Vacuum Casting Process Research Articles

Coarsening of needle-shaped precipitates in CoNiCrAl alloys during isothermal heat treatment: Kinetics in length and thickness

This paper investigated the coarsening kinetics of needle-shaped γ precipitates in CoNiCrAl alloys after isothermal heat treatments at 900 °C and 1100 °C. The CoNiCrAl alloys were prepared by vacuum induction melting and casting process. They were characterised to exhibit a two-phase γ + β structure and some needle-shaped secondary γ precipitates were formed within the primary β phase during isothermal heat treatments. The coarsening of the needle-shaped secondary γ precipitates occurred with heat treatment time and became more rapid at elevated temperatures. In particular, the coarsening kinetics of needle-shaped γ precipitates in length and thickness were specifically studied. It was found that the coarsening kinetics in length and thickness was a volume diffusion governed process and generally followed the classic Lifshitz-Slyozov-Wagner (LSW) theory. An analytical model was proposed to estimate the lengthening and thickening of the precipitates, which considered the aspect ratio and volume fraction of the precipitates. The calculated coarsening rate in thickness agreed well with the experimentally determined value. But some discrepancies were found between the predicted and measured coarsening rate in length. This might be due to the termination migration effects of the needle-shaped precipitates which restricted the coarsening rate in length.

Microstructure evolution of as-cast CoNiCrAl bond coat alloys after isothermal heat treatments

In this paper, the microstructure evolution of two as-cast CoNiCrAl bond coat alloys after various isothermal heat treatments were investigated. The CoNiCrAl bond coat alloys were prepared by vacuum induction melting and casting process. The as-cast alloys were subjected to heat treatments from 550 °C to 1300 °C for periods up to 100 h to study the effects of temperature on the microstructure and phase distribution. The microstructure of heat treated CoNiCrAl bond coat alloys was characterised by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The CoNiCrAl alloys exhibited a two phase γ + β structure, with the β phase acting as the primary phase. It was shown that the precipitation of needle-like secondary γ phase was slow at temperatures below 600 °C but became rapid above 900 °C. It was found that the morphology of the secondary γ phase changed from needle-like to rod-like at 1100 °C. A homogeneous γ + β two phase structure was obtained at 1300 °C even after 2 h heat treatment. It was revealed that the heat treatment temperature had a significant influence on the formation and distribution of the secondary γ phase. In addition, the precipitation of sub-micron Cr-rich particles occurred at 1300 °C in both CoNiCrAl alloys, which was due to the low solubility of Cr in the β phase and rapid coalescence of γ phase at elevated temperatures.

Evaluation of the Heat Transfer Performance of Stearic Acid PCM/ Porous Aluminium Thermal Composite Structures for Heat Storage Applications

Phase change material (PCM) thermal composites consisting of porous aluminium/stearic acid phase change material have been produced for heat storage applications. Porous aluminium/stearic acid composite structures were produced by infiltrating stearic acid PCM into open- cell porous aluminium materials prepared by using dissolvable spherical salt beads in combination with vacuum casting process. Scanning electron microscopic analysis has been used to characterize the empty porous aluminium materials and the results reveal a cellular structure consisting of spherical pores which are interconnected with smaller windows. The thermal response of empty porous aluminium structures and those infiltrated with stearic acid was measured using an infrared camera. The result showed that the heat transfer performance of the PCM thermal composites was significantly improved and largely dependent on the relative density of the porous structures.

Study on Aqueous Humour Hydrodynamics of Glaucoma Condition Using 3D Printed Model and Particle Image Velocimetry (PIV)

This study aims to explore the knowledge on fluid flow properties of the aqueous humour (AH), specifically on the anterior segment (AS) of the human eye for a medical condition called Glaucoma. The research objectives are to study on fluid flow characteristics of velocity and pressure of the AH on the AS of the eye using enlarged 3D printed model and computational analysis, and also to analyse the suitability of the 3D generated anterior AS in fluid flow analysis application on particle image velocimetry (PIV). Using polyvinyl alcohol (PVA) as a water-soluble 3D printing filament, a 3D model of the AS of the human eye was generated with SolidWorks 2018 and printed using Creality Ender 3. This printed model serves as the pattern for silicon rubber mould production using vacuum casting process. Analysis of AH flow hydrodynamics are conducted with computational analysis using ANSYS Workbench 19.2. Key findings support that use of PVA material suite the creation of specific shapes and patterns for 3D modelling applications alike, and silicon rubber moulding creates a non-reactive and long-lasting mould for PIV applications. Computational analysis findings support the use of the generated model for PIV applications. Overall, the study successfully supports the use of 3D printed model for PIV application and future work that can be induced include direct experimentation of the mould with PIV.

