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Hybrid moulds are an increasingly considered alternative for prototype series or short production runs. This type of tools resorts on the use of Rapid Prototyping and Tooling (RPT) to produce the moulding elements (blocks or other inserts). This study was developed using a hybrid injection mould with exchangeable moulding elements that were produced by additive manufacturing (AM), namely vacuum epoxy casting, stereolithography and ProMetal. A full steel tool was also used as a reference. The processing conditions for the polypropylene moulded parts using the hybrid mould were monitored for pressure, temperature and ejection force. The hybrid mould performance was assessed in terms of pressure and temperature evolution during the injection cycle and the AM moulding elements for physical integrity. The data from the polypropylene moulded parts and the moulding inserts are compared with structural and rheological simulations using ANSYS Workbench and MOLDEX 3D. The results show that the hybrid mould performance and the structural integrity of the moulding elements depend on the properties of the materials used. The moulding shrinkage, when resin cores are used, is also affected by the core deformation caused by the injection pressure. info:eu-repo/semantics/publishedVersion

Przeprowadzono badania dotyczące wykorzystania nanokompozytów na osnowie dwuskładnikowych żywic poliuretanowych typu RenPIM-VG 5286 (PUR) z dodatkiem nanonapełniaczy: Nanobent® ZR1 i ZR2, modyfikowanych oktakis(tetrametyloamonio)oktasilseskwioksanem i oktakis{3-[N-(hydroksyetylo)dimetyloamino]propylo}oktasilseskwioksanem w technologii vacuum casting (VC). Zbadano reaktywność kompozycji odlewniczych (czas żelowania i maksymalną temperaturę utwardzania) oraz właściwości tiksotropowe, które mają istotny wpływ na przebieg procesu technologicznego wytwarzania prototypów kół zębatych w matrycach silikonowych. Oznaczono także wpływ rodzaju nanonapełniacza na właściwości użytkowe uzyskanych kompozytów. Wykazano, że dzięki wprowadzeniu układu hybrydowych napełniaczy, uzyskano ograniczenie skurczu promieniowego i osiowego, co dało radykalną poprawę dokładności wymiarowej odlewanych kół zębatych.

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 progressive deterioration, as the isocyanate component of the polyurethane resin diffuses into the mold cavity surface during the casting process, thus limiting their durability. Here, we present the first comprehensive description of the underlying chemical and physical mechanisms on a molecular level. It is shown that the isocyanate polymerizes inside the polydimethylsiloxane matrix with moisture to polyurea. Polyurea clusters, which emerge from the resulting interpenetrating polymer network with continuing isocyanate exposure, promote fissure formation under mechanical demolding stresses. The mechanism was investigated with a wide variety of characterization methods, and qualitative variations were demonstrated using different commercial materials. Influencing factors such as mold geometry, process flow, and different aspects of the material composition were examined experimentally. A thorough understanding of the deterioration mechanism paves the way for the development of durable molds and an economical midseries technology in plastics processing.

Casting-forging combination forming process is an advanced manufacturing technique which is applicable to manufacture the parts with both complex shape and high performance. As a fundamental research of casting-forging combination forming process, as-cast 40CrNiMo alloy steel is obtained through vacuum casting by using metal mold. The isothermal compression tests of as-cast 40CrNiMo alloy steel are implemented on a Gleeble-3800 thermal simulation machine at deformation temperatures of 800, 900, 1000 and 1100 ℃, with strain rates of 0.001, 0.01, 0.1, 1 and 10 s−1. The results indicate that the true stress-strain curves present typical dynamic recovery type under low deformation temperature and high strain rate. With the increases of deformation temperature or the decreases of strain rate, the true stress-strain curves gradually transform to dynamic recrystallization type. The Arrhenius-type constitutive equation with Zener–Hollomon parameter is determined for constitutive analysis. The kinetic model and kinematic model of dynamic recrystallization are deduced to describe the dynamic recrystallization behavior. Keywords: As-cast 40CrNiMo alloy steel, Isothermal compression test, Constitutive analysis, Dynamic recrystallization, Kinetic model, Kinematic model

The as-cast 40CrNiMo alloy steel with uniform microstructure is obtained through vacuum casting by using metal mold. The hot deformation behavior of as-cast 40CrNiMo alloy steel is investigated by isothermal compression tests. The Arrhenius constitutive model and processing maps of as-cast 40CrNiMo alloy steel are constructed. The results indicate that the true stress–strain curves present typical dynamic recovery type under low deformation temperature and high strain rate. With the increases in deformation temperature or the decreases in strain rate, the true stress–strain curves gradually transform to dynamic recrystallization type. Through the analysis of processing maps and microstructures, it can be found that the area of plastic instability increases with the increase in the strain and gradually expands to the region of high deformation temperature and low strain rate. The deformation temperature range of 850-1050 °C and strain rate range of 0.001-0.01 s−1 are recommended as the reasonable hot-working process conditions. Results of this research can provide references for the selection of process parameters in casting–forging combination forming of 40CrNiMo alloy steel.

