微量润滑系统参数对加工残余应力影响试验

微量润滑(MQL)切削是一种绿色加工技术。为了解MQL系统对加工残余应力影响,通过45钢车削正交试验,研究MQL系统的空气压力、润滑液用量、喷射距离、油雾温度对加工残余应力的影响。试验结果表明:油雾温度对加工残余应力的影响最大,润滑液用量也有一定的影响,空气压力和喷射距离的影响不显著;油雾温度降低,残余(拉)应力变小;润滑液用量增加,残余(拉)应力变小;MQL系统对加工残余应力的影响机制是通过改变油雾的冷却能力和渗透性,改变残余应力热力耦中的热效应。     

Modelling, simulation and experimental investigation of chip formation in internal traverse grinding

We present recent developments in modelling and simulation of internal traverse grinding, a high speed machining process which enables both a large material removal rate and high surface quality. We invoke a hybrid modelling framework, including a process scale model, simulations on a mesoscale capturing the proximity of a single cBN grain and an analysis framework to investigate the grinding wheel topography. Moreover, we perform experiments to verify our simulations. Focus in this context is the influence of the cutting speed variation on the grain specific heat generation.     

高温合金磨削热力耦合及其对表面完整性的影响研究现状

高温合金具有耐热性、耐腐蚀性等优良性能,被广泛应用于航空发动机的精密制造与修复。磨削能够提高部件的加工精度和表面完整性,是加工高温合金材料的重要方法。在磨削过程中,高温合金因材料的高强韧性,使得磨具磨损严重,并且磨削时冷却液难以进入磨削弧区,导致高温合金的磨削力和磨削温度较高。在多刃磨削加工下,复杂的热-力耦合过程对高温合金表面完整性有着重要影响,表面完整性直接影响服役性能。从产生机理、表征方法及控制等方面阐述了磨削热和磨削力的研究现状,首先介绍了高温合金磨削热及磨削力产生的机理及原因,进而从刚性磨削和柔性磨削的角度综述了磨削温度和磨削力的预测模型及方法,从冷却润滑、工艺参数优化及砂轮结构改进等方面调研了磨削温度和磨削力的控制策略。从间接耦合法的角度介绍了磨削热-力耦合建模过程。最后,在概述磨削热力耦合的基础上,总结了在磨削热力耦合作用下高温合金的表面粗糙度、表面形貌、组织结构及残余应力等方面的研究成果,并对高温合金磨削热力耦合作用的研究方向进行了展望。     

An investigation on surface grinding using graphite as lubricant

Grinding requires high specific energy and the consequent development of high temperature impairs workpiece quality by inducing tensile residual stress, burn, micro cracks etc. Control of grinding temperature is achieved by providing effective cooling and lubrication. Conventional flood cooling is often ineffective due to the relative inaccessibility of the fluid to the actual grinding zone, film boiling etc. Further these fluids are also a source of health hazards. Minimization and possibly the elimination of fluid coolants by substituting their functions by some other means is of current research interest. This paper deals with an investigation on using graphite as a lubricating medium to reduce the heat generated at the grinding zone. An experimental set-up has been developed for this and a detailed comparison has been done with dry and coolant flooded grinding in terms of forces, specific energy, temperature and surface finish. Results show that grinding force, energy and temperature are reduced and resultant surface finish depends on workpiece material.     

面向绿色制造的快速点磨削磨削液供给参数计算

高速／超高速磨削条件下，砂轮边缘的高速空气带会阻碍磨削液注入磨削区。空气带压力与砂轮速度的平方成正比。快速点磨削是一种新型高速／超高速磨削技术，接触区很小，实际磨削功率低，冷却及散热效果好。在分析了高速／超高速磨削砂轮周围旋转空气带动压力及速度分布特点的基础上，根据热力学原理及快速点磨削特点，分析并建立了磨削液的供给流量和供液速度的理论模型。在此基础上，建立了面向绿色制造的快速点磨削的磨削液喷嘴直径及供液压力的工程计算公式。     

Effect of different production phases on residual stress field in double-layer cast rolls

