工件曲率对沟槽犁切成形影响的有限元研究(英文)

为了研究工件曲率对犁切过程中沟槽成形的影响,以软件 DEFORM 为工具,利用有限元法分析不同曲率下犁切沟槽的成形过程。分别比较不同曲率条件下成形的沟槽几何尺寸、有效应力分布和犁切力。采用实验验证了曲率在 0.133 mm-1条件下卷曲沟槽的成形。此外,为了分析沟槽成形变化的原因,建立了不同曲率工件的犁切过程系列几何模型。相比于负曲率或平面,正曲率对沟槽成形的影响最为显著。这主要是由犁切刀成形面对沟槽成形过程的影响而造成的。     

Free forming of locally heated specimens

A novel manufacturing method is investigated, in which a steep temperature gradient within the workpiece is induced to facilitate material flow locally. By this method, complex shapes can be formed without complicated dies. The feasibility of the idea is analyzed experimentally and numerically. Local heating is realized either by means of induction or laser heating. Experiments using materials 16MnCr5, X5CrNi18/9, and Ti6Al4V have been conducted under various process conditions. These experiments have also been modeled by finite element method (FEM) validating the analysis procedure. Electromagnetic models are used to analyze the heat generation pattern on the workpiece by induction. It is found that the most important process parameters are the thermal diffusivity and the temperature sensitivity of the flow curve of the workpiece material. The lower the thermal diffusivity and the higher the temperature sensitivity, the more differentiated local shapes can be formed. For the analyzed geometries, induction heating has been observed to be more effective. Deformation rate and initial workpiece geometry have also a significant effect on the achievable local deformations. Various failure modes such as unintended deformations, damage by fracture, and melting of the workpiece material are described. It is concluded that the new idea of forming local shapes by local heating is a feasible and controllable manufacturing alternative.     

Generalized transient temperature behavior in induction heated workpieces

Electromagnetic–thermal coupled numerical analysis of induction heating is time intensive if three-dimensional models are used. In this study, by processing the results of finite element computations, a dimensional analysis is carried out to predict the transient temperature rise time at the surface of an induction heated workpiece. A unique set of curves is found that describes the transient dimensionless temperature at a point on the surface as a function of the electromagnetic skin depth alone. The effectiveness of the approach is verified by numerical calculations and comparing the dimensionless temperature curves for different heating cases and materials. Effect of temperature dependent thermal properties is also investigated. The consistency of numerical results is also verified by comparison with experiments.     

Creation of Flat-End V-Shaped Microgrooves by Non-Rotational Cutting Tools

The study deals with the creation of V-shaped microgrooves with flat-end, which play an important role in case of generating intermittent grooves. Microgrooves by use of rotational cutting tool have a long radius in disengagement from the workpiece. Thus, two cutting methods by use of non-rotational cutting tool are devised so that V-shaped microgrooves with flat-end can be created. The first method makes use of straight chips generated under some cutting condition. Non-rotational cutting tool compresses the chips at the groove end and cuts the excessive parts of chips over the plane. The second method is to transcribe the surface of a tool indented vertically into a workpiece. As a result, it is experimentally found that the methods enable the creation of flat-end microgrooves.     

银-石墨烯新型电触头材料的合成与性能研究

采用化学沉积和粉末冶金方法,合成了一种新型石墨烯增强银基电触头材料(Ag-G),并对其微观结构、加工性能及物理性能进行分析。结果表明,Ag-G材料组织致密、均匀,退火态抗拉强度与断后伸长率分别达到128 MPa和12.1%。DC 25V/15A阻性负载条件下,与传统石墨增强银基电触头材料(Ag-C)比较,Ag-G材料质量损耗、电弧参数及接触电阻均较Ag-C材料偏低,且电寿命为Ag-C材料的2.5倍左右。因其具有优异的加工性能与电接触性能,Ag-G材料有望成为一种替代传统Ag-C的新型电触头材料。     

银-石墨烯新型电触头材料的合成与性能研究

采用化学沉积和粉末冶金方法,合成了一种新型石墨烯增强银基电触头材料(Ag-G),并对其微观结构、加工性能及物理性能进行分析。结果表明,Ag-G材料组织致密、均匀,退火态抗拉强度与断后伸长率分别达到128 MPa和12.1%。DC 25V/15A阻性负载条件下,与传统石墨增强银基电触头材料(Ag-C)比较,Ag-G材料质量损耗、电弧参数及接触电阻均较Ag-C材料偏低,且电寿命为Ag-C材料的2.5倍左右。因其具有优异的加工性能与电接触性能,Ag-G材料有望成为一种替代传统Ag-C的新型电触头材料。     