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 °.

In recent years, polymer gears have gradually become more widely employed in medium or heavy-duty conditions based on weight reduction in transmission systems because of low costs and low noise compared to metal gears. In the current industry, proposing a cost-effective approach to the manufacture of polymer gears is an important research issue. This paper investigates the wear performance of polymer gears fabricated with eight different kinds of materials using differential pressure vacuum casting and additive manufacturing techniques. It was found that both additive manufacturing and differential pressure vacuum casting seem to be an effective and cost-effective method for low-volume production of polymer gears for industrial applications. The gate number of one is the optimal design to manufacture a silicone rubber mold for differential pressure vacuum casting since the weld line of the polymer is only one. Polyurethane resin, 10 wt.% glass fiber-reinforced polylatic acid (PLA), or 10 wt.% carbon fiber-reinforced PLA are suggested for manufacturing gears for small quantity demand based on the deformation and abrasion weight percentage under process conditions of 3000 rpm for 120 min; epoxy resin is not suitable for making gears because part of the teeth will be broken during abrasion testing.

This work investigates mechanical behavior and sliding wear performance of hybrid AA7075 alloy composites having SiC (0–12 wt% @ 3%)/graphite (3 wt%)/copper (3 wt%) as reinforcing phase, fabricated using high-temperature vacuum casting method. The samples of various compositions are characterized for physical, mechanical, and sliding wear (on pin-on-disk tribometer) as per standards. Taguchi design of experiment methodology was adopted for parameter selection, optimization, and experimental trials. The various performance parameters like density, voids content, tensile strength, specific wear rate, etc. are taken for decision making using the Preference Selection Index (PSI) technique. It has been observed that with the reinforcing phase, the properties like wear performance, density, voids content, compressive strength, impact strength, and tensile strength of composites increases considerably while flexural strength diminishes. The hybrid alloy composites having 12 wt% show superior overall properties and also verified form as the outcome of the PSI technique.

The article is devoted to the development of vacuum casting technology with directional crystallization of the casting. The technology of layer-by-layer cooling of a casting is considered, which ensures the formation of a casting with a uniform fine-grained metal structure. This effect is achieved due to the slow filling of the cooled mold cavity with cooling liquid due to the difference in the flow rate of the liquid at the inlet and outlet. At each moment of time, the cooling of the metal is carried out by a thin layer of the casting, which ensures the uniformity and fine-grained structure of the casting material, the absence of shrinkage and internal stresses.

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.

9Cr ferritic/martensitic (F/M) steels with 0 and 0.3 wt.% yttrium (Y) addition were fabricated via vacuum casting technique and were creep tested at 650 °C and 120 MPa. The creep property of 9Cr F/M steel was improved by the addition of yttrium. Even though the initial creep rates of 9Cr-0Y and 9Cr-0.3Y were almost the same, the creep rupture life of 9Cr-0.3Y specimen was extended about 2˜3 times with the longer steady state creep stage and the lower minimum creep rate than 9Cr-0Y specimen. The coarsening of grains and martensitic laths occurred during creep, and M23C6 carbides, MX/M2X-type carbonitrides and Fe2W/Mo Laves phase were identified along the boundary in both specimens. For 9Cr-0.3Y, the nano-sized oxide clusters were formed during creep, because of the diffusion and local segregation of the dissolved yttrium and oxygen atoms at high temperature and with the promotion of creep stress. The softening of microstructure recovery is compensated by the dispersion strengthening of nano-particles and the balance of them was the reason of longer steady state creep stage of the creep curves. Keywords: 9Cr steel, Yttrium, Vacuum casting technique, Creep properties, Microstructure characteristics

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%.

