加热温度对22MnB5微观组织和奥氏体晶粒的影响

热成形过程中的加热温度对板料性能影响非常显著。本文研究了在不同加热温度下板料的微观组织,并通过氧化法和晶粒边界腐蚀法显示22MnB5钢奥氏体晶界,测定板料晶粒尺寸的变化。结果表明:随着加热温度的升高,板料微观组织马氏体板条束宽度和奥氏体晶粒尺寸随之增大,在900℃时晶粒尺寸适中且分布较为均匀,且氧化法较晶粒边界腐蚀法显示的晶粒尺寸偏细。测定板料抗拉强度,在900℃时出现峰值,且此温度下板料硬度值约为550HV,因此,加热温度900℃,保温时间3min,板料综合性能较好。     

基于ANSYS的D406A钢局部焊后热处理温度场计算机仿真研究

基于ANSYS大型有限元分析软件,建立了适合D406A钢圆筒构件焊后热处理有限元模型,对焊后热处理温度场进行了模拟,分析了加热过程中不同时间段焊接接头附近温度场分布情况,研究了加热宽度对相变区宽度的影响。结果表明,焊后热处理过程中,随着加热时间增加,高温区域扩大,轴向温度分布逐渐均匀,最高温度在焊缝区域,随着离焊缝中心距离增加温度逐渐降低;随着加热宽度的增加,焊缝中心最高温度明显提高,相变点以上温度区域宽度逐渐扩大,当加热宽度由10 mm提高至15 mm时增幅较大,继续增加宽度时增幅逐渐减小。     

挤压态7075铝合金半固态加热过程中的组织演变

研究了加热温度和保温时间对部分重熔再结晶方法(RAP)制备7075铝合金半固态坯料过程中的组织演变的影响。结果表明,通过在半固态温度区间加热可以将挤压态7075铝合金的纤维组织转变为半固态颗粒状晶粒组织。随着加热温度的提高和保温时间延长,挤压态组织逐渐消失,颗粒状晶粒经再结晶生长并合并长大;颗粒状晶粒的尺寸随加热温度和保温时间的增加而变大。在试验条件下,高温短时间加热比低温长时间下获得的半固态组织更加细小均匀。通过试验得出RAP法制备7075铝合金半固态坯料的优化工艺参数为600℃下保温5min。     

加热工艺参数对12%Cr钢晶粒长大行为的影响

研究了不同加热工艺参数下(加热温度1050~1300 ℃,保温时间0.25~24 h)12%Cr超超临界转子钢的奥氏体晶粒长大行为,并通过光学显微镜(OM)观察晶粒尺寸的变化规律,建立晶粒长大数学模型。结果表明:随着加热温度增加,晶粒尺寸逐渐增加,加热温度低于1150 ℃时,晶粒尺寸增加明显,而温度高于1150 ℃后,晶粒尺寸逐渐趋于稳定;随着保温时间的增加,晶粒尺寸逐渐增加,保温时间增加到3 h后,晶粒尺寸增加趋势放缓。采用非线性回归方法和Arrhenius晶粒长大模型,建立了该钢的晶粒长大数学模型。     

冷却工艺对热轧V微合金化钢板组织性能的影响

本文通过热模拟试验, 分析了不同加热温度对V微合金化510 MPa级钢板原始奥氏体晶粒度的影响规律, 并通过工业试验分析了冷却工艺和奥氏体晶粒尺寸对钢板组织和性能的影响。试验结果表明: 当加热温度为1 230 ℃, 卷取温度一定时, 可以通过控制中间温度得到等轴铁素体或针状铁素体组织。当加热温度为1 160 ℃时, 随着终轧温度、中间温度和卷取温度的变化, 钢板组织和性能变化不明显。     

电火花线切割加工表面微织构技术研究

表面微织构加工是一个相当复杂的过程,涉及微织构的尺寸、质量及形貌等问题。为解决制备微织构存在的问题,利用数控电火花线切割加工技术,在45钢表面加工微槽织构,研究线切割制备微织构的尺寸、形貌。试验分别采用钼丝、铜丝作为电极丝,设计脉宽、脉停、电流等线切割正交试验,切割宽度小于400μm的微槽织构,分析不同线切割参数、电极丝材料对微槽尺寸精度和微槽切口处光整度的影响。通过采集、测量试验所得工件表面微槽织构,发现线切割参数对微槽尺寸精度和切口处光整度有较大的影响;在较小线切割参数下,钼丝切割的微槽尺寸大于铜丝,在较大的线切割参数下,铜丝切割的微槽尺寸大于钼丝;对比微槽切口处光整度,发现钼丝切割的微槽整体质量优于铜丝。试验列出不同线切割参数切割的微槽尺寸,为电火花线切割加工微织构提供了试验数据。     

