Investment Casting Process Research Articles

Nickel–titanium shape memory alloy mechanical components produced by investment casting

This work aimed to produce mechanical components of nickel–titanium shape memory alloys using investment casting processes. Then, in order to validate processing, different designs of nickel–titanium shape memory alloy components as staple implants, Belleville springs, meshes, helical springs, screws and hexagonal honeycombs were produced and submitted to thermal and mechanical characterization. Thermoelastic martensitic transformation of the nickel–titanium shape memory alloy parts was determined by differential scanning calorimetry and electrical resistance with temperature, while the superelastic behaviour was verified by cyclic tensile and compression tests. It has been demonstrated that the employed investment casting processes are suitable to manufacture nickel–titanium shape memory alloy mechanical components with simple and complicated designs as well as functional properties related to phase transformation and superelasticity.

Characterization of A356 investment cast component produced using controlled liquid metal cooling technique

In this work Controlled Liquid Metal Cooling (CLMC) integrated in gravity investment casting process is evaluated in order to minimize the internal defects and subsequently improve the casting yield and mechanical properties. A356 was cast and cooled using conventional air cooling and controlled liquid metal cooling technique. Optical light stereo-microscopy, optical light microscopy, scanning electron microscopy equipped with energy dispersive x-ray scope and tensile tests were performed to investigate internal defects, microstructural features, grain sizes, shapes and performance. Microstructures of CLMC sample showed modified eutectic structure with spherical, dendritic primary alpha grains and reduced shrinkage porosity. Mechanical properties of CLMC are competitive to conventional air cooled samples.

Numerical simulation for the investment casting process of a large-size titanium alloy thin-wall casing

To optimize the investment casting process when producing high quality large-size titanium alloy thin-wall components is a time-consuming job due to the complicated metallurgical process. Numerical simulation is a high-efficiency method compared with trial and error, and therefore is introduced to the investment casting process optimization to shorten the new product development cycle and reduce the production cost. In this study, weakly compressible model (WCM) and ununiformed finite difference mesh (UFDM) was developed to reduce the memory consumption and ensure the simulation efficiency. The precision of the WCM and UFDM were verified by numerical simulation of cavity heat convection in a square cavity and hydraulics simulation of centrifugal filling in a transparent cavity. The numerical simulation of the investment casting process of a titanium alloy thin-wall casing under different process conditions was accomplished using a self-developed software, and the distribution characteristics of potential shrinkage defects were predicted. It was found that the predicted defects in the titanium alloy casing matched well with the actual X-ray experimental results. For the components investigated in this paper, more numerical simulation results show that the centrifugal casting process with respect to gravity casting had no obvious improvements in the concentrated shrinkage defects, and the gravity casting process can be more reasonable from the engineering point of view.

Design and Improvement of the Investment Casting Process for the Ring-shaped Aluminum Alloy based on PROCAST software

The investment casting process of a ring-shaped ZL101 alloy is investigated based on PROCAST software, the alloy phase diagram and the thermophysical properties are analyzed. Besides, the initial casting temperature and the casting process were determined. After the analysis of the geometry model and temperature field model during the casting solidification process, results shows as: 1) the shrinkage and porosity is formed at the two sides and bottom end of casting pieces in the initial casting process, while slag inclusion is enriched at the top. 2) To avoid these two kinds of defects, the casting process is optimized and simulated. The simulated result is in compliance with the experiment, the agreement confirm that the improved process is reasonable. 3) The improved casting process is finally designed and the simulation shows that the experiment is in good agreement with the simulation results, which provides the actual guidence for the design of other casting pieces as well.

B-spline contour curve approximation and deformation analysis of complex ceramic core

Complex ceramic core is the critical part for manufacturing hollow turbine blade in the investment casting process. The complex geometry, small inner structures and high-precision requirements of ceramic cores make them difficult to fabricate, and the shape and dimensional accuracy of ceramic cores are very low in factory practice. To understand the deformation characteristics of ceramic cores, a noisy points recognition algorithm, an extraction method of measuring cross-section contour points and a B-spline iterative fitting algorithm using dominant points of chord deviation are proposed. First, the cross-section contour points were provided through registration, slicing and intersection methods. Second, the noisy points were deleted by convex noisy points and concave noisy points recognition algorithms. Third, the cross-section contour curve of the ceramic core was fitted through B-spline iterative fitting method with chord deviation dominant points. The curves fitted with chord deviation points and curves fitted with local maximum curvature points were compared with simulating data and scanning data, respectively, and the results show that B-spline fitting curve needs fewer chord deviation points than local maximum curvature points, 24.4% fewer in simulation validation and 12.5% fewer in experimental validation. In the end, the bending deformation, torsion deformation and shrinkage deformation errors of ceramic core are established by fitting contour curves of serial cross sections of the ceramic core.

