Welding Plastic - A Plastic Weld Guide

You may not realize it, but you’re surrounded by things created by plastic welding. From vinyl siding to disposable cutlery, to medical equipment, to pool toys, plastic welding is responsible for an abundance of things in our everyday lives. Without plastic welding, our lives would be very different. We might not have things like artificial joints, sewing machines, electrical cable insulation, or plastic containers if it weren’t for plastic welding. Adhesive and mechanical fasteners can only do so much when it comes to joining plastics. So thankfully, plastic welding has become an ideal option in the creation of limitless things needed and wanted in our lives. And did you know that with a quality plastic welder product, you can take plastic repairs and projects into your hands? It’s true!

How to use this guide?

1. Get fully educated and read the whole darn thing.
2. Select the topic you are interested in learning more about and get transported through a click of a button to that specific process heating section.[1]
1. What is Plastic Welding?
2. Three Main Steps in Plastic Welding?
1. Pressing
2. Heating
3. Cooling
3. Methods of Plastic Welds
1. Hot Air Welding
2. Ultrasonic Welding
3. Radio Frequency Welding
4. Spin Welding
5. Vibration Welding
6. Laser Welding
7. Hot Plate Welding
8. Contact Welding
4. Benefits and Advantages of Plastic Welding
5. Tips for Welding Plastics
6. What to Consider when Welding Plastics?
7. Types of Welding Seams
8. Takeaways to Consider When Buying a Plastic Welder
1. Quality
2. Warranty
3. Support
4. Temperature Control
5. Built-in Blower
6. Nozzles
3. Additional Plastic Welding Information
1. How to repair plastic? A Plastic Repair Guide
2. How to weld plastic? Welding plastic with the Triac ST

What is Plastic Welding?

Plastic welding is a process of uniting in a molecular bond two compatible thermoplastics generally with the aid of heat. In other words, thermoplastics (a polymer plastic that can be melted and shaped several times) are joined together by melting the surfaces and pressing them together.

Three Main Steps in Plastic Welding

There are three main steps for a good join between thermoplastics, which are pressing (ensuring sufficient pressure when pushing the plastics together), heating (achieving the right melt temperature), and cooling (length of time the join is allowed to cool before releasing the pressure).

• Pressing: The application of pressure, which is often used throughout both the heating and cooling stages, is used to retain the parts in the proper orientation and to improve melt flow across the interface.
• Heating: The purpose of the heating stage is to allow intermolecular diffusion from one part to the other across the faying surface (melt mixing).
• Cooling: Cooling is necessary to solidify the newly-formed bond; the execution of this stage can have a significant effect on weld strength.

Methods of Plastic Welds

There are several methods of plastic welding, which are primarily differentiated by their heating methods, and all processes are divided into two general categories of internal and external heating. The most common methods of plastic welding are the following:

• Hot Air Welding

Hot air welding is also known as hot gas welding and is a process that utilizes the heat of hot gas, usually air that has been heated by electric heating elements in the welding gun. A specifically developed welding gun generates very hot air using a feed just for plastic, which enables the various components to melt and then join together.

• Ultrasonic Welding

Ultrasonic plastic welding is the joining or re-forming of thermoplastics through the use of heat generated from high-frequency acoustic vibration. This process is accomplished by converting high-frequency electrical energy into high-frequency mechanical motion. That mechanical motion, along with applied force, creates frictional heat at the joining points, thereby resulting in a molecular bond between the parts, and weld times are typically one-tenth to two seconds.

• Radio Frequency Welding

Radio frequency welding is similar to ultrasonic welding, but instead of using acoustic vibrations, it uses high-frequency electrical energy (radio waves). It’s a preferred method for welding thin plastics and has a weld time of two to five seconds.

• Spin Welding

The spin welding process consists of two parts brought together by friction from the rotation of one part at high velocity while the other part remains stationary. Friction between the two parts causes molting, fusing the pieces, and the weld time is typically one-half to five seconds.

• Vibration Welding

The vibration welding process (also known as friction welding) is when parts are rubbed together at a certain frequency and amplitude, causing friction and generating heat. The heat melts the plastic in the joint region, and the pieces are fused together, and the weld time is typically one to five seconds.

• Laser Welding

In the laser welding method, two parts are pressed together, and a laser beam moves along the joining line. Once the plastic solidifies, it creates a permanent bond, and the weld time is typically three to five seconds.

