泡沫剂中表面活性剂浓度对盾构施工的影响

为了在盾构施工中节约泡沫剂,充分发挥泡沫剂的效能,对其重要成分表面活性剂进行研究。以SDS(十二烷基硫酸钠)为例,利用电导率仪和恒温箱测定不同温度下不同浓度SDS溶液的电导率。结果发现,在1~40℃,SDS的CMC可用一个二次多项式来表达,且误差小于2.31%。SDS在不同温度下CMC的确定,为盾构泡沫剂在不同施工温度下浓度的选择提供了依据。     

富水砂层条件下双螺旋土压平衡盾构施工技术

在富水砂层地质条件下,采用双螺旋土压平衡盾构施工比采用泥水盾构、单螺旋土压平衡盾构有较大优势。依托施工案例,详细总结了双螺旋土压平衡盾构的工艺原理、特点及施工控制关键技术。通过对比分析总结,形成以下结论:二级螺旋输送机的采用,拓宽了盾构机的功能,能够有;效保持渣土仓稳定,减少突涌事故的发生,保持密封仓内水土压力,避免发生地表塌陷;与采用泥水盾构相比,双螺旋输送机盾构节约成本达392万元,经济效果显著;采用二级螺旋输送机可有效降低盾构掘进喷涌事故的发生,减少了施工现场泡沫剂的使用,在一定程度上降低了对周围环境的污染。     

大埋深盾构地下拆解扩大洞室地层加固技术分析

在大埋深盾构地下拆解施工过程中,经常会面临软弱围岩、深埋高压、洞室稳定性不足等问题,在无管片结构支护的情况下,在地下进行盾构拆解极容易发生地下坍塌、施工人员和拆解设备遭到损伤的状况。本文通过实际案例,分析当前盾构拆解模式的研究现状,探讨大埋深盾构地下拆解以及扩大洞室地层加固技术,以期为相关工程项目提供安全技术参考和借鉴。     

锥面刀盘盾构主参数确定理论及模拟分析

由于盾构在地下土质工程全断面开挖的独特优势及其技术密集的特点,被赋予"国之重器".但目前应用的盾构都是平面刀盘盾构,这样盾构在孤石、古树根或建筑物桩基等地质段的施工一直是工程界的难题.为此,通过深入研究,提出了锥面刀盘盾构的概念;进一步研究发现,其主参数——盾构推力和刀盘扭矩与平面刀盘盾构相比有着本质的差异,为此,以土力学理论为基础,深入研究了锥面刀盘盾构作业过程中的力学特点并因此建立了锥面刀盘盾构推力和刀盘扭矩的力学模型.当锥顶角为180°时得到的模型解与对应平面刀盘盾构主参数的相对误差分别是:盾构推力为5.5％,刀盘扭矩为7.8％.模拟显示,掌子面与土仓的压差随锥面刀盘锥顶角的增大单调减小,即,在掌子面压力不变的情况下,土仓压力随锥顶角的增大单调增加,这说明,锥面刀盘土仓压力小于平面刀盘,掌子面土体较平面刀盘具有较大的流动推力;而对螺旋输送器中的柱塞效应要求降低,亦即,锥面刀盘盾构具有更好的土体适应性.     

注浆量精确测量方法的研究与实现

介绍了地铁盾构施工中测量注浆量的一种新方法。使用该方法设计了相应的测量装置:并应用于实际的盾构施工过程中。通过对盾构施工采集的实时数据进行分析和处理,计算出实时注浆量。经过与实际注浆量对比验证,可知这种注浆量测量方法精度要比传统测量方法精度高。     

城市隧道工程带"火"盾构市场

伴随着我国城市化战略的实施,大、中城市建设地下施工成套设备的需求将有较大幅度的增长,将显著带动地下掘进设备的高速增长.盾构属于掘进机的一个品种,主要用于建设地下工程,在软土隧道工程施工中是关键性设备,有关人士介绍,与传统施工方法比较,使用盾构通常速度快4～10倍,并且完成的工程质量高,因而很受施工企业欢迎.     

