Chapter 9 Storage & Warehouse Systems

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1 FACILITIES PLANNING & DESIGN Alberto Garcia-Diaz J. MacGregor Smith Chapter 9 Storage & Warehouse Systems 1. Warehouse Layout Model 2. Storage Equipment 3. Automated Storage & Retrieval System 1 Dedicated & Random Storage Section 9.3 Dedicated Storage A set of storage locations assigned to a specific product Decision variable x jk = 1 or 0 for assigning or not assigning product j to location k Measure of effectiveness Minimize total expected distance traveled 2 1

2 Input Data q = number of storage locations n = number of products m = number of input/output points (docks) S j = number of storage locations required by product j T j = number of trips in/out of storage for product j p i = percentage of travel in/out of storage to/from point i d ik = distance or time required to travel from point i to location k 3 Mathematical Model Min n j= 1 q k= 1 Tj S j ( m i= 1 p i d ik ) x jk n j= 1 x jk 1, k = 1,..., q q k= 1 x jk = S j, j = 1,..., n x jk = 0, 1 for j = 1,..., n; k = 1,..., q 4 2

3 Min n j= 1 q k= 1 Tj S j ( m i= 1 p i d ik ) x jk f k = m i= 1 p i d ik Min n j= 1 T S j j ( q k= 1 f k x jk ) = n j= 1 T S j j ( f 1 x j1 + f 2 x j2 + + f q x jq ) 5 Solution Procedure (a) Relabel the products according to the decreasing order of their T j / S j values (b) Find the values of f k location k and docks) (expected distance traveled between (c) Assign the locations to products according to their f-values from lowest to highest 6 3

4 Example 9.1 Warehouse s dimensions: 40 x 40 ft Storage Location: 10 x 10 ft One receiving dock at the northeast corner of the layout One shipping dock at the midpoint of the west side Two products A and B Product A: 100 pallets per week (T A =100) Product B: 80 pallets per week (T B =80) Product A requires 10 storage bays (S A =10) Product B requires 4 storage bays (S B =4) p 1 = 180/360=0.5 p 2 = 180/360= T A =100 S A =10 T A /S A =10 T B =80 S B =4 T B /S B =20 Consider Product B first and Product A second. p 1 = B B B B p 2 = A A A A A A A A A A 8 4

5 STORAGE SYSTEMS RACK STORAGE CAROUSELS AS/RS (Automated Storage Retrieval Systems) 9 RACK STORAGE SYSTEMS One of the primary methods of material storage Utilizes the vertical space in the warehouse Highly cost efficient 10 5

6 RACK TYPES Walk Through Racks Push Back Rack Very Narrow Aisle Racks Drive-in Racks Gravity Flow Racks Mobile Racks Double Deep Racks Rollout Shelf Racks Reel Racks Cantilever Racks Stacker Systems Wire Coil Racks Sheet Storage Racks 11 WALK THROUGH RACKS 12 6

7 FEATURES Provides easy accessibility to the adjacent aisles Pickers time is greatly reduced Allows more lighting into aisles Higher utilization of vertical space 13 PUSH BACK RACKS 14 7

FEATURES Pallet loads are literally pushed back into the rack When pallet is retrieved, the deeper pallet load automatically advance to the aisle High density and high accessibility

8 FEATURES Pallet loads are literally pushed back into the rack When pallet is retrieved, the deeper pallet load automatically advance to the aisle High density and high accessibility Used to store large number of pallets for a long time and then remove and ship them as seasonal products Used mostly in combination with drive-in racks 15 VERY NARROW AISLE RACKS 16 8

FEATURES Permits aisle widths less than 5 feet Provide significant floor space reduction Used at heights of 40 feet to 50 feet Provides 100% selective

9 FEATURES Permits aisle widths less than 5 feet Provide significant floor space reduction Used at heights of 40 feet to 50 feet Provides 100% selective storage Pallets are accessed with turret or side loader lift trucks Sometimes racks are designed with top and bottom monorails 17 DRIVE-IN IN RACKS 18 9

handling device used Parts are typically stacked one

10 FEATURES Used for bulky and light weight parts Parts are mainly in cartons Fork lift is the material handling device used Parts are typically stacked one over the other in large numbers 19 GRAVITY FLOW RACKS 20 10

ease Easy to move parts along the same row as less effort

11 FEATURES Used for parts in cartons Parts are supported on rollers in the rack system Material transfer is done with ease Easy to move parts along the same row as less effort is required due to the presence of rollers 21 MOBILE RACKS 22 11

FEATURES High density storage systems 100% utilization of pallet positions Number of rows of racks mounted on mobile bases Storage carriages are driven by electric

12 FEATURES High density storage systems 100% utilization of pallet positions Number of rows of racks mounted on mobile bases Storage carriages are driven by electric motors Used mainly in cold or ultra-cold warehouses where aisle space is at a premium Used when speed of product movement is not a major concern 23 DOUBLE DEEP RACKS 24 12

13 FEATURES It is like placing two rows of racks together Uses a deep reach lift truck for storage and retrieval Increases floor space usage to about 60% to 65% Used for high throughput operations Low initial cost High productivity Less equipment damage 25 ROLLOUT SHELF RACKS 26 13

14 FEATURES Specialized storage Mainly for delicate and costly parts Used for dies, measurement tools 27 REEL RACKS 28 14

