Products change constantly: a cheaper component is approved, a dimension is adjusted after a field problem, a supplier discontinues a part, a customer requests a modification. Each change touches drawings, BOMs, stock, open orders, tooling, inspection plans and sometimes customers. When changes are communicated by email or word of mouth, some departments switch and others don't — and the result is wrong parts made, wrong material bought, or obsolete stock piling up.
An engineering change management process makes sure every change is evaluated, approved, communicated and implemented consistently.
Step 1: Engineering change request (ECR)
Anyone can propose a change — design, production, quality, purchasing, service or a customer. The ECR records what should change, why (cost, quality, safety, supplier, customer request), the affected parts and documents, and supporting evidence such as test results or field data. Capturing requests in one place prevents good ideas from being lost and bad ideas from being implemented informally.
Step 2: Impact analysis
Before approving, assess the impact across the business:
- Products affected — via where-used searches in the BOM.
- Stock — quantities of old parts in stores, WIP and at suppliers.
- Open orders — purchase orders for old parts, work orders in progress, customer orders committed.
- Tooling and fixtures — modifications or new tools required.
- Quality — inspection plans, validation tests, customer approvals.
- Cost — change in product cost and implementation cost.
- Service — impact on spares for products already in the field.
Good impact analysis prevents surprises like scrapping a large stock of old parts that could have been used up.
Step 3: Review and approval
A cross-functional review — design, quality, production, purchasing, and sales where customers are affected — decides whether to approve, reject or modify the change. The level of review should match the impact: minor documentation fixes may need one approver; changes to safety-critical features need several, and possibly customer approval.
Step 4: Engineering change notice (ECN)
Once approved, an ECN formally communicates the change: what changes, new revisions of drawings and BOMs, the effectivity (from which date, serial, lot or order the change applies), disposition of old stock, and tasks for each department.
Step 5: Effectivity
Effectivity defines when the change takes effect. Options include a date, a production lot or serial number, the next purchase order, or when old stock runs out. Clear effectivity prevents mixing old and new designs unintentionally and makes traceability possible later.
Step 6: Implementation tasks
Each department completes its tasks: design releases new drawings; the BOM owner creates the new revision; purchasing updates supplier orders; production updates work instructions and tooling; quality updates inspection plans and performs first-article inspection; stores relabels or segregates old stock; service updates spares lists. Tracking tasks to completion ensures nothing is forgotten.
Step 7: Verification and closure
After implementation, verify that the change works: first parts inspected, initial production monitored, problems resolved. Then close the change with a record of everything that was done.
Minor versus major changes
Not every change needs a full committee. Define categories — for example, documentation-only, minor (no form, fit or function impact), major (affects form, fit, function, cost or customer) — with appropriate routes. This keeps the process fast for simple changes and rigorous for important ones.
Common problems without a process
- Production building to old drawings after a change.
- Purchasing ordering obsolete parts.
- Large stock of old parts scrapped unnecessarily.
- Inspection plans not updated, so new parts are rejected or bad parts accepted.
- No record of why or when a change was made.
- Customers surprised by changes they should have approved.
Linking to BOMs and drawings
Engineering change is most effective when connected to the BOM and drawing systems: approving an ECN creates new revisions automatically, with effectivity and history. Where-used searches and stock checks run from the same data. See drawing revision control and BOM best practices.
Measuring the process
Track the number of changes, average time from request to implementation, changes by reason and changes that caused problems after implementation. Long cycle times may indicate bottlenecks in approval; frequent changes on one product may indicate design issues.
How software helps
Engineering change software provides request forms, automatic impact analysis from BOM and stock data, approval workflows, ECN generation, revision control and task tracking — with a complete history of every change. See engineering change management software.
Talk to us about controlling engineering changes in your business.
Engineering changes in small companies
Small manufacturers sometimes feel a formal change process is bureaucracy. A simple version still pays off: a single change form, a quick check of stock and open orders, one or two approvers, and a short notice to everyone affected. It takes minutes and prevents the expensive mistakes that informal changes cause.
Frequently asked questions
What's the difference between an ECR and an ECN?
An engineering change request (ECR) proposes and evaluates a change. An engineering change notice (ECN) communicates an approved change and how it will be implemented.
Does every small change need the full process?
Use a lighter path for minor, low-risk changes (for example, a drawing typo) and the full process for changes affecting form, fit, function, cost or customers.
Who should approve engineering changes?
Typically design or engineering, quality, production, purchasing and, where relevant, sales or the customer. The approvers depend on the change's impact.
How do we handle existing stock when a part changes?
Impact analysis decides: use up old stock, rework it, return it or scrap it. The effectivity date is often set to allow old stock to be consumed.
Should customers be informed of changes?
If the change affects form, fit, function or agreed specifications, many customers require notification or approval before implementation.
