Welding is a common way to combine two metals because it provides a strong, lasting bond. It is also one of the best ways to join materials that are hard to bond permanently otherwise. Welding is a great choice for metals, but what about other materials you have lying around the workshop, such as plastic?
Many people are hesitant to apply heat to plastic since they’ve heard horror stories about how dangerous plastic is once it melts. However, welding is actually a very useful way to join plastic together. In manufacturing, people working with thermoplastics frequently use welding to join them.
Here is what you need to know about welding plastic.
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Can You Weld Plastic?
The first question to answer is, can you even weld plastic? The answer is yes, you can weld plastic. In industrial manufacturing, factories often weld plastic to produce materials we use daily, from toys to industrial-strength piping. DIY welders can weld plastic to try to repair cracks that occur around the home.
To make welding plastic possible, you must keep a few things in mind. First, the techniques and tools you use differ from when welding metal (more on those later).
Second, you need to make sure that you are welding the right type of plastic. Thermoplastics hold up well to welding. However, you cannot weld thermoset plastics because those set completely once someone forms them and will not soften or reheat, no matter how hard you try to weld them.
Methods to Weld Plastic
As with any other type of welding, there are a few different methods to weld plastic. Here they are so you can decide which one works best for you.
Radiofrequency welding is one of the most common methods welders use for plastic. Instead of using heat or gas, the welding machine sends high-frequency radio waves, or electrical waves, into the plastic. Then, the waves convert to thermal energy, which melts the edges of the plastic and fuses them together.
Radiofrequency welding seams are extremely strong and can withstand even the toughest environmental conditions. They form quickly, and you usually only need two to five seconds for the joint to set. It is very popular in industrial settings.
However, radiofrequency welding does not work for all plastics. You can only use this welding method with polar plastics, or plastics that has a polar charge in their mechanical composition. It also works best with thin sheets, not thicker plastic.
Ultrasonic welding is a welding method that manages to combine two materials without actually melting them. Instead, the machine sends high-frequency, or ultrasonic, vibrations through the two pieces, similar to radiofrequency welding. Then, the electrical energy is converted into kinetic energy, which is in turn converted into thermal energy. The friction deforms the plastic until the materials fuse together.
Ultrasonic welding is a relatively new form of welding, but it is rapidly becoming popular. It is great for welding plastic because it is more affordable, cleaner, and more efficient. It takes less than a second to seal together two plastic pieces.
However, ultrasonic welding is usually just for industrial applications. It’s pretty hard to get your hands on an ultrasonic welder for your DIY workshop, as they cost thousands of dollars.
Laser welding is another high-tech method for welding plastic. To heat the plastic, you use a welding machine that uses a laser beam. The two pieces of plastic are held together; then you run the beam across the joint. In just a few seconds, they are welded together.
Laser welding is becoming more and more popular than traditional forms of welding for a few reasons. It is very precise, delivering heat only at the joint instead of heating the rest of the plastic. It also involves minimal mess and clean-up.
However, laser welding is another form of welding that is most common in heavy industrial applications, not your DIY workshop. If you look up the cost of a laser welding machine, make sure that you are sitting down first because they are pricey.
Vibration welding is another important plastic welding method in industries. Two pieces of plastic are brought together and continuously vibrated. The vibrations produce friction, which in turn generates heat, melting the plastic and fusing it. Vibration welding creates flat, even seams but is also inaccessible to DIY welders.
Hot Air Welding
Hot air welding is exactly what it sounds like. The welding machine heats gas located in the welding gun. Then, the gas releases into the joint, melting the edges of the plastic. The melted plastic then fuses together into one continuous sheet.
Hot air welding has a few advantages over other types of welding. It is better for larger projects since you can expel the gas in a long, continuous stream. It is pretty flexible, making it easier to use on-site. Hot air welding is also fast and water-resistant. However, it is not useful if you want to join three pieces in a joint since you can only work with two pieces simultaneously.
How to Weld Plastic
When you have selected the right welding method, here are the steps to welding plastic.
1. Prepare Your Materials and Workspace
Cleaning and preparing your workspace are important when welding anything, but it is particularly important with plastic. You want to make sure your workspace is well-ventilated, so you don’t accidentally inhale fumes. Clean the area of any debris that could affect the plastic.
Then, you want to prepare your plastic. Thoroughly clean the materials because impurities will make the weld joint weaker. Strip stains with liquid solvent and jagged edges with sandpaper. Make sure you know which type of plastic you are working with so you can match it with the right welding rod (usually they will have the same letter markings).
Finally, you want to prepare yourself. Make sure you are wearing the right safety equipment. Wear work gloves, boots, and long clothing. You also want to wear a dust mask, goggles, and visor to protect your face. While you don’t need a full welding mask for plastic, you still want to protect yourself from particles.
2. Position the Plastic
The second step is positioning the plastic for welding. Place the plastic on your workbench so the pieces are close together. Clamp them in place so they don’t move. You can also use foil or tape to hold the pieces close together as long as you leave the area you will be welding exposed.
3. Preheat the Welding Gun
Once your workstation is ready, you can get your welding gun ready. Make sure it is at the right temperature for welding plastic, about 392–572 degrees Fahrenheit. The exact temperature will vary depending on the type of plastic you are working with. Preheating will take about two minutes.
4. Weld the Plastic
Finally, it is time actually to weld the plastic. Use tack welding to hold the joint together so it won’t move as you work. Then, prepare your welding gun and speed nozzle. Starting from the top and working your way down, weld the plastic together. Work steadily, making sure the plastic melts before you move on. Keep your hand at a consistent angle, about 45 degrees.
5. Finish the Weld
There are a few final steps before your plastic is ready to use. The first step in finishing the weld is letting the plastic cool down to room temperature (but you don’t want it to cool completely). Then, while the joint is still warm, sand it down so it is smooth like the rest of the material.
How to Set Up Your Welding Machine for Plastic
To weld plastic, you can use a specialized plastic welding machine or any welder or heat gun you have at home. The first thing you should probably do is lower the temperature setting since plastic melts at a much lower temperature than metal. Change out the welding tip and ensure you have the right tip for the type of plastic you use. Have your feeding rod on hand since you need to feed continuously as you weld.
Here is some of the basic equipment you need for welding plastic:
- A plastic welder or heat gun
- A welding rod for plastic
- A tack welding tip
- A speed nozzle
- Safety equipment such as goggles, gloves, and a mask
- Cleaning equipment such as solvent and sandpaper
Tips and Tricks
These tips and tricks can help you perfect plastic welding once you decide to do it.
First, make sure you are using quality equipment. This applies to all welding but also to plastic welding.
Make sure you are welding like-to-like, meaning that the substrate and welding rod are the same type of plastic.
Consistency is key so maintain a steady speed and angle as you weld.
Welding plastic is a sturdy way to join two pieces together, and if you follow this guide, you won’t have to struggle.