A significant amount of work has been conducted on thermally-assisted machining with a great deal being focused on laser-assisted machining. The body of work has shown that preheating of the workpiece (usually localized heating) makes it possible to machine certain structural ceramics with a conventional cutting tool, improves the machinability of superalloys, and improves the micro-end milling of metals. A variety of metrics have been used to ascertain the impact of thermal assistance on the machining of these materials including: specific cutting energy, tool wear rate, surface roughness, residual stress, material removal rate, material removal mechanism, cost, and surface integrity. Combined, these quantities provide a good but incomplete description of the process and efficacy of thermal assistance. This manuscript looks at the flow of energy in thermally-assisted machining in an attempt to determine how beneficial preheating is. Some efficiency metrics are suggested and used to study the data that has been collected to date. The total thermal energy deposited in the workpiece is compared to the theoretical minimum required to heat the removed material in order to determine what percentage of the deposited (i.e. absorbed) energy is actually used in assisting the cutting process. This enables a comparison between cutting processes (e.g. end milling and turning) and operating conditions to determine how efficiently the added thermal energy is being used. Compared with other machinability metrics the thermal energy efficiency is used to evaluate how beneficial preheating is to the machining processes studied. Two sets of data are studied: laser-assisted turning of silicon nitride and partially-stabilized zirconia. The specific energy for LAM of silicon nitride is compared to that for grinding of silicon nitride. It is hoped that this presentation will spark debate in the manufacturing community and provide more insight into thermally-assisted manufacturing.

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