Shell Mold Research Articles

Application of Vacuum Techniques in Shell Moulds Produced by Additive Manufacturing

This research shows the feasibility of the additive manufacturing technique (AM), Binder Jetting (BJ), for the production of shell moulds, which are filled by vacuum suction in the field of aluminium parts production. In addition, this study compares the gravity pouring technique and highlights the advantages of using vacuum techniques in AM moulds. A numerical simulation was carried out to study the behaviour of the liquid metal inside the moulds and the cooling rate of parts was analysed. The results show that in the gravity-pouring mould, the velocity in the gate causes moderate turbulence with small waves. However, vacuum suction keeps the velocity constant by eliminating waves and the filling process is homogeneous. Regarding dimensional accuracy, the staircase effect on the surface of the 3D moulds was the most critical aspect. The vacuum provides very homogeneous values of roughness across the entire surface of the part. Similarly, 3D scanning of castings revealed more accurate dimensions thanks to the help of vacuum forces. Finally, the microstructure of the cross section of the moulded parts shows that the porosity decreases with the vacuum filled. In both cases, the origin of the pores corresponds to gas entrapment and shrinkage during the filling process, the binder vaporization and nucleation points creation, leading to pores by shrinkage, gas entrapment or a mixture of both. This is the first study that uses vacuum filling techniques in moulds created by BJ, demonstrating the feasibility and advantages of AM using vacuum techniques, as an alternative to traditional casting.

Effects of Mold Materials on the Interfacial Reaction between Magnesium Alloy and Ceramic Shell Mold during Investment Casting

In order to suppress the interfacial reaction between the ceramic shell mold and the magnesium molten alloy during the investment casting process, a mold material with a high thermodynamic stability based on alkaline zirconium sol (CH4NO3Zr) binder and corundum (Al2O3) powder was prepared. The effects of the mold materials and casting thicknesses on the interfacial reaction were investigated by an optical microscope, X-ray diffraction, a scanning electron microscope, and an energy dispersive spectroscope analysis. The results suggested that the casting poured by the conventional ZrSiO4 mold has a serious reaction on the surface, and the reaction was more severe when the casting thickness was increased. The oxidation layer was approximately 300 μm in some severe areas of 45 mm thickness. The XRD and EDS results showed that the reaction interface mainly contains MgO and Mg2Si. While the casting poured by the Al2O3 mold provides a light and smooth surface, the reaction layer was only 1.5 μm on average. The reaction interface mainly contains MgO and Mg2F.

Ceramic shell moulds with zircon filler and colloidal silica binder for investment casting of shrouded low-pressure turbine blades

Zircon (ZrO2·SiO2) powder filler and colloidal silica binder were used to prepare the ceramic shell moulds for investment casting of shrouded low-pressure turbine blades (LPTB). Ceramic slurries were prepared by using two types of colloidal silica binders (polymer-free binder A and polymer-containing binder B). The samples prepared from binder B showed lesser self-load sag values than those developed from binder A. Ceramic shell moulds made from an optimized slurry composition (having binder A) yielded aeronautical grade casting of blades at 1500 °C with required dimensional accuracy and average surface roughness (Ra). The blades cast from shell moulds (having binder B) showed dimensional accuracy at 1500 °C as well as at 1525 °C. The Ra values of blades cast at 1500 °C and 1525 °C by using shell system with binder B were observed to be higher than those cast from shell system having binder A.

The influence of coating sand materials on shell mold properties of Investment casting process

Abstract The investment casting process is well known for the production of accurate complex casting products. The time of shell mold production is remarkable. It plays an important role on shell mold properties in the post treatments after shell production. It decides the quality of casting. In present work, Fused silica and Alumina-silicate based ceramic sand materials selected as a backup coat to understand its effect on properties. Shell drying time, Modulus of Rupture (MOR) and thermal expansion of mold is observed in the work. Drying time of shell varies from 84 to 86 h in the shell mold production. Modulus of rupture results 94 kg/cm2 strength in Alumina-silicate type materials compared to 49 kg/cm2 strength of Fused silica sand shell. In the firing of shell, thermal expansion observed up to 1200 °C temperature. Fused silica provides stable nature against thermal expansion from highest 0.054 to lowest −1.139 with increasing temperature upto 1200 °C.

