Refrigerated cooling air cutting of difficult-to-cut materials

One approach to enhance machining performance is to apply cutting fluids during cutting process. However, the use of cutting fluids in machining process has caused some problems such as high cost, pollution, and hazards to operator's health. All the problems related to the use of cutting fluids have urged researchers to search for some alternatives to minimize or even avoid the use of cutting fluids in machining operations. Cooling gas cutting is one of these alternatives. This paper investigates the effect of cooling air cutting on tool wear, surface finish and chip shape in finish turning of Inconel 718 nickel-base super alloy and high-speed milling of AISI D2 cold work tool steel. Comparative experiments were conducted under different cooling/lubrication conditions, i.e. dry cutting, minimal quantity lubrication (MQL), cooling air, and cooling air and minimal quantity lubrication (CAMQL). For this research, composite refrigeration method was adopted to develop a new cooling gas equipment which was used to lower the temperature of compressed gas. The significant experimental results were: (i) application of cooing air and CAMQL resulted in drastic reduction in tool wear and surface roughness, and significant improvement in chip shape in finish turning of Inconel 718, (ii) in the high-speed milling of AISI D2, cooling air cutting presented longer tool life and slightly higher surface roughness than dry cutting and MQL. Therefore, it appears that cooling air cutting can provide not only environment friendliness but also great improvement in machinability of difficult-to-cut materials.     

Effects of minimum quantity lubrication on turning AISI 9310 alloy steel using vegetable oil-based cutting fluid

This paper presents the effects of minimum quantity lubrication (MQL) by vegetable oil-based cutting fluid on the turning performance of low alloy steel AISI 9310 as compared to completely dry and wet machining in terms of chip–tool interface temperature, chip formation mode, tool wear and surface roughness. The minimum quantity lubrication was provided with a spray of air and vegetable oil. MQL machining was performed much superior compared to the dry and wet machining due to substantial reduction in cutting zone temperature enabling favorable chip formation and chip–tool interaction. It was also seen from the results that the substantial reduction in tool wears resulted in enhanced the tool life and surface finish. Furthermore, MQL provides environment friendliness (maintaining neat, clean and dry working area, avoiding inconvenience and health hazards due to heat, smoke, fumes, gases, etc. and preventing pollution of the surroundings) and improves the machinability characteristics.     

The influence of minimum quantity of lubrication (MQL) on cutting temperature,chip and dimensional accuracy in turning AISI-1040 steel

In metal industries, the use of cutting fluid has become more problematic in terms of both employee health and environmental pollution. But the use of cutting fluid generally causes economy of tools and it becomes easier to keep tight tolerances and to maintain workpiece surface properties without damages. Because of them some alternatives has been sought to minimize or even avoid the use of cutting fluid in machining operations. Some of these alternatives are dry machining and machining with minimum quantity of lubrication (MQL). This paper deals with experimental investigations in the role of MQL on cutting temperature, chip formation and product quality in turning AISI-1040 steel at different industrial speed-feed combinations by uncoated carbide insert. The results have been compared with dry machining and machining with soluble oil as coolant. The experimental results indicate that such MQL enables substantial reduction in the cutting temperature, dimensional inaccuracy depending upon the levels of the cutting velocity and feed rate. It was also noted that the chip formation and chip–tool interaction become more favorable under MQL condition. Therefore, it appears that MQL, if properly employed, not only provides environment friendliness but can also improve the machinability characteristics.     

Drilling of Multi-Layer Composite Materials consisting of Carbon Fiber Reinforced Plastics (CFRP), Titanium and Aluminum Alloys

In this paper results are presented concerning the realization of economical drilling processes of multi-layer materials. Different carbide drill designs with improved geometries and coatings were investigated and compared by characterizing the cutting forces, tool wear, hole quality, and chip formation. Investigations have shown that dry machining of titanium workpiece layers leads to increased tool wear, chip formation problems, and surface damage in the aluminum and CFRP-layers. Consequently, the drilling experiments were carried out with minimum quantity lubrication (MQL) using different cutting fluids and supply strategies. The investigations were mainly focused on the development of the optimum drilling condition with respect to tool shape, tool material, and machining parameters. Another objective of the investigations was to analyze surface defects of the hole and the resulting diameter tolerances due to the high mechanical and thermal loads when machining titanium.     

