What is Plastic Welding? 5 Most Important Processes Explained

Plastic welding is really not that different from welding metals. It is, as the name suggests, the act of welding together plastics. Similar to classical welding, you create a bond between the two items you are welding together, usually by heat but there are also other methods such as force/pressing. It depends on the specifics of the plastics, the strength of the bond you want, and the type of plastic welding machine you are using.

This article is to tell you about the various core processes – how they work, which plastics to use, and what situations they are helpful. Below, we’ve listed the most popular plastic welding processes.

Different Plastic Welding Processes

1. Ultrasonic Plastic Welding

3 step diagram of ultrasonic welding

Ultrasonic plastic welding utilizes a quick, high-frequency mechanical motion that joins, combines, or reforms plastics. It’s considered very fast and efficient, and can be used to create a clean hermetic seal which improves production time but still has a high level of quality. It’s best used for packing such as in medical devices and special equipment that requires the perfect seal. The mechanical motion is combined with applied force and creates a heat through mechanical friction at the plastic’s surface. Because of this, the plastic will melt and form a bond between the two objects.

The two plastics being joined actually vibrate back and forth, pulling away and towards each other as if they are bashing surfaces at about 20,00 and hz and 40,00 hz. This is past the range of what humans can hear typically, but because of subsequent vibrations there may be a low humming sound that results from the vibrations, but it typically isn’t very loud.

With the use of good machinery and process flow, it is fairly automated and extremely fast, which is why it has been popular for so long.

In fact, this process has been around for three-quarters of a century, about 75 years. An additional benefit to this type of welding is that with little by-product it is very sustainable since it doesn’t have a heavy reliance on packaging material and you won’t need as many chemicals.

Some great uses include:

  • small electronics
  • medical device packaging
  • pills packaging

Keep in mind the plastics you are welding need to be chemically compatible. Not following this rule will lead to weak bonds or failure.

2. Vibration Welding

Vibration welding is actually similar to ultrasonic welding in the approach, but the difference is how the vibrations are created to introduce heat and meld the plastics. While ultrasonic uses a vibration where the two items being welded together are hitting each other, the motion from vibration welding is side to side, similar to how you would rub your hands together to warm them up. Vibration welding is very quick and a weld can be as fast as 1-5 seconds, depending on the size of the object and machinery you are using.

ultrasonic and vibration welding motions diagram

Vibration welding usually vibrates 130-250 times a second, or 130-25o hz. Because this is within the frequency humans can hear, it can be very loud. In a workshop that uses vibration welding, you’ll want sound dampeners and want to consider earplugs to prevent long term damage.

Some example use cases include:

  • Power tools (chainsaws, jackhammers)
  • Medical instruments
  • Large home appliances

3. Spin Welding

  • spin melt and hold - spin welding diagram

Similar to the previous 2 welding techniques spin welding uses friction to generate heat and melt together the surfaces to form the weld. However, as the name suggestions, it utilizes the rotational motion of one part on another to create that friction, making it great for rounded joint welds. How fast and how long it takes depends a lot on the machine, but one of the leaders is https://www.extolinc.com/.

Pros:

  • Strong welds
  • Hermetically sealed
  • Great for round weld joins (fast and cost-effective)

4. Infrared Welding

Infrared welding was first discovered in the 1800’s, but it was extremely expensive. It wasn’t until WW II it became more viable, but still quite expensive until the turn of the century, in the 1990s, when the appropriate equipment became much more affordable.

This technique of plastic welding is very different from the previous welding techniques we discussed. Rather than using friction, infrared uses radiation to heat up the plastic parts and apply the weld. Infrared emitters are used to generate energy that oscillates and melt the atoms together. Based on the material of what is being welded, the material can absorb some of the radiation.

It is a non-contact form of welding, in contrast to the previous 3 methods which do require contact. There are 3 types of infrared welding, but we won’t go into too many specifics here.

What are good materials for infrared welding?

  • Polystyrene
  • PolyAmide
  • PolyButylene Terephthalate

Some products that rely on infrared welding include:

  • IV bags
  • CO detectors
  • Brake transmission lines

6 steps to infrared welding:

  1. Parts are placed into the grips of the holding fixtures
    put plastics in holding fixtures diagram
  2. Holding fixtures close to prepare with the platen
    add platen
  3. Infrared energy is applied, only targeting the joint
    apply infrared energy diagram
  4. The area reaches molten temperature and the platen is removed
    plastics begin melting
  5. Holding fixture closes, putting the two parts together where the join should be
    two plastics are put together diagram
  6. The parts cool and once completely done the holding fixture releases the newly welded item
    the newly welded piece cools

Benefits:

  • little electricity used
  • can perform intricate welding
  • low maintenance

5. Laser Welding  / Laser Beam Welding (LBW)

LBW is a welding technique that uses a precise laser beam to melt the plastic in the joint areas. Extremely accurate, laser welding is great where reliability is important such as structural engineering and manufacturing of important things such as automobiles. More information for laser beam welding can be found here.

There are different lasers that can be used, including the following:

  • solid state
  • gas
  • fiber

These vary in pricing and will have different use cases, based on exactly what type of weld you need and the materials you have. There are various types of laser weldings that depend on the laser as well, but the most popular is the transition method, which was first created in 1985. This utilizes a block to transfer the energy and heat up the objects, as opposed to direct laser welding which applies the laser directly on the surface of the materials of the joint.

Last Updated On:

About the Author Gregory

Hi, my name is Gregory! I have been welding practically all of my life and love it. As I have gotten older I have started to weld less and less, so in order to continue my love for welding I created this website. I like to write about my experiences and help you all become welders. I hope that you enjoy the site!

Leave a Comment: