Center for Precision Forming (www.cpforming.org) Taylan Altan, Director (email: altan.1@osu.edu) A short Review July, 2011

Introduction The Ohio State University (OSU) and have established the Industry/University Cooperative Research Center (I/UCRC) on Precision Forming (CPF) focusing on research needs of metal forming industry. Funding is provided by National Science Foundation (NSF) and member companies. CPF (www.cpforming.org) benefits from research conducted at Engineering Research Center for Net Shape Manufacturing (ERC/NSM – www.ercnsm.org).

Objectives Improve existing metal forming processes/products and develop new innovative processes, tooling and equipment. Conduct projects in close collaboration with industry and transfer the results to the member companies. Train and educate engineers in the fundamentals and practice of metal forming science and technology.

Current Members Boeing Cincinnati Inc Dienamic Tooling Systems ESI North America EWI Honda Hyundai Interlaken Technology Corp. POSCO (Korea) IM Steel Scientific Forming Technologies (SFTC) Corp. IMRA America Metalsa Tyco

Research and Development in Sheet Metal Forming R & D at The Center for Precision Forming Research and Development in Sheet Metal Forming Center for Precision Forming (CPF) (formerly Engineering Research Center for Net Shape Manufacturing) www.cpforming.org / www.ercnsm.org The Ohio State University June 1st 2011, Columbus, Ohio © Copyright Center for Precision Forming (CPF). All Rights Reserved.

R&D in Sheet Metal Forming at CPF CPF 1.1 - Elevated temperature stamping and hydroforming (Mg, Al and alloys) CPF 1.4 - Control of springback and dimensional tolerances in forming AHSS parts CPF 2.1 – Determination of room temperature material properties (flow stress, formability, anisotropy) of sheet materials under biaxial conditions CPF 2.3 – Investigation tribological (friction/lubrication/wear) conditions in forming uncoated and galvanized AHSS CPF 2.5 – Evaluation of lubricants for improving stamping quality CPF 4.1 – Practical use of multi-point control (MPC) die cushion technology in production of stamped parts

R&D in Sheet Metal Forming at CPF CPF 4.2 – Tube hydroforming CPF 5.1 – Evaluation of bendability of AHSS CPF 5.2 – Prediction and elimination of edge cracking of AHSS in stretch flanging CPF 5.3 – Blanking and shearing of sheet metal CPF 5.5 – Hot stamping of boron steels CPF 5.6 – Applications of servo drive presses in stamping

Manan Shah Jose L. Gonzalez-Mendez Eren Billur CPF 1.1 - Elevated Temperature Stamping and Hydroforming (Mg, Al And Alloys) Manan Shah Jose L. Gonzalez-Mendez Eren Billur

Al, Mg, Ti & SS (Cup Diameter: 40 mm) (in cooperation with AIDA) Warm Forming of Al, Mg, Ti & SS (Cup Diameter: 40 mm) (in cooperation with AIDA) AZ31B-O AA5754-O T(°C) LDR RT 2.1 250 2.5 300 2.9 T(°C) LDR RT - 275 2.6 3.2 Velocity : 2.5-50mm/sec

(in cooperation with AIDA) Warm Forming of SS 304 (Cup Diameter: 40 mm) (in cooperation with AIDA)

Warm Bulge Test (up to 350C/660F)

(in cooperation with GM and Interlaken) Warm Forming FEA using PAMSTAMP 2G 2009 (in cooperation with GM and Interlaken) Punch stroke= 0 mm Punch stroke= 35 mm Punch Blank Holder Punch Blank Holder Sheet Fluid pressure Die Die Reverse Punch

Warm Forming FEA and Experiments

Nimet Kardes-Sever Yurdaer Demiralp Dr. Changhyok Choi CPF 1.4 - Control of Springback and Dimensional Tolerances in Forming AHSS Parts Nimet Kardes-Sever Yurdaer Demiralp Dr. Changhyok Choi

Load-Unload Tensile Test (in cooperation with EWI) Springback Load-Unload Tensile Test (in cooperation with EWI)

(in cooperation with EWI and IVF) Springback in S-Die Test (FEA and Experiments) (in cooperation with EWI and IVF) Material: DP 780, DP 600 thickness: 1 mm, 0.75 mm U-flanging without stretching U-bending without stretching U-flanging with stretching U-bending with stretching S-shape forming with – without stretching

