Subcontracting Manufacturing Management in ERP: Inventory, Routing, Work Orders, Cost and Supplier Control
The hard part of subcontracting is not that production happens outside the company. The hard part is keeping control when material, WIP, responsibility, quality, due dates and cost move beyond the plant boundary. This guide treats subcontracting as a family of operating models rather than a single purchasing or manufacturing transaction.
The material may be yours but not in your warehouse. The work order may be yours but not the machine. The due date may be yours but not the supplier's capacity. ERP must keep those realities connected without confusing physical location with ownership.
Table of contents
- Why subcontracting is not one process
- 13 core subcontracting models seen in ERP
- Same item, different item, or an intermediate WIP item?
- How an outside operation should fit into a routing
- Does material really leave inventory when sent to a subcontractor?
- Purchasing, service invoices and production cost allocation
- Who supplies the material? Four common supply patterns
- Supplier-to-supplier and supplier-to-customer flows
- Quality, scrap, by-products and over/under-consumption
- Lot, batch and serial traceability
- MRP, capacity and due-date planning
- Supplier reconciliation and management KPIs
- Industry examples: the form changes, the control logic does not
- ERP subcontracting design checklist
Why subcontracting is not one process
Subcontracting sits at the intersection of purchasing, manufacturing, inventory, logistics, quality, costing and supplier management. In one company the supplier performs a single routing operation; in another the supplier buys all components and delivers a finished item. In another, company-owned material is supplied to the subcontractor by a second vendor. The first design task is therefore classification, not configuration.
Start with five questions
Who owns the material? Where is it physically stored? Does the item identity change before and after processing? Is the supplier performing a routing operation or selling an item/service? Which work order, operation, product, project, lot or serial should carry the cost?
13 core subcontracting models seen in ERP
| Model | Physical flow | Typical ERP model | Primary control |
|---|---|---|---|
| 1. Turnkey subcontracting | Supplier sources components, manufactures and delivers. | Purchase subcontracted item; no company component issue. | Delivery, quality, lead time and purchase cost. |
| 2. Company-supplied material, different output item | Components go out; a different semi-finished/finished item returns. | Vendor-held stock + component consumption + output receipt. | Conversion ratio, scrap, lot genealogy. |
| 3. Company-supplied material, same item | Same part returns after coating, heat treatment, calibration, etc. | Keep item/serial identity; change operation/quality/value state. | Prevent processed and unprocessed stock from mixing. |
| 4. Outside routing operation | WIP leaves at a specific routing step and returns for the next operation. | Supplier work center/outside operation + linked purchase service. | Previous operation, shipment, receipt and operation completion. |
| 5. Service PO allocated to work order | Material movements are separate; supplier invoices the service. | Service PO/invoice allocated to work order/operation/cost object. | Correct production cost attribution. |
| 6. Labor/service-only subcontracting | Supplier provides labor/equipment while material may stay on-site. | Service item + operation/capacity; possibly no stock transfer. | Accepted hours/quantity and service confirmation. |
| 7. Mixed material ownership | Some components supplied by company, others by subcontractor. | Company inputs tracked at supplier; supplier inputs included in price. | Ownership and cost split. |
| 8. Direct supply to subcontractor | Another vendor ships purchased components directly to subcontractor. | External ship-to/dropship to subcontractor + ownership tracking. | Receipt, title, quality and invoice separation. |
| 9. Consecutive/multilevel subcontracting | Supplier A ships directly to Supplier B. | Multiple outside operations and supplier-to-supplier WIP transfers. | End-to-end ownership and WIP trace. |
| 10. Subcontractor direct to customer | Finished goods ship from subcontractor to customer. | Subcontract purchase + dropship/customer delivery linkage. | Sales delivery, quality and inventory accounting. |
| 11. Repair/rework/MRO subcontracting | Serialized/high-value part goes out and returns with same identity. | Maintenance/work order + outside service + serial traceability. | Same serial, replaced parts and service cost. |
| 12. Chargeable components | Company charges/sells material to subcontractor and later buys output. | Component sale/charge plus subcontract purchase and settlement. | Ownership transfer, price and financial netting. |
| 13. Toll/process manufacturing | Company supplies main input; supplier transforms/blends/packages it. | Recipe/BOM + batch/yield + service cost + by-products/scrap. | Mass balance, yield and batch genealogy. |
Model
1. Turnkey subcontracting
Physical flow
Supplier sources components, manufactures and delivers.
