Mfg Production Planning

MPS Process

1. Inputs: Demand forecast + customer orders + current inventory + safety stock targets
2. Logic: For each week, calculate: Production Needed = Demand - Beginning Inventory - Scheduled Receipts + Safety Stock
3. Output: Planned production quantities by week for each finished product
4. Constraint: Must not exceed available capacity (rough-cut capacity planning check)

MRP Process

1. Inputs: MPS (what to make) + BOM (Bill of Materials — what it's made of) + Inventory status + Lead times
2. Logic: "Explode" the BOM — for each finished good, calculate when each component/material must be ordered to arrive in time
3. Output: Planned purchase orders and production orders with dates and quantities
4. Key calculation: Order date = Need date - Lead time

Scheduling Algorithms

SMED (Single-Minute Exchange of Die)

Reduce changeover time to increase flexibility:

1. Separate internal setup (machine stopped) from external (can do while running)
2. Convert internal to external where possible
3. Streamline remaining internal steps
4. Practice and standardize

Output Format

# Production Plan: {Product/Period}

## Demand vs Capacity
| Week | Demand | Available Capacity | Gap |
|------|--------|-------------------|-----|
| W1 | {units} | {units} | {+/-} |

## Master Production Schedule
| Week | Product A | Product B | Product C | Total |
|------|----------|----------|----------|-------|
| W1 | {units} | {units} | {units} | {units} |

## Material Requirements
| Material | Quantity | Order Date | Supplier | Lead Time |
|----------|---------|-----------|----------|-----------|
| {material} | {qty} | {date} | {supplier} | {days} |

## Scheduling
| Work Center | Mon | Tue | Wed | Thu | Fri |
|------------|-----|-----|-----|-----|-----|
| {center} | {job} | {job} | ... | ... | ... |

Gotchas

• Forecast accuracy limits everything: MPS/MRP is only as good as the demand forecast. Track forecast accuracy (MAPE) and build safety stock proportional to forecast error.
• Lead time variability kills plans: If supplier lead time is "2-6 weeks" (4 week variability), you need safety stock for the worst case. Reduce variability through supplier management.
• BOM accuracy is critical for MRP: A wrong BOM means ordering wrong materials. Audit BOMs quarterly.
• Frozen zone: The first 1-2 weeks of MPS should be "frozen" (no changes) to allow stable execution. Changes inside the frozen zone cascade chaos through the system.
• Finite vs infinite capacity: Basic MRP assumes infinite capacity (ignores machine constraints). Always layer a capacity check (rough-cut or detailed) on top of MRP output.

References

• For S&OP process design, see references/sop-process.md
• For demand forecasting methods, see references/demand-forecasting.md