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In recent years, there has been a marked increase in the use of rapid prototyping techniques that support industrial processes. The analysis of studies on strength tests of parts manufactured using additive techniques from model materials and hybrid composites usually includes tests of material and strength parameters based on uniaxial tension, bending, and compression tests. For elements manufactured from polymeric materials using traditional methods (e.g. injection moulding), data obtained from these tests are sufficient to determine the strength of the material and to apply the results in the product design process. In the case of the layered extrusion method, due to the model construction process, strength data based on standard samples do not have a direct transposition on the strength of machine parts operating under various load ranges, especially torsional loads. The publication presents the results of tests on the torsional strength of cylindrical samples with splines produced by layered extrusion, vacuum casting technology, and hybrid technology, which combines both technologies. The test samples were made using a Prusa i3 MK3 3D printer and the plasticised plastic modelling (fused filament fabrication, FFF) method, while PolyJet technology was used to create a reference model. The findings indicate that hybrid technology, in which a thin-walled mould is filled with a chemically hardened polymer, achieves the desired strength for the manufactured parts while maintaining dimensional accuracy and shape. The research results show that producing rotating elements using the hybrid technology reduces the sample core’s ability to undergo plastic deformation due to the adhesion between the materials and the occurrence of notches resulting from the model production process using the layered extrusion method.

The application of casting technologies in the production of parts and assemblies of small-size gas turbine engines is justified in the paper. The technology of vacuum casting in gypsum molds was tested during the production of an experimental centrifugal compressor of a small-size gas turbine engine. On the basis of a 3D model of the designed centrifugal compressor, computational studies of vacuum casting were carried out and rational parameters of the technological process were determined. Prototypes of the developed centrifugal compressor of a small-size gas turbine engine were made. The results of calculations and the performed technological experiment confirmed the fill rate of the gating form and the absence of short pour. The distribution of shrinkage porosity and cavities corresponds to the design values and is concentrated in the central part of the casting that is subjected to subsequent machining. The area of the blades, disc and sleeve is formed without defects. The use of casting technologies in the production of parts and assemblies of small-size gas turbine engines assures the required quality with a comparatively low price of the finished product, making it possible to achieve the balance between the cost of the technology and the quality of the product made according to this technology.

Vacuum casting (VC) is a promising technique used for the production of functional plastic parts due to its fast production of high-quality prototypes. However, the mechanical properties of the fabricated products are affected by the composition of the molding materials. Additive manufacturing (AM) is also widely applied for low-volume prototyping applications. However, the mechanical properties of the fabricated products are affected by both build directions and printing angles. To investigate the difference in flexural strength of parts between vacuum casting and fused deposition modeling, glass fiber (GF) and carbon fiber (CF) are added to the matrix materials of polyurethane (PU) for improving the flexural strength of the molded products and three different printing angles and two build directions were applied in AM process. It was found that the flexure strength of the specimen fabricated by VC is generally greater than that of the specimen fabricated by AM. The highest flexure strength of the specimen fabricated by VC is 141 MPa, whereas the highest flexure strength of the specimen fabricated by FDM is only 102.7 MPa. The addition of short GF to the PU will increase the flexural strength. The flexural strength can be increased by about 41% when the PU is added with 4 wt.% short GF. The flexural strength can be increased by about 4.8% when the PU is added with 1 wt.% long GF. In contrast to above results, the flexural strength will be reduced when the PU is added with more than 2 wt.% long GF. On the contrary, the flexural strength can not be improved when the short CF or long CF is added to the PU. Finally, the flexural strength of the plastic prototype made by VC technology is superior to that of the plastic prototype made by FDM since the mechanical properties of the plastic prototype made by the FDM are affected by the build direction and printing angle. [ABSTRACT FROM AUTHOR]

