It depends what costs have already been expended and what you want to do with them.  If you close a work order, the costs in the order are all posted as an expense  to WIP Variance.  If you cancel the order, all materials issued are returned to stock and only labor is expensed to WP Variance.  If ANY finished production has been performed, you can not cancel and if materials have been cut, welded, or whatever and are not in a condition to be reused, you should close rather than cancel.