Casting Geometry Research Articles

Toward Reducing Casting Defects via 3D Risers via 3D Sand-Printing: A Simulation Study

AbstractThe 3D sand printing (3DSP) process is a binder jetting class of additive manufacturing process that can incorporate complex 3D mold designs and consolidate cores with intricate features that were previously inaccessible. Prior studies in 3DSP mold design have been shown to improve pouring and filling conditions for sand casting. However, the opportunity to improve casting quality by exploring 3D riser designs during the solidification stage has not yet been explored. In this research, three novel 3D riser geometries—ellipsoid, spherical, and a fusion riser (combination of cylindrical and ellipsoid riser) were investigated. The results were compared to the benchmark cylindrical risers to assess casting performance (e.g., reduction in shrinkage porosity, increase in solidification time). Computational solidification simulations have been presented to evaluate the characteristics of the novel risers for three different metal alloys- nickel aluminum bronze (NAB), low-carbon steel A216 (WCB), and aluminum alloy (A319) alloy. From the results of this research, spherical risers were found to provide 45% yield improvement of for the three alloys studied. In addition, the riser neck diameter using a spherical riser experienced up to 77% reduction when compared to the recommended dimensions from previous literature. Finally, one of the spherical riser designs provided 18% improvement in terms of riser-pipe safety height over the benchmark design. Findings from this research will help metalcasting industries to optimize their riser designs for complex casting geometries by implementing 3D riser geometries (via 3DSP) into traditional mold making for yield improvement and defect-free castings.

An optimization study focused on lattice structured custom arm casts for fractured bones inspiring additive manufacturing

In case of fractures, cracks or damage to bone tissues, it is important to use casts, fixatives and protective equipment. Especially in cases where long-term use of casts is required, soft tissue wounds may occur in the human body due to their moisture and airtight structure. For this reason, the use of casts with custom designs, breathable materials, and high mechanical properties has become widespread in recent years. This study focuses on the design of custom arm casts using advanced additive manufacturing technologies and lightweight materials. By utilizing Voronoi lattice structures and hexagonal surface meshes, optimized designs adaptable to additive manufacturing were obtained from a standard arm cast. All cast geometries were investigated under 196 N and 380 N forces. Then, the impact of a 100 g and 1000 g concrete piece with a speed of 12.5 m/s on the arm cast was investigated. As a result of the analyzes, stress, impact plate velocities, deformation, strain and deformation energy were evaluated. The results showed that the designed arm casts have up to 60% better impact strength compared to conventional arm casts. Based on the findings of this study, the use of custom arm casts with optimized lattice structures designed for additive manufacturing will demonstrate high performance.

Test of an baked anode of an aluminum electrolyzer with a new nipple socket design

The results of laboratory and industrial tests on a new design of a baked anode for aluminum electrolyzers are presented. At present, in the process of dismantling anodes from anode holders, there is a problem with the incomplete removal of cast iron filling from steel nipples. At loose contact of the nipple with the carbon block, there is the formation of a solid cast iron layer between the nipple and the anode, which leads to the formation of a thick solid bottom of the cast iron filling without a central hole provided in the corresponding drawing. This situation makes it difficult to remove the cast iron casting from the steel nipple. Moreover, the increased thickness of the bottom of the cast iron casting results in additional electrical resistance, which reduces electrical conductivity and adversely affects the voltage across the contact between the nipple and the anode. The anode of the new design offers a solution to this problem. A feature of the new anode design is the modification of the cast iron casting geometry by modifying the design of the anode holder nipple socket. The anode has trapezoidal protrusions located along the anode axis on both sides of the “lug” protrusion in the nipple socket. The new design provides stress concentration. It allows more efficient and less labor-intensive removal of the cast iron casting. Keywords: baked anode, anode dismantling, cast iron casting, electrical voltage drop, aluminum electrolyzer.

Optimization of Dimensional Accuracy and Surface Roughness of SLA Patterns and SLA-Based IC Components.

