Optimization of investment casting process for K477 superalloy aero-engine turbine nozzle by simulation and experiment

In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process, the effects of different gating systems on mold filling, solidification process, and prediction of shrinkage porosity of aero-engine turbine nozzle castings were investigated by simulation and experimental methods. Results show that the design of the vertical runner would cause greater turbulence of the melt in the riser during the mold filling process, and the outer runner is not necessary. With the decrease in number of runners, the hot spot moves down towards the casting, and the shrinkage and porosity defects are formed in the casting below the riser. In the original designs, a certain tendency of shrinkage and porosity defect is found in the vanes, inner rings, and outer rings of the castings by both simulation prediction and experiment. Finally, based on the processing optimization, the aero-engine turbine nozzle casting with no shrinkage and porosity defects is obtained.

     

Solidification studies on sand cast Al 6061–SiCp composites

Most of the automotive components are cast and their performance depends very much on the solidification phenomenon. Solidification is primarily a process of achieving solid crystals from the liquid melt by promoting zones possessing very high cooling rates to ensure super cooling of the melt. Till date enormous data is available as regards the solidification behaviour of popular light alloys such as Al 6061 and A 356 with regard to the casting process, mould materials used and other important processing parameters. Effect of chills on the solidification behaviour of the above materials has also been reported suggesting chills to be an important promoter of directional solidification. Directional solidification results in minimized solidification defects. However, there is a lack of information regarding the effect of chills on solidification behaviour of aluminium based metal matrix composites which are currently the most potential candidate materials in automotive industries as a replacement for conventional light alloys. In the light of the above, this work is aimed at experimentally studying the solidification behaviour of Al 6061–SiC_p castings in sand mould using copper and mild steel chills. Further, commercially available finite element analysis (FEA) software has been used to predict the cooling curves with and without the use of chills for the developed composite. The experimental and predicted cooling rates of the developed composites are not in good agreement. Use of copper chills resulted in promoting higher cooling rates during the solidification of developed composites.     

热铁(贴)冷铁在精密铸造工艺设计中的应用

在精密铸造工艺设计中,一般是采用在热节圆的位置开设浇口、设置浇道或增加冒口来解决铸件缩孔、缩松等缺陷,使铸件在冷却、凝固过程中有效地形成补缩通道,获得优质的铸件,工艺设计的主要原则也来自于铸件的结构本身.运用热铁(贴)、冷铁的工艺方案,减少精铸件缩孔、缩松,通过从铸件外部冷却环境的改变来改善精铸件品质.     

挤压铸造ZA27合金大高径比铸件

通常挤压铸造仅适用于高径比小于3.5的铸件,研究大高径比铸件的挤压铸造将扩大这种先进铸造技术的应用范围.用试验和计算机模拟的方法,研究了高径比为7的ZA27合金铸件的力学性能、凝固过程中铸件内的温度、压力以及缩松的分布.结果表明,增加挤压铸造的压力不能有效地减少大高径比铸件的缩松缺陷;合理控制浇注温度和铸型预热温度能有效地消除大高径比铸件内的缩松,获得力学性能高且均匀的铸件.     

1.5MW风力发电机组轮毂球墨铸铁件的浇注系统设计

为了解决1.5 MW风力发电机组轮毂球墨铸铁件在铸造过程中容易产生缩松缩孔缺陷的问题,采用计算机数值模拟技术对轮毂的浇注系统进行优化设计分析。研究了轮毂球墨铸铁件的凝固特点,明确了铸件产生缺陷的原因,利用三维造型软件和铸造模拟软件对风力发电机轮毂铸件凝固过程的温度场进行模拟,得出了铸造风机轮毂的优化工艺方案。模拟结果显示,优化工艺可以明显地改善风机轮毂在铸造过程中产生的缩孔缺陷。     

大平板类铝合金壳体铸件铸造工艺优化与设计

针对大平板类铝合金壳体铸件的外形尺寸大、结构复杂等特点，通过三维温度场数值模拟来揭示铸件的凝固过程。根据准固态力学行为和流变行为，进行应力场模拟，进而预测铸件在凝固过程中产生缩松、缩孔以及热裂和变形等倾向，合理地实现了铸件的铸造工艺优化设计。     

基于数值模拟技术镁合金压铸模浇注系统优化设计

设计3种类型的浇注系统,运用铸造专用模拟软件JSCAST对3种浇注系统进行压铸数值模拟试验,分析液态金属充型及凝固过程中的速度场和温度场的分布,根据凝固规律有效预测铸件中可能存在缩孔及气孔缺陷的分布,从而选取T型浇注系统作为缸盖罩的最佳浇注系统并对其进行优化。试验结果验证了优化设计的可行性以及压铸过程数值模拟的可靠性,对压铸生产具有一定的指导意义。     