Porous materials are widely employed in a wide variety of industrial applications due to their advanced functional performance. Porous aluminum is among the most attractive metallic materials. It can be produced using repeatable methods involving a replicated Al foam that also provides porosity control. In this work, a highly porous replicated Al foam was fabricated. First, the model of multifunctional packing density was used and corrected to select the appropriate space holders. Then, Al foam was produced using a double-granular sodium chloride space holder. The obtained results showed a maximum porosity of 65% that was achieved using a mix of coarse, irregular granules with spherical granules of intermediate size. © 2021 by the authors.

This paper discusses the castability, mixed viscoelasticity and voids of the propellant based AP/HTPB/TDI with HTPB-TDI binders. Several influential variables were observed including the plasticizer and the order in which the curing agent was added. Then the mixer used is also horizontal and planetary (vertical) mixers in order to obtain the scale up or scale down parameters between mixers. First experiment was mixed propellant formulation in a 5 kg horizontal sigma blade mixer, which was set up at 55°C and 60 rpm. The composition of propellant was 14% of HTPB, 7.5% of Al powder, 77.5% of AP with coarse, medium, fine ratio 1/1/1, and 1% of TDI. Propellant slurry as mixing product was casted into vacuum casting chamber then grained as desired, cured at 60°C for 2 days, was left in room temperature for a week. The propellant was X-Ray scanned and viscosity measurement at 3 rpm spindle speed. This experiment was repeated with the addition of TDI in the first sequence and the end sequence. The experiments were repeated with addition of DOA for 0.5 to 4%. The order of adding TDI in the propellant mixing process affects the viscoelasticity and castability of AP / HTPB / Al composite propellant. The mixing of the TDI at the end process will provide a better mixing space and evenly distributed particle distribution, is better applied to large rockets that require a longer treatment. Scale up and scale down of propellant mixers can use similarity while maintaining the same viscoelasticity and operating conditions. The addition of DOA increase pot life and viscoelasticity, but there are limitations to where the dough can be molded or processed. The maximum addition of DOA is 2.74% to produce a dough with an even distribution of particles with the added bonding agent.

Vacuum casting basin insulator and supprorting insulator are the key insulation components of GIS system. Their insulation performance, mechanical performance and aging resistance directly affect the safe operation of power grid. As the castable of insulation components, the performances and pouring process of epoxy resin composite are the key factors affecting the performance of insulation components. The problems of residual stress and various defects are easy to occur in the process of casting and molding of insulation components. The aging phenomenon of insulation components will occur due to equipment heating during the operation. In this chapter, the residual stress distribution and curing defects of epoxy resin casting insulation components during casting molding are studied. In addition, the thermal aging mechanism of epoxy composites is studied, and the comprehensive performance of epoxy composites is improved by chain-extended modification.

The current work deals with an endeavor to synthesis, metal composites by taking aluminum alloy (i.e. LM 26) as matrix material and porcelain (powder form) as reinforcement. The metal composites were fabricated with different weight percentages (0wt%, 2wt%, 4wt%, 6wt% and 8wt%) of recycled porcelain reinforced LM 26 aluminum alloy by using high temperature vacuum casting induction furnace and the physical, mechanical and wear properties were measured. The micro hardness, compressive strength, tensile strength and flexural strength were increased with the increase in porcelain weight percentage. From the results obtained, it was found that 6wt.% porcelain reinforced composite exhibits maximum wear resistance as compared to other compositions of composites. Furthermore, the surface morphology of the worn out surfaces and cross-sectional microstructure of the fabricated composites were analyzed by using scanning electron microscopy (SEM) to understand the wear mechanism and microstructural changes, respectively by increasing the composition of porcelain (0-8wt.%) for the base composition of Aluminum LM-26 alloy. The obtained findings indicate that LM 26 aluminum alloy containing 6wt.% porcelain can be recommended for tribological use of this composite in manufacturing automobile spare parts including piston material.

In the present study, an endeavour has been made to investigate the mechanical properties of hollow glass microspheres reinforced die cast magnesium alloy under vacuum die casting process. The particle size, mass fraction, stirring speed has been considered as input process parameters to analyze the mechanical properties such as hardness, compressive strength, porosity and density of the syntactic foams. Taguchi-Grey relational based multi response optimization has been utilized to compute the optimal process parameters and find the influence of those parameters on performance measures of casting process. From the experimental investigation, the optimal process parameters have been found as particle size (45 microns), mass fraction (20%) and stirring speed (600 rpm) among the chosen process parameters. The highest max–min indicates the particle size has higher influence on determining the mechanical properties of the syntactic foam owing to its importance on determining the porosity. It has been also observed that the density of syntactic foam decreases with increases in the mass percentage of hollow glass microspheres.

