mfg-production-planning
從 MPS 到 MRP 到現場排程，把生產計畫一層層排出來
中文翻譯
---
name: "mfg-production-planning"
description: "用 MPS（主生產排程）、MRP（物料需求規劃）和產能規劃設計生產計畫。使用者需要排生產、規劃物料採購、讓產能和需求取得平衡，或最佳化生產排序時使用，就算他們說的是「我們趕不上訂單」、「什麼時候該訂料」、「生產排程」或「下一季的需求要怎麼規劃」也一樣。"
metadata:
category: "WP-03 製造業"
tags: ["manufacturing", "production-planning", "mrp", "scheduling"]
---
# 生產規劃（MPS/MRP）
## 框架
```
IRON LAW: Plan Hierarchically — Demand → MPS → MRP → Shop Floor
Production planning flows TOP-DOWN:
1. Demand forecast / customer orders → what to make, when
2. MPS → master schedule for finished goods
3. MRP → material and component requirements (what to buy, when)
4. Shop floor scheduling → which machine, which sequence
Skipping levels (going from demand forecast directly to shop floor)
creates chaos — material shortages, capacity conflicts, missed deliveries.
```
### 規劃階層
| 層級 | 計畫 | 時間範圍 | 粒度 | 決定什麼 |
|-------|------|---------|-------------|---------|
| **策略層** | S&OP（銷售與營運規劃） | 12-18 個月 | 每月、產品家族 | 產能投資、人力規劃 |
| **戰術層** | MPS（主生產排程） | 3-6 個月 | 每週、最終產品 | 每週要生產什麼 |
| **作業層** | MRP（物料需求規劃） | 4-12 週 | 每日、零組件／物料 | 要訂什麼、什麼時候、訂多少 |
| **執行層** | 現場排程（Shop Floor Scheduling） | 1-2 週 | 每小時、工作中心 | 順序、機台指派 |
### MPS 流程
1. **輸入**：需求預測 + 客戶訂單 + 目前庫存 + 安全庫存目標
2. **邏輯**：每一週都計算：需要生產量 = 需求 - 期初庫存 - 預定到貨 + 安全庫存
3. **輸出**：每個成品每週的計畫生產量
4. **限制**：不能超過可用產能（做粗略產能規劃的檢查）
### MRP 流程
1. **輸入**：MPS（要做什麼）+ BOM（物料清單，也就是它是用什麼做的）+ 庫存狀態 + 前置時間
2. **邏輯**：「展開」BOM，針對每個成品，計算每個零組件／物料必須什麼時候下單才趕得上
3. **輸出**：附有日期和數量的計畫採購單和生產單
4. **關鍵計算**：下單日期 = 需求日期 - 前置時間
### 排程演算法
| 演算法 | 規則 | 最適合 |
|-----------|------|-----------|
| **FCFS**（先到先做） | 依收到的順序處理 | 複雜度低、公平性重要 |
| **SPT**（最短加工時間） | 最短的工作先做 | 最小化平均流程時間 |
| **EDD**（最早到期日） | 到期日最急的先做 | 最小化延遲交貨 |
| **瓶頸優先** | 先排限制條件，其餘從屬於它 | 受產能限制的環境（TOC 邏輯） |
### SMED（單分鐘換模）
縮短換線時間來提高彈性：
1. 把內部設置（機器停止時）和外部設置（運轉時就能做）分開
2. 盡可能把內部轉成外部
3. 簡化剩下的內部步驟
4. 練習並標準化
## 輸出格式
```markdown
# 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} | ... | ... | ... |
```
## 注意事項
- **預測準確度限制了一切**：MPS/MRP 的品質只會跟需求預測一樣好。要追蹤預測準確度（MAPE），並依預測誤差的比例建立安全庫存。
- **前置時間的變異會毀掉計畫**：如果供應商的前置時間是「2-6 週」（變異 4 週），你就需要為最壞的情況備安全庫存。要透過供應商管理來降低變異。
- **BOM 的準確度對 MRP 至關重要**：BOM 錯了，就會訂錯物料。每季都要稽核 BOM。
- **凍結區**：MPS 的前 1-2 週應該「凍結」（不改），讓執行保持穩定。在凍結區內改動，會讓混亂在整個系統裡連鎖擴散。
- **有限 vs 無限產能**：基本的 MRP 假設產能是無限的（忽略機台限制）。一定要在 MRP 的輸出上再疊一層產能檢查（粗略或詳細）。
## 參考資料
- S&OP 流程設計請看 `references/sop-process.md`
- 需求預測方法請看 `references/demand-forecasting.md`英文原文
---
name: "mfg-production-planning"
description: "Design production plans using MPS (Master Production Schedule), MRP (Material Requirements Planning), and capacity planning. Use this skill when the user needs to schedule production, plan material procurement, balance capacity with demand, or optimize production sequencing — even if they say 'we can't keep up with orders', 'when should we order materials', 'production scheduling', or 'how do we plan for next quarter's demand'."
metadata:
category: "WP-03 製造業"
tags: ["manufacturing", "production-planning", "mrp", "scheduling"]
---
# Production Planning (MPS/MRP)
## Framework
```
IRON LAW: Plan Hierarchically — Demand → MPS → MRP → Shop Floor
Production planning flows TOP-DOWN:
1. Demand forecast / customer orders → what to make, when
2. MPS → master schedule for finished goods
3. MRP → material and component requirements (what to buy, when)
4. Shop floor scheduling → which machine, which sequence
Skipping levels (going from demand forecast directly to shop floor)
creates chaos — material shortages, capacity conflicts, missed deliveries.
```
### Planning Hierarchy
| Level | Plan | Horizon | Granularity | Decides |
|-------|------|---------|-------------|---------|
| **Strategic** | S&OP (Sales & Operations Planning) | 12-18 months | Monthly, product family | Capacity investments, workforce planning |
| **Tactical** | MPS (Master Production Schedule) | 3-6 months | Weekly, end product | What to produce each week |
| **Operational** | MRP (Material Requirements Planning) | 4-12 weeks | Daily, component/material | What to order, when, how much |
| **Execution** | Shop Floor Scheduling | 1-2 weeks | Hourly, work center | Sequence, machine assignment |
### 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
| Algorithm | Rule | Best When |
|-----------|------|-----------|
| **FCFS** (First Come First Served) | Process in order received | Low complexity, fairness matters |
| **SPT** (Shortest Processing Time) | Shortest job first | Minimize average flow time |
| **EDD** (Earliest Due Date) | Most urgent due date first | Minimize late deliveries |
| **Bottleneck-first** | Schedule the constraint first, subordinate rest | Capacity-constrained environments (TOC logic) |
### 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
```markdown
# 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`