Table 5
The optimal scheme of design
Variable
|
Value
|
D
|
40mm
|
L
|
205mm
|
F
|
CDZ 1
|
First of all, the target to be achieved is that the forging must be completely filled. The optimized scheme described in Sect. 4 is that the billet diameter is 40mm, the billet length is 205mm, and the flash design as CDZ 1, as shown in Table 5. The distance between die and workpiece is zero, which is equivalent to a fully filled forging.
As shown in Fig. 14 of contact ratio (100% corresponds to the distance between die and workpiece is zero), the cavity of the crown forging is well filled. In order to conform the filling conditions of the left and right sides of the crown marked with red circles, the cavities filled with different forging steps are shown in Fig. 14. It is recognized that the left and right sides of the crown are fully filled in step 253 with contact ratio of 100%.
The diagrams in Fig. 15 illustrates the maximum loads of the preforming and finishing are 5.59 MN and 3.41 MN, respectively. Compared with the original design (as shown in Fig. 6), the optimized design increases the forging load by 60.47%, while the finishing load increases by 48.97%. Due to the increase in the diameter and length of the billet, the forming load becomes larger, but it improves the problem of filling defects, which are very important to the forging quality.
Figure 16 shows the optimized preforming dies mean wear depth of the crown forging. The preforming die mean wear depth per stroke is 6.64E-5 mm is shown in Fig. 16b. The severely worn area is located in the middle of the bottom die. Consequently, the flash design increases the mean wear depth of the die per stroke, which is in good agreement with the RSM analysis of Fig. 12. In comparing with the original design of the wear depth of each die and the size of the billet, due to the increase in the diameter and length of the billet, the average wear depth of each die of the upper and lower dies increased by 36.74% and 25.05%, respectively.
The diagram in Fig. 17 shows that the wear depth of the finishing die is uniform, and the wear is distributed around the forging die cavity. The average wear depth per stroke of the finishing top die is 1.62E-5 mm is shown in Fig. 17a. Compared with the wear depth of the initial finishing die, the average wear depth per stroke depth of the finishing top and bottom die increased by 35.19% and 49.98%, respectively. Therefore, the optimization of the preforming has a significant impact on the mean wear depth per stroke of the finishing die.
Figure 18 illustrates the color nephograms of the finishing forging of a crown forging including damage, plastic strain, effective stress and temperature. The damage indicates the location where the forging is prone to defects, as shown in Fig. 18. The diagrams in Fig. 18a shows the damage of the billet is uniformly transformed, and severe areas of damage appear in the flash, which is difficult to produce defects on the crown forging. Plastic strain denotes the degree of deformation in the deformation process of the billet. Figure 18b shows that the area of plastic strain is particularly increased from the junction of the crown forging and flash, which results in effective strain accumulation due to the greater resistance to metal flow in the flash area in the cavity. Therefore, in order to ensure the filling of the cavity, generally increasing the damping walls is an effective method. In Fig. 18c, the maximum effective stress region is in the junction of the crown forging and the flashlight. Consequently, the right and left sides of the crown are not easy to deform, and the CDZ is conducive to the filling of the cavity on both sides of the crown. Figure 18d shows that the maximum temperature reaches approximately 508℃. Since the material is concentrated on the corners, the highest temperature appears at the junction of the crown forging and the flashlight. Figure 18b verifies this in reverse. The temperature of the workpiece rises due to the heat generated during forging. In Fig. 18e, the velocity is uniformly distributed in the crown forging, and the maximum velocity occurred in the flash area. The diagrams in Fig. 18f illustrates the displacement is uniform, and the maximum displacement occurs in the cavities on both sides of the crown forging and flash.
Figure 19 demonstrates that the discussion of the effect of preformed dressing on the crown forging, the points tracking of the right crowns for shock absorber assembly. Figure 19a shows the cross-sectional view of the left and right crowns of the shock absorber assembly is red circled in Fig. 14. Because of insufficient filling of the left and right crowns of the shock absorber assembly (as shown in Fig. 10), six points are marked to investigate the effect of the damping wall in CDZ. In Fig. 19b, c, the effective stress point trend tracking and plastic strain point trend tracking are different according to the amount of change of the forging. The greater the amount of change of the forging, the greater the effective stress. However, the effective stresses of P4 and P5 are greater than other effective stresses. Figure 19d shows the velocity point tracking is periodic fall and rise; Thus, the tendency has been consistently justified. Figure 19e states that the temperature tracking trend is regular before the die stroke 20mm, but the temperature tracking trend at P4 and P5 is lower than other temperatures after the die stroke 20mm. Due to P4 and P5 are the fastest to contact the die cavity, and the die temperature is lower than that of the billet material, so P4 and P5 will experience the steepest temperature gradient as contrasted with other points. The temperature induced effect will inevitably inhibit the metal flow due to higher interfacial friction so the forming load will be higher, as well as the effective stress and plastic strain of the material will increase.
The production equipment for crown forging is shown in Fig. 20. The bending equipment is shown in Fig. 20a, it is 110 tons C-frame single crank power presses. Figure 20b illustrates the use of a high-frequency induction heated the billet after bending to the preforming equipment. The huge crank press is used to forge crown forging, which can provide 1000 tons of pressure, preforming and finishing forging as shown in Fig. 20c-d. Figure 20e shows a 60-ton C-frame single-crank power press, which is used to trim the flash of forging.
Eventually, through the air-cooled, the crown forging is shown in Fig. 21a. The diagram in Fig. 21b shows the actual bottom die is designed with RSM optimized damping walls (L = 142mm, W = 2mm) on the left and right sides of the crown forging cavity to increase the filling effectiveness of the forging and prevent excess metal from flowing out. Figure 21c shows the finite element simulation results (left) and experimental results (right) of the grain flow lines distribution after forging. As shown in Fig. 21d and Fig. 21e, a partially enlarged view shows the left side of the actual forging (blue square), in which the crystal grain streamlines of the forging are densely and orderly distributed. The grain flow lines at the bottom of the trench gradually form uniform flow lines along the edge of the trench, which is consistent with the finite element simulation result (orange square). Therefore, experimental grain flow lines distribution shows smooth and non-intersecting dense flow lines which is consistent with the simulation counterparts.