Good, Good Vibrations With Ultrasonic Welding

Image provided by Michael Karshis

Ultrasonic welders is a common industrial method found in many industries including electrical and computer, automotive and aerospace, medical, and packaging.It requires no bolts, soldering materials or glue – just good vibrations. Read on to see what I mean.

How ultrasonic welding works is by generating radio frequency waves that, when applied to plastic compounds, create a molecular bond between the workpieces. The RF waves cause the compounds to vibrate and become extremely hot. When the RF source is removed from the plastics, they cure together creating the weld.

ultrasonic welding howtoUltrasonic welders are available in variety of sizes and are suitable for a wide range of applications. It should be reassuring to know that whether you are using a hand held ultrasonic welders to seal plastic packages,  or using industrial welders to meld large sheet of polyethylene together during the manufacture of rafts and dinghies, the basic methodology is the same.

The following instructions are for welding plastic with an automated industrial ultrasonic welder as well as a hand held:

Step 1

Turn the knob on the ultrasonic welder labeled “psi” (pounds per square inch) to manipulate the pressure adjustment on an automated welder. The psi refers to the amount of pressure the welding horn puts on the anvil with the plastic in between.

For a hand-held welder, there is no pressure dial. The amount of pressure depends on how hard you push down on the plastic. Try to remain consistent. Pressure is one of the three key aspects of ultrasonic welding. Too little pressure, and the weld fails. Too much pressure, combined with too much heat for too long a duration, and the plastic melts and warps.

Step 2

Turn the time setting knob to adjust the time span of the weld on an automated welder. Welding occurs when the horn touches the anvil. Most welders have a maximum time limit of five seconds, but two or three seconds is usually sufficient.

Again, you determine the amount of time for a hand-held by holding the horn in contact with the plastic. Too much time combined with heat and pressure ruins a weld, but too little time and the plastic will not bond.

Step 3

Adjust the amp knob. Amplitude corresponds with heat. Both automated and hand-held welders have amplitude adjusters. The more amps, the greater the heat value during the weld duration. Amplitude is the most critical and sensitive factor. Adjusted too low, the weld fails. If there is too much amplitude, the welder ruins the plastic. Too little heat and the chemical bond fails occur.

Step 4

Test sample pieces of plastic. Put two pieces on the welding anvil. Press the “start” button on an automated welder to engage the hydraulic cylinder and lower the welding horn down to the PVC that rests on the anvil.

When the cylinder retracts, test the strength of the weld manually. Simply turn the “ON/OFF” switch on when using a hand-held. Adjust the amplitude, pressure and duration until the sample weld meets your specifications. Proceed to fabricating plastic welds.

Protip

You’re going to have to test with sample pieces of plastic first, since there are no industry standards for the pressure, amps and time required for melting different plastics.

Good luck and good vibrations!


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