Cutting temperature, tool wear, surface roughness and dimensional deviation in turning AISI-4037 steel under cryogenic condition

Machining of steel inherently generates high cutting temperature, which not only reduces tool life but also impairs the product quality. Conventional cutting fluids are ineffective in controlling the high cutting temperature and rapid tool wear. Further, they also deteriorate the working environment and lead to general environmental pollution. Cryogenic cooling is an environment friendly clean technology for desirable control of cutting temperature. The present work deals with experimental investigation in the role of cryogenic cooling by liquid nitrogen jet on cutting temperature, tool wear, surface finish and dimensional deviation in turning of AISI-4037 steel at industrial speed-feed combination by coated carbide insert. The results have been compared with dry machining and machining with soluble oil as coolant. The results of the present work indicate substantial benefit of cryogenic cooling on tool life, surface finish and dimensional deviation. This may be attributed mainly to the reduction in cutting zone temperature and favorable change in the chip–tool interaction. Further it was evident that machining with soluble oil cooling failed to provide any significant improvement in tool life, rather surface finish deteriorated.     

Effect of cooling and lubrication conditions on surface topography and turning process of C45 steel

At present coolants and lubricants are increasingly recognized as harmful factors for environment and machine operators’ health. Industry and research institutions are looking for new means of reducing or eliminating the use of cutting fluids, both for economical and ecological reasons. This can be done if quality properties of machined surfaces and process parameters in dry and wet machining are comparable. This paper presents an investigation into the influence of cutting zone cooling and lubrication on surface roughness, waviness, profile bearing ratio and topography after turning C45 steel. Dry cutting and minimum quantity lubrication (MQL) results are compared with conventional emulsion cooling. Cutting forces and their components were put under examination as well. The experimental outcomes indicate that the cooling and lubrication conditions affect significantly the investigated process and surface properties. However, the impact of the cooling and lubricating technique depends to a large extent on the applied cutting parameters, namely the cutting speed and feed rate. Turning dry or with MQL with properly selected cutting parameters makes it possible to produce better surface topography characteristics than turning with conventional emulsion cooling. Apart from improving the surface properties the MQL mode of cooling and lubrication also provides environmental friendliness.     

Performance evaluation of solid lubricants in terms of machining parameters in turning

High speed machining of steel inherently generates large cutting temperatures, which not only reduce tool life but also impair the product quality. Application of cutting fluids influences the performance of machining because of its lubrication and cooling actions. Due to the hazards posed by conventional cutting fluids to ecology and health of the workers, there is a greater need to identify eco-friendly and user-friendly alternatives. Modern tribology has facilitated the use of effective unconventional methods like dry cutting, cryogenic cooling, minimum quantity lubrication and the use of solid lubricants. The present work features a specific study on the application of a solid lubricant mixture like Graphite in SAE 40 oil and boric acid in SAE 40 oil in turning of EN8 steel. Experimental results are encouraging with reduction in tool wear and surface roughness as compared to dry and wet machining.     

内置式MQL喷射特性对车削GCr15轴承钢的影响

微量润滑(MQL,Minimum Quantity Lubrication)加工作为绿色切削技术,其应用逐渐广泛。相对于外置式MQL,内置式MQL具有渗透性好、切屑影响小、效率高等特点。为了寻求出内置式MQL的喷射特性对加工的影响规律,开发了车削内置式MQL系统,设计了四因素三水平的正交实验。以切削力和表面粗糙度为评价指标,切削液流量、空气流量、可生物降解润滑油及切削速度为变量,沿后刀面喷射,进行了车削GCr15轴承钢的正交实验,分析了喷射参数对加工的影响规律,并得到了优化的喷射参数,对机械加工工程应用具有参考意义。     

A Synthetic Ester as an Optimal Cutting Fluid for Minimal Quantity Lubrication Machining

Significant progress has been made in dry and semidry machining recently, and minimal quantity lubrication (MQL) machining in particular has been accepted as a successful semidry application because of its environmentally friendly characteristics. A number of studies have shown that MQL machining can show satisfactory performance in practical machining operations. However, there has been little investigation of the cutting fluids to be used in MQL machining. In this study, several fluids, including vegetable and synthetic esters, are compared on the basis of the physical properties that would be suitable for MQL applications. The cutting performance of fluids is also evaluated using actual MQL operations. As a result, biodegradable synthetic esters are found to be optimal cutting fluids for MQL machining.     

基于MQL的碳纤维复合材料制孔表面质量及切削力试验

目的 减少碳纤维增强复合材料(CFRP)制孔表面毛刺及边缘凸起等缺陷。方法 对比研究在干切削和微量润滑(MQL)2种加工条件下碳纤维增强复合材料(CFRP)的制孔,在切削速度一定时,探究切削方式、进给速度对制孔尺寸精度、表面质量、切削力的影响。采用方差分析对各影响因素及其权重进行分析。结果 得出了切削方式和工艺参数对制孔尺寸精度、切削力、表面质量的影响规律。试验结果表明,在微量润滑条件下,由于润滑和降温的影响,表面毛刺得到有效去除,纤维断面平整,剪切作用明显,抑制了由温升所引起的边缘隆起膨胀现象,试样的表面质量得到显著提高,切削力整体降低。在干切削和微量润滑条件下对制孔尺寸精度影响最大的是切削方式。对于切削力,在干切削时受到切削方式的影响最大,在微量润滑条件下受到进给速度的影响最大,随着进给速度的增大而增大。结论 在现有试验条件下,微量润滑的加工质量总体上优于干切削的加工质量,其制孔尺寸的精度整体更高,其切削力最大降低了84.26%。     

