When we think of welding plastic together, we do not always imagine it in its basic form. To put it simply, it is the process that allows two softened thermoplastics to be joined using heat.
Whilst this might sound easy, the process can be painstakingly long, and does require concentration, but you would not be here if you did not already have the patience for that!
The process uses two compatible thermoplastics which are exposed to heat and then bonded together. Whilst this happens, you will need to press the surface, apply pressure, as well as let it cool down.
This all then leads to plastic formation and nicely bonded materials – if done well.
Before we can even begin the process, we will need to look at what the advantages and disadvantages are of welding plastic together, and what to think about before you get going.
Fortunately for you then, you have stumbled upon the right place.
Why Weld Plastic Together?
As stated previously, the welding of plastic uses heat to bond two compatible thermoplastics together. It is useful because not only can it create something made out of plastic, but it can also repair cracks and broken pieces.
Whilst we know that the manufacturing of plastic is something that is done on a global scale, welding is something that you can do at home if you need to join several pieces of plastic together, or fix a plastic item.
To have the ability to weld plastic together is helpful in the production of sophisticated forms of plastic (for example, internet cables and medical supplies) and simple forms of plastic (for example, vinyl toys and disposable cutlery).
Advantages Of Welding Plastic
There are many advantages when it comes to welding plastic together rather than using another method (which we will discuss below).
Firstly, preparing the surface you will be working in is relatively easy, as well as preparing the plastic ready to work with. This means it is a doable process to do at home.
Welded plastic is also fairly lightweight and can create leak-proof and airtight seals.
Disadvantages Of Welding Plastic
Whilst it is quite advantageous to weld plastic, there are some disadvantages too. You will be limited by what you can weld due to the fact you need two compatible plastics.
If they are not compatible, it will produce a weak result.
Also, whilst you can weld plastic at home, it can be rather expensive compared to other methods which might not be suitable for those who are on a tight budget.
Lastly, it can be more difficult to weld joint designs which may become a problem if you require to do so.
What Plastic Cannot Be Welded?
Even though it might not seem it at first, there is a type of plastic that cannot be welded. This is thermoset plastic which once formed it will not be able to be reheated and molded.
This is because it is not affected by a heat source at all.
So, it is best to stick with thermoplastics.
Before You Start
Before you begin your project, make sure that the base material that you are using is pliable enough to create the desired effect that you are hoping for.
This will dictate the quality of the plastic that is produced.
The last thing you want is to begin welding plastic and for it to turn out terrible, so always make sure that the base allows you to weld plastic onto it well, and that it will produce a professional looking finish.
How To Weld Plastic Together (The Steps)
Before you can begin welding plastic, you need to set up the space you are going to be working in. So, let us get to it.
Preparing The Workspace
Firstly, you need to make sure that the area you plan to work in is well-ventilated. Before any project begins, it should be about protecting yourself and others.
You must wear appropriate protective gear, as well as long sleeves and heat resistant gloves. Also, think about wearing boots that will protect your feet during the process.
Preparing The Plastic
Using soap and warm water, remove any debris that may be on the surface of the plastic. Doing so will actually help to eliminate the weak points of the plastic during the welding process.
If you find that there is a stubborn stain that cannot be removed by regular soap, then try removing it by using a liquid solvent such as methyl ethyl ketone, or MEK for short.
You will need to moisten an old cloth with the solvent and scrub until the stain is removed.
Once cleaned, dry the plastic off using a clean cloth.
Label Plastic Correctly
You may have already noticed, but each bit of plastic has a letter that identifies the type of plastic that it is.
Using this information, you can select the correct rod of plastic you will need to match up with the plastic you are welding to.
For example, PE stands for polyethylene. So if you had polyethylene plastic, you would choose the PE rod.
Not sure what plastic you have? Invest in a rod testing kit. This has a variety of plastic rods included where you can choose a plastic that looks similar to the one you are welding to.
Apply heat to the end of the rod and attach it to the plastic. Once ready, try and pull it off with a pair of pliers. If it stays put, it is the correct type of plastic.
Forming The Joint
Now that you are sorted when it comes to the type of plastic, it is time to form a joint. Using a working bench, place the two plastic pieces together and secure them using clamps.
Also, wrap any foil around the pieces of plastic where needed to keep both the pieces close together.
Pre-Welding Pin Tack
Now that you are ready to join the plastic together, it is time to preheat the welding gun which should only take around 2 or 3 minutes.
Because different plastics melt at various temperatures, you should research the temperature needed for the chosen plastic.
However, there are recommended temperatures and these are around 3920 Fahrenheit to 5720 Fahrenheit, so this should give you a good idea as to what you may need.
To make the job easier, melt the ends of the joint to ‘pin tack’ the joint together.
You need to use a tack welding nozzle to complete this task. Just like with sewing, it means the pieces will not move as you weld them together.
Welding The Plastic Together
With a pair of pliers, trim the end of the rod diagonally, then insert it into the speed nozzle on a welding gun. This is designed to hold the rod as it melts along the joint line.
Doing it this way means you will need to feed the rod through the speed nozzle as you weld.
Whilst holding the welding gun at a 45-degree angle, move over the plastic slowly starting at the top of the area you wish to join. Make sure you are seeing the plastic melt as you move along.
This way you will know that the process is going well.
Another option, which is great for smaller areas, is called pendulum welding. This is a process that is done by holding a rod horizontally over a joint and sweeping the welding gun back and forth.
It will obviously take longer, but is still a great technique to try out.
Just a tip, always wait for the welding gun to cool down when you change the nozzles. However, always make sure it reheats back to the recommended temperature.
Post-weld
Once you have finished the welding process, wait around 5 minutes for the plastic to cool down to room temperature.
If you see any mistakes, make sure to work on the plastic before it completely cools down.
You can add more plastic rods if you do not feel it is smooth enough, for example.
To ensure it is consistent, once completely cool, you can use a 12-grit piece of sandpaper to sort out any unlevel areas. Be careful though, as plastic does tend to scratch easily.
Other Methods Of Welding Plastic Together
Whilst welding plastic together using the above method is good enough for you to do at home, there are other common ways to weld plastic together:
Laser Welding
For those who want to weld plastic together quickly, this method does it within 3-5 seconds. Two parts of plastic are compressed together whilst a laser beam passes across the joining line to permanently bond them together.
Ultrasonic Welding
This one sounds rather complicated, but it actually is not. The plastics are bonded together using the conversion of high-frequency electrical energy, which turns into high-frequency mechanical motion.
Along with other external factors, the mechanical motion creates frictional heat where the plastics meet. Once this happens, a molecular bond is produced by the heat that welds the pieces of plastic together.
Radio Frequency Welding
Instead of acoustic vibrations like with ultrasonic welding, this one uses radio waves. It is preferred over the other method, and it only takes around 2-5 seconds.
Gas Welding
Also known as hot air welding, this method uses hot gas. It is only produced when the welding gun has been heated electronically.
Final Words
Plastic is a good durable material, that if the correct type of plastic is used it can be remolded. The great thing about it is you can do this process within the home, due to it being an easy and creative thing to do.
I want XYZ to be an extension of my day job, to share my love and passion for 3D printing with others. This site will talk you through all aspects of 3D printing, laser cutting, and even welding, to provide you with all the information you need.
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