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Whenever you need to repair a piece of plastic or join plastic parts together, welding offers an easy way to solve the problem. Learning how to weld can take time and practice, but it isn’t a complicated process to learn. That’s certainly true when it comes to welding plastic because plastic is soft and flexible. While there are a few different methods you can use to weld plastic, all you need is a welding gun and the necessary welding rod.
So, how do you weld plastic to plastic?
- Using your welding gun and welding rod, you’ll first start by cleaning the plastic.
- Then, you’ll use your welding gun to melt ends of your plastic pieces so you can join them together.
- Once your plastic is joined together, you’ll need to smooth out your weld and make sure your plastic has a durable finish.
In this article, we’ll give you a brief overview of plastic welding, different methods you could use to weld plastics together, and then we’ll cover the step-by-step process of welding plastic. After you read this article, you should feel confident about your next plastic welding project!
Welding with Plastics
Any plastic you can weld is given the name “thermoplastic.” That’s because that plastic will melt when you heat it to a high temperature, meaning you can also fuse with plastic.
The plastics that are usually used for welding are all thermoplastics like Polypropylene, Polyethylene, Polyurethane, Polyvinyl Chloride, also known as PVC, and Acrylonitrile Butadiene Styrene (ABS).
If you are going to use hot air welding to join your plastics, then you’ll get a better weld if the material is thicker than 1/16 of an inch.
Since you want to create solid welds, you’ll be focusing on making welds that are equal to or stronger than the joining of the original plastics. We recommend that before you start any plastic welding projects, you practice on some scrap plastic so that you get to experience plastic welding for a while before tackling a real project.
Much like metal welding, learning how to weld with plastic will take some experience and a learning curve.
You’ll need to experiment with plastics a few times, even if you have experience welding metal pieces together. That’s because welding plastic materials is very different from welding metal materials together.
Welding Materials and Your Welding Rod
Check out our recommended plastic welding tools here.
When it comes to welding plastic, the usual rules of welding still apply. Your welding rod always has to use the same substance as the item you are welding.
Sometimes, you can figure out the exact equations for the content you are working on if you have that information provided by the product’s manufacturer. However, other times, you, unfortunately, won’t know the exact make-up of the materials you are welding.
The “Burn Test” – How To Tell What Kind Of Plastic You Are Going To Weld
Luckily, with plastic, there is a method you can use to figure out the kind of plastic with which you are working.
Using the “burn test,” you can simply burn the plastic and observe it as it burns. By taking note of the flame’s color, how the fire is burning, and how the item smells as it burns, you can typically figure out what comprises your plastic.
To conduct a burn test, you only need to use a small amount of plastic.
So, how do you tell what type of plastic you are working with when you try out the burn test? Below we’ve listed some brief descriptions covering the way each kind of plastic burns.
- With Polyethylene, you’ll notice a lack of smoke as it burns. Also, the flame should be a bluish tone, and the scent will remind you of a burning candle.
- With Polypropylene, you also won’t have much smoke. However, the flame will be an orange tint, and the odor will be very light.
- With Acrylonitrile Butadiene Styrene, the smoke will be black and sooty, like a fireplace. You’ll also smell a sweet scent as it burns.
- With Polyvinyl Chloride, you shouldn’t get a flame. This type of plastic is self-extinguishing.
- With Polyurethane, you’ll notice black smoke, and the flame will look like it is sputtering.
After you’ve identified the plastic substance you are welding with, you’ll be able to get the right welding rod using the same material.
Here’s a great video that explains the burn test in detail.
Figuring Out Welding Temperatures
If you’re going to perform an effective weld, then you’ll want to know the right temperature for your airflow.
Having the airflow coming from your heat gun at the right temperature will always give you the best welds. However, if you don’t have enough heat, or you have an overabundance of heat, then you’ll wind up making weak, poor welds.
So, we cannot emphasize enough the importance of knowing the correct welding temperature.
Below we’ve listed the welding temperatures you should use depending on the thermoplastic you are welding:
- Polypropylene should be welded at 575 degrees F.
- Polyethylene should be welded at 550 degrees F.
- Acrylonitrile Butadiene Styrene should be welded at 500 degrees F.
- Polyvinyl Chloride should be welded at 525 degrees F.
- Polyurethane should be welded at 575 degrees F.
Remember, before you start your welding project, you should always test your temperature output first.
When testing the production of temperature, heat your welding rod. If you’ve got your welding rod material at the right temperature, then it will start feeling soft and sticky.
However, if your welding rod is turning into liquid, then you’ll need to set the heat down a notch.
10 Ways You Can Weld Plastic
Now that you know how to test and set-up your plastic weld, we’ll review ten different welding methods you can use to weld plastic.
While our walkthrough steps below are a way to perform basic plastic welding, for the more experienced welders, we also wanted to provide options.
So, when you first learn to weld plastic, you’ll be able to use any of the below welding techniques to complete your project.
#1: Friction Welding
With friction welding, you use rapid, angled oscillations with the heat while joining the two plastic pieces.
Friction welding is similar to spin welding and typically works well when the plastic parts are not symmetrically even. Keep in mind that you’ll have to program your equipment to stop when you join your welds.
#2 Extruded-Bead Seal Welding (Extrusion Welding)
With this type of welding, you’ll be using a bead that’s made out of the same thermoplastic material with which you are welding.
You use this bead between the two plastic pieces you are welding, and then you press them together. The heat from your extruded pellet will fuse the bond.
#3 High-Frequency Welding
With high-frequency welding, you’ll be welding plastic pieces by heating them with the electrodes of an electrical generator with a high-frequency.
#4 Hot Plate or Hot Tool Welding
If you decide to use a hot plate or hot tool welding, you’ll hold your plastic pieces to a heated metal surface that should be shielded with PTFE so that your plastic doesn’t stick.
Once the surface area melts, you then bring the pieces together and place them underneath slight pressure as they start cooling.
#5 Hot Gas Welding
With hot gas welding, you’ll use a plastic welding gun that features a gas heated chamber that passes gas through it to help produce the weld. The gasses used are either dry air or nitrogen.
The gas is then heated and used to make the weld. At the same time, you’ll need to use a rod that’s made of the same thermoplastic materials is applied to the hot part of the weld.
#6 Laser Welding
When you use laser welding, you place your two thermoplastic pieces under slight pressure and use a laser along the line you want to create.
The beam hits the first piece and is then absorbed by the second piece, allowing you to soften the material so that you can create a weld.
#7 Induction Welding
You can also use induction welding when you are joining two plastic pieces. With induction welding, you’ll use a conductive metal insert at the point where you want to join your two plastic parts.
You’ll need to apply pressure to hold the pieces together and then heat the metallic insert. You’d heat the metallic insert by using a high-frequency generator.
The thermoplastic then softens and joins together as the joint starts cooling.
#8 Solvent Welding
When you use solvent welding, you’ll apply a solvent that can diminish your plastic surfaces so that you can press them and join them together.
As the solvent evaporates, it absorbs into the materials and helps to unite the plastic pieces together.
#9 Ultrasonic Welding
With ultrasonic welding, you use vibratory mechanical pressure for the heating, which is conducted with ultrasonic frequencies.
By doing that, the energy becomes ultrasonic vibrations and then is applied to the pieces to be welded by using a horn. After that, you’ll use heat from the friction of the waves to join your plastic pieces together.
#10 Spin Welding
With spin welding, you’ll be rotating your plastic parts and putting one part against the other until the heat created by the friction starts melting your pieces.
As the pieces melt, they become stable again under pressure when you stop rotating. You can also do this manually with a drill press and some chucks to hold down the parts.
Now that you know the different types of welding processes you can use when you weld plastic pieces together, we’ll give you a step-by-step overview of how you can fuse two plastic parts together.
How To Weld Plastic to Plastic in Steps
Whenever you want to combine two plastic pieces or fix a cracked piece of plastic, welding is a great way to get the job done.
To complete the steps we are giving you below, all you will need is an electric welding gun and the correct welding rod. We’ll cover the welding of plastic in three phases.
First, we’ll cover how you should clean your plastic and make sure you identify it. Second, we’ll cover how you can utilize your gun to weld the plastic together. Last, we’ll cover how you can complete the weld and smooth it out for a strong weld.
Phase I: Cleaning Plastic and Setting-Up
For our first phase, we’ll outline some steps so that you understand how to set-up your weld, and clean your plastic. We’ll cover each step in more detail below.
