Welding Plastics: Methods, Materials and Key Considerations
We work with plastics on a daily basis and know that welding is a vital part of many manufacturing processes. But which methods work best, and which materials are suitable for welding? Here, we go through the most common methods for welding plastics, as well as discussing material properties and common problems that may arise.
Methods for welding plastic
There are various methods for welding plastic, but the most common are hot-gas welding, extruder welding and friction welding. Hot-gas welding uses a gas flame to heat the plastic to its melting point, after which it is shaped and joined. Extruder welding uses an extruder to melt and shape the plastic, whilst friction welding uses pressure and friction to melt and join the plastic.
We have experience of working with these methods and find that hot-gas welding is one of the most flexible. But which materials can be welded using this method?
Materials suitable for welding
Some of the materials best suited to welding are PE-HD, PE-1000, PP and PVC. These materials have a relatively low melting point and are therefore easier to weld. PVDF is another material that can be welded, but it requires a higher temperature and careful control of the process.
But what happens if we try to weld materials such as POM C or PTFE? These materials are difficult to weld due to their high melting point and low ability to bond to one another. In fact, PTFE cannot be welded at all, due to its extremely low coefficient of friction and high melting point.
Why are some materials so difficult to weld? There are steps that can be taken to improve weldability, such as using a different welding method or adding a weld-promoting additive to the material.
Preparation of joints
An important part of welding is the preparation of the joints. It is important that they are clean and dry, and that they are the correct shape and size to be joined together. We often use a joint cutter to cut the joints to size, and then we clean them with a brush and cleaning fluid.
If the joints are not properly prepared, this can result in poor-quality welds and joints that do not hold up over time. It can also lead to damage to the material, or the weld not being strong enough.
Testing welds
Once the weld is complete, it is important to test it to ensure it is of a good standard. We often use a combination of visual and mechanical tests to check the quality of the weld. We examine the appearance of the weld and check that it is straight and even. We also test the strength of the weld by subjecting it to stress and seeing if it holds up.
If the weld is not up to standard, it may need to be redone or repaired. In some cases, it may be necessary to replace the entire piece of material.
Common faults that can occur
There are several common faults that can occur during welding. One common fault is that the weld becomes too hot, which can result in damage to the material or the weld not being strong enough. Another common fault is that the weld becomes too cold, which can result in the weld not being strong enough.
We have also observed that the weld can become porous, which can result in it not being strong enough. This may be because the material does not have the correct properties, or because the welding process has not been carried out correctly.
When welding is better than gluing
Sometimes welding is preferable to gluing. Welding is often better when the material is thick, or when the joint needs to be very strong. Gluing may be better when the material is thin, or when the adhesive is stronger than the weld.
If we cannot decide whether to weld or glue, it may be a good idea to try both methods and see which works best.
Welding plastic is a complex process that requires precision and experience. With the right materials, the right method and the right preparation, the weld can turn out very well. Do you have any questions or concerns about welding plastic? Please feel free to contact us!
Would you like to discuss your requirements for welded plastic components?
Welding Plastic: Methods, Materials, and Important Aspects