液压缸驱动式偏心盾构刀盘掘进机构设计和优化

介绍了一种新型的盾构机种--液压缸驱动的偏心盾构,是一种不同于往常使用的盾构机种.主要区别在于刀盘的驱动及结构形式.通过对刀盘受力进行分析,推导出盾构刀盘转速、阻力矩、切向力及液压缸流量之间的相互关系,并找出在工作过程中这些参数的合理值,为盾构控制系统的研究提供参考.     

斜井盾构地下可拆解刀盘结构设计

盾构斜井地下拆解受空间及地质条件等多方因素的影响,无法直接进行刀盘吊装拆解。为实现盾构刀盘在斜井地下有限空间内安全、快速、高效拆解,必须开展盾构刀盘可拆解结构形式研究。在盾构研发设计阶段,结合盾构施工斜井工程设备要求和盾构地下拆解施工条件,将刀盘分块设计理念植入到盾构刀盘结构设计中,对盾构刀盘的重量、结构尺寸等关键可拆解结构参数进行分析设计。     

基于模糊PID算法的盾构机土压平衡控制研究

盾构施工是城市地下交通建设中最常用的施工方式,土压平衡式盾构机能够在不影响城市地面正常功能的条件下顺利施工,其基本要求是密封舱内的土压与开挖面处的水土压力相平衡,否则将造成地面隆起或塌陷,甚至造成安全事故。然而,由于地下施工条件的复杂性,密封舱内的土压与外界泥土压力很难达到平衡,往往根据施工人员的经验来进行,不仅影响工程进度,且可靠性很难得到保证。基于模糊PID控制算法,对影响密封舱内土压力的因素进行控制,并借助LabVIEW平台,编写了对密封舱内土压进行控制的控制器,通过试验仿真验证了该算法的正确性,能够保证施工中土压平衡,为顺利实现盾构施工提供有效保障。     

城市软土地层盾构中穿越既有隧道影响及施工设备选取

随着我国城市地下铁路建设速度日益增快,地下交通线路相互交叉、错综复杂,盾构开挖工作也迎来新的挑战。依托于天津市某地铁建设工程项目,基于室内模型试验,深入研究了不同交叉角度下地铁隧道盾构掘进对既有隧道的影响。研究发现:软土地层盾构开挖会导致土层出现明显的松动,土层附加土压力逐渐减小;随着交叉角度的逐渐增大,盾构掘进对土层的附加土压力及既有隧道的附加内应力的影响越小。研究成果为我国滨海地区地铁建设工作提供了一定指导作用。     

Finite element prediction of blanking tool cost caused by wear

The total cost of a blanked part is determined by a large number of factors, including the material cost, manufacturing costs. Predicting the manufacturing costs of a blanked part requires accurate estimation of tool cost caused by wear. The aim of this paper is to develop a finite element model allowing for the numerical prediction of the blanking tool life which allows for the evaluation of the cost rate of blanking tool caused by wear needed to assess the total cost of a blanked part. A wear prediction model has been implemented in the finite element code Abaqus in which the tool wear is a function of the normal pressure and some material parameters. In the present work, the tool is modeled as rigid body hypothesis, and the wear variables are computed in the contacting elements. The altered tool contact surface and contact pressure tool shapes are updated iteratively to simulate wear over a long period of time of about 100,000 cycles. A damage model is used in order to describe crack initiation and propagation into the sheet. The distribution of the tool wear on the tool profile is obtained and compared to industrial observations.     

