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Bulk metal forming Simulation Techniques in Manufacturing Technology Lecture 4 Laboratory for Machine Tools and Production Engineering Chair of Manufacturing Technology Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Dr. h.c. F. Klocke © WZL/Fraunhofer IPT Contents 1 Introduction and basics of bulk metal forming 2 Chronology of FE simulation 3 Simulation of hammer forging process 4 Simulation of deep rolling process 5 Summary © WZL/Fraunhofer IPT Seite 2 Overview of bulk metal forming processes What is cold forming? The temperature of the workpiece amounts room temperature before forming No external heating of the workpiece (TBegin = 20 °C < TR) Process-related temperature increase of the workpiece because of dissipated deformation energy (TEnd up to 350 °C) Source: ThyssenKrupp Presta © WZL/Fraunhofer IPT Seite 3 Overview of bulk metal forming processes Material properties (carbon steel) T0: Room temperature Flow stress and fracture strain For cold forming applies: – Flow stress decreases because of increase of temperature – Fracture strain can be assumed as constant Strain Fracture strain φvf [-] – Strain rate – Forming temperature – Material Flow stress Flow stress kf [MPa] are a function of: Temperature T [°C] © WZL/Fraunhofer IPT Seite 4 Overview of bulk metal forming processes What is warm forming? External heating of the workpiece before forming Standard VDI 3166: Forming process with material strain hardening despite heating Forming temperature between 500 °C and 900 °C Source: Infostelle Industrieverband Massivumformung e.V. © WZL/Fraunhofer IPT Seite 5 Overview of bulk metal forming processes Material properties Tmin Increase of stability and decrease of ductility at non alloyed and low alloyed steels between 300 and 500 °C Blue brittleness © WZL/Fraunhofer IPT Strain Fracture strain φvf [-] Blue brittleness: Flow stress Flow stress kf [MPa] For the warm forming applies: – Flow stress does not decrease steadily because of blue brittleness – Fraction strain increases not steadily because of blue brittleness Tmax Temperature T [°C] Seite 6 Overview of bulk metal forming processes What is forging? Workpiece gets an external heating before forming Forming temperature is higher than recrystallization temperature TR = 0,4·TMelting Source: Infostelle Industrieverband Massivumformung e.V. © WZL/Fraunhofer IPT Seite 7 Overview of bulk metal forming processes Material Properties surface after 500 °C Scaling: Oxidation above 500°C. Aerial oxygen reacts with base material to Fe2O3 Flow stress Blue brittleness © WZL/Fraunhofer IPT Strain Fracture strain φvf [-] Scaling at the materials T0: Room temperature Flow stress kf [MPa] For forging applies: – Flow stress decreases steadily – Fracture strain increases steadily Tmin Temperature T [°C] Seite 8 Contents 1 Introduction and basics of bulk metal forming 2 Chronology of FE simulation 3 Simulation of hammer forging process 4 Simulation of deep rolling process 5 Summary © WZL/Fraunhofer IPT Seite 9 Simulation of bulk metal forming processes Considerations prior to a simulation study Definition of the simulation problem Objective of the simulation study Relevant physical mechanisms: – Mechanical, thermal, electro-magnetic… Type of the problem: – Linear – Non-linear Time dependency: – Static – Dynamic Simulation software & hardware: – Solvers for the intended objectives – Element types – Specific numerical technologies © WZL/Fraunhofer IPT Constituents of a model Geometry – Accurate form reproduction – Stock or special FE mesh generator – Critical areas, complex shapes Material – Material model formulation – Elasticity and Poisson’s ratio – Density, hardening – Thermal properties Boundary conditions – Process parameters – Process kinematics – Process steps Seite 10 Simulation of bulk metal forming processes FE Study process CAD model Idealization Discretization Boundary conditions Material modeling FE-Analyses Evaluation © WZL/Fraunhofer IPT Geometry of a workpiece and a tool. Often available as CAD Data. Universal formats for 3D data (STEP, STP, STL…) Simplification of the real geometry for a more structured mesh Meshing of an object into discrete domains Numerical reproduction of mechanic, kinematic, contact, electro-magnetic, thermal conditions of a real process Numerical formulation of relevant material properties (elasticity, plasticity, shear etc.) Calculation of elementary matrices, definition of the system matrix and a vector of outer forces, solution of linear equation systems for