(in cooperation with EWI and IVF) Springback in S-Die Test (FEA and Experiments) (in cooperation with EWI and IVF) U-flanging test U-bending test Schematic of S-shape punch U-bending sample on S-shape punch U-flanging sample on S-shape punch S-shape bending sample on S-shape punch

CMM measurements of S-Die Test Samples Calculation of springback for S-Die Test samples: Bending angle under load was measured by camera when possible. When the tool is closed it is not possible to take pictures. Therefore, it was assumed that the specimen geometry under load is determined by tool geometry. Bending angle after unloading was measured by protractor and camera when possible and Coordinate Measurement Machine (CMM). For complex samples, sections before and after springback were compared. Schematic of CMM measurements on a sample

Eren Billur Yurdaer Demiralp Nimet Kardes-Sever Ji You Yoon CPF 2.1 - Determination of Room Temperature Material Properties of Sheet Materials Under Biaxial Conditions Eren Billur Yurdaer Demiralp Nimet Kardes-Sever Ji You Yoon

Sheet Material Properties Viscous Pressure Bulge (VPB) Test (in cooperation with many companies) After Forming Laser Test Sample Viscous Medium Stationary Punch Pressure Transducer Before Forming Downward motion clamps the sheet Continued downward motion forms the bulged sheet

Sheet Material Properties Tensile Test vs. VPB Test Due to necking, flow stress data from tensile test is limited to low strains. Bulge test is useful to determine flow stress curve for metal forming applications and FE simulations. Bulge test is useful to determine the quality (formability) of sheet materials.

Determination of Sheet Formability Using VPB Test Graph shows dome height comparison for SS 304 sheet material from eight different batches/coils [10 samples per batch]. Highest formability  G , Most consistent  F Lower formability and inconsistent  H

Materials Tested with VPB Test at CPF (data available to CPF members) Steels St 14 DP 780-CR St 1403 DP 780-HY AISI 1018 Bare DP 980 Y-type X AKDQ Bare DP 780 T-Si type 1050 GA DP 780 T- AI Type DR 120 GA DP 780 Y-type U DDS GA DP 780 Y-type V BH 210  DQS-270F GA-Phosphate coated HSS  DQS-270D GA-Phosphate coated DP500 DP 590 DP 600 DP 780 TRIP 780 DP 980   Aluminum and Magnesium Alloys AA 6111 AA 5754-O X626 -T4P AZ31B AZ31B-O Stainless Steels SS 201 SS 301 SS 304 SS 409 SS 410 (AMS 5504) SS 444 LDX 2101

Eren Billur Ryan Patton CPF 2.3 - Investigation Tribological (Friction/Lubrication/Wear) Conditions in Forming Uncoated and Galvanized AHSS Eren Billur Ryan Patton

Evaluation of Die Materials/Coatings for Galling and Die Wear Using The Strip Drawing and Ironing Test (SDT/SIT) (in cooperation with HONDA ) Strip Drawing Test Galling observed on a die insert Strip Ironing Test Higher contact pressure accelerates the tool wear and galling, in stamping AHSS. Various die materials and coatings are evaluated by SDT and SIT.

CPF 2.5 - Evaluation of Lubricants for Improving Stamping Quality Soumya Subramonian Nimet Kardes-Sever Yurdaer Demiralp

Evaluation of Lubricants Using The Cup Drawing Test (CDT) (in cooperation with HONDA and several lubricant companies) Performance evaluation criteria (cups drawn to same depth): Higher the Blank Holder Force (BHF) that can be applied without fracture in the drawn cup, better the lubrication condition Smaller the flange perimeter, better the lubrication condition (lower coefficient of friction)

Evaluation of Lubricants Using The Cup Drawing Test (CDT) – Results (in cooperation with HONDA and several lubricant companies) Mill oil+

CPF 4.1 - Practical Use of Multi-point Control (MPC) Die Cushion Technology in Production of Stamped Parts Dr. Taylan Altan

Case studies in process simulation Multi-point Control systems (MPC) Hydraulic systems IFU flexible Blank holder / Binder hydraulic control unit Erie binder unit (hydraulic system) with liftgate tooling inside press (Source: IFU, Stuttgart) (Source: USCAR)

Application of MPC die cushion technology in stamping Case studies in process simulation Multi-point Control systems (MPC) Application of MPC die cushion technology in stamping Sample cushion pin configuration (hydraulic MPC unit) for drawing stainless steel double sink. (Source: Dieffenbacher, Germany) MPC is routinely used in deep drawing of stainless steel sinks

