Friday, April 11, 2008

Computer simulation aids casting.

In the design of die casting dies, the object is to produce sound casting as cheaply and rapidly as possible. At the same time consideration must be given to suitable die size, locations of gating system, and selection of an appropriate die casting machine. Foundries in many cases encounter difficulties to ensure shortened lead-time in designing a new die for new product. A lot of estimations have to be done which use fundamentally based on previous experience and application of various mathematical and empirical equations.

In this work, main die design procedures and related equations are presented in a logical way. A computer program is developed to estimate main die elements based on the geometry input of casting shape. After initial inputs have been given, the system does full calculations, optimizes selections, and lists main die element sizes. The program can present die characteristics and casting machine characteristics. From both characteristics the optimum die elements were optimized. Optimum filling time and gating dimensions among other elements of die are estimated. Cooling time, cooling channel locations, and flow rates relations are estimated and presented.


By Karlsson, LarsPublication: Modern Casting Date: Thursday, February 1 1996Subject: Steel industry (Equipment and supplies), Steel casting (Process) (Equipment and supplies), Computer simulation (Usage), Steel castings, Applications softwareProduct: Steel Castings, Applications Software NEC
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Computer simulation of filling and solidification at this Swedish foundry cut lead times, reduced scrap and ensured quality.
Since 1980, Svedala-Arbra's steel foundry, located in southern Sweden, has been developing methods to produce heavy steel castings using the vacuum molding method - the V-process. The steel foundry produces about 6500 metric tons (7150 tons) annually - mainly machine and
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Metal Injection MoldingMIM forms complex metal shapes without the need for machining. Technology Co., LtdSpecialized on investment castings, cf3m, Pctfe, Duplex, Monel, Peek and Process EquipUsed Foundry and Process Equipment Mullers, Melt, Blast, Pollution castings for crushers.
Compared to conventional sand molding, there are several benefits to using the V-process that result in a lower total production cost for the foundry and a high quality casting.
However, to obtain the desired casting results with the V-process, several precautions must be taken. The major cause of scrap is "mold collapses." As a mold fills with metal, the plastic melts and opens the mold up to the vacuum. If the air lost through the vacuum is not replaced with air from the atmosphere to equalize the pressure, the sand in the cope may fall in, causing a mold collapse. To prevent this from happening, air is drawn into the mold through a communicator, which could be a riser from the outside.
To minimize the risk of these defects, computer simulation can be used to analyze the filling sequences and optimize the casting and gating design. In this article, some examples of simulated and cast results of vacuum molded steel castings are presented.
Simulation Engineering
Simulation and calculation methods are used at Svedala for several different purposes. The development process can be described as a kind of simultaneous engineering. The design department is responsible for the coordination of the different activities during the process. The development work is carried out parallel in respect to time with the engineers from the involved departments. To avoid suboptimizing any part of the manufacturing process, engineers collaborate throughout the product development process.
Finite element-based software systems are used to analyze general solid mechanics and dynamic problems. When preparing the cast part for optimum castability, foundry engineers use a computer simulation program (MagmaSoft) based on the finite difference/finite volume method.
Simulation of Filling and Solidification
As a first step, a 3-D model of the cast part with gating and feeding system is created in a 3-D computer aided design (CAD) environment [ILLUSTRATION FOR FIGURE 1 OMITTED]. The CAD-model is then divided into elements [ILLUSTRATION FOR FIGURE 2 OMITTED]. The element mesh is generated automatically after setting a few parameters describing the mesh accuracy. Before starting the calculations, the operator sets different boundary conditions like heat transfer values, and initial conditions such as start temperatures for the appropriate materials, including the type of alloy and mold and core sands.
This article focuses mainly on the filling calculations needed to optimize the gating system to obtain calm filling. Filling calculations are often used primarily to find the right temperature distribution as start values to the solidification simulation. But with the V-process, a more detailed analysis of the filling calculations must be carried out to minimize the risk of the casting defects that might occur due to uncontrolled filling.
Filling Characteristics
When producing a vacuum mold, the pattern plate is mounted on a hollow patternbox connected to a vacuum system. A sheet of thin plastic is preheated and vacuum-formed to the contour of the pattern. After applying the mold coating, a special flask is positioned on the pattern plate and filled with dry, unbonded sand while vibrating the mold. The flask is then connected to the vacuum system. Following the separation of the pattern from the mold, the two half molds are set together with cores, insulating sleeves, etc. and transferred to the pouring station.