every integration point Analysis of the results and answering the objective of the study Seite 11 Simulation of bulk metal forming processes Chronology of FEM-Simulation: Material modeling Description of material behavior using mathematical material models CAD model Use of ideal-plastic material model is sufficient for bulk metal forming processes Idealization Material modeling Evaluation Nominal strain ε Plastic with hardening Nominal strain ε © WZL/Fraunhofer IPT Ideal plastic Nominal strain ε Stress σ Stress σ Postpro. Solver FE-Analyses Elastic Stress σ simulation of sheet metal forming processes Stress σ Boundary conditions Preprocessor Discretization Use of elastoplastic material models for Elasto-plastic with hardening Nominal strain ε Seite 12 Simulation of bulk metal forming processes Chronology of FEM-Simulation: FE-Analysis Implicit solution method: CAD model Discretization Boundary conditions Preprocessor Idealization – Small number of time steps (respectively long time increments) – Higher effort for iterations compared to explicit solution method – Often less computation time then with explicit solution method – Applicable especially for static and quasi-static problems Explicit solution method: FE-Analyses Evaluation © WZL/Fraunhofer IPT Postpro. Solver Material modeling – Length of increment depends on the speed of sound c, Young‘s modulus E and material density ρ; this requires a high number of increments – Longer computation time compared to implicit solution method – Applicable especially for highly dynamic problems (e.g. crash-simulations) Seite 13 Simulation of bulk metal forming processes Movie: FEM-Simulation cross joint Degree of damage Effective stress Mean stress True strain Velocity field CAD model Idealization Discretization Boundary conditions Material modeling FE-Analyses Evaluation Typical evaluation variables are stress-strain-profiles or characteristic values such as the degree of damage. © WZL/Fraunhofer IPT Seite 14 Contents 1 Introduction and basics of bulk metal forming 2 Chronology of FE simulation 3 Simulation of hammer forging process 4 Simulation of deep rolling process 5 Summary © WZL/Fraunhofer IPT Seite 15 Simulation of hammer forging process Tool concept Forge finishing process with balance in two steps Closing plate Forging blank Pre-stamping Radii according to drawings or experience based values Mandrel Die Ejector 1. Upsetting (remove scale and pre-stamping, if necessary) 2. Forge finishing (gearing) Source: The hammer forging simulation procedure is courtesy of Buderus © WZL/Fraunhofer IPT Seite 16 Simulation of hammer forging process Abstract of the process chain for FE model Real process chain of press line 3 by Buderus Heating Transportation Waiting time in air Waiting time after forging die Transport to forging die Waiting time before forging die Preforming and ejection Waiting time and transportation Forging and ejection Transportation and waiting time in upsetting press Transport und waiting time at interstage position Cooling Transport und waiting time preforming die Derived process chain for FEM-model Heating, transport and waiting time © WZL/Fraunhofer IPT Preforming and ejection Waiting time and transportation Forging and ejection Cooling Seite 17 Simulation of hammer forging process Simulation of process chain… … with rigid tool on a half section © WZL/Fraunhofer IPT … with rigid tool in complete view Seite 18 Simulation of hammer forging process Overview on the model structure Material model Time discretization: Forming: explicit Heating, spring back, cooling: implicit Geometrical interpolation: Linear Element type: 3D Element shape: Hexahedra Thermally coupled Reduced integration 400 350 300 250 200 150 100 50 0 1200 [1] [2] [3] [4] 0 Contact and boundary conditions Coulomb friction model: µ = 0.2 Normal contact: no penetration Contact type: Surface-to-Surface, thermally coupled BCs depend on the process step, e. g. temperature at the interstage position or forming velocity of forging punch Tool: X40CrMoV5 Workpiece: 16MnCr5 Flow stress σ [MPa] – – 0.5 1 True strain φ [-] Flow stress σ [MPa] Element definition [5] [6] [7] [8] 1000 800 600 400 200 0 1.5 0 16MnCr5 0.5 1 True strain φ [-] 1.5 X40CrMoV5 Thermal conductivity λ [W/m K] 43,39 Specific heat capacity cpm [kJ/kg K] Thermal expansion coefficient αm E-modulus E [GPa] < 30,25 474,14 < cpm < 685,71 11,04 [K−1] Density ρ [kg/m3] <λ < αm < 15,94 7821,8 < ρ 213,0 < 7373,0 < E < 46,5 22,95 <λ < 25,77 428,40 < cpm < 715,72 10,08 < αm < 27,70 7755,6 < ρ 213,8 < 6982,0 < E < 50,7 