Investment Casting Research Articles

The role of additive manufacturing in the investment casting process

The aim of this study was to systematically describe the additive manufacturing (AM) technologies used for various casting technologies and how rapid investment casting (RIC) is changing the field of casting. The capability and effectiveness of additive manufacturing to provide investment casting production solutions has been investigated. The traditional investment casting method is less efficient in terms of cost and time to develop new wax models of solid tooling for low volume production or prototypes. To overcome this problem, it is proposed to introduce additive manufacturing to these processes to produce investment casting models. This paper discusses specific applications of rapid prototyping in this area. The study concluded that the use of additive manufacturing for investment casting instead of the traditional method is more cost- and time-efficient. Terms and designations: RP – Rapid Prototyping, IC, RIC –(Rapid) Investment Casting, PM – Project Manager, AT – Additive technologies, AM – Additive manufacturing

Core shifting prediction in filling process of hollow turbine blade investment casting

Ceramic core shifting during the filling process of investment casting is one of the key factors that influence the wall thickness accuracy of hollow turbine blades. Although plenty of study has conducted to analyze and control the wall thickness accuracy, the mechanism of core shifting has rarely taken much attention. To fill this gap, this paper firstly analyze the movement of ceramic core under the casting condition combining computational fluid dynamics and motion simulation. Then, the shifting mode and final position of ceramic core were predicted based on the time-varying load in investment casting filling process. Afterwards, a casting experiment was conducted to verify the proposed prediction method and the results show a good match. In addition, a wax pattern reverse compensating approach was devised and validated based on the prediction result. After correction, the maximum displacement of the ceramic core has lowered by 51.6 %, indicating that the suggested approach is successful in improving the wall thickness accuracy.

Simulation of the solidification organization of X15CrNiSi20-12 alloy castings during investment casting based on the CAFE model

In this work, the CAFE (Cellular Automata Finite Element) model was used to simulate the grain growth of X15CrNiSi20-12 austenitic stainless steel during the investment casting process, and the effects of shell thickness, shell temperature, casting temperature, and cooling rate on the solidification organization were investigated by orthogonal tests. The results show that the cooling method has an important effect on the formation of equiaxed crystals. However, the shell temperature, shell thickness, and casting temperature have a smaller effect on the formation of equiaxed crystals. A more equiaxed fine grain structure can be obtained by using a shell thickness of 7 mm, shell temperature of 1143.15 K, casting temperature of 1913.15 K, and water-cooling conditions. In addition, a decrease in the shell thickness, shell temperature, and casting temperature can lead to an increase in the grain size, while an increase in the cooling rate will lead to smaller grain size and increase the number of equiaxed fine crystals, thus improving the mechanical properties of the material.

Rapid Prototyping and Tooling Technology to Assist the Development of Low-Cost Dies

This case study aims toward the importance of the application of rapid prototyping and tooling technology in die design and manufacturing. Many conventional machining processes of die manufacturing, including computer numeric control (CNC) machining and electric discharge machining (EDM), are used by the local manufacturers of die, but these processes are time-consuming and expensive. There is a need to explore opportunities to reduce die manufacturing costs. This paper aims to assist the development of low-cost dies through the application of rapid prototyping and tooling technology. For this purpose, solid works software was used to design the die of a 4-hole Lego Block. 3D printing was incorporated in the existing capability of investment casting process for die manufacturing. A proper gating system design consideration was taken into account to ensure the accurate flow of casting material for achieving fine surface finish. From the results, it has been observed that gating system design with four ingates gives the optimum value of surface finish (~3.4156μm). The proposed rapid prototyping and tooling technology makes the practitioners (tool makers) capable of making dies with complex shapes, superior surface finishes, and dimensional accuracy in less or no time.

Effects of process parameters on friability and surface quality in the rapid investment casting process

Effects of process parameters on friability and surface quality in the rapid investment casting process

Rapid prototyping of wax models for investment casting

This article discusses making wax models for precision casting technology. Our chosen method of making these prototypes consists in printing the positive of the model on 3D printer, which is then molded into rubber. The resulting rubber mold is used for casting the wax models. The focus of the article is mainly on the quality, speed, and accuracy of making wax models, while they will be compared with commonly produced wax models.