采煤机摇臂铸件缺陷分析及防止措施

为解决采煤机摇臂铸造生产中出现的铸造缺陷,对铸件的结构特点进行了分析,并运用顺序凝固理论,设计浇冒系统及内外冷铁的安放位置.采取提高砂芯的退让性、制定合理的浇注工艺等项措施.结果表明:铸件内形成了顺序凝固的温度梯度,缩孔、缩松、裂纹、夹渣、气孔等缺陷得到有效防止；经机加工和探伤等检验,产品满足技术要求.     

圆锥破碎机传动轴架的铸造工艺设计及模拟优化

运用传统的铸造工艺设计方法对圆锥破碎机传动轴架铸造工艺进行了初步设计,利用V-Cast模拟软件,对传动轴架初始工艺的充型和凝固过程进行了数值模拟,分析了初始工艺产生缺陷的部位和原因。在此基础上,通过添加冷铁,优化了铸造工艺,对优化工艺再次进行了模拟。模拟结果显示,优化工艺实现了传动轴架的顺序凝固,消除了缩孔、缩松等缺陷。生产实践表明,采用优化工艺生产的传动轴架内部组织致密,符合技术要求。     

The influence of internal chills on the structure and properties of aluminium alloy castings

Many of the drawbacks associated with the production of conventionally cast ingots and castings, such as the presence of pipes, centre-line segregation and columnar grains, can be attributed to the manner and extent of cooling inside the mould cavity and the problems of heat transfer from the centre to the outside of the casting. These result in lowering of the average mechanical properties and the yield of the casting. In the past, the use of external chills to reduce the above defects has had limited effects. This is because the influence of external chills becomes marginal beyond a certain distance. One of the potential methods of overcoming such problems is to employ heat sinks in the form of internal chills. Despite reported work by Russian and Japanese investigators on the use of internal chills, in the form of powder or strip, in iron and steel castings, no detailed information on the use of such chills in aluminium or other non-ferrous alloys is available in the literature.

This paper presents details and findings of an investigation carried out with Al-4.5% Cu (LM11) alloy using chills of cylindrical form of the same composition. The influence of such internal chills, placed centrally and non-centrally was assessed in terms of changes in solidification time, temperature gradient, percentage melting, microstructure, density, and the ultimate tensile strength of the castings.

The investigation has shown that solidification time decreases linearly with the percentage volume of the chills. Progressive structural refinement, corresponding to this reduction in solidification time, has also been observed. Distribution of the chills is seen to play an important role. One centrally-placed chill is essential in the refinement of the structure of the central region of an ingot, as well as to reduce the size of the central open pipe. The use of microchills in the form of turnings and powder has also been found to refine the structure considerably. The density and ultimate tensile strength of castings has been found to increase up to the optimum volume of chill, i.e. 2.5% at 75–115 K and 0.63% at 35 K superheat, and then decrease.     

Effect of chill cooling conditions on cooling rate,microstructure and casting/chill interfacial heat transfer coefficient for sand cast A319 alloy

A combination of experiments and numerical analyses were used to examine the cooling conditions, solidification microstructure and interfacial heat transfer in A319 cast in a chilled wedge format. Both solid copper chills and water cooled chills, with and without a delay in water cooling, were examined in the study. Various chill preheats were also included. The goal of the investigation is to explore methods of limiting heat transfer during solidification directly beside the chill and increasing cooling rates during solidification away from the chill. Within the range of conditions examined in the study, chill preheat was found to have only a small effect on cooling rates between 5 and 50 mm from the chill/casting interface, pour superheat a moderate effect and water cooling a significant effect. In comparison to the results for the solid chill, the solidification time at 5 mm with water cooling applied at the beginning of mould filling is reduced from 56 to 15 s and at 50 mm from 588 to 93·5 s. Furthermore, the average cooling rate during solidification is increased from 1·9 to 7·06°C s^?1 at 5 mm and from 0·18 to 1·13°C s^?1 at 50 mm. At 50 mm, for example, the increased cooling rate achieved with water translates into a reduction in secondary dendrite arm spacing from 40 to 25 μm or ～40%. Delaying the water cooling by 10 s facilitated slow cooling rates at 5 mm (similar to those achieved with a solid chill) and high cooling rates 50 mm from the chill. A temperature based correlation was found to be suitable for characterising the behaviour of the interfacial heat transfer coefficient in the solid shill castings, whereas a time based correlation was needed for the water cooled castings.     

