RF welding vs Ultrasonic welding-Difference between RF and ultrasonic welding

This page on RF welding vs Ultrasonic welding describes difference between RF welding and ultrasonic welding types.

RF Welding

The RF Welding is also popular as it does not require special joint designs and takes less time for welding. It is exclusively used for welding of thin sheets as well as films of thickness between 0.001 to 0.050 in.

In RF Welding electrodes are interfaced with high frequency (i.e. 27.12 MHz) and high voltage. It is limited to materials having higher dielectric losses. Refer RF welding advantages.

Following parameters are used in RF Welding:

Voltage: It refers to voltage needed at the electrodes
Frequency: It refers to frequency of the applied Electric field
Hold time: It is the time duration upto which parts are held under force after sonication
Weld force: Amount of force applied to part.
Electrode separation: Initially it is the thickness of the materials; at the end of welding cycle it is the distance between the electrodes.

Ultrasonic Welding

One of the popular technique for fusion bonding of thermoplastics as well as thermoplastic composites is Ultrasonic Welding. This type of welding is accomplished with the application of low amplitude (about 1 to 250 µm) and high frequency (about 10 to 70 MHz). This process results into cyclical deformation of the parts. This cyclical energy is converted into heat within the thermoplastic through intermolecular friction. The heat which is higher on the surface portions is sufficient enough to melt thermoplastic and hence to fuse the parts to be joined.

Ultrasonic welding is most often used for mass production as welding time duration is relatively short. The welding time is usually about less than 1sec.

Ultrasonic welding is applicable to both semicrystalline thermoplastics and amorphous. It is one of the technique used widely to join plastics. It is also one of the technique to bond dissimilar materials.

Following are the useful process parameters used in ultrasonic welding.

•  Amplitude: Motion of horn at horn or part interface
•  Weld time: Length of the time sonics are being activated
•  Hold time: The time during which parts are held under the force after sonication
•  Ramp time: Length of the time the sonic ramp up during the welding cycle
•  Weld Force: The amount of force applied to the parts.
•  Trigger force: Force at which sonics are being activated.
•  Melt down/collapse: Amount of weld down during the weld.
•  Mode: primary process variable which defines weld cycle, e.g. time, melt down, energy or peak power.

Ultrasonic energy can also be used to insert metal threaded bosses or any other components into a thermoplastic part. This is referred as ultrasonic insertion. The other technique referred as ultrasonic staking is used to join thermoplastic components to the second material for example metal.

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