Rapid fabricating process of zinc alloy moulds based on vacuum casting process

Abstract

A rapid fabrication process was developed by combining stereolithography prototype, silicone rubber mould and vacuum casting process for zinc alloy moulds. Transfer coating mould was introduced as casting moulds reproduced from silicone rubber moulds. Vacuum casting process was applied to improve filling ability of complicated mould with fine pattern surface. Vacuum reduces the gas counterpressure in the casting mould cavity and then improves the filling ability.     

镁合金真空低压消失模铸造的技术特征与实践

介绍了镁合金在真空低压消失模铸造下的技术特征。研究表明：真空低压消失模铸造的流动性受充型气体的流量与压力、浇注温度、涂层厚度、泡沫密度、真空度等多方面的因素影响；在低充型速度和低真空度的条件下，液态镁合金在真空低压消失模铸造过程中的充型形貌均呈现以内浇道为中心的拱形层状推进流动，如充型速度加快金属液流动前沿拱形形貌更加突出。而真空度增加会出现明显的“附壁效应”；与重力消失模铸造比较，真空低压消失模铸造镁合金铸件凝固更呈现“同时凝固”特征；由于快速充型、压力下凝固，镁合金真空低压消失模铸造零件的铸态抗拉强度（σh=180．8MPa）、屈服强度（σ0.2=113．2MPa）、伸长率（δ=4．4％），高于重力消失模铸造、树脂砂空型铸造的铸态性能，达到了金属型铸造的铸态性能，经热处理达到了压铸镁合金的性能范围。浇注实践表明，真空低压消失模铸造对液态镁合金，具有良好的抗氧化保护能力、优良的浇注充型性能和力学性能，可铸造出高精度的、薄壁复杂的镁合金消失模铸件，是一种极有潜力和优势的镁（铝）合金精密铸造技术。     

感应式高真空压铸模设计

在压铸生产过程中,铸件成型受到充填时间的限制,所以必须使用高速高压充型。在合金液凝固之前将其充满型腔才能保证铸件成型。在充型过程中,模具型腔内有部分气体来不及排放,以致使铸件内部形成气孔。本文介绍了感应式高真空压铸模具设计的要点,它是有效提高铸件质量的方法之一,供大家参考。     

Gas content in high pressure die castings

This paper presents the results of a quantitative study of the gas level in various types of castings from the high pressure die casting (HPDC) process using a vacuum fusion method. It was found that the major part of the gas was from the air entrapment during cavity filling. Other sources such as air entrapment during ladling, residual die lubricant and quenching water were also noticeable. Measurements of a large casting and castings from a multi-cavity die showed that the gas content was unevenly distributed. The modified vacuum fusion method has been proved to be a valuable tool for evaluating and quantifying the level of gas in castings as well as for an assessment of the influence of different process parameters on gas evolution in castings.     

基于模糊控制论的压铸浇注系统工艺参数设计新方法

运用模糊控制论方法来预测压铸浇注系统的基本工艺参数充填时间和内浇口速度，并结合压铸流体动力学理论，给出设计浇注系统的全部工艺参数。     

间接挤压铸造模具设计特点及研究

结合间接挤压铸造工艺的特点，提出了间接挤压铸造模具设计流程和模具结构设计中的基本思路及要点，对某些重要的设计程序进行了详细论述。指出浇道位置的选择首先要保证金属液沿着型壁顺序充填，以减少金属液的流动阻力；内浇道应使液态金属从制件厚壁处开始充填，以利压力的传递，消除缩孔，保证制件的质量。     

真空压铸中型腔真空压力的理论计算及试验研究

针对真空压铸中型腔真空压力的下降规律进行了理论计算和试验研究。针对具体的真空系统进行了型腔排气理论曲线和实测曲线的对比,验证了这种计算方法的可行性,指出了真空压铸为了达到理想的型腔真空压力对于低速工艺选择的限制要求,并提出了一种通过计算理论排气时间来对真空系统设计和低速工艺制定进行优化的方法。     

智能控制的真空差压反重力铸造工艺参数优化

对智能控制的真空差压反重力铸造的真空度、充型压力、升压时间和结晶压力等主要工艺参数进行了优化分析.研究结果表明,这些参数对薄壁铸件充型能力影响程度的大小依次为升压时间、结晶压力、真空度、充型压力.缩短升压时间,充型能力会大大提高;增大结晶压力,金属液在凝固阶段的补缩作用得到加强,充型能力增强;真空度越高,铸型中的反压就越小,充型能力提高;充型压力增大,充型的初始动量变大,有利于增强金属液对薄壁铸件的充填.     