基于离子束辅助激光的硬质合金表面微织构制备方法研究

目的 解决纳秒激光所制备的硬质合金表面微织构尺寸不可控且质量较差的问题.方法 提出了离子束刻蚀与纳秒激光复合加工技术.首次采用离子束辅助激光加工在WC/Co硬质合金表面制备凹坑型微织构,研究了激光扫描速度、重复频率、脉冲宽度和刻蚀时间4种不同加工参数对微凹坑表面形貌及结构尺寸的影响,并初步预测和建立了复合加工过程中微凹坑轮廓演变模型.结果 凹坑型微织构边缘熔融物堆积量随激光重复频率的增加而增加,与扫描速度和脉冲宽度成反比,其中激光重复频率的影响最大.制备的微凹坑直径和深度可以通过改变激光重复频率和刻蚀时间来调节,使用纳秒激光以20、25、30、35 kHz重复频率加工的微凹坑经离子束刻蚀150 min后,边缘的不规则凸起高度分别由1.112、1.675、2.951、3.235μm降低至0.222、0.689、0.976、1.364μm,且刻蚀速率与激光重复频率成正比.离子束刻蚀150 min后,抛光硬质合金表面粗糙度由0.022μm增加至0.079μm,而激光织构化硬质合金表面粗糙度随刻蚀时间的增加均有所降低.结论 建立了基于离子束辅助激光的表面微织构轮廓演变模型,实现了硬质合金表面微织构的高质量可控制备.     

超高频微区感应钎焊中加热温度的影响因素

提出了超高频微区感应钎焊工艺方法.重点分析了导磁体材料、线圈结构以及感应器与工件之间的间隙三个因素对感应加热温度的影响规律,并通过试验研究获得了微区感应钎焊的最佳工艺参数.采用优化的工艺参数进行微区感应钎焊金刚石磨粒试验.结果表明,钎料熔融区域宽度可控制在3 mm以内,钎料对金刚石磨粒浸润良好.扫描电镜(SEM)和X射线能谱仪(EDS)测试结果显示,金刚石与钎料界面附近的C和Cr两种元素存在相互扩散.     

激光复合加热制备金属纳米粉体材料

激光复合加热制备金属和合金纳米粉体材料,具有能量利用率高,工艺参数可调、产品质量可控、适应面广等特点。计算机数值模拟结果表明,在加热功率相同的条件下,不同受热金属的温度分布曲线差异较大;改变激光和感应热源的输入功率,可以改变温度分布曲线的形状。通过调节温度分布曲线和系统环境压力,可以改变激光复合加热蒸发区域的大小,进而改变金属和合金纳米粉体材料的产率。     

钛微合金化热轧高强钢奥氏体晶粒粗化行为

对钛微合金化热轧高强钢奥氏体晶粒粗化行为进行了实验研究。结果表明:当保温时间相同时,随着加热温度的升高,实验钢奥氏体平均晶粒尺寸呈现出先缓慢上升后迅速上升的趋势;当加热温度相同时,实验钢奥氏体平均晶粒尺寸随着等温时间的延长呈抛物线规律长大,1150℃加热奥氏体平均晶粒尺寸与保温时间的经验公式为:D1150℃=17.1 t0.2385,1250℃加热奥氏体平均晶粒尺寸与保温时间的经验公式为:D1250℃=29.9 t0.2916。综合考虑加热温度与保温时间对实验钢奥氏体晶粒尺寸的影响,并考虑微合金元素的溶解与析出规律,实验钢的加热温度定为1250℃左右,保温时间定为40 min较合适。     

BFe10白铜管材热冷组合铸型水平连铸凝固温度场模拟

建立了热冷组合铸型(HCCM)水平连铸管材温度场模拟模型,采用实验与模拟相结合的方法修正界面的换热系数条件。所建立的HCCM水平连铸全尺寸模拟模型和所施加边界条件的误差小于6%,可较好地模拟实际传热过程的温度场。模拟结果表明:当拉坯速度由20 mm/min增加到110 mm/min时,两相区宽度由20 mm增加至30 mm;当热型段加热温度由1 150℃提高到1 300℃时,两相区宽度由30 mm减小至12 mm;当冷型段冷却水流量由300 L/h增加到900 L/h时,两相区宽度由30 mm减小至20 mm;当采用增加热阻的改进铸型结构时,两相区宽度由25 mm减小至12 mm。d 50 mm×5 mm BFe10管材HCCM水平连铸合理的制备参数为:熔体保温温度1 250℃,连铸拉坯速度50~80 mm/min,热型段加热温度1 200~1 300℃,冷型段冷却水流量500~700 L/h。     

