涡流冷却静电润滑复合干式钻削技术研究

为降低机械加工过程中切削液对环境造成的污染以及处理切削液时高昂的成本,提出一种兼有涡流冷却效应和静电润滑效应的干式钻削技术与装置。将气体离子化、臭氧化后吹到切削加工区域,代替切削液实现润滑、冷却的作用,获得良好的断屑效果,同时延长刀具的寿命。基于结构参数对系统放电性能、臭氧浓度以及冷却效果的影响规律,优化装置结构,形成干式辅助钻削装置。实验结果表明：当电极锥度为15°、电极直径为1 mm、铜帽内径为3 mm、气体流量为20 L/min、驱动电压为6 kV时,臭氧浓度达到峰值34.2×10-6。通过与纯干式切削对比发现：所提技术的切削温度降低40.9%,刀具刃口基本没有损伤,切屑微观表面切痕分布清晰、条理均匀。所设计的涡流冷却静电润滑干式钻削技术在切削效应、冷却效果、刀具磨损以及切屑形态等方面均优于传统的干式钻削技术,可以用于六系铝材的钻削加工。     

干式切削加工技术的发展及应用

在切削加工中大量使用切削液,不但增加了加工成本,而且也带来了环境污染,甚至危害操作人员的身体健康。干式切削是解决这些问题的有效方法之一。在切削加工过程中,干式切削不使用任何切削液,既减少了环境污染,同时也避免了对切削液后处理所产生的大量费用。介绍了干式切削技术的研究现状、干式切削工艺的特点和干式切削技术的应用,着重分析了实现干式切削技术需要解决的相关技术问题,比如刀具材料的选择、刀具几何参数的优化以及机床结构的优化等,最后指出了干式切削技术未来的发展方向。     

干式加工--金属切削加工发展的趋势

干式加工是金属切削加工发展趋势之一。切削液在加工中对降低切削温度起了很好的作用，也有利于断屑和排屑；但同时也存在一些问题，如冷却液的使用、存储、保洁和处理等都十分烦琐，成本高，而且切削液对环境和操作者身体健康有危害。因此，未来加工的方向是采用尽量少的切削液，而耐高温切削材料和涂层使得干式加工变为可能。１干式加工刀具设计干式加工刀具必须具备下列条件：使用高耐热耐磨性的刀具材料；切屑和刀具之间的摩擦系数要尽可能小；刀具形状保证排屑流畅，易于散热；高的强度和冲击韧性。因此，干式刀具设计必须考虑如下３个…     

钛合金Ti-6Al-4V纵扭超声铣削残余应力试验研究

目的 提出将纵扭超声振动和铣削加工相复合,对钛合金Ti-6Al-4V进行试验研究,探索工艺参数对加工残余应力的影响规律,实现钛合金的压应力抗疲劳制造。方法 通过试验对比分析了纵扭超声铣削和传统铣削在切削力、切削温度和残余应力的差异性。采用正交试验和单因素试验相结合的方法,同时考虑因素交互作用,研究了加工参数、冷却润滑条件以及刀具磨损对加工残余应力的影响。结果 相较于传统铣削,纵扭超声铣削能够使平均切削力降低约16.3%,切削温度降低约25.6%,表面残余压应力值增加31.3%。在所选参数范围内,径向切深对表面残余应力的影响较大（贡献率为34.1%）,而振幅影响较小（贡献率为6.5%）。表面残余压应力值随着铣削速度、每齿进给量以及径向切深的增大有不同程度的降低,随着振幅的增大有一定程度的提高。采用乳化液作为切削液能够提高加工表面的残余压应力值,而干式切削能够获得和在水、油切削液条件下相当的加工表面残余压应力值。工件表面的残余压应力值随着刀具磨损的增加而逐渐减小。结论 纵扭超声铣削能够有效降低切削力和切削温度,提高加工残余压应力值,同时选择适当的工艺参数及润滑冷却条件可进一步增大表面压应力值,可作为一种可靠的压应力制造技术。     

干式切削中刀具选用试验

切削液的使用带来了许多负面问题,鉴于环境考虑,研究绿色加工技术将是机械制造业必须重视的课题.干式切削是解决途径之一,它不用切削液,可完全消除切削液带来的一系列负面影响.本文通过选用一些新型刀具,在干式切削条件下对不同的刀具材料、刀具几何参数和切削用量进行试验比较,以寻求适用于干式切削的刀具材料与切削规律.     

