Ultrasonic Welding in Contract Manufacturing
Rub your hands together rapidly and they warm up. The heat is due to friction. Now imagine rubbing your hands hundreds of times per second! The frictional heat generated can raise the temperature significantly in a very short time.
Similarly, high-frequency sound (ultrasound) causes rapid vibrations within the materials to be joined together. The vibrations cause the materials to rub against each other and the friction raises the temperature at the surfaces in contact. This rapid frictional heat is what sets the conditions for the materials to bind together.
The Process
Introduced in the 1940s the technique of ultrasonic welding uses high-frequency sound waves and pressure to bind metals together. The technique works very well in welding nonferrous materials, such as aluminum, brass, copper and nickel.
In its simplest form, ultrasonic welding uses a vibrating tool called a horn, which transmits ultrasonic energy to the area where the parts to be joined are interfacing. The ultrasonic vibrations split up oxides and films on the part surfaces, allowing direct contact between metals/work pieces. When the ultrasonic vibrations cease, a solid-state bond is formed.
Let’s take a closer look at the basic elements in an ultrasonic welding system.
1.) A press, either pneumatic- or electric-driven, to assemble two parts under pressure.
2.) A fixture, where the parts are placed and allowing the high frequency vibration to be directed to the interfaces.
3.) An ultrasonic stack composed of three components. All three components are tuned to resonate at the same frequency (typically 15-40kHz)
a.) Converter: Converts the electrical signal into a mechanical vibration using piezo electric effect.
b.) Booster: Modifies the amplitude of the vibration mechanically.
c.) Horn or Sonotrode: Takes the shape of the part, modifies the amplitude mechanically, and applies the mechanical vibration to the parts.
4.) A power supply, to deliver a high power electric signal with frequency matching the resonance frequency of the stack.
5.) A controller, controlling the movement of the press and the delivery of the ultrasonic energy.
The Advantages
Ultrasonic welding offers many advantages.
Increased productivity. The machines heat up and cool down fast. The assembly process can be highly automated, providing strict control over dimensional tolerances. Weld times are usually below 1 second. In addition, assemblers don't have to worry about allotting time for warm up or cool down. The overall cycle time is very low.
Clean-cut surface: Ultrasonic welding does not damage surface finish because the high-frequency vibrations prevent marks from being generated. Also there is no ventilation system required to remove heat or exhaust.
Cost-Savings. The power consumption is extremely low, compared to traditional welding.
The Applications
Due to its overall efficiency and increased productivity today ultrasonic welding has seen wide applications in various industries including wire harnesses, sheet metal, plastics, automotive parts, and medical devices.
Electronic Industries - Ultrasonic welding is often used to join wired connections and to create connections in small, delicate circuits.
Sheet Metal and precision machining - Aluminum is a difficult metal to weld using traditional techniques due to its high thermal conductivity. However, aluminum is easy to weld using ultrasonic welding because it is a softer metal and thus a solid-state weld is simple to achieve.
Medical devices- In the medical industry ultrasonic welding is often used because it does not introduce contaminants or degradation into the weld and the machines can be specialized for use in clean rooms.