The aim of this investigation was to determine the effect of different production operations and parameters on residual stress level in double-layer cast rolls. Using a hole-drilling method, residual stress depth distribution in surface layer was measured around and along the body of the double-layer cast roll after casting, heat treatment, turning and grinding. Furthermore, using different turning and grinding parameters (speed, feed), and heat treatment parameters (temperature, time), influence of these parameters on residual stress level and distribution was determined.Results of the investigation show that the conditions in the casting pit have an influence on the residual stress field generated in double-layer cast rolls, with surfaces exposed to faster cooling rates in general showing higher residual stress values. Very critical phase in rolls production is coarse grinding, which if not carried out properly will generate very high tensile stresses in the roll surface and cause surface cracking or even roll fracture. Heat treatment on the other hand results in uniform compressive residual stress field in the roll's surface. However, reduction in tempering time and especially increase in hardening temperature lead to increased residual stress level in the roll surface. Final machining of the roll surface further influences residual stress level in the roll. Increase in turning speed of up to 40% results in compressive residual stress increase of up to 60%, while less than 30% increase in feeding rate gives almost 100% increase in residual stress level.     

Improving grinding performance by controlling air flow around a grinding wheel

In grinding, high specific heat is generated, and hence, appropriate control of temperature through effective flow of grinding fluid is necessary to obtain a quality ground surface. It is known that in conventional fluid delivery method, most of fluid is wasted due to presence of a stiff air layer around the grinding wheel. This air layer is generated around the wheel due to the rotation of the porous grinding wheel at a high speed. To improve grinding performance, hence, penetration into this air layer is required.In this work, a pneumatic barrier set-up has been developed for controlling the stiff air layer around the grinding wheel. The formation of stiff air layer has been studied experimentally by measuring the variation of air pressure around grinding wheel periphery at different parametric conditions of pneumatic barrier. This pneumatic barrier tends to break the stiff air layer before the fluid flow area or grinding zone. A remarkable amount of reduction in pressure of the air layer is observed at the fluid flow zone. To observe beneficial effects of suppressing the air layer, grinding experiments are performed under dry, flood cooling and flood cooling with pneumatic barrier setup. Reduction of grinding forces and surface roughness are clearly observed with the use of pneumatic barrier setup, and hence, its applicability.     

基于旋转超声振动的氧化锆陶瓷小孔磨削加工质量研究

针对陶瓷材料小孔加工质量较差以及加工成本较高等问题,设计一种基于旋转超声辅助的氧化锆陶瓷小孔磨削加工工艺。首先分析旋转超声加工原理,然后在超声振动条件下利用金刚石刀具对氧化锆陶瓷小孔进行单因素磨削加工试验,并对小孔的内壁进行形貌分析和粗糙度检测,最后研究主轴转速、超声功率以及进给速度对小孔表面粗糙度的影响规律。研究结果表明:与普通磨削方式相比,在旋转超声辅助加工条件下,小孔表面质量和残余应力都得到较大改善,当超声功率达到300 W时,加工后的小孔表面粗糙度下降了52%,加工精度明显提高。      

热处理和磨削工艺对渗碳淬火汽车齿轮残余应力的影响

研究了渗碳热处理过程中淬火冷却和回火状况以及磨削加工对渗碳淬火汽车齿轮表面残余应力的影响.研究表明,充分淬火冷却有利于提高表面残余压应力,正确的磨削工艺不改变残余应力的分布,但过多的磨削热会导致在次表层产生高的拉应力.     

低温冷却磨削机理的研究

磨削是各种加工材料获得精确尺寸和表面完整性的主要加工方法，但在加工过程中，由于磨削区温度过高，经常导致工件表面热损伤、微裂纹和产生残余拉应力，严重影响工件表面质量和完整性的提高。本文通过采用低温CO2和液态氮为磨削冷却介质，有效地控制磨削区温度。实验结果表明，与干磨削和油冷却磨削相比，液态氮低温冷却磨削力、比磨削能、磨削区温度明显降低，工件表面质量和完整性显著提高，同时明显提高了砂轮的使用寿命和减少了冷却液对环境地污染。     

Applied mechanics in grinding—IV. The mechanism of grinding induced phase transformation

One of the most important problems in high precision grinding is the optimisation of the surface residual stress distribution of ground components. It has been realised that the heat generated in the grinding zone plays a central role in the phase transformation of workmaterials that would alter the residual stress formation. The purpose of this paper was to reveal the mechanism of phase transformation of workmaterials induced by grinding. The finite element method was used to simulate the grinding processes. The heat source generated during grinding was considered as a moving heat flux with a triangular profile. Effects of table speed, heat flux distribution, thermal properties of workmaterials and convective features of coolant were discussed in detail. It was found that an optimal combination of grinding conditions could minimise the depth of phase transformation. The results of this paper also offered essential information for the mechanism exploration of residual stresses in ground components.     

