Chinese-English Bilingual Teaching Chinese-English Bilingual Teaching

ForFor Logistics & Supply Chain Logistics & Supply Chain

Management Management

Chapter 7. Chapter 7. Stock ControlStock Control

余毅艺余毅艺Anniesyql@hotmail.comAnniesyql@hotmail.com

Office:8314BOffice:8314B

Ch.7 Stock ControlCh.7 Stock Control

Stock Classification Stock Classification 库存的分类库存的分类 Stock Identification Stock Identification 库存辨认库存辨认 Forecast Forecast 库存预测库存预测

Stock control is the determination and Stock control is the determination and

regulation of regulation of which itemswhich items are kept in stock and are kept in stock and

what quantitieswhat quantities of each are stocked without of each are stocked without

stock excess or stock deficiencies. stock excess or stock deficiencies.

The aim.The aim.

a high level of stocka high level of stock..

stockholding costs.stockholding costs.

The range and depth of stockholdings is The range and depth of stockholdings is

determined by an assessment of the following determined by an assessment of the following

factors.factors.

The nature of demand The nature of demand

Degree of protection against stock-outsDegree of protection against stock-outs

Purchasing costsPurchasing costs

Holding costs Holding costs

Lead-time Lead-time

1. 1. Stock classificationStock classification

80/20 80/20 in such cases 80% of the items in in such cases 80% of the items in

stock typically stock typically make upmake up only 20% of the only 20% of the

total stock value, while the remaining 20% total stock value, while the remaining 20%

of (high-value) items of (high-value) items account foraccount for 80% of 80% of

the total stock value. the total stock value.

这一法则是由这一法则是由意大利经济学家帕累托意大利经济学家帕累托在十九世纪在十九世纪末期提出的末期提出的 ,, 应该说这一法则具有普遍的适用性。应该说这一法则具有普遍的适用性。

1. 1. Stock classificationStock classification

ABC groups ABC groups

Category A items – Category A items – 10% of items by volume10% of items by volume

account for account for 70% of value70% of value; ;

Category B items – 20% of volume accounts for Category B items – 20% of volume accounts for

20% of value;20% of value;

Category C items – 70% of volume accounts for Category C items – 70% of volume accounts for

10% by values. 10% by values.

1. 1. Stock classificationStock classification

The stock control policy for the The stock control policy for the

categories might be as follows:categories might be as follows: Class A – Class A – close control and checked once a close control and checked once a

monthmonth; ;

Class B – Class B – medium controlmedium control and checked every and checked every

three months; three months;

Class C – Class C – minimum controlminimum control with free issue with free issue

2. Stock identification2. Stock identification

Stock consists of many different types of Stock consists of many different types of

individual items. individual items.

The easiest way to identify an item is by The easiest way to identify an item is by name name

or word descriptionor word description. .

The problem is that different people may The problem is that different people may

describe the same item using different words. describe the same item using different words.

This can result in duplication of the same item This can result in duplication of the same item

with with consequent higher than necessary consequent higher than necessary

stockholding levelsstockholding levels

2. Stock identification2. Stock identification

The development of a The development of a coding systemcoding system

follows a series of stages.follows a series of stages.

Identification of each item Identification of each item by function by function

and need.and need.

Specification of each item.Specification of each item. Classification into groups and Classification into groups and sub-sub-

groups.groups.

Application of code.Application of code.

2. Stock identification2. Stock identification

Classification into Classification into groups and sub-groupsgroups and sub-groups could could

be made on be made on any ofany of the following bases. the following bases.

Nature of materialNature of material

End use of materialEnd use of material

Location on storesLocation on stores

Source of supplySource of supply

End user customer End user customer

2. Stock identification2. Stock identification

所谓零件分类编码系统所谓零件分类编码系统 目前，世界上大约有目前，世界上大约有 100100 多种零件分类编码系统。多种零件分类编码系统。 OPITZOPITZ 系统系统 (( 德德 )) 、、 MNTPOФAHOBMNTPOФAHOB(( 前苏前苏

联联 )) 、、 BRISCHBRISCH 系统系统 (( 英英 )) 、、 KK-3KK-3 系统系统(( 日日 )) 、、 CODECODE 系统系统 (( 美美 )) 、、 MICLASSMICLASS 系统系统 (( 荷荷 ))等。等。

OPITZOPITZ 系统系统

2. Stock identification2. Stock identification

In theIn the BrischBrisch system there are 2 parts to the system there are 2 parts to the

code. The ‘code. The ‘surname’ comes firstsurname’ comes first and provides the and provides the

broad item classification.broad item classification.

