Ultrasonic Welding
Ultrasonic Welding
What are ultrasonics?
From the chirping of birds to the piercing screams - sound encompasses more than what we can simply perceive with our ears. It is generated by the physical vibration of objects, not only in the air but also in any elastic medium including gases, liquids, and solids.
Ultrasonics demonstrate that not every type of sound is audible to humans. High-frequency sound waves are utilized in both industry and medicine, even though they cannot be heard.
Sound waves are classified based on their frequency, which represents the number of waves per second. Ultrasonics, for instance, fall within the range of 20 kHz to 1 GHz. Ultrasonic welding, on the other hand, utilizes frequencies between 20 kHz and 70 kHz. The lower limit of this range is still perceptible to human ears, as the audible sound range for humans is only from 16 Hz to 20 kHz. Any oscillations exceeding this range are interpreted as vibrations at best.
How does ultrasonic welding work?
When ultrasonic vibrations are applied to a material, such as plastic, the molecular chains begin to oscillate, causing the molecules to move and generate energy known as friction heat. This process can cause thermoplastic materials to melt, which is utilized in ultrasonic welding. By applying additional pressure and a brief hold time, various components can be welded together at a molecular level in the joining area.
What is ultrasonic welding suitable for?
Ultrasonic welding is a process that occurs in a matter of seconds without requiring aids such as adhesives or screws. This technology is used to create a wide range of products, including packaging, car parts, and toys. Some specific examples of ultrasonic welding applications include:
1. Joining injection-molded parts, such as those used in toys
2. Embedding membranes, such as filter membranes in medical components
3. Fusing leather, nonwovens, and textiles, such as those used in air filters for cars
4. Staking different types of materials together, such as for airbags
5. Creating form-fit joints using a shaping technique, such as those used in magnet contacts for chargers
6. Countersinking sockets and magnets, such as encapsulated magnets used to activate sensors.
The ultrasonic welding system
The ultrasonic welding system is composed of multiple components. The active components produce and transfer the vibrations into the weld joints. The passive components absorb the resulting forces, hold the parts in place, and provide additional support to the weld joint point where the components are joined together.
Active:
Ultrasonic generator
Converter
Amplitude transformer (booster or amplitude coupler)
Sonotrode (weld tool)
The converter, booster, and sonotrode are combined to form what is referred to as the stack.
Passive:
Fixture
Anvil
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Process technology: The principle of energy focusing
To achieve precise melting of the component, the vibration energy needs to converge onto one point, which is known as energy focusing. This point experiences the strongest heat development, resulting in melting. This is particularly useful for a defined ultrasonic welding process that requires low energy consumption.
Types of energy focusing
When it comes to ultrasonic welding, getting the geometry of the parts or tools right is key. This ensures that the vibration energy is directed to the correct point. One approach is to use energy directors (ED) to focus the energy at the materials themselves. Alternatively, tools can be specially shaped to achieve the desired focus.
Energy focusing through joint design
When designing components that need to be joined together, the energy is focused on the area of the parts that will be joined. This area is usually given a specific shape, often with a tip or an edge. These shaped areas are called energy directors (or ED for short) because they focus the energy during the joining process.
Energy focusing through sonotrode design
The energy can also be directed by the ultrasonic welding tool. In this case, the shape of the sonotrode helps with the melting process. The energy is concentrated at the tip of the tool, which is the hottest point. This method of energy concentration is commonly used in ultrasonic staking applications.
Focusing of energy through anvil profiles
The most important process parameters for ultrasonic welding
Amplitude
Trigger point
Weld force
Weld time
Hold time
Which materials can be welded using ultrasonics?
In general, ultrasonics can be used to weld most thermoplastic materials (plastics that can be shaped when heat is applied). The harder the material, the more effective the process. Ultrasonic welding is also suitable for nonferrous metals like aluminum, nickel, brass, and copper.
Plastics
Plastic is a common material for many everyday objects, including TV remote controls, print cartridges, and children's toys. To securely and firmly bond these parts together, ultrasonics are used for sealing and joining. This method ensures a tight seal between the parts if needed.
Packaging
We aim to keep the cheese fresh for as long as possible and ensure that the coffee retains its aroma in the capsule. By using ultrasonic sealing, our food packaging is tightly sealed, which helps reduce the amount of packaging materials used and ultimately benefits the environment while also reducing food waste. As part of our commitment to sustainability, we are currently researching the properties of modern, bio-based, and biodegradable plastics for packaging.
Nonwovens
The application of ultrasonics is highly effective in the nonwovens industry, eliminating the need for a heat-up phase and adhesive use, as well as reducing machine cleaning intervals. Products commonly produced through the NONWOVENS Business Unit include surgical masks, diapers, cotton pads, and various feminine hygiene products. Ultrasonics can be utilized to join, perforate, emboss, or make precise cuts in nonwovens.
