Ultrasonic Plastic Welding Technology
What is ultrasonic welding?
Ultrasonic welding technology uses high-frequency vibration (ultrasonic) to precisely seal two thermoplastic components together in sub second time. Under precise pressure, the connection seals in less than 0.2 seconds.
Ultrasonic waves vibrate dozens or thousands of times per second. This vibration will be transmitted to the contact surface in direct contact with the plastic component. Due to the high acoustic impedance at the boundary of the welding area, high temperatures are generated. Plastic is a very poor thermal conductor and cannot dissipate heat until it changes from a solid state to a liquid state. Apply some pressure, which will cause the two parts to merge together as if they were a piece of plastic. Once the ultrasonic signal stops, the parts will harden again. This is the magic that creates a clean and very strong weld between two components. The strength of the weld seam is close to the strength of the raw material formed during injection molding.
Ultrasonic welding process
Step 1- Parts in the Fixture
Two thermoplastic components that need to be assembled are placed together, one on top of the other, in a support nest called a fixture.
Step 2- Tool Head Contact
The titanium or aluminum component called the tool head comes into contact with the upper plastic component.
Step 3- Apply pressure
Apply controlled pressure to the parts and clamp them onto the fixture.
Step 4- Welding Time
The tool head vibrates vertically at a speed of 20000 (20 kHz) or 40000 (40 kHz) per second for a precise amount of time - also known as welding time. Each component is precisely designed to direct energy to specific contact points between the two components.
Mechanical vibration is transmitted to the joint interface through thermoplastic materials to generate frictional heat. When the bonding interface temperature reaches the melting point, the plastic melts and flows, and the vibration stops. This allows the melted plastic to start cooling.
Step 5- Maintain Time
The clamping force is maintained for a predetermined amount of time to allow the components to fuse as the melted plastic cools and solidifies. This is called holding time. Improved bonding strength and airtight sealing can be achieved by applying greater force within the holding time. This is achieved by using dual pressure at different points within the holding time.
Step 6- Retract the tool head
After the melted plastic solidifies, remove the fixture and retract the tool head. These two plastic parts are now connected together, as if molded together, and removed from the fixture as a single component.
Ultrasonic welding for plastic assembly is a fast, clean, efficient, and repeatable process with extremely low energy consumption. No solvents, adhesives, mechanical fasteners or other consumables are required, and the finished components are sturdy and clean.
Important factors of ultrasonic plastic welding
The welding time and welding head pressure can be adjusted according to the amplitude determined by the configuration of the converter and welding rod. Generally speaking, the main variables are
1. Amplitude bar and converter
2. Welding head pressure
3. Welding time
4. Maintain time
Adjustments must be precise. If the frequency is too high or the signal is applied for too long, the plastic is easily deformed beyond the boundary of the connection point. If the applied energy is too weak, it will form a poor connection.
