THE COMPUTER SIMULATION FOR INVESTMENT CASTING FROM SUPER-ALLOYS NI Ing. Aleš Herman *

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1 THE COMPUTER SIMULATION FOR INVESTMENT CASTING FROM SUPER-ALLOYS NI Ing. Aleš Herman * *Department of Manufacturing Technology, Faculty of Mechanical Engineering, Czech Technical University (ČVUT) at Prague, Technická 4, Praha 6, Tel , Fax , hermana@fsid.cvut.cz Abstract The contribution deals with utilization simulation software for the casting made of superalloy on basis Ni (INCONEL) using investment casting technology. The methodology procedure of suggestion technology by using computer simulation and the methodology of obtaining data for material database are is described here. 1. INTRODUCTION Foundry simulation software simulates mainly pouring and filling of the mould by melted metal, followed by solidification and cooling of a casting. It makes possible to test the designed technology before the production starts. The advantage and the return of the investment of this software depended on the conditions in the particular foundry volume of its production (mass of castings, series, material etc.) and also willingness and preparedness of the technologists to use the SW. The profit is also closely connected with the choice of the particular simulation program from a wide offer of these products in our market and there are considerable differences in the price and quality. There are six important simulation software offered in the Czech Republic (MAGMA, PAM-CAST/SIMULOR, SIMTEC, NOVA FLOW&SOLID, PROCAST, SOLSTAR). They differ from each other in the principle of the calculation (FDM, FEM), hardware requirements, in the number of physical phenomenon involved and accuracy of their description, in accentuation on the certain materials of manufacturing process in some and of course, in the price (from 100 thousand to 1 million crowns). 1.2 Simulating SW on Department Manufacturing Technology in Faculty of Mechanical Engineering at The CTU in Prague We can use Iron CAD to constitute the geometry for simulation at The Department of Manufacturing Technology of the Faculty of Mechanical Engineering at the Czech Technical University (CTU) in Prague. It is quite easy system for users but very effective for designing of the exact 3D models of castings, their gating system, risers, cores and moulds. It contents an offer for pouring basins and other parts of gating system, different types of risers and insulation sleeves etc. It is possible to make the own selection of the most often used elements and also to draw the 2D drawings. The important fact for the foundry technologists is the possibility to work with the geometry of mechanical parts designed in an other CAD system, to modify the shape by machining allowances and drafts, technological additions, risers, gating system etc. and to export this modificated geometry into the simulating SW. We dispose of a special SW foundry technology II for proposing of risers and gating system. The simulations are processed by program Nova Flow + Nova Solid by the Swedish company NovaCast and by

2 program PAM-CAST/Simulor by the French company PAM-ESI Group. It reads the geometry in the STL (stereolithography) and DXF formats. 2. THE USING OF COMPUTER SIMULATION IN INVESTMENT CASTING TECHNOLOGY One the biggest problems in investment casting technology is the production of a wax pattern and following tests of the right function of gating and risering system. This phase requires the pouring of test castings and often also expensive modification of a metal (aluminium alloy) mould for the production of wax patterns. And this is the reason why this paper is aimed to this technology. 2.1 Modification of simulation software The first condition for computer using of this technology was the modification of simulating software. The software which we are using cannot work with this technology. Therefore I decided to use next ways for solving this problem. First way is to test the pouring to the shell moulds when I substitute classical mould sand by air. This way I am making the mistake because I change heat conduction with convection as the air has very low heat conduction and removal of heat by surface by convection and radiation is many time bigger than by heat conduction. In view of the fact that the testing is done on the casting being made I can find out and modify physical dependence on mould sand and air on the temperature. It will be only fictive data. These primary data for air are in the chart 1 Chart 1 Primary data for mould material air (real data for air) t [ o C] C p [kj.kg -1.K -1 ] 10 3 λ [W.m -1.K -1 ] ρ [kg.m -3 ] ` Where t is temperature λ heat conduction C p specific heat ρ density For the calculation of ρ was used the relation [1]: ρ ρ p 1 + γ. t p 0 =. [1] 0 Where ρ 0 =1,276 kg.m -3 is an initial density P 0 = 10 5 Pa initial pressure γ=0,00366 K -1 thermal cubic expansion coefficient p Pa pressure