Typical ERP model
Purchase subcontracted item; no company component issue.
Primary control
Delivery, quality, lead time and purchase cost.
Model
2. Company-supplied material, different output item
Physical flow
Components go out; a different semi-finished/finished item returns.
Typical ERP model
Vendor-held stock + component consumption + output receipt.
Primary control
Conversion ratio, scrap, lot genealogy.
Model
3. Company-supplied material, same item
Physical flow
Same part returns after coating, heat treatment, calibration, etc.
Typical ERP model
Keep item/serial identity; change operation/quality/value state.
Primary control
Prevent processed and unprocessed stock from mixing.
Model
4. Outside routing operation
Physical flow
WIP leaves at a specific routing step and returns for the next operation.
Typical ERP model
Supplier work center/outside operation + linked purchase service.
Primary control
Previous operation, shipment, receipt and operation completion.
Model
5. Service PO allocated to work order
Physical flow
Material movements are separate; supplier invoices the service.
Typical ERP model
Service PO/invoice allocated to work order/operation/cost object.
Primary control
Correct production cost attribution.
Model
6. Labor/service-only subcontracting
Physical flow
Supplier provides labor/equipment while material may stay on-site.
Typical ERP model
Service item + operation/capacity; possibly no stock transfer.
Primary control
Accepted hours/quantity and service confirmation.
Model
7. Mixed material ownership
Physical flow
Some components supplied by company, others by subcontractor.
Typical ERP model
Company inputs tracked at supplier; supplier inputs included in price.
Primary control
Ownership and cost split.
Model
8. Direct supply to subcontractor
Physical flow
Another vendor ships purchased components directly to subcontractor.
Typical ERP model
External ship-to/dropship to subcontractor + ownership tracking.
Primary control
Receipt, title, quality and invoice separation.
Model
9. Consecutive/multilevel subcontracting
Physical flow
Supplier A ships directly to Supplier B.
Typical ERP model
Multiple outside operations and supplier-to-supplier WIP transfers.
Primary control
End-to-end ownership and WIP trace.
Model
10. Subcontractor direct to customer
Physical flow
Finished goods ship from subcontractor to customer.
Typical ERP model
Subcontract purchase + dropship/customer delivery linkage.
Primary control
Sales delivery, quality and inventory accounting.
Model
11. Repair/rework/MRO subcontracting
Physical flow
Serialized/high-value part goes out and returns with same identity.
Typical ERP model
Maintenance/work order + outside service + serial traceability.
Primary control
Same serial, replaced parts and service cost.
Model
12. Chargeable components
Physical flow
Company charges/sells material to subcontractor and later buys output.
Typical ERP model
Component sale/charge plus subcontract purchase and settlement.
Primary control
Ownership transfer, price and financial netting.
Model
13. Toll/process manufacturing
Physical flow
Company supplies main input; supplier transforms/blends/packages it.
Typical ERP model
Recipe/BOM + batch/yield + service cost + by-products/scrap.
Primary control
Mass balance, yield and batch genealogy.
The classification generalizes common business patterns documented across SAP subcontracting, Oracle outside processing, Microsoft Dynamics 365 subcontracted route operations, IFS outside operations and Odoo basic/resupply/dropship subcontracting.
Same item, different item, or an intermediate WIP item?