• Hot Plate Welding

The hot plate welding process (also known as Butt welding) applies heat from a hot plate (hot plates are made from aluminum alloys) that is placed between the plastic surfaces needing bonding. The two plastic surfaces are either pressed against the hot plate or held next to it for some time, and then the hot plate is removed, and the parts are pressed together to form the weld. Typical welding time is ten to twenty seconds.

• Contact Welding

In contact welding, the heat is supplied with thermal conduction. The plastic components being welded are put together, and hot tips pinch them, melt, and join them all together.

• Automatic Welding

Automatic welding is a chosen process to manual welding. These plastic welding machines remove the manual process that takes years, training, and a specialist to actual doing the welding. The benefits to automatic plastic welding machines are endless. Click to learn more about automatic welding machines.

Benefits and Advantages of Plastic Welding

Joining plastics together can be done with adhesives, mechanical fasteners, and through welding. But what are the benefits and advantages of plastic welding?

• Plastic welding usually doesn’t require using any consumables, whereas adhesive joining does (consumables are messy and can be difficult to contain).
• Plastic welding usually doesn’t require intensive surface preparation steps, which adhesives do.
• A plastic weld is permanent, whereas mechanical fasteners and adhesives may not be.
• Plastic welds are light in weight.
• Plastic welding can provide a leak-tight, airtight seal.

Are there any specific advantages to the different methods of plastic welds? Absolutely!

Hot air welding advantages:

• Flexible, can be applied to most part geometries
• Can be very inexpensive
• Strong welds if parent material is cleaned and preheated

Ultrasonic welding advantages:

• Very fast process (typically < 1 second)
• Advanced, modern equipment with sophisticated control and monitoring features
• Economical

Radio frequency welding advantages:

• High energy efficiency
• Bonds films or thin sheets with complex circumference geometry

Spin welding advantages:

• Very fast process (typically < 1 second)
• Advanced, modern equipment with sophisticated control and monitoring features
• Economical

Vibration welding advantages:

• Applicable to large parts
• Internal walls can be welded
• Well-established process with excellent control possible

Laser welding advantages:

• Very clean process, little to no weld flash
• Precise control / selective heating
• Works with simple joint designs (uniform contact of mating surfaces)

Hot plate welding advantages:

• Simple and reliable
• Suitable complex part geometries, even in the joining plane
• Can be adapted for use with materials which have different melting temperatures and melt viscosities
• Relatively high tolerance to imperfections on the mating surfaces

Tips for Welding Plastics

When joining two plastics together, a key component is the type of plastic to be heated and joined. It is essential to weld like-plastic with like-plastic, such as polypropylene to polypropylene, polyurethane to polyurethane, or polyethylene to polyethylene. Once you’re sure that you have like-plastics, you’re ready to begin welding. Below are some tips to help you get ready to weld.

• Work in a well-ventilated area and use heat-resistant gloves and long-sleeved clothing for protection.
• Although plastic welding doesn’t give off a harmful light, it’s recommended to wear a welding visor, which can be clear.
• Clean the plastic with soap and water, or if needed, with a cleaning solvent like MEK (methyl ethyl ketone). Ensure to remove all debris and dry plastic with a lint-free cloth. If your plastic has paint on it, remove the paint with 80-grit sandpaper – but be careful not to scratch the plastic!
• Double-check what type of plastic it is that you’re welding. Usually, this can be found as letters on the plastic, such as PE (polyethylene), PP (polypropylene), or PVC (polyvinyl chloride). Then choose a welding rod that matches that type of plastic. If you can’t determine what type of plastic you have, you can get a welding rod testing kit (found at most hardware stores), which comes with different types of plastic welding rods and instructions on how to determine which rod will work for your plastic.
• Hold the pieces of plastic together with a clamp and tape and form the joint before you turn on the torch. Ensure to secure the joints tightly and in the correct position because you don’t want to worry about having to adjust them while you’re welding.
• Pre-heat the welding gun for at least 2 minutes.