Legend: [1] = 500 −1 @ = 800° [2] [email protected] [3] [email protected] [4] [email protected] [5] [email protected] [6] [email protected] [7] [email protected] [8] [email protected] Source: Landolt-Börnstein DB © WZL/Fraunhofer IPT Seite 19 Simulation of hammer forging process Reduction of the model to a two teeth concept Heating, transportation and waiting Forging blank Preforming and ejection Preforming punch Waiting time and transportation Forging blank Forging and ejection Forging punch / Mandrel Cooling in air Forging blank Closing plate 3 2 1 Transportation and waiting plates Preforming plate © WZL/Fraunhofer IPT Transportation and waiting plates Ejector Die Forging plate Seite 20 Simulation of hammer forging process Model structure: heating and transportation Data of the real process Volumes of forging blanks FE-model Forging blank (16MnCr5) Elastic, implicit, thermally coupled Heating – ϑWSK = 1270 °C Waiting time in air – t1 = 8 s, ϑair = 30 °C, ϑcontact = 50 °C Transportation to upsetting press – t2 = 7 s, ϑair = 30 °C, ϑcontact = adiabat t3 = 4 s, ϑair = 30 °C, ϑcontact = 120 °C Transportation to the interstage position – ϑair t5 = 5,5 s, ϑair = 30 °C, ϑcontact = adiabat Waiting time at the interstage position – ΔV16MnCr5,Δt = 1250 = -5,21 % VFT,kalt = 13 177 458,06 mm³ ΔVZunder = +0,5 % VFT,kalt,korr = 13 243 345,35 mm³ – – dmax,Ofen = 210 mm hESM = 382,36 mm Determination of the scale conditioned AESM = 321 526,32 mm² Dzowv = 0,205 mm Final geometry of the billet for the t7 = 5,5 s, ϑair = 30 °C, ϑcontact = adiabat t8 = 5 s, ϑair = 45 °C, ϑcontact = 170 °C – – – – t6 = 2,5 s, ϑair = 30 °C, ϑcontact = 50 °C Waiting time before preforming die – Consideration of thermal expansion surficial material loss (zowv) Transportation to the main press – VFT,warm = 13 863 688,62 mm³ Determination of the billet height (ESM) hESM,Sim t4 = 3,5 s, ϑair = 30 °C, ϑcontact = 120 °C – – – ϑWSK Waiting time after upsetting press – ideal form filling according to the tool Consideration of scale loss Waiting time before upsetting press – Finished part (FT) in a hot state after 3 2 ϑcontact 1 simulated model – – hESM,Sim = 382,3 – 2*0,205 = 381,95 mm dESM,Sim = 210,0 – 2*0,205 = 209,59 mm Waiting plates Legend: WSK = workpiece, ESM = billet, zowv = scale conditioned surficial material loss © WZL/Fraunhofer IPT Seite 21 Simulation of hammer forging process Analysis of the resulting temperature distribution Video: 01 – Heating Before the upsetting press After the furnace Before the preforming t1-8 = 42 s t1-2 = 16 s t3-8 = 26 s ϑWSK,OF = 1100 °C Temp [°C] +1270 3 2 ϑWSK = 1270 °C +1110 1 ϑWSK,min = 976 °C ΔϑWSK = -294 °C +950 Legend: Temp = Designation according to Abaqus Temperature in °C; OF = surface © WZL/Fraunhofer IPT Seite 22 Simulation of hammer forging process Analysis of thermal expansion After the furnace radial direction hESM,Sim = 381,95 mm Before the furnace U [mm] +8,398 3 2 t1-8 = 42 s Δ½d = +2,05 mm +4,199 1 After the furnace axial direction hESM,Sim = 389,75 mm Video: 01 - Heating +0 t1-8 = 42 s Δh = +7,8 mm Legend: U = Designation according to Abaqus; U = value of the displacement vector in all three coordinates 1, 2, 3 length change in mm © WZL/Fraunhofer IPT Seite 23 Simulation of hammer forging process Model structure: preforming and ejection Data of the real process FE-Modell Preforming – – – Press force FVSP = 1200 t stroke length h = 600 mm Engine power Eengine = 2x200 KW Preforming punch (X40CrMoV5) Elastic, thermally coupled Waiting time after preforming die – – – t1 = 4 s, ϑair = 45 °C, ϑcontact = 170 °C Transport to the mail forging die – – – t2 = 3 s, ϑair = 45 °C, ϑcontact = adiabat ϑWSK Forging blank (16MnCr5) Elastic-plastic, thermally coupled (Explicit, ALE) ϑair Waiting time before the mail forging die – – – t3 = 5 s, ϑair = 45 °C, ϑcontact = 170 °C ϑcontact Preforming plate (X40CrMoV5) Elastic, thermally coupled 3 2 1 Legend: ALE = Arbitrary Lagrangian Eulerian © WZL/Fraunhofer IPT Seite 24 Simulation of hammer forging process Calculation of punch force for preforming Model: 02-preforming Calculation of the punch force for preforming 70 60 (1) (3) Force3 [t] 50 (1) Application of punch 360°-model (2) Application of billet on the plate 40 Two-teeth-model 30 20 10 (3) Application of generated surface on the shoulders 0 Process time during preforming Δt [s] (2) 3 3 2 2 1 © WZL/Fraunhofer IPT 1 Seite 25 Simulation of hammer forging process Analysis of stress distribution in the workpiece Video: 02-preforming 25 % stroke 75 % stroke S [MPa] 100 % stroke σmax = 283 MPa +308 3 2 +154 1 +0 Δt = 0,32 s Legend: S = Designation according to Abaqus; S = Stress von Mises von Mises equivalent stress σV in MPa © WZL/Fraunhofer IPT Seite 26 Simulation of hammer forging process Analysis of stress distribution in the billet Video: 02-Preforming 25 % stroke S [MPa] 75 % stroke 100 % stroke σmax = 118 MPa +129 3 2 +65 1 +0 Δt = 0,32 s Legend: S = Relation according to Abaqus; S = Stress von Mises von Mises equivalent stress σV in MPa © WZL/Fraunhofer IPT Seite 27 Simulation of hammer forging process Analysis of stress distribution in the preforming punch Video: 02-Preforming 25 % stroke S [MPa] 75 % stroke 100 % stroke σmax = 158 MPa +173 3 2 +87 1 +0 Δt = 0,32 s Legend: S = Relation according to Abaqus; S = Stress von Mises von Mises equivalent stress σV in MPa © WZL/Fraunhofer IPT Seite 28 Simulation of hammer forging process Analysis of stress distribution in the preforming plate Video: 02-Preforming 25 % stroke 75 % stroke 100 % stroke σmax = 309 MPa S [MPa] +309 3 2 +180 1 +0 Δt = 0,32 s Legend: S = Relation according to Abaqus; S = Stress von Mises von Mises equivalent stress σV in MPa © WZL/Fraunhofer IPT Seite 29 Simulation of hammer forging process Analysis of temperature distribution in the billet Video: 02-preforming 25 % stroke 75 % stroke 100 % stroke Δϑ = 308 °C ϑmin = 983 °C ϑmax = 1291 °C Temp [°C] +1291 3 2 +1163 1 +983 Δt = 0,32 s Legend: Temp = Designation according to Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 30 Simulation of hammer forging process Analysis of the absolute radial strains in the billet Video: 02-preforming 25 % stroke 75 % stroke 100 % stroke U1 [mm] +47 3 2 Δd = +31,24 mm +24 1 +0 Δd = +46,86 mm Legend: U1 = Designation according to Abaqus; U1 = value of the first component of the displacement vector U radial length change in mm © WZL/Fraunhofer IPT Seite 31 Simulation of hammer forging process Analysis of the absolute radial strains in VS-plate Video: 02-preforming 75 % stroke 25 % stroke 100 % stroke Δh = -0,066 mm Mandrel of the preforming plate Application of the ESM on the plate. U3 [mm] +0 3 2 Δh = -0,066 mm -0,031 1 -0,066 Δh = -0,054 mm Legend: U3 = Designation according to Abaqus; U3 = value of the third component of the displacement vector U axial length change in mm; VS = preforming © WZL/Fraunhofer IPT Seite 32 Simulation of hammer forging process Model structure: forging and ejection Data of the real process FE-model Spindle forging press – – – – – Forging punch / mandrel (X40CrMoV5) Elastic, thermally coupled FSP = 10 000 t hstroke = 800 mm Eengine = 1050 kW vAuftreff = 583 mm/s FPrellschlag = 131 485 kN Forging blank (16MnCr5) Elastic-plastic, thermally coupled (Explicit, ALE + CEL) Ejector – – htable = 200 mm hStößel = 30 mm ϑWSK ϑair Temperatures – – ϑair = 45 °C, ϑcontact = 170 °C Die with the tooth geometry (X40CrMoV5) Elastic, thermally coupled Friction [MESS02] – Closing plate by means of spring (X40CrMoV5) Elastic, thermally coupled depends on pressure : 0.1 < µ < 0.2 ϑcontact Ejector (X40CrMoV5) Elastic, thermally coupled 3 2 Forging plate (X40CrMoV5) Elastic, thermally coupled 1 Source: [MESS02] Messner, C.: Reibung und Wärmeübergang beim Schmieden, 2002; CEL = Coupled Eulerian Lagrangian Method © WZL/Fraunhofer IPT Seite 33 Simulation of hammer forging process Calculation of the punch force for the forging Model: 04-Forging Calculation of the punch force for the forging ALE: 1927 t 2000 1800 CEL: 1939 t (1) Application of the forging punch/ mandrel (2) Application of the first mandrel platform 1600 (3) (1) 1400 Force F3 [t] (2) 1200 (3) Application of the second mandrel platform LAG: 1664 t 1000 800 600 400 LAG 200 CEL 0 ALE -200 Process time during forging Δt [s] 3 3 2 2 1 1 Legend: LAG = Lagrange calculation method, Standard; CEL = Coupled Eulerian Lagrangian Method, ALE = Arbitrary Lagrangian Eulerian Method © WZL/Fraunhofer IPT Seite 34 Simulation of hammer forging process Calculation of the closing plate force for the forging Model: 04-Forging Calculation of the closing plate force 300 250 (3) Force F3 [t] 200 150 LAG: 273 t (1) Application of the billet on the closing plate (2) Closing force due to mandrel movement (3) Forging punch in completely applied (4) Overcoming of the die inner pressure 100 50 (1) (2) 0 -50 -100 Process time during forging Δt [s] 3 3 2 2 1 © WZL/Fraunhofer IPT 1 Seite 35 Simulation of hammer forging process Analysis of the power requirements of the ejector Modell: 04-Forging Power requirements of the ejector 100 (1) Beginning of the ejection (adhesion) 90 80 LAG: 89 