Analytical modeling of quality parameters in casting process – learning-based approach

PurposeFoundry produces cast metal components and parts for various industries and drives manufacturing excellence all over the world. Assuring quality of these components and parts is vital for the end product quality. The complexity in foundry operations increases with the complexity in designs, patterns and geometry and the quality parameters of the casting processes need to be monitored, evaluated and controlled to achieve expected quality levels.Design/methodology/approachThe literature addresses quality improvement in foundry industry primarily focusing on surface roughness, mechanical properties, dimensional accuracy and defects in the cast parts and components which are often affected by numerous process variables. Primary data are collected from the experts working in sand and investment casting processes. The authors perform machine learning analysis of the data to model the quality parameters with appropriate process variables. Further, cluster analysis using k-means clustering method is performed to develop clusters of correlated process variables for sand and investment casting processes.FindingsThe authors identified primary process variables determining each quality parameter using machine learning approach. Quality parameters such as surface roughness, defects, mechanical properties and dimensional accuracy are represented by the identified sand-casting process variables accurately up to 83%, 83%, 100% and 83% and are represented by the identified investment-casting process variables accurately up to 100%, 67%, 67% and 100% respectively. Moreover, the prioritization of process variables in influencing the quality parameters is established which further helps the practitioners to monitor and control them within acceptable levels. Further the clusters of process variables help in analyzing their combined effect on quality parameters of casting products.Originality/valueThis study identified potential process variables and collected data from experts, researchers and practitioners on the effect of these on the quality aspects of cast products. While most of the previous studies focus on a very limited process variables for enhancing the quality characteristics of cast parts and components, this study represents each quality parameter as the function of influencing process variables which will enable the quality managers in Indian foundries to maintain capability and stability of casting processes. The models hence developed for both sand and investment casting for each quality parameter are validated with real life applications. Such studies are scarcely reported in the literature.

Achieving ultra-high strength in Be/Al composites by self-exhaust pressure infiltration and hot extrusion process

Beryllium particle reinforced aluminum matrix (Be/Al) composite with exceptionally high strength was fabricated from Be debris by self-exhaust pressure infiltration and hot extrusion process. The microstructures characteristics and mechanical properties of the Be/Al composite at as-cast and as-extruded state were systematically investigated in the current study. It was found for the as-cast composite that uniform distribution of beryllium particles with average size of 2.2 μm were achieved, the microcracks in beryllium particles were repaired in situ by infiltrating liquid aluminum into these microcracks under external pressure. The Be phase and Al phase were well bonded despite the presence of nano BeO at the interface. After hot extrusion, the beryllium particle deformed and elongated along the extrusion direction. The average grain size of Al was refined from hundreds of microns to 450 nm, and the dislocation density increased significantly. The tensile strength and yield strength of Be/Al composite reached 595 MPa and 494 MPa by hot extrusion, respectively. The ultra-high strength was mainly related to grain boundaries strengthening, dislocation strengthening, precipitation strengthening and load transfer strengthening. Compared with the composites prepared by the investment casting and powder metallurgy methods, the Be/Al composite showed more than 100% increment in strengthening efficiency and 80% increment in yield strength. It indicated that the self-exhaust pressure infiltration technology combined with hot extrusion process was a feasible and successful method to prepare high performance Be/Al composites.

Experimental and Simulation Analysis on the Mechanical Behavior of 3D‐Enhanced Al‐Based Tetrahedral Lattice Materials

Herein, the compressive mechanical behavior of novel 3D tetrahedral lattice materials is investigated by ways of experimental, numerical, and analytical methods with a good performance of accuracy. Samples with varied length–diameter ratios are fabricated through 3D printing combined with investment casting method. The compressive behavior, deformation characteristic, and energy property of the lattice materials are comprehensively recorded and analyzed with respect to the geometric parameter and compression directions. It is observed that the length–diameter ratio exhibits a significant influence on the mechanical performance and energy absorption of the materials, that is, the lower the length–diameter ratio, the higher the relative density, strength, and energy absorption. Good agreements are observed among the experimental, numerical, and analytical results within a relative acceptable error. Moreover, the mechanical properties and deformation characteristics of lattice materials depend on compression directions to a great extent. In addition, the novel tetrahedral lattice materials with reasonable relative density present superior performance features compared with the other cellular materials.

