You would think that welding is dedicated to metal alone, but plastic welding involves joining to pieces of plastic material together. The process of welding plastic is much the same as welding with metal. However, you do not have to use as much heat as you would with traditional metal welding.
Plastic welding can be used in instances from as small as modeling to construction jobs like joining main water pipes together, or welding a plastic car bumper together for a quick repair job. In fact, many of the plastic parts of a car can be welded for a strong repair instead of purchasing new parts.
Step 1 - Clean Plastic
Before you begin to weld any piece of plastic you want to clean it off of any debris, grime, grease, or resin from the factory. Use the degreaser and spray it onto the plastic. This should be done to at least 8 inches up from the edge. Let the degreaser set on the plastic for 5 to 10 minutes to work at the dirt and debris to loosen it. Use a clean, damp cloth and wipe the plastic clean of the degreaser and dirt. If there is still a little bit of grease left on the piece you want to weld, repeat this process.
Step 2 - Sand Plastic Ends Down
Take the 80 grit piece of sandpaper and sand the ends of the plastic so that they will butt against each other tightly. If you are fixing a hole in the fender, you would cut the piece of plastic you are using as the patch a little larger than the hole. Then sand it down to a tight fit.
Step 3 - Tape Ends Together
Before you do any welding of the plastic, you must fit it first. Put the pieces together so they fit tightly. Put pieces of foil tape onto the backside of the plastics so that they fit seamlessly. At this point, before you have welded anything together, it is important that you have the same type of plastic in place.
Step 4 - Heat Plastic
You heat plastic with an electric heating gun. They can be found at any hobby store, and are relatively inexpensive. Plug it in and let is warm up for about 10 minutes. When the heating gun is warmed enough (it should be hot, but not burning) then insert the plastic welding rod.
Step 5 - Plastic Welding
After you can see that the welding rod is starting to melt, then carefully feed the rod through the gun to that it will melt onto the joint of the two pieces of plastic. With the combination of the gun, and the melted plastic, it will melt the three pieces of plastic together to form a strong molecular bond. It will be as if they are one piece. Slowly work your way along the joint.
Step 6 - Let Cool and Sand
Let the plastic air dry until it is cool and sand down to a smooth finish with the 120 grit paper. Once it's seamless, paint it with the same color.