Tribological behaviors between commercial pure titanium sheet and tools in warm forming

The tribological conditions between tools and sheet are the major factors affecting the product quality,forming limits and service life of tools in thin-walled titanium components warm forming.Using the orthogonal design based twist compression test in the temperature range of 25-300 °C,the significant factors affecting the coefficient of friction（Co F） and the influencing rules in CP-3 titanium sheet warm forming are clarified and discussed by changing tribological conditions such as tool material,lubrication,temperature and normal pressure.The results show that the significant factors affecting the Co F are lubrication,surface roughness,tool material,sliding velocity,normal pressure and temperature;compared with unlubricated condition,the graphite and Mo S2 greatly improve the friction condition and the maximum reduction of the Co F is 0.318;the Co Fs of Cr12 Mo V/CP-3 and QAl10-3-1.5/CP-3 tribo-pairs show a similar tendency：the Co Fs increase with increasing surface roughness and sliding velocity,and increase firstly then decrease with increasing normal pressure and temperature.

Warm forming behavior of high strength aluminum alloy AA7075

The formability of aluminum alloy AA7075 at elevated temperature was investigated through experiment. Stress-strain relationship at different temperatures and forming speeds were investigated through tensile testing. Deep drawing and stretch formability were also tested through limiting drawing ratio （LDR） and limiting dome height （LDH） tests. Finally, post forming mechanical property testing was conducted to investigate the effects of exposure to warm forming temperatures on the mechanical properties. Results show that deep drawing and stretch formability of AA7075 can be significantly improved when the blank is heated to 140-220 °C. At temperature over 260 °C, formability and post forming mechanical properties begin to decrease due to the effect of the heating and forming processes on the material＇s temper.

Numerical Simulation of Warm Forming Behavior of High Strength Aluminum Alloy 7075

Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry.However,material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming.Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075),constitutive equations with strain rate sensitivity at 140,180 and 220 ℃ are developed.Anisotropic yield criterion Barlat 89 is used in the simulation.Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140,180 and 220℃are performed.Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results.Punch force and displacement predicted from simulation are compared with the experimental data.Simulation results agree with experimental results,so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.

Prediction of fracture limits of Ni-Cr based alloy under warm forming condition using ductile damage models and numerical method

The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit diagram(FFLD)was transformed into a stress-based(σ-FFLD)and effective plastic strain(EPS)vs triaxiality(η)plot to remove the excess dependency of fracture limits over the strains.For the prediction of fracture limits,seven different damage models were calibrated.The Oh model displayed the best ability to predict the fracture locus with the least absolute error.Though the experimentally obtained fracture limits have only been used for the numerical analysis,none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality(0.33<η<0.66).The deep drawing process window helped to determine wrinkling,safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions.Further,the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition.All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.

Measurement of friction coefficient in aluminum sheet warm forming

Aluminum alloy sheets are used more and more to manufacture auto panels. Because the friction behavior is very complicated, it is necessary to study the friction during the aluminum sheet warm forming process. The author has designed a new probe sensor based on an online tribotest method which directly measures friction coefficient in the forming process. Experiments of cup drawing have been conducted and the friction coefficients under different forming conditions have been measured. The results indicate that the forming parameters, such as forming temperature, blankholding force and lubrication status have great effect upon the friction coefficient.

Parametric analysis of warm forming of aluminum blanks with FEA and DOE

The effect of temperature distribution on warm forming performance was investigated for 5083-O (Al-Mg) sheet metal blanks. Combined isothermal/non-isothermal FEA with design of experiments tools were used to predict appropriate warm forming temperature conditions for deep drawing and two-dimensional stamping cases. In the investigated temperature range of 25?250 ℃, the formability of Al-5083 alloy is found to be greatly dependent on the temperature distribution of the die and punch. To achieve increased degrees of forming, different temperature levels should be assigned to the corner and body of the die and punch. And the optimal temperature distributions for warm deep drawing and warm two-dimensional stamping are not identical.