During filling of the mold cavity, three different "filling steps" occur with respect to the air flow in the cavity.
* When pouring begins, the air in the cavity is heated and escapes out of the cavity through the vents.
* After the filling gets more stable, air is drawn into the cavity through the vents as shown in Fig. 3. Because the plastic film becomes moist a few millimeters above the melt front, the underpressure causes the air to flow out of the cavity and into the mold. Air is drawn into the cavity through vents to prevent an underpressure in the cavity that could cause a mold to collapse.
* At the end of pouring, the airflow turns and the remaining air in the cavity and vents is pressed out through the vents. This part of the filling is critical and demands careful design of the venting system.
If the gating and venting design is incorrect, the scrap due to mold collapses and sand inclusions will increase. This unforgiving design is the major potential disadvantage with the V-process and must be treated with care.
Filling Simulation
All filling of V-process molds should be done smoothly. The metal should enter the lower part of the casting with a laminar flow, but with a higher flow rate than used in green sand molds. Three different castings of moderate complexity will be examined below. The examples focus mainly on how to analyze different types of filling problems.
Example 1: Pressurized or Unpressurized Gating System? - In general, an unpressurized gating system is preferable when using a bottom-pour ladle. However, for a vacuum-molded steel casting, the metal flow must never be turbulent. The casting in Fig. 4 is machined on all surfaces and experienced initial sand inclusions in its upper region. During filling with the original unpressurized gating system, the metal was flowing uncontrollably in a "wave-like fashion" next to the gate due to a pressure drop when the metal entered the cavity. By changing to a pressurized gating system, the flow is controlled and sand inclusions in the top of the casting were eliminated. Several hundred filler rings have been produced this way without any weld repair, resulting in shorter lead times and lower manufacturing costs.
Example 2: Multiple Filling - By controlling the pressure in the gating system for a multicavity mold, all the castings are filled simultaneously. This is necessary to prevent a mold collapse in the last-filled detailed. Figure 5 shows an example of a computer simulation designed to the dimensions of the different gates. The parting of the mold and other practical considerations determine the positions of the gates. Multiple-casting patterns are of course beneficial for the total capability of the vacuum molding plant.
Example 3: Velocity Drop in Curved Gating System - The often-used rule that a decreasing cross-section in a gating causes a proportionally related pressure drop is not necessarily true. For instance, a gating system with curved gatings [ILLUSTRATION FOR FIGURE 6 OMITTED] leads to frictional losses at the mold/metal interfaces. These losses cause a velocity drop that results in a longer filling time for the casting.
Originally, straight gates were used, but severe erosion at the steps of the mantle demanded a better solution. To prevent mold erosion or collapse due to high pressure, a refractory impact plate was placed at the lower end of the downspine. The new and improved design resulted in better surfaces and wear characteristics of the mantle.
Solidification Simulation
The simulation of casting solidification is an aid for foundryman to predict shrinkage and porosity in castings. Following are two examples of how solidification simulation can be used.
A simple, but important result of the collaboration between the design and foundry engineers is shown in Fig. 7. Computer simulated results of the original design indicated porosity in the area where the mantle is exposed to wear. Design changes were made, which allowed the part to be converted from hand to V-process molding. With the final design, no porosity was found.
In Fig. 8, a frame end with a casting weight of about 2.5 metric tons (2.75 tons), is shown at 50% solidification. When examining the internal cores (made from olivine sand) in Fig. 9, it can be seen that sintering occurs at the surfaces of the casting's center with accompanying surface defects on the casting. For this reason, chromite sand replaced olivine for the internal cores.
Computer simulation of the casting process gives the foundryman information on how to design the casting and gating system properly. The principle of the calculations can be generalized to more complex castings without any restrictions. A proper casting design results in lower scrap and less repair welding for the foundry. Using simulation, development times are decreased and the foundry gets as close as possible to a "right the first time solution."
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This article presents an approach to making an aluminum automobile prototype by integrating numerical simulation and rapid prototyping into investment casting. Following the integrated prototype procedure, a sound aluminum (Al-Si-7Mg) manifold prototype with excellent contour and an acceptable surface finish was made with only one casting trial. This study indicated that the potential of the rapid prototyping-investment casting coupling could be more effective with the aid of integrated numerical simulation, and numerical optimization of the casting parameters aids in minimizing the risk of casting failure and avoiding the iterative casting trials.