Investigations for mechanical properties and biocompatibility of SS-316L implant prepared as rapid investment casting for batch production

In this work, a detailed procedure for the development of biomedical implant (SS-316L) by combining fused deposition modeling (FDM), chemical vapor smoothing (CVS), silicon molding (SM) and investment casting (IC) for batch production has been outlined. In spite of being biocompatible and bioactive within the body, the implant must possess good surface quality and dimensional accuracy along with sufficient hardness in order to reduce the wear inside the body. So in this research work, investigations have been made on the surface finish, dimensional accuracy and hardness of the implants by varying two controllable factors of the IC process (drying time of primary coating and mould thickness). The tolerance grades for the selected dimension of the casted implants were within the allowable range as defined in UNI EN 20286-I (1995) standard of ISO. The process capability indices (Cp and Cpk) values greater than 1.33 for the surface hardness and radial dimension indicated that the proposed process is statistically controlled. Further, in order to evaluate the biocompatibility, an in vitro study was conducted to ensure the attachment of mouse embryonic fibroblasts cells (NIH-3T3) to the casted samples. The results of invitro study indicated that samples were capable of supporting cell adhesion and cell proliferation and hence can be used for tissue engineering.

Formulations, development and characterization techniques of investment casting patterns

Abstract Conventionally, unfilled wax has been used as a universal pattern material for the investment casting process. With increase in demand for accurate dimensions and complex shapes, various materials have been blended with wax to develop more suitable patterns for investment casting in order to overcome performance limitations exhibited by unfilled wax. The present article initially reviews various investigations on the development of investment casting patterns by exploring pattern materials, type of waxes and their limitations, the effect of filler materials and various additives on unfilled wax, wax blends for pattern materials, plastics and polymers for pattern materials and 3D-printed patterns. The superiority of filled and polymer patterns in terms of dimensional accuracy, pattern strength, surface and flow properties over unfilled wax is also discussed. The present use of 3D patterns following their versatility in the manufacturing sector to revolutionize the investment casting process is also emphasized. Various studies on wax characterization such as physical (surface and dimensions), thermal (thermogravimetric analysis and differential scanning calorimetry), mechanical (thermomechanical analysis, tensile stress testing, dynamic mechanical analysis) and rheological (viscosity and shearing properties) are also discussed.

Microstructure of As-cast Co-Cr-Mo Alloy Prepared by Investment Casting

The microstructure of a cobalt-base alloy (Co-Cr-Mo) obtained by an investment casting process was studied. This alloy complies with the ASTM F75 standard and is widely used in the manufacturing of orthopedic implants owing to its high strength, good corrosion resistance, and excellent biocompatibility. This work focuses on the resulting microstructures arising from normal industrial environmental conditions. The characterization of the samples was carried out using optical microscopy, field emission scanning electron microscopy and energy-dispersive spectroscopy. In this study, the as-cast microstructure is an γ-Co (face-centered cubic) dendritic matrix with the presence of a secondary phase, such as M23C6 carbides precipitated at grain boundaries and interdendritic zones. These precipitates are the main strengthening mechanism in this type of alloy. Other minority phases, such as the σ phase, were also detected, and their presence could be linked to the manufacturing process and environment.

Shell Mould Strength of Rice Husk Ash (RHA) and Bentonite Clays in Investment Casting

Investment casting process (IC) plays a major role in the modern manufacturing process in providing an economical means of mass production components with intricate shape and complex geometry as demand in various crucial applications including aerospace, automotive, military, biomedical and others. This casting technique, develop shell mould fabrication by coating the required pattern with a refractory mixture which offers the complex geometrical shape and sizes parts to be cast. However, the modern IC approach in shell mould production suffers from zircon’s cost and supply instability as it is the main material to be used. Zircon uses as refractory filler for slurry production, and also in the form of sand used as stucco particles, is favoured by the investment casting facilities and industries as it exhibits the most versatile properties such as low thermal expansion and low reactivity to the metal to be cast. During the period of zircon supply shortage, many facilities introduce several alternatives. Currently, the step taken to reduce the cost of primary slurry material is by using some alternate refractory material like, alumina, silica, to be used with zircon for shell mould production. In relation to that, several researches continue to search for alternatives approach for shell mould materials. This research introduces the alternative method in fabricating investment casting shell mould as recognized from investment casting industry located in Sungai Puar of Bukittingi Padang Indonesia. This industry employs several local resources to fabricate the shell mould. These materials consist of rice husk ash (RHA), and two types of bentonite clays. The bentonite clays were obtained nearly from Kota Payakumbuh in the western provinces. However, this industry suffers from weak shell mould strength and need to be investigated and consulted. In this paper, the investigation on shell mould strength made from rice husk ash (RHA), and bentonite clays were conducted. The strength was measured by its modulus of rupture (MOR) performed in 3 points flexural bending test. The green and fired shell mould strength was determined from five type of slurry composition. The results revealed that the highest green and fired strength obtained were 0.157 MPa and 0.361 MPa from shell mould sample C of RHA (46%) and bentonite (54%) of its composition.

