Definition of Ultrasonic Welding A solid state welding process in which coalescence is produced at the faying surfaces by the application of high frequency vibratory energy while the work pieces are held together under moderately low static pressure.
Ultrasonic Welding Process Clamping force Mass Process Description: • Components of ultrasonic welding system include: • Transducer • Sonotrode • Anvil wedge Transducer Sonotrode tip Vibration Weldment Anvil Force
Ultrasonic Welding Mechanism Clamping force Mass • A static clamping force is applied perpendicular to the interface between the work pieces. • The contacting sonotrode oscillates parallel to the interface. • Combined effect of static and oscillating force produces deformation which promotes welding. wedge Transducer Sonotrode tip 10-75 KHz workpiece Anvil Force
Process Variations • Spot Welding • Ring Welding • Line Welding - Linear Sonotrode • Continuous Seam Welding - Roller Sonotrode • Microminiature Welding
Typical 1500 ultrasonic spot-type welding machine Courtesy AWS handbook
100 W Lateral Drive Ultrasonic Welder
Typical Ring Welding Applications Tip in Shape of Weld
Tip Traversing Head for Continuous Seam Welding
Welding Variables Ultrasonic Welding Variables • Ultrasonic power • Clamping force • Welding time • Frequency • Linear Vibration Amplitude
Power Generation Ultrasonic Welding Power Generation • Electrical power of 60 Hz is supplied to the frequency converter. • The frequency converter converts the required 60 Hz signal to the welding frequency (from 10 to 75 kHz). Frequency converter Electrical energy Transducer Vibratory transducer
Power Generation Ultrasonic Welding Power Generation • Frequency is transformed to vibration energy through the transducer. • Energy requirement established through the following empirical relationship. • E = K (HT)3/2 • E = electrical energy • H = Vickers hardness number • T = thickness of the sheet Frequency Converter Electrical energy Vibratory transducer
Power Requirements Where: E = electrical energy, W*s (J) k = a constant for a given welding system H = Vickers hardness number of the sheet T = thickness of the sheet in contact with the sonotrode tip, in. (mm) The constant “K” is a complex function that appears to involve primarily the electromechanical conversion efficiency of the transducer, the impedance match into the weld, and other characteristics of the welding system. Different types of transducer systems have substantially different K values.
Sonotrode Tip and Anvil Material • High Speed Tool Steels Used to Weld • Soft Materials • Aluminum • Copper • Iron • Low Carbon Steel • Hardenable Nickel-Base Alloys Used to Weld • Hard, High Strength Metals and Alloys
Ultrasonic Welding Interfacial Interaction • Localized temperature rises resulting from interfacial slip and plastic deformation. • Temperature is also influenced by power, clamping force, and thermal properties of the material. • Localized Plastic Deformation • Metallurgical phenomena such as recrystallizing, phase transformation, etc..... can occur.
Ultrasonic Welding Materials Combinations Source AWS handbook
Extreme Interpenetration Nickel Foil (top) to Gold-Plated Kovar Foil Local Plastic Flow Dark Regions are Trapped Oxide Nickel Foil (top) to Molybdenum Sheet Very Little Penetration, Thin Bond Line, Fiber Flow Molybdenum Sheet to Itself AWS Welding Handbook
Comparison With Resistance Spot Weld AWS Welding Handbook
Advantages of Ultrasonic Welding • No heat is applied and no melting occurs. • Permits welding of thin to thick sections. • Welding can be made through some surface coatings. • Pressures used are lower, welding times are shorter, and the thickness of deformed regions are thinner than for cold welding.
Limitations of Ultrasonic Welding • The thickness of the component adjacent to the sonotrode tip must not exceed relatively thin gages because of power limitations of the equipment. • Process is limited to lap joints. • Butt welds can not be made because there is no means of supporting the workpieces and applying clamping force.
Other Process Variations • Ultrasonic Welding of Non-metallic • Ultrasonic Plastic Welding
Welds Can Be Made to Non-Metallic Substrate Materials Coated with Thin Layers of Metal Films Material Welded Metal Film Non-Metallic
Ultrasonic Welding of Plastics • Advantages • Fast • Can spot or seam weld • Limitations • Equipment complex, many variables • Only use on small parts • Cannot weld all plastics 0.1.1.2.5.T25.95.12
Applications of Ultrasonic Welding • Assembling of electronic components such as diodes and semiconductors with substrates. • Electrical connections to current carrying devices including motors, field coils, and capacitors. • Encapsulation and packaging. • Plastic parts
Note weld progression (no weld in center) AWS Welding Handbook
Starter motor armature with wires joined in commutator slots by ultrasonic welding Ultrasonically welded Helicopter access door. Courtesy AWS handbook
Field coil assembled by ultrasonic welding Courtesy AWS handbook
Wire Bundle Placed in Jaws Ultrasonic Tying Tool Metal Tape Fed Around bundle of Wires and welded once, then cut and welded again. Ultrasonic Horn Bundled Wires Welds Cut and Second Weld Made First Weld Made
Ultrasonic Stitch (Clad) Welding Sonatrode Anvil Louks, et al “Ultrasonic Bonding Method” US Patenet 6,099,670 Aug. 8, 2000
Ultrasonic Welding of Eraser Holder on Plastic Pencil Coinon, A, Trajber, Z, “Pencil Having and Eraser-Holding Ferrule Secured by Ultrasonic Welding” US Patent 5,774,931 July 7, 1998
Explosive Gas Generator For Auto Air Bag (Plastic Ultrasonic Weld) Gas Generating Explosive Powder Plastic Cap Welded to Plastic Base Primer Ultrasonic Weld Avory, et al “Electrical Initiator” US Patent 5,763,814 June 9, 1998.