For more information, contact M. Wu, Foundry Institute, Intzestrasse 5, Aachen, Germany D-52072; telephone 49 241 804067; fax 49 241 8888276; e-mail


Article Information
Parallelisation of a simulation tool for casting and solidification processes on Windows platformsClauss, C.; Schuch, S.; Finocchiaro, R.; Lankes, S.; Bemmerl, T.Parallel and Distributed Processing Symposium, 2006. IPDPS 2006. 20th InternationalVolume , Issue , 25-29 April 2006 Page(s): 8 pp. - Digital Object Identifier 10.1109/IPDPS.2006.1639606Summary: Since the beginning of computational engineering, the numerical simulation of physical processes is an essential element in the area of high performance computing. Thus, also the domain of metal foundry demands the computational simulation of casting and solidification processes. A popular software tool for this purpose has been developed by the RWP GmbH in Roetgen, Germany. This tool, named WinCast, is a complete software suite, which contains modules for pre-, main- and post-processing of simulation data sets. A core module of WinCast is TFB, which determines the chronological temperature distribution of a casting process based on a finite-element-method and a Gauss-Seidel solver. With the increasing demand for even higher precision of the simulation results on one hand, and a growing need for even larger data sets on the other hand, the parallelisation of this module became inevitable. In this paper, we present our work accomplished to parallelise the solving algorithm of this module. We have chosen an MPI based master-slave approach for compute clusters by using a self-developed MPI library for Windows platforms.» View citation and abstract


J Mater Sci Mater Med. 2002 Mar ;13 (3):301-6 15348628 (P,S,E,B)
Numerical simulation of the casting process of titanium removable partial denture frameworks.
[My paper] Menghuai Wu, Ingo Wagner, Peter R Sahm, Michael Augthun
Foundry Institute, University of Technology Aachen, Intzestr. 5, D-52072 Aachen, Germany.
The objective of this work was to study the filling incompleteness and porosity defects in titanium removal partial denture frameworks by means of numerical simulation. Two frameworks, one for lower jaw and one for upper jaw, were chosen according to dentists' recommendation to be simulated. Geometry of the frameworks were laser-digitized and converted into a simulation software (MAGMASOFT). Both mold filling and solidification of the castings with different sprue designs (e.g. tree, ball, and runner-bar) were numerically calculated. The shrinkage porosity was quantitatively predicted by a feeding criterion, the potential filling defect and gas pore sensitivity were estimated based on the filling and solidification results. A satisfactory sprue design with process parameters was finally recommended for real casting trials (four replica for each frameworks). All the frameworks were successfully cast. Through X-ray radiographic inspections it was found that all the castings were acceptably sound except for only one case in which gas bubbles were detected in the grasp region of the frame. It is concluded that numerical simulation aids to achieve understanding of the casting process and defect formation in titanium frameworks, hence to minimize the risk of producing defect casting by improving the sprue design and process parameters.
J Mater Sci Mater Med. 2001 Jun ;12 (6):485-90 15348262 (P,S,E,B)
Numerical simulation of the casting process of titanium tooth crowns and bridges.
[My paper] M Wu, M Augthun, I Wagner, P R Sahm, H Spiekermann
Foundry Institute, University of Technology Aachen, Intzestr.5, D-52072 Aachen, Germany.
The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a "feeding criterion", and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically "poured", and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control.
J Mater Sci Mater Med. 1999 Sep ;10 (9):519-25 15348102 (P,S,E,B)
Numerical study of porosity in titanium dental castings.
[My paper] M Wu, P R Sahm, M Augthun, H Spiekermann, J Schädlich-Stubenrauch
Foundry Institute, University of Technology Aachen, Intzestr. 5, D-52072 Aachen, Germany.
