the fillet is more than 2.95mm and the final thickness of the outer wall reaches 3.28mm.

(4) upsetting. The finite element model is shown in the left figure of Figure 3. The purpose is to increase the wall thickness of the bottom of the pulley by upsetting, from 3.16mm at the end of drawing 3 to more than 3.27mm. At the end of upsetting, the distribution of the wall thickness of the pulley is shown in the right figure of Fig. 3. It is not difficult to find that the bottom thickness of the pulley is only 3.18mm, and the thickness at the bending angle of the pulley is thinner. This requires that the thickness of the bottom of the pulley be increased in the subsequent improvement process.

(5) plastic surgery. The finite element model is shown on the left in Figure 4. At the end of shaping, the distribution of pulley wall thickness is shown in the right figure of Figure 4. It is not difficult to find from Figure 4 that the thickness of the bottom of the pulley is only 3.17mm, and it is thinner at the corner of the pulley, which is only 2.13mm.

In the above simulation, the forming tonnage is controlled within 350 tons. In view of the wall thickness in the simulation process does not meet the target requirements, the above process is modified. Because the problems mainly appear in the upsetting and shaping two steps, the improvement of the process is mainly concentrated in the last two processes.

Improved process and simulation analysis

In view of the shortage of material in upsetting and the situation that there is no corner or full in shaping, the reverse bending process is added before upsetting to increase the profile length at the bottom of the pulley. In shaping, a shaping process is added to ensure that the corner is full.

The improved process is as follows: drawing 1 → drawing 2 → drawing 3 → reverse bending stock → upsetting 1 → upsetting 2 → shaping 1 → shaping 2. The following mainly introduces the reverse bending material storage and subsequent processes.

(1) reverse bending storage. The purpose of adding this process is to store the material evenly at the part where the bottom of the pulley needs to be thickened, so that the bottom of the pulley can be thickened evenly when the die is upset at 500 tons. The load diagram of reverse bending storage is shown in Figure 5.

(2) upsetting 1. On the basis of the previous storage, through this process, the bottom thickness of the pulley reaches 3.48mm, and the bottom surface quality is better. The forming tonnage can be controlled below 500 tons. The three-dimensional and two-dimensional finite element simulation of upsetting 1 are shown in Fig. 6.

Figure 5 load diagram of reverse bending stock

Fig. 6 3D and 2D finite element simulation of upsetting 1

Fig. 7 upsetting 2 load diagram

Figure 8-1 two dimensional diagram of the beginning and end of finite element simulation

Figure 9.1 load diagram

(3) upsetting 2. The purpose of this process is to increase the storage material in the corner position, and lay the foundation for the next step of shaping. At the same time, the bottom of the pulley can be further flattened. The load diagram of upsetting 2 is shown in Figure 7.

(4) plastic surgery 1. The purpose of this process is to make the pulley initially form the required shape, and the forming tonnage is less than 500 tons. From the results, there are still some areas in the corner that are not full, so two shaping processes are added to improve. The two-dimensional diagram of the beginning and end of the finite element simulation of shaping 1 is shown in Figure 8, and the load diagram of shaping 1 is shown in Figure 9.

(5) plastic surgery 2. The purpose of adding this process is to make the corner full, and the result is shown in Figure 10. The final bottom thickness is 3.40mm, the forming tonnage is controlled below 500t, and the load diagram of shaping 2 is shown in Figure 11.