热处理工艺对高强高导Cu-Cr-V-Zr-RE合金性能的影响

对Cu-Cr-V-Zr-RE合金进行热处理,研究了固溶温度、固溶时间、时效温度以及时效时间对合金显微硬度和电导率的影响。结果表明,该合金的最佳热处理工艺为920℃×1h固溶,550℃×1h时效。在该热处理工艺下,合金可以获得较好的综合性能,其显微硬度达到134HV,电导率达到80.5%IACS。     

冲击区体积对感应加热中间包流动影响数学模拟

通道式感应加热中间包能够对包内钢水的热量进行及时有效的补偿,有利于提高铸坯质量。建立了某厂五流四通道感应加热中间包的数学模型,研究冲击区体积对中间包内钢液流动的影响。结果表明,冲击区体积占前腔比例的45%时,双峰和短路流问题得到有效解决,各流间钢水分配较为合理,中间包内部钢液能够获得较好的流动性能,中间包总体停留时间达到1020s,死区体积降低为11.5%,3个下水口达到峰值的时间较为一致,最大时间差为49s,达到峰值的平均时长为335s。     

美的电扇前罩注射模设计

通过用注塑模CAE软件MOLDFLOW对塑件进行模流分析,选择聚丙烯的成型工艺参数,设计了一模一腔的注射模具。按聚丙烯的平均收缩率设计计算模具成型尺寸,设计链传动机构,用旋转脱出的方法解决塑件细纹脱模问题。给出了模具结构装配图,并以开模前和脱模后的模具状态图展示了模具工作过程。模具一次试模成功,运行灵活可靠,塑件精度达到设计要求,外表面光洁,给企业创造了经济效益。     

Vaporization and precipitation characteristics of cerium nitrate precursor droplets heated by monochromatic irradiation

A novel experimental setup using radiative heating has been used to simulate the high heating rates of solution precursor plasma spray process and understand the thermophysical phenomena inside cerium nitrate precursor droplets. CO₂ laser having a heating rate comparable to that of the plasma has been adapted to heat pendant precursor droplets generated at the tip of a micro-needle. The process has been imaged with a high speed video camera. The images have depicted two distinct phases during the entire heating process. In the first stage, the surface evaporation is predominant while the second phase is dominated by precipitation phenomena. Inside the droplet during the heating process formation of explosive bubbles resulting in severe instability and shape deformation has been observed. The droplet deformation was found to be dependent on heating rate and solute concentration in the precursor solution. High laser power (high heating rate) makes the droplet prone to deformation while high concentration precursor solution being highly viscous increases the resistance against instability and deformation. It was also observed that the precipitate transitions through a series of chemical transformations from the initial gelatinous phase into the final solid agglomerate during the last part of the heating process. The SEM images of the precipitate showed a porous morphology. However high concentration precursors with low heating rate resulted in dense microstructure. It was also observed that the micro-structure exhibited irregular patterns, which is evidence of the presence of multiple nucleation sites. The number of nucleation centers increased with the increase of solute concentration and laser power, while XPS analyses confirmed the presence of Ce³⁺ and Ce⁴⁺ in the residue.     

电工钢渗氮的氮行为

利用场发射扫描电镜与辉光放电光谱,研究了经不同渗氮处理与等温退火后,氮在不同厚度层内的含量与氮化物析出的种类、形态及分布。观察了氮化物粒子在等温退火过程中的演变过程。结果表明,渗氮后氮化物主要沉积在样品表层。在随后等温退火过程中,表层的氮化物逐渐溶解并向内层扩散后重新析出。因此,尺寸细小的氮化物沿扩散层均匀的分布以稳定二次再结晶组织。     

AlN电热元件的研制

设计并制备了AlN电热元件，电热元件由AlN陶瓷基片及其附着其上的通电线路Pt组成。利用丝网印刷的方法在AlN表面进行Pt浆料布线，线条数目为10。烧成温度选为1000℃和1300℃。用红外测温仪测量不同电压下的电热元件的工作温度。研究发现，1300℃烧成的电热元件可稳定工作于1000℃以上，符合设计要求。AlN／Pt的结合界面SEM形貌表明AlN与Pt膜是紧密的机械结合。AlN表面氧化生成的氧化膜利于Pt膜与AlN陶瓷的结合。     

SiC电热元件的高温失效分析

对炉用ＳｉＣ电热元件在空气介质中于１０００℃－１５８０℃范围的高温失效行为进行了试验分析。元件表面在高温下形成熔融态ＳｉＯ２薄层。由于在氧化反应中生成气体而产生气泡,气泡破裂后材料表面失去保护层,导致了高温氧化的加剧。文中对ＳｉＣ电热元件在不同温度下的脱落物进行了分析,对ＳｉＣ电热元件高温失效的原因进行了综合讨论。     

