ESTIMATED TEMPERATURE ON A MACHINED SURFACE USING AN INVERSE APPROACH

An experiment devoted to the heat flux estimation in a workpiece during a machining process by turning is presented. The method is based on temperature measurement from thermocouples embedded in the workpiece, close to the heated surface. A model that expresses the heat flux according to the temperature at the sensors is developed. The stationary and linearity assumptions are used in order to decompose the three-dimensional original problem into two bi-dimensional problems. This decomposition can be realized given the difference between the cutting speed and feed velocity in two orthogonal directions. The temperature on the machined surface is calculated from the estimated heat flux and the heat transfer model in the workpiece. The application concerns hard steel machining, using a CBN insert tool. Three parameters are placed into evidence from this application: the temperature magnitude on the machined surface, the thermal gradient in the workpiece, and the `thermal persistence' that represent the heating time of the machined surface. This study leads to a better understanding of the influence of temperature during a hard steel turning process.     

DYNAMICS OF CUTTING TOOL TEMPERATURES DURING CUTTING PROCESS

An experimental study is performed to measure temperature variation of a carbide insert during metal cutting by means of fine thermocouples connected to a data acquisition system. A semiempiriad equation is developed based on transient conduction solutions combined with experimental data to predict temperature-time history in the cutting tool during operation. The governing parameters in the equation are derived, using AISI 1045 steel as the workpiece, to be the cutting speed, feed rate, and depth of cut at fixed rake and lead angles. Emphasis is placed on analyzing effects of the important factors on the cutting process, such as frictional heat generated at the tool-workpiece interface and wear of the tool. Dynamic behavior of the metal cutting process as predicted by the direct thermocouple measurement agreed with phenomenological observations reported in the existing literature.     

An approach based on tool mode control for surface roughness reduction in high-frequency vibration cutting

The presented research work, aimed at deeper understanding of vibrational process during high-frequency vibration cutting, is accomplished by treating cutting tool as an elastic structure which is characterized by several modes of natural vibrations. An approach for surface quality improvement is proposed in this paper by taking into account that quality of machined surface is related to the intensity of tool-tip (cutting edge) vibrations. It is based on the excitation of a particular higher vibration mode of a turning tool, which leads to the reduction of deleterious vibrations in the machine-tool-workpiece system through intensification of internal energy dissipation in the tool material. The combined application of numerical analysis with accurate finite element model as well as different experimental methods during investigation of the vibration turning process allowed to determine that the most favorable is the second flexural vibration mode of the tool in the direction of vertical cutting force component. This mode is excited by means of piezoelectric transducer vibrating in axial tool direction at the corresponding natural frequency, thereby enabling minimization of surface roughness and tool wear.     

高超声速飞行器热管冷却前缘结构一体化建模分析

针对高超声速飞行器工作时前缘恶劣的气动加热环境, 为了保证飞行器前缘的尖锐外形, 提出内嵌高温热管前缘结构. 针对热管内部复杂流动与换热情况, 对内嵌高温热管前缘结构进行一体化建模, 将模型的核心部件液态金属热管工作状况的计算与实验进行对比以验证模型的可靠性. 本文还分析了给定工况下内嵌高温热管前缘结构的热防护效果, 其中壁面最高温度下降了11.6%, 最低温度上升了8%, 高温区和低温区均被封闭在前缘外层区域, 内层温度更加均匀, 实现了热流由高温区向低温区的转移, 削弱了高温区的热负荷. 本文还分析了接触热阻对热管冷却前缘结构效果的影响. 关键词： 热管 前缘 疏导式热防护 气动热     

锯齿型通道流动和换热的周期性研究

本文对锯齿型通道内流动与换热的周期性进行了数值模拟.在Re=550～700范围内,入口段后的各几何周期的平均Nu数已随时间发生振荡,且随Re数增大,振荡起始位置朝入口方向移动;发生振荡的各几何周期的流场、无量纲温度场虽然在同一时刻不尽相同,但在不同的时刻可以找到近乎相同的流场和温度场,而且各几何周期平均Ⅳu数其振荡幅度基本相同,对时间求平均值后也基本相同,因此仍具有周期性充分发展的一些特性.     