Step #1: Create Your Workspace
First, you’ll need to focus on setting up your workspace. You’ll want to use a ventilated area so that you don’t breathe in anything harmful (check out our Recommended Respiratory Equipment here).
Keep in mind that there are a few safety concerns that you’ll need to review before you start any weld.
If possible, try to work outside, or at least make sure you have a sound ventilation system around you. Also, open up any nearby doors as well as windows, and put some fans around you so that you are airing the fumes away from your workspace.
You’ll also need to wear a dust mask and some welding glasses (or some solid welding goggles) or a welding helmet when you start cleaning the plastic.
Make sure that you tell other people to stay out of your area while you are welding. You want as few issues as possible surrounding you when you weld, and you especially want to make sure that you aren’t endangering other people.
#2 Dress Yourself in Heat-Resistant Gloves and Protective Clothing
Next, you’ll need to ensure your safety by putting on some heat-resistant gloves and wearing long-sleeved clothing or a welding jacket to protect your body.
Check out some of our recommended welding gloves here.
Heat-resistant gloves are usually comprised of leather and will keep you safe from burns. You’ll also want to make sure you have a long-sleeved shirt or welding jacket, pants, and closed work boots. Keep your face safe with a welding visor.
To conduct these thermoplastic welds, you won’t have to wear a full welding mask if you would rather avoid it. Plastic welding doesn’t produce harmful light, unlike metal welding (or staring at the sun).
#3 Clean the Plastic
Now you’ll need to clean your plastic using some soap and warm water. Scrub away all the debris that you can with a sponge.
If that isn’t enough, you can also wash the plastic with dish soap. Get rid of any dirt, grease, or other particles that might weaken the weld as you clean your plastic.
After your plastic is clean, get a lint-free cloth and dry off your pieces.
#4 Select a Matching Welding Rod
You’ll need to know the type of plastic you are welding. Some plastics have letters on them that help identify what they are, like PE for Polyethylene or PVC for polyvinyl chloride.
You’ll need to select a rod that matches the plastic you are welding.
#5 Test Your Plastic if You Cannot Identify It
If you still cannot tell what type of plastic you have, you can use the “burn test” we described above, or a welding rod testing kit.
#6 Remove Paint with Sandpaper
Using some 80-grit sandpaper, you’ll want to remove the paint you find on the plastic. If you see that the area of plastic you want to weld still has color on it, you’ll need to get rid of the color by using sandpaper.
You may need to sand the plastic for a while before you see the bare plastic below the shade.
If you have a sanding wheel and a drill, or an abrasive disc, you could also use either one of these processes to create the same effect.
Or, you could use a paint scraper if that’s easier for you. Whatever tool you use, make sure you don’t scratch the plastic under the paint while you clean it.
#7 Clamp the Plastic Pieces Together
Now you’ll need to clamp, and also possible tape, your plastic parts together so that the joint stays in place.
Make sure you’ve formed your joint before you start your torch. Then, put your plastic parts on your bench and place them very close together. Grab your C-clamps and hold down the pieces to the table.
Use some foil tape to get the pieces very close together, but make sure you don’t cover your welding area.
Now that you know how to clean the plastic and set-up your workspace, we’ll move onto the second phase, which is combining your pieces of plastic.
Phase 2: Combining Your Plastic Pieces Together
After you are done cleaning and preparing your workspace, you’ll be ready to combine your plastic pieces. Below we’ll cover the steps so that you can join your plastic parts.
#1: Preheat Your Welding Gun
When you preheat your welding gun, you’ll need to leave it on for at least two minutes. However, depending on the type of plastic you are welding, you’ll need to set your temperature appropriately.
Most plastics melt at temperatures between 392 degrees F and 572 degrees F.
If you aren’t sure what temperature to set your welding gun at, review the information we gave you above covering that.
#2 Tack Weld the Plastic Ends
You’ll need to secure your plastic and tack weld the plastic’s ends. However, don’t immediately move into welding.
You’ll first need to pin loose parts of the plastic by melting your joint’s ends. Grab a tack welding nozzle and add it to your welding gun. Then, you’ll need some heat.
Once the plastic starts melting, you can join the pieces together. Now, the plastic won’t move as you continue.
#3 Trim a Welding Rod’s End Using Angle Cutting Pliers
It’s straightforward to trim a rod. Grab your pliers and angle them diagonally as you face the rod’s end. Snip it to a point.