凝固模拟在上梁件工艺优化中的应用

ＦＴ－ｓｔａｒ凝固数值模拟系统为铸造工艺的优化设计提供了科学的依据。该系统的彩色后处理显示能直观、定量地预测铸件的缩孔、缩松缺陷。本文通过凝固模拟上梁件工艺进行优化,减少了冒口重量,实现了用现有设备能力,在极限的钢水量下完成的梁铸造。     

数值模拟在烧结机台车体铸造工艺设计中的应用

运用ViewCast软件对烧结机台车体铸件的凝固过程进行了数值模拟,分析了其缺陷产生的部位和原因.根据模拟结果并结合理论分析,通过ViewCast软件设计了冒口尺寸和分布,经过多次模拟,进行铸造工艺优化,最终获得了合适的工艺.结果表明,优化工艺实现了铸件的顺序凝固,消除了缩孔、缩松缺陷.生产实践表明,采用ViewCast软件设计的铸造工艺,铸件组织致密,符合技术要求.     

Numerical simulation and optimization of shell mould casting process for leaf spring bracket

Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting.The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting;and the formation mechanism of the gas pore,and shrinkage porosity defects were analyzed.The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment,insufficient feeding and non-sequential solidification.Subsequently,through changing the position of risers,adding a connecting channel between the risers,and setting blind risers at the U-shaped brackets,an optimized gating and feeding system was established to improve the quality of the casting.After optimization,the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated.The experiment results with the optimized casting process are in good agreement with the numerical simulation,which verifies the validity of the finite element model in the shell mould casting.     

计算机对“T”型铸钢件接头凝固特性的研究

本文针对普通铸钢件,用数值模拟法计算研究了不同比例、不同尺寸的“T”型接头在普通砂型铸造条件下凝固时间分布规律、凝固系数变化和拐角冷铁对其凝固过程的影响。得到有益于认识铸件中此类接头凝固特性和热节位置的变化规律,对工艺设计者认识和防止成型过程中产生凝固收缩缺陷是很必要的。     

Numerical simulation of low pressure die-casting aluminum wheel

The FDM numerical simulation software, ViewCast system, was employed to simulate the low pressure die casting (LPDC) of an aluminum wheel. By analyzing the mold-filling and solidification stage of the LPDC process, the distribution of liquid fraction, temperature field and solidification pattern of castings were studied. The potential shrinkage defects were predicted to be formed at the rim/spoke junctions, which is in consistence with the X-ray detection result. The distribution pattern of the defects has also been studied. A solution towards reducing such defects has been presented. The cooling capacity of the mold was improved by installing water pipes both in the side mold and the top mold. Analysis on the shrinkage defects under forced cooling mode proved that adding the cooling system in the mold is an effective method for reduction of shrinkage defects.     

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…     

数值模拟在后桥壳体铸造工艺优化中的应用

采用三维造型软件对后桥壳体铸件进行造型,添加浇冒系统和铸型,用华铸CAE软件进行凝固过程的数值模拟,通过比较不同工艺条件下的凝固过程中的液相动态分布过程,预测了形成缩孔缺陷的不同倾向,并对比了不同工艺方案下铸件的缩孔分布及工艺出品率,对铸造工艺进行改进和优化,将改进后的铸造工艺应用于生产,既解决了铸件的铸造缺陷,又缩短了生产制造周期。     

大型铸钢件补浇工艺的凝固模拟研究

结合工厂实际生产条件,对特殊的砂型铸造工艺－补浇工艺进行了铸钢件温度场模拟和缩孔缩松的预测。同时为了满足工艺设计的要求,对铸件本身和浇注系统,冒口的质量进行了精确统计。所有的温度场模拟,缩孔缩松的预测结果和质量统计结果对制定工艺起到了辅助设计的作用,依照模拟结果制定铸造工艺,该按工艺进行实际生产,浇注结果较为满意。在此工艺的制定过程中,计算机凝固模拟技术起到了很好的辅助设计作用。     

湿型球墨铸铁件收缩特性的试验研究

采用正交试验的方法，浇注一系列铸件，测量铸件的冷却曲线；解剖铸件，测定铸件质量、铸件及缩孔体积。研究了碳当量、孕育、铸件模数以及铸型条件对湿型球铁件收缩特性及缩孔缩松的影响。为开展数值模拟预测球铁件缩孔、缩松的工作打下了基础。