Machining and Phase Transformation Response of Room-Temperature Austenitic NiTi Shape Memory Alloy

This experimental work reports the results of a study addressing tool wear, surface topography, and x-ray diffraction analysis for the finish cutting process of room-temperature austenitic NiTi alloy. Turning operation of NiTi alloy was conducted under dry, minimum quantity lubrication (MQL) and cryogenic cooling conditions at various cutting speeds. Findings revealed that cryogenic machining substantially reduced tool wear and improved surface topography and quality of the finished parts in comparison with the other two approaches. Phase transformation on the surface of work material was not observed after dry and MQL machining, but B19′ martensite phase was found on the surface of cryogenically machined samples.     

Cooling techniques for improved productivity in turning

The past century has witnessed significant advancements in turning process, cutting tools, machine controls and coolant/lubricant chemistry. These developments have particularly enhanced the machining of difficult-to-cut materials, which are used for aerospace, steam turbine, bearing industry, nuclear and automotive applications. In turning operation, friction and heat generation at the cutting zone are the frequent problems, which affect the tool life and surface finish apart from other machining results. This mechanism of heat generation plays quite a negative role during the turning of modern materials due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation. A good understanding of the methods of lubrication/cooling at the cutting zone, reduction of heat generation will lead to efficient and economic machining of these modern materials. This paper presents an overview of major advances in techniques as minimum quantity lubrication (MQL)/near dry machining (NDM), high pressure coolant (HPC), cryogenic cooling, compressed air cooling and use of solid lubricants/coolants. These techniques have resulted in reduction in friction and heat at the cutting zone, hence improved productivity of the process. A brief survey of modeling/FEA techniques is also performed.     

Tribological Characteristics and Cutting Performance of Lubricant Esters for Semi-dry Machining

In semi-dry machining, such as minimal quantity lubrication (MQL) machining, a very small amount of a lubricant plays an Important role to achieve a successful operation. This study investigates the tribological behavior of lubricants for semi-dry application in connection with their cutting performance. In MQL turning, synthetic biodegradable esters are superior to a vegetable oil and provide the satisfactory cutting performance compared with a conventional cutting fluid of flood supply. Their tribological action is further evaluated with the aid of tool surface analysis and the adsorption characteristics of a model ester are fundamentally examined using a controlled atmosphere machining apparatus.     

Feasibility study of the minimum quantity lubrication in high-speed end milling of NAK80 hardened steel by coated carbide tool

High-speed milling of hardened steels generates high cutting temperature and leads to detrimental effects on tool life and workpiece surface finish. In this paper, feasibility study of the minimum quantity lubrication (MQL) in high-speed end milling of NAK80 hardened steel by coated carbide tool was undertaken. Flood cooling and dry cutting experiments were conducted also for comparison. It is found that cutting under flood cooling condition results in the shortest tool life due to severe thermal cracks while the use of MQL leads to the best performance. MQL is beneficial to tool life both in the lower speed cutting and the higher speed cutting conditions. A less viscous oil of MQL is essential in high cutting speed so that cooling effect can be effective. SEM micrograph of the insert shows that the use of MQL in high-speed cutting can delay welding of chips on the tool and hence prolongs tool life as compared with dry cutting condition. The application of MQL also improves machined surface finish in high-speed milling of die steels.     

Burr formation in short hole drilling with minimum quantity lubrication

Machining with minimum quantity lubrication (MQL) is state of the art. Previous investigations were, however, concerned with tool optimisation and the surface quality of workpieces as well as coating technology. By now the same or partly better machining results than in conventional cutting with flood lubrication can be achieved due to adjusted tool geometries, workpiece materials and coatings. Tests about burr formation in short hole drilling exist for dry cutting or the machining with emulsion. This paper expands these results to the burr formation in machining with MQL.     

High-speed grooving with applying MQL

The performance of minimum quantity lubrication (MQL) in high-speed cutting was evaluated in grooving 0.45%C carbon steel with a carbide tool coated with TiC/TiCN/TiN triple coating layers. MQL with supplying vegetable oil at a small and constant rate of 7 ml/h reduced the corner and flank wears more effectively than a solution type of cutting fluid at high cutting speeds of 4 and 5 m/s. In MQL grooving, the wears decreased drastically with increasing the pressure of air supply. This suggested that the air supply took an important role in transporting the oil mist to the interface between the flank wear land and machined surface. Then, a controlled oil mist direction (COD) tool was devised and its performance was proved to be high at a reduced rate of oil supply.     