Case studies in process simulation Multi-point Control systems (MPC) Previous work at CPF in Blank Holder/Binder Force (BHF) determination CPF in cooperation with USCAR consortium developed software to program MPC die cushion system in stamping. Methodology for BHF determination (Numerical optimization techniques coupled with FEA) Inputs required BHF at each cushion pin as function of punch stroke Software developed at CPF for BHF determination Quality control parameters (wrinkling, thinning) No. of cushion cylinders (n) Tool geometry (CAD) Material properties Process conditions FEA Software (PAM-STAMP, LS-DYNA)

Multi-point Control systems (MPC) Case studies in process simulation Multi-point Control systems (MPC) Use of Multi-point Control (MPC) die-cushion systems helps to control metal flow. Each cushion pin is individually controlled by a cylinder (hydraulic/ nitrogen gas /servo control). Location of cushion pins/ cylinders in the die MPC can be used to accommodate variations in sheet properties & assist in forming AHSS.

Multi-point Control systems (MPC) Case studies in process simulation Multi-point Control systems (MPC) FE model Die Estimation of BHF varying in each cushion pin & constant in stroke, using FE simulation coupled with numerical optimization, developed at CPF (OSU). Geometry : Lift gate inner Material : Aluminum alloy, AA6111-T4 Initial sheet thickness : 1 mm Sheet Beads Segmented blank holder [Source: USCAR/OSU] Inner Binder Cushion Pin Outer Binder Punch

Multi-point Control systems (MPC) Case studies in process simulation Multi-point Control systems (MPC) BHF predicted by FE simulation in individual cushion pins for forming Aluminum alloy (A6111-T4, sheet thickness = 1 mm) Pin 1 2 3 4 6 5 7 8 9 10 11 14 12 13 15 Pin locations and numbering

Experimental validation of BHF prediction by FE simulation Case studies in process simulation Multi-point Control systems (MPC) Experimental validation of BHF prediction by FE simulation Bake Hardened steel (BH210, t = 0.8 mm) No wrinkles, no tears Aluminum alloy (A6111 – T4, t = 1 mm) Minor wrinkles, no tears Dual Phase steel (DP600, t = 0.8 mm) No wrinkles, no tears Using a hydraulic MPC system installed in mechanical press, the auto-panel was formed successfully - with three different materials/sheet thicknesses in the same die - by only modifying BHF in individual cushion pins.

CPF 4.2 - Tube Hydroforming Dr. Taylan Altan

CPF 5.1 - Evaluation of Bendability of AHSS Xi Yang Nimet Kardes-Sever Yurdaer Demiralp Dr. Changhyok Choi

Prediction of Springback (in cooperation with Cincinnati Inc.) in V-Die Bending (in cooperation with Cincinnati Inc.) a) Before unloading b) After unloading Calculation of springback for V-die bending samples: Bending angle under load was measured by camera. Bending angle after unloading was measured by protractor and camera.

Prediction of Springback with FEA and BEND in V-Die Bending (in cooperation with Cincinnati Inc.) FEA BEND Punch Sheet V-die Schematic of FE model in DEFORM 2D Screenshot from BEND

Prediction of Springback With BEND in V-Die Bending (in cooperation with Cincinnati Inc.) The program BEND was developed based on the analytical model to predict the springback in air-bending. (Channel Die or V-Die) Parameters input to the program Material’s properties Strain hardening exponent (n ) Strength coefficient (K ) Initial yield stress (YS ) Young’s modulus (E ) Poisson’s ratio Initial thickness (t0) Sheet width (w0) Friction coefficient (m) Tool Dimensions Punch radius Die radius Die opening

to Evaluate Formability/Fracture Stretch Bending Test to Evaluate Formability/Fracture Punch diameter: 152.4 mm Lock Bead Round and Strip Sample before forming after forming By changing Rd and Rp, we can obtain different stress/strain conditions at fracture.

CPF 5.2 - Prediction and Elimination of Edge Cracking of AHSS in Stretch Flanging Soumya Subramonian

(in cooperation with US Steel and TUM) Blanking and Flanging (in cooperation with US Steel and TUM) Factors Influencing Hole Expansion •Edge quality of the hole •The method used to finish the hole (e.g. blanking, reaming, etc.) •Punch/die clearance used in blanking •Positioning of burr with respect to punch •Sheet material Hole Expansion Test • To investigate the stretch-ability of the finished edges. • A conical punch, flat bottom punch or spherical punch can be used.

