Investment Casting Process Research Articles

Data-Physics Fusion-Driven Defect Predictions for Titanium Alloy Casing Using Neural Network.

The quality of Ti alloy casing is crucial for the safe and stable operation of aero engines. However, the fluctuation of key process parameters during the investment casting process of titanium alloy casings has a significant influence on the volume and number of porosity defects, and this influence cannot be effectively suppressed at present. Therefore, this paper proposes a strategy to control the influence of process parameters on shrinkage volume and number. This study constructed multiple regression prediction models and neural network prediction models of porosity volume and number for a ZTC4 casing by simulating the gravity investment casting process. The results show that the multiple regression prediction model and neural network prediction model of shrinkage cavity total volume have an accuracy of over 99%. The accuracy of the neural network prediction model is higher than that of the multiple regression model, and the neural network model realizes the accurate prediction of shrinkage defect volume and defect number through pouring temperature, pouring time, and mold shell temperature. The sensitivity degree of casing defects to key process parameters, from high to low, is as follows: pouring temperature, pouring time, and mold temperature. Further optimizing the key process parameter window reduces the influence of process parameter fluctuation on the volume and number of porosity defects in casing castings. This study provides a reference for actual production control process parameters to reduce shrinkage cavity and loose defects.

Improving Microstructural Homogeneity of Investment‐Cast Single‐Crystalline Ni‐Base Superalloys by Using Fluidized Carbon Bed Cooling

One impeding factor for faster solidification in typical investment casting processes is the limited heat removal capability. This study compares the classical Bridgman technique and the fluidized carbon bed cooling (FCBC) casting method. In particular, the influence of the thermal design is investigated in terms of microstructural and compositional homogeneity in single‐crystalline CMSX‐4. These investment casting processes mainly differ in the baffle type used to insulate the hot and cold zones inside of the casting vessel. While the Bridgman process is based on radiation cooling, the FCBC casting process relies on a dynamic baffle made of expanded graphite that is buoyant on fluidized bed of glassy carbon beads. Such a dynamic insulation layer can adapt to the cross‐sectional variation of ceramic shell molds and provide a better thermal insulation, which results in more uniform solidification conditions. This enables a reduction in the primary dendrite arm spacing by up to 26%, an increase in the homogeneity of the microstructure and composition, as well as a reduction in overall porosity and mean pore size of 41%.

Tailored solidification microstructures for innovative use of high-density materials in lightweight products

As more industries move to capitalize on the technological benefits of additive manufacturing, researchers are exploring ways to design new alloys with properties that cannot be achieved through traditional manufacturing methods. One approach is to tailor the solidification microstructures of lightweight components using dense materials. This study examines the microstructures and mechanical properties of near eutectic Al-Cu alloys under different thermal histories, covering both high and low solidification rates found in various additive manufacturing techniques. Slow cooled lattice structures of diamond type unit cell were produced at a relatively low cooling rate by a hybrid investment casting process involving 3D printing of the lattice patterns, and rapid solidified powders of various sizes were generated by Impulse Atomization. Microstructural analysis revealed different eutectic morphologies and spacing depending on the cooling rate and location. The alloys strength was increased by spheroidization of their eutectic phases. The alloys eutectic structures were spheroidized using two spheroidization mechanisms, including (i) Thermo-mechanically by plastic deformation of as solidified samples, followed by heat treatment, and (ii) Chemically by addition of Mg and Si to the near eutectic Al-Cu alloy. Both the thermo-mechanical and the chemical spheroidization mechanism are found to improve the mechanical properties of the alloys. This study demonstrates a potential cost-effective use of heavy alloys in high-performance applications through additive manufacturing (e.g. using lattice structures) by optimizing microstructures and enhancing mechanical properties.

Core shift limitation in investment casting process of hollow turbine blade

The deviation in wall thickness caused by core shift during the investment casting process significantly impacts the strength and service life of hollow turbine blades. To address this issue, a core shift limitation method is developed in this study. Firstly, a shift model is established based on computational fluid dynamics and motion simulation to predict the movement of the ceramic core in investment casting process. Subsequently, utilizing this model, an optimization method for fixturing layout inside the refractory ceramic shell is devised for the ceramic core. The casting experiment demonstrates that by utilizing the optimized fixture layout, not only can core shift during the investment casting pouring process be effectively controlled, but also the maximum wall thickness error of the blade can be reduced by 42.02%. In addition, the core shift prediction is also validated, with a prediction error of less than 26.9%.

