Upload
buidang
View
215
Download
1
Embed Size (px)
Citation preview
1
Warehouse Inbound and Storage
Chen ZhouFall, 08
4/14/2005
Major operations in a DC or warehouse
Receiving Function
Unload/stage Inspect Put Away
StorageFunction
Shipping Function
Load Pack Order Pick
CrossDock
Avg Operation Cost 55%
2
4/14/2005
Receiving
TasksCheck, inspect, unload, Record, stage, re-palletize
FacilitiesDocks, lift trucks, forklift, mobile conveyors, cart, Computer terminals, bar code printer
DecisionsSchedule of arrivalsPrioritiesStagingProblem handling
Cost ~ 10% of operation cost
4/14/2005
Putaway
TasksMove goods storage locations
FacilityPallet truckLift truck more in following slides
DecisionsWhere WhenEquipment
Cost ~ 15% 2-pallet pallet truck
3
4/14/2005
Counter-balanced forklift
Most popularRequires 12 - 18 aisleCapacities 3000 lbs - 80,000 lbsCan stack two upCan go highGasoline, propane, natural gas, electric
4/14/2005
Narrow Aisle straddle trucks
Require 7 - 8 aislesCapacities available are 3000# & 4000#Load must be uniformLoad must fit between outriggersBottom beam in rack recommendedTypically custom built
Require floor with high flatness, especially when heavy loads are going high
4
4/14/2005
Turret truck (for very narrow aisles)
Requires 48 - 72 aisle25 & higherUp to 4000# capacityAbility to be maneuvered in & out of aisleServices both sides of aisleFull pallet put awayFull or partial pallet pickingLoads must be positions at the aisle by other equipmentDemand high quality floors
Storage and Handling
Chen ZhouSummer, 08
5
4/14/2005
Storage
TasksHold inventory
MethodsFloor, floor stackingPallet rackGravity flow rack, push back Bin shelving
ObjectivesSpace utilizationResponseLabor cost
DecisionsFloor, equipment, slotting,
How to measure the efficiency of storage?
4/14/2005
Warehouse parameters: pick face
2 D space with direct access of unique skus
6
4/14/2005
Warehouse parameters: sku density
Sku density = No. of skus / unit floor footageIn floor stacking example
Floor: 30 foot length, 4 skus. Sku density = 4/30 = 0.133
In binsRack: 12 foot, 360 skus, Sku density = 360/12 = 30
The higher the sku density, the higher the potential for shorter travel in order pickingWhat do we loose with higher sku density? Volume
4/14/2005
Warehouse parameters: pick density
Pick density = picks / unit distance traveledEg.
In a large warehouse, the distance from the I/O to the far most corner is 400 meters. Each pick is for one pallet which is uniformly distributed throughout the warehouse. The average pick density is 1 per 200 meters traveled. In a picking zone that is 50 meters long, a picker on an averagepicks 100 skus in each sweep, the average pick density is 2 skusper meter traveled.
Is higher density good?How to gain higher pick density? A major design and operation challenge.
7
4/14/2005
Storage: floor stacking
No storage equipment is requiredItems must be able to support the weight: special packaging may be requiredCan achieve good space utilization with limited SKUsDoes not support FIFOLow sku density
4/14/2005
Floor storage with tier rack
More flexible than pallet racksOften used for storage centric applications
8
4/14/2005
Pallet racks and bin shelving
4/14/2005
Gravity flow racks
Allows higher sku density while maintain high volume for each skuYOU may have seen gravity flow storage in supermarket: milk
9
4/14/2005
Effectiveness of pallet flow racks
4/14/2005
Carousels: parallel processing
10
4/14/2005
Vertical carousels
Small itemsValuable items
4/14/2005
AS/RS with stacker crane
AS/RSMiniloadUnitload
11
4/14/2005
Space requirements estimates
Recall 3PL for home appliance company?Throughput per day
Receiving 50 - 75 truckloads, Assume 2,560 ft3/truck
Holds 4 weeks of inventoryLittles Law
WIP = TH * CT
WIP = 75 * 2,560 ft3/day * 4 weeks * 5.5 days/week = 4,224,000 ft3
Assume stacking 20 ft high, space for storage = 211,200 ft2
Space utilization: 50 (70%), plus aisles, etc. Reality: 657,000 ft2 (14 football fields), 140,000 unit storage
4/14/2005
Slotting priority: cubit-per-order index (activity ratio)
What factor (s) should we consider to prioritize the slotting with known economic terrain (contours)?