Fabrication of Ceramic Moulds Using Recycled Shell Powder and Sand with Geopolymer Technology in Investment Casting

Lost-wax casting, also called precision casting, is the process of casting a duplicate metal sculpture cast an original sculpture. The ceramic shell mould used in lost-wax casting usually consists of several layers formed with fine zircon and granular mullite particles using silica gel as a binder. However, it is a complicated and time-consuming process. Large amounts of waste moulds that need to be disposed and recycled become an environmental concern. In this study, waste shell sand from the recycled mould and calcium carbonate/metakaolin were used as raw materials to prepare geopolymer slurry and coating. The influence of mixing ratio and the SiO2/K2O modulus of the alkali solution on the setting time and green/fired strength were evaluated. Ceramic shells with one to four layers of geopolymer slurry and waste sand sprinkling were fabricated and tested for their permeability and green/fired strength. It was found that geopolymer shells had higher green/fired strength and better permeability than the original zircon/mullite shell. For foundry practice, metal casts were fabricated using recycled ceramic shell moulds with one to four layers of geopolymer coating. All cast results have their dimensions all within tolerance limitation and up to 13 h can be saved for the preparation of shell moulds.

Study of Surface Quality During End Milling of SiC Reinforced Aluminium Metal Matrix Composite

In today’s world the composites materials are replacing many conventional materials due to their excellent properties. Aluminum is a less weight and cheap metal that is available in plenty. Silicon carbide is hard abrasive material with good mechanical properties. The aluminum silicon carbide metal matrix composite is finding increased applications in many fields such as automobile and aeronautical applications due to its excellent mechanical properties like high strength, light weight, high specific stiffness and good coefficient of thermal expansion. But their usage is restricted due to the difficulty in the machinability. In this paper two Al/SiC metal matrix composites (Al6061/10-SiCp and Al6061/5-SiCp) by varying the composition of SiC. The composites consist Silicon Carbide (SiC) of 5% and 10% by weight. The composites are prepared by stir casting process. Shell moulding technique is used in manufacturing of the composite materials. The microstructure, tensile strength, compression strength and hardness of the composites are studied. End milling operation is performed on the metal matrix composite slabs by varying the machining parameters. Feed rate and depth of cut were varied by fixing a single spindle speed. The number of experiments is determined using design of experiments (DOE). The effect of the machining parameters on the surface finish is observed by measuring the surface roughness. This process is done on the two metal matrix composites. The effect of SiC percentage in composite and variations in machining parameters on the surface finish was observed.

PROGRESSIVE TECHNOLOGIES OF FOUNDRY PRODUCTION OF COMPLEX DETAILS

The authors present the results of consideration of advanced technologies of foundry production of complex parts. In mechanical engineering, about 50% of the mass of machinery and machinery is cast, in machine tools - about 80%. This is explained by the number of advantages of foundry production in comparison with other methods of obtaining blanks or finished products. The molds are provided with blanks of both simple and very complex shape with internal cavities, which are impossible or very difficult to obtain in other ways. Some special casting methods allow castings to be obtained with a high surface cleanliness and precision in size, which reduces or completely eliminates subsequent machining. Special casting methods allow you to partially and sometimes completely abandon the use of molding and core mixtures, to carry out complex mechanization and automation of the whole process. In the foundry industry, the following technological processes are progressive: casting in shell molds and smelting models under vacuum conditions, which prevents oxidation of the metal; casting of single-crystal workpieces from heat-resistant alloys by vacuum suction method; casting by gas models; spray molding; modelless casting

Achieving environmental sustainability in the shell mould foundry through thermal reclamation

Shell moulding is a process for producing simple or complex near-net-shape castings and maintaining tight tolerances with a high degree of dimensional stability. The main objective of the present research is to achieve environmental sustainability by thermal reclamation of the used shell mould foundry sand and present the results of achieving environmental sustainability. The investigations indicate that the thermal reclamation of the used foundry sand helps in achieving sustainability, and the selection of optimal process parameters like percentage of resin, catalyst, and fresh silica sand addition are very important in the shell mould foundry.

