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Abstract

The cutting tool is a key element in the milling process; it determines the process performance and the quality of the machined pieces. For best performance, cutting fluids are applied as close as possible to the area between the tool and the work piece. Its primary functions are chip evacuation, cooling of the tool and piece as well as lubrication. Recent developments allow the injection of the fluid through the spindle, the tool holder and finally through a central hole in the cutting tool. For tools with large diameters (> 6mm) one or several central straight channels are used. For tools with small diameter (< 1 mm) no technology exists so far to lubricate the individual cutting edges, at best the internal channels end at the cone of the shank, well before the active cutting part. Due to the limited available space and not to weaken the tool stiffness, lateral holes of a diameter of about 0.1-0.3 mm are required. The position, diameter, shape and angle of these holes have been optimized by means of complex CFD fluid simulations. A 10 pico-second laser was used for drilling the holes in order to avoid thermal impact in the tungsten cobalt (Wc-Co) – hard metal that would occur using other methods like EDM-drilling. For the milling tool of Ø 1.0 mm, the lateral holes have a diameter of 0.12 mm and, for the milling tool of Ø 2.5 mm, the lateral holes are Ø 0.3 mm. The diameter of the central blind hole is identical for both tools, i.e. Ø 0.3 mm. The paper focuses on the hole trepanning technology, i.e. the parametrization of both the laser and the scanner. The tools developed were tested by processing stainless steel with injection of a water based emulsion as cutting fluid with 20 bars through the tiny channels. A significant increase in the tool lifetime as well as an improved surface quality have been observed.

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