Low-temperature Machine Research Articles

Low temperature machining advantages for sintered NdFeB magnets: A comparative experimental study of WAWJ with laser and WEDM

Sintered NdFeB magnets exhibit excellent magnetic properties and high reliability, making them widely used in fields such as new energy vehicles and electronic communications. However, NdFeB magnets have a low Curie temperature and poor thermal stability. Common machining methods such as laser cutting and EDM (Electrical Discharge Machining) often involve cutting temperatures in the hundreds or even thousands of degrees Celsius, leading to defects such as melting and cracks on the magnet surface. These defects degrade the surface quality and magnetic properties of the magnet. To avoid thermal damage to the magnet during processing, WAWJ (Wet Abrasive Waterjet) cutting was employed on sintered NdFeB. Experimental results indicate that at an ambient temperature of 4.5 °C, the maximum cutting temperature remains below 50 °C, with an average cutting temperature below 25 °C. No heat-affected zones or oxidation layers are exhibited on the cutting surface of the magnet. Jet pressure is identified as the primary factor influencing the maximum cutting temperature, accounting for 96.13 %. With jet pressure increasing from 200 MPa to 280 MPa, the maximum cutting temperature rises from 38.7 °C to 47.9 °C. Furthermore, to validate the necessity of low-temperature cutting for NdFeB magnets, WEDM (Wire Electrical Discharge Machining) and laser cutting were employed on sintered NdFeB magnets. The cutting surfaces of both methods exhibit defects such as cracks, craters, and melting. Compared to the original magnet surface, no significant changes in elemental content were observed on the WAWJ-cut surface. Under high-temperature conditions, the oxidation rate increased, leading to a 18.9 % and 19.8 % increase in oxygen content on the WEDM and laser machined surfaces, respectively. Some neodymium (Nd) and iron (Fe) elements exist in the form of oxides such as FeO and Nd2O3, resulting in loss of magnetism. Moreover, the presence of oxides reduces the continuity of magnetic phases, adversely affecting the magnetic properties of the magnet.

Research on the influence of ultra-low temperature extreme environments on the surface quality and fatigue life of FeCoCrNiAl0.6 high entropy alloy

This study examines the impact of low-temperature cooling on the surface integrity and fatigue properties of the FeCoCrNiAl0.6 high entropy alloy during machining. Utilizing Abaqus2023/Fe-safe simulations, liquid nitrogen cooling, and fatigue tensile tests, it was observed that low-temperature machining improves surface quality and increases tensile strength and fatigue life compared to room temperature machining. At a cutting speed of 2800 mm/min while the temperature drops to −120 °C, the surface roughness can be minimized to the maximum extent possible. Yield strength and tensile strength increased by 7.6 % and 12.5 %, respectively, at this condition, compared to room temperature. Moreover, material strength improves significantly under low-temperature conditions, with yield and tensile strengths at −120℃ being 1.16 and 1.4 times higher than at room temperature. The fatigue life of specimens also improved under low-temperature conditions, with lives reaching 2.82 × 106 cycles at −120℃, an 86.9 % increase over room temperature. The study concludes that optimal machining performance is achieved at higher cutting speeds and shallower cutting depths under low-temperature conditions.

Surface Quality for Cryogenic Milling Mg-1.6Ca-2.0Zn Medical Magnesium Alloy

As an absorbable and implantable biomedical material, magnesium alloy has made great progress in the application of biomaterials in recent years because of its excellent biocompatibility and biomechanics. At the same time, the disadvantages of magnesium alloy materials are more obvious. Because of the large linear expansion coefficient of magnesium alloy, the high temperature during dry cutting will lead to the degradation of machined surface quality. In addition, due to the active chemical properties of magnesium, cutting fluid is easy to cause corrosion of machined surface, and it is easy to react with water in cutting fluid to release hydrogen, causing accidents. In this paper, the effect of cryogenic milling with liquid nitrogen on the surface quality of magnesium alloy was studied by comparing the prepared magnesium alloy in different cooling environments, and the surface roughness model was established for prediction and verification. The results show that the roughness value of the surface machined by liquid nitrogen cryogenic milling is smaller than that of dry cutting, and the hardness value is larger than that of dry cutting, which is very beneficial to improve the surface quality of workpiece. This paper aims to improve the low-temperature machining process of magnesium alloy, and provide theoretical and practical guidance for the preparation, processing and application of high-performance medical magnesium alloy.