镁合金板材轧辊流体传热液固耦合传热模型的建立及数值模拟

针对目前镁合金板材轧制过程轧辊温度控制方式简易,精度差,易造成板材的板形、板厚及裂纹等缺陷,本文采用流体循环流动传热的方式对轧辊进行温度控制,且使用fluent软件对二者间的流固耦合传热过程进行了数值模拟,并进行了实验验证,给出了其传热过程中轧辊温度场的趋势和规律。结果表明：该方法加热轧辊时,其表面温度分布较均匀,边部与中间的温差最大为6℃,且流体温度与速度对其影响较小;在不同的流体温度和流体速度下,轧辊表面温度均呈速率减小的趋势上升,流体温度升高及速度增大时,轧辊温升变快,且流体温度对轧辊温升的影响大于流体速度对其的影响;得出了在不同加热条件下,轧辊表面的温度值与时间的关系式;对轧辊停止加热后到轧辊表面开始温降有一段延续期,流体的温度越高,延长时间越长;轧辊温升阶段的模拟结果与实验结果相比,流体温度升高,其误差变大,轧辊温度升高,误差也变大,两者间最大误差为16.16%,总体结果较吻合,表明该模型可以正确表示流体加热轧辊的传热过程。     

大型常法辊铸造工艺设计与优化

大型轧辊铸件在铸造中很容易产生缩孔等铸造缺陷。本文从浇注方式、电加热技术、造型材料选用等方面进行研究,并利用“华铸CAE”铸造工艺分析软件,优化浇注温度、冒口参数等工艺参数。研究结果表明,这些改进措施可使每支大型常法辊的工艺出品率由80%提高到83%,节省成本约1.03万元。     

Fe—Cr—Al电热合金表面原位绝缘膜的生长动力学问题

试验了利用气相反应法在Fe－Cr－Al电热合金表面原位生成绝缘膜的可能性。获得了主要由a－Al2O3相组成的绝缘膜层,膜的生长符合抛物线规律,抛物线速率常数随反应氛中氧分压的增高而增大,Al2O3绝缘膜的微观形貌也与氧分压的大小有关。另外对绝缘膜的击穿性能进行了测试。     

Fe_3Al电热合金抗渗碳性能的研究

通过分析Ｆｅ３Ａｌ合金渗碳后显微组织、电阻率及力学性能发生的变化,并与０Ｃｒ２５Ａｌ５合金进行比较,发现碳的渗入使０Ｃｒ２５Ａｌ５和Ｆｅ３Ａｌ合金的室温电阻率都有所升高;在相同的实验条件下,０Ｃｒ２５Ａｌ５合金比Ｆｅ３Ａｌ合金更容易在晶内和晶界析出碳化物,使得合金的力学性能下降;Ｆｅ３Ａｌ合金晶界析出碳化物会使合金发生沿晶开裂,强度与塑性同时下降。     

Evolution of the health of concrete structures by electrically conductive GFRP (glass fiber reinforced plastic) composites

The function and performance of self-diagnostic composites embedded in concrete blocks and piles were investigated by bending tests and electrical resistance measurement. Carbon powder (CP) and carbon fiber (CF) were introduced into glass fiber reinforced plastic (GFRP) composites to provide electrical conductivity. The CPGFRP composite displays generally good performance in various bending tests of concrete block and piles compared to the CFGFRP composite. The electrical resistance of the CPGFRP composite increases remarkably at small strains in response to microcrack formation at about 200 μm strain, and can be used to detect smaller deformations before crack formation. The CPGFRP composite shows continuous change in resistance up to a large strain level just before the final fracture for concrete structures reinforced by steel bars. It is concluded that self-diagnostic composites can be used to predict damage and fracture in concrete blocks and piles.     

Optimisation of the geometry of ultrasound‐welded components made of rigid plastics

Various methods of heating in welding of pipelines are investigated. It is recommended to prepare an addition to the normalization–technical documents, in order to expand the range of application of KEN-type electric heaters in preheating and various types of electric resistance heaters, and also to remove stringent requirements on the control of preheat temperature from these documents.     

优化硬质合金涂层微槽车刀后刀面磨损失效对比研究

后刀面磨损量是衡量刀具寿命的重要指标,对刀具寿命其决定性作用。针对前期研制的优化硬质合金涂层微槽车刀,文章通过切削实验和理论分析,研究了优化微槽车刀和原车刀在切削过程中刀具后面磨损情况。从两车刀后刀面磨损失效现象的对比分析发现,在相同的切削时间内,微槽车刀后刀面磨损程度低于原车刀,在达到几乎相同的磨损程度情况下,微槽车刀经历的切削时间长于原车刀,即原车刀相较于微槽车刀更容易出现后刀面磨损失效。研究结果为优化硬质合金微槽车刀磨损失效机理的深入研究提供理论依据。