Pick (restock) frequency: fast movers should occupy better locations.
Space requirement for the item. This may not be obvious.
12
4/14/2005
E.g.
Skus A and B have same pick frequency of 10/day. A takes 2 pallet slots and B takes 1 slot (can be due to lower inventory turns or smaller cases). Which one should be placed in more convenient location?
A A BI/O
B A AI/O
355.2*101*102
1
=+== =i
iiAB DfTC
252*105.*102
1
=+== =i
iiBA DfTC
4/14/2005
Does this make sense
The objective is to visit closer cell more frequently, regardless of what is in there.pi pick frequency picks/weekvi vol in storage ft3The cell visit frequency is equal to
For the example: ARA = 10/2=5, ARB = 10
A A BI/O
B A AI/O
355.2*101*102
1
=+== =i
iiAB DfTC
252*105.*102
1
=+== =i
iiBA DfTC
i
i
vp
= COI)(or RatioActivity
13
4/14/2005
What can impact the storage requirements
Item size, storage/handling characteristicsReplenishment frequency
4/14/2005
E.g.
Top 6 items has steady daily demand in a small warehouse using dedicated storage. All orders consists of single item and there is no batching. The items are stored in pallets on shelves. Someone used EOQ model to decide the replenishments frequencies. Please find assignment priority. Let 1 week = 5 days.
A B C D E F Daily demand (cases) 200 100 1000 30 50 50
Cases/pallet 50 50 500 30 10 25 Replenishments Weekly Weekly Bi-wkly Daily Weekly Bi-wkly
Daily demand (pallets) 4 2 2 1 5 2 Space required (pallets) 20 10 20 1 25 20
AR 10 10 50 30 2 2.5 Priority 3 3 1 2 5 4
14
4/14/2005
Dedicated vs. randomized (shared) storage
Dedicated storage is more convenientShared storage provides higher storage efficiencyHybrid
Dedicated zones but shared within zonesDedicated in pick and and shared in reserve
=
niijmj
D vV1 1
max :storage Dedicated
=
niijmj
vVS11
max :storage Shared
4/14/2005
Comparison of randomized/dedicated
Randomized takes less storage requirements since averages variability across productsWhich provides higher pick density?
If all skus have similar activity ratio, the smaller space in ramdomized storage should lead to higher pick densityIf activity ratios vary a lot, the frequent visit to convenient locations in dedicated storage can lead to higher pick density
Hybrid - zone based storage
15
4/14/2005
Inbound and storage summary
DC operationsInbound operationsStorage methodsEquipment and handlingStorage metricSlotting priorities
4/14/2005
Questions
What are the important operations in a warehouse or DC?What are the pros and cons of high sku density?What can be used to achieve high sku density while maintain volume?Why DCs often use different equipment for transport and rack handling?What factors affect slotting priorities?What affect the storage volume requirement?
16
Order processing and order picking
Fall 08Chen Zhou
4/14/2005
Order picking
Most demanding: ~ 63% of operating costs in a typical warehouse, survey by the Warehouse Education and Research Council. It was identified as #1 area for improvementBecome more significant due to emphasis on just-in-time (JIT), cycle time reduction, quick response, and marketing strategies such as micro marketing and megabrand strategies
Smaller orders more frequently and more accuratelyMore stock keeping units (SKUs) be available for the customers.
What is involved to ensure high efficiencyLayout and storage strategiesSlottingOrder processingOrder picking system designOrder picking operational specifics
SequencingBatching
17
4/14/2005
Order processing
AvailabilityLoca tion
Generate
4/14/2005
Form of pick list: sequenced labels
Sequenced sticky labels
18
4/14/2005
Other form of pick list
Data table for PLC for pick to lightSequenced voice instructions to pick to voice (later)Instructions to automated systems
4/14/2005
Issues in order processing
ObjectivesMinimize travel (or other handling)
Subject toThroughputCycle timeLine balancingTime window, batch to waves
Day in a weekDeparting timeItems to pass to other DCs
WMS normally support this function.
