How to Weld Plastics: A Complete Guide

The plastic welding process takes place when heat and pressure are applied to join two pieces of plastic together. The plastic is melted at the joint and then pressed together to create a bond. There are several techniques used to do this, so it’s not always easy to determine how to weld plastic. With that in mind, here’s a crash course on welded plastics and how to weld them efficiently.

Common Uses of Welded Plastic

Welded plastics are commonly used in the automotive, construction, and manufacturing industries. Some of the projects include chemical tanks, water tanks, heat exchangers, and plumbing fittings.

Preparing to Weld Plastic

Once you figure out how to weld plastic, you need to make sure you’re prepared to complete the process.

Set up a safe space: You’ll want to weld your plastic in a well-ventilated area. You should also ensure you have protective gear, including a long-sleeved shirt, heat-resistant gloves, and goggles.

Prepare the plastic: Cleaning the plastic will get rid of any weak points during the welding process. Wash with a liquid solvent like Methyl Ethyl Ketone (MEK) and then dry with a lint-free cloth.

Label the plastic: Every plastic has a distinct letter on it that identifies what type of plastic it is. This will help you determine what type of welding rod you need to use.

Choose the right rod: If you don’t know what kind of plastic you have, use a welding rod test kit. After selecting a rod that closely simulates the plastic, take one end of the rod, and attach it to a clean surface on your plastic. If the rod and plastic stick together, they’re made of the same material.

Create your joints: Figure out where to place the joint. Place the plastic pieces on a workbench and push them close together. Then, pin the pieces to the table using clamps. Wrap foil around the pieces to keep them pressed together, but don’t cover the area that will be welded.

Prepare your welder: Preheat the welding gun for a few minutes, setting your welding temperatures in line with the materials to be welded. The temperature typically ranges from 390°F to 570°F

Common Plastic Weld Techniques

Before you figure out how to weld plastic, you need to decide which technique is right for you. Some of the most common ways to weld plastic include:

Hot Gas:  This is when you heat the plastic at the joint between two parts with a hot air gun or torch until it melts, fusing the parts together.

Hot Plate: The aluminum hot plate is heated, and the two plastic parts are placed on it until they reach the melting point. Once the plastic has melted, the hot plate is removed, and the two parts are pressed together until they cool and solidify.

Extrusion. This method is used for welding large plastic structures and involves melting the plastic welding rods with a heated extrusion gun and then applying the melted plastic to the joint between two plastic parts.

Ultrasonic: Mechanical vibrations with high frequency and low amplitude create frictional heat that will bond two plastics.

Laser: This process involves a laser beam to thaw the plastic and pressure is then applied to bond the welded joints.

High-frequency: High-frequency welding uses an electromagnetic field to generate heat inside the material.