干切削技术的研究和应用进展

针对传统切削加工过程中使用切削液的弊端,分析了干切削技术的特点,介绍了硬车削技术、静电冷却干切技术和低温冷风干车削技术等常见干式切削技术的原理及其国内外研究现状,指出干式切削技术具有很好的节能环保、降低加工成本等优点,具有广泛的应用前景.     

钛合金/铝合金叠层低温与干式钻削实验研究

钛合金/铝合金是飞机装配制孔中的典型叠层结构,目前多采用干式钻削,存在刀具磨损严重、孔加工质量难以保证的问题。为了探寻更有效的冷却润滑方式,研究利用超临界二氧化碳作为冷却介质,采用内冷的方式对切削区域进行快速冷却,进行低温叠层钻削实验,分析总结了低温钻削性能规律,并通过对比实验与干式钻削作比较。通过冷却介质出口温度梯度实验,研究了出口温度对钻削的影响。结果表明,相比于干式钻削,低温钻削能降低轴向力,降低表面粗糙度值,减小钛合金的出口毛刺高度,获得更好的孔径一致性。     

基于DEFORM的刀具几何参数与切削力关系的研究

切削力是切削过程中重要的参数之一,它对工件的加工精度、加工所消耗的功率及刀具的磨损程度等方面都有着重要的影响。影响切削力的因素是多方面的,如工件材料的性能、刀具的几何参数、切削用量的影响、切削液的使用情况等等[1]。文章以镍基合金为切削载体、以DEFORM为仿真平台,建立切削仿真模型,研究了刀具角度对切削力的影响,仿真结果与实际切削过程一致,验证了仿真的有效性,从而为研究者提供了一种实验成本低、实验时间短的方法来确定切削刀具工作角度。     

用AdvantEdge分析蠕墨铸铁切削时高压切削液的冷却润滑机理

使用AdvantEdge软件对不同切削液压力下车削蠕墨铸铁的过程进行二维仿真,研究切削过程中切屑变形、切削温度、刀-屑摩擦及切削力的变化规律,分析高压切削液的冷却润滑机理。仿真结果表明:增大切削液压力可以减小黏结摩擦区和滑动摩擦区长度,加快切削液与工件之间的热量传递速率;同时,高压切削液能够克服莱顿弗罗斯特效应形成的气体保护层,更好地对流换热和冷却;但切削液压力并非越大越好,在15～18 MPa时可以在减少能耗的同时获得较好的冷却润滑效果。      

水溶性合成酯极压添加剂的不锈钢切削实验

为了了解新型的水溶性合成酯极压添加剂KLG-3的切削效果,用乳化液(10%KLG-3)进行AISI 304不锈钢车削实验,通过粗糙度、刀具寿命、刀具磨损、切屑和切削力的比较,了解该微乳化液与多种传统切削液及干切削的切削效果差异。结论显示:10%KLG-3在减少刀具磨损和改善加工表面光洁度方面有良好效果,优于大部分传统切削液,因此非常适合于不锈钢切削。KLG-3的微乳化液的综合切削效果相对干切削效果有显著改善,已经达到传统切削液效果,可以代替传统切削液使用。     

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.     