Tailoring Surface Integrity of Biomedical Mg Alloy AZ31B Using Distinct End Mill Treatment Conditions and Machining Environments

Magnesium alloys are identified as the new generation degradable biomaterials in the biomedical industry. They can prevent secondary operation for the removal of the inserted implant. Nowadays, sustainable manufacturing is promoting the use of low-temperature machining environments over the traditional means. Surface integrity characteristics of the machined surface and tool wear have always been some of the key interests of the researchers. In this research, aluminum titanium nitride-coated cemented carbide end mills were employed in an untreated and cryo-treated condition to machine the biomedical magnesium alloy AZ31B. The experiments were designed using one-factor-at-a-time (OFAT) approach, and milling operations were conducted under three different machining environments, namely wet, cryogenic, and hybrid. Spindle speed, feed rate, and depth of cut were chosen as the input control variables for a comparative study to achieve lowest surface roughness and highest surface microhardness. The results displayed an improvement in the outcome at higher spindle speed (2800 rpm) and lower feed rate (80 mm/rev) and depth of cut (0.5 mm) produced by untreated end mill during cryo-milling. However, the treated end mill performed best with hybrid machining environment (simultaneous application of LN2 and cutting fluid) during milling. Moreover, in this case, the accumulated oxides were found to form the most uniform and thinnest passivation layer over the milled surface. Higher spindle speed in cryo-milling achieved 27.45 and 19.56% better surface finish than wet and hybrid-milling, respectively. Moreover, higher spindle speed in cryo-milling achieved 14.46 and 8.72% higher surface microhardness than wet and hybrid-milling, respectively. Higher spindle speed in hybrid-milling achieved 14.89 and 6.97% better surface finish than wet and cryo-milling, respectively. Furthermore, higher spindle speed in cryo-milling achieved 7.69 and 4.10% higher surface microhardness than wet and cryo-milling, respectively.

Enhancement of corrosion resistance to sterilization stages of a biomedical grade AISI 316L stainless steel by means of low-temperature machining

Austenitic stainless steels are currently used for the manufacture of reusable medical instruments, thanks to their combination of elevated strength, corrosion resistance, biocompatibility and low cost. However, during their service life, they are subjected to repeated sterilization cycles, which lead to the loosening of the surface oxide stability and, as a consequence, the decrease of their durability.In the present study, the in-service corrosion behaviour of the AISI 316L stainless steel was investigated after being machined using two low-temperature coolants, namely Liquid Nitrogen (LN2) and gaseous Nitrogen (N2) cooled by LN2 to -100°C, as well as using a conventional cutting fluid.Results showed that the AISI 316L microstructure near the machined surface was significantly affected by the machining cooling strategies with the generation of a hardened and more compressed layer when low-temperature coolants were used. Such surface integrity enhancements contributed to improve both the general and localized corrosion resistance to sterilization stages. From this basis, machining using low temperature coolants can be considered a suitable technique to manufacture medical devices of increased durability.

Low Temperature Machining of Nitrile Rubber

This paper presents an innovative methodology to improve machining of nitrile rubber. The research comprises of turning of nitrile rubber under ambient (dry) and low- temperature (dry ice) condition against HSS cutting tool. Individual machining force data for all the tests were documented with the help of a Kistler dynamometer. The low temperatures freeze the material previous to machining so that it cannot alter or adhere to the cutting edge, thus resulting in low wear on the edge and improved machining. To achieve a stable condition for the rubber machining, a mandrel was designed to hold the rubber workpiece. It was observed that 36.19% reduction in cutting force, 6.08% decrease in radial force and 23.3% drop in feed force were obtained when cutting was made at low-temperature machining as compared to dry cutting with cutting speed increased from 162.58 m/min to 226.19 m/min, with 1 mm depth of cut and tool feed of 0.5 mm/rev. This concludes that a remarkable decrease in cutting force value can be obtained by adopting low-temperature cooling. Thus, this new approach concludes that dry ice machining of nitrile rubber should be amended in a directive to acquire better machining results.

