Research on the Influence of Cutting Condition on the Surface Microstruct ure of Ultra-thin Wall Parts in Ultrasonic Vibration Cutting

In many fields of high-tech industry the ultra-t hi n wall parts are employed. In this paper the experiments were carried out to dis cuss the surface microstructure of the camera’s guided drawtube by applying ult rasonic vibration cutting device to the traditional lathe. The influence rule of the cutting condition on the surface roughness was put forward, which was drawn by comparing the ultrasonic cutting with the common cutting by use of the cemen ted carbide tool and the polycrystalline diamond (PCD) tool. The test results sh owed that the ultrasonic cutting performs better than the common cutting in the same condition. According to the test results analyzing, the surface characteriz ation is influenced clearly by the rigidity of the acoustic system and the machi ne tool, as well the setting height of the tool tip. Otherwise, the dense regula r low frequency vibration ripples will be scraped on the machined surface. When the tool tip is set higher than the rotating center of the work piece by three t imes of the amplitude of ultrasonic vibration, the vibration ripples behave alig ht; they turn light and shade alternatively when the tool tip is lower than the rotating center of the work piece by three times of the amplitude of ultrasonic vibration. According to the test result analyzing, the following conclusions are put forward: 1) The surface roughness in ultrasonic cutting is better than that in common cutting. Under a one third critical cutting velocity, the value of th e surface roughness in ultrasonic cutting rise slightly along with the cutting v elocity, while in common cutting it decreases contrast to the cutting velocity; the curves of the surface roughness in ultrasonic cutting and common cutting see m to be alike, both increase along with the feed rate and the cutting depth, but the value in ultrasonic cutting is smaller in the same condition.2) The influen ce of the coolant on the surface roughness cannot be ignored. The kerosene can b e employed to improve the surface roughness in ultrasonic machining.3) In ultras onic cutting process of aluminum alloy ultra-thin wall work piece, the PCD tool performs better than the cemented carbide tools.4) The vibration ripples result from the not enough rigidity of the acoustic system and the improper setting he ight of the tool tip. The departure of the tool tip from the rotating center of the work piece to some extent causes the vibration ripples on the machined surfa ce.

Cuticle and skin cell walls have common and unique roles in grape berry splitting

The skin protects a fruit from environmental stresses and supports the fruit’s structure.Failure of the skin leads to fruit splitting and may compromise commercial production for fruit growers.The mechanical properties of the cuticle and skin cell walls might influence the splitting susceptibility of fleshy fruits.Thin shell theory and fracture mechanics were utilized in this study to target the potential factors contributing to splitting susceptibility.The study analyzed the structure of the cuticle and epidermis in ripening grape berries and examined the temporal dynamics of berry splitting.Cuticular waxes were partially removed,and skin cell walls were manipulated using wall stiffening and loosening solutions that altered reactions involving hydrogen peroxide.A more than twofold difference in cuticle thickness among grape cultivars did not account for their differences in splitting resistance.However,while removing predominantly epicuticular wax did not alter the berries’splitting resistance,their surface appearance and increasing yield strength following partial wax removal support the notion that cuticular waxes contribute to berry mechanical properties.Immersing berries in H 2 O 2-based cell wall loosening solutions increased the splitting probability and accelerated berry splitting,whereas cell wall stiffening solutions decreased the splitting probability and delayed berry splitting.These results showed that both cuticle and skin cell walls contribute to the mechanical properties of grape berries and to their splitting resistance.The results also suggest that the two current explanations for fruit splitting,the critical turgor model and the zipper model,should be viewed as complementary rather than incompatible.

Wall Sticking of High Water-Cut, Highly Viscous and High Gel-Point Crude Oil Transported at Low Temperatures

Some crude oils with high water cut have the capability to flow below the oil gel point, while the oil particles adhere to the pipe wall in the form of paste, also called "wall sticking". Wall sticking is a serious problem during the pipeline transportation, leading to partial or total blockage of the pipeline and energy wastage. In this paper, a series of laboratory flow loop experiments were conducted to observe the wall sticking characteristics of crude oil with high water cut, high viscosity and high gel point at low transportation temperatures. The effects of shear stress and water cut on the wall sticking rate and occurrence temperature were investigated. Experimental results indicated that the wall sticking rate and occurrence temperature were lower under stronger shear stress and higher water cut conditions. A criterion of wall sticking occurrence temperature(WSOT) and a regression model of wall sticking rate were then established. Finally, the software was developed to calculate the pressure drop along the pipelines of crude oils with high water-cut. It was able to predict the wall sticking thickness of gelled oil and then calculate the pressure drop along the pipelines. A typical case study indicated that the prediction results obtained from the software were in agreement with actual measured values.

Numerical stress-deformation analysis of cut-off wall in clay-core rockfill dam on thick overburden

The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.

