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  • 1. International Journal of Engineering Research and Developmente-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.comVolume 3, Issue 3 (August 2012), PP. 11-16 Billet shape optimization for minimum forging load using FEM analysis Sunil Mangshetty1 , Santosh Balgar2 1 Prof., Department of Mechanical Engineering, P.D.A.College of Engg,Gulbarga,India 2 Student, Department of Mechanical Engineering, P.D.A.College of Engg,Gulbarga,IndiaAbstract––The objective of this project work is to obtain an optimal billet shape in the consideration of the influence ofthe metal flow deformation in closed die forging process. Finite element method in conjunction with optimizationalgorithm (APDL) was used to analyze the effect of billet shape on forging load in axisymmetric closed die forgingprocess. Finite element software (ANSYS) was used to Simulate closed die forging process and then performing a seriesof optimization iterations in order to obtain the optimal shape of the billet based on forging load minimization. Thematerial used is aluminium metal matrix composite ( AlMgSi matrix with 10% SiC particles). The goal of the simulationand optimization process is to minimize the forging load and produce crack-free forgings. The optimal shape of the billetthat gives minimum forging load was obtained after several optimization iterations. The approach used in this study couldbe extended to the optimization of more complicated forging products. Due to the advances in computer technology basedfinite element software, the forging loads can be easily estimated which is iterative process in the old technique ofprototype built up and destructive testing. In the present work considering 3 critical design parameters with criticalplastic strain limit as the state variable and keeping the forging load as the objective function and the billet shape isoptimized for different diameter to height.Keywords––Die Forging, Finite Element Method, Metal Matrix Composites, Optimization. I. INTRODUCTION Manufacturing Processes face major competitions in automotive industry to produce lighter, cheaper, and moreefficient components that exhibit more precise dimensions, need less machining and require less part processing. Todayforging industry is facing stiffer challenges from alternative manufacturing processes. Forging industry has to be cost andquality conscious if it has to maintain its position over other manufacturing processes. With the rapid increase in affordablecomputing power, metal forming simulation based on finite element method is becoming a practical industrial tool. By usingsuch tool, a forge designer could decrease cost by improving achievable tolerance, increasing tool life, predicting andpreventing flow defects, and predicting part properties. The optimization of forging process design and forging process plan for various work materials can be based onthe maximization of production rate, minimization of production cost, minimization of die cost, maximization of productquality, minimization of forging loads. The finite element method provide a prediction of the results of a metal formingprocess, but still relies on an experienced designer to interpret the results of the analysis and modify the process based onprior knowledge and experience. Current research efforts have sought to use computational resources to enhance andoptimize process designs based on a starting design, and improvement of the design is based on the process independentvariables, dependent variables and objective function. The main factors effecting the material flow deformation are dieshape, material properties, billet height/diameter ratio, and frictional condition at the billet/die interface. ANSYS parametricdesign language (APDL) is a scripting language that can be used to build the model in terms of parameters (variables). TheAPDL is used to build the model in a parametric form to enable changing these parameters during the optimization process,so that the optimal billet shapes is obtained. The design variable (DV) is as the billet height/diameter ratio. The equivalentstrain is given as a State Variable (SV). The state variable is working as constrain in the optimization process, forcing thedesign parameters to be adjusted in order to have a strain not higher than the fractural strain. II. FINITE ELEMENT METHOD A cylindrical billet is going to be forged to produce the final forged part shown in Fig. 1 with a minimum loadpossible by optimizing the billet height/diameter ratio. The billet is represented with initial radius and then the height iscalculated based on the volume of the die cavity. The initial billet is represented with geometrical model consisting ofassemblage of finite element. Equations relating the distribution of forces and displacements of the metal are established andthe boundary condition and die movement are imposed. 11