CPF 5.3 - Blanking and Shearing of Sheet Metal Soumya Subramonian Tingting Mao

Schematics of Blanking and Shearing (FEA and Experiments) (in cooperation with Tyco and Cincinnati Inc.) Shearing Blanking [www.custompartnet.com/wu/sheet-metal-shearing ]

Blanking and Shearing (FEA and Experiments) Different Zones of Blanked Edge Zr Zr Zs Zs Zf Zf (b) Zb Zr: rollover zone Zs: shear zone Zf: fracture/rupture zone Zb: burr (a) Different zones of the blanked edge (a) simulations and (b) experiments

Blanking and Shearing Critical Parameters Effects of the following parameters on the blanked edge quality and punch load/life are studied: Punch-die clearance Punch/die corner radii Stripper pressure and design Punch end geometry Coefficient of friction Punch misalignment Snap-thru forces / reverse loading Vibration and dynamics Snap-thru forces Analysis of snap-thru forces during blanking through simulations

CPF 5.5 - Hot Stamping of Boron Steels Eren Billur

Introduction/Hot stamping - Developed for automotive applications in the 80’s - Fast growing and an evolving technology for manufacturing crash resistant, light weight parts with reduced springback Parts manufactured using hot stamping

Introduction/Technology Overview - Manganese Boron steel (22MnB5) has ferritic pearlitic microstructure in as received condition. - These blanks are heated to austenitisation temperature(~950°C) for 5 minutes. - The heated blanks are formed and quenched in the press at a cooling rate higher than 27K/sec. - Quenching changes the microstructure from austenite to martensite and the final part is hardened and has an ultimate tensile strength of around 1500 MPa.

Introduction/Direct Hot Stamping Direct hot stamping process

Partners/Supporters National Science Foundation (NSF) - Supporting CPF/finite element simulations of hot stamping. IMRA , Japan - Data base of references and information in hot stamping. POSCO, South Korea Tooling System Group, USA COSKUNOZ (die maker), Turkey - Providing geometry and experimental data on example hot stamped components (details are proprietary).

International Co-operation CPF maintains good relationship with several leading research institutes active in Hot Stamping technology Lulea University of Technology, Sweden (Prof. Akerstrom) University of Erlangen-Nuremberg, Germany (Prof. Merklein) Leibniz University, Hannover (Prof. Behrens) University of Padova, Italy (Prof. Bariani) Tech.Univ.Graz,Austria (Prof. Kolleck) Toyohashi University of Technology, Japan (Prof. Mori) Technical University of Munich, Germany (Prof. Hoffman) Dortmund University of Technology, Germany (Prof. Tekkaya)

FE Simulation of Hot Stamping Status / Update Various companies/research groups are using combination of different FE codes like LS-Dyna, ABAQUS, PAMSTAMP, FORGE, MSC. Marc, AUTOFORM for simulating the entire hot stamping process Our Strategy Use PAMSTAMP and DEFORM 3D to predict -Temperature distribution -Thickness distribution -Metal flow -Elastic tool deflection -Cooling channel optimization Simulate and compare results with example parts a) from literature b) provided by our partner companies

Case Study-1/ AUDI B-Pillar Section -Bench Mark problem-3 given in Numisheet-2008. -2D section of the part is simulated. -The objective is to predict in the formed part: (a) thickness distribution, (b) hardness distribution, (c) potential defects. Tooling for hot stamping of B-Pillar

Case Study-1/ AUDI B-Pillar Section Input geometries for simulation Die Punch Assembly Blank Blank holder Reference: Benchmark problem-3, Numisheet 2008

Case Study-1/ AUDI B-Pillar Section Top die (75 C) 22 MnB5 Blank (810 C) Blank holder(75 C) Final simulation setup Punch (75 C) Initial simulation setup A critical section of the B-Pillar is chosen for 2-dimensional simulation (DEFORM 2D /Variable mesh density)

Case study-2/ Cooling Channel Design -For this case study, the geometry used in the case study-2 was chosen. -Heat transfer module available in DEFORM is used for simulation -Different combination of cooling channel configurations and examples from the literature are simulated to achieve uniform cooling and martensite microstructure Temperature distribution at the end of press stroke

Future plans ---Develop a simplified and practical procedure to simulate the entire hot stamping process with reasonable accuracy using commercial codes PAMSTAMP, LS-Dyna and DEFORM (predict thinning, defects, hardness) --Develop a simulation procedure to predict tool and part dimensions during hot pressing and correct the tool surface profile to obtain accurate part dimensions and desired hardness distribution (uniform or variable) --Estimate residual stresses in the part after hot stamping, quenching and cooling

