Chapter 2 – Product Storage & Handling (Supply Chain Logistics)

Determining Destination & Direction of Unloaded Products

  • All inbound materials arrive with a designated use (storage, distribution, production).
  • Immediately after unloading, items are usually placed in a staging area near the dock until their next destination is set.
  • Typical subsequent destinations:
    • Long- or short-term storage
    • Work-in-process / manufacturing cells
    • Order-picking zone
    • Outbound distribution lanes
  • Clearly marked delivery locations and legible product labels are mandatory.
  • Address / locator system (warehouse “street address”) gives structure for internal movement.
    • Mirrors postal addressing; every slot/rack/bin has a unique code.
  • Warehouse Management System (WMS) decides precise storage slot:
    • Matches SKU attributes & demand patterns with available space.
    • Tracks every movement; produces real-time inventory visibility.
    • Typical WMS logic questions:
    • Should SKU be co-located with regularly co-ordered items?
    • Will pallet be broken down later (unit → case → each)?
    • Environmental needs (temperature, humidity, hazardous segregation)?
    • Shelf-life / FIFO or LIFO requirements?
    • Bulk vs. rack suitability?
    • Special packaging or safety constraints?

Key Issues Affecting How Materials Are Stored

  • Twelve interrelated attributes, often grouped:
    • Mass, measurement, space
    • Volume, density, size
    • Depth, containment, process
    • Weight, configuration, delivery
  • Greatest impact: Volume, Density, Size
    • Volume
    • Combines quantity on hand & throughput (velocity).
    • Throughput=Units retrievedTime period\text{Throughput} = \frac{\text{Units retrieved}}{\text{Time period}}
    • Density
    • Large quantities → store as unit loads (pallets, large containers).
    • Higher volume ⇒ desire for high-density arrangements (less aisle space, smaller building footprint).
    • Particularly critical when high throughput & quick access are required.
    • Storage Density=Units storedFloor Area\text{Storage Density} = \frac{\text{Units stored}}{\text{Floor Area}}
    • Size
    • Most relevant for individual items or non-standard dimensions.
    • Pallets, cartons, totes tend to follow industry standards, so size matters less at unit-load level.
  • Summary mantra:
    • “Volume dictates the form; density refines the arrangement, provided throughput is not compromised.”

Forms in Which Materials Are Stored

  • Three typical outbound forms mirror inbound arrival:
    1. Pallet / Unit load
    2. Case / Carton
    3. Individual items (eaches)
  • Demand spectrum:
    • High demand → ship full pallets
    • Moderate demand → ship cases
    • Low or diverse demand → pick individual items
  • Facility context examples:
    • Manufacturing → Distribution Center: ships & stores mainly pallet loads.
    • Grocery DC → Retail store: stores pallets but picks & ships cases (e.g., soup cans).

Storage Options & Equipment Overview

Bulk Stacking (Floor Stacking)

  • Grouping identical unit loads directly on floor, stackable up to ceiling height.
  • Pros: no rack cost, rapid placement.
  • Cons: potential crushing, limited selectivity, poor rotation.
  • Decision factors: stackability, damage risk, dwell time, ceiling height.
Stacking Frames
  • Interlocking posts fitted to pallets; prevent crushing, allow multi-tier bulk stacks.
  • Disassemble for compact storage; costly & cumbersome.

Rack Systems

Selective Pallet Rack (single-deep)
  • Universal, aisle access to every pallet.
  • Variants
    • Standard (counterbalanced lift trucks)
    • Narrow-aisle (narrow-aisle reach trucks)
    • Double-deep (deep-reach trucks) – two pallets deep.
High-Density Rack Types
  • Drive-In / Drive-Through
    • Fork truck drives into lanes; 5–10 pallets deep; LIFO (drive-in) or FIFO (drive-through).
  • Push-Back Rack
    • Slightly inclined rails; carts slide; up to 5–6 pallets deep; LIFO.
  • Mobile Sliding Rack
    • Entire rack rows mounted on floor rails; open one working aisle at a time; maximizes density.
  • Double-Deep Storage
    • Two pallets deep per face; specialized deep-reach trucks; compromise between selectivity & density.
Cantilever Rack
  • Arms extend from single columns; ideal for long items (lumber, pipes, steel rods, sheet goods).

Repack / Small-Parts Storage

Shelving
  • Commercial-grade, heavier gauge than household.
  • Cheap, easy assembly, relocatable.
  • Joint methods: nuts & bolts, clips, rivets.
    • Evaluate vertical post gauge vs. load weight.
Bins & Kitting Stations
  • Small plastic/metal bins replenished by material handlers.
  • Support kitting (grouping items into kits: nuts & bolts for consumer products).
Drawer Storage (Cabinets)
  • For fragile or high-value items.
  • Lockable drawers with protective linings.

Palletized Storage & Pallet Considerations

  • Classic wood pallet still dominant; alternatives: plastic, rubber, paper, metal.
  • Material selection drivers:
    • Durability / number of trips
    • Load capacity
    • Cleanability (food, pharma) or corrosion resistance (chemical).
  • Mixed Pallet Loads: one pallet, many SKUs for a single customer order.
  • Pallet Pooling (e.g., CHEP, PECO)
    • Shared pallet pool reduces capital outlay, environmental impact, and storage burden.
    • Benefits: pay-per-use, spikes handled on demand, reduced waste, decreased staff oversight.