QT800—2凸轮轴磨裂产生的原因及对策

通过金相分析，表面应力测定及热处理工艺实验研究了ＱＴ８００－２凸轮轴等温淬火后磨削裂纹产生的原因及解决办法。结果表明，组织中存在的脆性相、马氏体与残余奥氏体的成分不均匀区域及磨削产生的温度和应力是导致其磨削裂纹产生的主要原因，这些缺陷可以分别通过改善热处理工艺，减少磨削加工余量进给量等措施得到改善。     

Heat generation and temperature prediction in metal cutting: A review and implications for high speed machining

Determination of the maximum temperature and temperature distribution along the rake face of the cutting tool is of particular importance because of its controlling influence on tool life, as well as, the quality of the machined part. Numerous attempts have been made to approach the problem with different methods including experimental, analytical and numerical analysis. Although considerable research effort has been made on the thermal problem in metal cutting, there is hardly a consensus on the basics principles. The unique tribological contact phenomenon, which occur in metal cutting is highly localized and non-linear, and occurs at high temperatures, high pressures and high strains. This has made it extremely difficult to predict in a precise manner or even assess the performance of various models developed for modelling the machining process. Accurate and repeatable heat and temperature prediction remains challenging due to the complexity of the contact phenomena in the cutting process. In this paper, previous research on heat generation and heat dissipation in the orthogonal machining process is critically reviewed. In addition, temperature measurement techniques applied in metal cutting are briefly reviewed. The emphasis is on the comparability of test results, as well as, the relevance of temperature measurement method to high speed cutting. New temperature measurement results obtained by a thermal imaging camera in high speed cutting of high strength alloys are also presented. Finally, the latest work on estimation of heat generation, heat partition and temperature distribution in metal machining is reviewed. This includes an exploration of the different simplifying assumptions related to the geometry of the process components, material properties, boundary conditions and heat partition. The paper then proposes some modelling requirements for computer simulation of high speed machining processes.     

高速超高速磨削工艺及其实现技术

高速超高速磨削加工是先进制造方法的重要组成部分，集粗精加工与一身，达到可与车、铣和刨削等切削加工方法相媲美的金属磨除率，而且能实现对难磨材料的高性能加工。本文主要论述了高速超高速磨削工艺技术的特点；分析了电主轴是高速超高速磨削主轴系统的理想结构，介绍了陶瓷滚动轴承、磁浮轴承、空气静压轴承和液体动静压轴承在主轴单元中的应用；超高速砂轮主要用电镀或涂层超硬磨料(CBN、金刚石)制成，介绍了超硬磨粒的特点和砂轮的修整，分析了在高速及超高速磨床上得到广泛应用的德国Hofinann公司生产的砂轮液体式自动平衡装置；介绍了高压喷射法，空气挡板辅助截断气流法，气体内冷却法，径向射流冲击强化换热法磨削液供给系统的特点；最后介绍了直线电机进给系统和声发射智能监测系统等实现高速超高速磨削的关键技术。     

钛合金材料砂带磨削表面残余应力形成模型及其实验研究

目的建立钛合金材料砂带磨削参数到磨削后表面残余应力之间的数学模型并验证其有效性。方法综合应用弹性力学和碰撞力学建立材料表面微观结构力学模型,通过对外力作用下的力学模型的分析计算得到数学模型,再利用Simulink对其进行仿真分析,得到了一定磨削参数下钛合金砂带磨削表面残余应力与时间的关系图,最后进行了钛合金砂带磨削实验,验证了该数学模型的有效性并进行误差分析。结果所构建的数学模型仿真值与实测值变化趋势相似,有着较好的仿真效果。但是,在引入热量系数?之前,最大误差为62.98%,平均误差为16.43%,结果不够理想;而在引入热量系数?之后,最大误差为9.87%,平均误差为5.75%,精度上升明显,能够有效地预测表面残余应力的取值。结论综合应用弹性力学和碰撞力学来构建出钛合金材料砂带磨削表面残余应力形成模型,能够有效地表征其在一定加工参数下的表面残余应力。     

