Rework teardown & serial cannibalisation: govern parent-child de-kitting, recertification holds, and WIP cost reversal

In high-value discrete manufacturing—electric-vehicle traction inverters, aerospace actuators, diagnostic medical imaging systems, industrial turbines, and defense communications gear, each finished unit is a serialized parent assembly (PARENT_SN) containing 10 to 80 serialized child sub-assemblies (CHILD_SN: PCBs, sensors, motors, castings). When a finished unit fails End-of-Line (EOL) functional testing, or when a desperate production manager robs ("cannibalises") a scarce micro-controller board out of a partially built unit on the shop floor to ship a quarter-end customer order, standard ERP systems break down in three ways. First, to issue a replacement IGBT module or PCB to the failed work order, the clerk either deletes the old serial link or issues a second module onto the same work order, leaving the ERP claiming that INV-48V-SN088 contains two power modules and costing the unit at $$1,790$ instead of $$1,420$.

Second, during a complete teardown where only 1 child component is faulty and 4 expensive child sub-assemblies are healthy, operators place the harvested good sub-assemblies back on the line-side shelf without routing them through a Quality Recertification Gate to check for ESD damage, bent connector pins, or thermal cycling exhaustion. Third, donor units robbed during informal floor cannibalisation sit half-gutted in a corner with corrupt WIP balances and untracked missing parts.

The direct solution is to implement a structured Disassembly / Teardown Work Order, Append-Only Serial Genealogy State Machine, and IAS 2 Cost-Reversal Engine in the ERP and MES (ERPNext Stock Entry Repack & Serial Ledger). Distinct from M035 (which covers simple in-line touch-up rework where no serialized components are removed) and M064 (aggregate labour/overhead variance reporting), this guide (M127) specifies parent-child serial de-kitting, teardown consumable destruction rules, harvested-part recertification holds, donor cannibalisation controls, and WIP cost-layer unrolling.

Scope and regulatory boundary

This article defines the ERP, MES, QMS, and cost-accounting record architecture for serialized product teardown, component harvesting, cannibalisation, and rebuild valuation:

• What this workflow governs: Executing partial component swaps (DEKIT_SWAP) vs full parent disassembly (FULL_TEARDOWN), updating append-only parent-child serial genealogy states, routing harvested child serials through mandatory QA recertification (WH-HARVEST-RECERT-HOLD), governing donor-to-recipient cannibalisation orders, and posting IAS 2 compliant cost reversals.
• What this workflow does not replace: Software genealogy transactions never replace Material Review Board (MRB) engineering dispositions, customer concession requirements, or regulatory airworthiness/medical-device signoffs. In aerospace (SAE AS9100D) and defense contracting, cannibalising parts from a customer-allocated or flight-certified assembly—or reusing a harvested component that has undergone thermal/stress acceptance testing—often requires explicit written authorization from the Engineering Authority and Customer Quality Representative.

Bounded rework tear down cannibalisation serial genealogy cost reversal verification and exception-routing workflow

Follow the workflow below, or open its complete text version.

Read the complete workflow as text

1. Capture rework tear down cannibalisa baseline record → Verify revision, unit Basis and cutoff alignment
2. Verify revision, unit Basis and cutoff alignment → Run deterministic reconciliation and tolerance check
3. Run deterministic reconciliation and tolerance check → Quarantine mismatched or unapproved lines
4. Quarantine mismatched or unapproved lines → Route exception to named domain and finance owner
5. Route exception to named domain and finance owner → Release verified record with immutable audit trail

Designing the four-pillar teardown, genealogy, and cost-reversal architecture

1. Append-only As-Built Serial Genealogy state machine (Never delete history). When Child Serial SN-IGBT-402 is bolted into Parent Serial INV-48V-SN088, pressurized, energized on the EOL test stand, and subsequently removed after failing a high-voltage leakage check, that physical event happened. Deleting the database row linking SN-IGBT-402 to INV-48V-SN088 falsifies the Device/Unit History Record (21 CFR Part 820) and hides the fact that the parent unit's mating busbars experienced a fault current event. Structure the as_built_serial_genealogy table as an immutable append-only event log:

• INSTALLED_ACTIVE: Component serial is currently mounted in the parent unit (build_pass = 1).
• REMOVED_DEFECTIVE: Component was unmounted under TEARDOWN_WO_ID; linked to NCR_ID and routed to WH-MRB-SCRAP or vendor RMA.
• REMOVED_HARVESTED_GOOD: Healthy component unmounted during parent scrap/teardown or authorized cannibalisation; routed to WH-HARVEST-RECERT-HOLD with harvest_cycle_count += 1.
• INSTALLED_REPLACEMENT: Replacement component serial mounted during rework (build_pass = 2, linked to replaces_genealogy_row_id).