Resource-Efficient Manufacturing Technology for Titanium Aluminide Aerospace Components

Titanium aluminide (TiAl) has been identified as a key material for achieving significant emission reductions in aircraft jet engines due to its high-temperature properties combined with its very low weight compared with conventional nickel-based alloys. Well-known engine manufacturers, therefore, introduced TiAl low-pressure turbine blades in their engines. To enter the market, all manufacturers initially relied on enormous machining allowances for safety reasons, thus accepting a poor buy-to-fly ratio: MTU Aero Engines AG used the casting/forging route with the alloy TNM [Ti–43.5Al–4Nb–1Mo–0.1B (at.-%)] for the highly stressed GTF (geared turbofan), Safran used machining of the alloy GE48-2-2 (Ti–33Al–2.6Cr–4.8Nb (wt.-%)) from the solid, and GE (General Electric) used ‘massive-overstock’ investment casting and 3D printing of GE48-2-2. More cost-effective and material-efficient processes are needed for titanium aluminide to establish itself sustainably in new aerospace applications in the long term. Access has, therefore, developed an economical TiAl investment casting process to industrial maturity, realizing a minimum machining allowance of 0.7 mm in a process-safe manner. In a study, it was evaluated that carbide cutters with AlTiN coating are excellently suited for machining TiAl. Extensive studies of the economic viability of TiAl investment casting have shown that it is competitive.

The Influence of Injection Temperature and Pressure on Pattern Wax Fluidity

In the investment casting process, the pattern made of wax is obtained in a die for further formation of a shell mold. The problem of die-filling by pattern wax is significant because it influences the quality of the final casting. This work investigates three commercial pattern waxes’ fluidity with a newly developed injection fluidity test. It was shown that the fluidity of waxes increased with increasing injection temperature and pressure, and the simultaneous increase in temperature and pressure gives a much more significant enhancement of fluidity than an increase in temperature or pressure separately. The rheological behavior of the waxes was also investigated at different temperatures using a rotational viscosimeter, and temperature dependences of waxes’ dynamic viscosity were determined. It was shown that wax viscosity is increased more than ten times with decreasing temperature from 90 to 60 °C. A good correlation between wax fluidity and its viscosity is observed, which is different from metallic alloys, where the solidification behavior is more critical. The difference in wax flow behavior in comparison with metallic melts is associated with the difference in dynamic viscosity, which for investigated waxes and metallic melts is 3000–27,000 mPa·s and 0.5–6.5 mPa·s, respectively. The difference in investigated filled waxes’ fluidity is observed, which can be associated with the type and amount of filler. The twice-increasing fraction of cross-linked polystyrene decreases fluidity twice. At the same time, terephthalic acid has a minor influence on wax fluidity.

A Digital Twin Based Residual Stress Prediction Method for Turbine Blades

The investment casting process is the conventional method for manufacturing turbine blades, and the residual stress generated through this process is widely regarded as a critical factor that markedly impacts the quality and serviceability of turbine blades. However, real-time measurement of residual stress is extremely complex and expensive, especially for single-crystal turbine blades. Current experimental measurement techniques such as X-ray or neutron diffraction can only measure residual stresses at specific points or within a very small area. Studies on residual stress of turbine blades are mainly performed by finite element (FE) simulation, but the accuracy is difficult to guarantee due to the inability to establish accurate mathematical models for complex physical systems. To address this issue, this paper proposes utilizing a digital twin (DT) model to predict residual stresses in turbine blades. By combining real-time sensor and FE simulation data, the DT model is able to update and correct the mathematical models, resulting in more accurate predictions compared to traditional FE simulations.