One of the most consequential design choices is whether the item before and after subcontracting should be represented by the same ERP item, a different item, or an intermediate WIP/subcontracting item. The decision should follow traceability, planning, valuation and quality needs rather than master-data convenience.
| Approach | Use when | Benefit | Risk |
|---|---|---|---|
| Same item | Core identity remains the same after processing. | Avoids item proliferation; serial identity can remain intact. | Processed and unprocessed stock can mix without status/location controls. |
| Different input/output items | The subcontracted result is a distinct semi-finished state. | Clear MRP, inventory, valuation and quality state. | Unnecessary use creates BOM/routing/master-data complexity. |
| Intermediate WIP/subcontract item | ERP must explicitly represent WIP held outside. | Makes supplier-held WIP visible. | Can become a technical workaround that causes code explosion. |
| By-product/scrap item | Recoverable by-products or material return from the process. | Supports mass/value balance. | Ignoring it distorts consumption and cost. |
Approach
Same item
Use when
Core identity remains the same after processing.
Benefit
Avoids item proliferation; serial identity can remain intact.
Risk
Processed and unprocessed stock can mix without status/location controls.
Approach
Different input/output items
Use when
The subcontracted result is a distinct semi-finished state.
Benefit
Clear MRP, inventory, valuation and quality state.
Risk
Unnecessary use creates BOM/routing/master-data complexity.
Approach
Intermediate WIP/subcontract item
Use when
ERP must explicitly represent WIP held outside.
Benefit
Makes supplier-held WIP visible.
Risk
Can become a technical workaround that causes code explosion.
Approach
By-product/scrap item
Use when
Recoverable by-products or material return from the process.
Benefit
Supports mass/value balance.
Risk
Ignoring it distorts consumption and cost.
How an outside operation should fit into a routing
Typical outside operation flow
- 1
Release work order
BOM and routing create the manufacturing demand.
- 2
Complete prior operation
Quantity ready for external processing becomes known.
- 3
Create subcontract procurement
Service/outside operation demand is linked to the work order.
- 4
Ship WIP/components
Company-owned material moves to supplier location.
- 5
Supplier performs operation
Actual quantity, time, scrap and quality are recorded.
- 6
Receive / complete operation
Processed WIP is received or moved directly to next operation.
- 7
Post service cost
Supplier cost is allocated to the proper operation/work order.
- 8
Continue routing
Next operation proceeds only after control conditions are met.
ERP products differ in how they represent intermediate WIP. Some use explicit stocked service/semi-finished items, while others keep WIP on the production order. The business requirement should drive the representation: physical visibility, traceability and cost control.
Does material really leave inventory when sent to a subcontractor?
Physical movement and ownership are different events. Free-issued components may leave the plant while remaining a company asset. A robust ERP model therefore needs visibility of company-owned stock held at each subcontractor.
- Show company-owned material balance by subcontractor and location.
- Do not consume material merely because it was shipped; link consumption to actual output/process completion.
- Separate unused returns from over-consumption.
- Support unrestricted, quality, blocked or similar states where required.
- Age supplier-held inventory to expose forgotten WIP and components.
- Record physical-count and reconciliation differences with approval.
Reconciliation equation
Quantity sent = actual consumption + unused return + approved scrap/by-product + ending balance at subcontractor ± approved adjustments.
Purchasing, service invoices and production cost allocation
The commercial document is usually a purchase order and supplier invoice; the operational cost object may be a work order, operation, project, product, lot or serial. ERP must connect the two.
| Pricing basis | Typical use | Costing question |
|---|---|---|
| Per piece | Assembly, coating, sewing, packaging | Good quantity or total processed quantity? |
| Per hour | Specialist labor, repair, machining | Actual hours vs invoiced hours? |
| Per kg / meter / m² | Paint, plating, textile, surface processing | Input vs output measurement and yield? |
| Per lot/batch | Heat treatment, furnace, bath processes | How is minimum lot cost distributed? |
| Fixed fee | Setup, tooling, inspection, logistics | Which products/orders absorb the fixed fee? |
| Tiered price | Volume-based contracts | PO, receipt and invoice variance treatment? |
Pricing basis
Per piece
Typical use
Assembly, coating, sewing, packaging
Costing question
Good quantity or total processed quantity?
