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6.1 Changeover Reduction (SMED)

In high-mix electronics manufacturing, the greatest threat to OEE (Overall Equipment Effectiveness) is not slow machine speed, but the idle time between production runs. An SMT line costing $1M generates zero revenue while stationary. Single Minute Exchange of Die (SMED) is the operational discipline of reducing changeover time to single digits (<10 minutes). This chapter mandates the separation of "Internal" and "External" setup activities to transform the changeover from a chaotic interruption into a choreographed "Pit Stop."

The SMED Philosophy: Internal vs. External

To achieve rapid changeovers, all tasks must be categorized and sequenced.

  • External Setup (OED)Techniques: Activities performed while the machine is still running the previous product.
    • Goal: Shift 80% of work to this phase.
    • Examples: Mounting reels to offline feeder carts, warming solder paste, retrieving stencils, verifying BOM data.
  • Internal Setup (IED): Activities performed while the machine is stopped.
    • Goal: Minimize this duration absolutely.
    • Examples: Unclamping the stencil, swapping the feeder cart, adjusting conveyor width.
  • The Mandate: Never perform an External task while the machine is stopped. Searching for swappinga stencil key or a missing reel during downtime is a process failure.

External Preparation Standards

Preparation must be completed and validated before the current run finishes.

  • Feeder Kitting: Components must be loaded onto "Mobile Feeder Trolleys" or "Exchange Banks" offline.
    • Validation: All reels must be scanned and linked to the feeder slot index using the offline docking station. This eliminates the need to scan/verify during the downtime window.
  • Stencil & Paste:
    • Retrieve the next stencil and visually inspect for damage 30 minutes prior to changeover.
    • Remove solder paste from the refrigerator 4 hours prior. Verify it has reached ambient temperature before the line stops.
  • Conveyor Settings: Pre-measure the width of the next PCB. Set manual conveyor spacers or record the digital width setting for immediate entry.

Internal Execution (The "Pit Stop")

When the last board of Product A exits the reflow oven, the changeover clock starts. This process requires a coordinated "Swarm" approach, not a single operator working sequentially.

  1. Printer Station:
    • Remove used stencil and squeegees immediately.
    • Load new stencil and apply fresh paste (already stirred).
    • Load new support pins (magnetic/vacuum) using a dedicated placement jig.
  2. Mounter Station:
    • Gang Swapping: Undock the entire feeder bank (Product A) and dock the pre-loaded bank (Product B). Do not swap individual feeders unless absolutely necessary.
    • Support: Adjust board support pins to Productthe Bdefined efficiently.coordinate map to prevent board flex.
  3. Reflow Oven:
    • Load the new thermal recipe immediately. Modern ovens require 5-15 minutes to stabilize temperatures. This should be the first step, not the last.

Streamlining the "Ramp-Up" (First Article)

The changeover is not complete until the first good board is produced. The First Article Inspection (FAI) is often the longest bottleneck.

  • Electronic FAI: Use a dedicated First Article Scanner (e.g., scanner with golden sample overlay) rather than manual caliper/microscope checks.
    • Target: FAI completion < 3 minutes.
  • Dummy Boards: Use a "Setup Board" (non-functional PCB) to verify print alignment and placement polarity before committing live components.
  • No "Tweaking": Program coordinates must be corrected in the offline CAD data, not "taught" on the machine during production. On-the-fly editing indicates a failure in process engineering.

Final Checklist

Metric / Action

Mandate

Changeover Target

< 10 Minutes (Last Good Board to First Good Board)

External Prep

100% Complete before line stop

Feeder Strategy

Mobile Cart Exchange (No single swaps)

Validation

Offline Scanning required

Oven Profile

Load First (to allow stabilization)

Paste Condition

Ambient Temp (verified)

Personnel

Min 2 Technicians (Swarm method)

Documentation

Digital Checklist (No paper searching)


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