2. Three-tier BOM Teardown Harvest Policy & Harvest-Cycle Ceilings. Every item on a Manufacturing BOM must carry an explicit teardown_policy flag:

1. MANDATORY_TEARDOWN_SCRAP ($100%$ Auto-Write-Off): Torque-to-yield (TTY) aluminium/steel fasteners, Loctite-coated screws, compressed elastomer O-rings, liquid FIPG gaskets, potting compounds, and thermal interface pads. Whenever a teardown or partial swap touches an operation that disturbs these items, the ERP automatically writes off $100%$ of the disturbed single-use items and forces the operator to scan a fresh replacement kit during re-assembly.
2. REUSABLE_AFTER_QA_RECERT (Quarantine & Cycle Cap): Machined housings, multi-layer PCBs, wire harnesses, and optical sensors. Upon de-kitting, the ERP moves these serials into WH-HARVEST-RECERT-HOLD (a non-allocatable quarantine warehouse). Additionally, because every thermal test and mechanical unbolting cycle stresses solder joints and threads, each serialized child item enforces a MAX_HARVEST_CYCLES cap (typically $1\text{ or }2\text{ teardowns}$)—automatically blocking a component that has already survived two previous teardowns from being harvested a third time.
3. FAULTY_MRB_QUARANTINE: The failed component triggering the teardown, locked in WH-MRB-SCRAP for root-cause failure analysis (RCFA) or supplier chargeback.

3. Controlled donor-to-recipient cannibalisation workflow. In an ideal factory, cannibalisation never happens; in real manufacturing, a customer aircraft-on-ground (AOG) or line-down order sometimes forces management to authorize robbing CHILD-PCB-99 from WIP Donor Unit SN-DONOR-105 to finish Recipient Unit SN-RECIP-102. To prevent informal "midnight toolbox robbing," enforce a 4-Rule Cannibalisation Transaction:

• Requires joint electronic signoff by Production Manager + Quality Manager (plus Customer Representative if contractually required).
• Executes a linked pair of transactions: a De-Kit from SN-DONOR-105 (moving CHILD-PCB-99 through a rapid QA visual/ESD check and incrementing harvest_cycle_count) and an Install into SN-RECIP-102.
• Automatically places Donor Unit SN-DONOR-105 into WIP_CANNIBALISED_SHORT_HOLD, deducts the exact value of CHILD-PCB-99 plus disturbed single-use fasteners from SN-DONOR-105's WIP valuation, and pegs the incoming purchase order for the replacement PCB directly to SN-DONOR-105's restoration work order.

4. IAS 2 WIP cost-layer unrolling (Preventing reworked inventory inflation). Under IAS 2 (Inventories, Paragraph 16), abnormal amounts of wasted materials, labour, or other production costs must be recognized as expenses in the period in which they are incurred—never capitalized into the balance-sheet value of the finished unit. For a parent unit with standard material cost $C_{\text{mat, std}}$ and standard conversion cost $C_{\text{conv, std}}$ ($C_{\text{total, std}} = C_{\text{mat, std}} + C_{\text{conv, std}}$):

• When a faulty component ($C_{\text{faulty}}$) and disturbed single-use consumables ($C_{\text{single_use}}$) are removed and replaced with fresh parts ($C_{\text{faulty}} + C_{\text{single_use}}$) using rework labour ($C_{\text{rework_lab}}$), the Net Rework & Scrap Period Expense ($V_{\text{rework_total}}$) is: $$V_{\text{rework_total}} = C_{\text{faulty}} + C_{\text{single_use}} + C_{\text{rework_lab}} - R_{\text{vendor_warranty}}$$
• The finished parent unit enters Finished Goods inventory at exactly $C_{\text{total, std}}$, while $V_{\text{rework_total}}$ posts immediately to GL-INTERNAL-REWORK-SCRAP-VARIANCE (or GL-VENDOR-WARRANTY-RECEIVABLE if caused by a supplier defect).

