Handle every design change in writing. Issue a new drawing revision, state which batch or date the change applies from, agree any cost and timing impact, and check the first parts made to the new revision. Changes made by phone or chat are the most common cause of mixed or wrong parts.
The same rule applies the other way. The factory should not change material, process, tooling or subcontractor without your written approval. Both sides need one named contact who can approve changes, so requests do not get lost between sales staff and the shop floor.
A simple change process
- Raise a change request that describes what changes and why.
- Issue a new drawing with a new revision letter and a list of changes.
- Ask the factory to confirm the impact on price, tooling, lead time and stock.
- Agree the effective point, such as a batch number, purchase order or date.
- Decide what happens to parts and material already made to the old revision.
- Approve first parts to the new revision with a dimensional report.
- Mark shipments so old and new revisions are never mixed.
Work in progress and stock
Changes mid-batch are costly. Material may already be cut, castings may already be poured and parts may be half machined. Decide whether to finish existing work to the old revision, rework it, or scrap it. Each choice has a cost, and the factory will expect you to agree who pays.
If tooling must change, the pattern, die or fixture may need modification. Ask the factory how long that takes and whether it affects tool life. Update your tooling register.
Group small changes where you can. Five changes released one week apart cause five rounds of confusion on the shop floor. One planned revision with all five changes is easier to control and to check.
Changes the factory proposes
Factories sometimes propose changes to save cost or time, such as a different material grade, a casting instead of a machined part, or a different thread. Some are good ideas. Treat them the same way: in writing, with samples and approval.
Put a clause in your contract that bans unapproved changes and requires notice. Many quality drops start with a small change nobody reported, as explained in why quality drops after the first container.
Keep the record
Keep a change log that lists each revision, its date, the effective batch and the approval. When a problem appears later, the log tells you which revision the parts were made to. Ask the factory to print the revision on its inspection reports and packing labels, so you can check it on arrival. For contract wording, see what an engineering purchase contract should include.
Next step
We check that factories work to the right revision and verify first parts after a change. Book a free sourcing review.