Rapid investment casting is a casting process in which the sacrificial patterns are fabricated using additive manufacturing techniques, making the creation of advanced designs possible. One of the popular 3D printing methods applied in rapid investment casting is stereolithography because of its high dimensional precision and surface quality. Printing parameters of the used additive manufacturing method can influence the surface quality and accuracy of the rapid investment cast geometries. Hence, this study aims to investigate the effect of stereolithography printing parameters on the dimensional accuracy and surface roughness of printed patterns and investment cast parts. Castable wax material was used to print the sacrificial patterns for casting. A small-scale prosthetic biomedical implant for total hip replacement was selected to be the benchmark model due to its practical significance. The main results indicate that the most significant stereolithography printing parameter affecting surface roughness is build angle, followed by layer thickness. The optimum parameters that minimize the surface roughness are 0.025 mm layer thickness, 0° build angle, 1.0 support density index, and across the front base orientation. As for the dimensional accuracy, the optimum stereolithography parameters are 0.025 mm layer thickness, 30° build angle, 0.6 support density index, and diagonal to the front base orientation. The optimal printing parameters to obtain superior dimensional accuracy of the cast parts are 0.05 mm layer thickness, 45° build angle, 0.8 support density index, and diagonal to the front model base orientation. With respect to the surface roughness, lower values were obtained at 0.025 mm layer thickness, 0° build angle, 1.0 support density index, and parallel to the front base orientation.

Employing additive manufacturing to create reusable TPU formworks for casting topologically optimized facade panels

Concrete is a building material with excellent structural qualities that can be molded into any shape. However, it is also responsible for approximately 8% of the world's total greenhouse gas emissions. There is a need to reduce material consumption during the design and construction of concrete structures. This research proposes a new manufacturing workflow for the design and fabrication of precast façade panels. Structural topology optimization (TO) is used to design perforated façade panels with optimized material distribution according to the panel's connection to a sub-structure. Structural simulations are conducted to validate the stiffness and strength of the TO panels. Finally, flexible Thermoplastic Polyurethane (TPU) molds are additively manufactured and repeatedly cast. The study results show that TO decreases the panels' volumes within a predefined WWR by anywhere from 23% to 30% of the total volume, while maintaining satisfactory structural performance. Additionally, the study demonstrates the potential of additively manufactured TPU molds for the repeatable casting of concrete while accommodating undercuts in the complex cast geometries. This study is novel as TO has not previously been used for designing façade panels. Furthermore, the use of 3D printed flexible molds made of TPU for repeatable casting of geometries is still in its early stages, with only one publication reporting the investigations at the time of writing this article. This workflow is innovative as a whole as it addresses material saving in the design phase through TO, as well as the creation of reusable 3D printed formworks in the fabrication phase.

Erosion resistant coating to stabilize the surface strength of the casting mold.

To obtain high-quality castings, molding and core mixtures, from which one-time molds are made, must have certain mechanical, technological and physical properties. The surface strength of molding mixtures is the most important factor in obtaining high-quality casting. This property of the mixture is defined as the resistance of the surface layer of the mold to abrasion, and is characterized by crumbling (GOST 23409.9‒78). The lack of surface strength is manifested by the ability of surface sand grains to easily separate with little friction (melt flow during pouring). Insuffi-cient surface strength of the mold causes defects in the castings, forming sand shells and blockages, i. e. particles of the molding material get into the casting, and the mismatch of the casting geometry, i. e., the removal of surface layers from the casting mixture. This phenomenon is caused by the occurrence of convective processes, which leads to the loss of process water in the surface layers of the mold, as well as to increased filtration flows of water in the thickness of the molding mixture. All these processes are carried out to a reduced concentration of water on the surface of the mold. Drying (required by technology) and storage (before using wet molds) are not always the cause of reduced surface strength. In production it is possible that abnormal conditions may occur, leading to crumbling. The situation occurs when the surface and deep layers of the form will be in different conditions. Such situations appear when the chemical composition of the melt does not match, when the melt is not ready for pouring, or when open half-forms accumulate on the conveyor. These factors lead to an increase in the standing time of the open surface of the half-forms, and as a consequence of the appearance of reduced surface strength, which leads to increased crumbling. The purpose of the work is to develop of an erosion resistant coating that prevents the crumbling of the surface layers of the molding mixture

Predicting the local solidification time using spherical neural networks

Castings are predestined for the application of structural optimization, but to date, the integration of process simulation into structural optimization is limited due to high computational cost and is therefore often neglected at the beginning of the design process. This leads to the need for surrogate models, which allow a fast and simplified evaluation of design proposals during the optimization in order to improve the integration. This article introduces a novel approach that estimates the solidification time of randomly created geometries solely based on the casting geometry. The approach uses ray-tracing methods to calculate the distance function along preset directions. The estimated solidification time is calculated using a Spherical Convolutional Neural Network (CNN). The training data is obtained by several thousand solidification simulations using the optimization toolkit of a commercial casting simulation software combined with further data augmentation. The model is experimentally validated for five different geometries in the sand casting process.

