If your project requires joining two pieces of plastic and need a stronger connection than you'd get with glue you can weld two pieces of plastic together by using a rotary tool to spin a plastic rod.

If you want to weld aluminum, you might think skill-intensive TIG welding is the only way. However, if you already own a MIG welder, an add-on spool gun is a viable option. Retailing for $276, Miller ...