Evaluating Silicon Carbide-Based Slurries and Molds for the Manufacture of Aircraft Turbine Components by the Investment Casting

Silicon carbide (SiC) is a promising material for the fabrication of ceramic shell molds due to its high mechanical strength, hardness, thermal shock resistance, and thermal conductivity compared with commonly used slurries. This article describes the test results of casting materials, i.e., SiC-based powders and aqueous binders with aluminum oxide nanoparticles, as well as the parameters of slurries used for prime coats and structural layers. Tests were also performed to evaluate the physical and mechanical properties of SiC-based shell molds for the manufacture of aircraft turbine components. Two SiC-based slurries with solid concentrations of 65 and 70 wt.% were prepared, and their viscosity, density, pH, quantity, thickness, and copper plate adhesion (plate weight test) were investigated. Fourteen days were required to prepare and evaluate the slurry parameters. The results showed that SiC-based slurries had a Zahn cup #4 outflow time of 33.1 s to fabricate the first two coats and 14.8 s to fabricate the shell mold structural layers. Three series of SiC-based shell mold samples were prepared: after dewaxing (PW1), after burnout preheating at 700 °C (PW2), and after annealing at 1200 °C (PW3). The bending mechanical strength, Young’s modulus, and Weibull’s modulus of the samples were calculated, and the roughness (Ra and Rq) and microstructures of samples were also analyzed (SEM). Inner defects were evaluated by CMT (µCT). The Ra and Rq values of the prime coat of the SiC-based shell mold did not exceed 5 µm. The fabricated SiC shell molds had bending mechanical strengths from 1.21–2.28 MPa, Young’s modulus of 102.97–207.66 MPa, and a Weibull’s modulus from 5.36–9.94. The shell molds fabricated on the technical scale met the requirements specified for industrial shell molds.

Modelling viscoplastic behavior of solidifying shell under applied electromagnetic breaking during continuous casting

Since several decades the continuous casting (CC) process became one of the dominant technologies for the metal production. The quality optimization and the production rate growth are the primary targets. Nowadays the numerical modelling is a valuable tool to assist in these aims. Moreover, it efficiently competes with the physical experiment and the industrial trials. One of the key issues with the high casting speeds especially for the thin slab products are the strong turbulent flow of the fresh melt being feed from the submerged entry nozzle (SEN) and the non-uniformity of the solidifying shell thickness. Thereby the electromagnetic braking (EMBr) is typically applied to damp the hot jets and to evenly redistribute the superheat. In the previous work it was shown by the authors that the presence of the highly conductive solid shell plays crucial role for the melt flow under the applied magnetic field. Excluding this interaction does not allow predicting the EMBr effects on the melt flow correctly during the solidification. Recently a viscoplastic deformation model was implemented to model a withdrawal of the solidified shell in a funnel type CC mold for a full 3D engineering geometry. An extended model was used to predict the macro-segregation during twin-roll casting of an Al-alloy using 2D assumption due to the large width / thickness ratio of the casted sheet. In the current study an effort is done to combine the viscoplastic deformation model of the solidified shell and the magnetohydrodynamics effects of the EMBr. The flow field alternation as well as the thickness of the solidified shell during CC are presented and analyzed with and without the magnetic field been applied.

Growth of solidified shell in bloom continuous casting mold of hypo-peritectic steel based on a FeS tracer method

