Newly developed vacuum differential pressure casting of thin-walled complicated Al-alloy castings

The newly designed vacuum differential pressure casting (VDPC) unit was introduced, by which the capabilityof the VDPC process to produce thin-walled complicated Al-alloy castings, that are free from oxides, gas pore andshrinkage cavity and thus enhance overall part quality, was studied. Experimental results were compared with those oftraditional gravity pouring and vacuum suction casting. The first series of experiments were focused on investigating thecastability of thin section Al-alloy casting. In the second series of experiments the metallographic evidence, castingstrength and soundness were examined. Finally, case studies of very interesting thin walled complicated casting applicationswere described. The advantages of the described technique have made possible to produce thin walled complicatedAl-alloy casting (up to a section thickness of 1 mm), which is not practical for gravity pouring and vacuum suction casting.

Physical Simulation of Mold-Filling Processing of Thin-Walled Castings under Traveling Magnetic Field

Mold-filling process of thin-walled castings under the condition of traveling magnetic field has been studied by physical simulation method using gallium melt and fast speed photography. Flow morphology and its formation mechanism were obtained and discussed for thin-walled casting. The influences of magnetic field density on the filling ability, filling velocity and mold filling time have been studied. The differences in filling capability between gravity casting and casting under the traveling magnetic field have been compared. The results indicate that the mold filling ability of the gallium melt increases greatly under the condition of traveling magnetic field; the filling time is shortened from 18 s under gravity field to 3 s under the traveling magnetic field and average flow rate of the melt increases from 1.6 to 8.68 cm3/s; the change law of the cross-section morphology of the gallium melt during the mold filling is that at first, the cross-section area does not change, then it decreases gradually. When the front of the melt reaches the end of the mold cavity, the front melt will backfill the mold; the wider the width of mold cavity, the better the mold filling ability. The mold filling ability of gallium melt in mold with upper magnetic conductor is better than that without upper magnetic conductor.

An improved cross entropy algorithm for steelmaking-continuous casting production scheduling with complicated technological routes

In order to increase productivity and reduce energy consumption of steelmaking-continuous casting(SCC) production process, especially with complicated technological routes, the cross entropy(CE) method was adopted to optimize the SCC production scheduling(SCCPS) problem. Based on the CE method, a matrix encoding scheme was proposed and a backward decoding method was used to generate a reasonable schedule. To describe the distribution of the solution space, a probability distribution model was built and used to generate individuals. In addition, the probability updating mechanism of the probability distribution model was proposed which helps to find the optimal individual gradually. Because of the poor stability and premature convergence of the standard cross entropy(SCE) algorithm, the improved cross entropy(ICE) algorithm was proposed with the following improvements: individual generation mechanism combined with heuristic rules, retention mechanism of the optimal individual, local search mechanism and dynamic parameters of the algorithm. Simulation experiments validate that the CE method is effective in solving the SCCPS problem with complicated technological routes and the ICE algorithm proposed has superior performance to the SCE algorithm and the genetic algorithm(GA).

Solidified structure of thin-walled titanium parts by vertical centrifugal casting

The solidified structure of the thin-walled and complicated Ti-6AI-4V castings produced by the vertical centrifugal casting process was studied in the present work. The results show that the wall thickness of the section is featured with homogeneously distributed fine equiaxial grains, compared with the microstructure of the thick-walled section. The grain size of the castings has a tendency to decrease gradually with the increasing of the centrifugal radius. The inter-lamellar space in thick-walled casting parts is bigger than that of the thin-walled parts, and the profile of inter-lamellar space is not susceptible to the centrifugal radius.

Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1mm. Therefore, in this study, thin-walled die casting of aluminum （Al-Si-Cu alloy： ALDC 12） in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation （MAGMA soft） and actual casting experiment （Buhler Evolution B 53D）. Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.

Filling mode and regularity of vertical centrifugal casting process of titanium alloy in thin-walled cylinder cavity

The mold filling process of titanium alloy in a thin-walled cylinder cavity under vertical centrifugal casting process was studied by means of the hydraulic simulation experiments. Results show that the filling mode of the melt in the cylinder cavity varies with casting wall-thickness. When the casting wall-thickness is less than or equal to the thickness of the first layer during the filling process, the melts fill the cavity from the bottom to the top.When the casting wall-thickness is greater than the thickness of the first layer during the filling process, the melts first fill the largest radius parts of the cavity with a certain thickness of the first layer from the bottom to the top of the cavity, and then they fill the cavity from the larger radius part to the smaller radius part. The melt filling ability increases with the increment of the mold rotational speed and the pouring temperature. In another aspect, the melt filling ability rises with the decrement of the melt viscosity, and the melt with the better filling ability is prone to fill the cylinder cavity layer by layer.