t (2) Stick-Slip effect (adhesion > sliding friction) Force F3 [t] 70 60 (3) Decreasing contact surface between the billet and the die 50 40 30 20 10 (1) (3) (0) Forging 0 (2) -10 Process time during forging Δt [s] 3 3 2 2 1 © WZL/Fraunhofer IPT 1 Seite 36 Simulation of hammer forging process Analysis of stress distribution in the tool Video: 04-Forging 25 % stroke 75 % stroke S [MPa] 100 % stroke σmax = 700 MPa +700 3 2 +350 1 +0 Δ t = 0,32 s Legend: S = Designation according to Abaqus; S = Stress von Mises von Mises equivalent stress σV in MPa © WZL/Fraunhofer IPT Seite 37 Simulation of hammer forging process Analysis of the temperature distribution in the billet Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke ϑ25,min = 917°C Δϑ = 288 °C ϑmin = 1035 °C ϑmax = 1323 °C Temp [°C] +1323 3 2 +1121 1 +917 Δt = 0,32 s Legend: Temp = Designation according to Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 38 Simulation of hammer forging process Analysis of temperature distribution in the forging punch Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δϑ = 86 °C ϑmin = 170 °C ϑmax = 256 °C Temp [°C] +256 3 2 +225 1 +170 Δt = 0,32 s Legend: Temp = Designation according Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 39 Simulation of hammer forging process Analysis of temperature distribution in the closing plate Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δϑ = 253 °C ϑmin = 170 °C ϑmax = 423 °C Temp [°C] +423 3 2 +275 1 +170 Δt = 0,32 s Legend: Temp = Designation according Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 40 Simulation of hammer forging process Analysis of temperature distribution in the die Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δϑ = 130 °C ϑmin = 170 °C ϑmax = 300 °C Temp [°C] +300 3 2 +235 1 +170 Δt = 0,32 s Legend: Temp = Designation according Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 41 Simulation of hammer forging process Analysis of temperature distribution in the forging plate Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δϑ = 35 °C ϑmin = 170 °C Temp [°C] ϑmax = 205 °C +205 3 2 +187 1 +170 Δt = 0,32 s Legend: Temp = Designation according Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 42 Simulation of hammer forging process Analysis of the temperature distribution in the ejector Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δϑ = 22 °C ϑmax = 192 °C ϑmin = 170 °C Δh = 200 mm Temp [°C] +192 3 2 +181 1 +170 Δt = 1 s Legend: Temp = Designation according Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 43 Simulation of hammer forging process Analysis of the absolute radial strains in the forging punch Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δ½d = 1,31 mm U1 [mm] +1.31 3 2 +0,5 1 -0,48 Δt = 0,32 s Legend: U1 = Designation according Abaqus; U1 = value of the first component of the displacement vector U radial length change in mm © WZL/Fraunhofer IPT Seite 44 Simulation of hammer forging process Analysis of the absolute radial strains in the closing plate Video: 04-Forging 25 % stroke U1 [mm] 75 % stroke 100 % stroke Δ½d = 0,42 mm +0,42 3 2 +0,18 1 +0 Δt = 0,32 s Legend: U1 = Designation according Abaqus; U1 = value of the first component of the displacement vector U radial length change in mm © WZL/Fraunhofer IPT Seite 45 Simulation of hammer forging process Analysis of the thermal expansion in the die Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δ½d = 1,08 mm U1 [mm] +1,08 3 2 +0,52 1 +0 Δt = 0,32 s Legend: U1 = Designation according Abaqus; U1 = value of the first component of the displacement vector U radial length change in mm © WZL/Fraunhofer IPT Seite 46 Simulation of hammer forging process Analysis of the thermal expansion of the forging plate Video: 04-Forging 25 % stroke 75 % stroke 100 % stroke Δh = -0,32 mm Mandrel of the forging plate U3 [mm] Δh = -0,32 mm +0 3 2 -0,18 1 -0,32 Δ t = 0,32 s Legend: U3 = Designation according to Abaqus; U3 = value of the third component of the displacement vector U axial length change in mm © WZL/Fraunhofer IPT Seite 47 Simulation of hammer forging process FE-model structure: cooling Main data of the real process FE-model Cooling – – ϑair = 30 °C, t = 24 h Forging blank (16MnCr5) Elastic, thermally coupled, implicit ϑWSK ϑair ϑcontact 3 2 © WZL/Fraunhofer IPT 1 Seite 48 Simulation of hammer forging process Analysis of the temperature distribution in the billet Video: 05-Cooling 24h 0h ϑ = 1312 °C ϑ = 20 °C ϑ = 20 °C Temp [°C] +1312 3 2 Δt = 4h +660 1 +20 Δt = 24h Legend: Temp = Designation according to Abaqus Temperature in °C © WZL/Fraunhofer