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L4 Inventories: planning and managing (• Material requirements planning…
L4 Inventories: planning and managing
• Inventory management
1 definition
The American Production and Inventory Control Society
1support production(Raw material/ WIG)
2 support activities (maintenance/Repair/operating supplies)
3 customer service (finished goods and spares)
How it recorded on balance sheet
Waller 的兩個圖（p7,8）
2 Types
Bozarth and Handfield 2008
2 type of demand
dependent/
Product stucture
independent
2 type
cycle stock
safety stock
Drivers and Impact
4 type
1/smoothing inventory 2/避險 Hedge
3/ Anticipation 4/Transportation
老師個人意見
lean thinking on Inventory
3 Inventory control
When
1 PRS Periodic review system 定期評估法
restocking level
Oreder Quantity (Q) = R ‐Ｉ
determind safety stock
Trade off between oreder (delivery) and holding cost
前 average demand during the reorder period and the order lead-
後 standard deviation of demand during the reorder period and the order lead-time
考量平均需求和Uncertainty
Cons
not suitable for expensive items
didnt concern the tradeoff between holing and ordering
2 Continuous review systems
Re-order point
restocking level
R= D x L
balance demand and supply
and desire safety stock levels
No uncertainty
Constant demand
the replenishment order arrives just-in-time to prevent a stock-out.
How many
The Economic Order Quantity (EOQ)
ABC Classification
ABC classification (Parieto)
• Material requirements planning
Definition
a set of techniques which uses the bill of materials, inventory data, and the master production schedule to calculate requirements for materials.
Specific Noun
Master Production Scheduling/ BOL
MRP Record card.......
Parameters
Planning horizon
• Size of time bucket
• Lot sizing rules
• Regeneration vs.. net change
Uncertainties in MRP
Environmental uncertainty
• System uncertainty
Dealing with uncertainty in MRP
(Murthy and Ma 1991)
Safety due date
Over-planning ‐
Safety lead-times
Timing uncertainty
Yield factors
Safety stocks
Quantity uncertainty
• MRP nervousness / instability
(Ho 1989)
Solutions
1 Stable MPS
2 Carefully change any parameter changes •
3 Use different lot sizing rules at the high and low levels of the product structure
Causes
• Demand uncertainty
• Product structure characteristics
• Incorrect lot-sizing rules
MRP Problems
• Quality of the model • Bill of materials structure • Non-material activities • Validity of the assumptions • Lack of 2 way time analysis • Quality of data • Regeneration / computational effort • Poor visibility • Operational aspects
How to implement MRP
Planning Horizons
long/strategic
medium/
short/tactical