Investigation of thermal behavior on cylinder liner during its boring process

Research was conducted on the effect of cutting conditions on temperature rise of cylinder liner during cylinder-boring process. A finite element method (FEM) model was developed to confirm suitable cutting conditions by predicting the temperature distribution in a cylinder liner and thermal expansion of the cylinder liner. To analyze the temperature distribution in the cylinder liner during machining, the partition of the total heat generated during machining which flows into the cylinder liner has to be investigated. A method combining experiment with analysis, called an “inverse heat transfer method”, was used to estimate the heat percentage flowing to the cylinder liner in this paper. To capture the required data for the inverse heat transfer method, sets of dry and wet boring experiments were conducted to estimate the temperature distribution in the cylinder liner wall and the cutting force during machining. The influence of the cutting conditions (for example: cutting speed, feed rate, depth of cut, cutting fluid) on the cutting force and temperature distribution in a cylinder during machining was investigated, and the heat partition flowing to the workpiece under various cutting conditions (especially, under high-speed cutting, with a maximum cutting speed up to 900 m/min) was then determined. A three-dimensional FEM analysis model was developed to simulate the temperature distribution in the cylinder liner and thermal expansion of the cylinder liner during machining. Then, the suitable cutting conditions in cylinder boring were confirmed by FEM analysis. To investigate the influence of the air cooling on the temperature distribution in the cylinder liner after machining, the change of temperature distribution in the cylinder liner under air cooling was predicted.     

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.     

On temperatures and tool wear in machining hypereutectic Al–Si alloys with vortex-tube cooling

This study investigates dry machining of hypereutectic silicon–aluminum alloys assisted with vortex-tube (VT) cooling. The objective is to reduce cutting temperatures and tool wear by enhanced heat dissipation through the chilled air generated by a VT. A machining experiment, cutting mechanics analysis, and temperature simulations are employed to (1) model the heat transfer of a cutting tool system with VT cooling applied, (2) explore effects of cooling setting and machining parameters on the cooling efficiency, and (3) evaluate VT cooling effects on tool wear. A390 alloy is machined by tungsten carbides with cutting forces and geometry measured for heat source characterizations as the input of temperature modeling and simulations. VT cooling is approximated as an impinging air jet to estimate the heat convection coefficient that is incorporated into the heat transfer models. The major findings include: (1) VT cooling may reduce tool wear in A390 machining depending upon machining conditions, and the outlet temperature is more critical than the flow rate, (2) cooling effects on temperature reductions, up to 20 °C, decrease with the increase of the cutting speed and feed, and (3) tool temperature decreasing by VT cooling shows no direct correlations with tool wear reductions.     

Machining Ti–6Al–4V alloy with cryogenic compressed air cooling

A new cooling approach with cryogenic compressed air has been developed in order to cool the cutting tool edge during turning of Ti–6Al–4V alloy. The cutting forces, chip morphology and chip temperature were measured and compared with those measured during machining with compressed air cooling and dry cutting conditions. The chip temperature is lower with cryogenic compressed air cooling than those with compressed air cooling and dry machining. The combined effects of reduced friction and chip bending away from the cutting zone as a result of the high-speed air produce a thinner chip with cryogenic compressed air cooling and a thicker chip with compressed air cooling compared to dry machining alone. The marginally higher cutting force associated with the application of cryogenic compressed air compared with dry machining is the result of lower chip temperatures and a higher shear plane angle. The tendency to form a segmented chip is higher when machining with cryogenic compressed air than that with compressed air and dry machining only within the ranges of cutting speed and feed when chip transitions from continuous to the segmented. The effect of cryogenic compressed air on the cutting force and chip formation diminishes with increase in cutting speed and feed rate. The application of both compressed air and cryogenic compressed air reduced flank wear and the tendency to form the chip built-up edge. This resulted in a smaller increase in cutting forces (more significantly in the feed force) after cutting long distance compared with that observed in dry machining.     