HL-1装置脉冲送气的数值研究

本文采用一维等离子体输运模型,研究了脉冲送气对HL-1装置等离子体的影响。脉冲送气使等离子体密度提高1—2倍,能量约束时间增长50％,离子温度也有所提高;脉冲送气过程中,等离子体边缘迅速冷却,电流通道收缩,中心区域电子温度平直化。     

EXPERIMENTAL AND NUMERICAL METHOD FOR DETERMINING TEMPERATURE DISTRIBUTION IN A WOOD CUTTING TOOL

A 2-D boundary-element model was used to solve the steady-state heat conduction problem in a wood cutting tool. Cutting experiments were conducted in order to measure temperatures at remote locations on the tool rake face and at the tool/holder interface. The tool/holder interface temperatures were used as inputs into the boundary-element model. Heat input into the tool was adjusted until predicted temperatures on the rake face agreed with experimental results. The proportion of the machining power conducted into the tool as heat was determined as a function of the cutting geometry, specific cutting energy, and cutting speed.     

中高温热泵工质及试台研究

本文介绍了作者自行搭建的中高温水源热泵机组试验台,以及在此装置上对新的中高温环保工质HTR01的试验 研究。试验台的特点是利用自然平衡压力点,设计了冷热混水系统,达到即节能又易于控制的目的。通过对新工质HTR01 的大量热工性能试验,以及对试验结果的误差和性能分析,为中高温水源热泵大型样机的设计提供了基础。     

中高温工质在蒸发器中的换热模拟分析

本文采用分布参数的方法,建立了水源热泵中普遍采用的壳管式蒸发器稳态数学模型.通过中高温水源热泵试验台的实验数据同模拟计算结果的对比,验证了数学模型的准确性。应用此数学模型对中高温工质HTR01、HTR02及R134a在蒸发器典型制热运行工况,进行了模拟计算。得出了三种工质制冷剂侧换热系数沿管长的变化关系并对三种工质的换热性能进行了对比分析,为采用中高温工质的水源热泵换热器设计提供了参考依据.     

单晶金刚石刀具后刀面沟槽磨损的石墨化生成过程分析

单晶金刚石刀具切削单晶硅时后刀面会发生剧烈沟槽磨损,严重影响零件加工质量和刀具寿命。为了从金刚石石墨化转变角度揭示沟槽磨损生长扩展机制,建立了金刚石刀具后刀面具有初始沟槽的分子动力学模型,模拟了切削单晶硅时初始沟槽处的工件材料流动行为与金刚石刀具晶体结构变化情况。结果表明,初始沟槽的存在改变了工件材料的流动状态;并且这种材料流动引起了刀具初始沟槽附近温度和能量的变化,温度升高了8%,势能提高了1.4%;通过分析金刚石刀具晶体结构发现,初始沟槽处的刀具材料发生了石墨化转变,并通过计算采样点处原子间键角,得到了石墨化转化率随着切削的进行不断升高,并最终趋于恒定的规律,当切削进入到稳定切削阶段时,石墨化转化率约为6%。     

管式换热器积灰特性的实验研究

在实验室建立了气侧污垢热阻实验台，实验研究了管式换热器管内微粒污垢的积聚特性，结果表明积灰随时间呈现渐近特性，没有发现诱导期。同时还考察了流体速度，颗粒直径和浓度对渐近污垢热阻的影响．     

着火油罐燃烧过程预测的通用模型

本文根据油罐火灾的燃烧特点,从基本的传热规律和燃烧机理出发,以油品表面热反馈的能量平衡为前提,并利用化工热力学方法计算了火焰的平均温度,通过迭代方法,并结合相关的实验数据和结果,提出了油罐火灾燃烧过程的通用模型,该模型可适用于多种碳氢类燃料。本文以汽油为例,通过计算可以得到着火油罐的多项燃烧特性,包括燃烧速度、平均火焰温度等,是获取油罐周围热辐射规律的基础和前提,计算结果可为火灾现场战术的决策以及预案的制订提供依据。     

Experimental study of whistle noise generated by insert edge and oil separator model of refrigeration cycle

The compressed air experiments are conducted to investigate the whistle noise radiated from the oil separator component of refrigerant cycle system. Two types of insert edge and a height-adjustable oil separator model are adopted. The acoustic characteristic of flow through plain top insert edge is more likely to be broadband. Flow through ramp top insert edge would induce whistle peaks at Mach number higher than 0.1197 and the oil separator model works like an acoustic amplifier. Moreover, the Strouhal number jumps are captured inside oil separator model and two mechanisms are presented to clarify the phenomena. First, the whistle noise at Modes A1, A3, B1 and B3 is regarded as coupling of shear layer instability with resonance acoustic modes of oil separator model. Second, the whistle noise at Modes A2 and B2 is regarded to be the feedback loop of flow-acoustic interaction in fluctuated shear layer and defined as jet-cavity interaction tones.     