CPF 5.6 - Applications of Servo Drive Presses in Stamping Adam Groseclose

Servo-Drive Characteristics 1/2 Precise ram position and velocity control, anywhere in stroke Adjustable stroke length (TDC and BDC) Ram position/ velocity can be synchronized with automatic part transfer In deep drawing, cycle times can be shorter than in mechanical presses Considerable savings in energy Dwell at BDC/ restriking/ vibrating and variable blank holder force (BHF) Max. motor torque available during the entire stroke

Servo-Drive Characteristics 2/2 The flexibility of slide motion in servo drive (or free motion) presses. [Miyoshi, 2004]

Servo-Drive Mechanisms Low Torque/ High RPM Motors Use Ball Screws or/and Linkage Mechanisms High Torque/ Low RPM Motors Use Existing Crank and/or Link Press Drives

Low RPM/High Torque Motor Drive Power Source Balancer tank Main gear Servomotor Capacitor Drive Shaft b) Stroke-Time program for warm forming of Al and Mg sheet a) C-Frame Servo Press (Aida)

Modern Stamping Lines Using Large Servo-Drive Presses BMW- Leipzig and Regensburg (Germany)/ 2500 ton servo-drive drawing press (Schuler)/ 17 SPM (2009) HONDA- Suzuka (Japan)/ 2500 ton servo-drive drawing press (Aida)/ 18 SPM (2009) New large press lines are planned BMW-Schuler- 2011 HONDA-Aida- 2011

Schematic of Servo-press line (Aida/Honda) 2500 ton/ 18 SPM draw press (2009) Improved Formability Improved Productivity Energy-Saving ・System with optimized press forming requirements for each product ・Press-to-Press Loading Motion: System is optimized for each product. ・Die cushions have an energy regeneration system

Suzuka Plant Production Picture (Honda/Aida)

Applications- Deep Drawing 1/3 Comparison between the slide motions of an 1100 mechanical and servo drive press for identical slide velocity during forming [Bloom, 2008].

Applications- Deep Drawing 2/3 Decrease in cycle time by reducing the stroke length and operating the servo press in “pendular” mode (progressive die stamping, 200% increase in output) [Bloom, 2008]

Applications- Deep Drawing 3/3 Decrease in cycle time as well as in impact speed using a servo press (150% increase in output) [Bloom, 2008]

Side Panel Outer Deep Drawing Case Example (Honda/Aida)

High-speed/ High Accuracy Servo-Press (Honda/Aida)

Servo-Hydraulic Cushion 1/2 (Courtesy-Aida) Die Cushion Force (kN) Elimination of Pressure Surge in the Die Cushion

Servo-Hydraulic Cushion 2/2 (Courtesy-Aida) During Down Stroke, Cushion Pressure Generates Power

Optimization of Ram Velocity for Deep Drawing with Servo-Drive Presses New CPF Project- in cooperation with the University of Darmstadt (Germany) Objective Develop a methodology to optimize the ram velocity during deep drawing of sheet metal parts with a servo-drive press.

Summary Process simulation using FEA is state of the art for die/process design. Determination of reliable input parameters [material properties /interface friction conditions] is a key element in successful application of process simulation. Advanced FE simulation + reliable input data helps to predict process parameters for forming the part and save tryout/setup time, cost, material & energy. Multi-point control (MPC) die -cushion systems offer high flexibility in process control, resulting in considerable improvement in formability. MPC systems offer advantages in forming high strength materials.

Summary Warm forming of selected Al- and Mg- alloys shows improvement in formability at temperatures in the range of 250-450°C. Reliable flow stress data at elevated temperature is required as an input for accurate FE simulation of the warm forming process. Considerable research on warm forming process and its application to production is in progress. Hot stamping technology will increase rapidly (Process simulation and die design/manufacturing are major issues). Electric/Mechanical servo-drive presses will be increasingly used, also in higher tonnages (2,000-4,000 tons).

Summary/Questions CPF is supported by the National Science Foundation and 10+ member companies. With a staff of 20 (post docs, PhD students, MS students), CPF is conducting R&D in metal forming, with emphasis on forming AHSS. CPF is maintaining close contacts with many other forming research labs, world wide. For questions, please contact Taylan Altan (altan.1@osu.edu) or Linda Anastasi (anastasi.2@osu.edu) For detailed information, please visit www.cpforming.org and www.ercnsm.org 79