Turning of Inconel 718 Using Liquid Nitrogen: Multi-objective Optimization of Cutting Parameters Using RSM

The objective of this research was to investigate the effectiveness of application of liquid nitrogen (LN2) in turning of Inconel 718 compared to flooded cutting and select suitable LN2 cutting parameters using response surface methodology (RSM). The results of turning experiments conducted by spraying LN2 to the cutting area of Inconel 718 bar showed that using either low or high cutting parameters, cutting performance of Inconel 718 under the cryogenic condition was generally worse than the flooded cutting. However, using the medium cutting parameters the cutting performance was as good as flooded cutting showing the values of 90 N of cutting force, 60 µm of flank wear and 0.5-0.6 µm of surface roughness (Ra). These parameters were further optimized using desirability function of RSM to determine the set of parameters that provide the lowest cutting force, flank wear and Ra and the highest material removal rate (MRR) under cryogenic cutting. Analysis of variance (ANOVA) performed on the developed regression models showed that cutting speed was the significant factor on cutting force. Feed rate was the most influential parameter on flank wear. Feed rate and depth of cut was significant factors affecting Ra. Multi-objective optimization showed that a cutting speed of 87 m/min, a feed rate of 0.06 mm/rev and a depth of cut of 0.37 mm constituted the optimum cutting parameters for achieving the, cutting force of 78 N, flank wear of 58 µm, Ra of 0.49 µm and the MRR of 1.97 cm3/min under cryogenic cutting condition.

Study increase the mechanical characteristics of tool materials by cryogenic treatment

In this work, the hypothesis of taking into account a specific thermoEMF to determine the degree of hardening of the cutting tool by cryogenic hardening is put forward, which is the most convenient and important value from the point of view of information content. As a result of studies of improving the mechanical characteristics of instrumental materials by cryogenic treatment, the values of the absolute and specific values of thermo emf were revealed depending on the temperature of three instrumental materials obtained by tarrying them together with platinum. The values of temperatures at the maximum values of the specific thermo emf, have been obtained. It was found that deep cooling of the metal increases the degree of ordering of its structure and increases the vibrational energy of the crystal lattice. The results of the study showed that the resistance of the cryogenic cutting tool increases by up to three times, this positively affects the energy efficiency of the use of such a tool in production. The reduction of energy costs is expressed in the reduction of kilowatt-hours associated with the costs of sharpening the tool and can reach up to 30% of the total amount of electricity consumed.

Cryogenic orthogonal turning of Ti-6Al-4V

Cooling of machining operations by liquid nitrogen is a promising approach for reducing cutting temperatures, increasing tool life and improving the workpiece surface integrity. Unfortunately, the cooling fluid tends to evaporate within the supply channel. This induces process variations and hinders the use of nitrogen cooling in commercial applications. In this work, the coolant is applied via the tool’s rake face during orthogonal turning of Ti-6Al-4V. The effect of a nitrogen supply pressure adjustment and a subcooler usage—proposed here for the first time for machining—is analyzed in terms of process forces, tool temperatures and wear patterns, taken dry cutting as a reference. Thereby, reliable cooling strategies are identified for cryogenic cutting.

Investigation on the Effect of Low Temperature on Impact Properties of Ti-6Al-4V Titanium Alloy

Cryogenic cutting is becoming an attractive machining method for difficult-to-cut materials. However, it’s very difficult to analyze directly their cutting mechanism at low temperature. In order to better understand the various physical phenomena in the cryogenic cutting of titanium alloy, the Charpy impact test of Ti-6Al-4V titanium alloy at low temperatures (as low as -196 °C) was undertaken in this work. The Charpy absorbed energy of Ti-6Al-4V titanium alloy at low temperatures was investigated firstly. Then, by observing the microscopic and macroscopic morphology of the fracture, the impact properties and fracture modes of Ti-6Al-4V titanium alloy at low temperatures were analyzed. It was found that the impact toughness of Ti-6Al-4V titanium alloy reduces when the temperature decreases from 20 °C to -196 °C, and the fracture appears a tendency to become brittle. Meanwhile, three kinds of areas, i.e. shear lip area, fiber area, and radiation area, were found on the fracture morphology at each temperature. Those areas correspond to the shear fracture zone, crack initiation zone, and crack extension zone, respectively. With the decrease in temperature, the proportion of fiber area decreases, and the radiation area appears and increases gradually. However, fiber areas were still observed on the macroscopic morphology of the fracture under − 196 °C, which suggests that Ti-6Al-4V titanium alloy still has the ability to deform plastically at such low temperatures. The research result in this work provide a fundamental support for analyzing the cutting mechanism of Ti-6Al-4V titanium alloy at low temperatures.