Surname Surname ：： 1st figure = main classification 1st figure = main classification 主族分类 主族分类 2nd figure = sub-group 2nd figure = sub-group 子组 子组 of main of main

classificationclassification

3rd figure = item classification 3rd figure = item classification 项目分类 项目分类

2. Stock identification2. Stock identification

The The ‘forename’ which follows describes each ‘forename’ which follows describes each

item in detail item in detail e.g.e.g.

Forename:Forename:

4th figure = length4th figure = length

5th figure = diameter5th figure = diameter

6th figure = type of head6th figure = type of head

7th figure =surface finish7th figure =surface finish

2. Stock identification2. Stock identification

So 100- 5648 could mean:So 100- 5648 could mean:

1 = bought out parts, 0 = fasteners and 1 = bought out parts, 0 = fasteners and

fixingsfixings 扣件扣件和装备和装备 , 0 = nuts and bolts , 0 = nuts and bolts 螺螺母螺栓母螺栓

5 = 2cm, 6 = 10mm, 4 = hex RD hex (5 = 2cm, 6 = 10mm, 4 = hex RD hex ( 六六角，角， radial direction radial direction 径向径向 ), 8 = zinc ), 8 = zinc

coatedcoated

2. Stock identification2. Stock identification

The coding details of all stock items are normally The coding details of all stock items are normally

maintained in a list ormaintained in a list or catalogue catalogue called the called the stores stores

vocabularyvocabulary. .

This facilitates stock rationalization, whereby This facilitates stock rationalization, whereby

stock codes can be analyzed and any duplicate stock codes can be analyzed and any duplicate

stock can be easily highlighted. stock can be easily highlighted.

As well as codifying items into unique part As well as codifying items into unique part

numbers, inventory can also be broken down into numbers, inventory can also be broken down into

generic constituent areas. generic constituent areas.

2. Stock identification2. Stock identification

Categorization of stock may Categorization of stock may also be used foralso be used for

accounting or analytical reasons. accounting or analytical reasons.

Maintenance stock Maintenance stock

Project stock Project stock

Insurance stock Insurance stock

Strategic stock Strategic stock

3. 3. ForecastForecast

An effective stock control system involves An effective stock control system involves

decisions on:decisions on: how much stock to holdhow much stock to hold using forecasts of using forecasts of

usage and replenishment; usage and replenishment;

how much to order——order how much to order——order quantityquantity; ;

when to order for stock——when to order for stock——timing timing of orders. of orders.

3. 3. ForecastForecast

Each item stocked, decisions on how much Each item stocked, decisions on how much

should be held are made on the basis of demand should be held are made on the basis of demand

forecasting. forecasting.

Forecast comparisons use Forecast comparisons use sales datasales data and and

production dataproduction data from the from the bill of materials.bill of materials.

它它是是 MRPMRP 的重要文件，几乎所有的管理部门都要到它。的重要文件，几乎所有的管理部门都要到它。它能详细表列出装配结构中的零件状态及装配组件或零件它能详细表列出装配结构中的零件状态及装配组件或零件中包含的参数。中包含的参数。

3. 3. Forecast Forecast --- (1) EOQ --- (1) EOQ

经济订货批量 经济订货批量 EOQ =EOQ =

annual usage (annual usage ( 商品商品年年需求量需求量 // 使用量使用量 ))

acquisition cost per order (acquisition cost per order ( 每次每次订货成本订货成本 ))

stockholding cost per unit (stockholding cost per unit ( 单位单位商品年保管费商品年保管费 //库存费库存费 // 单位库存维持成本单位库存维持成本 ))

unit per costng Stockholdi

order per costn acquisitiousage years2

3. 3. Forecast Forecast 库存预测库存预测 --- (1) EOQ--- (1) EOQ

EOQ exampleEOQ example

经济订货批量经济订货批量 EOQ =EOQ =

So order quantity is 37.So order quantity is 37.

Annual usageAnnual usage 400400

Acquisition costAcquisition cost £50 per order£50 per order

PricePrice £150£150

Holding costHolding cost 20% of price20% of price

150%20

504002

= 37 units

3. 3. Forecast Forecast ---(2)---(2) safety stocksafety stock

This is the ‘This is the ‘lead-timelead-time’’（提前期） （提前期） which includes which includes

things like:things like:

time to identify then authorize replenishmenttime to identify then authorize replenishment

time to establish supplier contact and complete time to establish supplier contact and complete

paperworkpaperwork

time for the supplier to obtain or produce the time for the supplier to obtain or produce the

goodsgoods

time to have the goods deliveredtime to have the goods delivered

time for goods inwards/receiving and quality time for goods inwards/receiving and quality

checking time.checking time.