It requires customization and adaptation
19
Order picking
Chen ZhouSummer 08
4/14/2005
What is involved in order picking
TravelSearchPick(sort)Put(sort)
20
4/14/2005
What affects order picking
StorageType of storage affects sku densitySku density affect pick densitySlotting affect total travel
Order picking system designOne at a timeBatching in various ways
OperationsSequencingSchedule
TechnologiesPick to light can reduce search time and improve accuracy
4/14/2005
Parameters of orders
Number of line itemsNumber of items in a lineSize and weight of an item
PalletCases (cartons)Break pack
21
4/14/2005
Picking strategies
One item or one line per tripBigSorting or consolidation is needed later
One order per trip
201361
No
54
321
NameSku ID
4/14/2005
Picking strategies
A batch of orders per tripSort while pick or sort after
6
1No
2
1
NameSku ID
2
6
1No
3
2
1
NameSku ID
22
4/14/2005
Picking strategies
A portion of an order (zoning)Too bigFor faster responseConsolidation while picking or later
20
19
18
17
16
15
14
13
12
11
10
9
8
7
20
1
3
6
1
No
6
5
4
3
2
1
NameSku ID
4/14/2005
Picking strategies
A portion of many orders (batching + zoning)
Economy of scaleHigher pick densitySorting while picking or sort after
20
19
18
17
16
15
14
13
12
11
10
9
8
7
20
1
3
6
1
No
6
5
4
3
2
1
NameSku ID
20
19
18
17
16
15
14
13
12
11
10
9
8
7
20
1
3
6
1
No
6
5
4
3
2
1
NameSku ID
20
19
18
17
16
15
14
13
12
11
10
9
8
7
20
1
3
6
1
No
6
5
4
3
2
1
NameSku ID
23
4/14/2005
Travels
Pick one at a time
4/14/2005
One order at a time
Benefit/drawbackTravel: downSearch: no changePick: may have some change due to handlingPut: may have some change
24
4/14/2005
Batch picking: multiple-orderone-picker
Benefit/drawback Travel: downSearching: not muchPicking: not muchPutting:
up if sorting on the tourno change if sort later but sorting is required downstream
Almost always good for single line orders
4/14/2005
Batch picking of large orders with truck
25
4/14/2005
Batching picking with push carts
Pick to order specific containers, no sorting is required afterwards
4/14/2005
Time based batching: wave picking
Many DCs organize batches based on time window Truck/ship/train departure timesShiftsCycle timesDelivery requirements
DesignationsMacon wave10 AM waveYellow wave
26
4/14/2005
Zone picking: one-order-multiple-picker
Benefit/drawbackTravel: not much changeSearch: downPick: no changePut: no changeLess training, higher accuracy
4/14/2005
Zone picking examples
No Sorting is required Sorting is required
27
4/14/2005
Batching + Zoning
Very useful in regional distribution centers that supply many storesBenefit/drawback
Travel: downSearch: downPick: can go down with sophisticaded design.Put: down because sorting is normally later
4/14/2005
Order picking strategy: fast pick area
Benefit/drawbacksTravel: down in pick areaSearch: not muchPick: may reduce if more convenientPut: similarRequire replenishment or double handling
ReserveForward/Fast pick
Restock
28
4/14/2005
Forward/reserve
The forward takes convenient locationsNear the shippingAt floor levelNear conveyor
The reserve takes less convenient locationsFar awayHigher levels that require special equipment for picking
Forward requires Quick searchEasy managementOften dedicated storage
Reserve requiresSpace utilizationOften shared or randomized storageThe share may be restricted to a special area, like one rack - hybrid
4/14/2005
A pick/reserve module
The pick at the bottom Reserve above
29
4/14/2005
Pick from pallet in a rack module
Fast pick from frontPick from reserve in the backReplenish from back
4/14/2005
Pick from reserve
Requires expensive equipmentTakes more time
30
4/14/2005
Pick from pallet to conveyor
4/14/2005
Finding skus and volume for fast pick area
Engineering for fast pick areaWhich sku should go to fast pick areHow much if know number of skus to share know number of volume?
n no. of skus in fast pickfi flow vol/year, m3 / year (month) pi pick frequency, picks / year, cpoi cubic per order, m3 / order, vi vol of restock to fast pick area of i, m3 / restockV total volume available in fast pickcr cost of restock, $/restock (assuming constant)s savings of a pick: fast pick vs. reserve.