Low-temperature machining in a fully submerged cryogenic environment

ABSTRACTThe role of an immersive cryogenic environment in affecting material response in machining was explored using dynamometry, calorimetry, electron microscopy, and microindentation. Effects of tool rake angle on energy dissipation, stored energy of cold work, deformed microstructure, and hardening were evaluated for machining under a fully submerged cryogenic cutting environment and a dry cutting environment. Sustained immersion of the cutting zone in liquid nitrogen resulted in greater energy dissipation and hardening in the work and machined subsurface. This increased hardening at low temperature was directly linked to greater microstructure refinement and a lower fraction of dissipated energy stored in the form of added defects and grain boundaries. Various microstructure types with domain sizes from microscale to nanoscale were developed in the machined chips, depending on the rake angle and temperature used.

A Thermo-Economic Study of Storage Integration in Hybrid Solar Gas-Turbine Power Plants

A thermo-economic simulation model of a hybrid solar gas-turbine (HSGT) power plant with an integrated storage unit has been developed, allowing determination of the thermodynamic and economic performance. Designs were based around two representative industrial gas-turbines: a high efficiency machine and a low temperature machine. In order to examine the trade-offs that must be made, multi-objective thermo-economic analysis was performed, with two conflicting objectives: minimum investment costs and minimum specific carbon dioxide (CO2) emissions. It was shown that with the integration of storage, annual solar shares above 85% can be achieved by HSGT systems. The levelized electricity cost (LEC) for the gas-turbine system as this level of solar integration was similar to that of parabolic trough plants, allowing them to compete directly in the solar power market. At the same time, the water consumption of the gas-turbine system is significantly lower than contemporary steam-cycle based solar thermal power plants.

Metal Low Temperature Brittleness and Low Temperature Machining

Most metal materials tend to produce brittle fracture at low temperature. Nominal stress of producing brittle fracture is low, generally lower than yield limit. By use of this property, the machinability of the workpiece, tool life and workpiece surface quality can be improved. Classification and application of low temperature machining was introduced in the paper. Tests of low temperature machining were carried out. The test results show low temperature machining is superior to the cutting in normal temperature for the aspects of tool life and the roughness of workpiece surface.

Decontamination of laundry at low temperature with CuWB50, a novel copper-based biocidal compound

Traditional laundry decontamination relies on thermal disinfection that degrades textiles. We investigated the ability of a novel copper-based biocidal compound, CuWB50, to assist in the decontamination of swatches purposely contaminated with Staphylococcus aureus and Acinetobacter during "real-life" low-temperature machine washing with and without 2 commercial detergents. Contaminated and noncontaminated swatches were attached to ballast sheets and washed in cold water for 15 minutes in an industrial Electrolux machine. We assessed colony-forming units (cfu) on the swatches and in the postwash water. Low-temperature machine washing produced only partial reductions in viable methicillin-resistant Staphylococcus aureus and Acinetobacter calcoaceticus baumannii counts on swatches and resulted in cross contamination of other swatches in the same wash. Washing with CuWB50 alone at high concentration (100 mg/L), however, resulted in superior decontamination compared with water alone, whereas washing with a combination of detergent and CuWB50 at low concentration (5 mg/L) yielded synergistic and complete decontamination of swatches and postwash water. Our results show highly effective laundry decontamination using CuWB50 with detergent at low temperature and are timely both in terms of rising energy costs and textile degradation issues.

Wear of cutting tools

The various types of tool material are discussed in relation to properties required for effective performance. Tool wear is considered from a practical point of view (i.e. the influence of machining conditions on the form and magnitude of wear). Methods of reducing tool wear, such as surface treatment of cutting tools, application of cutting fluids and the effect of high and low temperature machining are reviewed.