U型管传热量影响因素的数值模拟研究

地下换热器是地源热泵的重要组成部分,竖直U型管是最常见的地下换热器形式. U型管与土壤间的传热受诸多因素的影响.为分析这些因素对于U型管传热的影响,本文建立了地源热泵竖直U型管地下换热器的三维全尺寸数值模型,在此基础上采用CFD软件FLUENT对U型管的埋管深度、进口水温、管内流速等一系列因素在冬夏不同工况下对U型管传热量的影响进行了数值模拟研究.经过整理分析得出的各种因素对传热量影响可以为优化工程设计提供依据.     

双成分模型及YBCO/Pb结沿c轴的Josephson效应

根据巡游载流子与具有负U关联的近局域载流子相杂化的双成分模型研究了YBCO/Pb结沿c轴的Josephson效应．在此模型中巡游载流子具有s波对称性，能隙较小．近局域载流子具有d波超导电性，其临界温度决定体系的转变温度，沿c轴的Josephson电流I_c主要由s波贡献．由计算得到的s波能隙大小及其相应的临界温度较好地解释了实验观测到的零温隧穿电流与结电阻之积I_c（O）R_N以及I_c随温度的变化．此外，该模型还能解释在施加 关键词：     

压气机叶片前缘分离流动

用实验方法研究了压气机叶片前缘分离流动结构。实验是在低速叶栅风洞中完成的。考察了分别具有圆形和椭圆形前缘的NACA65叶型和CDA叶型前缘附近的流动情况。给出了细致的叶片前缘和分离区内的压力分布情况以及叶片前缘附近流动结构。     

微细铣刀位姿同轴全息重建方法

微细铣刀在主轴上存在装夹偏角时,会加剧刀刃磨损,降低刀具使用寿命.为了精确观测微细铣刀在机倾斜状态,提出了基于景深的微细铣刀三维位姿重建方法.利用激光同轴数字全息实验装置得到微细铣刀全息图,并通过菲涅尔再现算法获得再现像.在再现像中提取刀具边缘点作为关键点,采用小波变换局部方差算子求出关键点的聚焦程度,确定铣刀对应的轴...     

Ultrasonic excitation affects friction interactions between food materials and cutting tools

In the food industry, ultrasonic cutting is used to improve separation by a reduction of the cutting force. This reduction can be attributed to the modification of tool–workpiece interactions at the cutting edge and along the tool flanks because of the superposition of the cutting movement with ultrasonic vibration of the cutting tool. In this study, model experiments were used to analyze friction between the flanks of a cutting tool and the material to be cut. Friction force at a commercial cutting sonotrode was quantified using combined cutting–friction experiments, and sliding friction tests were carried out by adapting a standard draw-off assembly and using an ultrasonic welding sonotrode as sliding surface. The impact of material parameters, ultrasonic amplitude, and the texture of the contacting food surface on friction force was investigated. The results show that ultrasonic vibration significantly reduces the sliding friction force. While the amplitude showed no influence within the tested range, the texture of the contact surface of the food affects the intensity of ultrasonic transportation effects. These effects are a result of mechanical interactions and of changes in material properties of the contact layer, which are induced by the deformation of contact points, friction heating and absorption heating because of the dissipation of mechanical vibration energy.     

小流量涡流管特性的实验研究

本文用实验方法研究了小流量涡流管制冷的特性。实验中分别对入口压力和工质等因素对涡流管特性的影响进 行研究。在实验中发现了涡流管冷端制热和热端制冷的反常现象,并对其进行了解释。     

热管式相变蓄热换热器储/放能过程中传热特性的实验研究

将热管作为换热元件应用于相变蓄热系统中,研制了一套热管式相变蓄热换热器。采用石蜡作为蓄热材料,对其储、放能过程即内部石蜡的融化与凝固过程进行了实验研究。测定了储、放能过程中不同时刻换热器内石蜡的温度分布; 改变供、取热流体参数,分析了供/取热流体的入口温度与流量对换热器储/放能过程的影响;分析了储、放能过程中能量随时间的变化情况。结果表明,热管在本换热器内极好地发挥了换热元件的作用,换热器运行状况良好,各项功能均能较好地实现。