Pricing basis
Per hour
Typical use
Specialist labor, repair, machining
Costing question
Actual hours vs invoiced hours?
Pricing basis
Per kg / meter / m²
Typical use
Paint, plating, textile, surface processing
Costing question
Input vs output measurement and yield?
Pricing basis
Per lot/batch
Typical use
Heat treatment, furnace, bath processes
Costing question
How is minimum lot cost distributed?
Pricing basis
Fixed fee
Typical use
Setup, tooling, inspection, logistics
Costing question
Which products/orders absorb the fixed fee?
Pricing basis
Tiered price
Typical use
Volume-based contracts
Costing question
PO, receipt and invoice variance treatment?
If subcontracting invoices are posted only to overhead without a production reference, product cost and project margin become unreliable. Direct service cost and relevant indirect logistics/quality cost should be traceable to the appropriate manufacturing cost object.
Who supplies the material? Four common supply patterns
| Pattern | Flow | ERP implication |
|---|---|---|
| Subcontractor supplies all | Company purchases only the processed/final item. | No company component issue. |
| Company ships from own warehouse | Components transfer to supplier-held stock. | Track provision and actual consumption. |
| Second vendor ships directly to subcontractor | Purchased material bypasses company warehouse. | External ship-to while ownership/receipt remains controlled. |
| Mixed sourcing | Some components company-owned, others supplier-owned. | BOM and cost must separate ownership. |
Pattern
Subcontractor supplies all
Flow
Company purchases only the processed/final item.
ERP implication
No company component issue.
Pattern
Company ships from own warehouse
Flow
Components transfer to supplier-held stock.
ERP implication
Track provision and actual consumption.
Pattern
Second vendor ships directly to subcontractor
Flow
Purchased material bypasses company warehouse.
ERP implication
External ship-to while ownership/receipt remains controlled.
Pattern
Mixed sourcing
Flow
Some components company-owned, others supplier-owned.
ERP implication
BOM and cost must separate ownership.
Supplier-to-supplier and supplier-to-customer flows
Consecutive outside operations do not need to return physically to the plant. Supplier A can ship directly to Supplier B, and a subcontractor can sometimes ship the finished product directly to the end customer. ERP should model the real ship-from and ship-to chain instead of inventing warehouse movements that never happened.
Consecutive subcontracting example
- 1
Company
Ships WIP to Supplier A.
- 2
Supplier A
Completes first outside operation.
- 3
A → B
Ships directly to second supplier.
- 4
Supplier B
Completes next operation.
- 5
Company/customer
Receives the final controlled output.
Quality, scrap, by-products and over/under-consumption
Receiving the right good quantity does not prove that the subcontracting process is under control. Planned and actual component consumption may differ, unused inputs may return, scrap may occur, and recoverable by-products may be received.
- Track good, rejected, rework and scrap quantities separately.
- Allow subsequent correction of component consumption when actual differs from plan.
- Use reason codes for supplier loss, normal yield loss or master-data error.
- Return under-consumed material to supplier-held balance or physical stock.
- Receive by-products/recoverable scrap when economically meaningful.
- Prevent uninspected receipts from becoming unrestricted stock when quality control is required.
- Link rework, return, repair or scrap decisions to the original subcontract transaction.
Lot, batch and serial traceability
| Scenario | Traceability requirement |
|---|---|
| Same serialized part returns | Preserve serial; append outside operation and quality history. |
| One lot splits into several | Maintain parent-child lot relationship and quantities. |
| Several lots are blended | Output batch genealogy must show all consumed input lots. |
| Supplier uses its own lot number | Store cross-reference between supplier lot and internal lot. |
| Yield changes in process subcontracting | Track input batch, output batch, scrap and by-products together. |
Scenario
Same serialized part returns
Traceability requirement
Preserve serial; append outside operation and quality history.
