When you hear the term welding, the first thing that comes to mind is the process of joining metal parts using heat, pressure, or both. However welding not only applies to metals, but also plastic pieces and even wood.

Welded plastic is an essential component in various industries and it’s easy to see why. It is reliable, cost-effective, and aesthetically pleasing.

In this article, I’ll guide you through the basics of welding plastics. We’ll also cover the common plastic welding techniques as well as their advantages and disadvantages. Read on!

What is Plastic Welding?

Plastic welding is the process of using heat and pressure to fuse two or more plastic materials. This operation involves melting plastic at the joint section and pressing the plastic pieces together to form a strong molecular bond.

Plastic welding creates joints that are just as strong as the surrounding material. Further, this process can be used for a wide range of plastic materials including Polyvinyl Chloride (PVC), Polyethylene(PE), Acrylonitrile-Butadiene-Styrene (ABS), Polymethyl Methacrylate (PMMA), Polyethylene Terephthalate (PET), Polypropylene (PP), and Polycarbonate (PC). Thanks to its versatility, this plastic joining method is preferred in the automotive, aerospace, construction, medical devices, and manufacturing industries.

There are numerous welding methods out there. However, they all follow a common basic principle. To weld plastics, you’ll need to follow these general steps regardless of your chosen technique.

Step 1: Surface Preparation

Plastic welding requires that you clean the surfaces before joining them. This can be done using soap and water. Once the plastic surfaces are clean, dry them off with a lint-free cloth.

If the thermoplastics have stains, you can remove them using solvents or sandpaper. Surface preparation ensures a high-quality joint.

Step 2: Application of Heat and Pressure

To weld plastic parts together, the operator needs to apply heat to the pieces being joined. This calls for welding equipment such as a welding torch, soldering iron, welding gun, welding rods, etc. Most operations also have devices that hold the plastic parts together.

Anyone welding plastics needs to wear protective gear such as heat-resistant gloves and eyewear. This will protect the welder from heat and any debris.

Step 3: Cooling

The final step is to allow the melted plastic to cool down and reach room temperature. As the weld joint cools and solidifies, it forms a strong, permanent bond.

Now that we’re familiar with the basics of how to weld plastic, let’s explore the different plastic welding techniques.

Welding Processes for Plastics

There are numerous welding methods, each employing a different technique to join plastic parts. Selecting the right operation ensures a high quality welded joint.

The choice of welding technique will depend on factors such as;

Size of plastic pieces
Weld joint geometry
Type of plastic
Preferred strength of the welded joint.

Each plastic welding process has its strengths and weaknesses. For example, pendulum welding is suitable for joining small plastics and welding hard-to-reach areas. However, it is slower compared to speed welding and extrusion welding.

Here are the common plastic welding methods.

Laser Welding or Laser Beam Welding (LBW)

Laser welding uses a high-powered laser beam to melt and bond two plastic components. An optic fiber delivers a focused laser beam onto the joint area. Therefore, this plastic welding process offers high precision and minimal heat damage to the surrounding parts. Thanks to these aspects, laser welding has found applications in the aerospace, automotive, and electronics industries.

Different types of laser beam welding include hybrid, single-pass, contour, and simultaneous.

Advantages of Laser Welding

It is a fast process.
Can be used when welding plastics with intricate designs.
Laser welded joints are known for their high aesthetic quality or clean look.
Laser welding is highly precise and efficient.
It minimizes the risk of thermal damage to the surrounding plastic parts.

Disadvantages of Laser Welding

Works for specific types of plastics. Laser welding is suitable for transparent or translucent plastics that allow the laser beam to pass through.
Laser welding equipment is quite costly. Therefore, this process requires a significant initial investment.

Ultrasonic Welding

Ultrasonic plastic welding utilizes high-frequency vibrations to join plastic components. Pressure is applied to the plastic parts while ultrasonic vibrations are directed to the joint area. These vibrations generate frictional heat that causes the thermoplastics to melt and join.

Ultrasonic welding produces precise, strong, and high-quality welds. Therefore, this process is used in the manufacture of medical devices, electronics, and automobiles.

Advantages of Ultrasonic welding

It produces high-strength welds that can withstand stress, vibrations, and other environmental factors.
Ideal for heat-sensitive plastic materials.
Ultrasonic welding is an eco-friendly process. It does not generate harmful emissions or other pollutants.
It is cost-efficient as it doesn’t require extra materials such as adhesives and fasteners.

Disadvantages of Ultrasonic Welding

Ultrasonic plastic welding is only applicable to specific joint types, i.e., overlapping joints. It’s not suitable for edge, tee, or corner joints.
It is not suitable for some types of plastics.

Hot Gas Welding

Hot gas welding, also known as hot air welding, uses a plastic welding heat gun to join thermoplastics. The plastic heating gun releases a stream of hot air that heats a plastic welding rod made of the same material as the parts to be joined.

Since the heating temperatures exceed the melting point of the welding rod, it softens forming molten plastic. Pressure is applied, and this joins the two plastic components using the molten weld rod. Upon cooling, it creates a solid welded joint.

Hot air welding is often used to join thermoplastics that are too thick for other welding techniques. This process is also useful in repairing plastic components such as tanks.

Advantages of Hot Gas Welding

Uses portable hand-held equipment.
Hot air welding is relatively easy to perform.
It can be used for a range of thermoplastics.
Effective for both big and small welds.
Can be performed without electricity.

Disadvantages of Hot Gas Welding

Hot gas welding is a slow process.
It generates fumes and odors during the welding process.