薄壁铜管游动芯头拉拔过程拉拔力影响因素分析

为准确把握薄壁铜管游动芯头拉拔过程的拉拔力,该文应用非线性有限元分析软件ABAQUS建立了薄壁铜管游动芯头拉拔过程的弹塑性有限元模型,分析了内外模具锥角、游动芯头定径段长度、延伸率、摩擦因素以及拉拔速度等工艺参数对薄壁铜管拉拔过程中拉拔力的影响规律。研究表明,芯头或外模的锥角存在一个最佳组合范围,芯头定径段长度和拉拔速度对拉拔力的影响作用非常小,延伸率和摩擦系数的增加将引起拉拔力的明显增加。研究结果为实际生产中的工艺改进提供了科学依据。     

工艺参数对薄壁铜管游动芯头振动拉拔过程拉拔力影响分析

在金属塑性成形中加入振动,可以有效降低材料变形抗力并提高产品质量。以薄壁铜管游动芯头拉拔为研究对象,分析了振动对铜管拉拔过程中拉拔力的影响,并通过有限元分析软件MARC,对不同的工艺参数(拉拔速度、外模模角和芯头锥角)进行数值模拟。研究结果表明:针对本模型,存在一个最佳外模半锥角和芯头锥角组合(外模半锥角α为12°,芯头锥角β为9°),使得薄壁铜管游动芯头振动拉拔过程中的拉拔力最小,而拉拔速度对拉拔力的影响较小。     

Enhancement of dimensional accuracy of dieless tube-drawing process with vision-based fuzzy control

Dieless tube drawing offers flexibility to reduce the cross-sectional area of a tube only by adopting a drawing speed higher than the feeding speed without requiring dies or a mandrel. However, this promising technique faces the technological challenge of enhancing the drawn part accuracy. The deformation behavior of the process depends on the processing conditions. Therefore, real-time monitoring and control are necessary. A vision sensor was employed to monitor the minimum outer radius, and a fuzzy controller was selected to control the deformation according to the desired geometries by adjusting the drawing speed. Shift reference was introduced to compensate the deformation delay of dieless tube drawing. The dimensional accuracy of the drawn part improved after implementing the proposed control system. However, an oscillation of the profile on the drawn part caused by improper adjustment of drawing speed. An adaptive fuzzy controller was introduced to perform appropriate adjustment of drawing speed on the basis of the deformation characteristics. The result shows that a drawn outer radius accuracy of up to 99.6% was achieved with a 1.6% variation on the axial direction at a 44% reduction ratio. This performance was verified under various reduction ratios and feeding speeds.     

A new method for production of variable thickness aluminium tubes: Numerical and experimental studies

Tube drawing is one of the mostly used techniques for producing tubes in various sizes. In this method, tube passes through the die and mandrel to produce constant wall thickness tube. In some applications like transportation industry, design necessities cause requirement for these kinds of tubes. Furthermore some manufacturing processes like tube hydroforming dictate have a tube with variable thickness. In this study, with a modification made to the classical tube drawing process, the sinking and fixed-mandrel tube drawing methods were mixed together to produce tubes with variable thickness in the axial direction. An optimization method, namely the leapfrog optimizer for constrained minimization, was coupled with a finite element model to study design specifications i.e. effect of initial tube geometry on this new process. The obtained results from finite element method (tube drawing force, the minimum and maximum final thickness of tube) were compared with the experiments performed in the designed and manufactured machine and acceptable agreement was observed. Based on these results, the maximum and minimum thicknesses in the final produced tube are mostly dependent on the thickness and outer diameter of initial tube respectively.     

Progress in abrasive fluidized bed machining

The use of abrasive fluidized bed equipment in a broad range of manufacturing processes is reviewed. In particular, applications in deburring and finishing of complex-shaped metal components, in super-finishing of dies for injection molding, in cleaning and polishing of electronic devices, and in surface preparation of tungsten carbide milling tools are reviewed. Attention is focused on the effects of the most important process parameters, such as machining time, abrasive type and mesh size, and flow or jet speed. The extent of material removal and the change in surface roughness as a function of the process parameters are addressed. Selected numerical and analytical models that are useful for automation and control purposes are discussed. Finally, the industrial sustainability of the processes and equipment investigated is highlighted.     