Scenario
One lot splits into several
Traceability requirement
Maintain parent-child lot relationship and quantities.
Scenario
Several lots are blended
Traceability requirement
Output batch genealogy must show all consumed input lots.
Scenario
Supplier uses its own lot number
Traceability requirement
Store cross-reference between supplier lot and internal lot.
Scenario
Yield changes in process subcontracting
Traceability requirement
Track input batch, output batch, scrap and by-products together.
MRP, capacity and due-date planning
Creating a subcontract purchase order is not the same as planning the due date. ERP should time component availability at the supplier, include transport and processing lead times, and reflect practical supplier capacity where that constraint matters.
- Include outside-operation lead time in routing/MRP.
- Separate transportation time from processing time.
- Represent supplier weekly/monthly capacity commitments when material.
- Plan components required at the subcontractor separately from in-house demand.
- Re-plan purchasing/shipment dates if the prior operation slips.
- Support partial shipment and partial completion.
- Define sourcing logic when alternate subcontractors differ in price, quality and capacity.
Supplier reconciliation and management KPIs
| KPI/control | What it reveals |
|---|---|
| Company stock at subcontractor | Assets held outside by supplier/location. |
| Age of subcontract stock | Forgotten/slow-moving material and WIP. |
| OTIF | Due-date reliability. |
| Subcontract cycle time | Elapsed time from shipment to usable return. |
| Planned vs actual consumption | BOM/yield/process variance. |
| Scrap/reject rate | Quality/process loss. |
| Rework rate | First-pass yield. |
| PO-invoice variance | Commercial/cost variance. |
| Open subcontract WIP | Work-order quantities still outside. |
| Capacity adherence | Supplier commitment vs actual output. |
KPI/control
Company stock at subcontractor
What it reveals
Assets held outside by supplier/location.
KPI/control
Age of subcontract stock
What it reveals
Forgotten/slow-moving material and WIP.
KPI/control
OTIF
What it reveals
Due-date reliability.
KPI/control
Subcontract cycle time
What it reveals
Elapsed time from shipment to usable return.
KPI/control
Planned vs actual consumption
What it reveals
BOM/yield/process variance.
KPI/control
Scrap/reject rate
What it reveals
Quality/process loss.
KPI/control
Rework rate
What it reveals
First-pass yield.
KPI/control
PO-invoice variance
What it reveals
Commercial/cost variance.
KPI/control
Open subcontract WIP
What it reveals
Work-order quantities still outside.
KPI/control
Capacity adherence
What it reveals
Supplier commitment vs actual output.
Industry examples: the form changes, the control logic does not
| Industry | Typical outsourced processes | ERP focus |
|---|---|---|
| Machinery / metal | Laser, machining, grinding, heat treatment, plating, paint | Outside routing, WIP, serial/lot, piece/kg pricing. |
| Automotive suppliers | Pressing, welding, coating, machining, assembly | Quality, genealogy, due date, reject/rework. |
| Textile / apparel | Cutting, sewing, dyeing, printing, washing | Color/batch, kg/meter/piece, yield and supplier balance. |
| Plastics | Injection, extrusion, printing, assembly | Tooling, resin supply, scrap, cycle. |
| Food | Milling, blending, filling, packaging | Batch, shelf life, mass balance, quality. |
| Electronics | PCB assembly, cabling, test, assembly | Serial, revision and component traceability. |
| Furniture | CNC, paint, upholstery, metal parts | Order/project link, component sets and due dates. |
| Chemicals/process | Blending, reactor processing, filling, coating | Batch, recipe, yield and by-products. |
| Aerospace/defense | Special processes, NDT, plating, heat treatment | Serial/lot, certificates and approved suppliers. |
| Maintenance/service | Repair, overhaul, calibration, rework | Same serial identity, maintenance order and service cost. |
Industry
Machinery / metal
Typical outsourced processes
Laser, machining, grinding, heat treatment, plating, paint
ERP focus
Outside routing, WIP, serial/lot, piece/kg pricing.