Accuracy and precession of 3d printed cast produced by two printing techniques

Aim: This study analyses the tolerance and accuracy of 3D printed casts created by two printing techniques and cast geometry deformations after six months. MISC. Methodology. An A 28-year-old volunteer with full dentition was scanned using 3shape's TRIOS3. 3Shape's Dental System converted the scan to STL. NextDent 5100 DLP and Forms Lab Form 2 SLA printers received the STL file. Each printer made 10 casts. Every cast was scanned using a 3Shape E3 Scanner (E3 Scanner from 3Shape). A cloud comparison tool compared each scan to the volunteer's original scan. The two printers' accuracy was measured at the time of the scan and six months afterward using IBM's SPSS 28 for a one-way ANOVA. Shapiro Wilk statistics were not significant P> 0.05, proving normality. ANOVA was used to compare printers' accuracy. Results. Table 1 shows the means and SDs. Wilk's Lambda of p.05 (F = 95.533 and partial eta squared = 0.841) reveals an initial and six-month accuracy difference. A P 0.05 within-subject’s tolerance effect was found. P=.503 demonstrates printer type doesn't affect participation. The study's mean was.995, with a standard error of.066 and CI of.856 to 1.134. Conclusion. The accuracy measurement decreased significantly between the initial and six-month measurements. There was no difference in accuracy between the two measurements for either printer. There was a statistically significant difference between each cast and each printer's first STL file information. However, the distinction was within the accepted tolerance of -/+ 42 µm (Envision TEC reported an accepted tolerance level).

Analysis of Defects Associated with Manufacturing Keys for Brass Musical Instruments

This article deals with the problematics of the production of small castings using gravitational investment casting. These are castings with a relatively complex shape, which are used as parts of trigger assembly for musical wind instruments. During their production, various defects occur which are connected with the casting process. The aim of this article is to describe the defects and suggest possible methods for removing them. The first step was to find and identify these defects using metallographic and EDX microanalysis. Furthermore, a simulation calculation of the casting process was used to determine the influence of the casting geometry on casting quality. Based on these analyses, the most suitable alloy and casting system geometry were proposed for the production of the casting.

A thermal-stress modelling methodology in ABAQUS for fundamentally describing the die/casting interface behaviour in a cyclic permanent die casting process

This manuscript describes a novel method for thermal-stress modelling of a cyclic, permanent die casting process in the commercial software package ABAQUS. The key element in this method is that it updates the casting's geometry according to the deformed die at elevated temperature before filling the die cavity. Using this method, the evolution of gap and/or pressure at the die/casting interface has been predicted. This in turn has allowed for a more fundamental and less empirical description of the evolution in resistance to heat transfer at the interface during a casting cycle. The new methodology has been compared to a previously published methodology, and the comparison shows a noticeable difference between the two approaches in predicting the temperature field in the die and the casting and prediction of areas prone to shrinkage-based porosity. This methodology also predicts the stress distribution in the die in the cyclic steady-state operation, which may be of value in predicting die fatigue life.

The role of cooling rate on microstructure in a sand-cast Al-Cu–Ag alloy containing high amounts of TiB2

ABSTRACT The present work describes the challenges and methodology used to measure transient temperatures during solidification of an Al-Cu–Ag-TiB2 alloy. Transients were measured using multiple thermocouples embedded in four different casting geometries. Solidified microstructures and the related morphologies in the regions surrounding the thermocouple tips were empirically related to the calculated cooling rates. The relation incorporates the grain refiner (TiB2) level and an approximation of the alloy-specific growth restriction factor. Results indicate that the measured grain sizes () of the primary α-Al phase for all sampled material is highly correlated to initial solidification cooling rates () ranging from 0.02 to 2.08°C/s as Micro-computed tomography confirms that the primary phase observed using standard metallography solidifies with equiaxed grains in the presence of such thermal gradients.

Effect of material-technological properties on the reconstruction of utility parameters of bells

An important utility parameter of bells, including church bells, is their sound – that depends on geometry of the body, changes in section thickness and material from which they are made. Knowing the geometry of casting and chemical composition of the alloy, it seems that the current state of art allows recreating not only solid, but also acoustic properties of the casting. Hence, the purpose of this work is to make a casting using reverse engineering tools, compare acoustic properties of the newly formed bell with the prototype, and test material for a bell alloy. For the host and casted bell the note and octave are identical, the sound differs only in the number of cents away from the exact note. Compared with the numerical model, the acoustic properties of newly formed bell were found with slight deviations. The reasons for registered differences between the components of the original sound and the copy are seen as differences during melting, pouring and solidification processes of the alloy. Material tests carried out on samples taken from the new bell also showed microporosity of the casting and change in microhardness of the α and eutectoid phase (α + δ) along height of the bell cross-section. The chemical composition of bronze also varied along with the change of measuring points at the rib height and the fraction of eutectoid in the alloy structure. Material tests showed a significant influence of cast porosity on its acoustic properties.