A shrinkage prediction method of investment casting based on geometric parameters

During investment casting process, the design of die cavity is the key factor to ensure the dimension accuracy of casting. The design principle of die cavity is based on computer-aided design model of casting. However, the casting will shrink in the die cavity with the decrease of temperature. Thus, the finalized design of die cavity is determined by the shrinkage and computer-aided design model of casting. It is necessary to predict the shrinkage of casting. A prediction method which based on adaptive learning idea of BP artificial neural network and construction of mapping model idea of regression method is proposed in this paper. The method is used for predicting shrinkage of casting. In this method, a series of I-beam castings that were divided into training samples and testing samples are designed for casting experiment and shrinkage measurement. Training samples are used for building shrinkage prediction model. Testing samples are used for verifying accuracy of the shrinkage prediction model. The results show that the shrinkage prediction method has higher fitting precision than regression method in fitting these training samples. Besides, for the training and testing samples, the prediction accuracy has positive correlation with fitting precision. The shrinkage can be well predicted by the prediction method through the known geometric parameters of computer-aided design model of casting.

Research progress on refractory composition and deformability of shell molds for TiAl alloy castings

At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.

Estimation of Shrinkage & Distortion in WaxInjection using Moldex3D Simulation

The dimensional and geometrical accuracy of wax patterns used in the investment casting process has a direct effect on the quality of the final casting. Wax patterns are produced by injecting wax in the die cavity. The quality of wax patterns depends on the injection parameters. The objective of the paper is to analyze the influence of various injection parameters on the dimensional deviations of the component. Predicting the shrinkage and warpage associated with the wax injection process helps in avoiding costly and time consuming iterations involved in die design and development. Simulation of wax injection in the die cavity provides insight in the flow process in terms of weld lines, air trap, drop in temperature and pressure during filling, packing and cooling stages of the process. The stresses developed in the component is estimated which determines the warpage in the component.

Analysis of Shrinkage & Warpage in Ceramic Injection Molding of HPT Vane Leading Edge Core of a Gas Turbine Casting

Gas Turbines in Aerospace applications operate at extreme conditions of temperatures and stresses. The Blade/Vane components of these turbines have sculpted, twisted and hollow aerofoil geometry made using Nickel based super alloys through the investment casting process. Hollow wax patterns produced with use of ceramic cores are the first input to the investment casting process. The quantification and prediction of dimensional deviations due to shrinkage & warpage, which are dependent on injection parameters, shape of part and gating system adopted, is mandatory to arrive at acceptable tooling and castings. The insight of flow pattern in the die cavity imparts knowledge of possible weld lines, air-trap, jetting etc. The gating system may be designed, based on simulation results, to minimise such defect. The effects of injection molding parameters such as holding time, packing pressure and melt temperature on shrinkage and warpage of green part using moldex3D software are studied in this paper

Prediction of shrinkage allowance for tool design of aluminium alloy (A356) investment casting

Investment casting process has been adopted by the industries to produce castings having good surface finish, complex shape and better dimensional accuracy. Gradually, dimensional tolerance is decreasing day by day to reduce the overall weight of the casting. Manufacturing of dimensionally stringent investment casting products require number of shop floor trials and pattern die/tool rework to produce castings with acceptable dimensional tolerance. This is because of uneven shrinkage of a casting during the solidification process in complex shape castings. In this paper shrinkage allowances were determined for H-shape investment casting made up A356 alloy. Experiments were conducted for three types of H-shape castings (small, medium and big). There are two types of shrinkage (free and restricted) has been identified and determined for H-shape casting. The dimensions of die tooling, wax pattern and casting were measured, in order to determine the actual shrinkage allowance for the die. The results revealed that the shrinkage percentage of free and restricted solidification areas is different. However, both shrinkage allowance factor is linear in nature. Further, the shrinkage pattern at free and restricted area has been correlated with microstructure to support the new findings. This study has enlightened the importance of shrinkage allowances during tool making of investment casting products to achieve the desire dimension of the casting. Therefore, it is necessary to identify the free and restricted shrinkage area of a casting before we assign the shrinkage allowance to the die/tool for a particular investment casting product. As a result, number of shop floor trials can be avoided, time required to develop of a casting may be reduced resulting reduction of energy utilization and cost of production.

Application of lost wax casting for manufacturing of orthopedic screw: a review

Normally manufacturing of small screw uses special function machine or CNC machine, but these machines are complex and expensive. To solve this challenge another manufacturing process needs to be investigated. An investment casting process offers production of screw with acceptable accuracy. One of the investment casting method is by lost wax casting. This paper attempts to review and summarize the recent research and developments of lost wax casting for screw production. This method considered as an alternative manufacturing process that able to produce a screw with high accuracy and low cost investment.

