Investigation of the machinability by milling of the laser sintered Inconel 625/NiTi-TiB2 composite

OBRABOTKAMETALLOV Vol. 23 No. 1 2021 TECHNOLOGY methods [7], which is most likely caused by the higher strength characteristics of the alloy obtained by laser sintering. Another feature of the studied composite is that it includes titanium diboride TiB 2 , which has a high hardness and negatively affects the durability of the cutting tool. There are no recommendations on the choice of cutting modes for metal matrix composites obtained from powders with the addition of ceramics. Due to the low thermal conductivity coef fi cient of such alloys, the heat produced during processing is transferred more to the tool than to the workpiece, thus causing excessive heating of the cutting edge and, as a result, tool wear [3]. In the process of milling hard-to-machine materials, the processing speed and the feed rate have the greatest impact on the tool life, surface roughness, and cutting forces [8]. According to the reference manual [9], milling heat-resistant nickel alloys is recommended to perform by a hard alloy tool at low cutting speeds of about 15...20 m/min with a feed of 0.02 mm/tooth. However, in the literature [10, 11], heat- resistant alloys milling is recommended to perform at more aggressive cutting modes by a hard-alloy tool with a wear-resistant coating, i.e., processing should be carried by cutdown milling technique at a cutting speed of 20 to 50 m/min at feeds of 0.10...0.15 mm/tooth. In addition, the paper [12] argues that ceramic tools show greater resistance when processing some heat-resistant alloys (such as Inconel 718), but such tools are much more expensive. To improve the machinability of heat-resistant materials, ultrasonic vibrations are applied to the tool or workpiece, which reduces cutting forces, temperature, and tool wear. The paper [13] describes the possibility of processing nickel-based materials on DMG MORI ULTRASONIC machines. However, literature analysis showed that this technology is mainly used for processing brittle materials, glass, and carbon fi ber plastics [14, 15]. At the same time, the work [16] describes the positive effect of ultrasonic vibrations during the milling of a hard-to-machine Ti-6Al-4V alloy. Importantly, the literature on the choice of cutting modes provides information for choosing cutting speeds and feed, while there are almost no recommendations for choosing the depth and width of milling. The authors [17–21] described the method of High-Ef fi ciency Milling (HEM). This method is intended for roughing metals using a small milling depth t and a large milling width B . Milling, which usually uses a large t value and a small width B , causes a concentration of heat in a small part of the cutting tool, accelerating the wear process. The use of the entire available length of the mill allows distributing wear over a larger area, thus prolonging the service life of the tool, as well as dissipating heat and reducing the probability of the mills’ failure. The HEMmethod assumes the use of 7...30 % of the milling cutter diameter in the radial direction and twice the milling cutter diameter in the axial direction in combination with an increased feed rate [17]. Therefore, the machinability study of this nickel-based composite with the addition of ceramics has not been studied, so the work is relevant. The main tasks of this work are: 1. to determine the technology options of end mills processing of a composite based on Inconel 625 with the addition of NiTi-TiB 2 . 2. to determine the cutting speed based on the conditions of minimal tool wear and minimal cutting forces that occur during processing. 3. to determine the optimal ratio of the milling depth to width based on the conditions of minimal tool wear and minimal cutting forces. Research Methodology All work was carried out on a Haas VF1 vertical milling machining center with a CNC, (USA). The processing was carried out by the cutdown milling technique. As a tool, we used solid-carbide end mills Ø10 mm of the model ZhT641 manufactured by the company “PC MION” (Russia), designed for processing heat-resistant titanium alloys. The main geometric parameters of this mill have the following values: the front angle γ = 4  , the rear angle α = 10  , the helix angle of the tooth ω = 38  , the number of