3 For the calculation dependence on pressure on the temperature p was used the relation [2]: p = ρ r. t where r = 287,04 J.kg -1.K -1 is a gas coefficient. For approximately calculation this dependence on we can used next the relation [1]: Pressure is increased of 1,5x10 4 Pa per 100 o C. After the testing and checking these values for mould material air will be deposite and it will be possible to optimalize the casting with a view to rise of interior defects and optimalization of gating system. (It is shown in Chart 2 ) Chart 2 The final data for mould material air (fictive data for air) t [ o C] C p [kj.kg -1.K -1 ] 10 3 λ [W.m -1.K -1 ] ρ [kg.m -3 ] The specification of the thickness of shell and insulation measures For modelling of shell mould we can choose two procedures. a) To use the possibilities of simulation software and to set up here the shell part of mould. Main disadvantage of this is a constant thickness around all casting. b) The second possibility is to model the shells in 3D CAD system with view of special mood of forming sand (thicker wall in the corners, thinner walls in exterior edges). This way is much more complicated but more exact with a view of the removal of heat by different thickness of material. If the shell is isolated then isolation must be modelled in cad system. This isolation is then put into the simulation software in modul Import 3D data. 2.3 The choosing of initial conditions At first we place the casting into the space of mould box and we set the initial conditions up. Then we do the dividing of casting into the elements. This dividing must be done in the way of compact element. And then we have to set the shell up by constant thickness of shell. When the size of mould box is set I can define the materials. a) The material of casting pouring temperature b) The material of mould air, initial temperature - about 40 o C c) The material of shell - initial temperature o C [2]

up, I save it and I can simulate. Fig.1.

4 After this I must set up the gate point and I can set up the thermocouples and air-gap. When I have the initial conditions set up, I save it and I can simulate. Fig.1. 3D model the blade and 3D model of casting blade with gating and risering system Fig.2. 3D model the part of rotor and 3D model of casting with gating and risering system Fig.3.The creation of shell 3D model in the simulation software

5 Fig.4.The phases of filling the field of liquid phases Fig5.. The phases of solidificatio n the temperature field

6 2.4. Links to Internet pages - Material databases The problematic of searching data on web is very complicated. There doesn t existed any web page or service on web, which would give to all type of data field. The data have to searched in different chemical charts, different databases. The data obtaining of this way is necessary experimental to verify by way of cooling curves. For filling database super-alloy of Ni was used next free databases on Web: Web elements - Here you can look at the properties of each alloying element JSC Pathfinder materials & K&K Associates Materials - Ductile Iron Society - A great resource about Ductile Iron data Another great link page - with downloadable databases Huge Steel link page MatWeb w.matls.com/ 3. CONCLUSION There are still not too many foundries, which use the simulation SW. The reason is the price of the SW, the bad financial situation of the Czech foundry and also the fact that it is still not common to use the network or the discs for the drawing to came from the designers to the foundry. The geometry pattern and the whole process of technology is hold back in flexibility this way. Although the technologist s capabilities and experience is important, the simulation SW can be a useful help, which will be effective to optimise the whole process, increase metal use, decrease the percentage of the waste and this way to improve the fabrication. The simulation also helps to understand the connection and to educate the technologist in the profession. From all mentioned here we can deduced the way of optimation of the gating and risering system for the investment casting technology. This optimation is demanding mainly owning to problematic shapes of castings, shapes of gating systems (it is possible to have up to tens of patterns in one sprue), to shape of risers and to the conditions of pouring. But from the results gained up to this time we can see the practical and theoretical meaning of this work. This research has been supported by the research intention No. CEZ:J04/98: References: 1. Herman, A. Využití počítačových simulací pro technologii přesného lití metodou vytavitelného modelu, Disertační práce v přípravě 2. Herman, A Svarovsky, M Computer aided foundry technology, TRANSCOM 1999, Proceedings, Section 6, p Nožička, J. Sdílení tepla, skripta ČVUT Praha Nožička, J. - Termodynamické tabulky, ČVUT Praha Vohlídal, J. Julák, A. Chemicke a analyticke tabulky, GRADA, 1999

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