Vacuum Casting Research Articles

A Three-Dimensional-Printed Home-Based Flexible Nasopharyngeal Explorer With Diamond Cuts1

A Three-Dimensional-Printed Home-Based Flexible Nasopharyngeal Explorer With Diamond Cuts1

Wear Behaviour of Cryogenic Treated Recycled Carbon Fibers Filled Epoxy Composite

Mechanically ground recycled carbon fibers (rCFs) reinforced polymer composites were investigated in this paper. The rCFs were collected from the woven prepreg waste. The as-received (rCFs-AR) and cyclic cryogenic treated (rCFs-T) carbon fibers were incorporated separately in the epoxy matrix composite. The objective of this study is to study the wear behaviour of the epoxy composites with respect to the as-received and treated rCFs. Prior to the composite fabrication, the surface morphologies of rCFs-AR and rCFs-T were examined with the scanning electron microscope (SEM). It is found that the cryogenic treatment is effective in removing the epoxy resin from the carbon fiber due to the mismatches in the thermal expansion at the interface of rCFs and epoxy. The rCFs-AR and rCFs-T were homogeneously distributed in epoxy resin through ultrasonication. The void-free samples were then fabricated using vacuum casting technique. Micro Pin-on-disc Tribotester (CM-9109) was used to test the tribological behaviour of the polymer composites. The coefficient of friction (CoF) and wear rate of epoxy composites revealed that the reinforcement effect of rCFs-T is better than that of the rCFs-AR as the incorporation of rCFs-T decreases the CoF and improves the wear resistance of epoxy composites in comparison with rCFs-AR. The tribological results clearly showed that the rCFs was a valuable product worth to be reused as reinforcement in the new composite, as the incorporation of treated rCFs was effective in improving the tribological properties of the epoxy composites.

Fabrication of Ni-Based Superalloys Containing Nb and Their High Temperature Oxidation Behaviors

Ni-based superalloys with different contents of Nb addition were fabricated by vacuum melting and casting. High temperature oxidation behaviors of the designed alloys were investigated by thermogravimetry. Microstructure and phase constituent of the oxidation scales were studied using scanning electron microscope and X-ray diffraction (XRD), respectively. Results showed that irrespective of the composition, all specimens obeyed the parabolic law during different stages. The scales on specimens B and C with 2.0 wt.% and 2.5 wt.% Nb addition, respectively, were mainly comprised of Cr2O3 and NiCr2O4. However, specimen A, with no Nb addition showed only NiO in the outer scale. The oxidation scales all exhibited a layered structure. With 2.0 wt.%Nb addition, the superalloy's high temperature oxidation resistance was enhanced by about 25%.

Rapid-Manufacturing-Process for Elastomeric Components

The Selective Laser Sintering Process of
 thermoplastics (SLS) enables the manufacturing of
 components with complex shape in a short time period
 without the manufacturing of a specific mold. However, this
 manufacturing process is limited by the restricted range of
 materials. In contrast to this primary shaping process,
 vacuum casting allows a quick, inexpensive and highly
 accurate process but it is limited to the reproduction of
 already existing models. In a novel rapid tooling method,
 these two processes are combined. Thus, silicone parts can
 be manufactured using SLS molds. The manufacturing of
 elastomeric parts in the vacuum casting process using SLS
 molds is being investigated. Therefore, the adhesion of
 silicone to the SLS mold, as well as the resulting mechanical
 properties of the elastomeric parts are investigated. The combination of the SLS process and the vacuum casting process allows the rapid manufacturing of complex elastomeric parts with sufficient mechanical
 properties. The surface roughness of the SLS mold influences the adhesion of the casting material to the mold, as well as the mechanical properties of the manufactured elastomeric components. The synergy of using selective laser sintered molds with the vacuum casting technique displays a
 novel rapid manufacturing method.

Microstructure and formation mechanism of grain-refining particles in Al-Ti-C-RE grain refiners

The Al-5Ti-0.2C-based grain refiners with different contents of rare earth (RE) were successfully prepared via powder metallurgy and vacuum casting. The microstructural evolution has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the RE addition resulted in the formation of TiAl3/Ti2Al20RE core-shell structured primary particles, and the size of TiAl3 core decreased, while the thickness of Ti2Al20RE increased with increase of RE contents. As compared to Al-5Ti-0.2C grain refiner, the grain refining efficiency was gradually improved with increase of RE contents, which was mainly attributed to the TiAl3/Ti2Al20RE core-shell structured primary particles and insoluble TiC nuclei formed in a-Al matrix. The formation mechanism of core-shell structure was further investigated based on Ginstling-Brounstein model.

