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Lesson 10·Vendor handoff

Vendor handoff: what goes on the print to the heat treater, nitride house, and polisher

Three annotated print callouts for the three outside vendors in a forge die build, and the line items to keep off the print so the spec stays right-sized.

8 min readLesson 10 of 13

Tying it together

What this means on the shop floor

A complete heat treat callout is eleven lines, a complete nitride callout is ten lines, and a complete polish callout is six lines. Anything shorter leaves vendor discretion in the spec.

The witness coupon is the evidence that turns the certificate into something more than testimony. A heat-treat coupon carries hardness, retained austenite, and a microstructure photomicrograph. A nitride coupon carries a microhardness traverse, a compound-layer cross section, and the Kn log. A polish coupon carries Ra by zone.

Substrate, process, and inspection definitions move together across the three callouts. The heat-treat final temper temperature sets the nitride upper bound. The nitride compound layer thickness sets the polish removal budget. A print that handles each handoff in isolation leaves gaps the vendor chain fills with assumptions.

Pushback questions for the vendor chain

  1. What is the cycle trace, witness coupon, and acceptance documentation each vendor will return, and how does each artifact map back to a print callout?
  2. Where does each vendor's standard recipe differ from the print, and which differences are acceptable substitutions and which are not?
  3. What is the substrate state at delivery between vendors (heat-treat to nitride, nitride to polish), and what cleanliness or surface preparation does the next vendor expect?
  4. Which line items on the print drive the most schedule overhead, and which of those line items the application actually needs?

Common confusions

A print that names the standard without the parameters is incomplete. "Heat treat per AMS 2759/3" defines the documentation chain but does not commit the vendor to a specific austenitize temperature, quench medium, or temper sequence. The standard is a framework, not a recipe.

A witness coupon is not optional on a controlled job. Without a coupon, the certificate documents a process the vendor ran without verification that the process produced the result. The coupon is the evidence. The certificate is the chain of custody.

A single drawing or routing should travel the full vendor chain. Each vendor needs to see what the previous vendor delivered (surface state, hardness, distortion budget consumed) and what the next vendor needs (cleanliness, case depth, masking). A heat-treat-only print that does not mention the downstream nitride leaves the heat treater free to over-temper the core for an extra HRC of margin that the nitride cycle then drops by 4 HRC because the temper temperature was too close to the nitride temperature.

Up next: the big four failure modes and how the build prevents them.

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