Investigation of the Biocompatibility of Laser Treated 316L Stainless Steel Materials

In this study, 316L stainless steel materials, which are widely used in the industry, were produced by investment casting management. Depending on the microstructure, the hardness values constitute an important stage of the properties that can be developed and controlled. For this purpose, the differences between the microstructure and hardness properties of 316L stainless steel, which is produced by the investment casting method, and 316L stainless steel, which is currently used commercially, were examined. The changes caused by the fiber laser on the surface of 316L materials produced with two different production methods were examined. It was observed that the laser used made different changes in the surface structure of the 316L material produced by both methods. Since the surface of the material is a buffer between body fluids and biomaterial, it is known that there is a relationship between surface properties and biocompatibility. In this study, the L929 cell growth test, one of the cytotoxicity tests, was applied and thus, how laser surface treatment affects the biocompatibility of 316L materials produced by both methods was comparatively examined.

Viscosity of fused silica suspensions for investment casting

Проведено исследование вязкости суспензий, применяемых при литье по выплавляемым моделям, как одного из самых важных свойств. Представлены результаты измерений вязкости суспензии на основе этилсиликата и плавленого кварца разных фирм-производителей. В ходе работы сделаны выводы о необходимости проведения входного контроля суспензий на литейных предприятиях.

Experimental simulation of volumetric compacts formation from spherical waxy elements

The growth in metal intensity of industrial production and the volume of consumption of finished metal products determine the relevance of development and research of energy efficient technological processes aimed at reducing costs by reducing the number of operations while maintaining product performance. In mechanical engineering, the problem of obtaining blanks with increased dimensional and geometric accuracy and complex configuration is solved by using a common method of investment casting. Expansion of the use of such technological approach to produce blanks in mechanical engineering is hindered by a number of physical phenomena associated with the thermal expansion of investment and ceramic materials, which leads to an increase in the product final cost. A significant number of defect-forming factors can be eliminated by applying an innovative solution consisting in the formation of porous removable models by compacting mixtures based on waxy materials. This solves the problem of material shrinkage and increases the crack resistance of ceramic molds, which significantly reduces the share of machining in the overall volume of technological operations. Technical tests of the new method have revealed the reason why the machining of castings cannot be completely eliminated at present. The problem mainly lies in elastic response of compacted material of the model mixture, which, in some cases, affects the increase in the compacts size. This paper considers the effect of initial packing of spherical-shaped elements simulating one- and two-component model mixtures on the stress-strain state of a powder body subjected to unilateral compaction in a rigid cylindrical matrix to technologically justified density values. The results of the experiment are presented in the form of stress-strain relations. Preferable conditions of compact formation with minimal values of elastic response of the compacted material are considered.

Impacts of the Additive Manufacturing Process on the Roughness of Engine Scale Vanes and Cooling Channels

Abstract By leveraging the additive manufacturing (AM) platform, development time and costs for turbine component testing can be reduced relative to traditional investment casting. Surface roughness is a key characteristic of the additive manufacturing process that can impact flow, heat transfer, and mechanical integrity of printed components. There are multiple design and build considerations that result in variability in surface roughness, especially when additively fabricating complicated three-dimensional vanes and internal cooling passages. This study characterizes the surface roughness of internal cooling passages, vanes, and flat external surface samples made using additive manufacturing, specifically the direct metal laser sintering process. The samples were manufactured with various wall thicknesses, layer thicknesses, build locations, build directions, and on different AM machines. A combination of computed tomography scanning and optical profilometry was used to evaluate surface roughness levels. The data indicate that the dominant factors in roughness for a given layer thickness are a function of wall thickness, build location, and build direction.

Flexible Investment Casting Wax Patterns for 3D-Printing: Their Rheological and Mechanical Characterizations.

The mechanical and rheological characterizations of flexible investment casting patterns capable of 3D printing are reported. The wax pattern was composed of microcrystalline hydrocarbon wax (DMW7478), Piccotex 75 (a copolymer of α-methyl-styrene and vinyl toluene with a 75/25 molar ratio, respectively) and Escorene (a copolymer of ethylene and vinyl acetate with a 72/28 mass ratio, respectively). It was found that in order to obtain a wax pattern with appreciable mechanical properties, the content of the microcrystalline hydrocarbon wax in these blends should not exceed 30% (m/m). Thus, a series of patterns with 28% (m/m) wax and varying Piccotex and Escorene contents spanning from 0 to 72% (m/m) was prepared. The dependence of the dynamic viscosities of the wax patterns on the composition was described using a stretched exponential model, whereas their variations with the temperature were interpreted in terms of the Arrhenius-Guzman equation. Furthermore, the slopes of the lines fitted to the viscosity versus temperature curves at the pour point decreased linearly with the Piccotex content. Non-Newtonian changes in the shear stress with the shear rate and shear stress crystallization were observed at temperatures near the pour points. The mechanical properties were evaluated using the uniaxial tensile mode and by three-point bending experiments. It was found that the stress (σ) versus the relative elongation (ε) curves can effectively be rendered by means of the standard linear solid (SLS) viscoelastic model. In addition, it was also established that the Young's modulus varied according to a sigmoid-type curve with the piccotex content, while the yield stress decreased linearly with the concentration of Piccotex. In addition, based on the spooling suitability and printability, the patterns were rated and it was found that the most appropriate wax pattern compositions for 3D printing were those which contained 30% (m/m) and 35% (m/m) Piccotex.