Research and development on cutting scale machine in the coal mine shaft

The deposit scale in the coal mine shaft usually causes serious accidents, such as making rope broken, cage seized or dropped. To solve this kind of problems, the re-search of the cutting scale mechanism was made, and a new type of removal scale equipment was made with using imported hard alloy material. The cutting experiment and actual cutting show that it can adapt to abominable condition in the shaft, such as narrow space, wet and excessive shaft crevice water and so on, and can work safely and reliably, and has high cutting scale efficiency. It can also cut out the deposit scale in the circular section of shaft.

基于有限元分析的走刀策略对铝合金薄壁筋铣削仿真工艺研究

铝合金薄壁筋具有弹载计算机结构件的典型特征,其结构简单但整体刚性差,在加工过程中极易产生加工变形,影响工件的加工精度。为合理选择走刀策略,使用ABAQUS软件对铝合金薄壁筋铣削过程进行有限元仿真建模,分析了不同走刀策略下铣削过程中的铣削力及工件铣削后的变形情况。同时设计对照试验组进行试切验证,通过三坐标测量仪分别测量了薄壁筋在不同走刀策略下的形变,验证了仿真分析结果的正确性。

急倾斜薄矿体采场围岩及假底应力分布规律研究

急倾斜极薄矿脉是有色、黄金矿山常见的矿体形态,多采用人工假底的留矿法或削壁充填法回采,研究采动过程中围岩和人工假底的受力分布对于设计假底参数和安全开采具有重要意义。以某金矿削壁充填采场为工程背景,模拟研究了人工假底及围岩采动过程中应力变化规律。上、下盘围岩采动后最大主应力和最小主应力减小,回采区域顶板应力集中。假底中心处垂直压力最小,越靠近上、下盘边壁垂直压力增加,随着采高增加,假底各部位的垂直压力增加,最后呈收敛趋势。人工假底主要是剪应力破坏,假底破坏主要是上、下盘高水平应力未作用在同一轴线而产生的剪应力造成的。根据散体侧压力和采动应力变化规律,提出在采场内每隔10m利用混凝土铺底,增加人工假底中混凝土强度及垂直方向的配筋,提高假底抗剪强度,从而提高深部采场回采的安全性和人工假底的稳固性。

空腹混凝土坝振动响应试验研究

针对平原地区土层条件较差和地形条件有限的情况,提出一种新型坝——空腹混凝土坝。采用振动台模型试验技术,研究加速度峰值、库水位及防渗墙对该新型坝动力响应的影响。结果表明:(1)在自由场坝基中设置结构可以降低坝基的超孔压响应,削减坝基液化程度。(2)非自由场工况中,加速度峰值的增大加强了坝基的振动幅度,加剧液化程度;坝体上游库水位的存在增加了坝基的有效应力从而降低液化程度;坝基中防渗墙的存在增加了孔压的消散从而降低液化程度。总体来说,加速度峰值对液化程度影响最大,库水位影响次之,防渗墙影响最小。(3)库水位的存在增加了坝体的受力程度导致坝体水平位移响应大于空库工况,防渗墙的存在降低了坝基中的水力梯度导致坝体响应低于无防渗墙工况。但在试验过程中坝体并没出现明显的水平位移变化。

渠式切割水泥土连续墙的应用和发展

作为超深、等厚、连续、可靠的截水挡土帷幕,渠式切割水泥土连续墙在国内有广泛应用。本文概括了渠式切割水泥土连续墙在国内的引进、应用和发展历程。结合对国内200多个既有应用案例的统计分析,研究了渠式切割水泥土连续墙的施工设备保有情况、成墙深度范围、常用墙体厚度和主要应用场景;罗列了渠式切割水泥土连续墙在复杂地层施工的辅助措施以及典型案例;指出了渠式切割水泥土连续墙在敏感环境微扰动施工的控制要点;介绍了渠式切割预制装配式混凝土连续墙的设计要求和用途,尤其是内插预制板材的截面设计和制造工艺;最后用工程实例表明渠式切割预制装配式混凝土连续墙同时继承了渠式切割微扰动和地下连续墙支护刚度好的特点,无论是切割成墙期间还是土方开挖期间,施工对周边环境的影响都较小。

薄壁零件数控加工质量的提升策略

薄壁零件在机械制造中的应用越来越广泛,但其加工难度较大。提升薄壁零件的数控加工精度,可以改善零件质量,提高生产率,降低费用,进而推动先进设备制造业的发展。文章分析影响薄壁零件数控加工质量的因素,包括加工工艺、外部荷载、温度系数及刀具等,并提出提高加工质量的措施,如合理选用刀具、选择合理的切削用量和技术方案、保证尺寸的精度以及适当延长切削时间等。

