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SMED (Single Minute Exchange of Die)

Definition of SMED

• SMED stands for Single Minute Exchange of Die.
• A lean production technique developed by Shigeo Shingo.
• Aims to dramatically reduce the time required to switch a manufacturing process from producing one product to another.
• The term 'single minute' does not literally mean one minute; it implies that changeover should take fewer than ten minutes (i.e., fewer than a single-digit number of minutes).

Importance of SMED

• In Learning Unit 7 (LU7), process flexibility is identified as one of the eight characteristics of a lean production environment.
• Quick changeover is the practical tool that delivers this flexibility.
• Long setup times force manufacturers to produce in large batches to justify the downtime, which leads to:
    - Overproduction.
    - Excess inventory, both classified as waste by Shingo.
• SMED directly eliminates these forms of waste.

Core SMED Concepts

1. Internal Setup
      - Refers to tasks that can ONLY be done while the machine is stopped (e.g., physically swapping a die or mould).
      - Goal: Minimize these steps to reduce downtime.
   
2. External Setup
      - Refers to tasks that can be done WHILE the machine is still running (e.g., pre-staging tools, pre-heating materials).
      - Goal: Convert internal tasks to external tasks to reduce machine idle time.
   
3. Streamline
      - After identifying internal and external tasks, further simplify and standardize remaining internal steps to cut time even further.

Benefits of SMED (as per LU7)

• Enables smaller, more economical batch sizes, supporting pull system logic.
• Reduces Work-In-Progress (WIP) inventory buildup.
• Results in shorter lead times, enabling faster response to customer demand.
• Improves floor space utilization.
• Makes it possible for the Kanban system to function effectively by allowing rapid production response.

South African Example — SMED at a Beverage Bottling Plant

• Example: Coca-Cola Beverages SA at a bottling line in Wadeville, Gauteng.
• The plant produces both 330ml and 500ml cans on the same filling line.
• Previous Situation:
    - Switching between can sizes required a 90-minute stoppage for manual adjustments of filler heads, conveyor guides, and labeling equipment.
• After Implementing SMED Principles:
    - Conveyor guide adjustments were changed to external setup, utilizing pre-adjusted guide rails on a trolley that can be adjusted in under 2 minutes.
    - Filler head changes were standardized with color-coded quick-release clamps, drastically reducing internal setup time from 60 minutes to 8 minutes.
    - Total changeover time decreased from 90 minutes to under 12 minutes.
• Result:
    - The plant can now switch products more frequently in response to weekly retailer orders (e.g., from Shoprite or Pick n Pay).
    - Finished goods inventory was reduced by 30%, and overproduction waste was eliminated.

The Kanban Principle

Definition of Kanban

• Kanban (Japanese: signboard or visual card) is a pull-based signaling system that authorizes and controls the flow of production or materials.
• It is a cornerstone of lean production and Just-In-Time (JIT) manufacturing.
• Under the Kanban system, nothing is produced or moved until a downstream process sends a signal (a Kanban card) indicating it needs more stock.

Key Distinction: Pull vs Push Systems

• PUSH System (MRP)
    - Produces based on forecast and schedule.
    - Risk of overproduction and excess inventory occurs.
    - Top-down driven by Master Production Schedule (MPS).
• PULL System (Kanban)
    - Production occurs only when a demand signal is received.
    - Inventory kept minimal; only what is needed is produced.
    - Demand-driven from the shop floor upward.

Types of Kanban Cards (as per LU7)

1. Production Kanban
      - Authorizes a work center to produce a specific quantity of a component or product.
      - Triggered when downstream stock falls below the reorder point.
   
2. Withdrawal Kanban
      - Authorizes the movement of items between work centers (or stores).
      - Controls the flow between stages without overloading the system.

How Kanban Works — Step by Step

1. The assembly line uses the last container of Part X.
      - The Withdrawal Kanban on that container is detached and sent back upstream.
2. The upstream work center receives the Withdrawal Kanban.
      - This serves as the signal to release a full container of Part X.
3. The Production Kanban at the upstream center authorizes the manufacturing of a new batch of Part X to replenish the empty container.
4. The replenished container, bearing its Production Kanban, moves to the point of use.
      - Nothing extra is produced during this process.

Key Rules of the Kanban System

1. No component is produced or moved without a Kanban authorization.
2. Each container holds exactly the specified quantity — no more, no less.
3. Defective parts are never passed to the next stage.
4. The number of Kanbans in the system controls the maximum WIP level.
5. Kanban quantity is gradually reduced over time as part of a continuous improvement mechanism.

South African Example — Kanban at an Automotive Parts Supplier

• Example: Shatterprufe/Metair automotive glass supplier in Tshwane.
• The supplier provides cut windscreens to a nearby vehicle assembly plant.
• Previous Situation:
    - Operated on a push schedule based on weekly MRP forecasts, which led to large batches of unsold glass taking up floor space.
    - Resulted in frequent mismatches between production and actual daily needs of the assembler.
• After Implementing a Two-Bin Kanban System:
    - The assembly plant maintains two storage bins of pre-cut windscreens at the fitting station.
    - Upon emptying the first bin, the Withdrawal Kanban card is sent electronically to the supplier.
    - This serves as the supplier's only signal to initiate replenishment.
    - The supplier's cutting cell processes the Production Kanban and cuts exactly one bin-quantity of windscreens (e.g., 24 units).
    - The replenished bin arrives at the assembly plant within 4 hours, just in time.
• Result:
    - Finished glass inventory at the assembly plant was reduced by 60%.
    - The supplier no longer overproduces, which cut storage costs and breakage losses significantly.
    - This reflects the lean principle from LU7: Produce only what is needed, when it is needed.

Summary Comparison of SMED and Kanban