A commercial software package, MAGMASOFT (MAGMA Giessereitechnologie GmbH, Aachen, Germany), was used to study shrinkage and gas porosity in titanium dental castings. A geometrical model for two simplified tooth crowns connected by a connector bar was created. Both mold filling and solidification of this casting model were numerically simulated. Shrinkage porosity was quantitatively predicted by means of a built-in feeding criterion. The risk of gas pore formation was investigated using the numerical filling and solidification results. The results of the numerical simulations were compared with experiments, which were carried out on a centrifugal casting machine with an investment block mold. The block mold was made of SiO2 based slurry with a 1 mm thick Zr2 face coat to reduce metal-mold reactions. Both melting and casting were carried out under protective argon (40 kPa). The finished castings were sectioned and the shrinkage porosity determined. The experimentally determined shrinkage porosity coincided with the predicted numerical simulation results. No apparent gas porosity was found in these model castings. Several running and gating systems for the above model casting were numerically simulated. An optimized running and gating system design was then experimentally cast, which resulted in porosity-free castings.
Adv Space Res. 1986 ;6 (12):85-99 11537847 (P,S,E,B)
Bioscience experiments in the German Spacelab mission D-1: introduction and summary.
[My paper] G Horneck, G Greger, P R Sahm
DFVLR, Institute for Aerospace Medicine, Koln, FRG.
The German Spacelab mission D-l was performed from 30 October through 6 November 1985. Payload operation in orbit was managed by DFVLR for the Federal Ministry of Research and Technology. The scientific program of the mission placed emphasis on microgravity research. In bioscience, the role of gravity in vital functions of biological systems was investigated, such as intracellular and intercellular interactions, developmental processes as well as regulation and adaptation in highly organized systems including human beings. In addition, the biological significance of cosmic radiation or altered zeitgeber within the complex matrix of all relevant spaceflight components were studied. Most of the experiments were accommodated in the following three payload elements: The Bioscience Experiment Package, and the ESA facilities Vestibular Sled and BIORACK. The information gained from the individual experiments will be compiled to help answer pending questions of space bioscience.
Mesh-terms: Adaptation, Physiological; Animals; Biological Sciences; Cell Physiology; Circadian Rhythm; Cosmic Radiation; Exobiology; Germany; Gravity Perception; Human; Laboratories; Research Design; Space Flight :: instrumentation; Space Flight :: organization & administration; Space Flight :: trends; Weightlessness;
Dent Mater. 2001 Mar ;17 (2):102-8 11163378 (P,S,E,B)
Application of laser measuring, numerical simulation and rapid prototyping to titanium dental castings.
[My paper] M Wu, J Tinschert, M Augthun, I Wagner, J Schädlich-Stubenrauch, P R Sahm, H Spiekermann
Foundry Institute, University of Technology Aachen, Intzestr.5, D-52072, Aachen, Germany.
OBJECTIVES: This paper describes a method of making titanium dental crowns by means of integrating laser measuring, numerical simulation and rapid prototype (RP) manufacture of wax patterns for the investment casting process. METHODS: Four real tooth crowns (FDI No. 24, 25, 26, 27) were measured by means of 3D laser scanning. The laser digitized geometry of the crowns was processed and converted into standard CAD models in STL format, which is used by RP systems and numerical simulation software. Commercial software (MAGMASOFT) was used to simulate the casting process and optimize the runner and gating system (sprue) design. RP crowns were 'printed' directly on a ModelMaker II 3D Plotting System. A silicone negative mold (soft tool) was made from the RP crowns, then more than hundreds wax crowns were duplicated. The duplicated crowns were joined to the optimized runner and gating system. By using the investment casting process 20-25 replicas of each crown were made on a centrifugal casting machine. All castings were examined for porosity by X-ray radiographs. RESULTS: By using the integrated scanning, simulation, RP pattern and casting procedure, cast crowns, free of porosity, with excellent functional contour and a smooth surface finish, were obtained from the first casting trial. SIGNIFICANCE: The coupling of laser digitizing and RP indicates a potential to replace the traditional 'impression taking and waxing' procedure in dental laboratory, with the quality of the cast titanium prostheses also being improved by using the numerically optimized runner and gating system design.
Mesh-terms: Calcium Sulfate; Computer Simulation; Computer-Aided Design; Crowns; Dental Casting Investment :: chemistry; Dental Casting Technique :: instrumentation; Dental Materials; Dental Models; Dental Prosthesis Design; Human; Imaging, Three-Dimensional; Lasers; Porosity; Radiography; Silicones; Software; Support, Non-U.S. Gov't; Surface Properties; Titanium :: chemistry; Tooth Crown :: anatomy & histology; Waxes;
Eur J Oral Sci. 1999 Aug ;107 (4):307-15 10467947 (P,S,E,B)
Numerical simulation of porosity-free titanium dental castings.