  • 2. Billet shape optimization for minimum forging load using FEM analysis Fig 1: Overall geometry of close die process Two dimensional geometry is represented for die, container and billet are shown with dimensions in figure 1. Allmajor initial dimensions are represented in the problem. Ansys mixed approach is used to built the geometries. For dieshape, bottom approach and other geometry top down approach is used in the problem. The geometry is built as per thedimensions and connectivity is not maintained to carry nonlinear large deformation contact analysis to simulate closed dieforging process.2.1 Aluminium Metal Matrix Composites Aluminium is the most popular matrix for metal matrix composites (MMCs). Aluminium alloys are attractive dueto their low density, their capability to be strengthened by precipitation, their good corrosion resistance, high thermal andelectric conductivity, and high damping capacity. Aluminium matrix composites (AMCs) offer a large variety of mechanicalproperties depending on the chemical composition of the Aluminium matrix. Forging MMCs cause particles and whiskers breakage, and normally result in cracks at the outer surface of thebillet. To avoid fibres and particles breakage which lead to cracks, the equivalent strain of the material must be kept lowerthan the fractural strain shown in Fig.2, which is ε = 1.05. The fractural strain is used in the optimization process as a statevariable maximum limit. Figure 2 Flow curve of AlMgSi+10% SiC particles.2.2 Problem statement The main objective the project is to reduce the wastage of billet material and minimize the forging load required toforge that material by using finite element simulation in Ansys environment.2.3Objectives  Finite element model preparation.  Finding the optimal billet shape for proper die filling.  Finding the minimum forging load to get crack free forging product.  Finding the material reduction error for experimental and analysis method.  Finding the load reduction error for experimental and analysis method.2.4 Material Description (AlMgSi + 10% SiC Chemical composition) Al Mg Si SiC Density (gr/cm3) 86% 1% 3% 10% 2.72% 12
  • 3. Billet shape optimization for minimum forging load using FEM analysis Fig 3 Design VariablesDesign Variables (DV): D1 – Die Movement, R1 – Billet radius and H1- Billet Height The figure 2 shows design variablesused in the problems. These regions are selected due to its critical nature in deciding the forging load and plastic conditions.Design variables are nothing but geometry construction variables like diameter and height. A total of 2 design variables areconsidered for optimisation of the design cycle for load optimization.State Variables (SV): Maximum plastic strain allowed for the problem equal to 1. Beyond which cracks will start in theforging process.Objective Function (OF): The load required for the forging process is taken as the objective function. Here the main workis to limit the forging load in the process by design optimising the process for design variables and state variables. Fig 4 Contact Pair Creation Contact elements are defined between die and billet interface, billet and contaner interface. Targe169 andConta172 elements are used for representation. Contact manager is used to build the contact pairs between the members.Target elements are the rigid elements and contact elements are the flexible members. Separate contact pairs are createdwith reduced penetration tolerance. A friction model of 0.1 is used for simulating the problem. Contact elements are thesurface elements which have the algorithem to represent possible sliding and penetration which movement of the membersrelative to each other. The die nodes are used to apply the displacement loads. Contact elements uses lagrangian approachfor better results. The status of contact, contact penetration, sliding etc can be observed in the contact simulation Fig 5 Vonmises stress results for initial structure 13
  • 4. Billet shape optimization for minimum forging load using FEM analysis Analysis results for vonmises stresses are presented above. Maximum vonmises stress of 330Mpa can be observedin the problem. Left picture is represented in 2dimensional domain and right side picture is represented in three dimensionaldomains Fig 6 Displacement Plot along the length of the sheet The graph indicates displacement along the top nodes of the billet. The graph almost resembles inverse shape ofdie. The graph almost follows the curvature of die. Fig 7 Stress Plot The results are shown in figure 7 for radial, hoop and vonmises stresses. Similar stress pattern can be observed forradial and hoop stresses. But vonmises stress is high in the beginning and later reducing along the path of the top nodes.Maximum stresses can be observed in the higer deformation regions where the members reaches to plastic state and lesserstresses in the lower deformation regions. Fig 8 Contact Pressure in the problem Analysis results for contact pressure are shown in fig 8 Contact pressure indicates metal flow reaching to thecontainer and interface condition of die and the billet. Higher contact pressure indicates higher closeness of the object. 14
