| Summary: | 碩士 === 國立虎尾科技大學 === 創意工程與精密科技研究所 === 98 === Orbital forging is a new process featuring a local contact, which forces the metal material to gradually deform by incremental approach. This process has the advantages of labor-saving, high precision, and low noise, etc., and so is highly valued by many scholars and industry experts and is widely applied too. However, due to the complicated action modes and hard-controlled material flow, its theoretical research has not been mature until now. Because difficulties increase in production design, problems with extended production cycles and product manufacturing appear, and therefore the applications and development of orbital forging are restricted.
In general, metal is softened after heating, and at a certain temperature range, the higher temperature enhanced the higher softening effect, and metal flow become easier. Based on this physical phenomenon, a new dieless forging, thermal-differential forging, has been developed, which makes the metal flow in certain regions become easier. If the temperature distribution could be suitably controlled, the complex parts could be initially formed by using simple forging method, thus the near net shape forming will be achieved.
To effectively understand the influence of local heating on forming of orbital forging, the three-dimensional rigid-plastic finite element method was applied in the current study to the numerical simulation of differential thermal orbital forging. Namely, to effectively promote the deformation of the billet, the poorly deformed region was locally heated at a high temperature. In addition, the influence of the upper die orbital angle, rotation speed, and lower die feed rate on the thermal differential hot forging for bevel gear were also explored.
Results showed that local heating in the lower zone of billet could not only effectively improved the deformation ability of orbital forging, but also generated obvious temperature gradient. Due to the uneven deformation in orbital forging processes, the equivalent strain distributed over the bevel gear was less consistent, but the maximum strain value could be found at the bottom and top of the die/billet contact regions. As for the influence of process parameters, the forming load was greater when the orbital angle was greater and rotation speed higher, but the forming load was lower when the feed rate was slower. The forming effect was better at higher temperature, but the orbital forging was less affected by the friction factor.
Temperature and deformation are the major factors in affecting the microstructure of metal, and the grain refinement is more obvious as the temperature gets higher. Because the interface of billet and die in orbital forging is a local contact deformation, the distribution of heat energy transfer is more uneven. Therefore, the distribution of dynamic recrystallization in different regions is not uniform. It requires longer time in phase transformation when it is at higher temperature, and the structural strengths were different when using diverse quenching media.
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