Numerical Simulation of the Liquid-Gas Interface Shape in the Shot Sleeve of Cold Chamber Die Casting Machine

A mathematical model has been developed to simulate the flow pattern of molten metal and to predict the liquid-gas interface shape in the shot sleeve of a cold chamber die casting machine during the injection stage. The flow pattern in the shot sleeve is known to be closely related to the extent of gas entrapment of molten metal in the sleeve during the injection operation. In this study, a Variable Spacing Even Mesh (VSEM) method is proposed to incorporate with a computational fluid dynamics technique, named SOLA-MAC, to simulate the flow pattern in the shot sleeve. SOLA-MAC can deal with free surface flow problems while the VSEM method is used to handle the problem where the space in the shot sleeve keeps decreasing as the plunger moves to push the molten metal. The model is then tested on the shot sleeve of a cold chamber die casting machine. Four plunger speeds are tested to demonstrate the effects on the flow pattern of molten metal in the shot sleeve. The critical speed found in this study is 38 cm/s and it is close to the reported critical speed under the conditions that the space between the plunger and the sleeve end is 5 cm in diameter and 30 cm in length, and the fill ratio is 50%. As the plunger speed is slower than the critical speed, the wave front propagates along the sleeve faster than the plunger and reflects against the end wall of the sleeve. The remaining air in the shot sleeve is entrained as the wave front enters to the gate. As the plunger speed is higher than the suggested critical speed, the melt is immediately pushed higher in front of the plunger and forms a surge. The surge traps air in the early stage of the injection process.     

基于数值模拟的压铸过程低速工艺优化

低速压射过程中冲头的运动分为封闭浇料口、匀加速和匀速低速三个阶段,各个阶段的工艺参数对压室内金属液的流动形态都有重要作用,进而影响铸件中气孔缺陷的产生。采用数值模拟技术来研究不同工艺参数下压室内金属液的流动形态,对低速工艺进行优化。针对压射过程冲头的运动特征,引入了移动速度、压力边界条件,开发了压室压射过程三维数值模拟程序。结合慢压射临界速度理论,模拟了不同料口封闭速度、加速度和慢压射速度下压室内金属液波形的发展。模拟结果表明采用优化的工艺参数可以降低压室内的卷气。     

压室液态金属流动耦合温度场三维数值模拟

压铸过程中,压室内液态金属卷入的气体是影响铸件质量的原因之一.针对压室压射过程,引入冲头的移动规律以及流动过程中热量传递的计算,实现并开发了压室压射过程的流场耦合温度场的数值模拟程序.采用所开发的模拟程序对压室金属流动及传热过程进行了模拟,模拟结果与FLOW-3D的计算结果以及临界速度理论作比较,两者均吻合.采用压室模拟能够优化冲头的运动规律,使卷气最小.     

On the optimum plunger acceleration law in the slow shot phase of pressure die casting machines

The objective of this paper is to analyse a plunger acceleration law that is expected to minimize air entrapment in the slow shot phase of pressure die casting in horizontal cold chambers, and thus to reduce porosity in manufactured parts. The study is carried out using results from an analytical model of the flow of molten metal in the shot sleeve, which is based on the shallow-water approximation, and whose predicted optimum acceleration parameters are in good agreement with available experimental results. The results for the surface profiles of the wave formed during plunger movement using plunger acceleration laws which are typically used in pressure die casting are compared with those corresponding to the proposed law. Some analytical predictions for the wave profiles and for the mass of trapped air are compared with numerical results obtained from a finite-element code, which solves momentum and mass conservation equations. The limiting values of the initial filling fraction required for appropriate operating conditions are determined for wide ranges of acceleration parameters and pouring hole locations.     

压室慢压射过程流场模拟

气孔是压铸生产中的常见问题,导致这一缺陷的原因之一就是在慢压射过程中压室内的金属液流动卷入了气体.文中在压铸流场模拟的基础上,增加了移动边界条件处理冲头的移动过程,模拟了慢压射过程中压室内流体的流动形态.模拟结果与理论计算值及国外商品化软件的计算结果进行了比较,均比较吻合.     