Surface characteristics and high cycle fatigue behaviors of Ti47Al2Cr2Nb alloy subjected to different surface processes and thermal exposure

The Ti47Al2Cr2Nb alloy fatigue specimens were prepared by investment casting, and three kinds of surface processes were applied to fatigue specimens. These three processes were sand-blasting (SB), sand-blasting and shot-peening (SBSP) and sand-blasting and mechanical grinding (SBMG). The surface characteristics before and after thermal exposure at 700 °C for 24 h were investigated. The high cycle fatigue behaviors of specimens after thermal exposure were evaluated. The results showed that the surface roughness (Ra) values after SB, SBSP and SBMG processes were 1.71, 0.99 and 0.06 μm, respectively. After thermal exposure, they increased slightly for all three processes. The SB process caused work hardening in the near-surface region and the work hardening reached saturation after the SB process. Due to the mechanical grinding process removing an uncertain thick hardening layer, the maximum hardness after SBMG process was noticeably lower than those after SB and SBSP processes. After thermal exposure, the maximum hardness after all three processes significantly recovered. Deformed layers were formed beneath SB and SBSP surfaces. After thermal exposure, a depth-dependent gradient microstructure was formed in the surface layer. The SBMG specimens had the highest fatigue limit of 350 MPa. This was attributed to the SBMG specimens having very smooth surfaces and keeping some work hardening in the surface layers. The fatigue fractures were typical brittle cleavage fractures. The fracture modes included interlamellar and trans-lamellar fractures. The dislocation slip and mechanical twins were the main deformation mechanisms.

Morphological structure of shell mould in investment casting

The stress state (SS) of multilayer shell mould (SM) is significantly influenced by its morphological structure, its variants, and the connections between the contacting layers. The purpose of this work is to establish the effect of sliding without friction of one of the layers of SS relative to the neighboring contacting layer on SS of the multilayer SM. The process of determining the stress-strain state (SSS) in the SM is modeled when it is filled with steel, in which there is a surface between the layers, where one layer of the SM is completely sliding relative to the adjacent neighboring layer. The task is to find the geometric location of a given surface by thickness of SM from the condition of the formulated objective function with the corresponding system of constraints. The construction of the mathematical model is based on equations of the linear theory of elasticity, the equations of thermal conductivity, solution of which is carried out by a proven numerical method. In the axisymmetric formulation, a complex three-component system is considered: liquid metal, solid metal, ceramic SM. Solid metal and SM are considered to be isotropic. Crack resistance of the SM is estimated by the stresses arising in it. On contact with the support filler (SF), it is possible to move the SM surface from the SF during the liquid metal cooling. In this case, the contact problem is solved – reassignment of the boundary conditions. An algorithm for solving the problem is compiled. The results of numerical modeling are displayed graphically in the form of plots. A detailed analysis of the obtained results was carried out. The inconsistency of manufacturing such a multilayer mould is shown. The results of the research can be useful in calculations of other functional multilayer shell systems.

Large Scale Vat-Photopolymerization of Investment Casting Master Patterns: The Total Solution.

The material properties and processing of investment casting patterns manufactured using conventional wax injection Molding and those manufactured by vat photopolymerization can be substantially different in terms of thermal expansion and mechanical properties, which can generate problems with dimensional accuracy and stability before and during ceramic shelling and shell failures during the burn-out of the 3D printed casting patterns. In this paper and for the first time, the monofunctional Acryloyl morpholine monomer was used for 3D printing of casting patterns, due to its thermoplastic-like behavior, e.g., softening by heat. However, the hydrophilic behavior of this polymer led to an incorporation of up to 60 wt% of Hexanediol diacrylate, to control the water absorption of the network, which to some extent, compromised the softening feature of Acryloyl morpholine. Addition of a powdered wax filler resulted in a delayed thermal decomposition of the polymer network, however, it helped to reduce the thermal expansion of the parts. The dimensional accuracy and stability of the wax-filled formulation indicated an excellent dimensional tolerance of less than ±130 µm. Finally, the 3D printed patterns successfully went through a burn out process with no damages to the ceramic shell.