Experimental study of oil-filled high-speed spin forming micro-groove fin-inside tubes

This paper presents an oil-filled high-speed spinning process of manufacturing micro-groove fin-inside tubes. In spinning, a high-pressure oil-film, which squeezes the tube outer-wall, is formed as the spinning speed increases. A floating mandrel extrudes the tube inside wall to form the micro-grooves/fins continuously. By experiments of spinning micro-groove fin-inside tubes, this paper analyzes the influences of each process parameter on the formation quality, and optimizes each parameter. The experimental results show that the dynamic pressure can significantly improve the stability of spinning and the quality of finished surface; the minimum thickness of oil-film is decided by the spinning speed and the oil viscosity directly. In the case of full oil dynamic lubrication, there is no obvious scrape on tube surfaces. The main factors affecting the groove depth and the surface roughness are the ratio (α) of the wall thickness of the tube before drawing to the finished one, the material plasticity, the ratio (β) of drawing to spinning, the spinning speed (n), and lubricating state, etc. The axial drawing force mainly depends on the friction between the floating mandrel and the tube internal wall, the friction between the reducing mold and the outer surface, and plastic deformation resistance in the reducing mold area and spinning area as well.     

Isothermal and thermomechanical finite-element analysis of the tube drawing process using a fixed tapered plug

Quality is a very important feature in the manufacturing of products such as tube. Nonhomogeneous deformation, common to most metalforming operations, leaves the product in a cold worked state, resulting in a pattern of residual stresses. Depending on the nature and magnitude of residual stresses, they may be detrimental or beneficial to the strength and reliability of the product. To evaluate the residual stresses in the product, a complete stress analysis of the workpiece throughout the deformation history is required. In this study, a large deformation, nonlinear, elastic-plastic finite-element code was used to investigate the effect of friction, drawing speed, degree of plastic work (reduction in area), and the die/plug geometry on the extent of temperature increase, induced residual stresses, and the required drawing load in the drawing of oxygen-free high-conductivity (OFHC) copper tube using a fixed, tapered plug. Complete simulations of the tube drawing process were conducted by tracing its deformation history from the point at which it entered the die area until it exited the die. The resulting thermal effects were then used to determine the required drawing loads and induced residual stress distributions throughout the tube wall thickness. Similar simulations were conducted without taking into account the thermal effects. Equivalent plastic strain, equivalent stress, longitudinal stress, and circumferential residual stresses are presented and compared for both the isothermal and the thermally coupled analysis.     

飞秒激光制备梯度润湿性单晶硅表面∗

针对化学气相沉积、自组装技术等表面制备方法存在化学污染、表面结合强度低等问题,运用飞秒激光在单晶硅表面加工正方形微凹坑阵列制备梯度润湿性表面,使用白光干涉仪、扫描电子显微镜、能谱仪和接触角测量仪分别测量单晶硅表面粗糙度、微观形貌、化学成分及接触角。 通过改变激光能量密度制备不同梯度润湿性表面,研究不同激光能量密度下液滴在梯度润湿性表面上的铺展规律。 结果表明:随激光能量密度增大,表面粗糙度参数算术平均高度、均方根斜率和界面扩展面积比整体呈增大趋势,表面接触角整体呈减小趋势。 由于激光能量密度增大导致的单晶硅表面平行微凹槽、重凝层及不规则微纳结构使均方根斜率、界面扩展面积比及表面接触角出现波动。 液滴在梯度润湿性表面定向铺展分为加速与减速两个阶段,减速阶段速度伴随明显波动现象,小体积液滴的铺展速度更快。 实现了飞秒激光高精度、非接触、过程可控的梯度润湿性表面制备,结果可为制备单晶硅微流控器件提供理论参考。     

Oxidation behaviour of Fe‐Cr‐Al alloys during resistance and furnace heating

The behaviour of thin Fe‐Cr‐Al heating element strips was investigated with respect to the oxidation limited life times and geometrical changes during resistance and furnace heating. For this purpose, isothermal and cyclic oxidation tests varying in their total exposure time and cycle duration were performed in the temperature range 1050–1200 °C. Specimens subjected to rapid cyclic, resistance heating revealed shorter life times than calculated for specimens subjected to isothermal exposure. The life times were found to increase with increasing cycle duration and hence decreasing number of cycles for a given time at temperature. This life time decrease is related to an “hour glass” waviness of the specimens, which develops during prolonged thermal cycling. The development of this plastic deformation also occurred during furnace heated, thermal cycling tests. A two‐step mechanism is introduced combining an oxidation kinetics related time to the onset of significant waviness with an enhancement of this waviness as a result of a ratcheting effect. The latter seems to strongly depend on the number of cycles and on the plastic deformation generated during each cycle rather than on the total time at temperature. The development of an “hour glass” waviness leads to an enhanced aluminium depletion due to an increase of the specimen surface area. Additional deformation phenomena like “hot tube” or “corkscrew” behaviour occur during the resistance heating tests. These are related to a temperature gradient that develops over the specimen width due to the poor aspect ratio of the specimens.