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This paper presents a novel indirect cryogenic cooling system, employing liquid nitrogen (LN 2 ) as a coolant for machining the difficult-to-cut ASTM F-1537 cobalt-chromium (CoCr) alloy. The prototype differs from the already existing indirect cooling systems by using a modified cutting insert that allows a larger volume of cryogenic fluid to flow under the cutting zone. For designing the prototype analytical and finite element, thermal calculations were performed; this enabled to optimize the heat evacuation of the tool from the rake face without altering the stress distribution on the insert when cutting material. Turning experiments on ASTM F-1537 CoCr alloys were performed under different cutting conditions and employing indirect cryogenic cooling and dry machining, to test the performance of the developed system. The results showed that the new system improved surface roughness by 12%, and cutting forces were also reduced by 12% when compared with the existing indirect cryogenic cooling technique.

In order to make clear the effect of heat-force on tool wear for milling Ti-6Al-4V alloy in cryogenic cooling. The thermal-mechanical calculation models were established. Compared with conventional cutting, the thermal-mechanical effect rules and thermal action characteristics were analyzed in cryogenic cooling. As well as the cryogenic cooling milling method was executed for a series of processing experiments. The influence of heat-force on chip morphology and surface quality are researched. Meanwhile, the regular tool wear and mechanism were discussed. The results show that the measurement data and change tendency of milling forces are similar to the calculated data; the model is basically effective. Besides, when the cutting micro-unit is kept away from the tool nose, the tool-workpiece contact temperature and cutting force are all slow change compared with conventional cutting in cryogenic. Because of the tool-workpiece interaction squeezing action, the plastic-brittle deformation is obtained under the effect of liquid nitrogen cold quenching. Furthermore, the built-up edge in tool nose is not formed in cryogenic with unobvious thermal softening effect, so the friction effect of hard material is reduced. As a result, it improves obviously the workpiece machining quality and tool life, even as the stable wear range of tool has been transformed from 0.075–0.2 to 0.05–0.26 mm. Therefore, the thermal- mechanical effect influences tool wear, and controlling heat-force is evident, effective for improving tool life through cryogenic cooling.

The current trends in the creation of high-energy repetitively pulsed continuous wave lasers with pulse energies of tens and hundreds of joules are considered. Active media are analyzed for their use in such lasers. The Yb:YAG active crystalline and ceramic elements produced in Russia are experimentally studied at temperatures from 100 to 295 K. The data of the cryogenic cooling system for active elements are presented. A diode pumping system for active elements and a homogenizer for its emission are described. The physical and technical characteristics of the pumping system are given. Fresnel losses, absorption losses, and losses due to enhanced spontaneous emission, which reduce the energy stored in the inverse population, are measured experimentally. The results of measuring the gain in multi-pass circuits with different sets of active elements are presented.

Aerospace metal honeycomb materials with low stiffness had often the deformation, burr, collapse, and other defects in the mechanical processing. They were attributed to poor fixation method and inapposite cutting force. This paper presented the improvement of fixation way. The hexagonal aluminum honeycomb core material was treated by ice fixation, and the NC milling machine was used for a series of cryogenic machining. Considering the similar structure of fiber-reinforced composite materials, the milling force prediction model of ice fixation aluminum honeycomb was established, considering tool geometry parameters and cutting parameters. Meanwhile, the influence rule on milling force was deduced. The results show that compared with the conventional fixation milling method, the honeycomb processing effect is improved greatly. The machining parameters affect order on milling forces: the cutting depth is the most important, followed by the cutting width, then the spindle speed and the feed. Moreover, too small cutting depth ( a p  = 0.5 mm) will cause insufficient cutting force, while a p  > 2 mm with higher force will reduce the processing quality of honeycomb. Simultaneously, the honeycomb orientation ( θ ) has a great influence on processing quality. Using the model, the predicted and measured error values of the feed and main cutting force are all small in θ  < 90°. But, the rate is 33 and 26% for the main cutting force and feed force error in θ  > 90°, respectively, while they all exhibit the smallest error in θ  = 60°. This bigger error mainly is due to unstable cutting force with obtuse angle. In addition, the tool rake angle has little influence on cutting quality in θ  < 90°, but bigger on that in θ  > 90°. Furthermore, the calculation model successfully conforms to the main deformation mechanism and influences parameters of the cutting force in the milling process, and it can accurately predict the cutting force in θ  < 90° and guide the milling process.

