Flame hardening, which increases the local hardness of a metal die, is an essentialprocess for the press dies that punch out necessary shapes from steel. Witha 5-m size press die, moving a torch so that it smoothly follows the shape of thedie is a difficult feat that only some skilled workers can accomplish, and eventhough those skilled workers may be able to achieve greater hardness than thetarget value, when it comes to hardness variations their performance is inconsistent.In an effort to reduce quality variations due to human and environmentalfactors, we attempted to turn skill into technology in three steps. Step 1 wasto establish optimum conditions through parameter design. Step 2 was to confirmchanges in the S/N ratio due to human and environmental factors. Step 3was system and tool development aimed at specific factors. Through use of aspecial jig developed by this procedure, it became possible to perform more consistentflame hardening and eliminate hardness defects in press dies.