Specialty & Reusable Containers

  • Plastic Totes
    • Variety of sizes; protect & unitize; individual workers can hand carry.
  • Metal Containers
    • Corrugated steel walls; durable; high weight or abusive environments.
  • Wire-Mesh Containers
    • Collapsible; visibility; fold flat when empty.
  • Wooden Crates
    • Custom-built; economical one-way; favored by military (non-sparking with explosives).
  • Corrugated Paper Pallets & Boxes
    • Lightweight; improved via coatings/additives (moisture, fire resistance).
  • Slip Sheets
    • Thin corrugated sheets replacing pallets; require push-pull lift-truck attachments; reduce weight & cube.
  • Drums & Barrels
    • Liquids / powders; metal, plastic, or wood; lift-truck handling with special clamps.

Other Storage & Retrieval Methods

Carousels

  • Horizontal: bins travel around horizontal track; operator stands in one spot.
  • Vertical: bins/shelves travel in vertical oval (dumb-waiter style); enclosed for security.
  • “Goods-to-person” principle reduces walk time, improves ergonomics.

Vertical Lift Module (VLM)

  • Tower with inserter/extractor elevator between front & rear column of trays.
  • Higher throughput than carousels; multi-floor access points possible.

A-Frame Dispensing System

  • Two opposing sloped walls (forming “A”); slots pre-loaded with eaches.
  • Automated control drops items onto takeaway belt per order wave.

Flow Rack (Gravity Rack)

  • Skate wheels/rollers on slight incline.
  • Load rear / pick front (FIFO); higher density, fewer aisles.

Mezzanine

  • Elevated platform creating extra floor area above operations.
  • Common over shipping/receiving docks; underneath used for shelving or work cells.

Automated Storage & Retrieval Systems (AS/RS)

  • Family of computer-controlled rack systems using cranes or shuttles.
Man-on-Board AS/RS
  • Operator rides with cradle; ideal for piece or case picking in very high racks.
Fully Automated AS/RS
  • No onboard operator; CNC-like control.
  • Key components: storage rack, SRM (crane/shuttle), conveyors I/O, WMS interface.
  • Operate in very narrow aisles; guidance via floor rails or wire.
  • Advantages: reduced labor, higher security, optimal cube utilization, fast/high throughput.

Terms to Know (Quick Reference)

  • AS/RS: High-density automated rack system with automatic vehicles.
  • Cantilever Rack: Rack for long/oversized items; arms cantilever outward.
  • Double-Deep (Deep-Reach): Rack two pallets deep.
  • Drive-In / Drive-Through Rack: Fork truck drives into lanes for deep storage.
  • High-Density Storage: >1 unit deep/high; minimal aisles.
  • Kitting: Grouping items into a single shipment or production kit.
  • Mobile Sliding Rack: Rack rows on floor rails; open aisle as needed.
  • Push-Back Rack: Inclined rails; carts push previous loads back.
  • Single-Deep Storage: One pallet deep per face.
  • Vertical Lift Module (VLM): Elevator-based automated tray storage.

Ethical / Environmental & Practical Implications

  • Pallet Pooling & Reuse align with sustainability goals; reduce timber usage, landfill waste.
  • High-density systems lower building footprints → less land, energy for HVAC.
  • WMS & automation enhance inventory accuracy, reducing write-offs & obsolescence.
  • Drawer & secure storage protect high-value assets, lowering shrinkage.
  • Safety: Proper rack selection & load limits prevent collapses; specialized containers prevent sparks (military munitions) or contamination (food-grade plastics).

Real-World Connections & Previous Principles

  • Builds on fundamental materials-handling principles: unit load concept, standardization, space utilization.
  • Shows interplay between transport packaging (pallet, tote) and material flow (from dock → storage → picking → outbound).
  • Reinforces just-in-time (JIT) inbound: many items arrive only hours before inclusion in outbound customer orders.
  • Automation topics (AS/RS, VLM, WMS) connect to Industry 4.0, IoT, and data-driven supply chain management.

Key Numerical / Statistical References & Equations

  • Volume & throughput definitions above.
  • Density equation above.
  • Pallet depth examples: drive-in racks store 5–105\text{–}10 pallets deep.
  • Double-deep rack: 22 pallets deep; Deep-reach truck required.
  • Push-back rack typical depth: 4–64\text{–}6 pallets.

Study Tips

  • Memorize criteria triad: Volume→Form,Density→Arrangement,Size→Exceptions.\text{Volume} \rightarrow \text{Form}, \quad \text{Density} \rightarrow \text{Arrangement}, \quad \text{Size} \rightarrow \text{Exceptions}.
  • Be able to match storage method with product attributes (e.g., “long & heavy → cantilever”, “small high-value → drawer”).
  • Understand flow vs. static: gravity flow racks, carousels, VLMs all bring goods to picker.
  • Draw a diagram of warehouse zones: dock → staging → reserve storage → forward pick → outbound; note equipment in each.
  • Review safety & environmental checklists (hazard segregation, sanitation, pallet pooling benefits).