  • 5. Billet shape optimization for minimum forging load using FEM analysis Table 1 : ITERATIONS RESULTS Billet(DV) S.No Strain value Radius Height Volume Force in KN Observation (SV) (mm) (mm) (mm3) (OF) 01 1.2164 19 19.5 21550.978 1587.2 INFEASIBLE 02 0.99E+7 20.473 28.393 37392.149 9999 INFEASIBLE 03 0.99E+7 23.087 25.988 43522.52 9999 INFEASIBLE 04 0.99E+7 21.493 27.824 40384.97 9999 INFEASIBLE 05 1.5184 21.178 20.681 29143.89 5203.20 INFEASIBLE 06 0.99E+7 21.328 27.606 39455.72 9999 INFEASIBLE 07 0.99E+7 22.554 20.742 33151.56 9999 INFEASIBLE 08 1.7100 18.887 19.521 21879.33 83.023 INFEASIBLE 09 0.99E+7 19 19.5 22118.109 9999 INFEASIBLE 10 1.5333 19.001 19.532 22156.74 91.660 INFEASIBLE 11 1.4360 19 19.509 22128.32 104.850 INFEASIBLE 12** 1.008 21 24.962 34587.89 106.250 FEASIBLEThe above table represents optimisation results. The structure has been optimised for the design constraints and best setshown with’*” mark in the above table. Totally 12 sets are obtained for five design variables. The optimised forging load isshown as 106.250KN. The limiting strain requirement of 1 is very difficult to get due to higher depth of die in to the billet.To satisfy the requirements, large number of iterations is required by varying height and radius of billet. The only feasibleset available is satisfying the design and state variables requirement. Table 2 : EXPERIMENTAL RESULTS Billet Volume S.No Radius Height (mm3) Load in KN Load in KN (mm) (mm) 01 11.8 115.758 24 21.5 38910.528 02 11.7 114.777 03 11.6 113.796 04 11.8 115.758 05 11.6 113.796 06 11.8 115.758 07 11.7 114.777 08 11.8 115.758 09 11.6 113.796 10 11.8 115.758 11 11.8 115.758 12 11.6 113.796Calculations 1) % of volume reduction = V experimentally - V analysis --------------------------------- V experimentally = 38910.528 - 34587.89 ------------------------------- 38910.528 = 0.1110 15
  • 6. Billet shape optimization for minimum forging load using FEM analysis = 11.10% 2) Force reduction = F experimentally - F analysis = 115.758-106.250 = 9.508 KN III. RESULTS AND DISCUSSIONFrom the above calculation by ansys shows the following results. Case Experimentally Simulation Billet size R=24 mm, H=21.5 mm R=21 mm, H=24.962 mm Volume in mm3 38910.528 34587.89 Case Experimentally Simulation Force in KN 115.758 106.250From the above discussion it shows the following results:  As per Ansys results the billet size is (R=21 mm, H=24.962 mm) and experimentally the billet size is (R=24 mm, H=21.5 mm).  The 11.10% of material reduction error can be observed in the measurement.  As per Ansys results the force required is 106.250KN and experimentally the force required is 115.758KN.  The 9.508KN of force reduction error can be observed in the measurement. IV. CONCLUSION & FURTHER SCOPE4.1 Conclusion:Finite element analysis in conjunction with optimization techniques, are used to develop a system for the design of optimalbillet height/diameter ratio of closed die forging process. The finite element model was built parametrically using ANSYSParametric Design Language. The optimization Billet Shape Optimization for Minimum Forging Load module used theanalysis file to search for the minimum objective function (forging load) by changing billet height/diameter ratio. Theoptimal set is listed in Table I (*set 12*) with billet radius (21 mm) and height 24.292 and forging load (106.250 kN).4.2 Further scope: * Analysis process can be carried out with thermal effects. * Problem can be executed in three dimensional space * Impact analysis can be carried out to find behaviour of the members in contact. * Topology optimisation can be carried out to find optimum thickness required for dies and containers. * Composite usage can be checked. REFERENCES [1]. Mohammad Haider, K. K. Pathak, Geeta Agnihotri ” Preform design for near net shape close die gear forging using simulation technique” Scholars Research Library Archives of Applied Science Research, 2010. [2]. Harshil Parikh, Bhavin Mehta, Jay Gunasekera ” Forging Process Analysis and Preform Design”. [3]. Mladomir Milutinović, Dejan Movrin1, Miroslav Plančak1, Saša Ranđelović2, Tomaž Pepelnjak3 , Branimir Barišić4 ”DESIGN OF HOT FORGING PROCESS OF PARTS WITH COMPLEX GEOMETRY IN DIGITAL ENVIRONMENT” 15th International Research/Expert Conference ”Trends in the Development of Machinery and Associated Technology” TMT 2011, Prague, Czech Republic, 12-18 September 2011. [4]. Lirio Schaeffer, Alberto M.G.Bito, Martin Geier.”Numeriacl simulation using finite to develop and optimize forging process” metal work laboratory, steel research int.76 2005 No.2/3. [5]. M. Jolgaf, S.B. Sulaiman, M. K. A. Ariffin, A. A. Faieza and B. T. H. T. Baharudin” FE Analysis and Optimization of Plate Forming Process” 3rd Engineering Conference on Advancement in Mechanical and Manufacturing for Sustainable Environment April 14-16, 2010. [6]. Nassir S. Al-Arifi, Abu S. Zamani, and Jalaluddin Khan ”Billet Optimization for Steering Knuckle Using Taguchi Methodology” International Journal of Computer Theory and Engineering, Vol. 3, No. 4, August 2011. [7]. ANSYS, ANSYS Release 10.0 documentation. Canonsburg, PA 15317, USA.: ANSYS, Inc,2005. 16