Process for reinforcing SLS parts by epoxy resin

Purpose – The purpose of this paper is to report on the use of a combination of selective laser sintering (SLS) and vacuum casting to create plastic composites made by additive manufacturing. Design/methodology/approach – The research has been carried out by approaching a new concept of the final part consistent in a plastic component, where the main body is made by SLS and the internal long fibres for reinforcing are made by vacuum casting of high-resistance epoxy resin. The part is designed for optimal number and distribution of the internal fibres taking into account the target relative stiffness (N/mm*kg). The methodology is applied to a pedal clutch of a car which has been tested in an equipment for fatigue and durability, being compared to the correspondent design for injection moulding. Findings – Research has proven that the approach introduces relevant improvement in mechanical properties of the base resin consistent in PA 3200GF (EOS), reinforced by internal long fibres of resin VG SP5. Experiments showed significant increase of stiffness in the pedal clutch made under this procedure, where the stiffness was 77 per cent higher than the conventional SLS part and only 11.7 per cent lower than the one made by injection moulding of PA 66 with 50 per cent fibreglass. Originality/value – The developed method introduces an alternative procedure for increasing the mechanical properties of plastic parts developed in SLS. Optimal orientation and distribution of long fibres clearly achieves better mechanical properties at low cost.

Influence of Hot Extrusion on Microstructure and Hardness of SiC Particle Reinforced Al-Zn-Mg-Cu Alloy Matrix Composite

In this paper, the microstructure and mechanical property of the Al-Zn-Mg-Cu aluminum matrix composite reinforced by SiC particles with the contents of 2.5, 4.5, and 6.5wt% through vacuum casting are studied. The homogenization treatment was conducted at 465°C heat insulation for 24h. The purpose of this study is to analyze hot extrusion influence on the microstructure and hardness of the Al-Zn-Mg-Cu aluminum matrix composite. SiCp under pre-processing possesses good wetability with the analysis of Laser Particle Sizer and XRD. Metallurgical microscope, XRD, SEM and EDS is applied to analyze the microstructure of the Al-Zn-Mg-Cu aluminum matrix composite. It has proved that the hot extrusion can effectively improve the homogenization of SiCp and dissolve the second rough phases to reinforce the dispersal of CuAl2and MgZn2phase. The hardness of Al/SiCp composite rises as the increase of the SiCp content. It is shown that when the SiCp content is above 5%, its hardness obviously reinforced as well as that of the Al/SiCp composite.

HYDRODYNAMIC TESTING OF A BIOLOGICAL SHARKSKIN REPLICA MANUFACTURED USING THE VACUUM CASTING METHOD

Numerous facts have validated that sharkskin possesses the obvious drag reduction effect in certain turbulent flowing stations, and it has huge potential and important applications in the fields of agriculture, aerospace, industry, transportation, daily life and so on, which have attracted increased attention throughout the world. To meet the increasing requirements of practical applications, it has been progressively developing into an urgent problem to manufacture sharkskin surfaces with perfect forming quality and high drag-reducing effect. In this paper, the vacuum casting method is put forward to fabricate the drag-reducing surface with the real sharkskin morphology by eliminating the air bubbles from the bottom of sophisticated morphology in the pouring process. Meanwhile, a novel and facile “marking key point” method is explored and adopted to search for the corresponding biological sharkskin and negative template, a more convincing way to evaluate the replicating precision is systematically illustrated and the hydrodynamic experiment is carried out in the water tunnel. The results indicate that wall resistance over sharkskin surface replicated by the vacuum casting method can be decreased by about 12.5% compared with the smooth skin. In addition, the drag reduction mechanism hypotheses of sharkskin are generalized from different respects. This paper will improve the comprehension of the sharkskin fabrication method and expand biomimetic sharkskin technology into more applications in the fluid engineering.

