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Effect of cooling circuit duration on formation of solidification shrinkage in A356 casting automative wheels

机译:冷却回路持续时间对a356铸造自动轮凝固收缩形成的影响

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摘要

Low Pressure Die Casting (LPDC) process is one the most common casting process to produce structural automotive components, such as alloy wheels and suspension components. It has been identified that cavity filling and solidification process are two most critical aspects to produce premium quality casting components.During the solidification process of casting alloy, it is a well known phenomenon that metal experiences volumetric shrinkage due to its density difference between liquid and solid phase. When this volumetric shrinkage is not properly compensated, then a casting defect commonly known as solidification shrinkage occurs. The solidification shrinkage has very detrimental effects on structural integrity required for premium quality casting such as aluminium alloy wheels.Literature and practical experiences of foundry men show that it is critical to achieve unidirectional solidification pattern by avoiding an isolated hot spot in order to minimise the solidification shrinkage. However, it is found that the geometry of industrial casting applications is often constrained by other design factors that would not naturally avoid these isolated hot spots. The subject of this research, aluminium alloy wheels, is not excluded from this constraint.In aluminium alloy wheels, an isolated hot spot is commonly observed in an area known as rim and spoke junction due to its geometry constraints. Consequently, the solidification shrinkage is commonly experienced, which is undesirable due to its detrimental effects for the structural integrity of alloy wheels. In order to minimise the solidification shrinkage, forced cooling method is applied to avoid an isolated hot spot. The control of this forced cooling is achieved by cooling media, flow rate of cooling media and duration cooling circuit. Foundry experiments in industrial environment were conducted producing aluminium alloy wheels using commercially treated A356 (Al-Si) alloy, where different durations of cooling circuit were used to understand the sensitivity of solidification shrinkage formation to the duration of cooling circuit. This was followed by metallurgical structure analysis and numerical modelling to suggest the sensitivity of cooling circuit duration in controlling solidification shrinkage.The major finding conclusion of this research is that control of the shrinkage formation is not very sensitive to the duration cooling circuit. It is suggested that as casting solidifies initially from the mould wall, it retracts away from the cast-mould interface due to thermal contraction. Consequently, air gap is formed between casting and mould interface, creating an effective thermal resistance layer. Thereafter, heat transfer across the cast-mould interface is not sensitive to the change in the cooling channel which is a distance to the cast-mould interface.Some limitations of numerical modelling and metallurgical analysis were also identified during this research and recommendations were made to improve the accuracy of local hot spot prediction in production of aluminium alloy wheels. More specifically, numerical modelling of the effect of grain refinement and use of non homogeneous material property (particularly fraction of solid) for rapidly chilled area. Fraction of eutectic rather than secondary dendrites arm spacing is a proper microstructure parameter that can be used to locate the hot spot.
机译:低压压铸(LPDC)工艺是生产汽车结构件(例如合金轮毂和悬架部件)的最常用铸造工艺之一。已经发现腔填充和凝固过程是生产优质铸件的两个最关键的方面。在铸造合金的凝固过程中,众所周知的现象是金属由于其液体和固体之间的密度差而经历体积收缩。相。当该体积收缩率没有得到适当补偿时,就会出现通常称为凝固收缩率的铸造缺陷。凝固收缩对优质铸件(例如铝合金轮毂)所需的结构完整性有非常有害的影响。铸造人员的文学和实践经验表明,通过避免孤立的热点以最小化凝固来实现单向凝固模式至关重要。收缩。但是,发现工业铸造应用的几何形状通常受到其他设计因素的约束,而这些设计因素自然不会避免这些孤立的热点。本研究的主题不限于铝合金轮毂。在铝合金轮毂中,由于其几何形状的限制,通常在称为轮辋和轮辐的区域观察到孤立的热点。因此,通常会发生凝固收缩,这是不希望的,因为它对合金轮毂的结构完整性有不利影响。为了最大程度地减少固化收缩,采用了强制冷却方法,以避免出现孤立的热点。这种强制冷却的控制是通过冷却介质,冷却介质的流量和持续冷却回路来实现的。进行了工业环境下的铸造实验,使用经过商业处理的A356(Al-Si)合金生产铝合金轮毂,其中使用不同的冷却循环时间来了解凝固收缩形成对冷却循环时间的敏感性。随后进行了冶金结构分析和数值模拟,表明冷却回路持续时间在控制凝固收缩率方面的敏感性。本研究的主要结论是,控制收缩率对冷却回路持续时间不是很敏感。建议当铸件最初从模具壁凝固时,由于热收缩而从铸模界面缩回。因此,在铸件和模具界面之间形成气隙,从而形成有效的热阻层。此后,通过铸模界面的传热对冷却通道的变化不敏感,该变化是与铸模界面的距离。在此研究中还发现了数值建模和冶金分析的一些局限性,并提出了一些建议提高了铝合金轮毂生产中局部热点预测的准确性。更具体地说,对快速冷却区域的晶粒细化效果和非均匀材料特性(特别是固体分数)的使用进行了数值建模。共晶分数而不是次生树枝晶臂间距的分数是可用于定位热点的适当的微结构参数。

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    Lee Rafael Jung Hoon;

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  • 年度 2007
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