Principles and Applications of High Power Ultrasonics Karl Graff Ultrasonics Group 614.688.5269 [email protected] The Field of Ultrasonics High frequency ultrasonics High power ultrasonics What is High-Power Ultrasonics? HPU … application of intense, • Power supply high-frequency acoustic Ultrasonic energy to change materials, Transducer processes. 60 ~ Ultrasonic energy Transmission causes change in Material or Process Material/Process Outline … Ultrasonic vibrations and waves Vibrations Transducers and systems Physical effects of HPU x Applications of HPU Transducers Effects Applications US Vibrations & Waves HPU … application of • Power supply intense (i.e., high- Transducer power), high-frequency (i.e., ultrasonic) 60 ~ acoustic energy to create change in Transmission materials and processes. • Vibrations & Waves enter at every stage of HPU Material/Process Ultrasonic energy causes change in Material or Process Oscillator iωt Foe k x m Λm c x k ω = n m Teaches … • Natural frequency Timoshenko, S., Young, D.H. and Weaver, W. Jr., “Vibration Problems in Engineering,” • Resonance Fourth Edition, John Wiley & Sons, New York, 1974, Fig. 1.33. • High Q Equivalent Circuits F eiωt LR o I k m iωt C Voe c x (a) (b) F - force on the mass V - voltage applied to the circuit v - velocity of mass I - current in the circuit k - spring stiffness L - inductance m - mass R - resistance Longitudinal Vibrations Basic Vibration Concepts • Expansion/contraction nature of longitudinal vibrations Stress • Natural frequency • Nodes and antinodes • Amplitude, stress distribution • Wavelength - λ x c E cylinder-20khz.avi Node Antinode f = , c = (1 MB) 2l ρ Amplitude Steel, Al: c ≅5.1×103 m/ s λ/2 at 20 ×103Hz (20kHz) c 5.1×103 →l = = 2 f 2 ×20×103 =0.128 m =12.8cm ≅5in. Wave (Bar, Rod) Velocities c ~ Wave velocity in rod = (E/ρ)1/2 Bar velocity Material m s-1 x 10-3 in. s-1 x 10-4 Aluminum 5·23 20·6 Brass 3·43 13·5 Cadminum 2·39 9·4 Copper 3·58 14·1 Gold 2·03 8·0 Iron 5·18 20·4 Lead 1·14 4·5 Magnesium 4·90 19·3 Nickel 4·75 18·7 Silver 2·64 10·4 Steel 5·06 19·9 Tin 2·72 10·7 Tungsten 4·29 16·9 Zinc 3·81 15·0 Note: Titanium ~ steel, aluminum, magnesium Longitudinal Vibration Modes n=1 x c f1 = 2l n=2 Node Antinode c f2 = nc l fn = 2l n=3 3c f = n = 1, 2, 3, … 3 2l Note on “Mode Counting” nc n=3 f = 3c n f = 2l 3 2l Mode counting “with a vengeance ” λ λ/2 λ/2 λ/2 λ/2 λ/2 n = 5 Equivalent Circuits C LR F V ρ,E,A C 0 f = 2l π 2AE 1/C = 2l ρAl L = , R = loss 2 Ultrasonic Horns Ularge M = Stepped Usmall Stepped : Alarge M = Tapered Asmall Tapered Horns 1. Conical 2. Exponential 3. Catenoidal Merkulov, L.G., “Ultrasonic Concentrators,” Soviet Physics- Acoustics, v. 3, no. 6, pp. 246=255, 1957, Fig. 4. Large Horns – Lateral Strain (“Poisson” effect), etc. • Wide parts need wide horns, but … ? Large Horns (From Branson product literature) Bending Vibrations 2 2 aβ 2 Ic f = a = 2π A A, I A = Cross-section area I = Moment of inertia of cross-section 1 2 3 β1/=1.875 β2/=4.694 β3/=7.855 HPU Processes Transducers Transducers • Transducer … Transducer 60 ~ Power supply Transducer Piezoelectric 20 kHz, 60 kHz, ... A ~ 25 μ, 40 μ... Magnetostrictive Piezoelectricity, Piezoelectric Effect F Δ VV Van Randeraat, J. and Setterington, R.E., Piezoelectric Van Randeraat, J., op. Cit., Fig. 2.2 Ceramics, N.V. Phillips’ Gloeilampenfabrieken, Einhoven, The Netherlands, Second Edition, 1974. Fig. 2.1. Piezoelectric Equations σ= cDε ~ Elastic solid E= βD ~ Capacitor σ= cDε + hD ~ Piezoelectric material E = -hε + βD σ,ε = stress, strain E,D = electric field, displacement cD,β = elastic, dielectric constants h = piezoelectric constant Transducer (Converter) V Resonator “Real” Transducer … • Precompression • Electrical safety • Heating • Vibration amplification • Assembly • Gripping/holding • Tooling attachment HPU Piezoelectric Transducer Steel back Flange for case Titanium or aluminum front mass attachment driver (front mass). Ti/Al front, Steel back provides boost Center bolt (for precompression) Electrodes Piezoelectric disks (4 or 6 typical) Transducer Designs High-Power Ultrasonic System Power supply Transducer Booster Horn/Sonotrode Transducer Vibration Anvil Workpieces 60 ~ Power Supply Lateral Drive Welding System Static Force Transmission HPU System Material/Process Power Matching Transducer Load Supply Circuit Impedance matching At ‘series’ resonance Z Z Z Z Trans Cap balanced out Transformer gives 50ohm Much lower Z Trans Cap Load Load only Transformed Load Power Matching Transducer Load Supply Circuit Feedback Control k m Power supply Transducer c 60 ~ Transmission Material/Process System Frequency Variation Recall … Equivalent Circuits F eiωt LR o I k m iωt C Voe c x C F LR ρ,E,A V Transducer Equivalent Circuit I V L V Z = V/I Co R C Transducer