Casting Geometry Research Articles

A geometry-based model for determining solidification isotherms of basic casting sections

A Unit Area approach based method was presented as an alternative to the geometry-based modelling of solidification to determine the solidification isotherms of basic casting geometries. This method was applied to square external corners, rectangular casting sections, sections of cylinders, discs, spheres and internal corners. Adequate solutions for these basic casting sections were obtained by using Unit Area based modelling. The results for the square external corners and rectangular casting sections, internal corners and “T” type casting sections showed a good correlation with Section-Modulus and modified Section-Modulus based methods. UnitArea based alternative method is significantly expressing the solidification behaviour of basic casting geometries without any modification.

Predicting the volume shrinkage while manufacturing the GTE turbine blades

The process analysis of manufacturing the castings of turbine moving blades demonstrated that approximately 5% of the blade blanks from a lot are rejected to a considerable geometric distortion of the blade airfoil. The turbine moving blade casting manufactured by the casting method with directed crystallizing may differ in its geometric and dimensional-accuracy parameters from the design model. The casting geometry varies as a result of high temperature and structural shrinkage deformations which are manifested as the hindered volumetric shrinkage and contraction during crystallizing and upon the casting knockout from the ceramic mould. High-temperature deformations may result in contraction of the casting mould and ceramic core shaping the inner blade cooling channels. As a result, to obtain the blade of the geometric form as set by the designer, it becomes necessary to predict the stress-deformed state of the moving blade casting in order to consider the volumetric shrinkage and deformation in advance. Therefore, predicting and considering the total volumetric shrinkage during the manufacture of the moving blade castings ensuring the minimum contraction of the process system “ceramic mould – casting – ceramic core” is a relevant problem for the modern blank production.

Effect of Solidification Time on Microstructural, Mechanical and Fatigue Properties of Solution Strengthened Ferritic Ductile Iron

Microstructural, mechanical, and fatigue properties of solution strengthened ferritic ductile iron have been evaluated as functions of different solidification times. Three types of cast samples with increasing thickness have been produced in a green sand automatic molding line. Microstructural analyses have been performed in order to evaluate the graphite nodules parameter and matrix structure. Tensile and fatigue tests have been carried out using specimens taken from specific zones, with increasing solidification time, inside each cast sample. Finally, the fatigue fracture surfaces have been observed using a scanning electron microscope (SEM). The results showed that solidification time has a significant effect on the microstructure and mechanical properties of solution strengthened ferritic ductile iron. In particular, it has been found that with increasing solidification times, the microstructure becomes coarser and the presence of defects increases. Moreover, the lower the cooling rate, the lower the tensile and fatigue properties measured. Since in an overall casting geometry, same thicknesses may be characterized by different microstructures and mechanical properties induced by different solidification times, it is thought that the proposed methodology will be useful in the future to estimate the fatigue strength of cast iron castings through the numerical calculation of the solidification time.

Regenerated Bragg Grating Sensor Array for Temperature Measurements During an Aluminum Casting Process

An array of regenerated fiber Bragg gratings (RFBGs) was employed to monitor the temperature distribution during an aluminum cast process. Significant temperature gradients in the cast part were observed during the cooling and solidification period. The direction and velocity of the solidification front was revealed by the temperature data obtained by the RFBGs at different measurement points. A generalized calibration curve was established and applied to the RFBG array, avoiding the need of individual calibration measurements of each sensor element of the array. Temperatures measured using the RFBGs and a thermocouple placed in a reference arm of the mold showed excellent agreements and indicated that no thermal drift of the RFBGs sensor elements occurred during the casting. The RFBG measurements were carried out with only a single fiber, which reduced the amount of lead cables in the melt and hence minimized the sensor-induced disturbances to the casting process. In addition, the limited number of cables enables the RFBG sensors to be deployed in small and complex cast geometries. Multipoint temperature sensors based on RFBG arrays can become important tools to improve the quality of casting processes.

