Production Planning Software: From Spreadsheets to APS

The short answer

Production planning answers three questions: what to make, from what and when, on which machine. A spreadsheet handles this while the product range is small and there are only a few work centers. When one planner spends hours "rebuilding the plan" after every urgent order, it is time for software.

The usual path:

1. Spreadsheet — manual plan, manual material check.
2. MRP (Material Requirements Planning) — calculates which materials and semi-finished goods are needed and when to order them.
3. APS (Advanced Planning and Scheduling) — builds a realistic schedule that respects machine capacity, shifts, changeovers and priorities.

Two sides of planning

Material planning starts from demand (orders and forecast), explodes it through the bill of materials (BOM) and subtracts stock and open purchase orders. The result is a list of what to buy or produce and by which date.

Capacity planning checks whether the work centers can actually do the job. Here it matters whether the system plans with:

• infinite capacity — it assumes any amount of work fits into a day, and you see overloads afterwards;
• finite capacity — it never loads a machine beyond its available hours and shifts the job to the next free slot.

Classic MRP mostly works with infinite capacity. APS is built around finite capacity, which is why its schedule is closer to reality.

Scheduling constraints that break simple plans

A real schedule must respect:

• routings — the sequence of operations and which machines can do each one;
• setup and changeover times, often depending on the previous job (color, size, material);
• shift calendars, planned maintenance and holidays;
• material availability — a job cannot start before its components arrive;
• tools, molds and qualified operators as shared resources;
• batch sizes, minimum runs and transfer batches between operations;
• due dates and priorities of customer orders.

A spreadsheet usually captures two or three of these. Everything else lives in the planner's head.

Signs spreadsheets have broken

• Several versions of the plan circulate and nobody knows which one is current.
• Material shortages are discovered on the shop floor, not during planning.
• Sales cannot get a reliable delivery date without calling production.
• One person knows how the file works, and their vacation is a risk.
• Replanning after a breakdown or rush order takes hours.
• Formulas reference cells nobody dares to touch.

How to move step by step

1. Clean the master data. Item codes, BOMs, routings, standard times and machine lists. Without accurate data any system will produce a confident but wrong plan.
2. Start with MRP. Connect orders, stock and purchases so material needs are calculated automatically. This often removes most of the daily firefighting.
3. Collect actual times. Record real operation start and finish times from the shop floor — manually through a tablet first if needed. APS is only as good as its time standards.
4. Pilot APS on a bottleneck. Choose the work center that limits output and schedule it with finite capacity. Keep the spreadsheet in parallel for a few planning cycles and compare.
5. Extend to other work centers once planners trust the result.
6. Close the loop. Feed completed operations back so the schedule updates itself, and give sales a view of realistic dates.

How to choose a system

Sometimes a ready product fits; sometimes a custom module on top of an existing ERP is simpler, especially when the logic is specific to one plant.

Common mistakes

• Buying APS before BOMs and routings are accurate.
• Trying to model every constraint on day one.
• Letting the system plan while the shop floor still works from paper.
• Not training planners to understand why the system made a decision.