Numerical study on the dynamics of an electrical discharge generated vapor bubble in EDM with different shapes of the tool and the workpiece

In this paper, the effect of the shapes of the tool and the workpiece on the dynamic behavior of an electrical discharge generated vapor bubble in the process of EDM (Electrical Discharge Machining) is investigated. The boundary integral equation method is employed for numerical simulation of the problem. Results show that in the case of the concave tool and workpiece the lifetime of the electrical discharge generated vapor bubble is longer than the case of the flat tool and workpiece. By increasing the concavity of the shapes of the tool and the workpiece, the lifetime of the bubble increases. Results also show that in the case of the convex tool and workpiece, the lifetime of the electrical discharge generated vapor bubble is shorter than the lifetime of the bubble in the case of the flat tool and workpiece. In this case also, by increasing the convexity of the shapes of the tool and the workpiece, the lifetime of the bubble decreases. Numerical results show that in the case of the concave tool and workpiece the rate of pressure drop on the surface of the workpiece is higher than the rate of pressure drop on the workpiece in the cases of the flat and convex tool and workpiece. The high rate of pressure drop on the surface of the workpiece leads to the ejection of more molten material from the crater and consequently leads to more material removal rate.     

金属切削中刀具月牙洼磨损模型的研究

刀具的前刀面月牙洼磨损和后刀面磨损在刀具磨损的研究中占据同等地位,但月牙洼磨损轮廓和刀屑交界面上的切削过程变量不易测量等因素,导致真正依据月牙洼磨损测试获取月牙洼磨损模型的研究非常少。基于硬质合金刀具切削低碳钢的月牙洼磨损实验,提出了一个经验磨损模型。该模型综合了黏结磨损和扩散磨损,考虑了刀屑交界面温度和压力对月牙洼磨损的影响。研究结果表明,该模型能够分析并预测相似切削条件下的月牙洼磨损轮廓。     

Numerical and experimental study on the effect of vibration of the tool in ultrasonic assisted EDM

In this paper the effect of ultrasonic vibration of the tool in the process of electrical discharge machining is investigated. The ultrasonic vibration of the tool has significant effect on the dynamic behaviour of the vapour bubble generated between the tool and the workpiece due to the electrical discharge. The computational simulation of the bubble behaviour is carried out by employing the boundary integral equation method. Results show that when the electrical discharge occurs in the closest position of the tool to the workpiece, the vapour bubble expands to the largest maximum volume of the bubble and the lifetime of the bubble is the longest. This in turn makes the pressure inside the bubble decrease rapidly to the lowest magnitude and causes melted material at the sparked point vaporize and leave the crater on the surface of the workpiece.     

The performance of ceramic and cermet cutting tools for the machining of austempered ductile iron

In this study, the machinability of austempered ductile iron (ADI) having a ferritic structure was examined. For this purpose, three types of ductile iron materials (as cast, ADI-250, ADI-375) and two different types of cutting tool materials (ceramics and cermet) were used. To emphasize the role of austempering process, ductile iron (DI) specimens are first austenitized in salt bath at 900°C for 120 minutes after which they are quenched in salt bath at 250°C (ADI-250) and 375°C (ADI-375) for 120 min. Machining tests were carried out at various cutting speeds (100–500 m/min) under the constant depth of cut and feed rate. The performance of both ceramic and cermet tools were evaluated based on the workpiece surface roughness and flank wear. Wear conditions of the cutting tools were characterized by scanning electron microscope. The results point out that the lower austempering temperature results in increasing of the cutting forces, while better surface roughness is obtained. Additionally, the results indicate that the tool wear occurs mainly on the flank face. However, higher cutting speed results in chipping formation in cermet cutting tool.     

基于“差分”磨损模型的车削刀具磨损仿真预测研究

研究表明,切削过程中的刀具磨损与刀面温度、刀/屑和刀/工界面的接触压力及相对滑动速度等切削过程变量有关,借助于有限元分析法可对这些切削过程变量进行仿真预测。基于“差分”磨损模型,提出了一种对切削过程中刀具轮廓磨损变化的预测方法,以硬质合金刀具切削AISI1045材料为例,介绍了该方法的原理和实施步骤,并对刀具前后刀面磨损的预测结果进行了试验验证,分析了预测结果与试验结果存在误差的原因。     

EFFECT OF COOLANT PRESSURE,NOZZLE DIAMETER,IMPINGEMENT ANGLE AND SPOT DISTANCE IN HIGH PRESSURE COOLING WITH NEAT OIL IN TURNING Ti-6AL-4V