The adiabatic shear band (ASB) is easily generated in high-speed cutting, as well as the serrated chip. The main factors are high temperature and elastoplastic instability. An adiabatic shear energy dissipation model was established and analyzed. A series of milling experiments were systematically conducted with cryogenic and conventional cooling. Meanwhile, the characteristics of the workpiece and chip were investigated and compared. The results show that under the conventional cooling, at the cutting speed of 150 m/min, the ASB and generated serrated chip can be produced with the high-frequency oscillation cutting force. In cryogenic, the chip is serrated at all kinds of cutting speed, especially high speed, and the sawtooth is regular with no obvious ASB. The serrated chip formation is mainly associated with brittle cutting in cryogenics. When the cutting parameters are unchanged, the energy dissipation is mainly determined by the main cutting force and shear strength. Compared with the conventional cooling process, the energy dissipation in cryogenic is more than the former one, and the ability of producing instantaneous adiabatic shear is weaker. Furthermore, due to the instantaneous cold brittleness of liquid nitrogen, the generating condition of the ASB is not satisfied in the shear zone.

Because of its outstanding strength-to-density ratios, corrosion resistance, and other superior properties, Ti-6Al-2Zr-1Mo-1 V titanium alloy (TA15) is widely employed in aeronautics and astronautics. TA15 is a typical difficult-to-cut material with low heat conductivity, a high cutting temperature, and an easy adhesion characteristic. When machining difficult-to-cut materials, cryogenic machining is an efficient way to lower the cutting temperature. There is, however, few research on machining TA15 under cryogenic cooling conditions. In this study, tensile tests were performed under different low-temperature cooling conditions. By analyzing the changes of material properties under different low temperatures, the machining mechanism of TA15 under cryogenic cooling conditions was revealed. Then, cutting experiments were carried out under three cooling conditions: dry, cutting fluid (wet), and liquid nitrogen internal cooling (cryogenic). The results show that under cryogenic conditions, TA15 can effectively reduce plasticity and adhesion. The cutting experiments also prove that machining TA15 under the cryogenic cooling condition can reduce the surface adhesion, improve the machining quality of the machined surface, and effectively reduce the generation of tool adhesion wear.

Owing to superior physio-chemical characteristics, titanium alloys are widely adopted in numerous fields such as medical, aerospace, and military applications. However, titanium alloys have poor machinability due to its low thermal conductivity which results in high temperature during machining. Numerous lubrication and cooling techniques have already been employed to reduce the harmful environmental footprints and temperature elevation and to improve the machining of titanium alloys. In this current work, an attempt has been made to evaluate the effectiveness of two cooling and lubrication techniques namely cryogenic cooling and hybrid nanoadditive–based minimum quantity lubrication (MQL). The key objective of this experimental research is to compare the influence of cryogenic CO 2 and hybrid nanofluid–based MQL techniques for turning Ti–6Al–4V. The used hybrid nanofluid is alumina (Al 2 O 3 ) with multi-walled carbon nanotubes (MWCNTs) dispersed in vegetable oil. Taguchi-based L9 orthogonal-array was used for the design of the experiment. The design variables were cutting speed, feed rate, and cooling technique. Results showed that the hybrid nanoadditives reduced the average surface roughness by 8.72%, cutting force by 11.8%, and increased the tool life by 23% in comparison with the cryogenic cooling. Nevertheless, the cryogenic technique showed a reduction of 11.2% in cutting temperature compared to the MQL-hybrid nanofluids at low and high levels of cutting speed and feed rate. In this regard, a milestone has been achieved by implementing two different sustainable cooling/lubrication techniques.

