Often when the plastic casing for an object gets cracked, people simply buy a new one. Plastic, however, is by nature quite malleable and can be easily melted and reattached. Cosmetically the repaired object may not look as good as new, but with a little practice a smooth plastic weld can be attained. Plastic welding does not have to be limited to repairs, though -- the same skills can be used for artistic and fabrication projects. If you already have a soldering iron, you don't need to purchase a plastic welding kit. You can start plastic welding right away.
Clean the plastic with soap and degreaser, if necessary. Sand down the edges to be welded just enough that they are not jagged.
Plug the soldering iron in and allow it to heat up for a few minutes.
Push the two pieces of plastic together. Run the soldering iron tip back and forth over the seam to partially melt the plastic together.
While the plastic pieces are hot and can still be moved, check and adjust to get them exactly in place.
Add more plastic onto the seam to strengthen it by laying smaller pieces of plastic along the seam. Melt them fully by pressing on the small pieces with the soldering tip until they become liquefied. Spread the melted plastic evenly along the seam with the soldering tip.
Go over the seam and surrounding area with the soldering iron using fast, smooth strokes to create an even, smoothly welded surface.
Experiment on some scrap plastic first to know how long to keep the soldering iron on a particular point. Every type of plastic will melt at a slightly different rate.
Fumes from melting plastic can be caustic, as well as the melted plastic itself. Do this project in an open area outdoors.