Effect of casting vacuum on thermodynamic and corrosion properties of Fe-based glassy alloy

The effect of casting vacuum on thermodynamic and corrosion properties of Fe61Co7Zr8Mo5W2B17 in shape of cylinder of 3 mm in diameter and ribbon of 20–40 μm in thickness and 2–3 mm in width were investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC), dilatometer (DIL), scanning electron microscopy (SEM) and electrochemical station. It is found that high casting vacuum can improve the glass forming ability (GFA), the contraction degree during heating, and the pitting resistance of the glassy alloy, which can be ascribed to the fact that the dissolution of tungsten in the melt is improved under the high casting vacuum.

Effect of Single, Double and Triple Particle Size SiC and Al2O3 Reinforcement on Wear Properties of AMC Prepared by Stir Casting in Vacuum Mould

The aim of present research work is to study the effect of single particle size (SPS), dual particle size (DPS) and triple particle size (TPS) of SiC and Al2O3 reinforcement as hybrid solute on wear properties of aluminium matrix composite (AMC) prepared by stir casting in vacuum mould. The ABS plastic based master pattern (prepared with fused deposition modelling setup) for vacuum mould has been used in the present study. The friction and wear tests were carried out using a pin-on-disc type tribo-test machine under dry sliding condition. The results of study suggest that SPS based AMC exhibited better wear resistant properties as compared to DPS and TPS. The study also highlights the effect of other controllable process parameters of vacuum moulding process (namely: vacuum pressure, sand grain size and proportion of solutes) on wear behavior of AMC.

Dielectric properties of multi-layer epoxy resinimpregnated crepe paper composites

Epoxy resin-impregnated crepe paper (RIP) composites have been used as the inner insulation of dry condenser bushing in the ultra-high voltage direct current (UHVDC) power transmission system. In order to study the dielectric properties of pure epoxy resin and RIP composites, four kinds of samples (pure epoxy resin, RIP composites with 1, 2, 3 layers of crepe paper respectively) were prepared via the vacuum casting process. The Fourier transform infrared spectroscopy (FTIR) as well as three typical dielectric properties, i.e. complex permittivity, dc conductivity, thermally stimulated depolarization current (TSDC) have been investigated. It shows that the addition of crepe paper nearly brings about larger values of relative permittivity as well as dielectric loss factor than the pure epoxy resin. Samples containing crepe paper also have larger dc conductivities and TSDC currents. These differences are related to the abundant hydroxyl groups in the cellulose paper. The hydroxyl groups are polar groups and easy to absorb water or other impurities which resulting in larger permittivity and dc conductivity. Moreover, the crosslinking degree of the epoxy resin matrix decreases with the introduction of crepe paper. Then, the polarized dipole moments are easier to relax, which is responsible for the decrease of the trap depth corresponding to the process of glass transition.

Rolling Contact Fatigue of Superelastic Intermetallic Materials (SIM) for Use as Resilient Corrosion Resistant Bearings

Superelastic intermetallic materials (SIM), such as 60NiTi, are emerging as candidates for corrosion and shock-resistant rolling element bearings. Compared with metals, the intermetallic materials are more brittle and may be prone to rolling contact fatigue degradation. In this paper, a series of three ball-on-rod rolling contact fatigue tests were conducted using polished steel balls and NiTi rods prepared by vacuum casting and powder metallurgy techniques. The test protocol matched that used in ASTM STP 771 except that the steel balls were not intentionally roughened. In general, the NiTi rods exhibit fatigue damage at much lower stress levels than commercial bearing steels. At the lowest stress level tested (1.7 GPa), 60NiTi rods that were largely free from processing defects gave acceptably long lives, and testing was terminated without failure after 800 h. At elevated stress (2.5 GPa), failure occurred for some specimens, while others reached the preset test length goal of 800 h. Improperly prepared 60NiTi rods that had unconsolidated particles or significant ceramic inclusions occasionally experienced surface fatigue prior to completion of the test period even at the lowest stress level. Alloyed NiTi rods containing small amounts of Hf as a microstructural processing aid generally endured higher stress levels than the baseline 60NiTi composition. Two predominant fatigue failure mechanisms were observed: intergranular (grain boundary) fracture and intragranular (through the grains) crack propagation. The results suggest that further fatigue capability improvements could be obtained through process improvements, microstructural refinements and alloying. SIM currently available are recommended for mechanically benign applications involving modest stress levels and rates of stress cycle accumulation. Applications that include high continuous loads (stress) and high speeds for long durations should be avoided.