Technological Insights into the Evolution of Bronze Bell Metal Casting on the Korean Peninsula

Bronze cast bells have been designed and developed for hundreds of years, with the worldwide spread of several faiths and religions such as Buddhism, Catholicism, and Protestantism. The exceptional ringtones of bronze bell metals have scientific healing and cultural importance. In this review article, we highlight the evolution of bronze bell metal over the decades, its composition, and the complex fabrication technologies used to date. Furthermore, we overview ancient and modern casting alloy technology, especially bronze bell castings in Asia. The bell shape, materials, and alloy casting technology have undergone dramatic change over the years. For comparison, we include different bronze cast bells and their characteristics produced from the Middle Ages to the present times. Based on the data obtained from the bell casting technology surrounding the Korean Peninsula, the major trends in the evolution of bronze bell castings and long-standing traditions of mold materials and alloys are described. In the present review, the effects of different elements on bell materials are qualitatively overviewed, with an assessment of the material and casting properties, service life, and bell sound. We also highlight the challenges of conventional bronze casting and possible solutions for future investment castings and rapid prototyping of bronze bells.

Orthodontic Bracket Friction Affected by Design Selection Material and Manufacturing Process

One of the problems in orthodontic treatment is friction. Some of the factors that support friction are archwire material, archwire dimensions, bracket material, surface roughness, type of ligation, environmental humidity, and bracket position, angulation angle between bracket and wire, changes in the surface of the archwire and bracket. The aim of this study is to analyse the difference in friction between the two branded bracket designs and a new patented bracket (patent no. IDP000069597). The production method for this new bracket is different, however, uses the same material of 17-4 PH stainless steel. There are three groups in this research, one sample of bracket each from two different branded and one sample of a new bracket design. All three groups were tested for microstructure, then tested for measurement of friction between bracket slots and archwire. The microstructure of the two branded brackets has a martensitic phase that is not as dense as the new bracket, which is due to the different manufacturing method processes. The two branded brackets use the metal injection molding method, while the new brackets use the investment casting method. The friction test results show that there are significant differences between the three groups of brackets. One of the branded brackets (A) has the lowest friction, but branded bracket (B) does not have different friction with the new bracket. Differences in design and manufacturing methods of orthodontic bracket affect the friction between orthodontic brackets and archwires even though they use the same material.

New process solutions in the manufacture of thermochemically resistant ceramic molds for casting titanium alloys

The paper provides the results of studies on interaction between titanium melts and silica-containing investment molds. Pure silicon, compounds of titanium oxides and silicides were detected by X-ray diffraction analysis in the contact zone. The problem of the negative impact exerted by the mold on the casting is solved by using thermally stable and chemically resistant monocorundum molds based on an alumina sol binder. A refractory suspension was developed for investment casting containing special additives to improve wax mold wetting with the suspension, and to increase the mold shell strength. The article studies sedimentation properties of suspension. A method was developed for accelerated curing of sequentially applied refractory suspension layers by vacuum drying and subsequent chemical curing with a gaseous reagent. The formation time is reduced from 3–5 h to 20–30 min per layer. Comparative studies of kinetics of alumina sol binder convective drying and vacuum dehydration were conducted. The process of moisture removal per unit surface of the applied refractory layer in a vacuum of 5–10 kPa increases by 2–6 times. X-ray phase analysis was used to study the alumina sol conversion during high-temperature heating. The solid gel of the α-Al2O3 stable phase is obtained in the alumina sol mold shell when the calcination temperature rises to 1300–1350 °C with a sufficient strength of 9–12 MPa provided by sintering additives added to the suspension. Recommendations are given for additional protection of refractory ceramic layers after vacuuming and drying: treatment of the last layer with gaseous curing agents and application of a polyvinylacetal solution with a density of 1100–1200 kg/m3. The process solutions proposed will make it possible to increase both the efficiency of titanium alloy forming and casting processes and the quality of castings.