The Deterioration Mechanism of Silicone Molds in Polyurethane Vacuum Casting

The industrial production of prototypes made of polyurethane via silicone molds in the vacuum casting process is one of the most widespread applications of rapid tooling. The silicone molds show pr...

Comparison of different additive manufacturing patterns on the performance of rapid vacuum casting for mating parts via the Taguchi method

Rapid vacuum casting has been proven to be a successful method in producing high-quality parts in small series. However, a challenge lies in the selection of proper Additive Manufacturing (AM) technologies for the development of a master pattern for the vacuum casting process. Each AM technologies differ from one another in terms of dimensional accuracy, surface finish, cost and lead times. The aim of this study is to investigate the performance of casting mating parts based on different additive manufacturing patterns for small batch. Three types of AM-based patterns: Fused Deposition Modeling (FDM), Stereolithography (SLA) and Multi-Jet Fusion (MJF) were compared. The Taguchi method, Signal to Noise ratio (S/N), Analysis of Variance (ANOVA) and T-test were conducted in determining the optimized parameters. From the findings, curing time is shown to be a significant parameter for dimensional accuracy and surface finish. Dimensional deviation varies in different directions of parts. For surface finish, there was only a slight change from the master pattern whereas the surface roughness of casting parts decreased within the range 0.23% to 2.85%. Tolerance grades for the selected dimensions of the parts were in the permissible range, based on ISO286-1:2010. When using distinct kinds of AM patterns to create replacement components, design tolerance is needed. It was suggested to select AM technology similar to that had been used for the original components. Battery cover was selected as a case study to represent the mating application parts.

Optimization of vacuum casting process parameters to enhance tensile strength of components using design of experiments approach

Vacuum casting is one of the widely used methods for small-volume production of plastic parts. The main challenge of this method is to choose the optimal working parameters to manufacture plastic parts with better mechanical properties. The conventional vacuum casting (CVC) technology uses gravity to make the casing material to fill the mold cavity, resulting in the yield of the molded components with high tensile strength is relatively low. Vacuum differential pressure casting (VDPC) can overcome this disadvantage since the filling mechanism of the casting material is different from CVC process. In this study, integration of design of experiments approach and the VDPC technique was employed to enhance tensile strength of molded components. It was found that the most important control factor affecting the tensile strength of the fabricated component is the mold cavity temperature, followed by the material mixing time, the differential pressure time, and the mixing chamber inlet valve angle. The optimal process parameters for producing components with better tensile strength are the mold cavity temperature of 35 °C, the material mixing time of 40 s, the differential pressure time of 8 s, and the mixing chamber inlet valve angle of 60 °.

Filling mechanism for prototype parts produced by vacuum differential pressure casting technology

Vacuum casting (VC) is the most economical production process for producing small numbers of prototype parts under vacuum conditions. The filling of the casting material in the conventional VC process only depends on the gravity. Thus, some defects of the cast part are observed. In this study, differential pressure (DP) VC was proposed to reduce the filling time and improve the quality of cast parts. In this study, the filling mechanisms in both horizontal and vertical directions were investigated theoretically and experimentally. The actual filling situations of the acrylonitrile butadiene styrene resin in both the horizontal and vertical directions are similar to the simulation results. The relationship of the filling time for DP time, sprue diameters, and mold cavity capacities was investigated. The filling time can be estimated in terms of DP time, sprue diameter, and mold cavity capacity.

Shrinkage Effect of Vacuum Casting Process Parameters using Taguchi Method

This paper investigates the optimization of vacuum casting process by using Taguchi method. Vacuum casting process is a one of the method in Rapid Tooling Technology. The parts produced by vacuum casting process has it accuracy varies with the changes of the process parameters of the machine such as resin temperature, vacuum pressure time, mould temperature and some others. In order to optimize 3 parameters which are resin temperature, mould temperature and vacuum pressure time, the L’9 orthogonal array was used. From the results, it shows that the optimum parameters that may improve the shrinkage effect are resin temperature (30 °C), mould temperature (60 °C) and vacuum pressure time (5 min.). The shrinkage values between default and optimum parameter are 0.159mm and 0.336mm respectively. Thus, the improvement on shrinkage effect was 52.4 percent. The study demonstrates that the better dimensional accuracy of vacuum casting process can be optimized using Taguchi Method.

