Deep-Hole Drilling in Stainless Steel with Small Diameter Twist Drills

In this paper results of manufacturing tests are described done in order to evaluate the performances of twist drills of diameter d = 1.2 mm and 1.4 mm respectively, if boring into stainless steel X90CrMoV18 (1.4112). Deep-hole drilling was realized thus, that the depth of the bore hole was greater than 10 times the diameter of the twist drill (L/d >10). In order to reduce the impact on the environment caused by the coolant, it was found that minimum quantity lubrication (MQL) can be applied. Hence, the ecology of the mass production of perforated discs for the food processing industry can be improved. The performance of the several small diameter twist drills was determined and evaluated by, firstly, their deep-hole drilling capability, e.g. assessed by the variation or even increase of cutting forces with increasing depth and travel, whether the forces exceed a critical level due to poor chip extraction. In addition, the suitability to use or rather implement the different small diameter twist drills for high-speed cutting (HSC) and finally the individual tool service life for each investigated twist drill. This research project has shown that the accomplishable performance and operating time are strongly dependent on tool cutting material and the tool geometry, especially the size of the chip flutes of a twist drill, as well as the individual coating of the cutting tools.