The main purpose of biomedical implant is to replace the damaged/injured parts in the human body. Titanium, cobalt-chromium alloys and stainless steel (SS-316L) are the commonly used materials for the implants due to their bioactive & biocompatible nature as well as superior mechanical properties. In this work, a systematic procedure for development of tailor made SS-316L hip implant by using the combined route of fused deposition modelling (FDM), chemical vapor smoothing (CVS), vacuum casting (VC) and investment casting (IC) has been outlined. Further, the effect of two controllable parameters of the IC process (drying time of primary coating and mould thickness) has been investigated on the surface roughness of fabricated implants. Finally, mathematical models have been developed for prediction of surface roughness by using Buckingham’s Pi-theorem. It has been observed that the models are highly suitable for data prediction.

We present an in-depth investigation of the aging effects in silicone molds for vacuum casting processes. Their lifetime is limited to a few production cycles due to contamination with the diisocya...

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.

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.

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.

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.

Vacuum casting of polyurethane in silicone molds is a widely used method for prototype replication and holds great potential for application in small batch production. Products produced in this way offer extremely good shape accuracy even in the nanometer range and high surface quality, as well as flexible material properties that are convenient for serial production. In this work, we present a new method for increasing the feasible output of silicone casting molds in vacuum casting processes. By supplementation of polyamide 12 powder, which is a waste product of the selective laser sintering process, to the silicone rubber the maximum output of the casting molds could be increased by up to 38.5% while the amount of new silicone used has been substituted by up to 20%. Both generic silicone samples and representative silicone molds have shown that with increasing polyamide content, aging characteristics decrease as the output increases. The improvement was quantified by comparative weight, hardness and thermogravimetric measurements. As surface energy and roughness measurements as well as extensive casting experiments have shown, the silicone surface and thus the product surface remains unimpaired.

Sample preparation is an important step when testing the mechanical properties of materials. Especially, when carbon nanotubes (CNT) are added to epoxy resin, the increase in viscosity complicates the casting of testing specimens. We present a vacuum casting approach for different geometries in order to produce specimens from functional nanocomposites that consist of epoxy matrix and oxidized multi-walled carbon nanotubes (MWCNTs). The nanocomposites were characterized with various mechanical tests that showed improved fracture toughness, bending and tensile properties performance by addition of oxidized MWCNTs. Strengthening mechanisms were analyzed by SEM images of fracture surfaces and in-situ imaging by digital image correlation (DIC).

Pouring temperature also affects the mechanical properties of aluminium. High pouring temperature will make aluminium grains become large and a lot of gas will be trapped into the liquid metal when the metal is poured into the mould. The right temperature will prevent metal porosity and the metal does not freeze before filling the entire moulds cavity. The casting process used permanent mould. Temperature of the moulds was 150 °C and the pressure 0.35 atm (absolute pressure). Pouring temperature were 750, 800 and 850 °C. The increasing pouring temperature reduce the tensile strength and specific density of aluminium. Pouring temperature aluminium in vacuum casting system at 750 °C produce the highest tensile strength (130.26 MPa). The specific density of the aluminium is 2.65 g/cm3

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.

In the low cost application of vacuum casting in rapid prototyping, a mould cavity with high modulus is necessary for producing plastics parts in small quantity. In this work, a silicone matrix was reinforced with natural fibers to improve the modulus of composites to mould and to reduce the cost of silicone materials. Sisal fiber with different compositions was reinforced with silicone in a compression moulding process. Mechanical properties were studied. An increase in tensile strength, tear strength, and better hardness was observed in sisal fiber composites . The silane-treated fiber improved the adhesion between fiber and matrix and enhanced the mechanical properties of the composites. The swelling method was adopted to determine the cross-linking density of composites through the Flory-Rehner equation. The flexibility of silicone composites decreased for higher fiber loading and there was an increase in cross-linking of the fiber network to improve modulus of the composites. A morphological study was conducted using X-ray tomography and scanning electron microscopy (SEM) to predict the defects, orientation, debonding, fractography, and interfacial adhesion of fiber/matrix composites.