3. 3. Forecast Forecast ---(2)---(2) safety stocksafety stock

Safety stock (or buffer stock) Safety stock (or buffer stock)

A fixed quantityA fixed quantity

A given day’s worthA given day’s worth

A quantity calculated statistically based on A quantity calculated statistically based on

usage and supply factorsusage and supply factors

3. 3. Forecast Forecast ---(3)---(3) ROLROL

Re-order levels Re-order levels are used to trigger consideration are used to trigger consideration

of stock reordering action. of stock reordering action.

It is It is a stock levela stock level at which new stock at which new stock must be must be

ordered ordered if replenishment is to arrive before a if replenishment is to arrive before a

stockout occurs, provided demand remains as stockout occurs, provided demand remains as

predicted. predicted.

Understanding InventoryUnderstanding Inventory

The inventory policy is affected by:The inventory policy is affected by:

Demand CharacteristicsDemand Characteristics

Lead TimeLead Time

Number of ProductsNumber of Products

ObjectivesObjectives

Promote service levelPromote service level

Minimize costsMinimize costs

Cost StructureCost Structure

Cost StructureCost Structure

Order costs (acquisition/administrationOrder costs (acquisition/administration costs )costs ) FixedFixed VariableVariable

Holding Costs (stockholdingHolding Costs (stockholding costs ) costs ) InsuranceInsurance Maintenance and HandlingMaintenance and Handling TaxesTaxes Opportunity CostsOpportunity Costs ObsolescenceObsolescence

EOQ: A View of Inventory*EOQ: A View of Inventory*

Note:• No Stockouts• Order when no inventory• Order Size determines policy

Time

Inventory

OrderSize

Avg. Inven

EOQ: Calculating Total Cost*EOQ: Calculating Total Cost*

Purchase Cost ConstantPurchase Cost Constant

Holding Cost: Holding Cost: (Avg. Inven) * (Holding (Avg. Inven) * (Holding

Cost)Cost)

Ordering (Setup Cost):Ordering (Setup Cost):Number of Orders * Order Number of Orders * Order

CostCost

Goal: Goal: Find the Find the Order QuantityOrder Quantity that that

Minimizes These CostsMinimizes These Costs

EOQ:Total Cost*EOQ:Total Cost*

0

20

40

60

80

100

120

140

160

0 500 1000 1500

Order Quantity

Co

st

Total Cost

Order Cost

Holding Cost

EOQEOQ

EOQ: Optimal Order Quantity*EOQ: Optimal Order Quantity*

Optimal Quantity = Optimal Quantity =

(2*Demand*Setup Cost)/holding cost(2*Demand*Setup Cost)/holding cost

Setup Cost Setup Cost 采购采购 /(/( 生产生产 )) 准备成本 准备成本

经济订货批量（经济订货批量（ EOQEOQ ）模型）模型

经济定货批量经济定货批量 (Economic Order Quantity,EOQ)(Economic Order Quantity,EOQ) 的的假设条件。假设条件。

需求已知且常量；需求已知且常量； 一次订货量无限制；一次订货量无限制； 采购、运输无价格折扣；采购、运输无价格折扣； 订货提前期已知且常量； 订货提前期已知且常量； ...... 经济订货批量（经济订货批量（ EOQEOQ）模型的目标）模型的目标 经济订货量是一种决策模型，在一系列假设的基础上计算订经济订货量是一种决策模型，在一系列假设的基础上计算订货的最优数量。经济订货批量平衡了订购和持有存货的变动货的最优数量。经济订货批量平衡了订购和持有存货的变动成本。成本。

EQQ （定量订货法 Stationary）

经济采购 / 订货量（ Economic order quantity ， EQQ ）定义：使采购成本及存货持有成本加总值最小的采购量。适用于需求及成本都很稳定的情况。

模型假设：

每次订货的订货量相同，

订货提前期固定，

需求率固定不变。

经济订货批量计算公式如下： 2DS

Q*=

Ci

式中： Q*—— 经济订货批量 D—— 商品年需求量

S—— 每次订货成本

Ci—— 单位商品年保管费

EQQ （定量订货法 Stationary）

例：某仓库某种商品年需求量为 16000 箱，单位商品年保管费 2 元，每次订货成本为 40 元，求经济订货批量 Q* 。

EQQ （定量订货法 Stationary）

Q*= 2×16000×40

2

=800 箱

Q & Q & A !A !