Effect of PCBN cutting tools wear on surface integrality in high-speed hard turning

In this paper, the effect of of flank wear polycrystalline cubic boron nitride （PCBN） tools on residual stresses, white layer and roughness of machined workpiece surfaces is studied. Experimental results indicate that with the increase of the tool wear, the surface of the machined workpiece tends to generate tensile residual stresses, and white layer becomes clearly thicker and uneven on the workpiece surface. The effect of the flank wear on the surface roughness is less within some range of flank wear value. The results show that it is possible to produce ideal surface integrality levels by controlling the tool flank wear.

Gas Film Disturbance Characteristics Analysis of High-Speed and High-Pressure Dry Gas Seal

The dry gas seal（DGS） has been widely used in high parameters centrifugal compressor, but the intense vibrations of shafting, especially in high-speed condition, usually result in DGS＇s failure. So the DGS＇s ability of resisting outside interference has become a determining factor of the further development of centrifugal compressor. However, the systematic researches of which about gas film disturbance characteristics of high parameters DGS are very little. In order to study gas film disturbance characteristics of high-speed and high-pressure spiral groove dry gas seal（S-DGS） with a flexibly mounted stator, rotor axial runout and misalignment are taken into consideration, and the finite difference method and analytical method are used to analyze the influence of gas film thickness disturbance on sealing performance parameters, what＇s more, the effects of many key factors on gas film thickness disturbance are systematically investigated. The results show that, when sealed pressure is 10.1MPa and seal face average linear velocity is 107.3 m/s, gas film thickness disturbance has a significant effect on leakage rate, but has relatively litter effect on open force; Excessively large excitation amplitude or excessively high excitation frequency can lead to severe gas film thickness disturbance; And it is beneficial to assure a smaller gas film thickness disturbance when the stator material density is between 3.1 g/cm3 to 8.4 g/cm3; Ensuring sealing performance while minimizing support axial stiffness and support axial damping can help to improve dynamic tracking property of dry gas seal. The proposed research provides the instruction to optimize dynamic tracking property of the DGS.

Influence of Cutting Speed, Feed Rate and Bulk Texture on the Surface Finish of Nitrogen Alloyed Duplex Stainless Steels during Dry Turning

This paper presents the results of experimental work carried out in dry turning of cast duplex stainless steels (ASTM A 995 Grade4A and ASTM A 995 Grade5A) using TiC and TiCN coated cemented carbide cutting tools. The turning tests were conducted at five different cutting speeds (80, 100, 120, 140 and 160 m/min) and three different feed rates (0.04, 0.08 and 0.12 mm/rev) with a constant depth of cut (0.5 mm). The influence of cutting speed and feed rate on the machined surface roughness was investigated. Texture analysis (Bulk) was also carried out to study the impact of preferred orientation on the resulting surface roughness. The result reveals that the increasing cutting speed decreases the surface roughness till a particular point and then increases whereas;the surface roughness value decreases with the decreasing feed rate. Presence of alpha fiber (Bulk texture analysis) in the austenite phase of 4A work piece material leads to better surface finish. Among both the grades, surface finish of grade 4A is better than grade 5A work piece material.

Grey Relational Optimization of Turning Parameters in Dry Machining of Austenitic Stainless Steel Using Zr Based Coated Tools

The present work aims at the microstructural characterization of TiAlZrN/ Al2O3 and TiAlZrN/Si3N4 coatings deposited via lateral rotating cathodes. The coatings were deposited using Lateral Rotating Cathodes (LARC) technology. The deposited coatings were studied for its cross sectional morphology using scanning electron microscopy. Energy Dispersive Spectrometry was also conducted along the cross section to determine the elemental composition. Micro Vickers hardness test was conducted to determine the hardness of the coatings. The scanning electron microscope images showed that TiAlZrN/Al2O3 coatings showed preferred columnar grain orientation with multilayered structure while TiAlZrN/Si3N4 coatings exhibit a dense grain structure. The TiAlZrN/Si3N4 coating shows a hardness of 31.58 GPa while TiAlZrN/Al2O3 coating shows a hardness of 25.40 GPa. Dry turning tests were performed on AISI 304 stainless steel. The TiAlZrN/Si3N4 coatings show reduced flank wear. Both the coatings even under severe cutting conditions impart surface roughness of less than 1.5 μm.