15 FEATURES Special type of storage Mainly for cables and wires in reels 29 CANTILEVER RACKS 30 15

16 FEATURES Used to store long pipes and wood Parts are stored using the fork lifts Highly economical Can be used till heights of 22 feet 31 STACKER SYSTEMS 32 16

17 FEATURES Provided with an integral crane Easy handling of heavy items High storage and retrieval speeds Eliminates fork lift usage 33 WIRE COIL RACKS 34 17

18 FEATURES Used to store wire coils Used to house rubber hoses and hose assemblies 35 SHEET STORAGE RACKS 36 18

19 FEATURES Store material in the form of sheets Can be used to store glass Permits a height of 10 feet 37 CAROUSELS STORAGE ADVANTAGES High pick rates Motorized, computer controlled and independent rotating aisles of shelving Parts are carried to the picker rather than the picker going to the parts like in the case of racks Mostly set up in pods of 2 or 3 Pick rates vary from picks/person hour 38 19

20 CAROUSELS STORAGE DISADVANTAGE Adding more people cannot significantly increase pick rate Only one picker can operate at a given time Thus reduces the ability of the warehouse to respond to surges in demand 39 TYPES OF CAROUSELS STORAGE Horizontal Carousels Vertical Carousels Independent Rack Carousels 40 20

HORIZONTAL CAROUSEL 41 FEATURES It is a series of rotating bins of adjustable shelves driven on the top or bottom by a motor Rotation takes place on an axis perpendicular to the floor at

21 HORIZONTAL CAROUSEL 41 FEATURES It is a series of rotating bins of adjustable shelves driven on the top or bottom by a motor Rotation takes place on an axis perpendicular to the floor at about 80 feet/minute Horizontal lengths vary from 15 feet to 100 feet Height varies from 6 feet to 25 feet Prices start from $5000 and increases with the number of bins and weight capacity 42 21

VERTICAL CAROUSEL 43 FEATURES It is a horizontal carousel placed on its end and enclosed in sheet metal Height ranges from 8 feet to 35 feet They include

22 VERTICAL CAROUSEL 43 FEATURES It is a horizontal carousel placed on its end and enclosed in sheet metal Height ranges from 8 feet to 35 feet They include excellent item protection and security Only one shelf of items is exposed at a time All items cannot be looked at, at the same time Prices range form $10,000 onwards 44 22

23 INDEPENDENT RACK CAROUSELS FEATURES They are multiple one level horizontal carousel stacked on top of one another Order picker accesses several pick locations at any time Each levels operate independently and have their own power and communication link Hence they are very costly 45 AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (AS/RS) Improved Space Utilization 75 % of rack space can be recovered High saving in pickers time Allows quick access to goods via a system of shelves operating on a shuttle mechanism It brings the exact pick/store location to the operator Increases retrieval productivity by more than 2.5 times 46 23

24 AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (AS/RS) Access area of the system is ergonomically designed to present stored items at an ideal height for picking High employee safety and improved throughput 47 AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (AS/RS) 48 24

25 WAREHOUSE DESIGN STRATEGY 49 Automated Storage & Retrieval System Unit Load: W x L x H L H W 50 25

26 Bay: A vertical stack of unit loads from floor to ceiling Row: A series of bays located side by side Aisles: Spaces between rows The aisles are used for stacker cranes to move up and down between rows Each crane serves both sides of an aisle Light loads of less than 2500 pounds require a 6- inch clearance for rack support and crane entry Heavier loads require 9 inches 51 L H W Rack Length Crane Clearance Rack Aisle Aisle Unit Crane Bay Width Bay Height Bay 52 26

27 Some facts Racks may be feet high Served by computer-controlled stacker cranes carrying pound loads Can travel at speeds of 500 feet per minute in aisles that are only 6 inches wider than the cranes Savings of as much as 20 percent of the inventory cost Fully mechanized system requiring little labor to operate Single operator can handle a warehouse with 1000 s of parts Minimizes need of material handling equipment and material handling operations 53 Design Process 1. Dimensions and weight of the load to be stored 2. Number of units to be stored 3. Throughput rate per hour 4. Number of cranes needed 5. Number of rows required 6. Building height and load height 7. Number of bays 8. System length 9. System width 54 27

28 Number of cranes = throughput per hour (cycles/hour)x(efficiency) Loads stacked per bay = height of storage building (load height + clearance between stacks) -1 Bays per row = number of units to be stored (number of rows)x(number of loads vertically stacked per bay) System width = (aisle unit) x (number of cranes) System length = (width of bay + clearance) x (bays/row)+ (crane clearance) 55 Example Unit load: 36 x48 x24 pallet having a weight of 1400 lb 75 dual cycles per hour Total storage is 18,000 unit loads Height of the building is 80 Clearances of 4.5 from the ceiling and 6 from the floor for rack support Clearance equal to 6 between stacks Availability factor of 85% for cranes 56 28

29 L=4 Solution W=3 H=2 1. Loads stacked per bay = [80 ( )]/[ ] = Number of dual cranes = 75/(22 x 0.85) = 4.01 = 5 3. Number of rows = Bays per row = 18,000/(10 x 30) = Width = (aisle unit) x (cranes) = [3(4)+2](5) = 70 feet 6. Length = ( ) x = 235 feet 7. Height = 80 feet 57 29

P11 Handling and Storage E212 - Facilities Planning and Design

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