Eliminating shrinkage defects and improving mechanical performance of large thin-walled ZL205A alloy castings by coupling travelling magnetic fields with sequential solidification

ZL205 A alloys with large thin-walled shape were continuously processed by coupling travelling magnetic fields(TMF)with sequential solidification,to eliminate the shrinkage defects and optimize the mechanical performance.Through experiments and simulations,the parameter optimization of TMF and the influence on feeding behavior,microstructure and properties were systematically studied.The results indicate that the magnetic force maximizes at the excitation current of 20 A and frequency of 200 Hz under the experimental conditions of this study,and increases from center to side-walls,which is more convenient to process thin-walled castings.TMF can break secondary dendritic arm and dendrites overlaps,widen feeding channels,prolong the feeding time,optimize the feeding paths,eliminate shrinkage defects and improve properties.Specifically,for as-cast state,TMF with excitation current of 20 A increases ultimate tensile strength,elongation and micro-hardness from 186 MPa,7.3%and 82.1 kg/mm^(2) to 221 MPa,11.7%and 100.5 kg/mm^(2),decreases porosity from 1.71%to 0.22%,and alters brittle fracture to ductile fracture.

Numerical simulation for mold-filling of thin-walled aluminum alloy castings in traveling magnetic field

The numerical simulation for mold-filling of thin-walled aluminum alloy castings in horizontal traveling magnetic field is performed. A force model of Al alloy melt in the traveling magnetic field is founded by analyzing traveling magnetic field carefully. Numerical model of Al alloy mold-filling is founded based on N-S equation, which was suitable for traveling magnetic field. By using acryl glass mold with indium as alloy melt, the experiment testified the filling state of alloy in traveling magnetic field. The results of numerical simulation indicate that the mold-filling ability of gallium melt increases continually with the increase of the input ampere turns.

Microstructure and mechanical properties of BFe10 cupronickel alloy tubes fabricated by a horizontal continuous casting with heating-cooling combined mold technology

A new horizontal continuous casting method with heating-cooling combined mold （HCCM） technology was explored for fabri- cating high-quality thin-wall cupronickel alloy tubes used for heat exchange pipes. The microstructure and mechanical properties of BFe 10 cupronickel alloy tubes fabricated by HCCM and traditional continuous casting （cooling mold casting） were comparatively investigated. The results show that the tube fabricated by HCCM has smooth internal and external surfaces without any defects, and its internal and external surface roughnesses are 0.64 μm and 0.85 μm, respectively. The tube could be used for subsequent cold processing without other treatments such as surface planning, milling and acid-washing. This indicates that HCCM can effectively reduce the process flow and improve the pro- duction efficiency of a BFel0 cupronickel alloy tube. The tube has columnar grains along its axial direction with a major casting texture of {012}〈 621 〉. Compared with cooling mold casting （6 = 36.5%）, HCCM can improve elongation （3 = 46.3%） by 10% with a slight loss of strength, which indicates that HCCM remarkably improves the cold extension performance of a BFe 10 cupronickel alloy tube.

Effect of depressurizing speed on mold filling behavior and entrainment of oxide film in vacuum suction casting of A356 alloy

The effect of depressurizing speed on mold filling behavior and entrainment of oxide film of A356 alloy was studied. Themold filling behavior and velocity fields were recorded by water simulation with particle image velocimetry. The results show thatthe gate velocity first increased dramatically, then changed with the depressurizing speed: the gate velocity increased slowly atrelatively high depressurizing speed; at reasonable depressurizing speed, the gate velocity kept unchanged; while at lowerdepressurizing speed, the gate velocity decreased firstly and then kept unchanged. High gate velocity results in melt falling backunder gravity at higher speed. The falling velocity is the main factor of oxide film entrainment in vacuum suction casting. The designcriterion of depressurizing rate was deduced, and the A356 alloy castings were poured to test the formula. The four-point bend testand Weibull probability plots were applied to assessing the fracture mechanisms of the as-cast A356 alloy. The results illuminate amethod on designing suitable depressurizing speed for mold filling in vacuum suction casting.

Casting: Pearls and pitfalls learned while caring for children's fractures

Casting is a routine procedure used for fracture care in the pediatric population. The purpose of this review is to provide pearls and pitfalls that our institution has learned from previous literature. When applying the cast, we recommend using cotton padding for the liner and fiberglass or plaster depending on how much swelling is expected. A well-molded cast must be applied in order to prevent further fracture displacement.Cast valving is a valuable technique that allows a decrease in pressure which prevents discomfort and complications like compartment syndrome. Preventing thermal injuries, skin complications, and a wet cast are other important considerations when caring for casts.Appropriate use of a cast saw, avoiding pressure spots,and properly covering the cast are ways to respectively prevent those complications. Lastly, patient education remains one of the most valuable tools in ensuring proper cast maintenance.

2-D boundary-fitted coordinate grid generation for casting with complex shape

In order to overcome the zigzag grids generated by conventional finite difference method on complicated casting boundaries in the simulation of casting process, the generation program for 2-D boundary-fitted coordinate grid has been developed by solving a set of partial differential equations (PDE) numerically. The STL format files were treated as input data for 2-D physical regions. The equipartition method for boundary points was used to improve the self-adaptability of grid according to the characteristic of the STL format files. The program was demonstrated through some examples. The comparison between the conventional finite difference method and the proposed method shows that this program is effective and flexible for generation of boundary-fitted grid in any arbitrary 2-D complex domain, and the grid is in accordance with the variety of boundary curvature finely. The program also provides two types of boundary-fitted grids for double-connected region, O-type and C-type. The limitation of the step-like boundary with the rectangle grid could be avoided effectively. Therefore, the computational accuracy and efficiency would be improved and the computational time would be saved significantly by the application of boundary-fitted grids.