You can also use a trimming knife to create a point if you can’t find your pliers.
Remember, you want to point the end of your rod so that you wind up with a smooth weld and no bubble of plastic residing where you began.
#4 Insert the Welding Rod into the Welding Gun’s Speed Nozzle
You’ll find an opening to place your welding rod while you melt the joint in your speed nozzle. If you notice that you didn’t get one when you purchased your heat gun, then you can buy it separately.
Once you get the nozzle fitted on your welding gun, you’ll need to feed the rod into the second top opening. Remember, start with the clipped end in first.
As you do this, avoid touching the tack nozzle if it is still heated. You’ll need to either wait for that nozzle to cool off or swap it out and use a different nozzle.
#5 Use the Welding Gun’s Tip Slowly
Use the welding gun’s tip and slowly hover over the plastic for your weld. Begin at the top of the plastic’s cracked area if you are fixing it, or on the area, you are joining.
Angle your gun down using a 45-degree angle and touch the nozzle’s edge to the plastic. After that, heat the plastic until it starts to melt.
Then, push the welding torch towards the joint, and start feeding your welding rod with your other hand.
Remember, you need to stay consistent whenever you are welding if you want to make great pieces. If you move at a specific pace, you should be able to successfully melt the plastic and welding rod so that you can combine them and not burn either.
However, if the plastic does start to burn or it starts changing its color, you’ll need to start moving more quickly with your torch. Remember, don’t linger too long in one particular spot or you’ll apply too much heat, and possible burn part of the plastic.
#6 Mimic a Pendulum Weld
Now you’ll need to move your welding gun from side to side, much like you would if you were performing a pendulum weld.
When you do this, keep the nozzle about a full inch above the crack area you are welding. As you do that, tilt your welding gun using a 45-degree angle on the opposite side.
Keeping the rod in place, now move the nozzle across it a few times to melt it. Then, move down the rest of the area to finish the plastic weld.
If you don’t own a plastic gun that also has a speed nozzle, then pendulum welding can help.
That’s because pendulum welding can be done just using a propane torch. You can also use pendulum welding anytime you want to fill a problematic joint your speed nozzle can’t seem to handle or reach.
Remember, though, and you will need to control the torch along with the welding rod simultaneously, so sometimes this step takes a bit of practice.
Keep in mind that you have to move consistently so that your plastic won’t burn.
Now that you know how to weld two plastic pieces together, we’ll cover phase three of welding plastic to plastic, which is finishing the weld.
Part 3: Finishing the Weld
When you are ready to finish your mold, you’ll want to start by allowing the plastic you’ve been working with to cool first. You need to wait for five minutes, possibly more, for this to happen.
Step #1 Fix the Plastic if Necessary, then Cool the Plastic
Wait for the plastic to return to room temperature before you finish your weld. You’ll notice right away that welded plastic cools much more quickly than welded melded.
Still, you can wait as long as you feel it is necessary. Make sure you check to ensure that the plastic is turned solid. Also, wave your hands around it to make sure there is no further heat coming off of the plastic before you begin.
Also, if you need to fix a part of your weld, you’ll want to do that before the plastic cools off.
Check to make sure your welds look good and smooth. You will need to add more of the welding rod or use your gun to smooth the plastic out before you let it cool down.
At this point, you are ready to put your welding gun away. Make sure you store it in a safe place until it has cooled down.
#2 Sand Your Welded Joint
Start sanding down your welded joint using 120-grit sandpaper. With the sandpaper, smooth out any rough areas of the weld so that everything has a smooth, consistent look.
You’ll need to use slight pressure as you do this and rub the sandpaper up and down the plastic piece. Do your best to make the weld look as level as the other parts of the plastic surrounding it.
However, be careful not to scratch the plastic as you are doing this. You can also use a sanding wheel on a rotary if you have one.
#3 Finish the Product
Now you’ll need to get some 180 and 320-grit sandpaper as well. Start using the finer sandpaper options to make the weld look as smooth as possible.
Remember, although this sandpaper is less abrasive than what we just used, you can still wind up scratching the plastic if you don’t watch closely.
Now that you know how to weld plastic to plastic, you should be able to create beautiful, plastic welds in no time! So, get out there and start welding some plastic today!