Ultrasonic Welding For Plastics And Metals

ultrasonic welding

Common techniques for joining two materials include fastening, stitching and glueing but there’s no denying that welding provides the best results. More specifically, one of the most modern methods is ultrasonic welding. Compared to other joining methods, welds create stronger bonds that last remarkably longer and a much better finish.

Types of Welding

There are several welding codes, each different in their own ways with applications based on the requirements and the type of material involved. These include BS 4872, BS EN 287-1, ASME IX and EN ISO 9606-1. Below is a brief breakdown:

  • ASME IX (pronounced ‘asmey nine’) is an American qualification generally for inclined pipe joints
  • BS 4872 is the British Standards qualification and refers to plate work or beam welding joints prominent in the construction sector
  • BS EN 287-1 is a European standard in machinery and industry which is also considered the European equivalent of ASME IX
  • More recently, the EN ISO 9606-1 supersedes the BS EN 287-1

What Is Ultrasonic Welding?

As the name suggests, ultrasonic welding uses ultrasonic vibrations to join different materials. Applying high ultrasonic vibrations to the contact points causes the material to melt. These materials are held together under pressure as the acoustic vibrations are applied to create a solid-state weld. The typical frequency used in ultrasonic welding is between 15 and 40 kHz.

Since the equipment can concentrate the vibration on a localized spot, the welds are incredibly precise. One of the major advantages of ultrasonic welding is that you can use it not only on metals but also thermoplastics. Joining complex injection moulded thermoplastic parts can be challenging but ultrasonic welding equipment can easily be customised to the part’s exact specifications.

Industry Applications

Ultrasonic welding is mostly used with small parts such as mobile phones, consumer electronics, disposable medical tools and toys among others. However, it can also be used on larger parts including small automotive instrument clusters and home appliances.

It is typically limited to small welds of thin and malleable metals like aluminium, copper and nickel. Considering the high power requirements, companies won’t use ultrasonic welding for a vehicle’s chassis or combining bicycle parts.

Advantages Of Ultrasonic Welding

Ultrasonic welding has several benefits compared to traditional welding techniques preferred by many industries. We’ve listed a few of the major advantages below:

  • Welding occurs at low temperatures relative to other methods
  • Not using flammable fuels and open flames make it a much safer operation
  • The process occurs in mere seconds making it considerably faster than other methods
  • Contact surfaces melt or fuse when welded producing a very clean and exceptionally strong joint
  • The ultrasonic welding machine can easily be placed in a safety box or cage and operators can use ear protection gear to reduce exposure to high-frequency sounds

Disadvantages

While ultrasonic welding is clearly impressive, it does have some limitations which you need to understand.

  • You can only use it on lap joints and it has a limited weld area (250×250 mm2)
  • It is not suitable to weld thick and hard metals as they don’t vibrate as much
  • Ultrasonic welding can be limited as it works best when welding together similar materials (plastics or metals of the same type)

Interesting Facts

Ultrasonic welding dates back to the 1940s and it remains the preferred welding method for clean and powerful bonds between different materials. While it is incredibly effective at sealing or welding plastics, it is not suitable for all types.

Consider welding polyethene and polypropylene; the materials may melt together but there won’t be a chemical bond which is important for creating strong weld joints.

Ultrasonic welding is used across various sectors but a best-case example is using it to make athletic shoes. Those bonds in the upper part of the shoes are actually done by ultrasonic welding and not stitching.

Conclusion

There are continuous research and development in the field of ultrasonic welding with the intention of increasing its scale of operation. Ultrasonic welding not only creates a better finish than stitching or glueing but also a superior bond.

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