Effect of Boron and Cross-Section Thickness on Microstructure and Mechanical Properties of Ductile Iron

Eeffect of Boron addition on the microstructure and mechanical properties of ductile iron, GJS-500-7 grade was studied. Three cast batches with the Boron content of 10, 49 and 131ppm were cast in a casting geometry containing plates with thicknesses of 7, 15, 30, 50 and 75mm. Microstructure analysis, tensile test, and hardness test were performed on the samples which were machined from the casting plates. Addition of 49 ppm Boron decreased pearlite fraction by an average of 34±6% in all the cast plates. However, minor changes were observed in the pearlite fraction by increasing Boron from 49 to 131 ppm. Variation in the plate thickness did not affect the pearlite fraction. The 0.2% offset yield and ultimate tensile strength was decreased by an average of 11±1% and 18±2%, respectively. Addition of 49 ppm Boron decreased Brinell hardness by 16±1%, while 11±2% reduction was obtained by addition of 131ppm Boron.

Critical Thinking on the Introduction of Digitization Within Engineering Training Systems in the Manufacturing Stage of Cast Parts

The paper aims to present a methodology for the analysis of the engineering training systems at the manufacturing stage of castings through critical engineering thinking. Its use [4, 5] requires the development of procedures capable of responding to the problems faced by engineering training in terms of acquiring the tools and procedures. The structure of the analysis took into consideration the following aspects: the motivation to use the proposed procedure, considerations on the engineering behavior, the design of the reasoning adapted to the analysis of the engineering training systems, the determination of the correlations in the processes of obtaining the cast products, the definition and calibration of the digital experiment, the definition and analysis of the factors influencing the last solidification area (the nature of the alloy, the shape of the mold and the casting geometry).

Re-Thinking Design Methodology for Castings: 3D Sand-Printing and Topology Optimization

Additive manufacturing of sand molds and cores for metal castings, often called 3D sand-printing (3DSP), is an efficient “freeform” fabrication process that enables rapid production of sand metal castings. The ability to create highly complex molds and cores for advanced metal casting geometries via 3DSP provides unparalleled design freedom, particularly for low-volume production. However, there is a need to thoroughly understand the opportunities and restrictions of 3DSP in a systematic approach similar to well-established design guidelines for traditional sand casting. This study presents a knowledge-based design framework for 3DSP with the goal of developing new part design guidelines under such 3DSP framework. In particular, constrained topology optimization approach for the part redesign is developed for 3DSP. The presented design framework is compared with traditional sand-casting rules and validated through a case study on an existing metal component. Advantages of the developed 3DSP design framework are illustrated and validated through a case study where a 30% improvement in factor of safety and a 50% reduction in weight of a mechanical part is achieved. Other advantages, such as reduced lead time and production cost, are also observed. This research provides the first known investigation into systematic implementation of simultaneous constraints of 3DSP sand-casting rules mechanical strength through the integration of topology optimization and novel design rules to castings via 3D-printed molds. 3DSP also eliminates multiple design constraints in conventional mold-making and core-box fabrication. Findings from this study can be applied for a wide range of alloy systems, part geometries and loading conditions for sand castings in industrial applications.

Influence of solidification defects on the fatigue behaviour of heavy‐section silicon solution–strengthened ferritic ductile cast irons

AbstractMechanical and fatigue properties of heavy section solution–strengthened ferritic ductile iron (SSF‐DI) castings have been examined in this contribution. Amounts of silicon varying from 3.2 to 3.55 wt% have been used. The effect of antimony on counteracting the formation of chunky graphite has been evaluated. In order to estimate the influence of solidification defects (microshrinkage porosities or degenerated graphite particles) on the fatigue strength of the investigated materials, scanning electron microscope observations of the fracture surfaces and extreme value analysis of the crack initiating defect dimension, √area, have been performed. The propagation of the fatigue crack through the material has been observed by means of microstructural analysis of the cross sections of the fracture surfaces. It has been found that the treatment with Sb is useful to avoid the formation of degenerated graphite particles. Moreover, it has been observed that the most of the fatigue life is spent in the crack initiation stage, where the microshrinkage porosities play a major role. The presence of chunky graphite affects mostly the propagation stage. Finally, mechanical and fatigue properties of SSF‐DI have been compared with those obtained from traditional ductile cast iron specimens taken from the same casting geometry.