Surface quality investigation in high-speed dry milling of Ti-6Al-4V by using 2D ultrasonic-vibration-assisted milling platform

Ultrasonic-vibration-assisted milling(UVAM)is an advanced method for the efficient and precise machining of difficult-to-machine materials in modern manufacturing.However,the milling efficiency is limited because the ultrasonic vibration toolholder ER16 collet has a critical cutting speed.Thus,a 2D UVAM platform is built to ensure precision machining efficiency and improve the surface quality without changing the milling toolholder.To evaluate this 2D UVAM platform,ultrasonic-vibration-assisted high-speed dry milling(UVAHSDM)is performed to process a titanium alloy(Ti-6Al-4V)on the platform,and the milling temperature,surface roughness,and residual stresses are selected as the important indicators for performance analysis.The results show that the intermittent cutting mechanism of UVAHSDM combined with the specific spindle speed,feed speed,and vibration amplitude can reduce the milling temperature and improve the texture of the machined surface.Compared with conventional milling,UVAHSDM reduces surface roughness and peak-groove surface profile values and extends the range of residual surface compressive stresses from−413.96 MPa to−600.18 MPa.The excellent processing performance demonstrates the feasibility and validity of applying this 2D UVAM platform for investigating surface quality achieved under UVAHSDM.

High-Speed Machining of Malleable Cast Iron by Various Cutting Tools Coated by Physical Vapor Deposition

The coating material of a tool directly affects the efficiency and cost of machining malleable cast iron.However,the machining adaptability of various coating materials to malleable cast iron has been insufficiently researched.In this paper,turning tests were conducted on cemented carbide tools with different coatings(a thick TiN/TiAlN coating,a thin TiN/TiAlN coating,and a nanocomposite(nc)TiAlSiN coating).All coatings were applied by physical vapor deposition.In a comparative study of chip morphology,cutting force,cutting temperature,specific cutting energy,tool wear,and surface roughness,this study analyzed the cutting characteristics of the tools coated with various materials,and established the relationship between the cutting parameters and machining objectives.The results showed that in malleable cast iron machining,the coating material significantly affects the cutting performance of the tool.Among the three tools,the nc-TiAlSiN-coated carbide tool achieved the minimum cutting force,the lowest cutting temperature,least tool wear,longest tool life,and best surface quality.Moreover,in comparisons between cemented-carbide and compacted-graphite cast iron machined under the same conditions,the wear mechanism of the coated tools was found to depend on the cast iron being machined.Therefore,the performance requirements of a tool depend on multiple factors,and selecting an appropriately coated tool for a particular cast iron material is essential.

Energy field-assisted high-speed dry milling green machining technology for difficult-to-machine metal materials

Energy field-assisted machining technology has the potential to overcome the limitations of machining difficult-to-machine metal materials,such as poor machinability,low cutting efficiency,and high energy consumption.High-speed dry milling has emerged as a typical green processing technology due to its high processing efficiency and avoidance of cutting fluids.However,the lack of necessary cooling and lubrication in high-speed dry milling makes it difficult to meet the continuous milling requirements for difficult-to-machine metal materials.The introduction of advanced energy-field-assisted green processing technology can improve the machinability of such metallic materials and achieve efficient precision manufacturing,making it a focus of academic and industrial research.In this review,the characteristics and limitations of high-speed dry milling of difficult-to-machine metal materials,including titanium alloys,nickel-based alloys,and high-strength steel,are systematically explored.The laser energy field,ultrasonic energy field,and cryogenic minimum quantity lubrication energy fields are introduced.By analyzing the effects of changing the energy field and cutting parameters on tool wear,chip morphology,cutting force,temperature,and surface quality of the workpiece during milling,the superiority of energy-field-assisted milling of difficult-to-machine metal materials is demonstrated.Finally,the shortcomings and technical challenges of energy-field-assisted milling are summarized in detail,providing feasible ideas for realizing multi-energy field collaborative green machining of difficult-to-machine metal materials in the future.