31
4/14/2005
Fast pick calculatoin
Fast pick priority, descending order of
i
i
cpop
i = ciencyLabor Effi
4/14/2005
E.g. Please prioritize the claim to fastpick area
1333330.0060.10.30.1400200I
415630.2560.80.40.4800400H
59410.850.81.01.0850800G
92051.01.02.0250100F
72890.8640.60.60.61000250E
81110.450.50.51.09050D
66940.721.00.80.6750500C
343220.23140.51.50.2512341000B
255560.450.510.545002500A
PriorityEfficiency^2
Cpo
VB/A
H
E
W
D
L
C
No/mthB
Picks/mthA
Sku
32
4/14/2005
Fast pick volume assignment, n skus, vol V
Equal volume
Equal time
Optimum with respect of total cost
nVvi =
Vf
fv n
jj
ii
=
=
1
Vf
fv n
jj
ii
=
=
1
4/14/2005
E.g.
Consider 2 skus. The flows are 16 and 1 m3/ yr. They are to share 1 m3 storage in fastpick.
Equal Space Equal time Optimal V f/v v f/v v f/v
A 0.5 32 16/17 17 4/5 20 B 0.5 2 1/17 17 1/5 5
Total 1 34 1 34 1 25
DiscussionsWhat does optimum mean?
33
4/14/2005
Order picking summary
The most important operation in a DCTry to reduce time for travel, search and othersStrategies
Storage and handling SlottingBatchingZoningForward/reserveTechnologies (to follow)
ConveyorsPick to light (voice), put to light
4/14/2005
Order picking review questions
What is pick list?What are the order picking strategies?Are the priorities for slotting and fastpick the same?What strategy is suitable for which type of orders?What is one of the most important direct efficiency objectives in a DC?
34
Order Picking Technologies
Chen ZhouFall, 2008
4/14/2005
Popular technologies that assist order picking
ConveyorsPick to light and put to lightPick to voiceA framesHigh speed sorting systems
35
4/14/2005
Conveyor
ConveyorsTransportBuffer: smooth flow and improve utilizationExtends the good locations throughout the facilityCan yield very high throughput
Important for high throughput systems, more and more popular in US, often miles to tens of miles in a facilityRequires significant investment
North
EASTCENTRALSOUTHWEST
Satellite Merges
Final Merge
Main Merge
: Accumulation
A
B
C&D
Sortation Reciculation Zone for PickCrossdocked items
SorterSpurs
How to draw economic terrain
contours
4/14/2005
Schematic of a picking zone
Receiving docks
Sort to shippingdocks
Pick module Forward
Reserve
36
4/14/2005
A graphical view of a pick module
A case picking zone
Restockpick
pick
pickRestock
4/14/2005
Pick to light in station lighting
Reduce search timeIncrease accuracyReduce training
37
4/14/2005
Put-to-light
Present one sku to the pickerScan the skuLights associated with order containers will come onPut items into light indicated boxes
Put as indicated
4/14/2005
Differences between pick to light & put to light
Pick to lightSkus are stationary and wait to be pickedOrders triggers the light
Put to lightOrders are batched and waitSku triggers the light
38
4/14/2005
Application example
A DC has two types of productsStapleFlow through
Sales would try to convince you their technology is best for bothWhat do you think?
