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There is an increasing demand in automated manufacturability analysis of metal castings at the initial stages of their design. This paper presents a system developed for virtual manufacturability analysis of casting components. The system can be used by a casting designer to evaluate manufacturability of a part designed for various manufacture processes including casting, heat treatment, and machining. The system uses computational geometrics and geometric reasoning to extract manufacturing features and geometry characteristics from a part CAD model. It uses an expert system and a design database consisting of metal casting, heat treatment and machining process knowledge and rules to present manufacturability analysis results and advice to the designer. Application of the system is demonstrated for the manufacturability assessment of automotive cast aluminum components.

Cast austenitic stainless steels, such as 1.4837Nb, are widely used for turbo housing and exhaust manifolds which are subjected to elevated temperatures. Due to assembly constraints, geometry limitation, and particularly high temperatures, thermomechanical fatigue (TMF) issue is commonly seen in the service of those components. Therefore, it is critical to understand the TMF behavior of the cast steels. In the present study, a series of fatigue tests including isothermal low cycle fatigue tests at elevated temperatures up to 1100°C, in-phase and out-of-phase TMF tests in the temperature ranges 100-800°C and 100-1000°C have been conducted. Both creep and oxidation are active in these conditions, and their contributions to the damage of the steel are discussed.

A significant amount of residual stresses can be developed in aluminum castings during heat treatment. This paper reports an experimental study of the residual stress distributions in aluminum castings after solution treatment and water quench. The residual stresses in aluminum castings are measured using both optical and resistance strain rosettes. The optical strain rosette technique was recently developed in conjunction with ring-core cutting method for residual stress measurement. The measured residual stresses from optical and resistance strain rosettes are compared with the results of X-ray and neutron diffraction measurements. The advantages and disadvantages of various measurement methods are discussed.

Heat treated cast aluminum components like engine blocks and cylinder heads can develop significant amount of residual stress and distortion particularly with water quench. To incorporate the influence of residual stress and distortion in cast aluminum product design, a rapid simulation approach has been developed based on artificial neural network and component geometry characteristics. Multilayer feed-forward artificial neural network (ANN) models were trained and verified using FEA residual stress and distortion predictions together with part geometry information such as curvature, maximum dihedral angle, topologic features including node's neighbors, as well as quench parameters like quench temperature and quench media.

Cast Al-Si alloys are widely used in automotive industry to produce structural components, such as engine block and cylinder head, because of the increasing demands in reducing mass for improved fuel efficiency. The fatigue performance of the castings is critical in their application. Porosity is highly detrimental to the fatigue behavior of cast Al-Si alloys. Therefore, accurate measurement of pore sizes is important in order to develop the correlations between porosity and fatigue strength. However, quantification of porosity is challenging and shows large variation depending on the measurement methods, particularly for micro-shrinkage porosity due to the torturous and complex morphology. The conventional metallographic image analysis method in the 2D polished surface often underestimates the actual pore size particularly when the porosity morphology is complex.

For the cases where perfect interface is not assumed and crack propagation path is unknown, the fully embedded zero-thickness cohesive element model (FECEM) is an alternative simulation method to model crack growth. In our newly developed FECEM model, the common element is triangle 3-node element under two-dimensional condition and the interface element is a quadrilateral cohesive element with zero thickness. From the simulation by FECEM, it is found that the elastic modulus of the second phase particle in a ductile matrix has a significant effect on crack propagation behavior. When the particle encounters the propagating crack, if it is softer than the matrix, the crack will be attracted towards the particle and then will puncture into it. If the particle is harder than the matrix, it will slow down the propagation of the crack.

Cast aluminum alloys are normally quenched after solution treatment or solidification process to improve aging responses. Rapid quenching can lead to high residual stress and severe distortion which significantly affects dimension stability, functionality and particularly performance of the product. To simulate residual stress and distortion induced during quenching, a finite element based approach was developed by coupling an iterative zone-based transient heat transfer algorithm with material thermo-viscoplastic constitutive model. With the integrated models, the numeric predictions of residual stresses and distortion in the quenched aluminum castings are in a good agreement with experimental measurements.

Simulating quasi-static crack to obtain crack tip stress field is a criterion to evaluate whether a numerical simulation model is good at modeling discontinuous problems such as cracks. In this study, a fully embedded zero-thickness cohesive element model (FECEM) was developed based without assuming a perfect interface. By using XFEM (extended finite element method) and FECEM, respectively, 2-D finite element models were constructed to simulate the unilateral I-type and II-type cracks and mixed I-II type crack on 2-D rectangular plate. In XFEM simulation, J-integral was used to calculate the stress intensity factor on the crack tip, which was compared with the theoretical solution. Comparison of the simulated results by XFEM and FECEM models confirms that our newly developed FECEM model has a high reliability in simulating quasi-static crack without assuming a perfect interface.

With the increasing use of aluminum shape castings in structural applications in automobiles, assurance of cast product integrity and performance has become critical in both design and manufacturing. In this paper, the latest understanding of the relationship between casting quality and mechanical properties of aluminum castings is summarized. Examples of newly developed technologies for alloy design, melting and melt treatment, casting and heat treatment processes in aluminum casting are reviewed. Robust design and development of high integrity aluminum castings through an Integrated Computational Materials Engineering (ICME) approach is also discussed.

Aluminum alloy castings are attractive when a light weight, inexpensive, near net shape component is desired. Unfortunately, the presence of internal porosity within these materials can have a significant detrimental effect upon the mechanical properties, appearance, and function of these parts. Hot isostatic pressing (HIP) and Densal® (a proprietary hot isostatic densification process) have been employed to reduce or eliminate porosity in cast metals. This paper compares the fatigue strength and microstructures of end chill sand cast A356 and high pressure, die cast 380 and 383 aluminum alloys which have undergone either HIP or Densal® processing with identical components in the as-cast condition. The castings which underwent isostatic processing show decreased porosity and improved fatigue strength and functionality. Additionally, the economics and suitability for high volume production of these two post-cast processes are reviewed.

Cast aluminum alloys are increasingly used in cyclically loaded automotive structural applications for light weight and fuel economy. The fatigue resistance of aluminum castings strongly depends upon the presence of casting flaws and characteristics of microstructural constituents. The existence of casting flaws significantly reduces fatigue crack initiation life. In the absence of casting flaws, however, crack initiation occurs at the fatigue-sensitive microstructural constituents. Cracking and debonding of large silicon (Si) and Fe-rich intermetallic particles and crystallographic shearing from persistent slip bands in the aluminum matrix play an important role in crack initiation. This paper presents fatigue life models for aluminum castings free of casting flaws, which complement the fatigue life models for aluminum castings containing casting flaws published in [1].