Step 1: Understanding Plastics
Hot melt adhesive or simply hot glue is really a plastic. It is very sticky when molten and is called an adhesive for that reason. It is specially formulated for adhesion. Nevertheless, it is still just another kind of plastic. It is softer and more flexible than ABS plastic. It is a very useful plastic on its own and can be used to make all kinds of things. Don't be afraid to experiment.
In this instructable, I will demonstrate how to not only repair a broken piece of plastic, but even to do some rudimentary molding to fabricate plastic parts. The piece I will be repairing is a large cover for an air handler in a automobile.