Spin Welding

Also known as rotational frictional welding, spin welding is used for fusing thermoplastic parts with a circular or cylindrical shape.

This plastic welding technique involves spinning one component against another at a high speed. As one of the parts rotates, the second is held stationary. Frictional heat is generated, causing the joint interface to melt. The two surfaces are held together under pressure until they fuse and form a strong weld.

Advantages of Spin Welding

It is suitable for different thermoplastics including polyvinyl chloride, polypropylene, and polyethylene.
It is fast and creates high-strength, durable welds.
Spin welding is a relatively easy process that does not require much technical expertise.
It creates strong welds without using additional materials or adhesives.
Minimal risk of heat damage to the surrounding plastic parts.

Disadvantages of Spin Welding

It is only suitable for circular or cylindrical parts.
It requires a high initial investment. Equipment such as a spin welder can be quite costly.
Spin welding is not ideal for large parts.

Vibration Welding

As the name suggests, vibration welding relies on mechanical vibrations to join two plastic components. Pressure is applied to the parts, and one part is vibrated at a high speed against the other.

The vibrations produce frictional heat which melts the plastic at the joint section. As the molten plastic cools down, it solidifies creating a strong weld between the two parts.

There are two types of vibration welding; linear vibration welding and orbital vibration welding. This welding technique is often used for parts with complex shapes.

Advantages of Vibration Welding

Produces high-strength, durable welds.
The welding process does not require surface preparation.
It is a versatile process that works for plastics with varying thicknesses and shapes.
There is no need for consumables.

Disadvantages of Vibration Welding

This process requires expensive equipment.
It is limited to specific plastic materials.

Hot Plate Welding

This plastic welding process involves using a heated plate to join plastic parts. The hot plate is usually made of copper or aluminum, and it is heated to a particular temperature depending on the thermoplastics being joined.

With this technique, the hot plate heats the two plastic parts until they reach their melting points. They are then pressed together and allowed to cool down creating a strong, molecular bond.

Advantages of Hot Plate Welding

It forms strong, durable welded joints.
It is well-suited to welding large plastic components or parts with complex shapes.
Hot plate welding can be used for a variety of thermoplastics including PE, PVC, and PP.
It offers high precision which creates uniform and consistent joints.

Disadvantages of Hot Plate Welding

Hot plate welding equipment requires significant maintenance.
The plastic parts to be joined require surface preparation. The presence of contaminants or irregularities on the plastic surfaces would result in a lower-quality weld.
Hot plate welding is a slow process.

Friction Welding

Friction welding utilizes frictional heat to join plastic materials together. While one of the plastic components is held stationary, the other is rotated at a fast pace.

This movement produces frictional heat that melts the plastic surfaces at the joint interface. Pressure is then applied and the two plastic parts fuse as the molten plastic cools down and solidifies.

Friction welding is further grouped into two; continuous induce friction welding and inertia friction welding.

Advantages of Friction Welding

It is an eco-friendly process.
Creates high-quality welded joints.
It is a fast process.
Suitable for different plastic materials.
Minimal heat affected zone.

Disadvantages of Friction Welding

Equipment such as a friction welder can be expensive.
Friction welding is limited to specific types of plastic parts.

Extrusion welding

Extrusion welding utilizes plastic welding rods to bind two plastic parts to each other. In this process, a plastic welding rod is inserted into an extrusion welding gun which heats and melts the rod.

The molten plastic is then extruded through a nozzle and used to weld the two parts together. In most cases, the plastic weld rod is made of the same material as the plastic parts being joined.

Advantages of Extrusion Welding

Produces strong and durable welds.
Effective in welding large plastic sections.
Suitable for joining parts with complex shapes.
Can be used for thick materials.

Disadvantages of Extrusion Welding

It is expensive to set up.
The welding process may release fumes and odors.

Frequency Welding

Frequency welding is also referred to as radio-frequency or high-frequency welding. This process involves using an electromagnetic field to weld plastics.

The setup consists of two metal bars that are positioned to hold the two plastic parts together under pressure. These metal bars are also used to generate a high-frequency electromagnetic field. Plastic molecules in the electromagnetic field will oscillate at a high frequency. This generates heat which melts the plastic at the joint section.

The electromagnetic field is then removed, and the plastic parts are held together until they solidify and form a permanent bond. High-frequency welding is typically used for materials such as polyurethane and PVC.

Advantages of Frequency Welding

It is a fast and efficient welding technique.
Creates strong and long-lasting welds.
It can be used for parts with irregular shapes,
Minimal distortion of the material.

Disadvantages of Frequency Welding

It is expensive to set up.
It is not compatible with thick plastic materials.
High-frequency welding is limited to specific materials.

Solvent Welding

Unlike the other welding processes that we’ve discussed above, a solvent weld does not require a plastic filler rod or softened plastic to form a welded joint. Instead, this process uses a solvent such as methyl ethyl ketone (MEK).

Once the solvent is applied, it temporarily dissolves the polymer. This allows the dissolved polymer chains to move freely and the two plastic components mix. When the chains eventually lose their mobility, you end up with a solid consisting of mixed-up polymer chains. Solvent welds are commonly used to join PVC and ABS pipes for plumbing purposes.

Advantages of Solvent Welding

Inexpensive.
Relatively simple process.
Ideal for welding plastic pipes.

Disadvantages of Solvent Welding

Requires surface preparation.
Improper solvent application can compromise the joint quality.

Author

Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.

Plastic Welding: Definition and Their Types