I²FG Workshop Impulse Forming May 7 th, 2013 Gent, Belgium Determination of suitable driver materials for electromagnetic sheet metal forming Soeren Gies
Agenda Introduction Effect of driver sheets State of the art Experimental setup and procedure Results Summary and Outlook 2 I 27
Agenda Introduction Effect of driver sheets State of the art Experimental setup and procedure Results Summary and Outlook 3 I 27
Introduction Objective: Electromagnetic forming of stainless steel 1.4301 and 1.4509 Challenge: Low electrical conductivity of stainless steel Copper Aluminum Steel Stainless steel CU-ETP CU-DHP EN AW-1050A EN AW-5083 DC06 1.4301 1.4509 57 MS/m 43 MS/m 34 MS/m 16 MS/m 8 MS/m 1.5 MS/m 100% 75% 60% 28% 14% 2,6% Solution: Use of driver sheets 4 I 27
Introduction Working principle of driver sheets: Upper tool (Forming die) t D t W Workpiece Driver sheet Coil winding Coil winding Lower tool (Flat working coil) Workpiece: 1.4301, t W = 0.8 mm Driver: Aluminum, t D =0.8 mm 5 I 27
Agenda Introduction Effect of driver sheets State of the art Experimental setup and procedure Results Summary and Outlook 6 I 27
Effect of driver sheets Use of driver sheets causes two opposing effects in the energy conversion sequence Ohmic heating Magnetic flux lines in the air Elastic energy in the die Energy supply Charging energy Coil energy Kinetic energy Forming energy Formingresult electromagnetic system (ƞ 1 ) mechanical system (ƞ 2 ) magn. pressure Energy conversion sequence: Risch, 2009 7 I 27
Effect of driver sheets Use of driver sheets causes two opposing effects in the energy conversion sequence Ohmic heating Magnetic flux lines in the air Elastic energy in the die Energy supply Charging energy Coil energy Kinetic energy Forming energy Forming energy driver sheet Formingresult electromagnetic system (ƞ 1 ) mechanical system (ƞ 2 ) magn. pressure Trade off: higher magnetic pressure vs. additional forming energy 8 I 27
Effect of driver sheets Use of driver sheets is beneficial if the following condition is fulfilled: Additional kinetic energy Additional forming energy for driver Optimum MAX Additional kinetic energy E kin Additional forming energy for driver E form Self-evident consequences: - High electrical conductivity E kin - Low yield strength E form Question: Which driver material and which driver thickness t D maximize the energy ratio? 9 I 27
Agenda Introduction Effect of driver sheets State of the art Experimental setup and procedure Results Summary and Outlook 10 I 27
State of the art Scientific investigations using driver sheets: Seth et al. (2004) Workpiece: Driver: Li et al. (2012) Workpiece: Driver: Low-alloy carbon steel, t W = 0.1 mm 0.38 mm Aluminium EN AW-6111 T4, t D = 1 mm Ti-6Al-4V, t W = 0.5 mm CU-DHP, t D = 0.5 mm Andersson and Syk (2008) Workpiece: Driver: Srinivasan et al. (2010) Workpiece: Driver: Ishibashi et al. (2011) Workpiece: Driver: X5CrNiMo17-12-2, t W = 0.25 mm / DP600, t W = 0.7 mm Copper, t D = 0.6 mm Titanium, t W = 0.076 mm Copper, t D = 0.381 mm X5CrNi18-10, t W = 0.15 mm EN AW-1050-H24, t D = 0.3 mm Workpiece thickness Driver thickness Skin depth 11 I 27
State of the art Scientific investigations using driver sheets: Tillmann et al. (2008) Workpiece: DC04, t W = 0,8 mm Driver: Copper (sputtered), t D = 0,65 mm (optimum) Recommendation: t D = σ s Bely et al. (1977) Recommendation: Desai et al. (2011) Workpiece: Driver: Recommendation: t D = 0,5 σ s Stainless steel Aluminum, Copper Aluminum t D = 0,8 σ s / Copper t D = σ s Contradicting recommendations No recommendation regarding optimal driver material No consideration of mechanical workpiece parameters Workpiece thickness Driver thickness Skin depth 12 I 27
Agenda Introduction Effect of driver sheets State of the art Experimental setup and procedure Results Summary and Outlook 13 I 27
Experimental Setup and Procedure 1 Free forming of workpiece and driver Upper tool (Drawing ring) Coil winding Lower tool (Flat coil) 100 mm 80 mm t D t W 65 mm 17 mm Pulse generator used: Maxwell Magneform 7000 Max. charging energy E C = 20 kj Short circuit frequency f* = 25 khz Inner resistance R i = 4.2 mω Inner inductance L i = 60 nh 14 I 27