You’re now ready to start welding, so consider these instructional tips:

• Secure the plastic together by tack welding the ends. Using a tacking nozzle, run the tip of the nozzle along the weld line, which ensures a slight melting of the two plastics together, thus closing up the joint interface and preventing the plastics from moving as you complete the weld.
• Trim the end of the welding rod using angle cutting pliers. By doing so, you’re increasing your chances of getting a very smooth weld without any plastic bubbling.
• Insert the welding rod into a speed nozzle on your welding gun.
• Move the tip of your welding gun over the plastic, touching just the edge of the nozzle to the plastic. Heat until you see the plastic begin to melt.
• Be consistent in terms of pressure and pace. Move at a steady, deliberate pace so you can melt the plastic just enough to bind them without burning them.
• Upon completion of your weld, wait at least 5 minutes for the plastic to cool.

What to consider when welding plastics?

There are several things to consider when welding plastics. Let’s take a look at considerations for the heat, the welding rod, the welding gun, and the welding kit.

• The Heat - Likely, you’ll need the temperature within the range of 200 and 300 °C (392 and 572 °F). Below or above that range will result in not melting enough or burning the plastic. Ensure to know what temperature you need based on what type of plastic you are welding.
• The Welding Rod – It’s crucial that the welding rod is the same material as the plastic to be welded and to ensure the end of the welding rod has been trimmed so that it’s in pencil-point form.
• The Welding Gun – Manual (hand-held) welding tools are used for small fabrication work, detailed projects, and repair work, and should not be used for thicknesses beyond 10mm. For larger fabrications, use extrusion welding tools.
• A Welding Kit – For beginners, plastic welding kits are a great option because they are fully equipped with what you need for most repairs. Kits come with a welder, varying welder rods, welding tips, and a guide to help you through your welding process.

Types of Plastic Welding Seams

Plastic welds have a similar appearance to metal welds, and therefore, many of the same welding techniques are used. Below are the six most common types of plastic welds:

• Fillet weld - The fillet weld is one of the most frequently-use seam geometries. It’s produced by welding two workpieces that meet in a T-joint.
• Interior corner seam - Interior corner seams are generally used on difficult-to-reach locations. Free forms and spline-shaped weld seam geometries are welded most efficiently like this.
• Corner seam appearance - The outer corner seam is a fillet weld in which the weld seam runs along the edge of the workpieces which are standing together. Consequently, the weld is made along the outer longitudinal side (edge).
• X-seam - The double-V seam is also known as an X-seam. It is a type of butt weld and consists of a combination of two V-seams on each of the two sides of the components to be joined.
• V-seam - To achieve the V-shaped angle that is typical for the V-seam, the workpieces are either beveled or positioned at an appropriate angle to each other.
• Lap seam - Lap seams are mainly used for plastic sheets. The sheets are arranged on top of each other, and the weld seam is laid on the upper exposed material edge.

If you’re considering buying a plastic welder, there are a handful of things to review before you make your purchase.

• Quality. First and foremost, look at the quality of the plastic welder. A quality welder will comply with worldwide welding standards put in place by the DVS (the German Welding Society). The DVS standards include ensuring a strong, structural, and molecular welding.
• Warranty. With a high-quality welder, you should find that it has a good warranty.
• Support. Check out the welder supplier’s support system. It’s not uncommon for spare parts, technical support, or application advice to be needed with the use of your welder. A good supplier will have both the knowledge and the experience to support your needs.
• Temperature Control. Having the accurate temperature needed for your project or repair is an absolute must. Your welding tool should have a built-in, precise electronic temperature control that is easy to use. Many plastic welders come with digital displays for ease of viewing.
• Built-in Blower. Not all welders may have a built-in blower. However, for the ones that do, it makes the welder much more portable and easier to use.
• Nozzles. Your plastics welding process will require some specific nozzles for you to get your desired weld. Always check out what kind of nozzles are available and how easy they are to use.

As we become more and more of a plastic dependent generation, it’s almost a necessity to have a handy plastic welder to help quickly and easily repair damaged plastic. Maybe you need to fix your cracked kayak, or fix your broken sunglasses, or fix your vehicle’s plastic molding, or fix your child’s plastic toy. A quality plastic welder can make you a hero! We know that you can buy plastic welding guns, tools, equipment, and kits from Harbor Freight, Amazon, Walmart, Home Depot, and the like - the choice is really up to you. However, our goal here at Assembly Supplies - Heatgun.com - is to help you in the decision process so you can buy the best plastic welding tools for your needs, whether it be top-of-the-line award-winning Leister tools or another competitor’s. Furthermore, we strive to provide you with useful how-to guides, YouTube videos, and other online resources that give you tips on how to have the best plastic welding experience possible. Our goal: to serve you.