Jeong-Kil Choi

Basic construction of intelligent expert system for riser design using database system and optimisation tools

Abstract Process design using computer simulation and optimisation has recently garnered a great deal of attention and much progress has been made through research in this area. Most research addresses the soundness of mass products, productivity optimisation, and improvement of product reliability. In the casting industry, a mainstay of the manufacturing sector, the design method of an optimal riser has also advanced greatly and it requires a clearly defined optimisation strategy. The purpose of working out a proper optimisation strategy is to minimise the time required for long series and iterations of calculations and thereby achieve an effective result. To this end, a database system was built by means of an image retrieval method. The authors also studied a way to automatically designate an appropriate point for installing a riser using solidification simulation and the Method of Modified Feasible Direction (MMFD), an optimisation method that uses the gradient search. The present study outlines the basic algorithm for the Intelligent Expert System (IES) for design of an optimal riser. It employs solidification simulation, a database system, and the MMFD. The study also addresses the application of the system to a simple cast.

Structural analysis considering shrinkage defect of cast part

Abstract Flow and solidification of fusion metal at high temperature may introduce defects in cast components. As a results, many components have unsound internal areas. However, most engineers do not consider the effect of shrinkage defects when designing components; it is generally assumed that the material is completely sound. The material property reduction method is one approach to taking into account the effect of unsound areas, but it cannot consider stress concentration effects around the shrinkage. To compensate for this limitation, a shape simplification method is proposed. The method reconstructs shrinkage defects as hollow spheroid primitives based on shrinkage shape data obtained from industrial computerised tomography. The shape simplification method offers a smaller number of elements than other methods for modelling of shrinkages, and is also able to calculate the stress concentration. The present study examines the effect of shrinkage on a component structure subject to practical loads. It is possible to improve the productivity and reliability of cast products by such considerations.

ESPI combined with hole drilling method to evaluate heat treatment induced residual stresses

Heat from manufacturing processes like casting and heat treatment may cause localized expansion in parts. When these parts are cooled subsequently, some areas cool and contract more than others, leaving residual stresses, which may exert a considerably negative influence on both the structures static strength and fatigue lifetime. So it is necessary to measure or predict the stress distribution in parts after heat treatment. In this study, residual stresses in the specimen are measured by ESPI (Electronic Speckle-Pattern Interferometry) combined with the hole drilling method. The material of specimen is SUS 304 austenitic stainless steel. It is quenched and water cooled subsequently. We also simulated the thermal stresses field induced by casting process by numerical analysis. As a result, comparisons of results from presented method as well as numerical solution are presented finally to give a conclusion on this residual stress measurement method in this paper.

Development of pre-/post-processors for 3D numerical simulation using cut cell method

Abstract Today, in the casting engineering field, various heat flow simulations are being applied to manufacturing processes. The most general flow simulation techniques have been improved and developed according to the characteristics where they are applied in the casting industry. In this study, the authors have developed a pre-/post-processing system to use a cut cell method, which is one of the finite volume methods among the numerical analysis methods mentioned above. In this paper, the authors will briefly introduce a pre-processor that requires only the user’s simple input information to automatically generate meshes and performs simulation and post-processing, which maps the simulation result data into an original computer aided design file directly. This paper will also examine a few cases of actual application of these technologies to casting products.

Calculation of thermophysical properties of iron casting alloys

Abstract A simple and easy calculation tool to determine thermophysical properties, such as density, heat capacity, liquidus and solidus temperature, thermal conductivity, latent heat, and volume contraction, of iron casting alloys based on equilibrium phase diagrams is introduced. It is well known that accurate thermophysical properties of iron casting alloys are necessary for a valid simulation of the casting process. While there are a number of thermophysical calculation programs, a specific knowledge of thermodynamics is required to operate them. The calculation method proposed in the present study does not require any special knowledge of thermodynamics, only information regarding the composition of the alloy. The proposed calculation tool is based on the CALPHAD approach for the modelling of multicomponent alloys using experimental published data. Comparison of calculated thermophysical properties for several conventional iron casting alloys with experimental results showed good agreement.

Numerical and experimental study on thermal stress in grey iron castings

Abstract Research on thermal stress analysis using the hybrid finite difference/finite element (FDM/FEM) computational method is still in its early stages, as the brevity of the bibliography attests. Inhomogeneous temperature distributions during the casting process lead to the generation of various thermal stresses during cooling from the pouring temperature to room temperature and from surface to core. It is impossible to measure residual stress experimentally during casting because the casting is covered by the moulds and its temperature is too high. Thus, the final thermal stress state and deformation must be inferred from measurements made at room temperature. Four moderately complex specimens, designed to be sensitive to residual thermal stress, were cast from grey cast iron. Residual stress levels were measured at various positions by the centre hole method using transducer strain gauges. These values, and cooling curves derived from thermocouple measurements, show reasonable agreement with the results of FDM/FEM simulations using a hybrid numerical model developed by the authors. Whole stage simulations suggest that section width has a stronger influence on residual stress than section length. The discrepancies between measured and calculated temperatures are attributed to the fact that the model does not incorporate the air gap or mould porosity effects.

The present and future application of computer simulation for casting design in Korean foundries

This paper shows applications and trials used to utilize computer-aided simulations for enhancing the productivity and quality of casting products in Korean foundries initially over a few decades. In Korea, KITECH (Korea Institute of Industrial Technology) took the important steps in developing and propagating computer simulation software for casting design. The “Z-CAST” developed by KITECH is the best computer simulation software for casting design in Korea and its schematics and application for the manufacturing field are introduced in this paper. Also, the future work of the casting industry is stated, especially, IES (Intelligent Expert System), the main stream of computer-aided production in Korea, is discussed.

Application of an automated water cooling system in the cyclic permanent mould casting process

Development and application of an automated water cooling system was carried out by the systematic research of numerical simulation and experimental verification in the cyclic permanent mould casti...

Summing up MCSP8

The 8th Pacific Rim Conference on Modeling of Casting and Solidification Processes (MCSP8) was organised by the Korean Institute of Industrial Technology at the Sheraton Hotel, Incheon, Korea. During the three days of technical sessions from 12 to 15 April 2010, 52 papers were presented in seven sessions: solidification, microstructure evolution, continuous casting, mould filling, deformation, new application of CAD/CAE, and casting process.

Approach to impact analysis of automobile Al alloy wheel in presence of casting shrinkage defect

Abstract The objective of the research was to evaluate the effect of casting shrinkage defects on the impact properties of cast aluminium alloy wheel for automobile. Most structure design engineers give the casting parts an overestimated factor of safety, specify extensive quality tests and perform extensive performance testing due to worries about unavoidable defects, such as shrinkages; however, all of these methods do not necessarily guarantee performance, and they are all somewhat costly. In this paper, an approach using computational impact analysis for an Al alloy, where shrinkage defect exists, was proposed to solve the motioned problem. The shrinkage defects were modelled by the shape simplification method. The method reconstructs the shrinkage defects to hollow spheroid primitive based on the shrinkage shape data obtained from industrial computerised tomography. The results of the simulation of wheel with shrinkage defect were compared with the results of ignoring shrinkage. Comparative results showed that when the impact analysis was applied to an Al alloy wheel, a traditional analysis without considering the shrinkage defect estimated the wheel safety; however, the results considering shrinkage defect show that the wheel would fracture under the same test condition.