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Material HandlingMaterial Handling
Material Handling System Design
Important calculations
OutlineOutline
Returnable containers
Space Utilization
Dedicated vs. random storage
Returnable containersReturnable containers
• Features– Stackability– Nestability
• Efficiency of returnable containers– Container Space Utilization
= usable cube(inside)/container envelope(outside)
– Storage Space Efficiency= usable cube(inside)/ storage cube(opening)
– Container Nesting Ratio= container height/ nested height
– Trailer Return Ratio= empty container capacity(#)/ loaded container
capacity(#)
usable
outside
Returnable Containers ExampleReturnable Containers Example
• Trailer Transports Returnable Containers– Containers are not palletized– No clearance between containers, or between
containers and walls
• Inside Dimensions: 18´´ x 11´´ x 11´´ • Outside Dimensions: 20´´ x 12´´ x 12´´ • Each Nested Container: 20´´ x 12´´ x 2´´ • Inside Trailer Dimensions: 240´´ x 120´´ x 120´´
Returnable Containers ExampleReturnable Containers Example
• Container Space Utilization = usable cube (inside) / container envelope (outside)
= (18´´ x 11´´ x 11´´ ) / 20´´ x 12´´ x 12´´
= 0.76
= 76% container efficiency
Returnable Containers ExampleReturnable Containers Example
• Storage Space Efficiency= usable cube (inside) / storage cube opening
• Assume the storage opening is 24´´ x 16´´ x 14´´
= (18´´ x 11´´ x 11´´ ) / 24´´ x 16´´ x 14´´
= 0.45
= 45% storage efficiency
Returnable Containers ExampleReturnable Containers Example
• Container Nesting Ratio = overall container height / nested height
= 12´´ / 2´´
= 6 : 1 ratio
Six nested containers use the same space as 1 closed container.
Returnable Containers ExampleReturnable Containers Example
• Trailer Space Utilization= space by max # containers in trailer / inside trailer dimensions– (Containers stacked vertically in one orientation)– How many containers fit in the trailer?
• 240´´ / 20´´ = 12 containers along the length• 120´´ / 12´´ = 10 containers along the width• 120´´ / 12´´ = 10 containers stacked vertically• Total # of containers = 12x10x10 = 1200
Trailer space utilization = = (18´´ x 11´´ x 11´´ ) (1200) / 240´´ x 120´´ x 120´´ = 0.76= 76% trailer utilization
Returnable Containers ExampleReturnable Containers Example
• Trailer Return Ration= empty container capacity(#)/ loaded container capacity(#)How many empty containers fit in the trailer?– One stack of empty containers
= 1 + (120´´ - 12´´) / 2´´ = 55– Total # of empty containers per trailer
= 55 x (240´´ / 20´´) x (120´´ / 12´´) = 6600
Trailer return ratio = = 6600 / 1200= 5.5= 5.5 full trips for every 1 return trip
Do we want to increase or decrease the Trailer Return Ratio?
Storage policies are also used to assign Storage policies are also used to assign slots to SKUsslots to SKUs
Dedicated (or Fixed Slot) Storage
A fixed number of slots is kept for each SKU
How many slots do we assign for each SKU?
Randomized (Open or Floating Slot) Storage Randomized (Open or Floating Slot) Storage does not assign fixed positions to SKUsdoes not assign fixed positions to SKUs
SKUs are stored in the closest open slot
Total number of slots must be equal to the maximum aggregate inventory
More difficult to control
Class-based storage is a mixture of Class-based storage is a mixture of Fixed-Slots and Randomized storageFixed-Slots and Randomized storage
?
?
Product families (classes) get fixed sections
Inside the section, SKUs are treated as randomized
Advantages? Which of the three uses less slots?
Let’s see which policy uses less spaceLet’s see which policy uses less space
0
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8 9 10
SKU1
SKU2
Aggregate
Max SKU1: 4
Max SKU2: 5
Max Agg: 6
Space Utilization - Storage patternsSpace Utilization - Storage patterns
Honeycomb Loss
Space you can’t use
Storing a different SKU would block access
Storing the same SKU would make FIFO difficult
Cube Utilization
=Load Cubic Volume
Storage Area Cubic Volume
Higher cube utilization Lower accessibility
Let’s see an example (Problem 7.30, p. Let’s see an example (Problem 7.30, p. 463)463)
42”36”
6”
48”Pallet and Load dimensions
Front viewFront view
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
Four tiers
Upper ViewUpper View
Flue: 15”
Aisle: 4.25’
Aisle: 4.25’
Palletized loads are stored one deep
What is the cube utilization of this storage arrangement?
First, let’s calculate the volume of the First, let’s calculate the volume of the load (including pallets)load (including pallets)
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
Load Volume = Height x Width x Depth
Height = 4 x (6” + 48”) = 216”
Width = 3 x 42” = 126”
Depth = 1 x 36” = 36”
Load Volume = 216 x 126 x 36 = 979,776 inches3
Now, let’s find the volume of the storage Now, let’s find the volume of the storage spacespace
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
Storage Volume = Height x Width x Depth
Height = 4 tiers x (pallet + load + clearance + beam)
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
48”
6”42”4” 4” 4”42” 42”
4”
3”3”
3”4”
Width = ½ beam + pallets + clearances + ½ beam
Depth = ½ flue + pallet + ½ aisle
Now let’s find the cube utilizationNow let’s find the cube utilization
Storage Volume = 244” x 145” x 94.5” = 3,343,410 inches3
Cube Utilization
= = 29.3%979,776
3,343,410
In the additional handout there are some In the additional handout there are some examples of typical rack configurationsexamples of typical rack configurations