The possibility of application of nanocomposites based on unsaturated polyester resin matrix (Polimal® 103 and Polimal® 109) and nanofillers Nanobent® (ZR1 and ZR2) in Vacuum Casting technology (VC) was investigated. The reactivity of the molding compositions (gel time and maximum curing temperature) as well as their thixotropic properties, which have an important impact on the technology process of prototyping gears in silicone matrices, were assessed. Using the optical measuring system ATOS II Triple Scan Blue Light (GOM) the dependence of geometric dimension accuracy of the gear wheel models on the type of nanofiller and its content in the composite was determined.

CaO filled silicon bronze (SiBr) alloy composites have been fabricated by a high temperature vacuum casting technique at five different weight percentages (0 wt%, 2.5 wt%, 5 wt%, 7.5 wt% and 10 wt% of CaO). The void contents, hardness and wear behavior of the CaO filled SiBr alloy composites were studied showing that the addition of particulates in base alloy reduces the void contents from 0.827 % to 0.504 % for 0 wt% to 7.5 wt% of CaO respectively. Similarly, the hardness of CaO filled SiBr alloy composites initially increases from 119.25 Hv to 140.8 Hv on addition of 7.5 % CaO but on further increase in filler content (10 wt%) the hardness decreases to 114.5 HV respectively. The specific wear rate of composite materials for applied load and sliding velocity factors showed surpassing behavior compared to unfilled alloy composites. To get the optimum response of wear behavior of composite materials the Taguchi L25 orthogonal array was applied and the result shows the higher S/N ratio i.e. 106.33 dB. The analysis of variance (ANOVA) result shows that the filler content plays a major effect compared to other factors. The particulate filled composites were examined through scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX) and atomic force microscopy (AFM) in order to understand the wear mechanism and morphology behavior of the composites.

The formation of the so-called α-layer when casting titanium alloys significantly impairs the mechanical properties of the metal and leads to the need for additional product surface treatment. It is known that simultaneously with the change in mechanical properties, the composition of the casting surface layer is often changed, and the composition change depth, as a rule, does not coincide with the depth of α-layer formed. The reason for α-layer formation, most often, is considered to be the introduction of foreign elements into the crystal lattice of a metal casting. According to our assumption, the mechanism of α-layer formation is two-stage, and it is associated with an intense diffusive effect on the melt structure in the casting outer layer, resulting from its boiling in vacuum during pouring into porous ceramic shells (CS). The paper suggests possible mechanism for composition changing of the surface α-layer in titanium castings due to the secondary processes of effusion saturation of the metal surface with reverse vapor flows coming from the porous ceramic shell after solidification of the casting. In this case, the primary process is the saturation of the CS pores due to the effusion of metal vapors during the boiling of the poured melt due to the high intrinsic vapor pressure exceeding the pressure in the foundry furnace. Chemical interaction of the alloy component vapors with the CS material leads to the volatile components: silicon, silicon II oxide, zirconium II oxide, saturating the metal surface layer due to reverse secondary effusion. The paper presents experimental results on α-layer formation when casting BT5JI alloy in CS having different composition and porosity. The research results confirm the assumption about both the diffusion mechanism of α-layer formation and the effusion mechanism of changes in its composition.

Molybdenum-added biomedical alloy has been prepared using a high-temperature vertical vacuum casting technique with five (0, 1, 2, 3, and 4 wt%) diverse weight percentages. The density, microhardness, and sliding wear behavior of the fabricated alloys were studied, showing that the addition of molybdenum content in the metal–metal alloy (i.e., Co–30Cr) increases the density from 7.2 to 8.7 g/cc for 0–4 wt% of Mo, respectively. Similarly, the hardness of prepared biomedical alloy also increases from 653 to 720 HV on addition of 0–4 wt% Mo particulate, respectively. The hardness is investigated by the microhardness tester. The aim of this current research work is to optimized the sliding wear behavior of molybdenum-added Co–30Cr alloy for implant material by Taguchi experimental design technique at five different normal loads (5–25 N), sliding velocities (0.26–1.3 m/s), sliding distance (500–2500 m), and reinforcement, i.e., Mo (0–4 wt%) respectively. To obtain the optimum wear response of prepared biomedical alloy added with Mo contents, the Taguchi L25 orthogonal array was implemented. The wear test is performed on a pin-on-disc tribometer against a hardened alloy steel (EN-31) disc under different operating conditions at room temperature. Afterwards, field-emission scanning electron microscopy and atomic force microscopy were utilized to analyze the microstructure, contour of wear mechanism, and 3D surface topography of samples after test run.