Modeling – 1D Pencil & Paper PiezoTran (British Node Antinode Navy sonar expert) 2 2 2 2 2 ∂ u/∂x = (1/co )∂ u/∂t 1/2 c0 = (E/ρ) Ford Motor Co. V V0 V0 0 3 1 .10 4 2,3 10,11 14,15 16,17 1 .10 4,5 6,7 8,9 12,13 0,1 18,19 I 20,21 i 5 1 .10 2 6 22 23 24 25 26 27 1 .10 7 1 .10 20 21 22 23 24 25 f ⋅0.001 i Modeling the Transducer Use of advanced FEA 6.5 6 Impedance-FEA 5.5 5 4.5 Impedance 4 3.5 3 15 16 17 18 19 20 21 22 23 24 25 Frequency (KHz) Impedance-exp. FemLab Resonance Heat Mesh Displacement Generation “Three (or four) Things” iwt Foe k m c Node Antinode x V L Co R C Physical Effects of HPU In fluids (gases, liquids) In solids HPU Effects in Fluids • Absorption/attenuation • Nonlinear waves • Radiation pressure • Acoustic streaming • Atomization • Cavitation HPU Effects in Solids • Anelasticity, absorption/heating • Fatigue • Deformation • Surface effects Anelasticity Higher order “constants” 2 Leads to harmonics T = C1ε + Cnε Affects horns, transmission lines Absorption/Heating Metals - grain structure Polymers - long chains “Macro description’” - loss moduli, viscous moduli Uses: Polymers - welding, processing; metals - usually a problem Deformation • Mechanism unclear (acoustic softening or superposition) • Uses: Many potential Fatigue Not necessarily just “Fast” low-frequency fatigue Testing Usually a problem Mechanical Impact • “Hammer” action of US tool • Uses: US machining, comminution, surface treatment, . Surface Effects Friction Effects on forming, flow, welding processes Friction and Shear Reduction • US vibrations disrupt friction forces • Uses: Compaction, sieving, flow enhancement HPU Applications – A Reminder HPU … application of intense, • Power supply high-frequency acoustic Ultrasonic energy to change materials, Transducer processes. 60 ~ Ultrasonic energy Transmission causes change in Material or PROCESS Material/Process Some Applications of HPU • Agglomeration, coagulation of particulates • Metal processing – molten metals • Atomization – combustion, humidification Melt degassing • Biological – cell disruption, … Solidification Crystal growth Casting (see metal processing, molten) • Composites • Chemical/sonochemical processing Atomization (powdered metals) • Cleaning • Metal processing – solid metals • Comminution Forming • Compaction, consolidation Heat treatment, annealing • Cutting, drilling, machining Surface hardening Mineral processing • Defoaming • Flotation, emulsification • Drying Disintegration of minerals, surface films • Emulsification/dispersion Defrothing, dehydration of ores • Filtering, sieving, separation, flow Hydrometallurgy enhancement • Mixing • Food processing – cutting, drying, … • Motors, ultrasonic • Forming of materials (see also metals) • Stress relief • Joining-welding, soldering • Surface treatment, cladding, plating • Liquid processing (non chemical) • Testing – erosion, fatigue, hardness • Medical – surgical, therapeutic • Transport/positioning – uses of levitation Manufacturing Applications • Molten metal • Metal deformation • Machining • Materials joining • Cleaning/compaction • Airborne US • Liquid processing HPU in Molten Metals Key Effects … Degassing Reduce grain size Control columnar structure Vary phase distribution Improve homogeneity Disperse inclusions Extensive Work in This Field Metals Treated with US … Pure metals (Fe, Al, Co, Zn, Sn, Bi) Low Melting (Bi-Pb-Sn-Cd, Bi-Cd, …) Aluminum, magnesium alloys Copper, silver Steels, cast irons Nickel-based superalloys Cavitation, Steaming Allied Processes • US-assisted crystal growth • Plating • Powder metallurgy – atomization • Composites Metal Deformation Processes Traditional Forming Processes Historical Note on US Forming Blaha/Langenecker (1955) introduced concept of ‘acoustic softening’ - launched extensive research in metal forming Question of ‘acoustic softening’ vs. ‘stress superposition’ not conclusively resolved – latter most supported US forming continues as active field – recent search shows 65 citations since ‘85 US Wire and Tube Drawing US Wire Drawing US Forming Operations Benefits of US Forming • Increased draw speed • Improved surface finish • Reduced draw force • Greater area reduction • Longer tool life US Impact Treatment (UIT) UIT – means of creating US “impact” against metal surface – and resulting local plastic deformation and residual stresses in the metal. Three primary means of creating US impact … Impacting Tool, Ball or Rod Local zone of plastic deformation and residual stress Direct intermittent Intermittent Intermittent impact of “hammering” impacts of metal US tool against rod with impact of US tool ball between US transmission of stress against metal tool and metal pulse into metal surface surface surface Features of UIP System ITL System Other US Impact