Material on time, even when it has to go out
Material requirements set the demand per item against what is in stock and what has been ordered. On the sales order, you see which purchase orders are planned for that order. So you know before planning whether the steel is there.
Off-site operations, such as galvanising or powder coating, have no separate out-and-back flow in Lean. How you follow them up in your orders and planning, we look at together at the start.