Effect of Cast Geometries on Particle Dispersion in Metal Matrix Composites

Metal composite materials are not being extensively used because of their complex processing, agglomeration and dispersion of particles in case of discontinuous reinforcement. Significant amount of research work has been carried to understand and improve primary processing of metal composites using liquid processing route. Most of the research revealed the fact that composites were cast either in plate geometry or geometry of crucible. Present work mainly focuses to examine effect of mold cavity geometries on dispersion of particles in solidifying composite slurries. Aluminium alloy composites using silicon carbide (SiC) particles were manufactured using stir casting technique. ‘T’ shape and plus shape geometries were cast in the present work. Critical velocity and solidification front velocity was analyzed to investigate effect of cast geometries on particle dispersion. Microstructural examination revealed that cast geometries have significant effect on dispersion of particles.

Optimal riser design method based on geometric reasoning method and fruit fly optimization algorithm in CAD

With the continuous development and improvement of computer simulation technology, computer simulation analysis has become an important means for judging the feasibility of casting process design. But computer consumption is also gradually increasing due to the more complex castings, the huge computation quantity and the long cycle of casting process design. Therefore, in order to reduce the computer consumption, a new method for optimal riser design based on geometric reasoning method and fruit fly optimization algorithm in CAD is proposed in this paper. The main focus of the method is to carry out the initial process optimization design of riser purely taking into account the casting geometry based on CAD techniques. Firstly, geometric reasoning method based on implicit surface is used to obtain every hot spot of casting. Secondly, the open source CAD application (HeeksCAD) is used to compute the volume and heat transfer area of casting which need to be compensated. Thirdly, fruit fly optimization algorithm (FOA) is used to optimize the riser geometric sizes. A cylinder sleeve casting is taken as an example to illustrate the feasibility of the methodology. Finally, numerical modeling method confirms the validity of the implementation of the new methodology for optimal riser design. The results indicate that the method could be useful in cutting down the expense and time of casting production cycle, particularly for casting process optimization stage.

Characterization and modeling of the mechanical behavior of high silicon ductile iron

This paper investigates the effect of the solidification conditions and silicon content on the mechanical properties of ductile iron and presents empirical models for predicting the tensile behavior based on the microstructural characterizations. Two ductile iron grades of GJS-500-7 and GJS-500-14 were cast with silicon content of 2.36% and 3.71%, respectively. The cast geometry consisted of six plates with different thicknesses that provided different cooling rates during the solidification. Microstructure analysis, tensile and hardness tests were performed on the as-cast material. Tensile behavior was characterized by the Ludwigson equation. The tensile fracture surfaces were analyzed to quantify the fraction of porosity. The results showed that graphite content, graphite nodule count, ferrite fraction and yield strength were increased by increasing the silicon content. A higher silicon content resulted in lower work hardening exponent and strength coefficient on the Ludwigson equation. The results for 0.2% offset yield and the Ludwigson equation parameters were modeled based on microstructural characteristics, with influence of silicon content as the main contributing factor. The models were implemented into a casting process simulation to enable prediction of microstructure-based tensile behavior. A good agreement was obtained between measured and simulated tensile behavior, validating the predictions of simulation in cast components with similar microstructural characteristics.

Simulation of Centrifugal Casting and Structure of Fe-Ni-Co Super-Invar Alloy

This paper is focused on multi-scale modeling of solidification and alloy microstructure evolution through computer-aided simulation of the technological processes. Microstructure characterization of cast alloy after centrifugal casting including grain size, dendrite cell size and porosity is of interest in this paper. The centrifugal technological process was simulated using special LVMFlow program for computer-aided analysis of casting technologies to predict shrinkage porosity in axi-symmetric part blanks. The cast blanks were made of Fe-Ni-Co alloy with low thermal expansion and after turning could be used as bearing parts in contact with glass or ceramics. A method of combined simulation of technological processes and operating regimes of cast components was developed. The proposed method of simulating the complicated model allows separating the component from casting geometry in CAE postprocessor and the plot distribution of calculated parameters over the component. Also, this method allows varying diameters of hollow cylindrical casting and choosing the best location of components relative to the predicted porosity in the blank for high quality turning. The distribution of temperature and porosity could be used for more precise calculation of internal stresses in cast component under loading conditions with respect to the structural factors. The structural parameter was stated on a base of the calculated temperature fields to associate grain structure of cast alloy with solidification conditions. The austenitic microstructure of Fe-Ni-Co super-invar alloy was studied on the samples, which were cut from the axi-symmetric part after turning the blank. The calculated structural parameter was assigned with the types of grain structure.