Effect of differential pressure on the transcription rate of micro-featured components

Vacuum casting is a widely employed method for small batch production of plastic prototype parts by the use of silicone rubber mold. However, some undesired defects of the cast part such as micro-bubbles, voids, weld lines, shrink mark, sink marks, warpage, blister, or short shot are observed in the conventional vacuum casting process. Vacuum differential pressure casting (VDPC) can overcome these drawbacks because of the filling mechanism of the casting material is different from conventional vacuum casting process. In this study, the VDPC was proposed to enhance the quality of casting parts. The process parameters related to the VDPC are investigated theoretically. Fabrication of components with microstructures using VDPC was investigated experimentally. It was found that the quality of VC parts with microstructures can be improved significantly using the VDPC. The transcription rate of the depth of the Fresnel lens can be increased from 41.9 to 99%.

CREATION OF COMPOSITE BRONZES REINFORCED BY STEEL DENDRITES

The paper studies the group of composite bronzes, BrFNCA 9-4-1-1, BrFNA 12-7-1 and others where brittle Cu3Sn intermetallics are «replaced» by steel dendrites. The mass transfer of Fe, Ni, Co, Al between the matrix and dendrites in these bronzes is investigated. Dendrite dispersion depending on the methods used to produce these bronzes can be increased by a factor of 10, for example, in the vacuum casting process. The mechanical properties of BrFNCA samples (σв = 372 МPа, δ = 25 %, ψ = 42 %) are higher as compared with the BrO10 prototype: by 50 % in terms of σв hardness, and by 4–5 times in terms of δ and ψ plasticity. The coefficient of friction is lower than that of BrO10 by 20–30 %, and wear resistance is higher by an order of magnitude. The fact of a significant effect of the dendritic component dispersion on the BrFNA bronze wear rate is found. Thus, the wear rate for 1 μm and 10 μm dendrite cross sections is 0,002 and 0,025, respectively, and the coefficient of friction remains unchanged, i.e. it does not depend on dendrite dispersion. The whole set of mechanical, processing and service properties makes it possible to consider that the semicommercial tests of this new class of BrFNCA composite bronzes reinforced with H12C7A maraging dendrites for sliding friction units are justified and promising.

Experimental investigations for dimensional accuracy and surface finish of polyurethane prototypes fabricated by indirect rapid tooling: a case study

In this research work, an effort has been made to study the influence of selected input parameters on the dimensional accuracy (linear as well as radial) and surface finish of polyurethane prototypes fabricated by vacuum casting (VC) process as a case study. The master pattern required for making a silicone mould has been fabricated by fused deposition modelling and its surface finish has been enhanced by chemical vapour smoothing process. Maximum shrinkage of 2.29 and 4.77% has been observed in the selected linear and radial dimension, respectively, after the VC process. Optimal parameter settings that were different for both the dimensions as well as surface finish have been obtained using Taguchi’s L18 orthogonal array. Finally, parameter setting that simultaneously minimizes the dimensional deviation and surface roughness has been found out using response optimization module of Minitab 17 software and the results obtained have been verified by performing the confirmation experiments. The tolerance grades for the selected dimension of the prototypes were found to be acceptable as per the ISO standard UNI EN 20286-I (1995) and DIN16901 for plastic materials. In addition, the C pk value greater than 1.3 indicated that the proposed process is highly capable. The surface finish and dimensional accuracy of prototypes are at par with the traditional moulding patterns, and hence, they can be used as end-products or plastic-based master patterns for investment casting applications.

Development of Resin Vacuum Potting Equipment

In order to resolve the problem of bubble defect after encapsulation, from the vacuum casting process requirements, the equipments were developed for the needs of production and scientific research. The development of the equipment adopts two schemes: final-mixed type and on-line mixing type. The equipment adopts compact design, automatic control, and easy to operate. The system functions of the prototype were tested and their technical indexes meet the design requirements. And the encapsulation parts encapsulated by the prototypes are tested to solve the bubble defect of the high-pressure module. Potting products have been detected, and it shows the two equipments effectively improved the bubble defects.

Kompozyty poliuretanowe o roznych osnowach napelniane mikrosferami szklanymi

The paper concerns composites made of polyurethane materials intended for the production of molds used in the vacuum casting process (VC). Two types of polyurethanes were applied to prepare the composites filled with glass microspheres. The influence of the filler on the properties of the resulting polyurethane composites was investigated. The viscosity of the premixes for the preparation of these composites was determined. The crosslinked composites were characterized using thermomechanical analysis (DMA), while their structure was investigated by infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The results of strength tests are also presented.

Dimensional accuracy and surface finish of biomedical implant fabricated as rapid investment casting for small to medium quantity production

In this work the feasibility of combined route of fused deposition modelling (FDM), chemical vapor smoothing (CVS), vacuum casting (VC) and investment Casting (IC) for the development of customized implant for small to medium quantity production has been investigated. Further, an effort has been made to optimize the dimensional accuracy and surface finish of the implant (hip joint) prepared by varying two controllable factors (namely: drying time of primary coating and mould thickness) each at three levels of the IC process. The master pattern of the hip joint has been prepared by FDM followed by the CVS process to enhance the surface finish and multiple replicas were produced by the VC process for batch production. The tolerance grades for the selected dimension of the implant/castings were found to be acceptable as per the ISO standard UNI EN 20286-I (1995). Also, the Cpk value greater than 1.3 indicated that the proposed process is statistically controlled.

