Study the Effect of Slow Shot Profile on the Air Entrapment of Melt Flow inside the Shot Sleeve in Die Casting Processes

• Main Authors: You-Chung Chang, 張又中
• Other Authors: 莊水旺
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/01156939390755390268

碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 95 === Abstract In cold chamber die casting processes, metal melt flow may induce air entrapment inside the shot sleeve and influence quality of castings as the slow shot velocity profile setting improperly on the filling process. Therefore, effectively selecting the slow shot velocity to reduce possible air entrapment inside the sleeve during initial filling is one of the targets to be reached for die casters. In this study, the first issue was to derive a proper critical value of slow shot speed in terms of process parameters, such as sleeve diameter and filling percentage, by using the hydrodynamics, in which there should be no air entrapped inside the shot sleeve. Then, a series of flow simulations was conducted to model the melt flow inside the sleeve with different conditions, that is, sleeve diameter, filling percentage, and slow shot speed, by using available software. It was revealed that as the filling percentage was larger than 50%, the calculated optimum slow shot speed was quite close to that derived by Garber and Tszeng However, the critical slow shot speed derived by Garber and Tszeng was higher than that obtained from this study as the filling percentage is lower than 50%, in which the air entrapment would be appeared in the analysis. This means that the formulae derived by Garber and Tszeng might be only good for higher filling percentage rather than filling percentage less than 50% which is general applied in the real die casting world. To obtain a usable formula for the application to a whole range of filling percentage, a series of numerical experiments was conducted in this study. The formula and its associated tables as well as graphs were proposed a larger range of fulling percentage, 30％to 60％. These could be utilized as a reference for die casters as setting the process conditions. Keyword: die casting process, air entrapment, flow analysis, critical velocity.