How do I send a supplier a design change after the PO is placed?
Ask the supplier to hold work, release the change as a new drawing revision, and issue a PO change that names the new revision, the quantity it applies to and what happens to parts already made. Don't restart work until the supplier confirms the new revision, price and delivery date in writing.
Why a change after the PO is different
Before the PO, a design change is an internal matter. Where no prior contract exists, the seller's acceptance of a purchase order forms a contract (Wikipedia, Purchase order). Treat the accepted PO as the job: a new drawing in an email does not change it on its own. If the PO names Rev B, Rev B is still the job.
The supplier may also have bought material, written programs or started parts. In SAP Ariba, for example, a changed PO is sent as a new version the supplier must receive and acknowledge, and conflicts can arise if goods already shipped against the old version (SAP Learning).
In our discovery calls with hardware teams, engineers described this going wrong in two ways: a supplier quoting or building from a superseded revision, and a change sent after the PO as a chat message with marked-up slides.
The basics of keeping a supplier on the current revision (revision on the PO line, matched PDF and STEP, written acknowledgment) are in How do I make sure my supplier builds the right revision? This note covers the change itself.
Worked example: 300-0127 pump manifold
PO 4471 is for 40 pieces of 300-0127 Rev B, machined 6061, due in four weeks. On day 9, a leak test shows the port 3 O-ring groove is too shallow. Rev C deepens the groove from 1.50 to 1.80 mm.
1. Hold the work the same day. Call or email the supplier: "Please hold machining on 300-0127, PO 4471. Rev C is coming. Can you tell us what is done?" Ask how far they are: material bought, program written, how many parts at which operation. In this case, 12 parts are through the operation that cuts the groove.
2. Release Rev C properly. Revision symbol at the groove, a line in the revision block saying what changed and why, files exported from the released revision. See How do you do revision control without PDM?
3. Decide the cut-in and what happens to finished parts. An engineering change order says when the change takes effect: immediately (scrapping current inventory), at the next production run, or at another milestone (Wikipedia, Engineering change order). Here the change removes material, so the 12 finished parts can be reworked to Rev C. The other 28 are made at Rev C.
4. Send one change package, filed under the PO:
/300-0127 Pump manifold/
/released/
300-0127.SLDPRT
300-0127.SLDDRW
300-0127_RevC.pdf
300-0127_RevC.step
/_obsolete/
300-0127_RevB.pdf
300-0127_RevB.step
/suppliers/PO-4471/
PO-4471_change-01.pdf line 1 now 300-0127 Rev C
300-0127_RevB-to-RevC_changes.pdf ballooned list of what changed
PO-4471_change-01_ack.pdf supplier's written confirmation
The email subject says what it is: "PO 4471 change 01: 300-0127 Rev B to Rev C." The PO change names the part number and revision, the quantity at Rev C, the rework of the 12 finished parts, and leaves price and date open for the supplier to quote.
5. Get it confirmed in writing. The supplier replies with Rev C, the price for rework and new parts, and the new ship date. Purchasing updates the PO; engineering files the acknowledgment.
6. Check the changed feature on the first Rev C parts. Ask for the groove depth measured on the first parts at Rev C, including the reworked ones. Some customers require more: Lockheed Martin Aeronautics' Quality Clause Q2A (Rev 11, 2015), for example, calls for a partial or full first article inspection after a design change affecting fit, form or function (Lockheed Martin Q2A).
7. Close it out. Move the Rev B files to _obsolete, ask the supplier to remove Rev B prints from the job, and write down why the groove changed, as in How do I document why a part was designed a certain way?
Ways to get a change to a supplier
| Channel | Good for | Main risk |
|---|---|---|
| Phone call or chat message | Stopping work today | Carries no revision and changes nothing on the PO |
| Email with the new PDF and STEP | Getting the files there fast | The PO still names the old revision |
| Marked-up PDF or slide | Showing what you mean before Rev C is released | The supplier builds from a picture, not a drawing |
| PO change with the released revision attached | Making the new revision the job | Slower when purchasing has to approve; expect a re-quote |
| Cancel the PO and place a new one | A change big enough to need a new part number | Possible charges for work already done, depending on PO terms; a new lead time |
| Accepting finished parts at the old revision | Parts that are fine for a known, limited use | Parts on the shelf that don't match the current drawing |
When this stops working
- Most of your POs get at least one change after they are placed.
- One PO has more than one open change, and nobody is sure which is current.
- Purchasing and engineering each have a different answer to "which revision is the supplier building?"
- Changes reach the supplier through chat or calls before the PO change exists, and the paperwork trails by days.
These are signs that changes need one place where engineering, purchasing and the supplier all see the same revision, not a better email.
FAQ
Do I need a new PO for a design change?
Usually not. A PO change that names the new revision, the quantity, and the agreed price and date is enough when the part number stays the same. If the change gets a new part number, it usually goes on a new PO line, or a new PO.
Who pays for parts already made to the old revision?
It depends on your PO terms and what the supplier had done when you told them. Agree on rework, scrap or use-as-is for those parts in the PO change, before work restarts.
Can I just email the new drawing to the supplier?
Email gets the files there, but the PO still names the old revision. Send the files with a PO change, and get the new revision, price and date confirmed in writing.
What should a supplier send back after a design change?
A written confirmation of the new revision, price and delivery date, and the status of parts already made. For the first parts at the new revision, measurements of the changed features.
Internal links
- How do I make sure my supplier builds the right revision?
- How do I check that a drawing revision lists every change?
- How do you do revision control without PDM?
- How do I document why a part was designed a certain way?
Sources
- Wikipedia, Purchase order: https://en.wikipedia.org/wiki/Purchase_order
- SAP Learning, Change a Purchase Order: https://learning.sap.com/courses/managing-purchase-orders-in-sap-ariba-buying-and-invoicing/change-a-purchase-order
- Wikipedia, Engineering change order: https://en.wikipedia.org/wiki/Engineering_change_order
- Lockheed Martin Aeronautics, Quality Clause Q2A, First Article Inspection: https://www.lockheedmartin.com/content/dam/lockheed-martin/aero/documents/scm/Quality-Requirements/Clauses/q2a_rev11.pdf
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