A design change rarely stays inside the CAD file. A hole moves, a material changes, a supplier becomes unavailable, or a customer asks for a new feature—and suddenly the drawing, BOM, manufacturing process, inspection plan, and purchasing information may all need attention.
That is why engineering change management matters. An Engineering Change Order, or ECO, is a controlled way to define what is changing, why it is changing, what is affected, who must approve it, and when the new revision becomes effective.
This guide explains a practical ECO workflow for mechanical engineering teams, especially small and mid-sized teams that still rely on shared folders, spreadsheets, email, and manual drawing revisions.
What Is an Engineering Change Order?
An ECO is the controlled instruction used to implement an approved engineering change. Terminology varies between companies: some separate an Engineering Change Request, Engineering Change Order, and Engineering Change Notice, while others use ECO as the main change record. The important principle is control and traceability.
A useful ECO answers five questions: what is changing, why is it changing, which items are affected, who approved it, and when does the change take effect?
ASME Y14.35-2025 defines practices for revising engineering product definition datasets and associated documents, including methods for identifying and recording revisions.
ECR vs ECO vs ECN
These terms are often mixed together, but separating them makes a workflow easier to understand.
- ECR: proposes a change and explains the problem or opportunity.
- ECO: defines the approved change and the work required to implement it.
- ECN: communicates that an approved change has been released or is becoming effective.
Not every company needs three separate documents. A small design team can combine these stages in one controlled change record if approval, revision, affected items, and effective date remain traceable.
When Should a Mechanical Engineer Raise a Change?
A change deserves formal control when it can affect fit, form, function, safety, manufacturability, cost, delivery, inspection, compliance, or downstream documentation.
- A bracket thickness changes from 3 mm to 4 mm.
- A hole pattern moves to solve an assembly interference.
- A material grade changes because the original material is unavailable.
- A supplier changes the manufacturing process.
- A tolerance is tightened after a functional failure.
- A customer requests a dimensional or aesthetic modification.
- A production team finds a feature that is difficult or expensive to manufacture.
A useful rule is simple: if another department could build, buy, inspect, or install the wrong version because of the change, control the change.
The Practical 8-Step ECO Workflow
1. Define the problem before editing CAD
Start with the reason for the change. Avoid vague descriptions such as update drawing. Describe the actual issue, for example an M8 fastener interferes with an adjacent bracket during assembly. A clear problem statement makes later review much easier.
2. Identify the affected items
List the part number, drawing number, assembly, BOM, specification, and any manufacturing or inspection documents that could be affected. Do not assume that changing one CAD part means only one file changes.
Changing a mounting-hole diameter can affect the part drawing, assembly clearance, fastener selection, inspection gauge, BOM, and supplier instruction.
3. Perform an impact check
Check at least five areas: design, manufacturing, procurement, quality, and schedule. For design, check interfaces and loads. For manufacturing, check tooling, process capability, scrap, and cycle time. For procurement, check supplier stock and purchase orders. For quality, check inspection methods. For schedule, check whether work-in-progress parts are already in production.
4. Update the design and revision
Make the CAD change deliberately rather than editing a released file without traceability. Update the drawing revision according to your company procedure and record the important change clearly.
ASME Y14.100 covers engineering drawing practices, while ASME Y14.35 covers revision practices for engineering product definition datasets and associated documents.
5. Update the BOM and downstream documents
A revised part can still be paired with an old BOM, work instruction, inspection sheet, CNC program, supplier drawing, or installation document.
Use an affected-document checklist and mark each item as update, verify, or not affected. This simple habit prevents the common situation where engineering updated the drawing but the shop used old information.
6. Review and approve the change
Approval should match the risk. A cosmetic correction may need a smaller review than a change to a pressure-containing component, load-bearing feature, safety-related assembly, or regulated product.
The reviewer should understand the reason, affected items, technical evidence, manufacturing impact, and release plan. Structured change-management systems commonly use approval workflows, impact analysis, and audit trails.
7. Release and communicate
Approval is not the finish line. Release the new revision through the controlled channel used by your company and communicate the effective point to production, procurement, suppliers, quality, and site teams as applicable.
A strong release message identifies the new revision, the revision it replaces, and the effective condition. This removes ambiguity for everyone downstream.
8. Verify before closing
Closure should confirm that the change was implemented, affected documents were updated, and required validation was completed. Keep the reason and evidence so a future engineer can understand why the design changed.
Worked Example: Moving a Mounting Hole
Imagine a sheet-metal equipment bracket with four M8 mounting holes. During assembly, one hole is found 3 mm too close to an adjacent frame member.
A weak process simply moves the hole in CAD and sends a new PDF. A stronger ECO process checks the whole chain:
- Record the assembly interference as the problem.
- Identify the bracket model and drawing as affected items.
- Confirm the new hole location clears the frame and washer.
- Verify the new location remains manufacturable.
- Check that the existing fastener remains compatible.
- Update the inspection requirement for hole location.
- Issue the next controlled drawing revision.
- Notify production and the supplier which revision is effective.
- Verify a first-off or sample assembly fits correctly.
The engineering edit may take minutes. The value of the ECO is making sure the rest of the organization receives the same answer.
A Simple ECO Checklist for Small Engineering Teams
You do not need expensive PLM software to start. A controlled template can cover the basics:
- Change ID and date
- Requester and responsible engineer
- Problem statement and reason
- Affected parts, drawings, assemblies, and documents
- Old and new revision
- Technical justification or test evidence
- Manufacturing and supplier impact
- Quality and inspection impact
- Cost and schedule impact
- Approvals
- Effective date or implementation condition
- Verification result and closure
Common ECO Mistakes
Changing CAD but not the drawing
The model may be correct while the released manufacturing document still shows old geometry.
Updating the drawing but forgetting the BOM
A component change can affect purchasing and assembly even when the drawing looks simple.
Using filenames as revision control
Files such as Bracket Final Final2 Approved are a warning sign, not a revision system. Use controlled revision identifiers and release states.
Ignoring production status
A technically correct change can still create scrap if the shop has already produced a batch using the old revision.
Closing without evidence
If the change required a fit check, test, measurement, or first-article verification, record the result before closure.
How PDM and PLM Help
As the number of parts, engineers, suppliers, and product variants grows, manual control becomes harder. Product Data Management systems centralize CAD files, documents, versions, and access. PLM extends that control into broader product-lifecycle workflows.
Modern PDM and PLM workflows can provide revision history, controlled release states, approval routing, BOM management, and traceability. The important point is not the software brand. It is having a reliable single source of truth for released engineering information.
Final Takeaway
Good engineering change management is not bureaucracy for its own sake. It is a practical defense against outdated drawings, mismatched BOMs, incorrect purchases, production rework, and confusion between engineering and manufacturing.
If you work in CAD, NPD, manufacturing, procurement, quality, or project execution, learn to think beyond the individual drawing. Every meaningful design change has a downstream impact.
Change the design. Control the revision. Check the impact. Communicate the release. Verify the result.
For related learning, see our guides on SolidWorks configurations, reading mechanical engineering drawings, and GD&T fundamentals.
Featured image: ThisisEngineering / Unsplash.
Technical note: ECO terminology and approval depth vary by company and industry. Use your organization’s documented quality, safety, regulatory, and change-control procedures where they apply.