76. On the feasibility of determining the Heat Transfer Coefficient in casting simulations by Genetic Algorithms
1The University of Manchester, Sackville street, Manchester M13 9PL, UK; 2National Technical Univerity of Athens, School of Mechanical Engineering, Heroon Polytehneiou 9, 15780 Athens, Greece.; 3National Technical Univerity of Athens, School of Naval Architecture and Marine Engineering, Heroon Polytehneiou 9, 15780 Athens, Greece.
In studying metal casting using simulation with commercially available software, the Heat Transfer Coefficient (HTC) between the casting and the mould surrounding it is not known, yet it is required and its influence on the accuracy and credibility of results is crucial. Temperature distribution, phase changes and mechanical properties as well as defects may appear significantly different to reality depending on the HTC employed in the simulation. Thus, typical HTC values are adopted, as commonly suggested by the software’s developpers. Furthermore, the HTC may differ from region to region, mainly due to the local casting modulus, i.e. the ratio of volume to surface of the different bodies that may comprise the casting. As a solution, it is suggested to use an intelligent search methodology based on a genetic algorithm (GA) that can presumably determine the correct value of HTC or indeed the different HTCs. The GA in essence tries different HTC values on the simulation program stochastically, until a stopping criterion is reached. The latter consists of an acceptably low difference between the real and simulation curves of temperature versus time at one or more points of the casting. In order to test this methodology, numerical casting experiments were conducted using a simple as well as a more complex casting geometry. The numerical casting experiments were conducted on ProcastTM assuming specific HTC values and, as a result, the temperature versus time curve for particular points of the casting were obtained. Then, the GA was setup and the HTC search methodology described above was implemented. In both casting cases, the GA succeeded in finding the HTC values originally employed. Furthermore, the influence of the most important GA parameters on the accuracy and speed of reaching the desired HTC values was explored.
98. Optimization of high pressure die casting process regarding small parts in zamak alloys
Instituto Superior de Engenharia do Porto, Portugal
The casting industry is one of the major industries in the world with a great impact in everybody`s life. Casted products can be found all over around, since the most tiny part like a bottom to the biggest naval ship motor parts and carcasses, all made by casting processes. The demand for a high quantity of products in order to respond to a higher demanding market, turn on the need to develop this casting process, creating a new branch in this industry, the die casting.
Die casting is a process where a permanent mould is used, and melted metal is injected by pressure, allowing smaller cycles and continuum parts production.
Die casting can be carried out in various ways, depending on the need of the project, depending on the need to have parts presenting finished bright and polished look if we are working in the decoration area, or in other hand we may need solid and resistant parts, if these ones are to be implemented in functional demanding works. The results will only depend on the parameters used in the process and on the molds design. The functional parts are far the most demanding in the parameters requirements, being need to have additional attention to avoid defects in the final product like porosities, segregations, cold joint, inclusions and incomplete fill that can occur due to temperature, pressure, retained gases, unappropriated cycle time or other points that might interfere with the casting.
This study is focused in die casting applied to automobile industry where many casted parts are used in their components. Car doors are no exception; therefore, zamak casted parts are used in command cables as cable cuts and working as functional parts. Is then necessary to have a very precise control over the entire casting process, so these parts can be obtained with less defects.
The study is then based on three different samples that are already in production, by analyzing their status as casted and identifying their defects by using magnifier views and x-ray exams. A second phase is then initiated with the help of finite elements software (FEM) dedicated to casting processes; here the main goal is to establish all the parameters to be improved, as well as the mould design in a way to obtain the finest parts as possible by the elimination of the defects that where obtained by the previous way.
The premises according to NADCA standards were established, so that all the existing and future parts could be created with excellent quality, as required by automobile industry.
115. Analytical cost estimation model in High Pressure Die Casting
1Università degli Studi di Parma, Italy; 2Department of Industrial Engineering and Mathematical Sciences, Università Politecnica delle Marche, via brecce bianche 12, 60131, Ancona, Italy
The present paper aims at the definition of an analytical model for the cost estimation of the High Pressure Die Casting (HPDC) process, which is based on two main pillars: (i) knowledge collection and (ii) cost estimation rules. The novelty of this approach is link between the analytical model (equations) and the geometrical features of the product under development. The relationship between geometrical features and cost items gives an accurate result in terms of cost breakdown and it can be used by product designer as a powerful tool for the application of Design-to-Cost rules in HPDC sector
171. Hot forging operations of brass chips for material reclamation after machining operations
Lund University, Sweden
Metal cutting chips are a by-product of all machining operations. When manufacturing components by machining, it is not unusual that a majority of the workpiece material is converted to chips. The chips from the cutting process needs to be disposed of in some way; the most common practice in industry is to send the chips back to the material supplier for recycling.
In this paper a method of recycling chips derived from the brass alloy CW614N by use of hot forging operations is presented. The general idea for the developed method is to find a relatively simple procedure that is possible to implement for recycling of materials in-house at small and medium sized enterprises, SMEs. By applying hot forging methods on pre-compacted cutting chips, it may well be possible to successfully forge blanks for subsequent machining having the same, or nearly the same, mechanical properties and application as a blank forged from raw material.
The results presented in this paper show the result from initial experiments for evaluating if the envisioned process is possible to implement, and which process parameters to evaluate to enhance future development of the method.
Experiments have been made regarding density of forged blanks, machining and function tests as well as Energy Dispersive X-ray, EDX, analysis on the chemical composition.
Density measurements show that the hot forged blanks all have close to the same density when compared with the raw-material.
A standardized function test used in industry for the machined components was performed on blanks machined to a finished product. The function test shows an acceptance rate of 62.5 percent for parts forged with chips derived from brass alloy CW614N.
Alloys containing zinc can be difficult to sinter due to the propensity for dezincification and therefore EDX-analyses of the chemical composition was made. When heating the material to forging temperature, there is a risk of changing the materials chemical composition compared to the raw material. The EDX-analyses show no difference in chemical composition between the raw material and the hot forged blanks. EDX line scan analyses show difusion bonding between some chips, forming a uniform material without significant changes in chemical composition. A few chip boundaries exist in the microstructure but the fact that some difusion bonding between chips has occurred shows that the tested method has a possibility to be implemented in the industry in the future after further development.
Thus, the current research show that partial difusion bonding between the chips has occurred and created a homogenous microstructure indicating a future potential for the envisioned process. This is further aided by the notion that heating and forging processes do not appear to affect the chemical composition of the material. However, additional research is needed before industrial implementation even though the evaluated method shows promising results.