Process-Property Relationships in Ultrasonic Additive Manufacturing of Lightweight Structures

Transcription

1 Process-Property Relationships in Ultrasonic Additive Manufacturing of Lightweight Structures Adam Hehr Department of Mechanical and Aerospace Engineering The Ohio State University Professor: Dr. Marcelo Dapino Acknowledgements: NSF I/UCRC Program, SVC IAB NSF Graduate Research Fellowship Program Ohio Third Frontier Wright Project

2 Talk Overview Ultrasonic Additive Manufacturing- UAM Bond Formation in UAM Welder Energy and Parameters Effect of Build Compliance on Effective Weld Power Power Compensation UAM Process Modeling Concluding Remarks 2

3 Ultrasonic Additive Manufacturing - UAM Recent technology that combines: Ultrasonic metal welding Additive manufacturing CNC machining center Low temperature process: Interface near ½ T melt Measureable temp near 100 o C for Al 6061-H18 [1] Enabling technology for dissimilar metal joining and low temperature applications [1] M. Sriraman, M. Gonser, H. Fujii, S. Babu and M. Bloss, "Thermal transients during processing of materials by very high power ultrasonic additive manufacturing," Journal of Materials Processing Technology, vol. 211, p ,

4 UAM Video 4

5 Fluid flow UAM Applications and Strengths Automotive Aerospace Efficient Cooling and Embedded Sensing Multi-Material Joints and Reinforcement Solid-State Actuation pump thermocouple cooling heater PVDF in Al Fiber Optic Cable Embedded Temperature Sensitive Sensors and Electronics Al Al Cu Alum SS tube inum Fib er Op tic s Complex Internal Cooling Carbon Fiber Al Al Ti Light-Weighting with Dissimilar Materials and Metals NiTi Al Smart Materials Integration

6 Bond Formation in UAM Bulk Tape Bulk Tape New Tape Grains Mixing Welded Layers New Grains New Baseplate Grains New Baseplate Grains Original Baseplate Grain Boundary Baseplate Baseplate Mixing Bulk Tape Recent advancements in delivered power and down force have remedied interface voids, i.e. gapless structures [2] Weld microstructure is composed of recrystallized small (~1 micron) equiaxed grains within narrow region of weld interface (~ 20 micron) [3-4] The degree of recrystallization is foretelling of the shear strain at the interface due to dynamic recrystallization being a function of (i) strain and (iii) temperature [5] [2] K. Graff, M. Short and M. Norfolk, "Very High Power Ultrasonic Additive Manufacturing (VHP UAM)," in International Solid Freeform Fabrication Symposium, Austin, [3] K. Johnson, "PhD Thesis: Interlaminar Subgrain Refinement in Ultrasonic Consolidation," Loughborough University, [4] R. Dehoff and S. Babu, "Characterization of interfacial microstructures in 3003 aluminum alloy blocks fabricated by ultrasonic additive manufacturing," Acta Materialia, vol. 58, pp , [5] F. Humphreys and M. Hatherly, Recrystallization and Related Annealing Phenomena, Elsevier,

7 Welder Energy and UAM Parameters Controllable Parameters: Vibration amplitude, δ (μm, % of max) Normal force (N) Sonotrode travel speed, V t (in/min) Baseplate temperature ( F) Fixed Parameters: Vibration frequency (~20 khz) E weld = P dt = 1 F ω δ dx V t Sonotrode roughness (~7 or 14 micron R a ) and material (tool steel) Tape thickness (~0.006 ) Typical weld power for Al 6061-H18 is near 2-3 kw Typical weld power for as rolled 4130 steel is near 5-7 kw 7

8 Percent Average Electric Power (W/W) Effect of Build Compliance on Effective Weld Power F s New Layer 120 UAM Stack with k eff stiffness Baseplate Amplitude available to weld foil Amplitude lost to compliance Imparted amplitude No. of Welded Layers Build compliance refers to the mechanical deformation of the part when subjected to shear force during the UAM process compliance increases with part height [6] Build compliance leads to a decrease in plastic deformation, i.e., a decrease in effective weld power Power compensation achieved by increasing weld amplitude manually % power loss [6] A. Hehr, P. Wolcott and M. Dapino, "Effect of Weld Power and Build Compliance on Ultrasonic Consolidation," Rapid Prototyping Journal, In Press. Uncompensated Compensated 8

9 Weld Power (W) Weld Power (W) Average Power (W) Power Compensation Uncompensated Power Compensated Power No. Layers vs. Steady-State Avg. Power Uncomp. Compensated Layer 2 Layer 5 Layer 10 Layer 15 Layer Weld Length (cm) Layer 2 Layer 5 Layer 10 Layer 15 Layer Weld Length (cm) Number of Welded Layers Does power compensation lead to stronger welds? Approach: Measured weld power for compensated and uncompensated stack builds Push-pin testing to evaluate bond strength Focused Ion Beam (FIB) imaging used to analyze interface microstructure 9

