| Summary: | 碩士 === 國立虎尾科技大學 === 機械與電腦輔助工程系碩士班 === 102 === Abstract
Over the past few centuries, the lightweight and renewable materials not only accounted for a considerable position in traditional industry but also played an important role in the cutting-edge industry and green consumer industry. Recently, aluminum and magnesium alloys increasingly favored by consumers. Especially aluminum is broadly used for not only 3C products but for transportation mechanisms. Modern industry processes 3C chassis with NC machining, however, time-consuming and low material processing rate are considered as major defects. While the people''s requirement rising, manufacture technology has been constantly evolved and progressed. Die-cast aluminum alloy (Pressure die casting) method and semi-solid forming method (Semi-Solid Metal Forming, referred SSF) had become the key to mainstream technology.
Compared to conventional casting technology process, semi-solid forming of aluminum alloy method has many advantages: brilliant anti-fatigue property and no shrinkage during process, which is the application of rheological characteristics on alloy material at the state of solid-liquid coexistence. However, the processes mentioned above are formed while contacting with the mold at a high temperature and liquid state, and this situation leads to mold-forming compound generating easily with aluminum diffusion reaction between the liquid aluminum and the metal mold. Moreover, it will result in molten aluminum contamination and damage to the mold which will lose accuracy.
Therefore, this paper will delve into the material thixotropic A356 forging technology process development, and it is expected that A356 produces tissue ball, refinement in forming, a near-net shape (Net Near Shape, NNS) and finished as a perfect combination of heterogeneous materials within the condition of temperature rising due to forging below the melting point. In this study, it is to establish design criteria of a thixotropic forging die and optimize critical process parameters required for future product developments.
The experiment results revealed that: (1) This study had successfully generated the effect of ball and diffusion bonding effect of the during forming process, and the heterogeneous aluminum had successful engagement as well; (2) there is strong relationship between ball forming, joining condition and die temperatures. High cycle heating method is better than the electrical resistance heating method, and the temperature difference between the mold and the billet is about 40 ℃ which can be called nearly constant temperature forming. Furthermore, the temperature difference between electrical resistance heating mold and the billet is about 300 ℃,and there is hardly ball and bonding effect; (3) Under the same forming temperature, the longer period the billet temperature stabilizes, the more forward position of crystal phase change and diffusion bonding in the flow path. Within the same period of one steady temperature, the higher of billet forming temperature, the more forward position of crystal phase change and diffusion bonding in the flow path; (4) the more ECAE turning points, the greater shearing force which is generated by the material, and the conditions of engagement and ball forming are more significant. While getting through the first and the second passes, the original tissue had gradually been ball and refinement. After processing the third pass, the tissue had been replaced by the primary crystal silicon eutectic aluminum and the billet had been fully engaged.
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