master-detial

Hi
I have 2 tables with a master details relationship linked on orderno
order (orderno, duedate)

details(id, orderno, part, duedate)
When I add a new record to the details table I would like details.duedate to be populated automatically with the header order.duedate.
If I edit I record I would like the details.duedate to be changed to the order.duedate (this may have changed since the record was first added).
Hope you can help.