D. Benny Karunakar

A review of rapid prototyping integrated investment casting processes

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.

A Study on Hot Tearing Susceptibility of Al–Cu, Al–Mg, and Al–Zn alloys

The present investigation deals with the hot tearing susceptibility of A206, A518, and A713 alloys. The hot tearing tests of the mentioned alloys were conducted at three different pouring temperatures using sand mold casting. Metallic cores designed to facilitate constrained radial contraction of the aforementioned alloys were used for casting. Macroscopic cracks were found in all the samples except in A518 alloy. It was observed that pouring temperatural and grain size have significant effect on crack susceptibility. Among the investigated alloys, A713 was found to be extremely prone to hot tearing. The microstructure characteristics of the alloys were studied using optical and scanning electron microscopy. Relationships between the pouring temperature, grain size and crack lengths of the alloys were also established.

Prediction of defects in castings using back propagation neural networks

Defects in castings often lead to rejection, which would result in loss of productivity. Expert systems developed by some investigators mostly act as postmortem tools, discussing and analysing a defect after it has occurred. A tool that could predict all the possible defects before the castings are actually made is not yet developed, which would be highly useful in the shop floor. Hence, in the present work, an attempt has been made to predict the major casting defects using back propagation neural networks. The neural network was trained with moulding properties, composition of the charge and melting conditions as the inputs and the nature of the defects as outputs. After the training was over, the set of inputs of the casting that is going to be made, were fed to the network and the network could predict whether the casting would be sound or defective. If defective, the nature of the defect was specified by the neural network.

Effects of grain refinement and residual elements on hot tearing of A713 aluminium cast alloy

Abstract Some investigations have been carried out on hot tears in the A713 cast alloy, which is one of the long freezing range alloys, with objective to minimize/prevent hot tears. Experiments were conducted by varying pouring temperatures at 700, 750, and 780 °C on the alloy with the addition of grain refiners like Al-2.5Ti-0.5C and Al-3.5Ti-1.5C. It was found that hot tearing was minimized by the addition of Al-3.5Ti-1.5C grain refiner, but grain refinement alone could not prevent hot tearing in A713 cast alloy. This has contradicted the findings of some earlier researchers. Experiments conducted on hot tearing with the addition of iron were found to be interesting. It was found that grain refinement along with iron addition to the A713 alloy has reduced the inter-dendritic separation so that interlocking could take place along the grain boundaries. Thus, iron, which comes as an impurity in commercial aluminum, can prevent hot tearing of A713 alloy.

A novel method of increasing ceramic shell permeability and optimizing casting shrinkage and tensile strength of the investment cast parts

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.

A prediction model for the lost wax process through fuzzy-based artificial neural network

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.

Enhancement of Porosity of the Ceramic Shell in Investment Casting Process Using Needle Coke and Camphor

Investment casting process has been a widely used process for centuries. It is known for its ability to produce components of complex shapes with dimensional accuracy and excellent surface finish. Investment casting has been used to make manufacture weapons, jewellery and art castings during the ancient civilization and today it is used to manufacture engineering components. In Investment casting wax patterns are made by wax injection and then coating of the wax patterns are done by ceramic slurry, made with silica flour and binder. After dewaxing and firing molten metal is poured in the shell and solidified casting can be achieved. Investment casting can be cast any ferrous and non ferrous metal which is difficult in die casting. Finishing operations are negligible and very thin sections as.75mm can also be cast which is not possible in sand casting but there are many challenges in Investment casting. It is relatively slow process because preparation of ceramic shell consumes a lot of time, permeability of shell is very low which causes gas permeability. Incorporation of chills is very difficult. Among all these challenges gas porosity is main problem because of poor permeability, entrapment of gases due to complex geometry of the shell, reuse of scrap metal. In the present work porosity of the shell can be increase by addition of mixture of Camphor and needle coke. After firing of the shell camphor and needle coke will be burnt leaving pores for the escape of entrapped gases. Mechanical properties of the both shell will be compared with each other.