Effects of tool material,tool topography and minimal quantity lubrication (MQL) on machining performance of compacted graphite iron (CGI)

Abstract

This paper addresses the tribological challenges involved in the machining of compacted graphite iron (CGI) through an investigation of the effects of tool material, local tool surface topography and minimal quantity lubrication (MQL) on machining performance. Turning experiments were undertaken using four different tools (flat coated carbide, grooved coated carbide, grooved coated cermet and chamfered ceramic) under dry and MQL conditions. The tests were conducted at two different cutting speed conditions with a constant feed and depth of cut. Results reveal that at low speed, the cermet tool provides a significant reduction in cutting forces in comparison to coated carbide. Cutting forces show an increase with the usage of MQL at high speed, suggesting a negative influence of the cutting fluid on CGI machining performance. Scanning electron microscopy/energy dispersive X-ray analysis of the tested tools reveal the absence of MnS layer on tools used for CGI machining, thereby reconfirming the findings by other researchers.     

Effects of cooling air temperature on cryogenic machining of Ti-6Al-4V alloy

This paper presents experimental investigations on influence of different coolant strategies such as dry, wet, minimum quantity lubrication (MQL) and MQL with cooling air on performance in milling of the Ti-6Al-4V alloy with uncoated cemented carbide inserts. Cutting force, tool wear, surface roughness and chip morphology are experimentally studied to compare the effects of different cooling air temperatures. The results showed that minimum quantity lubrication (MQL) with cooling air significantly reduces cutting force, tool wear and surface roughness. Unfortunately, MQL (without cooling air) condition cannot produce evident effect on cutting performance, and flaking wear on the flank surface of the insert has been found under this condition. Four different cooling air temperatures are used to investigate the effects of cooling air temperature on the machinability characteristics of Ti-6Al-4V alloy. Based on the experimental results, MQL with cooling air of −15 °C provides more favourable effects compared to other cooling air temperatures (0 °C, −30 °C,−45 °C). Short chips are produced under MQL with cooling air conditions due to the high velocity of cooling air enhances the chip brittleness for easy chip breaking, and the effective penetration of lubricant to the chip-tool interface results in lower friction. However, due to the dramatic increase in chip hardness at lower temperature, MQL with cooling air environments cannot promote chip curl to some extent.     

切削参数对碳钢微量润滑切削温度的影响

为了了解切削参数影响碳钢微量润滑切削温度的规律,通过45钢的车削实验,利用自然热电偶测温,探明在干切削、传统浇注润滑和微量润滑条件下,不同切削参数对切削温度的影响及原因。实验结果表明:MQL切削温度随切削参数增大而上升,切削速度对MQL温度影响最大,切削深度影响最小;在低切削速度时,MQL冷却效果优于传统浇注润滑,在中、高速时,MQL冷却效果比浇注润滑差;MQL冷却能力随切削速度和进给量增大而减弱,不随切削深度而变化。     

An experimental investigation of the effects of workpiece and grinding parameters on minimum quantity lubrication—MQL grinding

Coolant is a term generally used to describe grinding fluids used for cooling and lubricating in grinding process. The main purposes of a grinding fluid can be categorized into lubrication, cooling, transportation of chips, cleaning of the grinding wheel and minimizing the corrosion. On the other hand, grinding fluids have negative influences on the working environment in terms of the health of the machine operator, pollution and the possibility of explosion (for oil). Furthermore, the cost of the grinding fluid, filtering and waste disposal of the metal working fluids is even higher than the tool cost and constitutes a great part of the total cost. Additionally, grinding fluids can not effectively penetrate into the contact zone, are health hazard and their consumption must be restricted. Generally, compared to other machining processes, grinding involves high specific energy. Major fraction of this energy is changed into heat, which makes harmful effect on the surface quality as well as the tool wear. Since there is no coolant lubricant to transfer the heat from the contact zone in dry grinding, surface damages are not preventable. Alternatives to current practices are getting more serious consideration in response to environmental and operational cost pressures. One attractive alternative is the minimum quantity lubrication (MQL) grinding or the near dry grinding (NDG). In near dry grinding an air–oil mixture called an aerosol is fed into the wheel-work contact zone. Compared to dry grinding, MQL grinding substantially enhances cutting performance in terms of increasing wheel life and improving the quality of the ground parts. In this research, the influences of workpiece hardness and grinding parameters including wheel speed, feed rate and depth of cut have been studied on the basis of the grinding forces and surface quality properties to develop optimum grinding performances such as cooling, lubrication, high ecological and environmental safety.