[My paper] M Wu, M Augthun, J Schädlich-Stubenrauch, P R Sahm, H Spiekermann
Foundry Institute, University of Technology Aachen, Germany.
The objective of this research was to analyse, predict and control the porosity in titanium dental castings by the use of numerical simulation. A commercial software package (MAGMASOFT) was used. In the first part of the study, a model casting (two simplified tooth crowns connected by a connector bar) was simulated to analyse shrinkage porosity. Secondly, gas pores were numerically examined by means of a ball specimen with a "snake" sprue. The numerical simulation results were compared with the experimental casting results, which were made on a centrifugal casting machine. The predicted shrinkage levels coincided well with the experimentally determined levels. Based on the above numerical analyses, an optimised running and gating system design for the crown model was proposed. The numerical filling and solidification results of the ball specimen showed that this simulation model could be helpful for the explanation of the experimentally indicated gas pores. It was concluded that shrinkage porosity in titanium dental casting was predictable, and it could be minimised by improving the running and gating system design. Entrapped gas pores can be explained from the simulation results of the mould filling and solidification.
Mesh-terms: Chemistry, Physical; Comparative Study; Computer Simulation; Crowns; Dental Casting Investment :: chemistry; Dental Casting Technique :: instrumentation; Dental Prosthesis Design; Forecasting; Gases; Human; Models, Chemical; Porosity; Software; Support, Non-U.S. Gov't; Surface Properties; Titanium :: chemistry;
Dent Mater. 1998 Sep ;14 (5):321-8 10379262 (P,S,E,B)
Computer aided prediction and control of shrinkage porosity in titanium dental castings.
[My paper] M Wu, J Schädlich-Stubenrauch, M Augthun, P R Sahm, H Spiekermann
Foundry Institute, Aachen, Germany.
OBJECTIVES: The main objectives were to investigate the possibility and reliability of quantitative prediction and control of the concentrated shrinkage porosity (macroporosity) in titanium dental castings by means of a numerical simulation technique; and finally to optimize the filling and feeding system design for dental castings. METHODS: A commercial software, MAGMASOFT (Giessereitechnologie GmbH, Germany), was employed to simulate the mold filling and solidification process, and predict the shrinkage tendency in a sample dental casting, two simplified tooth crowns with a connector bar between them. The numerically predicted shrinkages were compared with the experimental results. The experiments were carried out on a centrifugal casting machine. The same geometric and processing parameters of the casting as in the simulations were strictly controlled. RESULTS: The computer predicted shrinkage porosity coincided with the performed experiments, demonstrating the reliability of the numerical model and the thermal physical data chosen for the calculations. Based on the above numerical model, several filling and feeding systems for the same casting were numerically simulated and compared. Finally an optimized design for this sample casting was proposed, and porosity-free castings were obtained. SIGNIFICANCE: It was expected that the numerical simulation technique could be further developed for dental laboratories to aid the real dental casting design.
Mesh-terms: Computer Simulation; Dental Alloys :: chemistry; Dental Casting Technique; Numerical Analysis, Computer-Assisted; Porosity; Support, Non-U.S. Gov't; Titanium :: chemistry;
Dtsch Zahnarztl Z. 1989 Nov ;44 (11):849-51 2700704 (P,S,E,B)
[Mathematical simulation of the cooling and solidifying process in improving the quality of dental castings]
[My paper] M Augthun, L Beckers, H Kreutzer, P R Sahm, W Schäfer, J Schädlich-Stubenrauch
CASTS-3D (Computer Aided Solidification Technologies) is a FEM software system for the simulation of heat transfer, melt flow and solidification problems for foundry purposes. This software system may basically be applied to dental castings as well--especially if the FEM software system is optimized and exact data on the thermophysical properties of the dental alloys are provided.
Mesh-terms: Computer Simulation; Crowns; Dental Alloys; Dental Casting Technique; English Abstract; Software;
Dent Labor (Munch). 1989 Jun ;37 (6):908-14 2676622 (P,S,E,B)
[Which sprue is best? Simulation of casting technic]
[My paper] H Kreutzer, W Schäfer, J Schädlich-Stubenrauch, P R Sahm
Mesh-terms: Dental Casting Technique :: instrument


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