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Thermoplastic Welding


Thermoplastics that can be softened or shaped by heat are weldable. The electric hot air/gas welder has made it possible for even inexperienced users to “get the hang of” welding plastic in a few hours. With study and practice you’ll be utilizing this lightweight, hand-held tool economically and with speed. Thermoplastic welding is also fairly safe; there is no flame, spark, or smoke involved.

Hot air/gas welding is usually performed on plastic 1/16” or thicker. The bond strength can be about 90% the strength of the original material. Whether fabricating thermoplastic stock or repairing, use a rod that is the same material as your base to produce the strongest weld.

Before you begin read the welder’s instructions from the manufacturer and the information on the type of plastic you will be using. Pay close attention to all safety warnings.

To avoid burning out the heating element, remember airflow first and airflow last. Start the airflow before the heating element. PSI should be set to 4 or 4 ½. When finished disconnect the electricity to the gun, but continue the airflow. The gun will cool faster and you’ll reduce stress on the heating element.

Your workspace should be tidy. And before you begin clean any dust or dirt from your materials. Use Methyl Ethyl Ketone (MEK) to remove oily substances. Materials must be dry before you weld.

Connect the welding gun to compressed air or inert gas. Plug in and use ground provided. Allow the welder to warm up for a few minutes. Select the proper tip. The tacking tip is for fitting up the work; no rod or strip is required. The round tip is best for small areas. The automatic feed tip is meant for larger areas and allows for more speed.

Tack Welding

To begin with a tack weld or temporary weld (after tip is installed), allow the hot air/gas to flow through the tip to warm it up. Line up the pieces to be welded. No rod or strip is necessary. Simply apply the hot tacking tip to the area or seam where the pieces will be joined. Repeat until you have done enough tack welds to hold the weight of the pieces together. For large pieces you may want to draw the tack tip along the entire length of the seam. Your objective is to fuse the pieces sufficiently to allow accurate, permanent bonding in the next step.

Avoid overheating the tack points. This will lead to discoloration, charring, and/or warping. You may wish to grind down the tack points for a smoother edge (especially for beginners, if you’re not satisfied with your weld).

Permanent Welding

The same types of welds are used with plastic as are use in metal welding; butt welds, fillet welds, lap joints, edge welds, and corner welds. After tack welding you’re ready for permanent welds.

Select your welding rod or strip (same material as base). Select a rod diameter close to the thickness of the base material. Set your welding temperature and air flow setting according to specs. Install the proper round or automatic feed tip. Let the tip heat up. Cut the end of the rod at a 60 degree angle. Hold the cut just above the weld starting point. Apply heat to rod end and base material seam simultaneously. Only the surfaces should be tacky. Press the tacky rod into the tacky starting point of the base. The rod should generally hold shape throughout the process.

Continue by holding the rod at a 90 degree angle to the weld seam. Press firmly and evenly into the joint as you apply heat with the seam. Use a short fanning motion. If you are welding at the correct temperature a loop will form where the rod joins the base. Small beads should form on either side of the weld. When the weld is complete cut the rod with a knife or pliers at a 30 degree angle. Cut the end of the new rod at a 60 degree angle to continue.

If using an automatic feed tip to weld at high speed, the rod or strip will be fed through the tip. A capable welder will be able to join two or three feet of material each minute. Be sure to remove the welding rod from the feeder tube immediately after completing your weld. Clean the tube with its brush before and after use.


Never weld with flammable gas. Never touch metal parts on the welding gun until they have had sufficient time to cool. Use pliers to change the tip on a welding gun (don’t over tighten). Do not put the welder in a vise to change the heating element.



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