铸瓷嵌体修复治疗磨牙缺损的临床疗效及牙龈状况的影响

目的 分析铸瓷嵌体修复在磨牙缺损患者中的治疗效果。方法 选取2021年4月—2023年3月绥阳县人民医院收治的86例磨牙缺损患者为研究对象,按照随机数字表法分为两组,各43例。对照组行常规树脂填充,观察组行铸瓷嵌体修复,治疗后随访6个月。对比两组修复成功率、修复效果、牙龈状况、咀嚼效率、生活质量和并发症发生情况。结果 观察组修复成功率为97.67%,高于对照组的81.40%,差异有统计学意义(χ^(2)=4.468,P=0.038)。观察组边缘密合、修复体完整性、牙龈健康、咬合舒适度占比高于对照组,并发症发生率低于对照组,差异有统计学意义(P均<0.05)。治疗后观察组的菌斑指数、牙龈指数低于对照组,咀嚼效率、生活质量综合评定问卷内各维度评分均高于对照组,差异有统计学意义(P均<0.05)。结论 铸瓷嵌体修复能够有效修复缺牙,具有较高的修复成功率,能够改善牙龈状况,提升咀嚼效率,提高患者生活质量,且并发症少。

复杂形状中空陶瓷部件的凝胶注模成型

通过仔细设计模具,并在研究了催化剂等对凝胶注模成型过程的影响以及脱模和干燥对成型坯体质量的影响的基础上,制备出了强度在24MPa以上、外观质量很好的复杂形状中空陶瓷部件。扫描电镜分析可知坯体的显微结构均匀,坯体比较致密,高聚物通过三维网络把陶瓷颗粒紧密地联结在了一起。

大型复杂薄壁铝合金铸件的真空增压铸造技术

论述了真空增压铸造技术原理。真空增压铸造具有提高合金的充型能力、改善铸件的致密度和针孔度级别的工艺特性和优点,适合于质量要求高、复杂程度要求高的铝合金铸件,尤其适合大型复杂薄壁铝合金铸件。介绍了铝合金铸造成型技术在美国导弹舱体制造中的应用,分析了某耐压铝合金导弹薄壁结构舱体的铸造成形,并提出了相应的技术对策。

基于SL模型的复杂壳体快速铸造的研究

为解决复杂壳体快速铸造中SL模型代替金属、木模具的问题,分析数据处理过程对造型工艺的影响;针对不同精度需求,可采取多项措施;对模型的制作进行优化;结合新型变速器壳体的开发,实现了新品开发的快速铸造。研究表明:该方法制模周期短,模型稳定,尺寸精度明显高于木模;浇铸系统是保证铸件质量的关键;非强化光敏树脂模型适用于20件内、形状复杂壳体类新品的快速铸造;SLS法提供蜡型的成本较高,SL模型使铸件的成本大大降低;造型过程SL模型增强成为模具寿命的关键。

基于无模铸型制造技术的复杂铸件快速制造

无模铸型制造技术是以树脂砂为成型材料,利用快速成型技术的离散/堆积成型原理,对三维CAD实体模型进行分层切片处理,得到不同高度截面层的信息,采用截面扫描、喷射固化工艺,直接获得树脂砂铸型或铸造模具的一种方法。在复杂铸件快速制造的实际应用中,无模铸型制造技术表现出造型材料易得、制造时间短、制造成本低、铸件质量好等优点,体现了快速敏捷制造的优势,也为快速成形技术在铸造中的应用开辟了一个新领域。

复杂薄壁铝合金铸件磁动力真空调压铸造工艺研究

磁动力真空调压铸造技术是在电磁充型低压铸造技术的基础上发展而来的一种铸造技术,其充型能力强,补缩能力高。通过研究磁动力真空调压铸造中影响金属液充型能力的因素,如真空度和浇注系统等,得出了磁动力真空调压铸造法的最佳充型工艺参数。该技术尤其适合复杂薄壁铸件的高品质铸造,具有广阔的发展前景。

复杂薄壁铸件浇注系统最小截面积的合理确定

目前多种金属复杂薄壁铸件在重力铸造条件下,计算其浇注系统最小截面积的几个常用公式存在许多问题。文章分析了这些公式存在的使用前提不明、适用范围窄、通用性差等缺点,介绍了一种用统计学方法回归推算出的、适用范围宽的金属铸件浇注系统最小截面积计算公式,并将其与近十多年来的生产实例进行了比照,证明其科学、可靠,且适用范围宽阔。

在并行工程环境下开发复杂铸件

针对近净形铸件开发中存在的问题，建立了适于对复杂结构铸件及其工装设计、铸件的可铸造性评价、铸件成形过程仿真和制作快速样件等的并行开发环境。并将其应用于铸件的实际开发中，应用结果表明，在所建立的并行环境中开发新产品，可以优化复杂铸件设计、改善质量。