4/14/2005
Pick to voice
Scan the orderActivate voice instructions for the pickerPicker pick and place into the order containerPicker confirm picking complete verballyNo Sorting is required in this example
39
4/14/2005
Comparison of pick to light and pick to voice
Sales people will try convince you their technology is the best in terms of
CostAccuracy
Voice: number of players required is proportional to Light: number of lights required is proportional to
Voice: Serial mediaVision: Parallel media
4/14/2005
Automated picking with A - Frame
A frameAutomated dispensing
40
4/14/2005
Automated order fulfillment initiation
Container typesLabels and tracking
4/14/2005
Sorting
ManualBarcode directedVision directedHigh speed sorters
41
4/14/2005
Sorting: High Rate Tilt Tray
12,000 items/hr.Unit sorterCan sort to two sides
4/14/2005
High speed conveyor sorters
Shoe sorter
Roller sorter
42
Other Outbound Operations
4/14/2005
Checking, packing and packaging
43
4/14/2005
Shipping
4/14/2005
Other: returns
44
4/14/2005
Warehousing review questions
What does SLP stand for and what does it involve?What is the default measure of distance between activities in typical software?What is the most direct quantitative measure of operational efficiency in layout problems?Are you comfortable with equal distance contours?
4/14/2005
Warehousing intro
What are the purposes of a warehouse (DC)?What are the main operations in a warehouse?Inventor positioning considerationsWhat are the direct and concrete objectives in a warehouse?
45
4/14/2005
Warehouse operations
What are some of the material movement equipment used?What are categories of loads moved?What are the storage methods?How do you measure the storage methods?What factors are the most important in deciding an skus location?What are the advantages of carousel vs. bin shelving?What is the advantage of flow racks (pallet or case)?
4/14/2005
Order picking
How do storage strategies affect order picking?What are the order picking strategies?What strategy is suitable for which type of orders?What are some of the technologies used to improve accuracy and speed?What does conveyor achieve in a DC?What are the pros and Cons of pick to light, put to light and pick to voice?What is one of the most important efficiency objectives in a DC?
46
4/14/2005
Wal-Mart DC Examples
Chen ZhouFall, 2008
47
4/14/2005
Port DC and RDC for Wal-Mart
Pallets are separate, some cases contain multiple skus
Fast movers are in palletsComments
400500People ~
100 cases/man hour45 cases/man hourProductivity15,000/hour6,250/hourThroughputSupport 85 storesSupport RDCs and storesFunction5,0003,000Skus ~
1.3 mil ft22 mil ft2 (35 football fielsds)Size
RDCPort DCMeasure
4/14/2005
Wal-Mart DC
48
4/14/2005
Overview of port DC and RDC
Port DCGoods come in mostly in cases in containersPalletizationStorage
Pick area: shared slots in zones in pallet racksReserve: tier racks, deep lane storage, floor stacking, high density difficult to pick
PickingPalletsCases
RDCGoods comes in from
Port DCManufacturersOther RDCs
Depalletization/palletizationStorage
RacksStaging
PickingCasesBreak pack23 miles of conveyors
4/14/2005
Robotic de-palletizer
49
4/14/2005
Port DC case picking
Order -> Barcode -> pallet(s), An associate place the pallet into pick areaPicker drives a fork lift picks cases in that aisle to the pallet, scan the case and the palletOnce completed, a pallet truck driver is informed to move the pallet to the dock
4/14/2005
Order picking schematic in port DC
Vertical economic terrainPallet picking vs. case picking
Slow moving takes better locations
Separation of picking and transporting
50
4/14/2005
Lagrange DC OperationMaterial Flow
MainMerging(16 to 4)
MiniMerging(4 to 2)
Sorter
Staple Goods(By Conveyor)
Distribution Goods(By Conveyor)
Distribution Goods(By Pallet Truck)
All Goods(By Conveyor)
Staple Goods(By Pallet Truck)
4/14/2005
Pick module in conveyorized system
Receiving docks
Sort to shippingdocks
Pick module Forward
Reserve
51
4/14/2005
Order picking
Pick to conveyorStack of bar code labelsPlace the label on carton, put the carton on conveyorBase pick rate: 450 cases/hour, or 8 second/case, including other times.Conveyor capacity: 20,000 cases/hour
Break packPeople to storagePick to lightPut to light
Wal-Mart do not open a case unless the orders will require its entire contentWhat does this mean in fill rate and inventory level?What will be the alternatives?
4/14/2005
Discussions
What additional engineering is needed to achieve high pick rate?
Sequence in SKU sequence along the pathUse large time windows to batch orders
52
4/14/2005
Questions and discussions