3.4 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"Contract" issued to the shop floor. It authorizes the consumption of specific materials to produce a specific quantity of goods by a specific date. A unit without a valid, active WO is "Unplanned WIP"—a ghost asset that exists physically but not financially.

The WO State Machine

Do not manage production on site.vague Itterms bindslike "started" or "finished." Adopt a rigid State Machine to control cost accumulation and schedule adherence.

1. Created (Planned)

• Owner: ERP / Planner.
• Definition: The demand exists, but resources (material/capacity) are not yet committed.
• Constraint: Invisible to the BillShop ofFloor Operators. Block Execution.

2. Released (Dispatch)

• Owner: Production Manager.
• Definition: Materials are allocated (components)picked), and the line is scheduled.
• Action: The MES locks the BOM Revision and Route Revision at this moment.
• Logic: If Master Data changes after release → Then WO does not update. (You cannot change the recipe while the cake is in the oven).

3. Running (Active)

• Owner: MES / Operator.
• Definition: The first unit has passed the first operation (Scan-in).
• Metric: WIP Time (Cycle Time) clock starts ticking.

4. Hold (Exception)

• Owner: Quality / Engineering.
• Definition: Production stopped due to shortage, machine breakdown, or quality spill.
• Constraint: Block all transactional movement (Move/Consume) until released.

5. Closed (TECO - Technical Completion)

• Owner: ERP.
• Definition: Target quantity reached or order short-closed.
• Action: Release unused material reservations. Post final Good Receipt. Calculate Variance.

The Digital Traveler (Route Enforcement)

Paper travelers are "Opt-in" compliance. Digital Travelers are "Forced" compliance. The WO dictates the Routing (path)Sequence of Operations), and the specificMES Serialenforces 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.it.

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 EnforcementSequential Logic

• IfRule: UnitA scansunit atcannot Stepenter 20Operation beforeN completinguntil Stepit 10has →successfully passed Operation N-1.System Blocks (Out of Sequence).
• If UnitOperator scans unit at StationOp X,30 (Test) but StationOp X20 (Assembly) is not mapped to the active Step"Incomplete/Fail" → SystemThen BlocksMES (rejects scan: "Invalid Route).Process Step."

WIP

Parallel States& (TheAlternative Lifecycle)

Routes

A unit does not simply exist; it exists inSometimes a state.line Definesplits strict(e.g., state3 transitionsparallel to prevent data corruption.testers).

Core States

• Queued:Logic: ReadyDefine forOp the30 station.as a "Operation Group" containing Resource_A, Resource_B, Resource_C.
• Active (In Process):Constraint: CurrentlyAny beingresource workedin on.
• Completed:the Successfullygroup finishedsatisfies 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 deletehard-code a failedWork testOrder record.to Keepa specific physical Machine ID. Bind it to a "Resource Group" (capability). This allows the "Fail"Floor resultLead to balance the line without IT intervention.

Splitting and appendMerging

Real production is rarely linear. You must handle partial movements without losing cost traceability.

The Split (Fork)

• Scenario: Order for 1,000 units. 100 units require rework; 900 are ready to ship.
• Action: Split WO-001 (1,000 qty) into:
• • WO-001 (Parent): Reduced to 900 qty. Proceed to Ship.
  • WO-001-R (Child): Created for 100 qty. Rerouted to Rework Loop.
• Costing: The Child WO inherits the accumulated cost of the Parent up to the split point.

The Merge (Join)

• Scenario: Combining multiple partial batches into a newfull pallet for shipping.
• Constraint: You can only merge WOs of the same Part Number and same Revision.
• Logic: If Rev A mixed with Rev B → Then Block Merge.

Quantity Control & Overproduction

Operators often build "Pass" result after rework. Auditors needextras" to seecover potential fallout. This is unauthorized inventory.

The "Cap" Logic

• Definition: Max_Qty = Ordered_Qty + Yield_Buffer (e.g., 2%).
• Control:
  • If Total_Good_Units >= Max_Qty → Then Disable "Start" button at Operation 10.
  • If Operator attempts to launch new PCB → Then Reject: "Order Fulfilled."

WIP Visibility (Work In Progress)

WIP is cash sitting on the failurefloor. toThe believeMES must provide a real-time snapshot of where every dollar is trapped.

The WIP Equation

At any second, the success.MES must answer:

WIP_Qty = (Started_Qty) - (Scrapped_Qty) - (Finished_Goods_Qty)

Drift Control

• Phantom WIP: Units physically missing but systemically "at Op 20."

• Rule: Implement a "Stale WIP" auto-flush.
• Logic: If Unit inactive > 30 Days → Then Flag for "Lost Audit."

Final Checklist

Category	Metric / Control	Threshold / Rule
SequenceLifecycle	RouteState Enforcement	100%No Hardexecution Blockallowed on out-of-sequence"Created" scansor "Hold" states.
ExecutionRouting	ModeStep SelectionLock	UseCannot skip Op N-1. "SingleBackward" Scan"movement forrequires manualauthorized lines < 2 min cyclerework.
ExecutionVersions	ModeFrozen SelectionConfiguration	UseReleased "DualWO Scan"locks forBOM/Route machines/ovensrevisions. Updates require new WO.
TraceabilityQuantity	CycleOverproduction Time (Mode B)Cap	IncludesBlock TransportInput Timescans (Deltawhen fromGood_Qty Prev.>= Station)Order_Qty + Allowance.
ReworkSplitting	LoopCost ControlInheritance	FailedChild unitsWOs mustinherit enteraccrued acosts designatedof Repairthe RouteParent at the split point.
HistoryHygiene	ImmutabilityStale WIP	NeverAuto-report overwriteany unit inactive for > 14 days.
Completion	Auto-Close	If Qty = Target → Then Auto-trigger "Fail"TECO" results;message appendto "Pass"ERP.