Theoretical prediction of forming limit diagram of AZ31 magnesium alloy sheet at warm temperatures

A theoretical prediction on forming limit diagram（FLD） of AZ31 magnesium alloy sheet was developed at warm temperatures based on the M-K theory. Two different yield criteria of von Mises and Hill＇48 were applied in this model. Mechanical properties of AZ31 magnesium alloy used in the prediction were obtained by uniaxial tensile tests and the Fields-Backofen equation was incorporated in the analysis. In addition, experimental FLDs of AZ31 were acquired by conducting rigid die swell test at different temperatures to verify the prediction. It is demonstrated from a comparison between the predicted and the experimental FLDs at 473 K and 523 K that the predicted results are influenced by the type of yield criterion used in the calculation, especially at lower temperatures. Furthermore, a better agreement between the predicted results and experimental data for AZ31 magnesium alloy sheet at warm temperatures was obtained when Hill＇48 yield criterion was applied.

Tribological evaluation of surface modified H13 tool steel in warm forming of Ti–6Al–4V titanium alloy sheet

The H13 hot-working tool steel is widely used as die material in the warm forming of Ti–6Al–4V titanium alloy sheet. However, under the heating condition, severe friction and lubricating conditions between the H13 tools and Ti–6Al–4V titanium alloy sheet would cause difficulty in guaranteeing forming quality. Surface modification may be used to control the level of friction force, reduce the friction wear and extend the service life of dies. In this paper, four surface modification methods（chromium plating, TiAlN coating, surface polishing and nitriding treatment）were applied to the H13 surfaces. Taking the coefficient of friction（CoF） and the wear degree as evaluation indicators, the high-temperature tribological behavior of the surface modified H13 steel was experimentally investigated under different tribological conditions. The results of this study indicate that the tribological properties of the TiAlN coating under dry friction condition are better than the others for a wide range of temperature（from room temperature to 500 C）, while there is little difference of tribological properties between different surface modifications under graphite lubricated condition, and the variation law of CoF with temperature under graphite lubricated is opposite to that under the dry friction.

Influence of viscous medium temperature distribution on sheet fracture in viscous pressure forming at warm temperature

Viscous pressure forming(VPF) of aluminum alloy AA3003 sheet metal at warm temperature was investigated by using coupled thermo-elastoplastic-viscoplastic finite element method. The influence of viscous medium temperature distribution on sheet fracture location was studied and the distributions of fracture factor at different temperatures were obtained by using ductile fracture criterion. The results show that the failure of sheet metal varies with increasing initial temperature of viscous medium. When the initial temperature of viscous medium is near that of sheet metal,the failure location occurs at dome center,and when the initial temperature of viscous medium is too low,however,the failure location occurs at die corner. The occurrence of fracture can be postponed and even prevented through controlling the temperature distribution in viscous medium.

Analysis and Optimization on Factors Affecting Forming Quality of Half Axle Gears Warm Precision Forging

Half axle gears is produced by precision forging popularly because of the advantages in minimum machining allowances, lower material consumption and good service properties. But the forming quality of precision forging is difficult to control. Many simulations and analysis of precision forging process were taken by previous researchers. But no concrete method is proposed to evaluate and optimize the forming quality of half axel gears. The primary purpose of this work is improving the forming quality of half axel gears by analyzing and optimizing the affected factors of forming quality. The enclosed-die warm forging process of half axle gears was developed, and a new type of die-set used on double action hydraulic press was brought forward. The main influential factors of precision forming quality were analyzed after the forming process had been simulated by using finite element method（FEM）. These factors include die structure, web thickness and web position. A method used to evaluate the forming quality was established, which investigated the maximal forming load, the metal filling rate and the material damage factor. The FEM simulations of half axle gears precision forging were evaluated by this method. The results show that the best forming quality can be achieved when the punches were added with bosses, the web located at the middle plant of the gear, and the web thickness was 30 percent of the inner hole diameter. Verification experiments taking the above optimized parameters were performed on a 7.8 MN double action hydraulic press. The trial products were formed well. And their geometric precision meets the demand. The verification result shows that the optimization of the influential factors, according to the simulations and the evaluation method, can improve the forming quality. The new structure of precision forging die-set and the new evaluation method guarantee a high forming quality ofhalfaxel gears.