Experimental Setup and Procedure 1 Free forming of workpiece and driver 2 Upper tool (Drawing ring) Coil winding 100 mm 80 mm t D t W Measuring of workpiece height h w h W Lower tool (Flat coil) 65 mm 17 mm Pulse generator used: Maxwell Magneform 7000 Max. charging energy E C = 20 kj Short circuit frequency f* = 25 khz Inner resistance R i = 4.2 mω Inner inductance L i = 60 nh h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D 15 I 27
Experimental Setup and Procedure Scope of investigations: Workpiece material 1.4301, t W = 0.5 / 0.8 / 1.0 mm 1.4509, t W = 0.5 / 0.8 / 1.0 mm DC04, t W = 0.5 / 0.8 / 1.0 mm EN AW-5083, t W = 1.0 mm Driver material CU-ETP, t D = 0.3 / 0.5 / 0.7 / 0.8 / 1.0 / 2.0 mm EN AW-1050A, t D = 0.3 / 0.5 / 0.7 / 0.8 / 1.0 / 2.0 mm Charging Energy E C E C = 1.0 / 1.8 / 2.4 kj 16 I 27
Agenda Introduction Effect of driver sheets State of the art Experimental setup and procedure Results Summary and Outlook 17 I 27
Results Workpiece: Material 1.4509 Thickness t W = 0.8 mm 100 mm 80 mm 24 17 mm 65 mm t D t W h W Forming height h w in mm 22 20 18 16 14 12 12 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D Driver thickness t D Skin depthσ S 18 I 27
Results Workpiece: Material 1.4509 Thickness t W = 0.8 mm Optimum t D 1.05 σ S 100 mm 80 mm 24 17 mm 65 mm t D t W h W Forming height h w in mm 22 20 18 16 14 12 12 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D Driver thickness t D Skin depthσ S 19 I 27
Results Workpiece: Material 1.4509 Thickness t W = 0.8 mm 100 mm 80 mm 17 mm 65 mm t D t W h W h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D Forming height h w in mm 24 22 20 18 16 14 12 12 0 Optimum t D 1.05 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Driver thickness t D Skin depthσ S E Form Driver Forming Energy E Kin Kinetic energy 20 I 27
Results Workpiece: Material 1.4509 Thickness t W = 0.8 mm 100 mm 80 mm 17 mm 65 mm t D t W h W h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D Forming height h w in mm 24 22 20 18 16 14 12 12 0 Optimum t D 1.05 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Driver thickness t D Skin depthσ S E Form Driver Forming Energy E Kin Kinetic energy 21 I 27
Results Workpiece: Material 1.4509 Thickness t W = 0.8 mm 100 mm 80 mm 17 mm 65 mm t D t W h W h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D Forming height h w in mm 24 22 20 18 16 14 12 12 0 Driver AL CU Charging Energy E C 1.0 kj 1.8 kj 2.4 kj 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Driver thickness t D Skin depthσ S 22 I 27
Results Workpiece: Material 1.4301 Thickness t W = 0.8 mm 100 mm 80 mm 17 mm 65 mm t D t W h W h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D Forming height h w in mm 24 22 20 18 16 14 12 12 0 Driver AL CU Charging Energy E C 1.0 kj 1.8 kj 2.4 kj 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Driver thickness t D Skin depthσ S 23 I 27
Results Workpiece: Material 1.4301 Thickness t W = 0.8 mm 100 mm 80 mm 17 mm 65 mm t D t W h W Forming height h w in mm Aluminium should be favoured 20 as driver material Optimum driver thickness t18 D,opt 1.1 σ s 1.2 σ s 24 22 16 14 12 12 0 Driver AL CU Conclusions Effect of charging energy E C because of varying strain Charging Energy E C 1.0 kj 1.8 kj 2.4 kj In case of very small strains (e.g. calibration) copper should be favoured 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 h w = Workpiece forming height t w = Workpiece thickness = Driver thickness t D Driver thickness t D Skin depthσ S 24 I 27
Results Comparision of optimum driver thicknesses t D,opt (Driver material: AL) Workpiece thickness t W Workpiece material 0.5 mm 0.8 mm 1.0 mm 1.4301 0.95 σ s 1.0 σ s 1.27 σ s 1.4509 1.0 σ s 1.05 σ s 1.29 σ s Conclusions: Increasing workpiece thickness t W Increasing optimum driver thickness t D,opt Rule of thumb: Optimum driver thickness σ s (AL) 25 I 27
Agenda Introduction Effect of driver sheets State of the art Experimental setup and procedure Results Summary and Outlook 26 I 27
Summary and Outlook Summary: Aluminum should be favoured as driver material Positive correlation between workpiece thickness t W and optimum driver thickness t D,opt Rule of thumb: Optimum driver thickness σ s (AL) Outlook: EMF of stainless steel into a conical die using the optimum driver material und thickness Analytical calculation of the optimum driver thickness t D,opt 27 I 27
Questions? 28 I 27