Development and application of inverse heat transfer model between liquid metal and shot sleeve in high pressure die casting process under non-shooting condition

To predict the heat transfer behavior of A380 alloy in a shot sleeve, a numerical approach(inverse method) is used and validated by high pressure die casting(HPDC) experiment under non-shooting condition. The maximum difference between the measured and calculated temperature profiles is smaller than 3 °C, which suggests that the inverse method can be used to predict the heat transfer behavior of alloys in a shot sleeve. Furthermore, the results indicate an increase in maximum interfacial heat flux density(q_(max)) and heat transfer coefficient(h_(max)) with an increase in sleeve filling ratio, especially at the pouring zone(S2 zone). In addition, the values of initial temperature(T_(IDS)) and maximum shot sleeve surface temperature(T_(simax)) at the two end zones(S2 and S10) are higher than those at the middle zone(S5). Moreover, in comparison with fluctuations in heat transfer coefficient(h) with time at the two end zones(S2 and S10), 2.4-6.5 kW ·m~(-2)·K~(-1), 3.5-12.5 kW ·m~(-2)·K~(-1), respectively, more fluctuations are found at S5 zone, 2.1-14.7 kW ·m~(-2)·K~(-1). These differences could theoretically explain the formation of the three zones: smooth pouring zone, un-smooth middle zone and smooth zone, with different morphologies in the metal log under the non-shot casting condition. Finally, our calculations also reveal that the values of q_(max) and h_(max) cast at 680 °C are smaller than those cast at 660 °C and at 700 °C.     

Heat transfer characteristics of lost foam casting process of magnesium alloy

1 Introduction The growing demand for mass reduction in aerospace and automotive industries has greatly increased the magnesium application. Currently, casting is the main industrial forming method for magnesium alloys, but the lag of research and develop…     

基于三维有限元铸轧工艺模拟及工艺参数优化的Mg-Al合金晶粒细化(英文)

为了获得质量优异的镁合金薄板材并研究铸轧工艺参数对AZ31镁合金薄板材的温度场和热应力场的影响,基于铸轧的对称性采用ANSYS软件建立了三维几何和有限元模型。在ANSYS软件中采用smart-sizing算法进行网格划分。进行了一系列不同工艺参数下的三维温度场和热应力数值模拟。结果表明,随着浇注温度的升高,液相区和液固两相区的长度都增加;随着辊/薄板间接触的对流换热系数的增大,液固两相区的长度减小;随着浇注温度和铸轧速度的提高,两相区的长度增大。将优化的工艺参数(铸造速度2m/min、浇注温度640℃、换热系数15kW/(m2·℃)及水淬)用于镁合金铸轧试验,得到平均晶粒尺寸为50μm的镁合金板坯。三维仿真结果能更好地理解相变区的温度变化和铸轧过程中热裂纹的形成机理,为设计和优化镁合金铸轧的工艺参数提供帮助。     

Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds

Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell, which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall thickness and increase in the casting thickness.     

New filling system design for bolster casting and computer simulation

The new filling system is smooth filling without gas gap.It works well in avoiding the generation of defects such as porosity and inclusion.The pouring basin,sprue,runner and the gate of the bolster casting were designed according to the principle of the new filling system.The filling and solidification process of the bolster casting were also simulated.It was found that the filling process was smooth,and air entrapment and shrinkage were avoided.Finally,a further validation of the new filling system of bolster casting was carried out in a foundry.     

Continuous squeeze casting process by mass production

S queeze casting has been widely used for automotive struc tural parts because it offers a vast material selection from aluminum and magnesium alloys. In comparison with low pressure die casting, squeeze casting also overcomes many fluidity problems and thus it can use both hypereutectic and hypoeutectic alloys such as 319, 383 and 390. Squeeze casting can also apply “spot solidification” technology in addition to directional solidification method. The shortcoming of directional solidificati…     

基于正交试验的液态模锻Al-Sn-Cu轴套中Sn的宏观偏析

采用正交试验法分析了液态模锻Al-Sn-Cu轴套中Sn的宏观偏析规律。结果表明:液态模锻Al-Sn-Cu轴套不可避免的产生Sn的宏观偏析,铸件中同时存在着正偏析和逆偏析,正偏析出现在浇铸中心的近端,逆偏析主要存在于浇铸中心的远端;铸件凝固后期,低熔点液相被强制挤压至热节位置,形成粗晶区和细晶区相间的双峰组织,细晶区Sn的质量分数明显较高。液态模锻工艺参数对铸件宏观偏析产生较大影响,对Sn偏析影响由大到小依次是浇注温度、模具温度、保压时间及比压;本次实验条件下,当浇注温度为700℃,模具温度为240℃,比压为80 MPa,保压时间为5 s时,轴套铸件中Sn元素分布较均匀,Sn元素的宏观偏析得到减轻。     

水平连铸BFe30-1-1白铜管坯凝固过程的数值模拟

根据空心管坯的凝固传热特点建立了空心管坯水平连铸数值计算模型,采用ANSYS软件计算了水平连铸过程中浇注温度、冷却强度及拉坯速度对BFe30-1-1白铜合金管坯糊状区宽度和液穴深度的影响。结果表明,浇注温度、拉坯速度和冷却强度均对管坯液穴深度和糊状区宽度有重要影响,而浇注温度则对糊状区宽度影响不大。在此基础上采用试验的方法制备了表面光滑、无裂纹缺陷的空心BFe30-1-1白铜管坯。     