Context: Three-dimensional printing technologies have been used recently for patients with maxillofacial deformities who seek esthetic prosthesis. The aim of the present study was to assess the accuracy, surface texture, marginal adaptation, patient satisfaction, and ease of fabrication of silicone auricular prostheses fabricated by the rapid prototyping technology (RPT) when compared to the conventional method (CM). Materials and Methods: A pilot study was conducted on five patients who had partial auriculectomy defects. Ear prostheses fabricated by CM and RPT were compared. RPT include the fabrication of prostheses by the duplication of polymer model fabrication or by injecting silicone to mold obtained by Vacuum casting method (VCM). The prostheses were evaluated by 15 randomly allotted trained independent observers based on the Likert Scale. The patients performed a self-rating assessment followed by a report from the clinician and technician. Statistical Analysis: The scores for each of the dimension were analyzed using the ANOVA. The cost, time, and quantity of silicone material were expressed in means for three fabrication methods. Results: Prostheses fabricated by RPT yielded superior scores in terms of accuracy, texture, and marginal fit; the vacuum casted prostheses being more precise. The patient perspective was in favor of RPT though not significant statistically. Time for fabrication and number of patient visits were less for rapid prototyping methods than CM. Conclusion: The present study demonstrated the potential benefits of digital method in the fabrication of auricular prosthesis using RPT in the field of maxillofacial rehabilitation.

Vacuum casting (VC) is a highly versatile manufacturing technique capable of producing parts in a wide range of polymers for end use plastic parts or prototypes. VC technology is ideally suited to low volume batch production compared with plastic injection molding since a silicone rubber mold (SRM) can be used to produce up to fifty to eighty parts. The main challenge of this method is that the both dimensional and form accuracies of the VC parts were affected by the fastening force of the SRM using tape due to the fastening force is inconsistent for different operators. In this study, an intelligent SRM clamping mechanism comprising a pressure sensor and Arduino pressure sensing module was developed for reducing the variations in both dimensional and form accuracies of the VC parts. It was found that the 14 kPa is the optimal clamping pressure. The angular deviation of the cuboid VC parts produced by the intelligent clamping mechanism falls within the range of one standard deviation (SD) to the average. The minimum zone circle deviation of the cylinder VC parts produced by the intelligent clamping mechanism falls within the range of − 1 to 2 SDs. In addition, the production cost of the SRM can further be reduced by about 23% using an intelligent clamping mechanism compared with that using the conventional method. [ABSTRACT FROM AUTHOR]

The article deals with vacuum casting technology and especially with the assessment of the influence of the tempering temperature of silicone molds on the dimensions of future castings. The aim was to evaluate the actual size of the castings, using different tempering temperatures of the molds and different casting materials. After examining the resulting dimensions of the individual castings, a procedure was established by which these effects could be minimized. In the end, a test of the proposed procedure is performed, which confirmed its correctness. [ABSTRACT FROM AUTHOR]

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.

The article deals with vacuum casting technology and especially with the assessment of the influence of the tempering temperature of silicone molds on the dimensions of future castings. The aim was to evaluate the actual size of the castings, using different tempering temperatures of the molds and different casting materials. After examining the resulting dimensions of the individual castings, a procedure was established by which these effects could be minimized. In the end, a test of the proposed procedure is performed, which confirmed its correctness.

Integrated processing of plant raw materials refers to the primary areas of use of natural resources and their rotection. During the primary processing of bast plants, a large amount of waste remains – a shives. Part of the shives is burned, the rest goes into the dump. Due to its chemical composition, high content of cellulose shives can be used in the production of eco-friendly packaging. Packaging can be obtained with the complete or partial replacement of waste paper in its composition. Thanks to this, the issue of the shortage of waste paper at the enterprises of recycling of secondary raw materials will also be resolved. The purpose of the work is the production of eco-friendly biodegradable packaging from flax shives in industrial conditions. The paper presents the results of samples of lumpy egg packaging obtained by vacuum casting with the use of flax production waste. In industrial conditions, it was possible to replace part of the waste paper on the fire. For more efficient use, the shives was pre-ground to the consistency of wood flour M-560. The following indicators were determined: humidity, strength, moisture absorption capacity, antibacterial properties. The obtained results showed the optimal ratio of the mixture components, processing modes. According to all indicators, the packaging with a bone is not inferior, and in the case of tensile strength and antibacterial properties exceeds the normalized values.

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. [ABSTRACT FROM AUTHOR]

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 °. [ABSTRACT FROM AUTHOR]

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.

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. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

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.

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

In conditions of dynamic market environment there is an increasing requirement for rapid development and production of complex and functional parts from different materials. In this paper, we present the process of development and production of small batches of functional parts in the integrated system of additive and vacuum casting technology. All advantages of this integrated approach were used during the research. Data obtained from the manufacturer were used for the proper selection of materials and they relate to the value of mechanical characteristics. [ABSTRACT FROM AUTHOR]

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.

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).