IPT Seite 49 Simulation of hammer forging process Deviations from the nominal values of the finish part Nominal geometry of the hot tooth acc. to the tool drawing Real geometry after forging (FEM) 24 h cooling hs,Ist = 32,84 mm (+0,84 mm) ½ dist = 202,72 mm (+0,72 mm) After cooling U1 [mm] hz,ist = 183,3 mm (+0,3 mm) ½ d24h = 199,3 mm (-3,42 mm) hTraganteil = 66,67 mm (-116,33 mm) hs,soll = 32 mm hz,soll = hTraganteil = 183 mm ½ dsoll = 202 mm +92,37 3 2 msoll = 101,67 kg 1 Vsoll = 184,85 ∙ 106 mm3 +46,63 0 mist = 101,71 kg (+0,04%) hz,24h = 180,22 mm (-3,1 mm) hs,24h = 32,28 mm (-0,56 mm) Finished part (acc. drawing) ½ dEnd = 196,8 mm (+2,5 mm) hz,End = 175,3 mm (+4,92 mm) Vist = 185,97 ∙ 106 mm3 (+0,6%) Legend: + X mm = Oversize due to the tool elongation, - X mm = th. shrinkage due to cooling; + X mm = machining allowance for finished part © WZL/Fraunhofer IPT Seite 50 Simulation of hammer forging process Iterative increase of the billet mass (V = 103%) Boundary conditions Real geometry after forging (FEM) Nominal geometry Compensation region ½ dist = 202,42 mm (+0,42 mm) hs,Ist = 32,61 mm (+0,61 mm) U1 [mm] +92,37 Burr hz,ist = 183,0 mm (+0,0 mm) Model Tool: rigid body Billet: elastic-plastic volumes 103%, optimized meshing 102%, 102,5% do not reach 100% form filling. developed to 100% at 103% billet. Boundary conditions of FE– – 101%, 101,5%, Nominal geometry is hTraganteil = 173,73 mm (-0,10 mm) hz,soll = 183 mm h = 173,83 mm hs,soll = 32 mm ½ dsoll = 202 mm Conclusion For V = 103% will be evaluated material flow, contact surface and forming force. For 103% the billet is also calculated with elastic tools. +46,63 0 Legend: U1: radial displacement © WZL/Fraunhofer IPT Seite 51 Simulation of hammer forging process Analysis of material flow with the rigid tools (V = 103%) 95% forming 97% forming 100% forming VR [mm/s] +450 +225 0 Compensation region is already filled, before the tooth top width is completely formed There is a high resulting flow velocity below ca. 45°, it means that the material flows in the compensating region and in the die The flowing velocity slightly increase Accordingly increases the material flow in compensation region The material flow on the tooth top at some places is almost zero, it means that the tooth there is maximally filled The material flow is located in the compensation region The tooth top width is under the requested percentage contact area is completely formed The flow velocity at the contact with the tool is zero Legend: VR = resulting velocity vector © WZL/Fraunhofer IPT Seite 52 Simulation of hammer forging process Analysis of the forming force for the rigid tools (V = 103%) Model: 04-Forging Calculation of the punch force for the forging V = 103%: 4437 t 4500 4000 (a) (b) Application of the first mandrel platform 3500 Punch force F3 [t] (b) (c) (a) Application of the forging punch/ mandrel 3000 2500 (c) Application of the second mandrel platform x2.67 2000 1500 1000 V = 100%: 1664 t 500 V=103% V=103%(starr) (rigid) 0 V=100% V=100%(elastisch) (elastic) -500 Process time by forging Δt [s] 3 3 2 2 1 1 Legend: V=100% (elastic) : Result of the simulation; V=103% (rigid): result of the simulation with the rigid tool © WZL/Fraunhofer IPT Seite 53 Simulation of hammer forging process Simulation of the forging steps in the case of el. tools (V = 103%) Boundary conditions Real geometry of the forging (FEM) Conclusion Nominal geometry Form filling with elastic Tools: elastic Billet: Elastic-plastic Volumes 103% Optimized mesh Optimized punch stroke, to compensate elastic upsetting of the punch (185 vs. 191 mm). U1 [mm] +92,37 hz,ist = 183,01 mm (+0,01 mm) Model hTraganteil = 128,53 mm (-45,3 mm) Optimized punch stroke Boundary conditions of FE– – tools in comparison to usage of rigid tools is not complete ½ dist = 202,9 mm (+0,9 mm) hs,Ist = 32,19 mm (+0,19 mm) hz,soll = 183 mm hs,soll = 32 mm h = 173,83 mm ½ dsoll = 202 mm compensates the upsetting of the punch. However the form filling is not reached The compensation region is already partially filled. Compensation region +46,63 0 Legend: U1: radial displacement © WZL/Fraunhofer IPT Seite 54 Simulation of hammer forging process Simulation of the forging steps in the case of elastic tools (V = 104%) Boundary conditions Real geometry after forging (FEM) Conclusions Nominal geometry An additional Tools: elastic Billet: elastic-plastic Volumes 104% Optimized meshing Optimized punch stroke Additional mesh optimization in compensation region U1 [mm] +92,37 hz,ist = 183,5 mm (+0,5 mm) Model hTraganteil = 