Effects of process parameters on morphology and distribution of externally solidified crystals in microstructure of magnesium alloy die castings

During the cold-chamber high pressure die casting(HPDC) process, samples were produced to investigate the microstructure characteristics of AM60B magnesium alloy. Special attention was paid to the effects of process parameters on the morphology and distribution of externally solidified crystals(ESCs) in the microstructure of magnesium alloy die castings, such as slow shot phase plunger velocity, delay time of pouring and fast shot phase plunger velocity. On the basis of metallographic observation and quantitative statistics, it is concluded that a lower slow shot phase plunger velocity and a longer delay time of pouring both lead to an increment of the size and percentage of the ESCs, due to the fact that a longer holding time of the melt in the shot sleeve will cause a more severe loss of the superheat. The impingement of the melt flow on the ESCs is more intensive with a higher fast shot phase plunger velocity, in such case the ESCs reveal a more granular and roundish morphology and are dispersed throughout the cross section of the castings. Based on analysis of the filling and solidification processes of the melt during the HPDC process, reasonable explanations were proposed in terms of the nucleation, growth, remelting and fragmentation of the ESCs to interpret the effects of process parameters on the morphology and distribution of the ESCs in the microstructure of magnesium alloy die castings.     

Effect of different processing parameters on interfacial heat-transfer behavior in high-pressure die-casting process

Vacuum die casting can reduce the “air entrapment” phenomenon during casting process. Based on the temperature measurements at metal–die interface with different processing parameters, such as slow shot speed (V_L), high shot speed (V_H), pouring temperature (T_p) and initial die temperature (T_m), inverse method was developed to determine the interfacial heat transfer coefficient (IHTC). The results indicate that a closer contact between the casting and die could be achieved when the vacuum system is used. It is found that the vacuum could strongly increase the values of IHTC and decrease the grain size in castings. The IHTC could have a higher peak value with increasing the T_p from 680 to 720 °C or the V_L from 0.1 to 0.4 m/s. In addition, the influence of the V_H and T_m on IHTC could be negligible.     

基于PtRh10-Pt热电偶的铸件温度测量方案设计和验证

基于PtRh10—Pt热电偶和Agilent34972A数据采集仪,设计了铸件浇注凝固过程的动态测温方案,并利用该方案对实际浇注过程进行了测量和验证。结果表明,该方案能快速准确地测量铸造生产过程中铸件任意点的温度变化情况,提供实时的温度场数据;同时该方案的适应性强,在铸件生产中具有较重要的参考和实用价值。     

软接触结晶器电磁连铸中初始凝固的基础研究

通过实验和数值模拟研究了软接触结晶器电磁连铸传热凝固特点,测定了金属Ｓｎ在连铸中的温度场,初始凝固点和坯壳厚度,得到了电磁场影响它们的基本规律。在数学模型中考虑了高频电磁场对金属的传热凝固的以下影响;（１）对结晶器的感应加热;（２）对金属的加热;（３）电磁力推斥液力金属,减少金属与结晶器壁接触的影响。     

压铸机压室温度分布与变形的二维模拟

针对卧式冷室压铸机压室的工作环境 ,提出三种不同的热传递数学模型。使用ABAQUS软件模拟压室在工作过程中的二维温度分布的几何变形状况。对比模拟和试验结果 ,得到了优化的数学模型     

A CELLULAR AUTOMATON-APPROACH TO SIMULATION OF GRAIN STRUCTURE DEVELOPMENT IN ELECTROSLAG CASTING

1.IntroductionElectroslagcastingcanproducepartsofgoodquality,ofwhichthemechanicalpropertiesarecomparablewithorsuperiortothoseofforgedproducts.Ithasbeenmoreandmoreutilizedtomakestructuresofcriticalimportance,whichconventionallywoulddoubtlesslybemadebyforging.Understandingandcontrolofmicrostructures,especiallyshape,sizeandorientationofcrystallitesinelectroslagcastingarethereforemoreandmoreimportantforsafetyconcernintheirapplication.Experimentalstudiesofthegrainstructuresandtheirdependenceonvario…     

TiAl基合金叶片吸铸成形缺陷的数值模拟

采用有限元软件ProCAST模拟TiAl基合金液在金属型真空吸铸成形铸造工艺中的充型凝固过程,分析在充型凝固过程中产生缺陷的原因,并进行了相关的实验验证。在模拟过程中发现铸件中确实存在模拟预测的缺陷,且缺陷主要集中在叶片隼部,在叶身部位出现少量的缩松缺陷,模拟和实际相吻合。