Solidification behavior in the mold region plays an important role in production efficiency and steel quality. To investigate shell growth within a mold, the sulfur prints of the entire shell thickness profile from the meniscus to 100 mm below the mold were obtained by adding FeS tracer into molten steel during bloom continuous casting of hypo-peritectic steel. The law of shell thickness evolution along mold height and circumference was analyzed. The results show that there are three weak regions of solidification, which are in the mold upper part, in the mold lower part, and just below mold exit, possibly resulting from periodic fluctuation of air gap between the shell and the mold, the impingement of melt jets on the solidification front, and the decreasing cooling intensity, respectively. Initial solidification point along casting direction appears at approximately 35 mm below the meniscus. Overall, the solidified shell thickness in the inner side of the mold is a little larger than that in the outer side, and the former and the latter reach 25.5 and 24.3 mm at the mold exit, respectively. The non-uniform shell growth in the inner side of the bloom is provided, while shell thicknesses in the narrow face and the outer side follow relatively regular growth. Out of the mold, the thinnest shells on the transverse section exist in the regions of 60–90 mm and 40–70 mm from the corners of the inner and outer sides, respectively, i.e., the off-corners.

Influence of Slurry Composition on Mould Properties and Shrinkage of Investment Casting

Ceramic shell mould plays a key role in achieving dimensional accuracy and quality of casting. This work investigates the effect of mould parameters such as silica concentration, filler to binder ratio and the number of secondary coats on mould properties, namely modulus of rupture, adjusted fracture load, and permeability. Experimental results report that enrichment in silica results in drastic growth in adjusted fracture load with a small increase in modulus of rupture and no change in permeability. Improvement in filler to binder ratio causes a significant increase in the adjusted fracture load and modulus of rupture with moderate decrease in permeability. An increase in number of ceramic coats increases the adjusted fracture load significantly and reduces permeability moderately. Impact of the adjusted fracture load on casting shrinkage has been studied by conducting various casting trials. Adjusted fracture load above 315 N is preferred which corresponds to 25–30% silica, filler to binder ratio of 1.25 and number of secondary coats as six to eight for reduced shrinkage variation.

Development of Non-reactive Mold for Investment Casting of Ti-48Al-2Cr-2Nb Alloys

The interfacial reactions between liquid Ti-48Al-2Cr-2Nb and various shell mold materials were investigated, and a cost-effective shell mold, containing a reacted component, was developed. Centrifugal investment casting was employed to supplement the low fluidity of the titanium aluminide alloy. The thickest part of the turbocharger was selected for analysis. The reaction-layer depth and the reacted product were evaluated using a micro-Vickers hardness tester and an electron microscope. The chemical composition and morphology of the molds were analyzed via X-ray diffraction and energy dispersive X-ray spectrometry. The TiAl alloys reacted with both colloidal silica and refractory materials in the alumina and zircon mold. However, only the colloidal silica reacted with TiAl in the yttria mold because of the high thermodynamic stability of the yttria refractory. The zircon mold showed the highest reactivity with TiAl because the zircon decomposed into ZrO2 and SiO2 at 1556 °C. The reactivity between TiAl and the mold decreased in the order of zircon > alumina > yttria ≥ rutile-containing alumina mold. The Ti5(Al, Si)3 or (Ti, Zr)5(Si, Al)3 phase was observed in the castings obtained using the conventional oxide mold. However, the reaction phase and layer were not observed in rutile-containing alumina mold. The molten TiAl penetrated the shell mold, especially in the colloidal silica site, although the penetration depth did not match the reaction-layer depth. The reaction and penetration of TiAl were controlled efficiently with the rutile-containing alumina mold.

Early Maastrichtian cheilostome bryozoans from the middle Volga River region

Eight species in six genera of cheilostome bryozoans are described from an early Maastrichtian outcrop located in the Saratov Region, middle Volga River region, southern Russia. The studied bryozoan assemblage includes a new species, Cheethamia volgaensis sp. nov., as well as Dionella sp., Cheethamia aktolagayensis Koromyslova et al., Rhagasostoma cf. saltans (Brydone), and Luganella goldfussi (von Hagenow). A few poorly preserved specimens are tentatively assigned to the genera Hoplitaechmella and Acoscinopleura. Some of the recorded species encrusted a Cataceramus shell and internal moulds of Baculites ammonoid shell fragments; whereas others produced erect, flattened, bifoliate colonies. A single species, L. goldfussi, had free-living, discoidal colonies. The palaeobiogeography of early Maastrichtian bryozoans is discussed. The recorded bryozoans belong to genera ubiquitous in the early Maastrichtian of Europe and, to a lesser degree, other regions.