Creating Technology and Numerical Analysis of Warm Plastic Forming for Non-symmetrical Axostyle

A creating technology of the part forming was discussed and finite volume method(FVM)was used to simulate the forming process of the non-symmetrical axostyle spring core-bar.The results show that the no-even radial flange on the top part of the eccentric peachy surface can remarkably block the metal flow and the eccentric peachy can be filled contentedly.Increasing the radius of punch near the inner pocket,the head bulge also can be filled contentedly.The temperature distribution in the part and the forming force,which helps to decide the forming temperature and to select the equipment,was also analyzed.The comparison between the simulation and the experiment result shows that they are accordant.

基于“阳化气,阴成形”从温阳法论治肺部结节

《素问·阴阳应象大论篇》中记载的“阳化气,阴成形”高度概括了人体脏腑组织的生命活动,阴阳失衡是导致疾病发生的关键。本文通过分析“阳化气,阴成形”理论,发现肺部结节发生和发展的核心机制是“阳化气不足,阴成形太过”。结节乃有形之体,是机体阳气亏虚,精血津液运行障碍,化为痰饮瘀毒,敛聚局部而生;结节本质乃阳虚阴结,本虚标实,本虚即脾肾阳虚,标实即痰饮、瘀血、浊毒。中医学强调治病求本,故基于“阳化气,阴成形”理论,以温阳化气为基本治则,探讨温阳法在肺部结节治疗中的应用,分别从温阳补肾、温阳健脾、温阳化痰、温阳活血、温阳解毒和温阳散结等角度辨证施治,以防“阴成形太过”,使“阳化气”之功能正常发挥,则机体阴阳平衡,百病不生。

何以赏冬?——南京瞻园西假山明代暖亭形制研究

南京瞻园西假山为明代遗构,据传假山山洞内有一供暖火房,与西假山顶原有铜亭配套。但查诸历代史籍图册,均无暖亭图像资料与之印证。现存西假山顶部扇亭为20世纪50—60年代刘敦桢先生主持瞻园修缮时重建,位置与原山顶亭址相当。笔者借主持瞻园西假山修缮之机,对几近塌毁的建筑遗址开展充分探查与测绘研究,发现并判断现瞻园西假山内坍塌淤塞的砖构设施应是明万历时期所建之供暖火房,以烟道供暖、地面辐射、铜柱散热方式为山顶暖亭提供热源。这一供暖方式体现了明代江南王公园林受北方取暖文化影响,在重要观景建筑营造上采取极其奢华建造方式的园林建筑案例,并且也因靡费过度在清初即被弃用。暖亭体系虽未能成为江南地区之后园林建筑的一种范式,但其性质的特殊性及其小冰河时期在明初江南的出现仍给人们带来诸多启发与思考。以现状勘察为基础,结合历史图像、文献资料,对瞻园西假山暖亭一组建筑形制进行复原研究,以期充分揭示这组独特的园林建筑遗产特色,并对其修缮保护提供依据与参考。

在线接触加热的高强钢板自由温折弯成形工艺研究

针对普通热成形工艺难以用于高强钢折弯等常见局部成形的现状,以NM450TP耐磨高强钢为研究对象,利用实验和数值模拟研究了基于局部在线接触加热的自由温折弯成形新方法,探讨了NM450TP材料的温成形特性、接触加热热传导行为以及温折弯变形等问题。结果表明,通过对坯料折弯变形区的局部、精确接触加热,NM450TP板自由温折弯性能得到了大幅提升,有效避免了自由温折弯的开裂。该方法具有模具结构简单、易于实现和加热效率高等优点,可为难变形材料的局部自由折弯温成形提供借鉴。

基于损伤耦合粘塑性模型的AZ31B镁合金温变形行为研究

为了准确描述AZ31B镁合金温变形中材料硬化、损伤和断裂行为,建立了基于位错密度的粘塑性模型与GTN损伤模型耦合的本构模型。在不同温度和应变率下对试样进行温拉伸试验,获得合金温变形下的应力-应变曲线。基于材料高温变形机理,以位错密度为内变量,建立粘塑性模型来描述材料的硬化行为,并采用智能算法来识别模型的材料参数。为描述材料温变形过程中的损伤演变,将GTN损伤模型与已建立的粘塑性模型进行耦合,建立温拉伸仿真有限元模型,利用Kriging代理模型结合智能算法反求损伤模型参数。最后,利用已建立的损伤耦合粘塑性模型分析温拉伸过程中的损伤演化和预测温胀形过程的破裂行为,并与试验结果进行对比。结果表明,该本构模型可以准确地预测AZ31B温变形过程中的损伤和断裂。