Matching-index-of-refraction of transparent 3D printing models for flow visualization

Matching-index-of-refraction (MIR) has been used for obtaining high-quality flow visualization data for the fundamental nuclear thermal-hydraulic researches. By this method, distortions of the optical measurements such as PIV and LDV have been successfully minimized using various combinations of the model materials and the working fluids. This study investigated a novel 3D printing technology for manufacturing models and an oil-based working fluid for matching the refractive indices. Transparent test samples were fabricated by various rapid prototyping methods including selective layer sintering (SLS), stereolithography (SLA), and vacuum casting. As a result, the SLA direct 3D printing was evaluated to be the most suitable for flow visualization considering manufacturability, transparency, and refractive index. In order to match the refractive indices of the 3D printing models, a working fluid was developed based on the mixture of herb essential oils, which exhibit high refractive index, high transparency, high density, low viscosity, low toxicity, and low price. The refractive index and viscosity of the working fluid range 1.453–1.555 and 2.37–6.94cP, respectively. In order to validate the MIR method, a simple test using a twisted prism made by the SLA technique and the oil mixture (anise and light mineral oil) was conducted. The experimental results show that the MIR can be successfully achieved at the refractive index of 1.51, and the proposed MIR method is expected to be widely used for flow visualization studies and CFD validation for the nuclear thermal-hydraulic researches.

Examination of the Aging Effects of Silicone Molds During Vacuum Casting Processes via Scanning Electron Microscopy

We present an in-depth investigation of contaminated silicone molds by use of scanning electron microscopy, that provides additional insight into the aging process of the molds. The molds lifetime in vacuum casting processes of polyurethane is limited due to contamination with the diisocyanate compound of the PUR resin. SEM investigations, combined with FIB cross-sections and EDX measurements show that three different types of particles are distributed in the contaminated silicone matrix. The particles differ in shape and size, with a range from 50 nm to 50 µm. This explains the loss in transparency and the hardened haptics of contaminated molds.

Investigation for Surface Quality Improvement of Barrel Finished FDM Patterns Based Vacuum Moulding

In this paper investigations have been made for surface quality improvement of barrel finished fused deposition modelling (FDM) pattern based vacuum moulding (VM) components. VM master pattern was prepared using p- 430 grade bs on fdm setup (uPrint-SE), whose surface finish was improved by using barrel finishing (BF) process. The controllable parameters of bf and vm process (namely: media weight, cycle time, vacuum pressure and grain size of refractory sand) were studied at three levels by using taguchi L9 orthogonal array to find out their effects on dimensional accuracy of the final casting. Aluminium 6063 alloy was used for preparing VM components.

The microstructure and mechanical properties of micro-scale Y2O3 strengthened 9Cr steel fabricated by vacuum casting

Casting process is not a common method in producing oxide dispersion strengthened (ODS) alloys due to its difficulty in distributing the oxides in matrix, especially for nano-scale oxide particles. In this paper, 9Cr steel strengthened by micro-scale 0.4 wt% Y2O3 was fabricated through vacuum casting technology containing electromagnetic stirring. Microstructural observation and energy dispersive spectrometry (EDS) analysis of the particles from tensile fracture dimples and extraction by dissolving metal elements, demonstrated that complicated oxides, several microns in diameter, containing elemental Y and O formed and evenly distributed in the steel matrix. The tensile strength was also improved after Y2O3 addition for the steels in both forged and heat treated states, the alloy matrix strengthened was due to the complicated oxides with Y element played a role as obstacles to dislocation gliding. The research confirmed that micro-scale Y2O3 was effectively added to the steel matrix during casting, which provided an alternative method for ODS alloy fabrication.