An experimental investigation on effect of minimum quantity lubrication in machining AISI 1040 steel

The growing demands for high productivity of machining need use of high cutting velocity and feed rate. Such machining inherently produces high cutting temperature, which not only reduces tool life but also impairs the product quality. Application of cutting fluids changes the performance of machining operations because of their lubrication, cooling, and chip flushing functions. But the conventional cutting fluids are not that effective in such high production machining, particularly in continuous cutting of materials likes steels. Minimum quantity lubrication (MQL) presents itself as a viable alternative for turning with respect to tool wear, heat dissipation, and machined surface quality. This study compares the mechanical performance of MQL to completely dry lubrication for the turning of AISI-1040 steel based on experimental measurement of cutting temperature, chip reduction coefficient, cutting forces, tool wears, surface finish, and dimensional deviation. Results indicated that the use of near dry lubrication leads to lower cutting temperature and cutting force, favorable chip–tool interaction, reduced tool wears, surface roughness, and dimensional deviation.     

Development of electrostatic solid lubrication system for improvement in machining process performance

Liquid lubricants have traditionally been used to control the high heat generation in machining; however, the use of cutting fluid has become more problematic in terms of both employee health and environmental pollution. Minimization or possible elimination of cutting fluids substituting their functions by some other means is emerging as a thrust area of research in machining. Solid lubricant assisted machining is a novel concept to control the machining zone temperature without polluting the environment. The focus of this study is to explore the possibility of application of graphite as a lubricating medium in drilling of AISI 4340 steel, as a means to reduce the heat generated due to friction, towards finding an alternative to conventional coolants. To this end, an optimized solid lubricant application method, electrostatic solid lubrication experimental setup has been envisaged for effective supply of solid lubricant mixture as a high velocity jet and at an extremely low flow rate to the machining zone, thus meeting environmental requirements. The process performance is judged in terms of thrust force, tool wear, chip thickness, hole diameter and surface finish of machined workpiece keeping the other conditions constant. A comparison with the results obtained in wet and dry machining is also provided. The results obtained from the experiments show the effectiveness of the use of the solid lubricant as a viable alternative to wet and dry machining through reduction in the cutting zone temperature and favourable change in chip–tool and work–tool interaction. The proper selection and application of solid lubricant can lead to low cost, and this concept could emerge as an effective alternative to conventional coolants.     

Capability of high pressure cooling in the turning of surface hardened piston rods

An experimental study was performed to investigate the capabilities of dry, conventional and high pressure cooling (HPC) in the turning of surface hardened piston rods used in fluid power applications. Machining experiments were performed using coated carbide tools at cutting speeds up to 160 m/min. The cooling capabilities are compared by monitoring of chip breakability, process regions of operability, cooling efficiency, tool wear, tool life and cutting forces. Test results showed that dry cutting could not be performed due to long and ductile chips that were formed for all investigated cutting conditions. In comparison to conventional cooling the significant increase of cutting speed and feed rate region of operability was recorded when machining with HPC. Tool life analysis proved a five times increase in tool life when machining with HPC. Furthermore HPC also improved chip breakability and reduced coolant consumption.     

Temperature of internally-cooled diamond-coated tools for dry-cutting titanium

The role of cutting fluids is well known for the importance of removing heat from the cutting edge, lubricating the sliding chip contact and transporting the metal chips away from the cutting zone. Dry machining leads to increased cutting temperatures and higher wear rates resulting in shorter tool life; this is particularly evident in the cutting of high strength materials. Diamond coated cutting inserts are not usually considered for machining titanium due to rapid oxidation of the coating at the temperatures typical of titanium machining. This paper examines the formation of hot-spots on the rake face during dry and near-dry turning of titanium using conventional cemented carbide inserts. Machining performance is assessed by measurement of tool wear and tool life. Trials with an internally cooled tool with a specially designed, diamond coated insert have shown that the heat from the cutting operation can be rapidly diffused over the entire surface of the insert and thus successfully drawn away from the tool via closed loop recirculation of coolant through the tool holder. This enables wear to be inhibited by management of rake face temperature to keep it below the critical temperatures at which these prominent wear mechanisms operate. Measurements of change in coolant temperature before and after circulation are used to quantify the heat removed from the cutting process. The low friction coefficient and high thermal conductivity of diamond, assisted by the indirect cooling, results in longer tool life whilst maintaining high standards of surface finish.