The heating neutral beam injectors (HNBs) of ITER are designed to deliver 16.7 MW of 1 MeV D0 or 0.87 MeV H0 to the ITER plasma for up to 3600 s. They will be the most powerful neutral beam (NB) injectors ever, delivering higher energy NBs to the plasma in a tokamak for longer than any previous systems have done. The design of the HNBs is based on the acceleration and neutralisation of negative ions as the efficiency of conversion of accelerated positive ions is so low at the required energy that a realistic design is not possible, whereas the neutralisation of H− and D− remains acceptable ( 56%). The design of a long pulse negative ion based injector is inherently more complicated than that of short pulse positive ion based injectors because: negative ions are harder to create so that they can be extracted and accelerated from the ion source; electrons can be co-extracted from the ion source along with the negative ions, and their acceleration must be minimised to maintain an acceptable overall accelerator efficiency; negative ions are easily lost by collisions with the background gas in the accelerator; electrons created in the extractor and accelerator can impinge on the extraction and acceleration grids, leading to high power loads on the grids; positive ions are created in the accelerator by ionisation of the background gas by the accelerated negative ions and the positive ions are back-accelerated into the ion source creating a massive power load to the ion source; electrons that are co-accelerated with the negative ions can exit the accelerator and deposit power on various downstream beamline components. The design of the ITER HNBs is further complicated because ITER is a nuclear installation which will generate very large fluxes of neutrons and gamma rays. Consequently all the injector components have to survive in that harsh environment. Additionally the beamline components and the NB cell, where the beams are housed, will be activated and all maintenance will have to be performed remotely. This paper describes the design of the HNB injectors, but not the associated power supplies, cooling system, cryogenic system etc, or the high voltage bushing which separates the vacuum of the beamline from the high pressure SF6 of the high voltage (1 MV) transmission line, through which the power, gas and cooling water are supplied to the beam source. Also the magnetic field reduction system is not described.

We demonstrate optical cycling and laser cooling of a cryogenic buffer-gas beam of calcium monohydride (CaH) molecules. We measure vibrational branching ratios for laser cooling transitions for both excited electronic states A and B . Furthermore, we measure that repeated photon scattering via the A ← X transition is achievable at a rate of ∼ 1.6 × 1 0 6 photons s −1 and demonstrate interaction-time limited scattering of ∼ 200 photons by repumping the largest vibrational decay channel. We also demonstrate a sub-Doppler cooling technique, namely the magnetically assisted Sisyphus effect, and use it to cool the transverse temperature of a molecular beam of CaH. Using a standing wave of light, we lower the transverse temperature from 12.2(1.2) mK to 5.7(1.1) mK. We compare these results to a model that uses optical Bloch equations and Monte Carlo simulations of the molecular beam trajectories. This work establishes a clear pathway for creating a magneto-optical trap (MOT) of CaH molecules. Such a MOT could serve as a starting point for production of ultracold hydrogen gas via dissociation of a trapped CaH cloud.

Torque sensors such as the torsion balance enabled the first determination of the gravitational constant by Henri Cavendish1 and the discovery of Coulomb’s law. Torque sensors are also widely used in studying small-scale magnetism2,3, the Casimir effect4 and other applications5. Great effort has been made to improve the torque detection sensitivity by nanofabrication and cryogenic cooling. Until now, the most sensitive torque sensor has achieved a remarkable sensitivity of 2.9 × 10−24 N m Hz−1/2 at millikelvin temperatures in a dilution refrigerator6. Here, we show a torque sensor reaching sensitivity of (4.2 ± 1.2) × 10−27 N m Hz−1/2 at room temperature. It is created by an optically levitated nanoparticle in vacuum. Our system does not require complex nanofabrication. Moreover, we drive a nanoparticle to rotate at a record high speed beyond 5 GHz (300 billion r.p.m.). Our calculations show that this system will be able to detect the long sought after vacuum friction7–10 near a surface under realistic conditions. The optically levitated nanorotor will also have applications in studying nanoscale magnetism2,3 and the quantum geometric phase11.A torque sensitivity of (4.2 ± 1.2) × 10−27 N m Hz−1/2 is achieved at room temperature. This sensitivity would be enough to measure vacuum friction.