基于翻孔试验的AZ31B镁合金薄板温成形特点研究

以1.6 mm厚的AZ31B镁合金板料为研究对象,利用Deform-3D软件探究了温成形翻孔工艺的成形特点,分析了成形温度、冲压速度和压边间隙对制件成形过程中等效应力、成形载荷及厚度变化的影响规律和机理,在此分析结果基础上提出了翻孔优化工艺,并通过对比优化工艺下仿真试验和物理试验中制件的变形情况,验证了模拟仿真的正确性。结果表明,扩孔阶段制件凸缘区材料应力波动幅度最大,达到141.29 MPa,减薄和增厚最严重的区域分别是伸长区底部和凸缘区,分别达到20.00%和3.13%,温度与材料的等效应力峰值及应力分布不均匀性呈负相关,较低的冲压速度可以给材料变形提供充足的缓冲时间,有利于降低等效应力峰值和增厚率,压边间隙主要影响材料厚度变化情况而对材料主变形区等效应力的影响较小,仿真试验与物理试验制件的终态材料厚度分布趋势一致,凸模峰值载荷误差为0.94 kN,仿真试验结果与物理试验结果具有良好的一致性。

先进高强双相钢DP780温度相关应力⁃应变关系

为了研究先进高强度双相钢DP780的温热成形力学行为,通过不同温度(300℃、400℃、500℃、600℃)及不同应变率(10-4~10-3 s-1)下的单向温拉伸试验获得了先进高强度双相钢DP780在相应条件下的基本力学性能指标和应力⁃应变曲线,并对试验结果进行了分析;为描述温热成形DP780板料应力⁃应变曲线,求解、修正了Grosman本构模型的相关参数;以单向拉伸试样为例,基于Fortran语言通过编写Abaqus⁃Vumat子程序进行了数值模拟验证。结果表明,所用Grosman模型预测值与试验数值拟合较好,验证了所求模型的有效性。

基于“阳化气,阴成形”理论浅谈中西医结合治疗肺癌机制

肺癌是临床上最常见的恶性肿瘤之一,其发病率逐年上升。自古代起,黄帝内经及历代医家就对肺癌提出了有效的治疗法则。他们认为“阳化气”不足,而“阴成形”太过,是导致肺癌发病的重要原因之一。文章旨在对“阳化气,阴成形”理论在中西医结合治疗肺癌方面的研究进行综述,以期为肺癌的治疗和研究提供新的思路。

基于数值模拟的20MoCr4钢温成形特征研究

20MoCr4钢是一种优良齿轮、齿圈等汽车关键零部件用到强度低合金钢。研究获得其材料性能参数是设计汽车零部件、制定成形工艺路线的前提条件。基于金属材料性能模拟计算软件JMatPro,获得了宽温度范围(25~1200℃)内详细全面的20MoCr4钢材料力学性能和热物理性能,结果表明:在500~750℃的温度变化范围内应力会出现较为明显跳跃式变化,在700~850℃之间热导率和比热容出现较为明显跳跃式变化,580~780℃为该材料较合适的温成形温度区间。相关材料性能数据和研究结果为20MoCr4钢滚轧等温成形过程热力耦合有限元分析提供基础。

预时效-温成形工艺参数对7075铝合金组织与性能的影响

对7075-T6铝合金进行了不同预时效温度(85,100,120℃)、预时效时间(0~32 h)、成形温度(150,200,250,300℃)的预时效-温成形处理,研究了工艺参数对合金组织和性能的影响,确定了最佳工艺参数。结果表明:随着预时效时间延长,7075铝合金晶粒尺寸无明显变化,析出相数量增加,硬度和强度均先增大后减小;相比预时效温度为100,120℃时,预时效温度为85℃时析出相的数量较少,尺寸较小,硬度和强度较大,断后伸长率较小;随着温成形温度升高,硬度和强度均减小;最佳预时效-温成形工艺参数为预时效温度85℃、预时效时间24 h、温成形温度150℃,此时合金综合性能最佳,抗拉强度和断后伸长率分别为T6态的95%和163%;成形后经180℃×30 min烘烤处理可提升其强度、降低塑性。