A new class of defects has been recently discovered, which are regarded as double oxide film defects. In this study, a number of Ni-based vacuum-cast test bars were investigated. The fractures in the broken test bars were observed by Scanning Electron Microscopy (SEM). Energy Dispersive Spectroscopy (EDS), as well as Wavelength Dispersive Spectroscopy (WDS) were used to characterize the chemical elements of the fracture's surface. Observation by SEM revealed the presence of inclusions identified as films that appeared to have initiated the growth of carbides. This study has added to the evidence that oxide film defects do exist in Ni-based super-alloy in certain vacuum casting conditions. It provides a reference for researchers' further study on the defects, and provides a possible direction for researchers to improve casting technology so as to remove these defects.

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. [ABSTRACT FROM AUTHOR]

Rockets are powered by composite solid propellant, which is a heterogeneous system consisting of solid oxidizer and metallic fuel dispersed in a polymeric fuel binder matrix. The slurry casting technique under vacuum/ gravity condition is well-established for performing a different class of large sized case bonded rocket motors. During propellant casting, the flow rate of slurry is a very critical parameter as it affects the product quality. The casting rate is governed by suficient degassing and viscosity buildup due to the progress of cure reaction. In the present study, casting rate and casting time have been numerically evaluated for fixed and varying percentages of valve opening, different viscosity of slurry, and different pressure drop (driving force). The velocity profile of propellant slurry inside feeding pipe and valve has also been evaluated. Furthermore, to get a flawless grain and to predict the slurry casting rate, a microscopic analysis has been carried out to model the flow behaviour of composite propellant slurry, where the momentum conservation law has been applied to express the mathematical model in an analytical form. The resulting differential and algebraic equations have been solved numerically using MATLAB, computing software. The numerical analysis is useful for designing new casting set-up and for giving the idea of maximum casting rate, which is achievable for given casting set-up and rheological properties of propellant slurry.

The need to develop products with special characteristics and high mechanical properties led to the introduction of plastic deformation of semifinished materials. Special purpose products are produced from slabs, blooms, billets or from different size ingots. One of the critical conditions to meet quality expectations after plastic deformation is that the material must be as high quality as possible. For refining steels, a range of methods have been developed that can remove harmful elements from the physical and mechanical product properties. For these products, the chosen casting method is one of the most important factors that can ensure product quality because casting can easily remove the beneficial effects of the refining process conducted during the development of the steel melt by contamination with refractory material from the casting assembly, re-oxidation of the metal bath and others. Depending on the complexity of the casting product and to obtain a superior quality product, several methods of casting have been developed. The usual method of casting high quality large ingots is in vacuum, the advantage is that the steel stream is protected from the surrounding atmosphere, this paper aims to highlight the benefits of vacuum casting with wide stream on the improvement of ingot quality by increasing purity and decreasing gas content.

The need to develop products with special characteristics and high mechanical properties led to the introduction of plastic deformation of semifinished materials. Special purpose products are produced from slabs, blooms, billets or from different size ingots. One of the critical conditions to meet quality expectations after plastic deformation is that the material must be as high quality as possible. For refining steels, a range of methods have been developed that can remove harmful elements from the physical and mechanical product properties. For these products, the chosen casting method is one of the most important factors that can ensure product quality because casting can easily remove the beneficial effects of the refining process conducted during the development of the steel melt by contamination with refractory material from the casting assembly, re-oxidation of the metal bath and others. Depending on the complexity of the casting product and to obtain a superior quality product, several methods of casting have been developed. The usual method of casting high quality large ingots is in vacuum, the advantage is that the steel stream is protected from the surrounding atmosphere, this paper aims to highlight the benefits of vacuum casting with wide stream on the improvement of ingot quality by increasing purity and decreasing gas content. [ABSTRACT FROM AUTHOR]

Abstract: A vacuum casting method to replicate shark skin surface accurately in large area was investigated to overcome some difficulties in the replication process. The fresh shark skin was pretreated as a replication sample, and the replication mold of shark skin was manufactured by casting the unsaturated polyester resin under vacuum and laying the multilayer glass fibers. Under vacuum condition, silicone rubber was poured into the resin mold to obtain the replication film of the shark skin with micro-riblets. The contour of the micro-riblet was measured by a Talysurf CLI2000 machine to evaluate the replication accuracy. Based on the contacting angle measurement, the hydrophobic property of the micro-riblet''s surface was investigated. It was found that the vacuum casting method was an effective replication technology which was suitable to form large-area and highly accurate micro-riblets on the surface of the shark skin. The experiment of drag reduction was conducted in a water tank. Based on the experimental results, the replicated film of shark skin played a significant role in reducing drag. The maximum and minimum of drag reduction rate were 18.6% and 9.7%, respectively. [Copyright &y& Elsevier]