Optimisation of Casting Geometries for A356 Alloy Composites Reinforced with Organic Materials using Box-Behnken Design Methodology

In an earlier article, the central composite design was applied to the determination of geometrical features of casts in a two-phase transformation process to produce the wheel covers of automobiles whereby the A356 alloy is reinforced with organic substances for composite property enhancement. This article reexamines the assumptions in that circumstance to revise and expand the optimisation through the response surface methodology to a new method, Box-Behnken design (BBD), to facilitate a comprehensive treatment of the sand casting product parameters. Casting geometrical optimisation can be modelled to involve lengths, breadths, widths, heights, densities of casts and weight loss, varied at three discrete levels. The parameters are translated into codes (–1,0,1) with specified actual, minimum and maximum values. The framework, validated by published literature data, indicates its feasibility in a real-life circumstance. This article assessed the effects of the casting geometry parameters on the responses. Besides, it examined the accuracy of the parameters to predict in the regression models deployed. It was concluded that the BBD and the regression models are adequate and predict correctly. The BBD can be applied by composite developers to improve casting dimensional accuracy and economics.

Geometrical effect on macrosegregation formation during unidirectional solidification of Al–Si alloy

Abstract In the production of single-crystal turbine blades for use in aircraft engines with unidirectional solidification techniques, it is confirmed that the casting geometry had great influence on the formation of macrosegregation or spurious/stray crystals. In this study, a two-phase solidification model is used to investigate the geometrical effect on the unidirectional solidification of Al–7.0 wt.% Si alloy. The study is based on the experiment of Ghods et al. (2016a) , in which the diameter of the sample is changed between ϕ9.5 and ϕ3.2 mm along the solidification direction to highlight the geometrical effect. The first part of the investigation is to verify the numerical model by ‘reproducing’ the experimentally obtained macrosegregation and phase distribution in an as-cast sample. The second part is to explore the macrosegregation mechanism. It is found that the main geometrical effect is the modification of the bulk and the interdendritic melt flow during solidification. Different flow patterns are found in different locations, e.g. below or above the cross-section contraction; however, details of the macrosegregation formation can be explained by a scalar product of two vectors, i.e. the flow velocity and the concentration gradient of the melt. Based on the positive/negative value of the scalar product, i.e. the flow direction in comparison with the direction of the concentration gradient, it is possible to determine where a negative/positive segregation will occur. The above scalar product is also found valid for analysing the possible formation of spurious/stray crystals, and it is numerically demonstrated that the cross-section expansion in casting geometry leads to high risk of spurious/stray crystals.

Sliver defect formation in single crystal Ni-based superalloy castings

Sliver is a typical grain defect in single crystal Ni-based superalloy castings produced by Bridgman directional solidification. However, its formation mechanism has yet to be fully understood. In this study, the formation of sliver defects was investigated with respect to the defect morphological features, the microstructure of defect initiation points, and the solidification conditions. Experiment results showed that sliver defects were originated from fragmentation of dendrite trunks and could developed to various morphologies. The misorientation range of sliver grains was between 3.2° to 12°. Microstructural analysis results indicated that the dendrites fragmented abruptly without significant plastic deformation. And the dendrite fragmentation could be facilitated by oxide inclusions and solidification pores. It was also found that the sliver defects were prone to occur at the interface where primary dendrite converge to the mold inner wall. Based on the low misorientation level of sliver grains in the experimental observation, the critical solid volume fraction range for fragmentation was suggested to be 0.6–0.8. The dendrite fragmentation was attributed to the non-uniform stress distribution in dendrite during solidification. In addition, the effect of airfoil geometry of a typical blade casting and defect prevention methodology were discussed.

A multiscale model for optimizing the flexural capacity of FRC structural elements

In the present work, a multiscale model for fibre reinforced concrete (FRC) beams failing in bending is presented. At the microstructural level, the fibre is modelled as a one-dimensional continuum with axial, shear and bending deformability, with cohesive-like interfaces to simulate the interaction with the surrounding concrete. At the macroscopic level, the response of the beam is simulated by discretising the cross-section into layers and by enforcing the proper compatibility conditions between the layers. In the post-cracking stage, the tensile capacity is assured by the fracture energy of the concrete and the fibre resisting mechanisms simulated by the fibre pull-out constitutive laws determined at the microstructural level. The model can account for fibre distribution and orientation, controlled by the casting conditions and geometry of the mould. By using experimental data available from the open literature, it is proved that such an integrated approach is able to derive, by inverse analysis, the stress-crack width relationship of FRC, which is the fracture mode I information in the material nonlinear analysis of FRC structures with approaches based on the finite element method.