142,24 mm (-31,59 mm) The elastic strains in Boundary conditions of FE– – increase of the billet mass to 104% as well as local mesh optimization of the compensation region do not lead to the 100% form filling ½ dist = 203,735 mm (+1,73 mm) hs,Ist = 32,16 mm (+0,16 mm) hz,soll = 183 mm hs,soll = 32 mm h = 173,83 mm ½ dsoll = 202 mm the tool are too large The compensation region is partially filled also here Compensation region +46,63 0 Additional mesh optimization in compensation region Contour V = 103 % Legend: U1: radial displacement © WZL/Fraunhofer IPT Seite 55 Simulation of hammer forging process Analysis of the material flow in the case of elastic tools (V = 104%) 95% Forming 97% Forming 100% Forming VR [mm/s] +450 +225 0 The flow velocity with the elastic tools is clearly smaller in comparison to the rigid tools and moreover is distributed within the whole part, but not focused in the domain of the compensated region. The flow diagram is hardly changed by 97%. The material flow on the tooth top is not zero, therefore there is not available any form filling due to distention of the tools. The compensation region is even at 104% billet mass not sufficiently filled, so the 100% form filling is not reached In the case of absence of the compensation region, the material situated there would flow in the die. Legend: VR = resulting velocity vector © WZL/Fraunhofer IPT Seite 56 Simulation of hammer forging process Analysis of the forming force in the case of elastic tools (V = 104%) Modell: 04-Forging Calculation of the punch force for the forging V = 103%: 4437 t 4500 (b) (c) (a) Punch force F3 [t] 4000 3500 3000 (a) Application of the forging punch/ mandrel (b) Application of the first mandrel platform (c) Application of the second mandrel platform 2500 V = 104%: 3173 t 2000 1500 1000 V = 100%: 1664 t 500 VV=100% = 100% (elastisch) (elastic) 0 (rigid) VV=103% = 103% (starr) -500 (elastic) VV=100% = 104% (elastisch) Process time during forging Δt [s] 3 3 2 2 1 1 Legend: V=100% (elastic) : Result of the simulation; V = 104% (elastic): result of the simulation in the case of elastic tool © WZL/Fraunhofer IPT Seite 57 Simulation of hammer forging process Analysis of the tool loads in the punch at V=104% Equivalent stress σv [MPa] Plot of the contact area P [MPa] +653,8 +1615 +356,6 +881,1 0 0 Legend: σv : von Mises equivalent stress; P = contact pressure per unit area © WZL/Fraunhofer IPT Seite 58 Simulation of hammer forging process Analysis of the tool loads in the die at V = 104% Equivalent stress Plot of the contact area 99% Forming 100% Forming σv [MPa] P [MPa] +471,3 +1354 +271,8 +676,8 0 0 Legend: σv : von Mises equivalent stress; P = contact pressure per unit area © WZL/Fraunhofer IPT Seite 59 Simulation of hammer forging process Performed optimization process Optimization process with the rigid tools To analyze the tool concept with the rigid tool Real geometry Mesh optimization Iterative increase of the billet mass until the form filling is reached Nominal geometry The optimum in the case of the rigid tools is the initial situation for the optimization for the case of the elastic tools Optimization process with the elastic tools To analyze the tool concept with the elastic tool © WZL/Fraunhofer IPT Optimization of the punch stroke Iterative increase of the billet mass Seite 60 Simulation of hammer forging process Optimization process in the case of the rigid tool Form filling (FF) is not reached at the billet volume of V = 100% and application To analyze the tool concept with the rigid tool of the rigid tool. Reasons are: – Volume loss due to insufficient meshing at the tooth root (~1%) – Volume loss in the burr due to adjusted tool geometry (0,5%) Meshing at the tooth root is optimized and billet mass is increased at 1,5% Form filling is not reached at volume of V = 101,5% with optimized mesh and in the case of rigid tool. Reason is: Mesh optimization – Precocious infilling of the compensation region prevents complete flow od the material in the die. Thus, there is no 100% form filling. Billet mass is increased at 0,5%, until 100% form filling is reached Form filling is reached at V = 103%, optimized mesh and rigid tools. Iterative increase of the billet mass until the form filling is reached Background: – Compensation region is filled in the way, that the material through the required percentage contact area of 100% is aligned to the die. Legend: © WZL/Fraunhofer IPT Derived procedures to optimize the identified deficit Seite 61 Simulation of hammer forging process Optimization process