Selection and Evaluation of Dry and Isentropic Organic Working Fluids Used in Organic Rankine Cycle Based on the Turning Point on Their Saturated Vapor Curves

The organic Rankine cycle(ORC)is a popular technique used in the utilization of low-grade thermal energy.Among wet,dry,and isentropic organic working fluids,the latter two types are more appropriate for ORC systems.In this paper,the definition of turning point on saturated vapor curve of dry fluid and isentropic fluid was given according to the shape of the saturated curve of working fluids in a T-s diagram.On this basis,the model of near-critical region triangle was established.Using this model,the thermodynamic performance of 57 kinds of dry and isentropic organic working fluids in ORC was evaluated.The performance includes the relation between turning point temperature and cycle thermal efficiency,the relation between near-critical region triangle area and cycle thermal efficiency,the relation between near-critical region triangle area and exergy at turning point temperature,the relation between near-critical region triangle area and reciprocal value of slope of saturated vapor curve.Moreover,working fluid selection was also conducted in terms of heat source type.It was found through theoretical analysis results that the popular R123 is an acceptable choice especially for the utilization of closed type heat source.Considering it will be phased out in near future,then cis-butene,butane,trans-butene,and isobutene are worth studying as its successor.Dodecane is worthy of attention and further research and it can be a good choice for utilization of open type heat source.

Nondestructive acquisition of the micro-mechanical properties of high-speed-dry milled micro-thin walled structures based on surface traits

Requirements for the service performance of aeronautic microelectronic components are increasingly strict.However,sever issues,that the acquisition of the service performance such as micro-mechanical properties is destructive,limit the subsequent application of the tested components.Addressing this issue,this paper proposes a nondestructive acquisition method of the micro-mechanical properties of the accelerometer micro-components,based on analyzing surface traits.To select qualified components without damage,we firstly developed a quasi-static microtensile tester and then established a combination prediction model of mechanical properties based on micro-milled surface traits.The model works due to the thin-walled structure,which makes the machined surface traits have significant influences on the mechanical properties such as Young’s modulus,yield strength,tensile strength,and elongation at break.Surface roughness,surface structure,and surface anisotropy are extracted to comprehensively present surface traits from different aspects.For improving the practicability of the model,the principal component analysis(PCA)is adopted to reduce high-dimensional traits explanatory variable space into two dimensions,and regression analysis models are comparative established in predicting the mechanical properties.Residuals analysis and error analysis are carried out to show the prediction accuracy.The maximum prediction error is about 10.62%,but the significance levels in the t-test of the predicted Young’s modulus and yield strength are not ideal.Therefore,kernel support vector regression(SVR)is imported to improve the prediction ability of the combination prediction model.The residuals analysis result shows that SVR is effective in enhancing the prediction ability of this model.

EFFECT OF COOLING/LUBRICATION MEDIUM ON MACHINABILITY OF Ti6Al4V

To better understand and know the roles of cooling/lubrication medium in the cutting process and expand their applicability,uncoated cemented carbide tools are used in high-speed turning Ti6Al4V.Dry,cold air,minimal quantity lubrication（MQL）,cryogenic MQL,and ionized air as the cooling/lubrication conditions are studied.Experimental results show that at speed 120 m/min turning Ti6Al4V,the cutting force under ionized air is smallest under all lubricant conditions,and tool life is best,next is cryogenic MQL.MQL and cold air almost have the same effect,a little better than dry.Meanwhile the smallest surface roughness is also obtained under ionized air condition.Flank wear and crater wear are the dominant failure modes when high-speed turning Ti6Al4V by SEM analysis.Finally the conclusion is drawn that ionized air and cryogenic MQL have better cooling/lubrication effects and can effectively improve the tool life.