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Illustrative worked example: 48V traction inverter EOL failure teardown, component harvest, and IAS 2 cost reversal

All figures below are illustrative and synthetic. An electric-drivetrain plant builds serialized 48V traction inverters (INV-48V-SN088) with a standard built cost of $$1,420.00$:

• Standard Material Cost ($C_{\text{mat, std}} = $1,240.00$):
  • $4\text{ Reusable Serialized Sub-Assemblies}$ (CNC liquid-cooled housing SN-HSG-88 at $$340$, Control PCB SN-PCB-88 at $$290$, DC-Link Capacitor Bank SN-CAP-88 at $$225$, Hall Current Sensor SN-SNS-88 at $$110$) = $$965.00$
  • $1\text{ Serialized 3-Phase IGBT Power Module}$ (SN-IGBT-402) = $$210.00$
  • $1\text{ Single-Use Fastener & Thermal Seal Kit}$ (silver-filled thermal phase-change pad, die-cut EPDM perimeter gasket, $12\text{ torque-to-yield busbar bolts}$) = $$65.00$
• Standard Assembly & EOL Test Conversion Cost ($C_{\text{conv, std}}$): $$180.00$.

During End-of-Line hot-load testing, INV-48V-SN088 fails Phase-W short-circuit protection due to an internal bond-wire lift inside IGBT Power Module SN-IGBT-402.

Step 1: Execute partial teardown (RWK-WO-088), scrap single-use kit, and install replacement IGBT.

The technician opens Rework Teardown Order RWK-WO-088 on INV-48V-SN088:

1. De-Kit Faulty IGBT & Auto-Scrap Single-Use Kit:
   • SN-IGBT-402 ($$210.00$) is scanned out to WH-MRB-SCRAP (STATE = REMOVED_DEFECTIVE).
   • Because unbolting the IGBT disturbs the thermal pad, housing perimeter gasket, and torque-to-yield busbar bolts, the MES automatically writes off the $$65.00$ single-use kit (STATE = DESTROYED_ON_TEARDOWN) and blocks re-closing the housing until a fresh $$65.00$ kit is scanned.
   • Total cost reversed out of INV-48V-SN088 WIP = $$210.00 + $65.00 = \mathbf{-$275.00}$ (bringing residual WIP down from $$1,420.00$ to $$1,145.00$).
2. Install Replacement IGBT (SN-IGBT-519) & Fresh Seal Kit:
   • The technician scans replacement IGBT SN-IGBT-519 ($$210.00$) and a fresh single-use seal/bolt kit ($$65.00$), adding $+$275.00$ back to INV-48V-SN088 WIP (restoring material + standard conversion to $$1,145.00 + $275.00 = \mathbf{$1,420.00}$).
   • Teardown, heatsink solvent cleaning, re-assembly, and full EOL re-test consume $1.90\text{ hours}$ at $$50.00/\text{hr} = \mathbf{$95.00}$ of rework conversion cost, which posts directly to GL-REWORK-LABOUR-VARIANCE.

Step 2: Compare naive uncapped ERP costing vs. IAS 2 compliant teardown accounting.

(Note: If the parent unit had instead suffered a cracked housing lug requiring a Full Unit Disassembly without rebuild, the $4\text{ good serialized sub-assemblies}$ worth $$965.00$ would enter WH-HARVEST-RECERT-HOLD with harvest_cycle_count = 1, while the $$210.00$ IGBT + $$65.00$ seals + $$180.00$ sunk conversion + $$45.00$ teardown labour would be expensed.)

For the rebuilt unit INV-48V-SN088, the ledger comparison is:

Independent arithmetic verification.

1. Material conservation on INV-48V-SN088: $$965.00\text{ (4 healthy sub-assemblies)} + $210.00\text{ (IGBT)} + $65.00\text{ (single-use kit)} = $1,240.00\text{ standard material}$; plus $$180.00\text{ standard conversion} = $1,420.00$.
2. WIP reversal and restoration: $$1,420.00\text{ (initial)} - $210.00\text{ (faulty IGBT de-kit)} - $65.00\text{ (single-use kit write-off)} + $210.00\text{ (new IGBT)} + $65.00\text{ (new kit)} = $1,420.00\text{ final FG valuation}$.
3. Total rework/scrap period variance: $$210.00\text{ (faulty IGBT)} + $65.00\text{ (destroyed single-use kit)} + $95.00\text{ (rework labour)} = $370.00$ ($26.06%$ of standard unit cost prevented from inflating inventory).

