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Investment casting (IC) is well known to produced castings with excellent surface finish quality and close dimensional accuracy. Shell cracking is the foremost cause of casting rejection in the IC process. There are many causes of shell cracking in the IC process. However, the leading cause is poor shell strength. The shells having poor strength would produce defects on the final cast part and degraded the mechanical properties of the part. In this research work, the main objective was to improve ceramic shell strength by adding glass fibers to the backup coat ceramic slurry. It can be observed that the addition of glass fibers enhanced the flexural strength of the modified shell when compared to that of the conventional shell. The highest flexural strength was exhibited by the shell, which was modified with 0.50 wt.% of glass fibers. Fiber-reinforced modified ceramic shells had a larger bonded area between the fibers modified ceramic slurry and stucco coating. FE-SEM was used to analyze the microstructure characterization. Permeability and inner layer roughness of conventional and modified shells were measured and compared with conventional shells. XRD analysis was carried out with 0.50 wt.% of glass-fibers of unfired and fired shells at 700°C, 800°C & 900°C. [ABSTRACT FROM AUTHOR]

In this research, microstructure and mechanical properties of stir rheocast AA2024/TiB2 metal matrix composite have been investigated. The working temperature was 640℃, which was the selected semisolid temperature that corresponds to 40% of the solid fraction. Two weight percentage, 4 wt%, and 6 wt% of the TiB2 reinforcements were added to the matrix. The field emission scanning electron microscope micrographs of the developed composites showed a uniform distribution of the particles in the case of the 2 wt% and 4 wt% of the reinforcements. However, the particles agglomerated as the weight percentages of the reinforcement increases to 6%. The optical microscope of the liquid cast sample showed the dendritic structure, whereas the rheocast samples showed a globular structure. The X-ray diffraction analysis confirmed the distribution of the reinforcements in the matrix and the formation of some intermetallic compounds. Mechanical properties significantly improved by the addition of the reinforcements in the matrix. An increase in tensile strength of 13.3%, 40%, 28%, and 5% was achieved for the unreinforced rheocast sample, 2 wt%, 4 wt%, and 6 wt% reinforced rheocast samples respectively, compared to the liquid cast sample. An increase in 20% of hardness was attained for the composite with 2 wt% TiB2 compared to the liquid cast sample. According to the fractography analysis, small dimples were observed on the fractured surface of the unreinforced rheocast sample, whereas small and large voids were dominant on the fractured surface of the 2 wt% composite, which shows the ductile fracture mode. [ABSTRACT FROM AUTHOR]

In the present investigation, the mechanical properties and hot permeability of the ceramic shell used in investment casting process were improved by modifying the ingredients of conventional slurry. The modifications were made by adding a varying content of nano alumina, camphor and a mixture nano alumina and camphor (hybrid mixture) individually into the conventional slurry. The properties, viz. green strength, fired strength, corner strength, load bearing capacity, self-load deformation and permeability of the modified shells were investigated and compared with conventional shell. The experimental results revealed that the green strength of all the shells increased with an increment of the additives into the slurry. The maximum green, fired and corner strengths were exhibited by the nano alumina modified shell with 1 wt% nano alumina addition. The lowest self-load deformation at elevated temperature was also attained by the nano alumina modified shell with 1 wt% nano alumina addition. The addition of camphor significantly improved the permeability of the shell among all the developed shells. But, addition of camphor decreased the strength of the shell. It was also found that addition of hybrid mixture into the slurry simultaneously increased the mechanical properties and permeability of the shell. [ABSTRACT FROM AUTHOR]

This study explores about enhancing the permeability of the ceramic shells used in the investment casting process using cheaply available sawdust particles. An increase in shell’s permeability augments the cooling rate of the casting which enhances its mechanical properties. It was found that the inclusion of sawdust particles into the ceramic slurries exhibited positive impact on the shell’s permeability. It is a well-known fact that electromagnetic stirring process increases the mechanical properties of the castings, but its effect on casting shrinkage has never been realized. Thus, this study further throws light on the impact of electromagnetic stirring in reducing the shrinkage and improving the tensile strength of the casting. In a nutshell, it was found that the final product quality of the investment cast part improved by the combinational treatments adopted in this research work. [ABSTRACT FROM AUTHOR]

Investment casting is competitive with all other casting processes where the size of the product is within a mutually castable range. Though investment casting is used to produce metal parts of any intricate shapes with excellent surface finish, it suffers from long lead time and high tooling costs, which makes it uneconomical for the production of either single casting, or small and medium production units. These problems could be overcome by the applications of rapid prototyping and rapid tooling technologies for low-volume investment casting production runs. The present article analyzes different classifications of rapid prototyping techniques and it reviews various investigations made on the usability of rapid prototyping- and rapid tooling-integrated investment casting process, with their advantages and limitations. The emerging areas of applications of rapid prototyping like dentistry, jewelry, surgical implants, turbine blades, etc., are accordingly discussed. Further, an elaborate discussion is made on the application of newer technologies for directly developing ceramic shells. This article also emphasizes on various future scopes possible in rapid prototyping-integrated investment casting process. [ABSTRACT FROM PUBLISHER]

The application of investment casting process is rapidly increasing, specifically for near net shape manufacturing of complex and small engineering components. The process begins with making of wax patterns, thereafter employing a precision mould, dewaxing, pouring molten alloy and knocking the shell, followed by minor finishing operations. This study is about predicting the quality of responses of the wax patterns namely linear shrinkage and surface roughness using fuzzy-based artificial neural network. The process parameters considered are injection temperature, injection pressure and holding time, and experiments have been performed as per Taguchi’s L18 orthogonal array. As optimum parameter levels were different for both the responses, fuzzy logic reasoning has been used to combine all the objectives and transform the experimental results into single performance index known as multi-response performance index. Later, modelling of the process has been done using artificial neural network with experimental process parameters as inputs and multi-response performance index as output obtained from fuzzy modelling. Further, experiments have been conducted at random combination of parameter levels to validate the developed model, and it has been found that the actual results agreed well with that of the predicted value on the basis of mean absolute percentage error and correlation plots. [ABSTRACT FROM AUTHOR]

In the present work, some investigations have been carried out on hot tears in the Al–1 wt.% Sn alloy, with the objective of preventing hot tearing in aluminum castings. Al–1Sn alloy is extremely prone to hot tearing due to its long freezing range and is an ideal model for studying hot tearing. Experiments were conducted with varying grain refiner (Al–5Ti–1B) percent and pouring temperature. Grain refiner was added to the melt up to 3.0% by weight, which is the conventional limit for grain refiner addition. However, it was found that the maximum addition of grain refiner could not prevent hot tearing, which contradicts the conclusions of some earlier researchers. A mathematical model developed from the experimental data (using regression analysis) has indicated that, among all the constituents present in the Al–1Sn alloy, tin highly increases hot tearing tendency, whereas titanium in the grain refiner decreases hot tearing tendency. The model has also indicated that iron, which is the common impurity in commercial aluminum, reduces hot tearing. Based on the aforesaid model, further experiments were conducted with the addition of iron, which has resulted in complete elimination of hot tearing. Microstructural analysis was carried out using a scanning electron microscope (SEM). The leaf-like structure containing the Al–Sn–Fe-rich phase held the adjacent grains together and thus prevented hot tearing. [ABSTRACT FROM AUTHOR]