Engineering change on the shop floor: executing a change without producing mixed builds

Effectivity has to be stated in terms the floor can apply

A change becomes effective from a date, from a serial or lot number, from the exhaustion of existing stock, or immediately on safety grounds. Each implies different action, and a change note that says merely to implement as soon as possible produces a period during which nobody can tell which units were built to which configuration. Pick one basis, state it, and make sure it is expressed as something an operator or a planner can check against the job in front of them. Where the change is safety-related or corrects a defect already in the field, immediate effectivity with recall of released work is the only defensible option.

Old stock, released orders and the run-out decision

The change owner has to decide what happens to purchased components already held, work in progress at various operations, finished goods in the warehouse and material on order with suppliers. Options are run out, rework to the new configuration, scrap, or sell the remainder as the superseded variant. The decision needs the value of the affected stock and the reason for the change: a cost-reduction change usually justifies running out, while a functional or safety change rarely does. Whatever is decided, someone must physically identify the affected stock, because material sitting in a bin does not know a change has been approved.

Everything that has to move together on the day

The list is longer than it appears and a change fails if one item is missed: drawings and work instructions at every station using them, setup sheets, inspection and test instructions, gauges and any fixture or tooling affected, test programmes, the bill of material and routing, packaging and labelling, customer-facing documentation, spare part references, and operator briefing. Missing the packaging spec or a label is the classic case, because the product is right and the box says otherwise. Build the checklist into the change record with a name against each item and a confirmation that it was done.

Mixed builds and telling them apart afterwards

During any transition both configurations exist somewhere, and the plant must be able to say which is which without dismantling anything. That normally means a visible identifier — a revision suffix on the label, a colour, a mark, or a serial range recorded against the change. Physical segregation of the two versions during the transition is worth the floor space it costs. The scenario to avoid is a customer complaint months later where the plant cannot determine whether a particular unit was built before or after the fix, because the containment then covers everything shipped in the whole period.

Verifying the change actually landed on the floor

Approval and implementation are different events, and the gap between them is where changes quietly fail. Somebody should go to each affected station after the effectivity point and check: is the current revision there, is the old copy gone, is the new fixture fitted, does the operator know what changed and why. Then confirm on the first units produced that the intended difference is present and the intended problem is gone. Closing a change record on the strength of a distributed document is the reason plants find superseded instructions in use, sometimes years later, on a change everybody believed was complete.

Frequently asked questions

Who should authorise an engineering change reaching production?

A small standing group with the functions that carry the consequences: engineering for the technical content, production for whether it can be built, quality for verification and customer impact, materials for stock and supplier effect, and commercial where price or contract terms move. One person chairs and the decision is recorded with the effectivity basis. Changes approved by engineering alone are the ones that arrive with obsolete stock nobody planned for and a fixture that has not been ordered.

How do we handle a change that a customer must approve?

Do not implement until the approval is in writing and on file, however obvious the improvement seems. Many supply agreements require notification or approval for changes to design, material, process or manufacturing location, and shipping a changed product without it can invalidate the arrangement regardless of whether the change was beneficial. Where the change is urgent for safety, notify immediately and agree interim arrangements rather than acting first and explaining later.

What do we do about changes made informally on the floor?

Find them, because they exist in every plant: a tool ground to a different profile, a parameter adjusted years ago, an extra operation someone added to make the part fit. Each is an undocumented change that the process now depends on and that nobody could reproduce after a retirement. Periodic comparison of documented method against observed practice surfaces them. Then either formalise the change through the proper route or remove it, rather than leaving the plant's real process undocumented.