连续光纤激光切割金属薄壁材料工艺研究

随着工业领域金属薄壁构件设计的多样化,在高速激光切割的同时,对切口形貌质量也提出了更高的要求。本研究采用连续光纤激光器对0.2 mm厚度304不锈钢薄板进行切割实验,研究了毛刺和熔渣飞溅区产生的机理,重点讨论了加工工艺参数中的激光功率、切割速度、离焦量对毛刺堆积量和熔渣飞溅区宽度的影响关系,通过实验分析获得了最佳加工参数组合。研究结果表明,毛刺厚度随着激光功率、离焦量的增大而增加,随着切割速度的增大先降低后增加。熔渣飞溅区宽度随着激光功率的增大而增加,随着切割速度的增大而降低,随着离焦量的增大出现小范围波动。根据加工结果分析,当激光功率为125 W,切割速度为10 m/min,辅助气体压强为1.2 MPa,离焦量为-0.3~-0.5 mm,可以获得0.2 mm厚304不锈钢薄板较好的加工效果。

土石坝加高工程老坝防渗墙施工时机优选

针对老旧水库大坝加高工程中混凝土防渗墙的修建时机对其自身应力变形影响很大,可能对坝体防渗系统造成安全隐患的问题,以某土石坝加高工程为例,采用三维有限元法对大坝加高过程进行模拟计算,分析比较了不同施工方案下防渗墙的应力变形特性,以优选防渗墙施工时机。模拟计算结果表明:在加高坝填筑至215 m或此之前修建老坝防渗墙时墙体应力变形较小,此时竣工期与蓄水期防渗墙顺河向最大位移分别为-1.56 cm与4.91 cm,大主应力极值分别为1.01 MPa与1.67 MPa,小主应力极值分别为-0.41 MPa与-0.66 MPa,防渗墙与连接板接缝的切向错动和相对沉降变形极值分别为4.84 mm与8.11 mm,能够满足安全运行要求。相比加高坝填筑后期施工防渗墙,在加高坝填筑开始前或填筑至与老坝同高之前完成防渗墙的施工,可改善防渗墙的应力变形状态并降低防渗墙与连接板接缝的切向错动和相对沉降。

初始残余应力的检测方法及其在薄壁叶片加工变形分析中的应用研究

薄壁叶片是航空发动机的关键部件,在加工过程中极易发生剧烈的变形。已有的变形研究控制重点关注在减小切削力和加工残余应力(Machining‑induced residual stress,MIRS)这两方面。本文利用材料热处理和锻造过程中产生的初始残余应力(Initial residual stress,IRS)来减轻薄壁零件受切削力与加工残余应力影响所产生的变形。由于初始残余应力测量困难且具有破坏性,本文提出了一种初始残余应力逆辨识方法来测量Ti6Al4V的初始残余应力。与传统的初始残余应力测量方法相比,逆辨识方法更符合应力分布和叶片变形的分布趋势。为了研究和解耦初始残余应力、加工残余应力和切削力之间对加工变形影响的相互作用,针对钛合金直纹叶片为对象进行实验验证,并建立了有限元预测模型。在分析切削力与加工残余应力对变形的影响后,可以得到切削力占变形程度的46.17%,平均值为26.36μm,而加工残余应力占变形程度的53.83%,平均值为30.70μm。耦合初始残余应力后使得整体的变形减小,受加工残余应力影响的最大挠度变形从35.32μm降低到15.50μm,该分析为利用初始残余应力减小薄壁叶片加工变形提供了新的方法。

基于正交试验的金属薄壁材料激光切割工艺优化

激光切割后,金属薄壁类零件的材料基体与下方的支撑板易产生粘连,严重影响切割质量。采用光纤激光对304不锈钢和GH605高温合金薄板进行切割实验,分析了激光切割不同材料发生粘连的机理。采用单因素试验法分析了激光切割工艺参数对热影响区及毛刺堆积量的影响规律。加工结果显示,在加入微连工艺的前提下,激光功率为165 W,切割速度为5 m/min,辅助气体压力为1.2 MPa时,切缝边缘光滑、无变形及残留黏附现象。

基坑盖板下逆作车站地下连续墙托换破除技术

附属结构与地铁车站连通常需要对地下连续墙进行破除,当地下连续墙上设有临时承重盖板时破除的施工难度更大,风险更高。以某地铁盖挖逆作车站的地下连续墙破除施工为依托,提出了利用局部破除体作为临时竖向支撑进行托换破除的施工方法。首先,采用数值计算分析了不同托换间距对盖板结构体系的受力影响,综合施工进度和作业空间考虑,确定预留1m宽的临时托换柱和不大于12m的破除间距为控制指标,能够满足各受力结构体系在临时托换施工下的承载性能要求;其次,对盖板下地下连续墙破除及切割块转运施工进行了详细分析,给出了分块尺寸、切割块吊装、预留柱节点等关键施工环节的控制指标与做法。实施结果表明:利用既有地下连续墙作为临时托换结构进行破除地下连续墙的施工方法,安全可靠,施工速度快,成本经济。

