Ultrasonic welding

Which plastics can be welded with ultrasound and which materials can be combined?

Ultrasound can be used to create reliable, sealed joins in moulded parts and to weld or seal films and technical textiles. The components to be joined should be made primarily of thermoplastics, which may be semi-crystalline or amorphous. Semi-crystalline thermoplastics include POM, CA, LCP, PEEK, PA, PBT, PE, PPS, PP and PTFE. Amorphous plastics include ABS, MABS, PMMA, PC, PET, PS and PVC. The best results are achieved when welding two components made from the same material, but you can also weld compatible pairings of different materials.

A list of compatible plastics can be found here.

How does the ultrasonic plastic welding process work?

“Welding” is defined as joining two or more workpieces or materials by applying heat to melt the adjoining surfaces, which creates a permanent join.

How does ultrasound weld plastic components together? - The ultrasonic welding process explained in brief

When ultrasonic welding is used to join thermoplastics, the mechanical ultrasonic oscillations – which have a pre-defined frequency, amplitude and pressure – are transferred to the plastic components for a set period of time. The oscillations create friction at a molecular level, which generates heat in the material. The existing molecular joins in the plastic are broken down by the heat and oscillations. This process automatically speeds up during the welding cycle. The plastic plastifies, softens and melts. When the ultrasound source and supply of energy is removed, the thermoplastic cools down rapidly and hardens. The molecules in both plastic components form new connections. During this hardening process, the joining pressure only needs to be maintained for a short time to achieve a homogeneous material structure and create a permanent join between the plastics.

The basics of ultrasonic plastic welding in brief

Watch this video to learn all about the basics of ultrasonic welding. We explain how the welding process works in detail.

What requirements can I meet with ultrasonic welding technology?

Ultrasonic welding could be a good process technology for your application if you need to create joins with high mechanical strength, because components welded using ultrasound are resistant to mechanical stress and loads. Furthermore, the joint is highly resistant to cracking. The weld seam is hermetically sealed against water, pressure and vacuums.

Alongside a need to fulfil stringent requirements for sealing and strength, there are many other reasons to opt for ultrasound technology. Ultrasonic welding is a very economical and fast joining process. Ultrasonic welding devices are ready for use very quickly; they take no longer to power up than a standard PC.

Another advantage is that ultrasonic welding produces very attractive results. Ultrasonically welded seams have no visible marks, there is no deformation of welded parts, and the seams themselves are highly precise.

Moulded parts must be designed for ultrasound compatibility – moulded part design

In order to weld two moulded parts together quickly and achieve a reproducible, high-strength result, one of the two components must be designed with integrated pointed elements.
These pointed elements, also known as energy directors or pinch seams, direct the ultrasonic oscillation into the second moulded part. This ensures that both moulded parts melt simultaneously along the seam to create a permanent join.

If there is no energy director or pinch seam, the surfaces will be welded together instead of a seam being formed. This type of welded join is not as strong; it also takes significantly longer to achieve and there is a risk of damage to the components.

Let’s take a closer look at the two most common join zone geometries:

The design of the moulded parts has an enormous impact on the seal, strength and look of the welding result. This is why it is very important to consult with RINCO ULTRASONICS right from the start of your project. We will be happy to advise you. Please contact us at info@rincoultrasonics.com or using the contact form below (on the right-hand side of the page).

Benefits of ultrasonic welding

Economical
Ultrasonic welding is a very economical technology. Compared to thermal welding, ultrasonic welding requires

• No warm-up time
• No cooling phase for the application
• Less material

Efficient
The welding cycle usually takes just a few tenths of a second. The weld seam also hardens in a fraction of a second.
And because the seams can be very narrow, you can also reduce material consumption.

Perfect weld seams
The weld seams can be designed to meet your exact requirements. Whether your goal is hermetically sealed seams or perfect visual results, your weld seams will always be strong and precise.

No additional materials
Ultrasonic welding is highly economical, as no additional materials are required to join the components. This also makes the materials easy to separate for recycling.
Welding without additional materials such as screws or adhesives also helps to make products safer – ideal if you manufacture children’s toys, for example.

Three-dimensional weld seams
The sonotrode – the actual welding tool – is designed and manufactured specifically to suit the customer’s requirements. As this design process is tailored to your needs, you can also opt for three-dimensional weld seams.

Frequently asked questions about ultrasonic welding