10 Force [kn] Power Compensation: Push-Pin Testing Comparative test Used to evaluate UAM interfacial bond strength Successfully used in recent Al 6061-H18 weld study [7]. Compensated Failure Thru All the Layersf Delaminationf Uncompensated Poor UAM Build Base plate Base Plate Plus 5-6 Layers Deep [7] P. Wolcott, A. Hehr, M.J. Dapino, Optimized welding parameters for Al 6061 ultrasonic additive manufactured structures, Journal of Materials Research 29 (17). Good F Notch Width 20 Total Layers 3-4 Layers Thick Energy Compensated Uncompensated Similar Peak Load Enhanced Mechanical Work Interface Delamination Stroke [mm] 10

11 Power Compensation: Weld Microstructure Uncompensated: Layer 5 Compensated: Layer 5 Uncompensated: Layer 15 Compensated: Layer 15 Unmixed zone Enhanced interface recrystallization with power compensation 11

12 Power Compensation: Energy Balance E surf + E plastic = E bulk + E recryst + E thermal Input Output Energy balance can be utilized to analyze bonding process E plastic measured remotely via transducer power consumption (E weld ) E recryst measured via quantity of new small grains at interface [8] Stronger welds achieved with larger E recryst due to Hall-Petch relationship [8] First time weld microstructure has been correlated with energy input [8] R. Abbaschian, L. Abbaschian and R. E. Reed-Hill, Physical Metallurgy Principles, Stamford: Cengage Learning,

13 UAM Process Modeling: LTI Model Inputs Linear System Outputs LTI Model electric current: i shear force: F s Welding Assembly Voltage: V weld velocity: jωδ jωδ V = H em H m H e H me i F s Sonotrode Lumped System: Welder Characterization Piezo Actuator 1 δ Actuator 2 V i C t Φ t δ 1:Φ t Φ t V M t δ D t 1/K t F s V V Lumped System: Welder Operation i Compression Rod Electroacoustics theory [9-12] F s i V i Ψ t δ Ψ t :1 1/M t Ψ t i K t 1/D t Fs δ [9] B. Richter, J. Twiefel, J. Wallaschek, Energy Harvesting Technologies: Ch4: Piezolectric Equivalent Circuit Models, Springer, [10] W. P. Mason, Electromechanical Transducers and Wave Filters, D. Van Nostrand Company, Inc., 1942 [11] F. Hunt, Electroacoustics: The Analysis of Transduction and Its Historical Backaground, Cambridge: Harvard University Press, [12 C. van der Burgt, H. Pijls, Motional Positive Feedback Systems for Ultrasonic Power Generators, IEEE Transactions on Ultrasonics Engineering 10 (1) 13

14 UAM Process Modeling: Characterization Analysis Computer Quattro Analyzer Welding Assembly Laser Vibrometer PowerAmplifier Charge Amplifier Shear force: High frequency modal hammer Weld velocity: Laser vibrometer Voltage and current: Linear amplifier Frequency response functions: Quattro analyzer Boundary conditions: In UAM machine 14

15 H e db Magnitude (A/V) UAM Process Modeling: Model Fit Exp. Fit Frequency (khz) H em db Magnitude (m/s/v) Frequency (khz) H m db Magnitude (m/s/n) Frequency (khz) H e Phase Angle (deg) H em Phase Angle (deg) H m Phase Angle (deg) Frequency (khz) Frequency (khz) Good agreement with measured and closed form FRFs Fit procedure found in literature [9] Frequency (khz) 15

16 Peak Velocity (m/s) Average Electric Power (W) Peak Voltage (V) Average Electric Power (W) Peak Velocity (m/s) Welder Frequency (khz) UAM Process Modeling: In-Situ Measurements Peak Weld Velocity Time (s) No Welding Welding LTI model assumption valid? Time (s) Yes, welder dynamics are pseudo-stable during operation Measurements support model assumptions Welder Frequency Average Electric Power (W)1000 Electric Power Draw Time (s) (a) Welder Velocity and Power Welder Voltage Power Calibration Measured Estimate Adj. Estimate Amplitude Level (%) Amplitude Level (%) Amplitude Level (%) 16

17 Average Electric Power (W) Welder Frequency (khz) UAM Process Modeling: Shear Force and Efficiency Time (s) Excitation Frequency Weld Power Time (s) Peak Force (N) Peak Velocity (m/s) Peak Weld Velocity Time (s) Peak Shear Force Time (s) No Welding Welding i i ref = Shear force near 2000 N, which is similar to de Vries [13]. Welder efficiency near 82%, which is near ultrasonic metal welding estimates [14] and below piezoelectric transducer efficiency [15]. Upward frequency shift from UAM build stiffening system. Shear Force Estimation P P ref F s = H em i jωδ H m Efficiency e = jωδ F s P Power Control Law P = 1 2 V Ψ t ΔF s [13] E. de. Vries, Mechanics and Mechanisms of Ultrasonic Metal Welding, Ph.D. thesis, The Ohio State University, Columbus, OH, USA (2004). [14] K. Graff, AWS Handbook 9th Edition: Volume3: Ultrasonic Welding of Metals, American Welding Society, [15] R. Friel, Power Ultrasonics: Ch13: Power ultrasonics for additive manufacturing and consolidation of materials, Elsevier,

18 Conclusion UAM enables fabrication of unique materials and products Weld power/energy correlation with bond quality Weld power as an in-situ process variable LTI model which uses shear force as a system input In-situ measurements of welder 18