超深混凝土防渗墙浇筑工效及单价计算方法研究

随着水电工程中采用越来越多的超深(大于100 m)混凝土防渗墙进行坝基防渗处理,现行水电工程概预算定额已远不能满足其混凝土浇筑工程单价编制需求。以狮子坪水电站大坝隐患治理超深(148 m)混凝土防渗墙工程为研究对象,采用“数字影像技术”对其混凝土浇筑工效进行为期1 a的现场测定及分析,得到了超深混凝土防渗墙浇筑平均工效随防渗墙深度增加的关系。并在此基础上,结合相关施工技术规范提出了超深混凝土防渗墙浇筑工程单价计算方法和计算要点事项。

特高含水期原油低温集输温度边界确定方法

随着国内油田逐渐进入开采后期,本文提出黏壁温度作为综合含水率70%~90%的高含水低温集油的评价指标已进入推广阶段且效果显著,但在现场降温试验中发现含水率90%以上的特高含水期原油管线实际运行温度与黏壁温度预测结果之间存在一定误差。因此,针对特高含水期原油开展低温集输温度边界条件研究,对完善油田低温集输技术具有重要意义。利用环道实验装置进行了特高含水期原油黏壁凝油冲刷实验,对特高含水期原油油水两相流动特性和油相黏壁特性进行分析,确定了屈服应力是阻碍黏壁凝油在管道内被冲刷剥离最主要的影响因素。编制了特高含水期原油低温集油温度预测软件,利用油田单井集油管线的现场降温试验进行了验证,误差在2℃范围内,满足工程运用需求。

单方向夹持悬伸薄壁结构件多轴切削工艺优化

以单方向夹持的悬伸薄壁结构零件切削加工为研究对象,通过工艺设计优化有效避免了断裂,振动过切,尺寸变形超差,振纹等加工缺陷。使用Siemens NX12.0和宏程序结合的方式完成零件的四轴加工程序编制。通过降低最小壁厚和伸出长度比值、宏程序螺旋铣削切断工艺方案,解决加工过程中切削振动造成曲面与连接底座容易断裂的难题。提出薄壁曲面分段加工和控制走刀方向相结合减少了薄壁曲面振动和过切,减少了表面振纹以及粗糙度超差的影响。严格控制零件圆柱体回转跳动误差,解决不具备RTCP功能数控系统定轴加工精度超差问题。多次实例证明零件达到加工技术要求,为悬伸薄壁复杂结构零件提高切削加工质量提供参考。

泡沫泥浆在防渗墙泥浆护壁中的应用

在土体粒径大、渗透性能好的地层中开挖防渗墙或打桩时经常会出现槽(孔)壁坍塌、泥浆渗漏量大和卡钻等问题。而利用泡沫密度小、黏度大的特性,在护壁泥浆中加入泡沫有助于防渗堵漏,具有较好的应用效果。阐述了为寻求泡沫泥浆的合理配比、探讨其护壁效果,选择α-烯基磺酸钠(AOS)、脂肪醇聚氧乙烯醚硫酸钠(AES)、十二烷基硫酸钠(K12)和复合植物蛋白发泡剂(HT)等4种发泡剂进行的发泡体积、半衰期测定并开展了泡沫泥浆基本性质试验和渗透试验,结果表明:4种发泡剂中,HT泡沫半衰期为500 min,保持稳定的时间最长,在泥浆中加入泡沫后可以提高泥浆的黏度,降低泥浆的动切力和静切力,使泥浆黏滞阻力减小并可减少环空能量损失;相同条件下,泡沫泥浆比普通泥浆渗漏量小,其渗漏量随着泡沫掺比的增加先减小、后增大,泡沫掺比为20%时渗漏量最小。

盖挖法基坑开挖对临近桥梁桩基的影响研究

城市交通建设往往临近既有建筑结构,为了掌握盖挖法深基坑开挖对临近桥梁桩基的影响,依托之江路输水管廊及道路提升工程,建立数值模型并对工程现场展开监测,分析对比了基坑开挖导致的围护结构变形及桥桩变形规律。结果表明:围护结构最大位移出现在基坑北侧坑中坑开挖后,为6.14mm,最大位移深度随基坑开挖而下移,且坑中坑开挖完成后,其对侧围护结构变形反而减小,坑中坑开挖布置在敏感结构对侧时对临近结构具有一定控制效果;桥梁桩基最大沉降出现在首道混凝土支撑安装后,但随基坑开挖而逐渐减小,盖挖造成的沉降主要水平影响范围距围护结构约为12.71m,对邻近桥桩的影响主要发生在基坑开挖的早期阶段,各项变形均在安全范围内,且不均匀沉降控制效果明显。