Abstract: An innovative dry electroencephalography (EEG) electrode has been successfully designed and tested, in which multiple micro-spike electrodes, each of them consisting of a micro-pillar with a micro-tip on top of it, were designed to pass through the hairs and establish electrical conduction at the skin-electrode interface by penetrate into the stratum corneum of the skin. For hygiene reasons, such electrodes should be made disposable, at the same time, should be cost effective. Therefore, a mass production technology, including the processing methods, such as casting, has to be designed and developed. In this project, the micro-spike dry electrodes were fabricated by a vacuum casting method using a master pattern piece made by CNC micro-machining, in which silicone rubber moulds are created and then used to vacuum cast polyurethane (PU), epoxy or epoxy-carbon micro-spike electrodes. In order to obtain a harder polymeric material, varying amount of carbon fillers were added to the epoxy resin, and the hardness of the resulting material were measured and compared. It was found that a higher concentration of added carbon fillers resulted in a harder cast polymer composite. Further to the vacuum casting, to create an electrically conductive layer on the vacuum-casted electrode, an Ag/AgCl electroless deposition method has been developed. The sputtering of the conductive layer was also carried out for comparison. The developed micro-spike electrodes showed better performance in terms of the impedance level and stability as well as a much higher efficiency in EEG measurement. [Copyright &y& Elsevier]

Micromoulds are generally produced by lithography methods that often use glass and silicon wafer as substrates, with the exception of the Lithographie Galvanoformung Abformung (LIGA) method, which uses metal substrate. These fabricated moulds are then integrated into the injection moulding machine for mass production. This paper presents the use of vacuum casting methods to produce micromoulds instead of lithography. Silicone rubber is used as the mould material, which is capable of achieving nanometre surface finish. The master pattern of 1-mm diameter microgear of 60-μm teeth width and 38-μm thickness was created by standard ultraviolet (UV) lithography using SU8 photoresist. Using the vacuum casting method, ten polyurethane microgear specimens of 1-mm diameter and 38-μm thickness using the silicone rubber micromoulds have been successfully cast under vacuum conditions as a demonstration. Measurement from white-light interferometry (WLI) showed that all of the microgear cavities in the micromoulds were dimensionally accurate and consistent to the master microgear, proving that its repeatability is possible. [ABSTRACT FROM AUTHOR]

Abstract: A micro-mould fabrication method based on vacuum casting was developed and its functionality and reproducibility were demonstrated. The micro-components used in this study were SU-8 photoresist micro-gears fabricated by UV photolithography. These micro-gears served as the master patterns from which silicone rubber micro-mould cavities were fabricated with the use of the vacuum casting technology. The process parameters that had an influence on the quality of the micro-mould cavities were identified and optimised. Using the optimised process parameters resulted in high fidelity silicone rubber micro-mould cavities at high resolutions. Dimensional analysis was carried out using white light interferometry. It was found that all the micro-gear cavities in the micro-moulds were dimensionally accurate and consistent to the master gear, with a dimension deviation less than 3% of the respective dimensions. Micro-casting was also carried out using the silicone rubber moulds. Micro-gears were successfully transferred from the silicone rubber moulds into PU resin and wax pieces under vacuum conditions, thereby demonstrating that the micro-mould fabricated was capable of producing functional micro-parts that were able to replicate micro-features. [Copyright &y& Elsevier]

Abstract: The present work concerns the hardware development of a mid-size humanoid robot, Bonobo, focusing on the use of an integrated application of CAD/CAM/CAE and rapid prototyping (RP) for the rapid development of the robot''s outer body parts. Most parts were three-dimensionally designed with 3D CAD, which enables effective connection with CAE analyses, the basis of which lays in kinematic simulation and structural analysis. To reduce the lead time and investment cost of developing parts, RP and CAM are selectively used to manufacture master parts for the body. These master parts are then replicated by using a vacuum casting process, from which we can repeatedly obtain plastic parts. Through this integrated approach, we successfully developed a prototype of Bonobo with a relatively low time and investment cost. [Copyright &y& Elsevier]