Carbon Break Even Conditions for Cooling Selection in Precision Turning

Minimum quantity lubrication can reduce fluid consumption while increasing compressed air demand, making its carbon advantage dependent on machining quality and tooling performance. This study develops an analytical method for selecting cooling strategies using emissions per accepted turned component. The method combines machine electricity, compressed air, net fluid consumption, cutting edge service and rejected workpieces within a consistent product boundary. Closed form expressions establish the minimum acceptable yield, maximum air demand and minimum cutting edge capacity required for minimum quantity lubrication to outperform flood cooling. An explicitly assumed steel turning case demonstrates the calculations without claiming experimental validation. At the selected electricity factor, minimum quantity lubrication reduces carbon intensity from 4.7177 to 4.6949 kg carbon dioxide equivalent per accepted component, a conditional improvement of 0.48%. Increasing rejection from 2% to 3% reverses that ranking. The corresponding air threshold is 1.558 cubic metres per attempted component. Joint interval analysis also identifies conditions under which neither strategy dominates. The contribution is a reproducible decision method that connects cooling selection to measurable production limits and identifies the evidence required for industrial verification.