柴油机气缸体消失模铸造工艺的优化设计

从泡沫模样的制作、型砂的选用、造型工艺以及浇注系统的设计诸方面阐述了直列四缸柴油发动机气缸体消失模工艺的优化设计。     

Characterization of A390 aluminum alloy produced at different slow shot speeds using vacuum assisted high pressure die casting

The effects of vacuum assistance on the microstructure and mechanical properties of high pressure die cast A390 alloy at different slow shot speeds were evaluated. Plate-shaped specimens of hypereutectic A390 aluminum alloy were produced on a TOYO BD-350V5 cold chamber die casting machine incorporated with a self-improved TOYO vacuum system. According to the results, the vacuum pressure inside the die cavity increased linearly with the increasing slow shot speed at the beginning of mold filling. Meanwhile, tensile properties of vacuum die castings were deteriorated by the porosity content. In addition, the average primary silicon size decreased from 23 to 14 µm when the slow shot speed increased from 0.05 to 0.2 m/s, which has a binary functional relationship with the slow shot speed. After heat treatment, microstructural morphologies revealed that needle-shaped and thin-flaked eutectic silicon particles became rounded while Al₂Cu dissolved into α(Al) matrix. Furthermore, the fractography revealed that the fracture mechanism has evolved from brittle transgranular fracture to a fracture mode with many dimples after heat treatment.     

真空浇注对充型过程的作用及其在快速铸造中的应用

液态金属铸造过程中施加真空是提高复杂铸件充型性能的有效措施。通过分析真空对充型过程的作用机理．认为真空可以有效减少型腔中的气体反压力，从而达到改善充型性能的目的。采用了真空浇注工艺，开发了真空浇注设备。将此设备应用于复杂薄壁铸件的快速铸造中，由于金属熔化后可以在真空环境中进行浇注和充型凝固．取得了良好的效果。     

铝合金低压铸造充型过程水模拟技术的研究

以相似理论为理论基础,对铝液的低压充型过程进行了模拟实验研究,利用气体向液面加压的同时对模具型腔进行抽真空。实验结果表明:上升的液面一直保持水平状态并沿着铅垂方向推进;当真空度为-0.02MPa、加压气压为0.02 MPa时,为最佳的加压工艺参数。并将模拟结果与原型的结果进行了比较,两者具有良好的一致性。     

汽车壳体低压铸造工艺与模具设计

介绍了汽车壳体零件低压铸造工艺与模具设计.内容主要有低压铸造工艺参数的设计,包括升液压力与升液速度、充型压力和充型速度的计算、浇注温度的确定、结晶压力和保压时间的计算等;模具设计,包括模具结构与壁厚的确定、型腔尺寸的计算、型芯和抽芯的计算、模具的三维造型.     

铝、镁合金真空低压消失模壳型铸造的缺陷分析

分析了采用泡沫模用精密铸造制壳,并用真空低压浇注成形铝、镁合金铸件的典型缺陷(主要是浇不足和冷隔、孔洞及粘砂缺陷)的行貌特征和形成机理,并提出相应的防治措施。结果表明,浇不足和冷隔缺陷主要由金属液充型速度慢、充型动力不足、浇注温度低等原因造成;孔洞缺陷主要由金属液浇注速度过快、保压压力小或保压时间短,浇注温度高,浇注系统设计不合理及型壳透气性差等原因造成。粘砂缺陷主要由型壳强度低、充型压力和真空度过大、造型型砂粒径大和激冷效果差等原因所致。     