A group of composite bronzes BrZhNKA 9-4-1-1, BrZhNA 12-7-1, etc., has been studied. Brittle intermetallic compounds of the Cu3Sn type are replaced by steel dendrites in them. The mass transfer of Fe, Ni, Co, and Al between the matrix and dendrites in these bronzes is studied. The dispersity of dendrites depending on the production method of the mentioned alloys can be increased tenfold, for example, with the vacuum casting method. The mechanical properties of the samples of the BrZhNKA type (σu = 372 MPa, δ = 25%, and ψ = 42%) when compared with the BrO10 prototype are higher: hardness σu by 50%, plasticity δ and ψ by a factor of 4–5, and wear resistance by an order of magnitude; the coefficient of friction is 20–30% lower. The fact of the substantial influence of dispersity of the dendritic component on the wearing intensity of the bronze of the BrZhNA type is established. For example, the wearing intensity with the transversal section of dendrites of 1 and 10 μm is 0.002 and 0.025, respectively, which is an order of magnitude lower, while the coefficient of friction remains herewith invariable; i.e., it is independent of the dispersity of dendrites. A whole complex of mechanical, process, and service properties makes it possible to consider the half-industrial approval of this new class of composite bronzes of the BrZhNKA type reinforced by dendrites of N12K7Yu maraging steel for sliding friction units substantiated and promising. © 2018, Allerton Press, Inc.

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.

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.

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.

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.

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 ...

The performed examinations concerning the process of filling the plaster ceramic moulds with aluminium alloys allowed to assess the influence of various methods of introducing the metal into the mould cavity on the macro- and microstructure of the obtained experimental castings. The comparison was performed for castings with graded wall thickness made either of EN AC-44000 alloy or of EN AC-46000 alloy, produced either by gravity casting, or by gravity casting with negative pressure generated around the mould (according to the Vacumetal technology), or by counter-gravity casting. It was found that the silicon crystals grow in size with an increase in wall thickness due to the slower cooling and solidification of castings

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).

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.

In this work we present a new method to enhance the durability of silicone molds, which are used in industrial processes for small batch production. The goal is to reduce the aging effects of the molds that occur after a minor number of casting processes and therefore get a higher output of these molds. First the source of the aging effects is identified. It is shown that the molds are nourished with the low molecular components of the polyurethane mixtures during the casting process, and that the diisocyanate component is responsible for the aging effects. For the removal of these components, several solvents are used. Acetone is shown to be most effective; the regeneration leads to a 30% higher output. Because acetone also removed free silicone oil from the molds, a mixture of the solvent with new silicone oil as regenerating agent was applied, which led to an overall improvement of lifetime of 60%.

The APG (Automatic Pressure Gelation) process of epoxy resin casting transformer had been studied in this paper, which was developed toward epoxy resin vacuum casting process. The raw materials, mold, the differences with vacuum casting process,casting process with its parameters were introduced. Also the factors that influences the partial discharge experiment of transformer were analyzed,especially the body making and casting processes.

The work deals with the influence of change in the filling conditions of the ceramic moulds with plaster binder on the presence of gaseous porosity and the microstructure of the achieved test castings with graded wall thickness. Castings made of EN AC-44000 alloy, produced either by gravity casting, or by gravity casting with negative pressure generated around the mould (according to the Vacumetal technology), or by counter-gravity casting were compared. The results of examinations concerning the density of the produced castings indicate that no significant change in porosity was found. The increased size of silicon crystals was found for the increased wall thicknesses due to the slower cooling and solidification of castings.

Conductive polyacrylonitrile film reinforced by multiwall carbon nanotubes was prepared via ultrasonic dispersion and vacuum casting. The structure of MWNT/PAN composite film was characterized by WAXD and FT-IR. The LOI of the blend was enhanced from 18.1 % to 24.5 % and TGA show better thermal stability. MWNT composite at 10 wt% MWNT loading showed an electrical conductivity of 10-2S/cm.

Due to the 3c products develop faster in the direction of thin, light, short and small, thin-walled plastic parts of the vacuum casting attaches great importance to people. The quality of the thin-walled plastic parts can be guaranteed with the method of vacuum casting numberical simulation . Using Moldflow, we analyze the best location of the gate、the fluidity of the material casted in the mold and produce a vacuum casting part .The vacuum casting basic process was described in this paper. The CAE (Computer Aided Engineering) analysis applied to vacuum casting effectively guide rapid mold made.