Material Handling System Design Important calculations Outline Returnable

Material Handling System Design Important calculations

Outline Returnable containers Dedicated vs. random storage Space Utilization

Returnable containers • Features – Stackability – Nestability outside usable • 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(#)

Returnable Containers Example • Trailer Transports Returnable Containers – Containers are not palletized – No clearance between containers, or between containers and walls • • Inside Dimensions: 18´´ x 11´´ Outside Dimensions: 20´´ x 12´´ Each Nested Container: 20´´ x 12´´ x 2´´ Inside Trailer Dimensions: 240´´ x 120´´

Returnable Containers Example • Container Space Utilization = usable cube (inside) / container envelope (outside) = (18´´ x 11´´ ) / 20´´ x 12´´ = 0. 76 = 76% container efficiency

Returnable Containers Example • Storage Space Efficiency = usable cube (inside) / storage cube opening • Assume the storage opening is 24´´ x 16´´ x 14´´ = (18´´ x 11´´ ) / 24´´ x 16´´ x 14´´ = 0. 45 = 45% storage efficiency

Returnable 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 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 = 12 x 10 = 1200 Trailer space utilization = = (18´´ x 11´´ ) (1200) / 240´´ x 120´´ = 0. 76 = 76% trailer utilization

Returnable 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 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 slots 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 does not assign fixed positions to 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 Fixed-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 space Max SKU 1: 4 Max SKU 2: 5 Max Agg: 6

Space Utilization - Storage patterns Storing a different SKU would block access Honeycomb Loss Space you can’t use Cube Utilization Storing the same SKU would make FIFO difficult Load Cubic Volume = Higher cube utilization Storage Area Cubic Volume Lower accessibility

Let’s see an example (Problem 7. 30, p. 463) Pallet and Load dimensions 48” 6” 42” 36”

Front view Four tiers 4” 48” 6” 4” 3” 42” 4” 3” 3”

Upper View Aisle: 4. 25’ Palletized loads are stored one deep Flue: 15” Aisle: 4. 25’ What is the cube utilization of this storage arrangement?

First, let’s calculate the volume of the load (including pallets) 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 inches 3

Now, let’s find the volume of the storage space Storage Volume = Height x Width x Depth Height = 4 tiers x (pallet + load + clearance + beam) Width = ½ beam + pallets + clearances + ½ beam Depth = ½ flue + pallet + ½ aisle

Now let’s find the cube utilization Storage Volume = 244” x 145” x 94. 5” = 3, 343, 410 inches 3 Cube Utilization 979, 776 = 3, 343, 410 = 29. 3%

In the additional handout there are some examples of typical rack configurations