Development of an oxide-dispersion-strengthened steel by introducing oxygen carrier compound into the melt aided by a general thermodynamic model.

In general, melting process is not a common method for the production of oxide dispersion strengthened (ODS) alloys due to agglomeration and coarsening of oxide particles. However, vacuum casting process has recently been employed as a promising process to produce micro-scale oxide dispersed alloys. In this paper, we report the process and characterization of in situ formation and uniform dispersion of nano-scale Y-Ti oxide particles in Fe-10Ni-7Mn (wt.%) alloy. The processing route involves a solid-liquid reaction between the added TiO2 as an oxygen carrier and dissolved yttrium in liquid metal leading to an optimal microstructure with nano-sized dispersed oxide particles. The developed thermodynamic model shows the independence of the final phase constituents from experimental conditions such as melting temperature or vacuum system pressure which offers a general pathway for the manufacture of oxide dispersion strengthened materials.

Evaluation of service life of silicone rubber molds using vacuum casting

Shortening the time-to-market is an important issue in the manufacturing industry. Indirect tooling technology was regarded as a promising approach of reducing time and cost to the market in a new product development phase. Silicone rubber mold was frequently employed in the indirect tooling. In this study, the service life of silicone rubber molds was investigated using both wax injection molding and vacuum casting. The experimental results revealed that the average roughness of the inner surface of silicone rubber mold were increased with increasing the number of test runs and saturated after 25 test runs. The degassing time needs to be increased with increasing the number of test runs in the vacuum casting process. The criteria for judging the service life of silicone rubber molds include surface quality of the parts fabricated, whitening regions in the inner wall surfaces of silicone rubber molds, and the overall elasticity of silicone rubber molds.

Fabrication of Self-Assembly Metal /Semiconductor Heterostructured Nanowires By Using Anodic Aluminum Oxide (AAO)-Assisted Molding Injection Process

Self-assembly metal/semiconductor heterostructured Cu-Ge alloy nanowires were successfully synthesized by using the anodic aluminum oxide (AAO) template-assisted vacuum casting process for the first time, analyzed their interface microstructures and fabricated single nanowire into device. AAO, a membrane with a controllable microstructure of nano-channel array, was utilized to synthesize nanowires of the identical stoichiometry to bulk materials, combining with solid-liquid-solid transformation process. Through choosing a suitable hypoeutectic or hypereutectic composition ratio the size effect will force the phases of nanowires to solidify alternatively along axial direction. Thus, self-assembly nanowires with an alternative metal/semiconductor heterostructure can be obtained. Furthermore, a single nanowire device was synthesized to investigate the relative electrical properties for semiconductor applications. This results are useful in developing metal/semiconductor heterostructured nanowires for advanced FET devices. Figure 1

Combining additive manufacturing and vacuum casting for an efficient manufacturing of safety glasses

This paper presents the possibility of integration of modern techniques of additive manufacturing and vacuum casting in the rapid manufacturing of complex parts. The prototype of safety glasses was directly developed from a CAD model, which is used as a main model for making moulds in a vacuum casting process. The development stages, which include additive production of glasses and the process of vacuum casting with the definition of material components, preheating temperature, the forming of silicone mould, the casting process, hardening and other parameters are presented in this paper. It is proved that by using this technique it is possible to produce complex functional parts quickly, with high precision, accuracy and surface quality, while significantly reducing costs of development and production compared to other similar technologies.

Study of the filling mechanism and parameter optimization method for vacuum casting

Warpage is the most common quality defect in parts produced by vacuum casting (VC). In this paper, the VC process and mold filling mechanism are analyzed, and a mathematical model of the filling process is constructed, incorporating fluid dynamical relationships. The filling process is simulated using a numerical simulation algorithm. A warpage optimization strategy combining response surface methodology (RSM) with the artificial fish-swarm algorithm (AFSA) is then proposed, in which the main function of the RSM is to fit the relationship between process parameters and warpage, while that of the ASFA is to obtain the optimized process parameters. Finally, the implementation of the optimization strategy is presented in detail, together with a specific example, and simulations and a real experiment are carried out. The experimental results verify the accuracy of the model and the reliability of the algorithm. In conclusion, the optimization method can reduce the warpage of VC parts and improve product quality, providing a reliable new low-cost method for optimizing the process parameters in VC technology.