in the case of the elastic tool Form filling in the case of the elastic tools and with the application of the To analyze the tool concept with the elastic tool optimization steps of the rigid process chain is not reached. Reasons are: – Elastic upsetting of the punch of about 6 mm, el. deflection of the die and the forging plate as well as precocious infilling of the compensation region Elongated punch stroke should compensate given elastic upsetting Form filling is not reached in the case of the elastic tools, optimized punch stroke, and the optimization procedures of the rigid proses. Reasons are: Optimization of the punch stroke – Elastic deflection of the tool and precocious infilling of the compensation region Iterative increase of the billet mass should fill the compensation region. Form filling is not reached at V = 104%, el. tools, optimized punch stroke, and the optimization procedures of the rigid proses. Reasons are: Iterative increase of the billet mass – Even more strong deflection of the die (~ 2mm) Main influencing parameter on the form filling: el. strains of the tools – Earlier infilling of the compensating region. Material in the compensating region could be used for the form filling Legend: © WZL/Fraunhofer IPT Derived procedures to optimize the identified deficit Seite 62 Contents 1 Introduction and basics of bulk metal forming 2 Chronology of FE simulation 3 Simulation of hammer forging process 4 Simulation of deep rolling process 5 Summary © WZL/Fraunhofer IPT Seite 63 Simulation of deep rolling process Modelling and verification of material behavior Baushinger test of 42CrMo4 Bauschinger-Versuch bei 42CrMo4 1200 0 -400 0 0 = 0 + ∞ (1 − − − 0 -1200 ) 0 -2% -1% 0% 1% 2% 3% ( − ) -1200 -3% = -2% − 0 -1% 0% 1% 2% 800 F F F 0 60 80 3% 60 80 GGG60 [2%] 1200 Initial state 400 40 Time t [s] Simulation Experiment Dehnung [%] 1200 20 -400 -800 Dehnung [%] Strain [%] Baushinger test of GGG60 Bauschinger-Versuch bei GGG60 Spannung [MPa] 400 -800 Kinematic part: -800 -400 800 400 0 -400 -800 -1200 -800 -1200 -3% 800 -400 Isotropic hardening model: 400 400 -1200 -3% 42CrMo4 [2%] 1200 800 Spannung [MPa] Spannung [MPa] 800 Simulation and verification Stress σ [MPa] Bbb Modelling Modelling of non-linear isotropic/kinematic material behavior by means of constitutive material descriptionBauschinger-Versuch according tobei GGG60 1200 Lemaitre-Chaboche Stress σ [MPa] Experiment Tension-Compression-tests at Karlsruhe Institute of Technology (KIT) at 2%, 4% and 6% strain 0 -2% -1% 0% 1% Dehnung [%] 2% 3% Tension Compression Tension 20 40 Time t [s] Strain [%] © WZL/Fraunhofer IPT Seite 64 Simulation of deep rolling process Modelling of press kinematic by rotationally sym. deep drawing Exemplary application Process kinematic Contact description ωK Kmax Simplified deep drawing tool r ωk , , r Workpiece © WZL/Fraunhofer IPT ω , , RP Seite 65 Simulation of deep rolling process Modelling of the chosen geometry element B Abstraction Abstraction C Geometry variation A A B 0 4 4 1 1 © WZL/Fraunhofer IPT 2 2 = ∞ Mises [MPa] C +1200 +600 +0 Seite 66 Simulation of deep rolling process Simulative evaluation of the residual stresses Residual stresses in axial direction (y) Eigenspannungen quer: S33(P) 400 Transverse residual stresses σ [MPa] 400 200 0 -200 -400 -600 -800 -1000 -1200 200 0 -200 -400 -600 -800 -1000 -1200 © WZL/Fraunhofer IPT P=175 P=250 3.00 2.16 1.33 0.50 0.45 0.40 0.35 0.30 0.25 0.20 Edge depth t [mm] Edge depth t [mm] pressure P=100 bar Walzdruck 0.15 0.10 0.05 3.00 2.16 1.33 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 -1400 -1400 0.00 Longitudinal residual stresses σ [MPa] Residual stresses in circumferential Eigenspannungen längs: S11(P) direction (x) P=325 P=400 pressure P=100 bar Walzdruck P=175 P=250 P=325 P=400 Seite 67 Contents 1 Introduction and basics of bulk metal forming 2 Chronology of FE simulation 3 Simulation of hammer forging process 4 Simulation of deep rolling process 5 Summary © WZL/Fraunhofer IPT Seite 68 Summary Bulk metal forming besides sheet metal forming is the most relevant group in metal forming In general, depending on the process temperature, one can distinguish between three main groups: – cold forming – warm forming – hot forming During product design one should consider advantages and disadvantages of all these three variants from technological point of view The detailed simulation procedures are presented for the hammer forging and deep drawing processes © WZL/Fraunhofer IPT Seite 69

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