Bucket Tooth For Excavator Forging Process

Taking a certain type of bucket tooth as an example, this paper analyzes the product structure and forging die structure, and proposes a precision roll forging-integral die forging bucket tooth forging forming process. Not only the roll forging die is designed, but also the roll forging and die forging process are numerically simulated and analyzed. Through the numerical simulation analysis of the forming process, the feasibility of the precision roll forging-integral die forging bucket tooth forming process is verified.

Since the roll forging machine is a blank making equipment, the blank is generally required to be relatively rough during roll forging, and the cross section of the lower half of the bucket tooth is a cross shape. If the blank size is too rough during vertical forging, it will be difficult to place the blank in the cavity, and it will also increase the wear of the mold during forming; during forming, the cross section of the upper half of the bucket tooth is relatively wide, and at the same time, due to the forging design of the pin seat hole, the metal flow can be improved by the protruding upper die during vertical forging, so the upper half can be simplified in design, and combined with the characteristics of the roll forging blank making process, the original bar size can be retained in this part; in order to reduce the number of roll forging passes during roll forging, and at the same time ensure that the blank is placed stably in the final forging cavity during vertical forging, and no upsetting instability occurs, the original bar diameter is selected as 100mm in this design. In summary, the schematic diagram of the preliminary design of the roll forging blank is shown in Figure 2.

As can be seen from Figure 2, the height of the undeformed round steel is still too high, with a height of 230mm and a height-to-diameter ratio of 2.3. Although it does not exceed 2.5, since its bottom is a tapered structure with a large top and a small bottom, and the punch diameter is 106mm, it is obviously not reasonable to use a round steel with a diameter of 100mm for direct upsetting. Therefore, it is necessary to add an upsetting process before final forging to upset the head into a short and thick shape. This process can not only increase the stability of the blank placement during final forging, but also make the lower metal flow better into the cavity, so that the cavity can be filled more smoothly during final forging.

Design of bucket tooth roll forging die

selection of roll forging pass

As can be seen from Figure 2, although the overall cross-section of the bucket tooth changes dramatically, the most dramatic change is at the tip of the bucket tooth. The changes in the middle and upper parts of the bucket tooth are not very large, and their cross-sections are all cross-shaped. In Figure 3, the characteristic cross-sectional area of the middle part of the bucket tooth is 3320 mm2, while the cross-sectional area of the original bar is 7853 mm2. The roll forging pass can be calculated according to formula (1).

The roll forging pass is selected according to the minimum cross section. The total elongation coefficient λZ of the section is first calculated according to the roll forging blank drawing:

Where A0 is the cross-sectional area of the original billet, and AN is the cross-sectional area of the billet after roll forging. The roll forging pass n is calculated as follows:

In the formula, λP is the average elongation coefficient, which is 1.6, so n=1.82, and after rounding, n=2.

Determination of the roll forging

groove system Reasonable hole design is the guarantee for the success of roll forging. Defects such as flash, instability, and scraping are not allowed to appear during the billet making process. In this design, due to the high elongation coefficient of the small head, in order to improve the elongation efficiency, the elliptical-circular hole type can be improved to an elliptical-elliptical hole type. According to the equal volume principle, the reverse method is used to reverse the cross-section of the second roll forging from the cross-section of the third roll forging, and then the cross-section of the first roll forging is reversed from the cross-section of the second roll forging. The cross-sectional dimensions of the third, second, and first grooves can be determined by looking up the table, as shown in Figures 4, 5, and 6, respectively.

The roll forging die drawing can be designed according to the shape of the roll forging. The die cavity size is relatively simple. The cross-sectional size of the blank is converted to the corresponding fan-shaped surface of the roll forging die. Since the blank is a typical front wall forming, the appropriate front sliding coefficient should be considered. When drawing the roll forging die, the characteristic hole type can be selected according to the cross-sectional shape of the forging. The characteristic hole type of this design is an elliptical cross-section and a cross-section, which transitions evenly along the ridge line on the fan-shaped die. According to the above design points, the roll forging die drawings of each pass are drawn, as shown in Figure 7. In order to reduce the flash of the roll forging in the length direction caused by inaccurate blanking size, a material storage bin will be made at the tail end of the roll forging die.

The geometric model established above is imported into the finite element numerical simulation software. The rotation and speed constraints of the roll forging die are set according to the actual rotation speed of the roll forging machine. At the same time, the blank is imported into the finite element numerical simulation software, the temperature and material of the blank and die are set, the grid is divided, the corresponding boundary conditions are set, and the finite element numerical model shown in Figure 8 is established.

After one pass of roll forging is completed, the blank is rotated 90 degrees and placed in the next die for roll forging. The simulation results of each pass of roll forging are shown in Figure 9. It can be clearly seen from Figure 9 that the cross-sectional shape of the third pass of roll forging basically meets the design requirements, the blank is reasonably distributed, and at the same time, there is no flash, scraping, instability, etc.; but since the roll forging process is a non-fully closed cavity, the metal can flow freely in the vertical direction of the hole, so its final shape cannot completely meet the roll forging cavity size.

The numerical model of roll forging is exported and placed in the upsetting head and final forging die to establish the finite element numerical model of upsetting and final forging, as shown in Figure 10. As can be seen from Figure 10, the shape of the roll forging basically meets the design requirements and can be smoothly placed in the upsetting head and final forging cavity, further verifying the feasibility of the roll forging design.

The forming effects of upsetting and final forging are shown in Figure 11. The size of the lower die cavity during upsetting is the same as that during final forging. As can be seen from Figure 11, the upsetting pressure is relatively small, only 221t, and the metal in the lower part of the blank basically does not flow during upsetting, and the metal flow occurs in the large head. The final forging forming load is 2750t. This design uses a 2500t electric screw press for production, and the allowable load of the press can meet the requirements. The cavity is completely filled during final forging, and the material utilization rate is as high as 92%. No defects such as folding and scraping occur. The flash is small and evenly distributed, which further verifies the feasibility of the process design.

Conclusion

Through the structural analysis of bucket teeth, the forming process of precision roll forging-integral die forging was proposed, and the relevant process design was carried out. The material utilization rate was 92%, and it can be smoothly formed on the existing φ560mm automatic roll forging machine and 2500t electric screw press, thus providing a new design idea for the same type of bucket teeth, which has a certain reference significance for the casting and forging process of bucket teeth.