Productivity and Quality improvement through DMAIC in SME

During the past three decades, researchers have been advocating the application of define-measure-analyse-improve-control (DMAIC) phases of Six Sigma concept to achieve productivity and quality improvement in small and medium enterprises (SMEs). In this context, the research reported in this paper was carried out in a SME by applying DMAIC phases in the production of the castings of a component called balance weight. While executing the DMAIC phases, it was found that green sand moulding process had to be replaced with shell moulding process to avoid the increase in hardness and rejection of castings due to pin hole defect. On implementing this solution, the productivity increased by 50.42 units per hour and the quality level increased from 3.2 sigma to 4.4 sigma. Altogether, it was found that DMAIC can be used in SMEs to achieve productivity and quality improvement so as to acquire competitive strength.

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.

About possibility of using of staurolite sand for manufacture of ceramic shell moulds for light alloys

The possibility for using of ceramic shell moulds for investment casting for light alloys when staurolite sand dusting is studied. It is found that such moulds have lower coeffi cient of linear expansion and provide higher accuracy of the resulting castings at lower price of dusting material.

Elimination of misrun and gas hole defects of investment casting TiAl alloy turbocharger based on numerical simulation and experimental study

Casting technology of thin-wall TiAl alloy turbochargers was studied by investment casting and numerical simulation. Misruns and gas holes were the main defects observed in preliminary work due to the poor fluidity of alloy, and to gas entrapment. In order to eliminate these defects, cast parameters, such as centrifugal rotation rate and mould preheating temperature, were optimized by numerical simulation, meanwhile, the structure of the shell mould was optimized to improve the filling capacity of TiAl alloy. Pouring experiments were carried out by vacuum induction melting furnace equipped with a water-cooled copper crucible based on the above optimization. The quality of the TiAl alloy casting was analyzed by fluorescent penetrant inspection and X-ray detection. The results show that a centrifugal rotation rate of 200 rpm, mould preheating temperature of 600 °C, shell preparation through organic fiber addition can dramatically improve the mould filling capacity, and integrated turbochargers were finally prepared.

Manufacturing of Herringbone Gear Model by 3D Printing Assisted Investment Casting

3D printing technology and investment casting are used to manufacturing of a herringbone gear. Four kinds of gating system are designed and the numerical simulation of the four gating systems are executed. It is determined that the optimal casting mode of herringbone gears is the top casting system. Subsequently, the investment mold is made with PLA material by 3D printing technology and the mold shell is made of gypsum. Finally, experiment is performed to verify the validation of the top gating system. The results show that the combination of 3D printing technology and investment casting can effectively improve casting accuracy and production efficiency.

Kinetics of annealing-induced detwinning in chemical vapor deposited nickel

Nickel carbonyl vapor deposition (CVD) is a high-efficiency process used to produce nickel shell molds with high yield strength, reasonable ductility, and strong corrosion resistance. Such advantageous properties arise from the nanocrystals and nanotwins inside CVD nickel. However, the nanotwins do not persist at high temperatures, transforming into dislocation cells after 40-min annealing at 800°C. Using experimental examinations and computational simulations, we investigated the kinetics of the annealing-induced detwinning in CVD nickel. TEM examinations showed that detwinning is realized by incoherent twin boundary (ITB) migration; meanwhile, plentiful dislocations are generated from coherent twin boundaries (CTBs). Our theoretical analysis revealed that these dislocations are necessary for the formation of the ITBs. Next, using molecular dynamics simulations, we found that the dislocations nucleated from CTBs during annealing are intrinsic grain boundary dislocations (IGBDs). Driven by the internal stress intensified by grain growth in the nanocrystalline regime, the IGBDs can separate from CTBs due to creep at 800°C, resulting in a higher dislocation density inside the twin lamella than that of the outside. These dislocations can trigger the formation of ITBs. Overall, unlike grain growth, stress is necessary for detwinning, so a monolithic nanotwin structure should be more stable than the nanotwins inside a nanocrystalline matrix.