Design and Development of Three-Bladed Propeller for Micro Air Vehicles

CSIR-National Aerospace Laboratories (CSIR-NAL) is having a major program on development of Micro Air Vehicles (MAV) for civil, surveillance, and defense use. Under this program, MAV components development has been undertaken in various divisions of NAL. Propulsion system for one of the configurations of NAL MAV having fixed wing is battery-driven miniature motor and mini propellers. Efficient propulsion system plays a major role in deciding the endurance, payload, and maneuverability of MAV’s. Design of efficient propellers for these classes of vehicles is a challenging task because of their lower operating Reynolds number as well as conservative power utilization to enhance the endurance. Earlier, 2-bladed, fixed pitch, variable speed, 6-inch diameter propellers with different plan form has been carried out and reported. The present requirement is for 3-bladed, fixed pitch, variable speed mini propellers to augment thrust within the geometrical constraints as envisaged in the design of two-bladed propellers. To meet the mission requirements, design of three-bladed, fixed pitch, variable speed mini propellers were carried out using minimum induced loss method, and Eppler-193 airfoil is used in the design in view of its higher lift to drag ratios at low Reynolds numbers. This resulted in slight penalty on weight as well as power consumption and reduced noise level. Propeller CAD model is generated using SOLID WORKS and used for analysis as well as for fabrication. Performance estimation for this propeller is carried out using blade element momentum theory and ANSYS FLUENT. Fabrication of this propeller is carried out using three methods namely rapid prototype (RPT) using poly carbonate and conventional vacuum casting using poly urethane material and CFRP material with conventional casting using aluminum mold. The overall performance parameters like thrust, propulsive efficiency and motor power are evaluated for CFRP propeller and tested at uninstalled condition. Overall performance of the propellers is evaluated at MAV Aerodynamics Research Tunnel (MART), CSIR-NAL for different wind velocities and propeller rotational speeds in uninstalled conditions. This paper brings out the work carried out on design, development and testing of three-bladed miniature propeller for MAVs and its analysis using computational tools at propulsion division, CSIR-NAL.

Copper alloys with improved properties: standard ingot metallurgy vs. powder metallurgy

Three copper-based alloys: two composites reinforced with Al2O3 particles and processed through powder metallurgy (P/M) route, i.e. by internal oxidation (Cu-2.5Al composite) and by mechanical alloying (Cu-4.7Al2O3 ) and Cu-0.4Cr-0.08Zr alloy produced by ingot metallurgy (vacuum melting and casting) were the object of this investigation. Light microscope and scanning electron microscope (SEM) equipped with electron X-ray spectrometer (EDS) were used for microstructural characterization. Microhardness and electrical conductivity were also measured. Compared to composite materials, Cu-0.4Cr-0.08Zr alloy possesses highest electrical conductivity in the range from 20 to 800 ℃, whereas the lowest conductivity shows composite Cu-2.5Al processed by internal oxidation. In spite to somewhat lower electrical conductivity (probably due to inadequate density), Cu-2.5Al composite exhibits thermal stability enabling its application at much higher temperatures than materials processed by mechanical alloying or by vacuum melting and casting.

Effects of pattern coating and vacuum assistance on porosity of aluminium lost foam castings

Lost foam casting (LFC) process has several advantages when compared to conventional sand casting techniques however formation of large amount of gaseous products during foam pattern removal increases porosity fraction of castings, especially for low melting point A1 and Mg alloys. In this study pattern coating and vacuum assistance at the time of filling were investigated and their characterizations in constant casting conditions have been determined. Green sand moulding technique was carried out for all moulds because it is necessary to obtain sound castings by using expandable polystyrene (EPS) foam patterns without refractory coating. Simple prismatic shaped patterns were prepared from cutting pieces from an EPS isolation board. A well-known A380 Al-Si-Cu casting alloy was cast at 730°C. As expected, pattern coating reduce the gas permeability and increase porosity however metal penetration into sand grains and surface roughening occurs without coating. Slight vacuum were applied to moulds with vacuum casting machine until solidification. Vacuum assistance enhanced gas removal and it has clear effect on decreasing porosity.

Hybrid composites with epoxy resin matrix manufactured with vacuum casting technology

The paper presents the methodology of the process of manufacturing of technical profile models on the example gear wheels made of epoxy composites cast in silicone molds using vacuum casting technology. Research on preparation of epoxy resin composites filled with hybrid modifiers has been carried out. Mechanical and processing properties of composites have been evaluated, particularly in terms of application in rapid prototyping of gear wheels. Considerable improvement of tensile strength (up to 44 %) and unnotched impact strength (up to 93 %) has been observed. Geometric accuracy of gear wheels prepared by casting of the analyzed hybrid composites has been determined using a coordinate measuring machine. Morphology of the brittle fracture of studied composites has been observed on brittle fractures using a scanning electron microscope (SEM).