A “welding” process of some type is necessary to join two individual pieces of plastic not manufactured as part of a larger whole. As you can imagine, if you were to even approach a piece of plastic with an Acetylene Gas or Arc welding torch, the intense heat would completely destroy the material.
Welding plastic requires the use of a completely different type of technology, known as Ultrasonic Plastic Welding. Ultrasonic plastic welding is quite literally a welding process that’s used to weld together plastic parts and components. But instead of intense heat, ultrasonic welding uses high frequency, low amplitude vibrations to create a state of super agitated friction between two pieces of plastic forced together in direct contact.
Ultrasonic Welding Machine
A basic ultrasonic welding machine consists of three components, often referred to as the “stack”:
- Converter
- Booster
- Weld Horn
Converter
The Converter creates the high frequency vibrations necessary to weld plastic, and is comprised of piezoelectric ceramic disks surrounding metal plates, that are clamped to a specially designed titanium cylinder and powered up by a high frequency electrical power module. When powered up, the ceramic disks expand and contract in response to the sinusoidal (the high frequency electrical signal generated by the electric module). This translates into a high frequency vibration that’s transmitted by the titanium cylinder to the rest of the stack.
Booster
The converter alone cannot create high enough vibrations to reach the required melt temperatures for most thermal plastics, so the Booster amplifies the vibrations, doubling the output by as much as twice what the converter alone is able to produce.
The level of boost required depends upon the circumstances of the situation and the particular materials involved.
The Horn
The Horn transmits the high frequency vibrations generated by the converter and amplified by the booster to the plastic material being welded. The horn also exerts the physical force necessary to weld the two pieces of plastic once they reach melt temperature.
The Ultrasonic Plastic Welding Process
The high frequency vibrations initiate the melt, and the force applied by the horn completes the bond. Each type of plastic has its own individual properties, and a process of trial and error is usually required to determine the correct vibration frequency for welding a particular type of plastic.
The success of the ultrasonic plastic welding process hinges upon three key factors:
- Amplitude
- Force
- Exposure
Amplitude
Amplitude is the measure of the high frequency vibrations used to bring plastic to melt temperature. The amplitude must be properly tuned for a particular piece of plastic to melt.
Force
Force refers to the physical force placed on the two pieces of plastic being welded together. Adequate force is required to ensure an effective bond between the individual plastic components.
Exposure
Exposure refers to the physical contact between the two pieces of plastic being welded together. Maximum exposure is necessary at the bonding point between the individual pieces of plastic to ensure a solid and securely sealed bond.