Effect of spray parameters on residual stress build-up of HVOF sprayed aluminium/tool-steel functionally graded coatings

The High Velocity Oxy–Fuel (HVOF) process is one of the most versatile thermal spray technologies and has found use in many industries due to its flexibility and cost effectiveness. It is normally used to protect components against wear, heat and/or corrosion and has the potential to produce functionally graded coatings. Gradual changes of microstructure in functionally graded coatings reduce possible residual stress build-up by gradually attaining property changes between the substrate and the coating. Effectively this is done by depositing layers of coatings of varying composition. The present study investigates the effect of spray parameters on residual stress build-up in aluminium/tool-steel functionally graded coatings (FGC). A simple 3³ factorial design of experiments was employed to establish the effects of spray parameters on residual stress. Residual stress was measured using Clyne's analytical method. Parameters such as flow rate ratio of the oxygen to propylene, flow rate of the compressed air and spray distance were varied during coating deposition. Apart from the thickness of the coated sample, the spray distance showed greater effect on residual stress build-up in the graded coatings compared to flow rate ratio of the oxygen to propylene, and flow rate of the compressed air. Finally a set of values of spray parameters giving the best compromise between low residual stress and high deposited coating thickness were identified. This paper concluded that the optimised set of parameters for FGC resembles the parameters recommended for the deposition of the powder with the lowest melting and boiling point; in this case aluminium.     

16CrNi4MoA 钢环形齿轮渗碳淬火畸变的控制

从锻造质量、热处理内应力、机械加工精度及其产生的残余应力等方面,分析影响环形齿轮渗碳淬火畸变的因素,阐述控制热处理畸变的几项措施,采用将加工精度提高半级、尽可能消除机械加工中产生的残余应力、使用专用夹具并优化相关的热处理工艺参数等。结果显示,环形齿轮的合格率从不到50%上升到80%以上,取得了明显的效果。     

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.     

氮气喷射沉积镁合金传热过程分析

针对氮气喷射沉积镁合金雾化过程中的快速散热阻燃行为,采用数学模型模拟了镁合金喷射沉积过程中雾化气体与液滴之间的传热情况.结果表明,雾化气体速度随着喷射距离的增加呈单调递减趋势;雾化液滴先加速飞行,在液滴和气体速度相等后开始减速,随着粒径增大,液滴的最大速度减小;传热系数先减小再增加,且随着液滴粒径减小而增大,其平均值均在l000W· m-2·K-1以上;液滴的温度持续降低;在雾化阶段,液滴与气体之间传热的最小速率远远大于反应放热的最大速率,避免了喷射沉积过程中热量的蓄积,从而保障了氮气喷射沉积制备镁合金过程的生产安全.     

Numerical modelling of in-flight particle dynamics of non-spherical powder

High velocity oxygen fuel (HVOF) is an important thermal spraying technology in depositing high quality coatings. Its ability to produce high particle velocities and relatively low particle temperatures is its most salient feature. Several computational fluid dynamic (CFD) models have been developed to study the in-flight particle behavior during thermal spraying. These models are limited to spherical particles, which are only appropriate for modelling gas atomised powders. On the other hand, hardmetal powders such as WC-Co are created using high energy ball milling and are not normally spherical. To examine the effect of particle morphology on particle dynamics, mathematical models are developed in the present paper to predict the in-flight particle behavior in a liquid fuelled HVOF thermal spray gun. The particle transport equations are coupled with the three-dimensional, chemically reacting, turbulent gas flow, and solved in a Lagrangian manner. The melting and solidification within the particles as a result of heat exchange with the surrounding gas flow are solved numerically. The results demonstrate that non-spherical particles gain more momentum and less heat during the HVOF process than spherical particles. Non-spherical particles are also predicted to stay closer to the center of the gas jet than spherical particles.