Toward the development of a thermal-stress model of an industrial counter pressure casting process

It is argued that the Counter Pressure Casting (CPC) process is superior over low-pressure die casting (LPDC) in terms of reducing defects and improving cast product performance. To date, there has been relatively little research conducted on the CPC process to provide reliable data to confirm this argument. In this work, a plant trial has been done on an industrial CPC process using a custom-designed ‘H-shaped’ die to acquire an extensive amount of quantitative process data. The data acquired includes temperatures obtained from within the die, the casting, the surrounding environment, and within specific die cooling channels. The data has been processed and analysed to support the development of a comprehensive thermal-stress model of the casting process in order to better understand and quantify the essential macro transport processes. This paper presents a methodology of a coupled thermal-stress model development on the CPC process, and the preliminary results obtained from the models. The results to-date clearly show the need for a fully coupled thermal-stress analysis for the particular casting geometry and process conditions examined. Some of the challenges associated with the current modelling approach are also identified and potential solutions presented.

Geometrical Parametric Optimisation of A356 Alloy Composite in a Two-Stage Casting Process for Automobile Wheel Covers using Response Surface Methodology

In recent years, novel products from out–of–use A356 alloy engine components are increasingly produced for the automobile industries. Despite being a promising method the sand casting of these products reveals an inadequately understood cast geometry phenomenon for the process. At present, there is no technical solution to the optimisation of cast geometries for A356 alloy reconfigured into composites through organic matter reinforcements. This paper models and analyse sand casting process product geometries in a two–phase method. It utilises the response surface methodology with data on inputs and outputs to create the regression. Volume and density of the first casting process and the weight loss were evaluated for the various groupings of casting process variables, including length, weight, height, width of product for the first casting, weight, length, breadth of the product for the second casting, and the total weight of organic materials. The input and output associations were established in two models of regression analysis representing the central composite design, CCD. The influences of the cast geometrical variables on the evaluated responses were analysed. Furthermore, the predictive accuracy of the two regression models was evaluated. Results revealed that the applied CCD and the regression models reveals statistical adequacy and are competent to predict accurately.

Simulation of Shrinkage Porosity Formation During Alloy Solidification

Porosity due to solidification shrinkage is a troublesome defect in metal casting. It results in low yields and increased costs in production and limits the performance of cast components in service. By reliably predicting porosity in casting process simulation, porosity can be minimized or eliminated. Here, a new model for simulating the formation of shrinkage porosity during solidification is presented. The model is based on the recent discovery that shrinkage porosity nucleates and grows in regions of a casting where the solid fraction is the lowest. It calculates the feeding flows and pressure distribution in the liquid while accounting for the density variation during cooling and solidification. It predicts the location, extent and amount of all types of shrinkage porosity in a casting, including riser pipes and large internal holes, surface sinks, and distributed micro-shrinkage. Porosity predictions are presented for simple casting geometries and for a more complex Mn-steel experimental casting. The comparisons to the observations made in the experimental casting demonstrate the capability of the model to accurately predict the various types of shrinkage porosity. Numerical studies are performed to investigate the sensitivity of the predictions to various model parameters.

Study and control of factors influencing casting shrinkage using DOE and numerical simulation

The purpose of this study is to predict the effect of various factors like alloying elements, Inoculation and Carbon Equivalent (CEV) on green sand casting shrinkage defect in gearbox housing, without changing the casting methoding system. Foundries are prone to have defects related to feeding and gating system, sand and process parameters. In some engineering applications, it is very difficult to alter methoding system due to specific casting geometry requirements. If not controlled during development stage, the rejections may seriously affect the productivity. This research work involves the optimization of various factors by DoE and numerical simulation to reduce the shrinkage defect. Unlike the prototype or sample lot trial, mass production of gearbox housing castings has been done in a foundry to achieve the research purpose. Effect of these factors on final casting hardness and tensile strength has also been studied and found to be on positive side, as these parameters are important for satisfactory performance under dynamic loading. Outcome was the reduction in shrinkage porosity from 10.9% to 3.2% with overall saving of 41k USD over the period of 4.5 months. Implication of this study involves standardization of optimum range of alloy elements and inoculation for different grades of grey cast iron.