Pre-heat strategy: getting the die to operating temperature without killing it

The crew habit that says the first three parts of every shift are scrap is not a process tolerance. It is a habit dressed up as one. If the first three parts are always scrap, the question is why. The answer is almost always preheat. A die that produces a first-article part in tolerance on hit one is a die that was preheated. A die that takes three hits to "warm up" is a die that is taking thermal damage during the warm-up.

The damage is invisible in the moment because heat-check at five or ten initiation sites is below the resolution of a shift-end visual. It shows up 30-50K hits later, when the network is mature enough to see on the die face, by which point the population of initiation sites has fixed the eventual repair-or-scrap outcome. The connection between the cold first hit and the deep heat-check at pull is real, and the durability literature on H13 thermal fatigue documents it across both lab cycle tests and shop case studies.

The shop-floor version of the engineering answer is the documented preheat process: target temperature on the die face at the engraved zone, soak time after that target is reached, surface-to-core delta before the first hit, and a hold authority that supersedes the schedule. A die change that runs over by 20 minutes because the soak is not closed trades 20 minutes of changeover time against 20-40K hits of service life on the back end. The numbers are not in dispute. The hold authority is the variable that decides which outcome the shop gets.