Industry
Automotive suppliers
Typical outsourced processes
Pressing, welding, coating, machining, assembly
ERP focus
Quality, genealogy, due date, reject/rework.
Industry
Textile / apparel
Typical outsourced processes
Cutting, sewing, dyeing, printing, washing
ERP focus
Color/batch, kg/meter/piece, yield and supplier balance.
Industry
Plastics
Typical outsourced processes
Injection, extrusion, printing, assembly
ERP focus
Tooling, resin supply, scrap, cycle.
Industry
Food
Typical outsourced processes
Milling, blending, filling, packaging
ERP focus
Batch, shelf life, mass balance, quality.
Industry
Electronics
Typical outsourced processes
PCB assembly, cabling, test, assembly
ERP focus
Serial, revision and component traceability.
Industry
Furniture
Typical outsourced processes
CNC, paint, upholstery, metal parts
ERP focus
Order/project link, component sets and due dates.
Industry
Chemicals/process
Typical outsourced processes
Blending, reactor processing, filling, coating
ERP focus
Batch, recipe, yield and by-products.
Industry
Aerospace/defense
Typical outsourced processes
Special processes, NDT, plating, heat treatment
ERP focus
Serial/lot, certificates and approved suppliers.
Industry
Maintenance/service
Typical outsourced processes
Repair, overhaul, calibration, rework
ERP focus
Same serial identity, maintenance order and service cost.
ERP subcontracting design checklist
- Classify the scenario against the core subcontracting models.
- Separate ownership from physical location.
- Document why input/output use the same item, different items or an intermediate WIP item.
- Show which BOM components are company-supplied vs subcontractor-supplied.
- Link outside-operation procurement to the work order and operation.
- Post component consumption against actual subcontract output/process completion.
- Test partial shipment, partial receipt, over/under-consumption and returns.
- Track scrap, by-products, rework and rejects as distinct events.
- Preserve lot/serial genealogy through the outside step.
- Allocate service invoices to the correct product/work order/operation/project.
- Support supplier-to-supplier or supplier-to-customer flows when physically used.
- Report supplier-held company inventory and aging.
- Align MRP, lead time and supplier capacity with the real calendar.
- Gate unrestricted use/next operation on quality acceptance where required.
- Reconcile stock, consumption, scrap, returns and ending supplier balance before closing.
Design principle
A good ERP model does not pretend the subcontractor is an internal warehouse or work center. It makes externally held material and externally executed operations visible without losing ownership, responsibility and traceability boundaries.
Frequently asked questions about subcontracting in ERP
- How is subcontracting different from standard purchasing?
- In subcontracting, company-owned material, production routing, work-order context or traceability can extend into the supplier process. Inventory and manufacturing links are therefore much stronger than in a simple purchase.
- Should components sent to a subcontractor be consumed immediately?
- Not if ownership remains with the company. They can physically leave the plant while remaining company stock held at the subcontractor until actual consumption is confirmed.
- Can the same item code be used before and after subcontracting?
- Yes, when the core item identity remains the same. Additional controls such as operation status, location, quality state or serial history may be required to prevent processed and unprocessed stock from mixing.
- Where should the subcontracting service invoice be costed?
- As far as practical, to the relevant work order, routing operation, product, project, lot or serial rather than generic overhead.
- Can Supplier A ship directly to Supplier B?
- Yes. Consecutive outside operations can use supplier-to-supplier shipment while ERP keeps the company-owned WIP chain intact.
- How should scrap and consumption variance be handled?
- Planned and actual consumption should be distinguished. Returns, over/under-consumption, scrap, recoverable by-products and adjustment reasons should reconcile to ending supplier-held stock.
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