真空压铸工艺参数对AM50镁合金力学性能的影响规律

采用阶梯试验模具及AM50合金,进行了系统的真空压铸试验,实测了不同厚度的阶梯试样在不同工艺条件下的密度及力学性能,研究了高真空压铸工艺参数对AM50镁合金力学性能的影响规律.结果表明,随着型腔真空压力的降低,铸件密度、抗拉强度和伸长率均随之提高;铸造压力对力学性能的影响在真空压铸和常规压铸中遵循基本相同的规律,即增大铸造压力可以使铸件的致密程度、抗拉强度、屈服强度和伸长率得到提高;随着高速速度的增大,薄壁铸件的抗拉强度、屈服强度和伸长率均表现出明显的增加,这一点与常规压铸的规律相反.结合高真空和高速工艺,可以使薄壁铸件的抗拉强度和伸长率得到较为明显的提升.     

Numerical simulation of heat transfer and fluid flow of molten metal in MMA–St copolymer lost foam casting process

In this study, a computational fluid dynamics (CFD) code was developed to calculate the filling pattern using volume of fluid (VOF) algorithm with donor–acceptor method for free surface simulation. This algorithm has been modified to include the pressure of the gas produced from foam degradation. For this purpose a heat transfer model and 2D foam degradation model were developed. In heat transfer model, radiation and conduction between foam and molten metal; and convection between gas and molten metal were considered. In order to evaluate the results of simulation, a bench scale casting apparatus was assembled and the casting was conducted in a transparent mold. The effect of several parameters such as coating thickness, foam density and vacuum level on the gap temperature, gap pressure and filling speed was studied with the developed software. It was found that the simulated results are in good agreement with experimental results.     

镁合金转向器铸件真空压铸过程的模拟研究

针对汽车镁合金转向器铸件,采用数值模拟的方法研究了其真空压铸成形过程,分析了在高真空度条件下金属液充型的特点,并在此基础上对比研究了在高真空度、低真空度以及常压条件下充型及凝固的规律。结果表明,提高型腔真空度能有效地提高金属液充型能力,避免铸件内气孔的产生,但对缩孔、缩松缺陷的形成没有影响。     

Accelerated method for testing soldering tendency of core pins

Abstract

An accelerated method for testing die soldering has been proposed and tested. High intensity ultrasonic vibration has been applied through a core pin to molten aluminium in order to simulate service conditions under die casting. Such conditions include high pressure and high impingement speed of molten metal on the pin. Soldering tendency of H-13 steel pins with or without commercial coatings was tested using this accelerated method. The experimental results indicate that soldering occurs within a few minutes of testing using this new method, much faster than that using the conventional methods. The coating failure mechanism identified in this new method is identical to that observed in the conventional methods, suggesting that the new method is suitable for testing soldering tendency of core pins under die casting conditions.     

Study on interfacial heat transfer coefficient at metal/die interface during high pressure die casting process of AZ91D alloy

The high pressure die casting (HPDC) process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today's manufacturing industry. In this study, a high pressure die casting experiment using AZ91D magnesium alloy was conducted, and the temperature profiles inside the die were measured. By using a computer program based on solving the inverse heat problem, the metal/die interfacial heat transfer coefficient (IHTC) was calculated and studied. The results show that the IHTC between the metal and die increases right after the liquid metal is brought into the cavity by the plunger, and decreases as the solidification process of the liquid metal proceeds until the liquid metal is completely solidified, when the IHTC tends to be stable. The interfacial heat transfer coefficient shows different characteristics under different casting wall thicknesses and varies with the change of solidification behavior.     

负压消失模工艺中EPS热解产物的研究

消失模铸造工艺中ＥＰＳ热解过程及热解产物的组成一直是消失模工艺研究的热点之一。采用气相色谱法对负压消失模工艺型腔中ＥＰＳ热解产物样品进行了分析,并且考察了合金浇注温度、负压度以及涂层透气性对解产物组成的影响,试验结果表明,浇注温度对ＥＰＳ热解产物的组成以及ＥＰＳ在型腔中的发气量有着决定性的影响,从而影响金属液流动前沿的形态;随着负压度和涂层透气必珠增加,ＥＰＳ热解产物能够更快地排出型腔,在高温区停