Surface roughness prediction using Buckingham’s Pi-theorem for SS-316L hip implant prepared as rapid investment casting

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.

Optimization of investment casting process parameters to reduce warpage of turbine blade platform in DD6 alloy

The large warping deformation at platform of turbine blade directly affects the forming precision. In the present research, equivalent warping deformation was firstly presented to describe the extent of deformation at platform. To optimize the process parameters during investment casting to minimize the warping deformation of the platform, based on simulation with ProCAST, the single factor method, orthogonal test, neural network and genetic algorithm were subsequently used to analyze the influence of pouring temperature, shell mold preheating temperature, furnace temperature and withdrawal velocity on dimensional accuracy of the platform of superalloy-DD6 turbine blade. The accuracy of investment casting simulation was verified by measurement of platform at blade casting. The simulation results with the optimal process parameters illustrate that the equivalent warping deformation was dramatically reduced by 21.8% from 0.232295 mm to 0.181698 mm.

Effects of hot isostatic pressing temperature on casting shrinkage densification and microstructure of Ti6Al4V alloy

The Ti6Al4V alloy castings were produced by the investment casting process, and the hot isostatic pressing (HIP) was used to remove shrinkage from castings. The processing pressure and holding time for HIP were 150 MPa and 20 min, respectively. Four different HIP temperatures were tested, including 750 oC, 850 oC, 920 oC and 950 oC. To evaluate the effects of temperature on densification and microstructure of Ti6Al4V alloy treated by HIP, non-destructive testing and metallographic observation was performed. The experimental results show that the shrinkage was completely closed at 920 oC and 950 oC. The densification of Ti6Al4V alloy increased as the HIP temperature increased below 920 oC. The lamellae were more uniform, the thickness of lamellae was obviously broadened and the structure was coarsen. Besides, the Norton creep equation was used to simulate the effect of different temperatures on the densification of Ti6Al4V alloy during HIP. The simulation results were in good agreement with the experimental results. It was also found that 920 oC is a suitable temperature for HIP for Ti6Al4V alloy.

Multi-objective optimization of dimensional accuracy, surface roughness and hardness of hybrid investment cast components

PurposeThe purpose of this paper is to optimize the process parameters to obtain the best dimensional accuracy, surface finish and hardness of the castings produced by using fused deposition modeling (FDM)-based patterns in investment casting (IC).Design/methodology/approachIn this paper, hip implants have been prepared by using plastic patterns in IC process. Taguchi design of experiments has been used to study the effect of six different input process parameters on the dimensional deviation, surface roughness and hardness of the implants. Analysis of variance has been used to find the effect of each input factor on the output. Multi-objective optimization has been done to find the combined best values of output.FindingsThe results proved that the FDM patterns can be used successfully in IC. A wax coating on the FDM patterns improves the surface finish and dimensional accuracy. The improved dimensional accuracy, surface finish and hardness have been achieved simultaneously through multi-objective optimization.Research limitations/implicationsA thin layer of wax is used on the plastic patterns. The effect of thickness of the layer has not been considered. Further research is needed to study the effect of the thickness of the wax layer.Practical implicationsThe results obtained by the study would be helpful in making decisions regarding machining and/or coating on the parts produced by this process.Originality/valueIn this paper, multi-objective optimization of dimensional accuracy, surface roughness and hardness of hybrid investment cast components has been performed.

Research on the influence of structure parameters on the fractional shrinkage of wheel shape casting

In the investment casting process, different parts of the casting always have various macroscopic structures. Different distribution of internal stress appears in these different parts in the casting, which let each part have different shrinkage distribution. As the design of die cavity can be based on computer-aided design model and fractional shrinkage in the casting process, it can be of benefit for the die cavity design if the fractional shrinkage can be predicted based on structural parameters of the computer-aided design model. Compared to the traditional die-repair method, it is favorable to achieve fast die-repairing and reduce trial-manufacture cost. As an initial study, a wheel shape casting is designed and it is divided into three parts. Fractional shrinkage of these parts is analyzed to research shrinkage rule. The research methods are casting simulation and experiment. The same process parameters are used in the two methods. The simulated and measured results of fractional shrinkage distribution in the corresponding parts show the same trend. It can be concluded that the simulated result can also reflect the fractional shrinkage distribution effectively. Besides, structural parameters that can influence fractional shrinkage are chosen. Then, the mapping model between these structural parameters and fractional shrinkage is built by regression method. Furthermore, the predicted values of the mapping model are compared with measured values. The result shows that the mapping model has a good performance in predicting fractional shrinkage of different parts in wheel shape casting.