Workflow, owner roles, exception handling and recovery controls

Bounded pilot and implementation check

Pilot append-only serial de-kitting, harvested-component recertification quarantine, and IAS 2 cost reversal on 1 serialized assembly line (e.g., EOL test & rework bay) over 3 weeks:

• Pilot boundary: Tag every BOM component with its teardown_policy (REUSABLE_AFTER_QA_RECERT vs MANDATORY_TEARDOWN_SCRAP), configure WH-HARVEST-RECERT-HOLD, and automate the WIP cost-reversal journal entry on rework orders.
• Acceptance tests:
  • ACT-M127-01 (Append-Only Genealogy Preservation): De-kit SN-IGBT-402 from INV-48V-SN088 and install SN-IGBT-519; confirm querying INV-48V-SN088 shows both serials with exact timestamps (REMOVED_DEFECTIVE at Pass 1 and INSTALLED_REPLACEMENT at Pass 2).
  • ACT-M127-02 (Mandatory Single-Use Kit Replacement Interlock): Open a teardown swap on an operation with a linked $$65.00$ gasket/TTY bolt kit; confirm the ERP automatically scraps the original kit and blocks rebuild signoff until a new kit is issued.
  • ACT-M127-03 (Harvest Quarantine & Cycle-Count Ceiling): Harvest 4 sub-assemblies from a torn-down unit; confirm they land in non-allocatable WH-HARVEST-RECERT-HOLD and that any serial with harvest_cycle_count ≥ 2 is blocked from returning to stock.
  • ACT-M127-04 (IAS 2 Standard Cost Cap Verification): Execute the $$275.00$ component replacement + $$95.00$ rework labour fixture and verify the finished unit posts to FG inventory at exactly $$1,420.00$ while $$370.00$ posts to period rework/scrap variance accounts.

Next actions

1. Make your As-Built Serial Genealogy table strictly append-only: Never DELETE or UPDATE an installed component serial in place; append a REMOVED_DEFECTIVE or REMOVED_HARVESTED state transition so full history survives for field recalls and warranty audits.
2. Flag every single-use fastener, gasket, O-ring, and thermal pad as MANDATORY_TEARDOWN_SCRAP on the BOM: Ensure your MES automatically writes off disturbed single-use items and forces the rework tech to scan fresh seals and torque-to-yield bolts.
3. Route all harvested components through WH-HARVEST-RECERT-HOLD with a hard MAX_HARVEST_CYCLES cap: Never let a component unbolted from a failed assembly go straight back to the line-side rack without QA recertification.
4. Reverse removed component costs out of WIP and expense rework labour in the current period: Comply with IAS 2 and keep reworked units at standard cost rather than inflating finished-goods inventory with buried failure costs.

Frequently Asked Questions

How should discrete manufacturers record finished-unit teardown, component harvest/recertification, and parent-child serial disassembly without corrupting warranty genealogy or double-counting component costs?.

Teams should govern rework tear down cannibalisation serial genealogy cost reversal by linking every transaction to its source evidence, timestamp, and assigned owner before permitting downstream posting. Distinct from M035 (NCR disposition) and M064 (variance analysis); M127 governs negative-issue disassembly orders, harvested serialized module recertification holds, and splitting salvage value from teardown labour variance. Rather than relying on informal spreadsheet overrides, the workflow enforces a documented verification gate and preserves the original observation whenever a correction is recorded.

How does mes quality management handle exceptions and mismatches?.

When a discrepancy occurs during mes quality management, the system routes the blocked record into an owned exception queue rather than silently dropping or auto-adjusting the balance. Assigned operational, quality, and finance owners must review and approve exceptions before posting. Each exception retains the original quantity, date, and counterparty reference until the designated reviewer resolves the variance with supporting evidence.

What should teams test before automating shop floor control software?.

Before scaling shop floor control software, run a bounded pilot using historical records that include partial receipts, late updates, duplicate messages, and rejected lines. Verify that the integration preserves idempotency, maintains a clear segregation of duties between operational entry and financial approval, and produces an auditable trail for every state transition.