Though titanium alloys are being increasingly sought in a wide variety of engineering and biomedical applications, their manufacturability, especially machining and grinding imposes lot of constraints. Titanium alloys are readily machinable provided the cutting velocity is in the range of 30–60 m/min. To achieve higher productivity, if the cutting velocity is enhanced to 60–120 m/min and beyond, rapid tool wear takes place diminishing the available tool life. Tool wear in machining of titanium alloys is mainly due to high cutting zone temperature localised in the vicinity of the cutting edge and enhanced chemical reactivity of titanium with the tool material. Rapid tool wear encountered in machining of titanium alloys is a challenge that needs to be overcome. High pressure cooling in machining is a very promising technology for enhancing tool life and productivity via appropriate cooling and lubrication. The present investigation is an attempt to study the effects of jet application parameters, i.e., coolant pressure, angle of impingement of the jet, spot distance and nozzle diameter on tool wear and chip morphology and to compare the effectiveness while turning Ti-6Al-4V bars under high pressure cooling with neat oil. Results indicated that at a cutting speed of 85 m/min and feed of 0.2 mm/rev, high pressure cooling provided a tool life of 24 min vis-à-vis 12 min under cryogenic cooling.     

2D FEM estimate of tool wear in turning operation

Finite element method (FEM) is a powerful tool to predict cutting process variables, which are difficult to obtain with experimental methods. In this paper, modelling techniques on continuous chip formation by using the commercial FEM code ABAQUS are discussed. A combination of three chip formation analysis steps including initial chip formation, chip growth and steady-state chip formation, is used to simulate the continuous chip formation process. Steady chip shape, cutting force, and heat flux at tool/chip and tool/work interface are obtained. Further, after introducing a heat transfer analysis, temperature distribution in the cutting insert at steady state is obtained. In this way, cutting process variables e.g. contact pressure (normal stress) at tool/chip and tool/work interface, relative sliding velocity and cutting temperature distribution at steady state are predicted. Many researches show that tool wear rate is dependent on these cutting process variables and their relationship is described by some wear rate models. Through implementing a Python-based tool wear estimate program, which launches chip formation analysis, reads predicted cutting process variables, calculates tool wear based on wear rate model and then updates tool geometry, tool wear progress in turning operation is estimated. In addition, the predicted crater wear and flank wear are verified with experimental results.     

土压平衡盾构机刀盘刀具布置方法研究

研究土压平衡(Earth pressure balanced,EPB)盾构机刀盘刀具的布置方法,目的是为了确保刀具结构布置的合理性和实用性。依据刀具磨损的等寿命原则,提出确定刀具数量的磨损系数法和掘进系数法;针对具体施工问题,可预测盾构在开挖区间,刀具的磨损量以及许用磨损情况下刀具的掘进距离,为保障工程的安全顺利进行提供参考。基于阿基米德螺旋线布置方法,计算以刀具磨损的等寿命原则下,主切削刀的布置曲线;提出刀具平面对称布局原则,分析刀具的切削过程,得到单把刀具的实际切深;建立EPB盾构刀盘上先行刀的立体布局方法,计算得到先行刀的超前量;结合南京地铁二号线TA07标段,验证了刀具布置方法的正确性。研究内容和研究方法可为EPB盾构机刀盘的选型和设计奠定理论基础。     

汽车钛合金连杆切削加工中的刀具磨损研究

以汽车钛合金连杆为研究对象,分析了钛合金连杆在切削加工工艺过程中的刀具磨损量、切削力和刀具寿命随着切削速度、润滑压力的变化规律。试验分析结果表明:刀具磨损量随着切削速度的增加而增加,随着水射流润滑压力的增加先减小后增加;刀具切削力和轴向力均随着水射流压力的增大先减小后增加,但轴向力的变化较切削力更加敏感,变化速率更快;刀具寿命随着切削速度的增加而减小,随着水射流压力的增加先增大后减小,钛合金连杆的最佳工况为切削速度75m/min,润滑压力10MPa。