Ensuring durability of small-sized drills in deep drilling

When drilling holes with a diameter less than 3 mm and supplying cutting fluid (CF) by irrigation, there is an effect of pumping the CF out of the cutting zone. In this case, the helical surfaces of the flute grooves of the drill play the role of a screw conveyor. The pair: the helical surface of the drill - the machined hole, constitute an element of the screw pump. The smaller the diameter of the drill and the higher the frequency of its rotation, the higher the performance of such a pump. Experiments show that when machining holes with a diameter of 1.5 mm and a depth of 20 mm at rotation frequencies of 3,000...6,000 rpm, the CF supplied by irrigation does not reach the cutting edges of the drill, and in fact, the cutting process is carried out “dry”. This requires frequent re-sharpening of drills. Sometimes workers-operators have to make up to 100 re-sharpenings of drills during one shift. An increase in the number of re-sharpenings per shift leads to an increase in the number of adjustments, a decrease in processing productivity, a reduction in resource and an increase in drill consumption. In some cases, it turns out that when drilling, all parameters of the holes are maintained according to the requirements of the drawing, but the drill loses its cutting ability after 3-6 holes and often on the first hole. In this case, they remove this drill, put the next one and re-adjust the operation. It has been established that the magnitude of the spread of the geometric parameters of drills with stationary sharpening can significantly affect the number of failures of the drills, cutting forces, cutting modes and, consequently, the productivity and technical reliability of the operation. The article discusses the possibility of increasing the durability of small-sized drills due to special sharpening, which provides a breakdown of the machined hole that is acceptable in terms of accuracy. This ensures the penetration of CF into the cutting zone. Application of the new sharpening method increased the average durability of drills by 28%.