How To Weld Plastic To Plastic

Since plastic is widely used due to its availability and low costs, people have also come up with ways on how to mold and join the pieces together for repair and other reasons. One that initially comes to mind is plastic welding. It is a recognized process joining softened thermoplastic surfaces with the use of heat. 

Have your welding machine ready and we will teach you everything that you need to discover about the process of welding plastic. By the end of this article, you would know that this process isn’t complicated at all, but just takes some patience and practice to be done effectively. 

Overview

The welding method is just one of the several processes done to join plastic surfaces together. If you’re a novice, it matters to assess the base material you’re working on first before you continue the procedure to make sure that they are weldable. The procedure typically starts with pressing the compatible surfaces together, then subjecting them to heat and pressure, and ending it by letting the product cool off. 

Now, let me help you learn the different methods of welding plastics, step-by-step guidelines, and other helpful information that you need to know.

Methods of Welding Plastic

Let us start our learning journey by looking into the summaries of the most common methods for plastic welding.

  • Ultrasonic Welding – Vibratory mechanical pressure is used for heating conducted with ultrasonic frequencies. Ultrasonic vibrations are then applied to the pieces to be welded with the use of a horn. After that, heat from the friction of the waves is utilized to join your plastic pieces together.
  • Radio Frequency Welding – With a turnaround time of between 2-5 seconds, this process is widely preferred by experts. This method utilizes high-frequency electrical energy or radio waves.
  • Hot Air Welding / Gas Welding – Uses hot gas that is typically generated once the air in the welding gun has been electrically heated.
  • Laser Welding – Two thermoplastic pieces are placed under slight pressure then a laser beam passes across the joining line forming a permanent bond. The turnaround time is 3-5 seconds.
  • Vibration Welding – The surfaces to be joined together are rubbed together under a specific amplitude and frequency, therefore building up heat from friction. The heat then melts thermoplastics at the joint region causing the pieces to fuse at a turnaround time of 1-5 seconds.

The Process of Welding Plastic

Now that you have taken note of the methods available, let us move forward and see how the procedure should go.

  1. Set up your workspace.

Before anything else, wear all your essential equipment such as gloves, helmet or protective gear, and long sleeves to protect yourself while doing the procedure. Set up everything in a well-ventilated place and prepare your plastics by washing any debris off and removing stubborn stains. Dry them off afterward. 

  1. Identify and label your plastic.

Before moving forward, label your plastics and identify the best rod to match the specific base material of the plastic that you’ll be working on. In case you have doubts about the kind of plastic you have, resort to a burn test or use rod test kits first. Conduct the burn test by burning your plastic and observing how it changes. The details below may help you out in determining your plastic.

  • Polyethylene – a lack of smoke, bluish flame, the scent is similar to a burning candle
  • Polypropylene – not much smoke, the flame is an orange tint, light odor
  • Acrylonitrile Butadiene Styrene, black and sooty smoke, gives off a sweet scent
  • Polyvinyl Chloride – no flame
  • Polyurethane – black smoke, sputtering flame.

For rod test kits, do this by carefully choosing a rod and heating one of its ends. Next, try to attach it to your material and pull it off from the rod using a pair of plastics. Plastic and rod sticking together only show that they are made of the same material and compatible with the process. 

  1. Clamp the pieces together.

Clamp and tape the plastic parts together to make sure that the joint stays in place. Use some foil tape to get the pieces close together without covering the welding area.

  1. Set the right welding temperature.

Firstly, preheat your welding gun for around 2-3 minutes. Take note that different kinds of plastic require a variety of temperatures to melt effectively. See the list below for the recommended temperatures needed by your material. 

  • Polypropylene – 575 degrees F.
  • Polyethylene – 550 degrees F.
  • Acrylonitrile Butadiene Styrene – 500 degrees F.
  • Polyvinyl Chloride – 525 degrees F.
  • Polyurethane – 575 degrees F.

The right temperature will help your rod become soft and sticky, if it is turning liquid, you may need to move your temperature down.

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  1. Tack Weld the Plastic Ends

Pin loose parts of the plastic by melting your joint’s ends. Grab a tack welding nozzle and add it to your welding gun. With the help of heat, plastic starts melting, and you can now join the pieces together making the plastic stay in place as you work.

  1. Trim the ends of the welding rods.

With the use of your pliers or trimming knife, snip it diagonally towards the rod. This step is necessary for a smooth weld and to get rid of bubbles of plastic.

  1. Insert a welding rod at the welding gun’s speed nozzle.

A nozzle plays a role in holding the rod while welding. After fitting the nozzle onto the gun, carefully place the rod on the opening. 

  1. Move the speed gun over the plastic.

Hold the gun at an angle of 45 degrees while touching the nozzle’s edge towards the plastic and gradually move to start from the top of the crack. Heat the plastic until it melts.

  1. Swing the welding gun during pendulum welding.

At a 45-degree angle, tilt your gun with the rod at the same angle from the opposite side. Swing the nozzle within a distance of about 2.5cm above the joint or crack. Continue this step until you complete the welding. 

  1. Finishing the welding.

Wait for a minimum of 5 minutes for the product to cool down before you try to fix any part of your weld. Next, sand down your welded joint using 120-grit sandpaper with little pressure up and down your piece. To complete the weld, get finer sandpaper to make your final piece smooth. 

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Pros and Cons

Additional details about the general advantages and disadvantages of this method are as follows:

Final Words

Although welding may not be the easiest and most convenient option to join plastics together, it can be very ideal.

With my help, I hope you can convince yourself to start welding and create beautiful plastic welds by now. 

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