Investment casting of semi-solid 6063 aluminum alloy using the GISS process

Investment casting has long been known as a process that can produce complex parts with fine details. However, it has not been used widely for parts that need to be anodized and whose nonuniform color is affected by the type of cast aluminum. Although 6063 aluminum is widely used in color anodizing for decoration purposes, it is almost entirely wrought. Some studies have used aluminum 6063 in cast aluminum, but no investment casting studies have been reported. The objective of this work is to develop a new semi-solid investment casting process using 6063 aluminum alloys to achieve a cosmetic anodized workpiece. To study the feasibility of the gas-induced superheated slurry (GISS) investment casting process, the effects of rheocasting time, mold temperature, and vacuum assistance were investigated. The results showed that the samples produced using the GISS process had a uniform microstructure and less porosity. The uniform color after anodizing and coloring also confirmed these processes. From the results, it can be summarized that the GISS process is feasible for application in aluminum 6063 investment casting for anodizing and coloring purposes.

Optimizing the Gating System for Rapid Investment Casting of Shape Memory Alloys: Computational Numerical Analysis for Defect Minimization in a Simple-Cubic Cell Structure

With the aid of virtual prototyping and casting numerical simulation, this work presents the optimization of an injection system used in a non-traditional investment casting process that applies perpendicular centrifugal force to inject the molten metal into refractory plaster molds. In this study, advanced techniques of simulation and production of complex geometries in Computer-Aided Design CAD (Computer-Aided Design) are used in the design of the casting system of a miniaturized simple-cubic cell structure. The cast part has a complex shape profile and needs a high surface finish with strict dimensional tolerance. The alloy used to fill the mold is an aluminum bronze shape memory alloy (SMA). CAD was used to model the part and the proposed models for casting optimization. ProCAST software was used for the numerical simulation of the casting process. Experimental parameters were used as input data for the numerical simulation. The simulation results were analyzed focusing on the identification of defects in the Cu–Al–Mn SMA simple-cubic structures. Different feeding systems have been designed to eliminate the identified defects. Concerning the molten recirculation, the optimal nozzle model has a truncated cone profile, with a larger radius of 6.5 mm, a smaller radius of 2.0 mm and a height of 8.0 mm (called here model 3). Experimental observations from cast SMA parts agree with the simulated results of the optimized nozzle model 3. In addition to the elimination of alloy recirculation with the nozzle optimization in this work, the shrinkage porosity at the upper base of the part was eliminated with the addition of a compensation volume close to the region where porosity is more intense. By exploring the possibilities offered by commercial software, the work contributes to advance the knowledge and application of the non-traditional investment casting process, highlighting its advantages and potential applications.

Porous wax patterns for high-precision investment casting

Aerospace, manufacturing, and shipbuilding industries strive to enhance their competitiveness by optimizing material utilization and improving production processes. The investment casting process offers the capability to fabricate intricate and precise components using a diverse range of alloys. However, this method is not without its drawbacks, including high manufacturing costs and a significant rate of defective castings, which can reach up to 30 %. These defects primarily arise from the stresses imposed on the wax patterns and ceramic molds, leading to their distortion. To address this issue, efforts have been made to reduce stress by employing compacted wax powders for the production of investment patterns. However, stress relaxation in the wax patterns remains a concern as it can result in elastic deformation of the compacted material and subsequent alterations in the final product dimensions. To mitigate this issue, a series of tests were conducted with the objective of studying stress relaxation under constant compression strain, as described by the Kohlrausch equation. The obtained results provide valuable insights that enable the prediction of the ultimate dimensions of patterns created using different grades of wax.

Castability of Cu-Al-Mn shape memory alloy in a rapid investment casting process: computational and experimental analysis

Castability of Cu-Al-Mn shape memory alloy in a rapid investment casting process: computational and experimental analysis

A mathematical examination of the impact of mould transparency to infrared radiation on solidification during the investment casting process

Investment casting is a highly dynamic process during which multiple competing physical phenomena are at work. Those seeking to understand and simulate such processes computationally are confronted with a considerable task, balancing accuracy with efficiency. Approximations and models based on well-understood and documented fundamental physics are powerful tools in a modeller’s arsenal. Driven by observed discrepancies between experimental thermocouple measurements and simulation predictions of casting temperatures, this work explores the additional alloy cooling mechanism of mould transparency to infrared radiation, targeting a new mathematical approximation applicable in such situations. Direct attenuation, scattering from coarse sand, sand distribution in the mould and material temperatures play a role in the extent of radiation transparency that must be considered. From this model, estimation of the additional cooling rate resulting from expected mould transparency can be determined and applied as a corrective measure to computation fluid dynamics (CFD) simulation results that do not capture this phenomenon.

Realization of High Pressure Turbine Blades of a Small Turbo Fan Engine through Investment Casting Process

Turbo-fan gas turbine engines, or simply turbo-fan engines (STFEs), are used for powering both manned aircrafts and unmanned air vehicles (UAVs). The high pressure turbine section of such engines use Ni-base superalloy cast rotor blades because of their good mechanical properties at high operating temperatures. The present paper provides the technical/technological details of the various aspects associated with development and manufacturing of high pressure turbine blades (HPTBs) for utilization in an indigenously-developed small turbo-fan engine. Vacuum investment casting process has been adopted for realization of the above equiaxed components using a Ni-base superalloy

Optimization of Hexagonal Structure for Enhancing Heat Transfer in Storage System.

Thermal performance was tested during cycling work for latent heat storage systems based on KNO3 and NaNO3 (weight ratio 54:46). For heat transfer improvement, cast aluminum honeycomb-shaped structures were produced via 3D printing of polymer model and investment casting. Different wall thicknesses were tested at 1.2 mm and 1.6 mm. The obtained results were compared to working cycles of pure PCM bed. The use of enhancers is reported to improve the rate of charging and discharging of the deposit. In the next step, the structures were examined with numerical simulation performed with ANSYS Fluent software. The wall thicknesses taken into consideration were the following: 0.8, 1.2, 1.6, and 2.0 mm. An insert with a greater wall thickness allows for smaller dT/dt and better heat distribution in the vessel. The investment casting process enables the manufacturing of complex structures of custom shapes without porosity and contamination.

Analyzing the influence of the investment casting process parameters on microstructure and mechanical properties of open-pore Al–7Si foams

Aluminum alloy foams with high specific compressive strength and good energy absorption capacity are widely used as structural materials and shock absorbers. The investment casting process offers an interesting opportunity for the production of open-pore aluminum foams. However, foam casting differs from casting of solid parts, and there is a lack of practical knowledge about the microstructure tuning of the ultra-thin cast struts. Our study focuses on the influences of the casting conditions such as mold temperature on the microstructure and consequently on the mechanical properties of aluminum-silicon alloy foams. We investigated microstructural features using various metallography techniques and defined mechanical properties under uniaxial compression test. Here, we observed improvements in the strut microstructure together with decrease of the mold filling by reduction of the mold temperature. Microstructure improvements involve transformation of a single dendritic aluminum grain in each strut to globular grains along with a more homogeneous distribution of the silicon particles across the strut cross-section. These changes bring higher ductility and energy absorption efficiency to the foams, which are evident from the smoother plateau of the stress-strain curves. Decline of the mold filling, on the other hand, has negative effect on the overall mechanical properties.

Modeling and experimental study on deformation prediction of thin-walled turbine blades during investment casting process

Due to variable cross-sections and a thin-walled structure, gas turbine blades have stringent dimensional, and geometrical tolerance requirements. Single-crystal hollow blades are manufactured using the following investment casting processes: ceramic core preparation, wax injection, ceramic coating, wax removal, metal casting, and finishing. The main causes of the final casting deformation are wax pattern deformation, core deflection, and metal solidification warpage. This paper proposes a numerical simulation method to predict the deformation of the wax pattern, core deflection, and the directional solidification (DS) process of large single-crystal blades. Additionally, it investigates the displacement field and the influence of casting process parameters on dimensional accuracy. Three groups of DS process parameters were selected for experiments, and the deformation prediction was in agreement with the experimental results. The selected blade section deformation is the smallest when the pouring temperature is 1530°C and the withdrawal rate is 5 mm/min. The proposed finite element model is efficient to predict the deformation in all the investment casting processes, providing geometric guidance for the control of the dimensional accuracy of the turbine blade.

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.

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

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.