Determination of die wear and forming load test scheme determination of die wear and forming load test scheme aiming at the problem of die failure in the hot forging process of driven spiral bevel gear blank, from the perspective of analyzing die wear and forming load of gear blank, the process parameters of closed die forging process of driven spiral bevel gear blank are optimized through the combination of finite element numerical simulation and orthogonal test analysis method, Thus, the production cost of closed die forging of driven spiral bevel gear blank is reduced.
(1) Orthogonal experimental design variables and optimization indexes
The experimental factor design aims to improve the objective function so that the parameter values can obtain the required high-quality parts without increasing the cost under the optimal process parameters. In the hot die forging process of driven spiral bevel gear blank, process parameters such as die preheating temperature, forging speed, die hardness and blank initial temperature have a great impact on the performance of the final product. Die preheating temperature affects the fluidity and deformation properties of materials, as well as the properties and surface quality of final forged products. Forging speed is usually used to control the strain rate, because many materials are very sensitive to the strain rate, which will have a great impact on the deformation behavior of materials in the forging process. Die hardness mainly affects die life and is an important index of die optimization design. Therefore, the factors such as die preheating temperature, forging speed, die hardness and blank initial temperature are selected as the variables of optimal design in this study.
Smaller forming load and die wear are two objectives of optimal design. In the forging process of spiral bevel gear blank, high forging pressure is easy to lead to overload, plastic deformation and fracture of forging die and high equipment failure rate. It is the most important factor to select forging equipment. Therefore, smaller forming load is selected as an optimization goal of forging process and die design. In addition, die wear failure is one of the failure forms of forging dies. Die wear directly affects the accuracy of forging workpiece and is also an intuitive judgment of die failure. Therefore, smaller die wear is also selected as another optimization objective of forging process and die design.
(2) Factor level table of orthogonal test
In the hot die forging process of driven spiral bevel gear blank, four factors such as die preheating temperature, forging speed, die hardness and friction coefficient are analyzed. Each factor is set at 3 levels, and a total of 9 groups of simulation tests need to be done, that is, the orthogonal test analysis is carried out by using the orthogonal table of L9 (34). The level of orthogonal test factors is shown in the table.
| Experimental factors | Die hardness / HRC | Forging speed / (mm / s) | Mold preheating temperature / ℃ | Initial temperature of blank |
| Level 1 | 50 | 30 | 150 | 950 |
| Level 2 | 55 | 40 | 200 | 1000 |
| Level 3 | 60 | 50 | 250 | 1050 |