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Production Planning (MPS/MRP)

生产计划（MPS/MRP）

Framework

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.
IRON LAW：分层规划——需求 → MPS → MRP → 车间现场

生产计划采用自上而下的流程：
1. 需求预测/客户订单 → 生产什么、何时生产
2. MPS → 成品主生产计划
3. MRP → 物料与组件需求（采购什么、何时采购）
4. 车间排程 → 使用哪台机器、生产顺序如何

跳过中间层级（从需求预测直接到车间现场）
会导致混乱——物料短缺、产能冲突、交付延误。

Planning Hierarchy

规划层级

LevelPlanHorizonGranularityDecides
StrategicS&OP (Sales & Operations Planning)12-18 monthsMonthly, product familyCapacity investments, workforce planning
TacticalMPS (Master Production Schedule)3-6 monthsWeekly, end productWhat to produce each week
OperationalMRP (Material Requirements Planning)4-12 weeksDaily, component/materialWhat to order, when, how much
ExecutionShop Floor Scheduling1-2 weeksHourly, work centerSequence, machine assignment
层级计划类型时间跨度粒度决策内容
战略层S&OP（销售与运营规划）12-18个月月度、产品系列产能投资、人员规划
战术层MPS（主生产计划）3-6个月周度、最终产品每周生产什么
运营层MRP（物料需求计划）4-12周日度、组件/物料采购什么、何时采购、采购量多少
执行层车间排程1-2周小时级、工作中心生产顺序、机器分配

MPS Process

MPS流程

  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)
  1. 输入：需求预测 + 客户订单 + 当前库存 + 安全库存目标
  2. 逻辑：每周计算：需生产量 = 需求量 - 期初库存 - 计划到货量 + 安全库存
  3. 输出：各成品每周的计划生产数量
  4. 约束：不得超过可用产能（需通过粗能力规划校验）

MRP Process

MRP流程

  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
  1. 输入：MPS（生产内容） + BOM（物料清单——产品构成） + 库存状态 + 提前期
  2. 逻辑：“拆解”BOM——针对每个成品，计算各组件/物料的订购时间以确保及时到货
  3. 输出：带日期和数量的计划采购订单与生产订单
  4. 核心计算：订购日期 = 需求日期 - 提前期

Scheduling Algorithms

排程算法

AlgorithmRuleBest When
FCFS (First Come First Served)Process in order receivedLow complexity, fairness matters
SPT (Shortest Processing Time)Shortest job firstMinimize average flow time
EDD (Earliest Due Date)Most urgent due date firstMinimize late deliveries
Bottleneck-firstSchedule the constraint first, subordinate restCapacity-constrained environments (TOC logic)
算法规则适用场景
FCFS（先到先服务）按接收顺序处理任务复杂度低、注重公平性的场景
SPT（最短加工时间）优先处理最短任务最小化平均流转时间的场景
EDD（最早到期日）优先处理最紧急到期的任务最小化交付延误的场景
瓶颈优先先安排约束环节的任务，其他环节配合产能受限环境（约束理论逻辑）

SMED (Single-Minute Exchange of Die)

SMED（单分钟换模）

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
缩短换模时间以提升灵活性：
  1. 区分内部换模（机器停机时操作）与外部换模（机器运行时可操作）
  2. 尽可能将内部换模转化为外部换模
  3. 简化剩余内部换模步骤
  4. 反复练习并标准化操作

Output Format

输出格式

markdown
undefined
markdown
undefined

Production Plan: {Product/Period}

生产计划：{产品/周期}

Demand vs Capacity

需求vs产能

WeekDemandAvailable CapacityGap
W1{units}{units}{+/-}
周需求量可用产能差距
W1{数量}{数量}{+/-}

Master Production Schedule

主生产计划

WeekProduct AProduct BProduct CTotal
W1{units}{units}{units}{units}
周产品A产品B产品C总计
W1{数量}{数量}{数量}{数量}

Material Requirements

物料需求

MaterialQuantityOrder DateSupplierLead Time
{material}{qty}{date}{supplier}{days}
物料数量订购日期供应商提前期
{物料名称}{数量}{日期}{供应商}{天数}

Scheduling

排程

Work CenterMonTueWedThuFri
{center}{job}{job}.........
undefined
工作中心周一周二周三周四周五
{中心名称}{任务}{任务}.........
undefined

Gotchas

注意事项

  • 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.
  • 预测精度决定一切：MPS/MRP的效果完全依赖需求预测的准确性。跟踪预测精度（MAPE），并根据预测误差比例设置安全库存。
  • 提前期波动会打乱计划：如果供应商提前期是“2-6周”（波动4周），则需为最坏情况准备安全库存。通过供应商管理减少波动。
  • BOM准确性对MRP至关重要：错误的BOM会导致采购错误物料。每季度审核BOM。
  • 冻结区：MPS的前1-2周应处于“冻结”状态（不允许更改），以确保稳定执行。冻结区内的变更会引发系统连锁混乱。
  • 有限vs无限产能：基础MRP假设无限产能（忽略机器约束）。务必在MRP输出之上叠加产能校验（粗能力或详细能力规划）。

References

参考资料

  • For S&OP process design, see 
    references/sop-process.md
  • For demand forecasting methods, see 
    references/demand-forecasting.md
  • 关于S&OP流程设计，请参考
    references/sop-process.md
  • 关于需求预测方法，请参考
    references/demand-forecasting.md