2-2 Ultrasonic Welding

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.Definition of Ultrasonic Welding

Ultrasonic Welding Process Process Description:Components of ultrasonic welding system include:TransducerSonotrodeAnvilAnvilMassSonotrode tipClampingforcewedgeTransducerForceWeldmentVibration

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.AnvilMassSonotrode tipClampingforcewedgeTransducerForceworkpiece Ultrasonic Welding Mechanism10-75 KHz

Process Variations Spot Welding Ring Welding Line Welding - Linear Sonotrode Continuous Seam Welding - Roller Sonotrode Microminiature Welding

Typical 1500 ultrasonicspot-type welding machineCourtesy AWS handbook

100 W Lateral DriveUltrasonicWelder

Typical Ring Welding ApplicationsTip in Shape of Weld

Attachment for Continuous Ring Welding

Traversing Head for Continuous Seam WeldingTip

Ultrasonic powerClamping forceWelding time Frequency Linear Vibration AmplitudeWelding VariablesUltrasonic Welding Variables

Ultrasonic Welding Power GenerationElectrical 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).Electrical energyFrequency converterVibratory transducerTransducerPower 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 sheetElectrical energyFrequency ConverterVibratory transducerPower GenerationUltrasonic Welding Power Generation

Where:E = electrical energy, W*s (J)k = a constant for a given welding systemH = Vickers hardness number of the sheet T = thickness of the sheet in contact with the sonotrode tip, in. (mm)Power RequirementsThe 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 MaterialHigh 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

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 DeformationMetallurgical phenomena such as recrystallizing, phase transformation, etc..... can occur.Ultrasonic Welding Interfacial Interaction

Source AWS handbookUltrasonic Welding Materials Combinations

Extreme InterpenetrationNickel Foil (top) to Gold-Plated Kovar FoilLocal Plastic FlowDark Regions are Trapped OxideNickel Foil (top) to Molybdenum SheetVery Little Penetration, Thin Bond Line, Fiber FlowMolybdenum Sheet to ItselfAWS Welding Handbook

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. Advantages 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.Limitations of Ultrasonic Welding

Other Process Variations Ultrasonic Welding of Non-metallic Ultrasonic Plastic Welding

Welds Can Be Made to Non-MetallicSubstrate Materials Coated with ThinLayers of Metal FilmsNon-MetallicMetal FilmMaterial Welded

Ultrasonic Welding of PlasticsAdvantagesFastCan spot or seam weldLimitationsEquipment complex, many variablesOnly use on small partsCannot weld all plastics0.1.1.2.5.T25.95.12

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 partsApplications of Ultrasonic Welding

**Typical components of an ultrasonic welding system are illustrated in the above figure. Linear ultrasonic vibrations are generated in the transducer and transferred to a sonotrode. The anvil holds the components in a fixed position and supports the clamping force.***There are five variables in ultrasonic welding. They are :(a) Ultrasonic power(b) Clamping force(c) Welding time (d) Frequency (e) Amplitude of Linear Vibration**The energy required to make an ultrasonic weld can be related to the hardness of the workpieces and the thickness of the part in contact with the sonotrode tip. Analysis of data covering a wide range of materials and thickness has led to the above empirical relationship. The constant k is a complex function that appears to involve primarily the electro-mechanical conversion efficiency of the transducer, the impedance match into the weld, and other characteristics of the welding system. Different types of transducer systems should have substantially different k values.*****Ultrasonic welding processes that can be used for plastic material bonding occur when vertical oscillations at frequencies of 10 to 50 kHz are transmitted through polymers and dissipated in a bond line. The parts to be joined are held together under pressure and are subjected to ultrasonic vibrations at right angles to the contact area. The high-frequency stresses produce heat in the material and, if the components are properly designed, this heat can be selectively generated at the joint interface. Heat is generated through a combination of friction and hysteresis. The amplitude of the oscillations can be in the range of 20 to 60 microns, significantly less than the amplitude of movement in friction welding. The sound energy oscillations are generated by the ultrasonic welder and transferred to the parts being welded by what is called a horn. The design of the horn as well as the anvil or base of the ultrasonic welder is critical to the success or failure of the process as it must transmit a specific wavelength of sound into a specific joint geometry. Ultrasonic welding equipment is typically costly, which makes it impractical for short production runs.Ultrasonic welding is probably the most commonly used method to join thermoplastics. It is fast (a few seconds or less), clean, and usually produces welds that are relatively free of flash. In addition, ultrasonic welding is relatively easy to automate since fixtures can act as anvils and the horn can be applied outside the part to produce a weld on an inside surface. Items commonly made by ultrasonic welding include, dashboard assemblies for automobiles, and 3-inch computer disks. Note that most of these items are small; size is a limitation of the process.*