Routings and Requirements Planning

A structure says what a product is made of. A routing says how it is made — the operations, in sequence, and where each happens.

Routings

Each operation carries its work centre, its sequence, and the time it takes, usually split between setup and run time. Setup is per batch and run is per unit, which is why doubling a batch rarely doubles the elapsed time.

Routings give you works instructions, capacity requirements per work centre, and a basis for costing labour and machine time against a product.

Requirements planning

Planning takes demand — orders, forecasts, minimum stock levels — explodes it through the structures, nets off what you already have and what is already on order, and tells you what must be made or bought and by when.

Netting is the part worth understanding. Requirements are not gross: if you need 100 and hold 30 with 20 on order, the requirement is 50. That is why stock accuracy determines whether planning output is useful. Planning against wrong stock produces wrong suggestions with complete confidence.

Lead times

Working backwards from a due date through each level's lead time is what produces the start dates. A component with a six-week lead time needs ordering six weeks before it is consumed, not before the finished item is due. Enter realistic lead times, including the ones your suppliers actually achieve rather than the ones they quote.

Planning suggests, it does not act

Output is a set of suggestions for a person to review and convert into real orders. It does not place purchase orders on its own. Treat a run that produces surprising suggestions as a question about the data — usually stock, lead times or an effectivity date — rather than as an instruction.

Before you rely on it

• Stock must be accurate, including reservations.
• Structures must be complete and correctly dated.
• Lead times must be realistic.
• Open purchase orders must be in the system, or planning will suggest buying what is already coming.

Run planning in parallel with your existing method for a cycle or two and compare, before anybody acts on it.