Prediction of mechanical performance of Ti6Al4V cast alloy based on microCT-based load simulation

The effect of porosity on the mechanical properties of cast titanium alloy was investigated in this work, specifically for investment-cast Ti6Al4V. X-ray micro computed tomography (microCT) was used to non-destructively analyse pores in 10 samples prior to mechanical testing. A finite element analysis was done on the microCT data providing a 3D view and quantitative values for maximum stress areas. All 10 samples were again analysed by X-ray microCT after physical testing. This allowed the location of failure to be correlated to pores and regions of high stress from the calculations. All samples showed high tensile strength with little effect of the pore size or simulated stress, most likely due to the simplified casting geometry. Irrespective of the microstructure, it was found that an increasing pore size results in increasing simulated stresses around the pores, which correlate strongly with a decrease in the measured ductility of the samples. This result indicates that induced stresses when a sample is put under load affects the ductility, since ductility depends on stress state of the material. Moderate correlation of the simulated stresses with ultimate tensile strength was found for samples with homogeneous microstructure.

Data-Driven Neural Network Model for Robust Reconstruction of Automobile Casting

In computer vision system, it is a challenging task to robustly reconstruct complex 3D geometries of automobile castings. However, 3D scanning data is usually interfered by noises, the scanning resolution is low, these effects normally lead to incomplete matching and drift phenomenon. In order to solve these problems, a data-driven local geometric learning model is proposed to achieve robust reconstruction of automobile casting. In order to relieve the interference of sensor noise and to be compatible with incomplete scanning data, a 3D convolution neural network is established to match the local geometric features of automobile casting. The proposed neural network combines the geometric feature representation with the correlation metric function to robustly match the local correspondence. We use the truncated distance field(TDF) around the key point to represent the 3D surface of casting geometry, so that the model can be directly embedded into the 3D space to learn the geometric feature representation; Finally, the training labels is automatically generated for depth learning based on the existing RGB-D reconstruction algorithm, which accesses to the same global key matching descriptor. The experimental results show that the matching accuracy of our network is 92.2% for automobile castings, the closed loop rate is about 74.0% when the matching tolerance threshold τ is 0.2. The matching descriptors performed well and retained 81.6% matching accuracy at 95% closed loop. For the sparse geometric castings with initial matching failure, the 3D matching object can be reconstructed robustly by training the key descriptors. Our method performs 3D reconstruction robustly for complex automobile castings.

Support for Ingate Design by Analysing the Geometry of High Pressure Die Cast Geometries Using Dijkstra’s Shortest Path Algorithm

A new approach for the analysis of high pressure die casting geometries concerning form filling is introduced. It enables the reduction of simulation cycles needed in the product development process, as they are highly time and cost intensive. Therefore, we developed an analysis tool, which uses shortest paths from each part of the geometry to the chosen ingate surfaces. This way, and by evaluating the information given by basic filling simulations, we can evaluate the usability of a given geometry for a high pressure die casting process and are able to suggest useful strategies to place ingates and to design a filling system.

Defect formation mechanisms in lamellar graphite iron related to the casting geometry

Although lamellar cast iron has been used in advanced applications for about 20 years, our knowledge about the mechanisms affecting microstructure and defect formation is relatively limited. The present paper summarises some solidification-related phenomena from a series of recently published peer-reviewed papers and scientific theses and suggests a mechanism of defect formation which is dependent on the shape of the solidifying casting geometry. When shrinkage porosity or metal expansion penetration occurs, evidence of material transport in the intergranular zone of primary equiaxed austenite grains in the casting and in the intergranular regions between the sand grains in the mould material is seen. Material transport occurs across the casting-mould interface, where the existence of or the permeability of the primary columnar zone determines if material transport can take place.

