Ultrasonic Welding Machine | Ultrasonic Plastic Welding | Ultrasonic Welding Basics

Ultrasonic Welding:

Ultrasonic welding is represented as a friction welding method, where oxides and other contaminants present on the material surfaces are broken up and also the components to be welded are brought together under simultaneous pressure. Molecular bonding, just like the conventional cold-press welding, then takes place. Ultrasonic welding is the conversion of high frequency electrical energy into high frequency mechanical energy. In ultrasonic welding spot welds in thin steels are produced by the local application of high frequency vibrating energy to work pieces held together under pressure. The work pieces are clamped together under a moderate static force applied normal to their face and oscillating shear stresses of ultrasonic frequencies (1 KHz to 40 KHz) with a power ranging of 700 to 6000 watts are applied parallel to the interface. The vibrating probe called “a sonotrode” induces lateral vibrations and slip between the surfaces fracturing the brittle oxide layers and softening the asperities because of localized heating. The combined effects of pressure and vibrations cause movement of metal molecule bringing about a sound weld.

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The bonding is achieved in solid state without application of external heat, filler rod or high pressure. There is also no need for any thorough cleaning before welding because all contaminants, oxides, moisture etc are removed by the vibrating motion.

Ultrasonic Welding Equipment:

The ultrasonic vibrating unit consists of following main components:

  1. Frequency converter,
  2. Booster,
  3. Horn or sonotrode,
  4. Pneumatic Press /Actuator,
  5. Ultrasonic power supply, and
  6. holding fixture

This converts 50 Hz – 60 Hz line power into high frequency electrical power and a transducer which changes the high frequency electrical power into ultrasonic vibratory motion that is transmitted to the joint. The weld is completed in 0.5 to 1.5 seconds.

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Ultrasonic welding of plastics:

Plastics are typically engineered materials consisting of polymers. Polymers are shaped by polymerisation that may be a chemical action during which two or more molecules are combined to make a larger molecule. Polymers are often classified as either thermosets or thermoplastics. Thermosets aren’t appropriate for ultrasonic assembly because they degrade when subjected to intense heat. Thermoplastics on the opposite hand soften when heated and cool when hardened and are thus ideally fitted for ultrasonic assembly.

Materials for Ultrasonic Welding of Plastics:

Most of the thermoplastic materials can be ultrasonic weldable. Teflon with low coefficient of friction and high melting temperature is impossible to weld using this process.

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Welding Temperature Achieved:

Ultrasonic welding produces a localized temperature rise from the combined effects of elastic hysteresis, interfacial slip and plastic deformation. The weld interfaces reach roughly 1/3 the temperatures required to melt the metals. Since the temperature doesn’t reach the melting point of the material, the physical properties of the welded material are preserved. As the ultrasonic welding method is an exothermic reaction, as welding time will increases so does weld temperature.

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The ultrasonic welding process has the advantage that since no bulk heating of the work pieces is involved and there is no danger of any mechanical or metallurgical bad effects. Although metals have up to 2.5 mm thick have been welded by this process. It is used mostly for welding foils. This process is suitable only for thermoplastics with the exception of thermosetting resins and Teflons. The process can be used on a variety of metals including the refractory metals. Even dissimilar metals can be welded because there is no fusion. The process can also be used on temperature sensitive materials because temperature rise is limited.

Ultrasonic Welding Technology | Ultrasonic Welding Frequency Range | Ultrasonic Welding Applications

Ultrasonic Welding:

The human ear can hear mechanical vibrations in the frequency range of 16 Hz to 16 KHz. Inaudible frequencies below 16 Hz are known as infrasound and those between 16 KHz and 100 GHz are known as ultrasound. Frequencies above 100 GHZ are known as hyper sound. The process is “green” in that it does not use solvents, adhesives, or mechanical fasteners. Its advantages over other assembly processes are that it is clean, efficient, and repeatable. Assemblies are cycled quickly making it an economical assembly process.

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Application:

1. It is used for the assembly of thermo plastic material

2. Alternative to using solvents or heat as bonding method

3. It is used in automotive, appliance, medical, textile, packaging, electronics and toy production such as

Appliance: Steam iron, Pump Housing, Vacuum cleaner, Dishwasher spray arm

Automotive: Lenses, filters, valves, glove box door, instrument cluster, air diverter, mass airflow sensor, headlamp parts, dashboards, buttons, seat belt locks, and air ducts etc

01-ultrasonic welding of parts - ultrasonic welding of automotive dashboards

Consumer appliance: assembly for ribbon cartridges, audio and video cassettes, watches, blister packs, pouches, tubes, storage containers and carton spouts

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Electrical and Electronics: Wire splicing, Wire Termination, Flex cable Termination, Tube sealing, Batteries, Heat sinks, Solar Panels, Coils, Contacts, Sensors, Data storage keys, Switches etc.

Medical: Arterial filter, catheters, medical garments, masks, cardiometry reservoir, blood / gas filter, face mask and IV spike / filter

01-ultrasonic welding of parts - ultrasonic welding of aluminum - ultrasonic welding of plastics

Advantages:

1. It is a very fast process

2. The process requires fairly rigid materials

3. It is attainable to affix dissimilar metals also, provided each have same melting temperatures.

4. It produces high strength, pressure tight hermetic seals.

5. It is best to spot weld plastic sections.

6. Glorious electrical, mechanical, and thermal connections between similar and dissimilar metals

7. Ultrasonic Metal Welding is that the ideal method for bonding conductive materials likes copper, aluminium, brass, gold and silver.

8. Excellent welds are achieved with otherwise difficult applications, such as welding materials that are dissimilar in thickness and composition.

9. The process is environmentally green as no solders, flux or braze material are required.

10. Low heat build up during the ultrasonic process (no annealing of materials)

11. Very little or no energy is being spent. A typical weld uses below 2000 watts and is completed in less than one-half second.

12. The process is a cold weld so that components are not annealed and no harmful intermetallic are formed during welding.

13. The ultrasonic weld is extremely reliable with built-in process monitoring to help assure zero rejects.

14. Compensation for normal surface variations of the material

15. Ability to clean surface oxides and contaminants prior to welding.

16. Ability to weld thin materials to thick materials.

17. Weld tooling typically lasts for several hundred-thousand cycles with no maintenance.

18. Large weld areas of up to 150 mm sq. can be produced with 6000 watt power supply.

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Disadvantages:

1. Large joints (>250 x 300 mm) cannot be welded in a single operation

2. Specifically designed joints are required

3. Ultrasonic vibrations can damage electric components

4. Tooling costs for fixture are high

5. Sound generation, which is typically of 90-95 dB