Effects of internal cooling by cryogenic on the machinability of hardened steel

The present study includes three parts—design and development of rotary liquid nitrogen applicator, investigation of machining performance under cryogenic application by using the developed applicator, and lastly comparison of the performances with dry and flood cutting. The surface milling of hardened EN 24 steel was performed at different speed-feed combinations corresponding to full factorial design plan (48 exp. runs). The effects of cutting speed, feed rate, and cutting conditions were investigated in respect of surface roughness, cutting force, and tool flank wear. The results of this study revealed the supremacy of cryogenic cooling in respect of all investigated quality characteristics. Lack of cooling and lubrication in dry cutting, and inadequate cooling and lubrication of flood cutting resulted in worse performance. On contrary, the double action cooling effect of cryogenic produces a superior performance, when passes through internal channel, firstly—due to an increased heat transfer rate caused by the primary and secondary flow within cutter, and secondly—because of the creation of a swirl flow at the outlet of the channel but within work surface.