Numeric simulations of a liquid metal model of a bloom caster under the effect of rotary electromagnetic stirring

At the voestalpine Stahl Donawitz GmbH the continuous casting of round steel blooms is commonly supported by electromagnetically induced stirring of the liquid steel flow. A number of beneficial effects are attributed to electromagnetic stirring in the mould region (M-EMS), e.g. the enhanced transition from columnar to equiaxed solidification, the homogenization of the liquid steel flow or the reduction of surface and subsurface defects. Although the positive effects of M-EMS can be seen on the blooms (e.g. in etchings), the link between electromagnetic stirring of the steel melt and the quality of the solidified bloom is not sufficiently understood. Theoretical considerations are often limited to general cases and their results are therefore not directly applicable to real continuous casting geometries. On the other hand, plant measurements can only be performed to a limited extent due to the harsh conditions and other restrictions (e.g. safety regulations). In this work an alternative approach is used to investigate the steel flow in a round bloom caster under the influence of M-EMS. In a 1:3 scale Perspex model of a round bloom strand, measurements of the flow under the influence of a rotating magnetic field can be conducted. These measurements provide a validation benchmark for the numeric simulations. A numeric model of the before mentioned 1:3 scale model is implemented, encompassing the strand, the submerged entry nozzle as well as the M-EMS device. In the modelling approach, the bidirectional coupling between liquid steel flow and the electromagnetic field/forces has to be considered because otherwise the resulting tangential velocities will be overestimated. With the validated modelling approach, simulations of real casting machines can then be conducted, stirring parameter influences can be shown and conclusions for the real casting process can be drawn.

Mechanical and Fatigue Properties of Heavy Section Solution Strengthened Ferritic Ductile Iron Castings

Recently, standardized solution strengthened ferritic ductile irons have met the interest of the industrial world since their improved mechanical properties and workability compared to standard ferritic–pearlitic ductile irons. For this reason, mechanical and fatigue properties of heavy section solution strengthened ferritic ductile irons castings are examined. Mechanical tests are carried out on specimens taken from the center of castings with long solidification times. Metallographic analyses are performed by using optical microscopy. Fracture surfaces of fatigue specimens are investigated in order to evaluate crack initiation and propagation zones. Finally, fatigue curves of the analyzed alloy are compared with those obtained from pearlitic ductile iron with the same casting geometry.

Grain refinement of gravity die cast secondary AlSi7Cu3Mg alloys for automotive cylinder heads

The effects of AlTi5B1 grain refinement and cooling rate on the microstructure and mechanical properties of a secondary AlSi7Cu3Mg alloy were reported. Metallographic and image analysis techniques have been used to quantitatively examine the macrostructural and microstructural changes occurring with the addition of grain-refining agent at different cooling rates by using a step casting die. The results indicate that the addition of AlTi5B1 produces a fine and uniform grain structure throughout the casting and this effect is more pronounced in the slowly solidified regions. Increasing the cooling rate, lower amount of grain refiner is necessary to produce a uniform grain size throughout the casting. On the other hand, the initial contents of Ti and B, present as impurity elements in the supplied secondary alloy, are not sufficient to produce an effective grain refinement. The results from the step casting geometry were applied to investigate a gasoline 16V cylinder head, which was produced by gravity semi-permanent mould technology. The grain refinement improves the plastic behaviour of the alloy and increases the reliability of the casting, as evidenced by the Weibull statistics.

Flow Dynamics of green sand in the DISAMATIC moulding process using Discrete element method (DEM)

The DISAMATIC casting process production of sand moulds is simulated with DEM (discrete element method). The main purpose is to simulate the dynamics of the flow of green sand, during the production of the sand mould with DEM. The sand shot is simulated, which is the first stage of the DISAMATIC casting process. Depending on the actual casting geometry the mould can be geometrically quite complex involving e.g. shadowing effects and this is directly reflected in the sand flow during the moulding process. In the present work a mould chamber with “ribs” at the walls is chosen as a baseline geometry to emulate some of these important conditions found in the real moulding process. The sand flow is simulated with the DEM and compared with corresponding video footages from the interior of the chamber during the moulding process. The effect of the rolling resistance and the static friction coefficient is analysed and discussed in relation to the experimental findings.