4.1 Work Order Execution Model

The Work Order (WO) is the executable container for the product. If the ERP is the "Architect," the WO is the "contractor" on site. It binds the Bill of Materials (components), the Routing (path), and the specific Serial Numbers (instances) into a single trackable entity.

The Routing (The Path)

The Routing is the logical sequence of operations a unit must traverse. It dictates where the unit goes; the SOP dictates what happens there.

Structure Hierarchy

1. Operation (Step): A logical activity (e.g., "Step 10: SMT Top Side").
2. Work Center: The group of interchangeable resources capable of performing the Step.
3. Station: The specific physical asset (e.g., "Manual-Assy-01").

Route Enforcement Logic

• If Unit scans at Step 20 before completing Step 10 → System Blocks (Out of Sequence).
• If Unit scans at Station X, but Station X is not mapped to the active Step → System Blocks (Invalid Route).

WIP States (The Lifecycle)

A unit does not simply exist; it exists in a state. Define strict state transitions to prevent data corruption.

Core States

• Queued: Ready for the station.
• Active (In Process): Currently being worked on.
• Completed: Successfully finished the step.

The "Single Active" Rule

• If a Serial Number is "Active" at Station A → It cannot be scanned at Station B.
• Reasoning: A physical object cannot be in two places simultaneously.

Station Execution Logic

Do not force a rigid "Start/Stop" process on high-speed manual lines. Select the execution mode based on the process type.

Mode A: Precision (Start-Stop / Dual Scan)

• Use Case: Automated Machines, Long Duration Manual Tasks (>5 mins), or Repair Stations.
• Flow:
  1. Scan In: Validates route, starts timer, changes state to "Active."
  2. Execute: Machine runs or Operator works.
  3. Scan Out: Stops timer, records result, changes state to "Completed."
• Benefit: Exact cycle time measurement (excluding transport time).

Mode B: Rapid (Single Scan / Backflush)

• Use Case: High-volume manual assembly, Visual Inspection, Packing.
• Flow:
  1. Execute: Operator performs the task before interacting with the system.
  2. Scan: A single barcode scan triggers the transaction.
• System Logic:
  • Action: The scan implicitly performs "Check In" + "Pass Result" + "Check Out" instantly.
  • Cycle Time: Calculated as (Current Scan Timestamp) - (Previous Station Scan Timestamp). Note: This includes transport time.
• Risk Control:
  • The "Wasted Value" Risk: Because the operator works before scanning, they might assemble parts onto a unit that failed a previous step but wasn't marked.
  • Mitigation: Use visual cues (Paint dots/stickers) from previous stations or Overhead Monitors to flag bad units before pickup.

Rework and Repair Loops

Failures happen. The system must handle them without breaking traceability. Do not allow operators to simply "put it back on the line."

The Repair Loop Logic

• Entry: When a unit fails, it leaves the Main Routing and enters a "Repair Sub-Routing."
• Action: Diagnostic codes and replacement parts are recorded.
• Re-Entry:
  • If critical component replaced → Force Re-Entry at Step 10 (Start Over).
  • If minor touch-up → Re-Entry at current Step.

Pro-Tip: Never delete a failed test record. Keep the "Fail" result and append a new "Pass" result after rework. Auditors need to see the failure to believe the success.

Final Checklist

Category	Metric / Control	Threshold / Rule
Sequence	Route Enforcement	100% Hard Block on out-of-sequence scans
Execution	Mode Selection	Use "Single Scan" for manual lines < 2 min cycle
Execution	Mode Selection	Use "Dual Scan" for machines/ovens
Traceability	Cycle Time (Mode B)	Includes Transport Time (Delta from Prev. Station)
Rework	Loop Control	Failed units must enter a designated Repair Route
History	Immutability	Never overwrite "Fail" results; append "Pass"