Repairing a plastic grill

Two different methods, 'welding' and bonding:
The chemicals best used for plastic welding depends on the plastic.
Some plastics can be welded with heat.
Some plastics can be bonded with adhesives (like epoxy) and some can't.

ABS is one of the more common plastics used for trim etc on cars.
More info in this thread
instrument cluster repair what glue to use