半固态触变成形坯料感应加热的数值模拟

半固态触变成形技术以其降低宏观偏析、减少多孔性、成形力小和近终成形等优点受到广泛关注.在触变成形之前,使坯料具有均匀的固-液相分布和球状晶粒是很重要的,这就要求加热快而迅速.为满足这一要求,目前普遍采用电磁感应加热.文中对感应加热进行了有限元理论分析,采用商用有限元软件ANASYS对半固态触变成形坯料感应加热进行了数值模拟,模拟了频率、加热时间、线圈电流强度系数、坯料尺寸半径、线圈尺寸大小等参数对坯料温度的影响.     

平纹编织碳纤维增强树脂复合材料离散电导率建模方法

编织碳纤维增强树脂复合材料(CFRP)的电阻抗分布具有各向异性、异质性、几何结构复杂等特点。建立电阻抗分布模型是利用电磁涡流无损检测技术获取编织CFRP缺陷及疲劳损伤信息的关键关节。基于电阻抗张量建模理论,采用多层编织结构CFRP二维平面的分块均化电学特性表征方法,建立编织结构CFRP的简化电阻抗分布模型,从而实现编织结构CFRP电磁特性的精确、快速有限元分析。在有限元仿真基础上,通过设计双空气旋转线圈电磁传感器对平纹编织CFRP进行电磁无损检测,选用阻抗的极坐标图描述被测材料沿不同方向的阻抗变化趋势,通过实验验证有限元建模的正确性。最后利用所提出的建模方法模拟了双空气旋转线圈传感器对平纹编织CFRP的结构缺陷及循环载荷疲劳的检测效果。      

高频电磁感应加热成形热源模型建立及数值模拟研究

基于高频感应加热涡流分布及透入深度的特点,为模拟钢板高频电磁感应加热成形的温度场,提高数值模拟计算精度,结合电磁感应加热头的形状尺寸,建立了一种用于模拟电磁感应加热成形的热源模型。模型建立过程中,对其能量分布给出了明确的热流表达式,利用有限元方法分析了电磁感应加热成形的热源模型的有效性。结果表明,利用该热源模型分析的温度场结果与试验结果吻合良好。高频电磁感应加热的峰值温度位于感应加热头作用区域,随着输出功率或感应加热时间的增加,峰值温度增加。     

真空系统内一种加热器温度场分布有限元分析

为了提高真空系统内一种加热器的温度场分布均匀性,利用有限元分析方法,借助ANSYS Workbench仿真温度场,通过对单圈钨丝结构外加圆倒角釜结构上的改进,确定了获取均匀的温度场的方法。在电阻丝加热功率为45 W,对直径50.8 mm的蓝宝石晶元加热温度均达到200℃的情况下,分别对两种加热器进行了仿真分析。结果表明:单圈钨丝结构外加圆倒角釜的加热器对晶元加热的温度场均匀性较差,温度差异为41.13℃。多圈钨丝螺旋结构外加抛物面釜对晶元加热的温度场均匀性较好,温度差异仅为2.30℃,可作为真空系统内一种理想的高均匀性加热器结构。对GaN阴极均匀性的检测表明:通过改进加热器结构,使得制作的GaN光阴极发射不均匀性由原来的28%改善为小于10%。研究成果为真空系统内部加热器的优化改进提供技术支撑。     

热金属气压成型电磁感应加热有限元模拟

应用感应加热理论,利用麦克斯韦方程组和温度微分方程,建立了电磁场与温度场耦合的有限元数学模型,使用有限元分析软件ANSYS对热金属气压成型工艺中的电磁感应加热过程进行了模拟与分析。模拟结果表明:随着电磁感应线圈电流频率的提高,在相等的加热时间内,金属钢管的升温速度不断增加,且最终达到的温度也进一步升高。随着电磁感应线圈电流密度的增加,在相等的加热时间内、相同的电磁感应线圈电流频率下,金属钢管的升温速度不断增加,加热效率得到有效提高,且最终达到的温度也逐步升高。随着金属钢管与线圈的间隔增加,金属钢管内、外表面的温度均逐渐降低;外表面温度的降低趋势越来越平缓,而内表面温度的降低趋势则不断加剧。     

感应耦合等离子体的功率耦合效率的理论分析与计算

基于变压器模型,本文对感应耦合等离子体中线圈产生的空间电场分布、等离子体电阻、电感及功率耦合效率等进行了数值计算.在计算过程中,考虑了低气压等离子体无碰撞随机加热机制的作用.结果表明,同心线圈的感应电场呈中空分布,径向和轴向均呈现很大的不均匀性;功率耦合效率随线圈品质因数Q及耦合系数K的增大而增大.功率耦合效率的理论分析和计算为线圈优化设计提供了依据.     

真空共晶焊接设备温度场设计及仿真优化

共晶焊接设备的温度均匀性直接决定焊接电子元器件的质量,因此设备的温度场设计成为共晶焊接设备的关键。本文首先设计了由加热元件(红外灯管)、热板、反射板和隔热板组成的加热组件;其次应用试验测试和有限元仿真相结合的方法,分别讨论了两组加热元件的排布方式对于热场温度均匀性的影响;最后采用真空共晶焊接设备验证了温度场设计的可行性。实验结果表明,采用加热元件变间距排布的方式,其温度场的均匀性能达到±5℃的要求,焊接电子元件的平均孔洞率和剪切强度分别达到了1.78%和9.8kg,符合了GJB 548B-2005对于电子元器件焊接质量的要求。     

CFRP筋在RPC中锚固性能的理论分析及试验研究

静载试验详细研究了碳纤维增强塑料CFRP筋在活性粉末混凝土RPC的锚固性能。试验结果表明:对于抗拉强度不大于3000MPa的表面压纹CFRP筋在抗压强度130MPa的RPC中的临界锚固长度为20倍CFRP筋直径;多根压纹CFRP筋的合理筋间距为1倍CFRP筋直径。平均粘结强度及其对应滑移量的公式具有较好的适用性。平均粘结应力与滑移之间的预测曲线与试验曲线吻合较好,验证了提出的粘结滑移本构关系。理论推导了锚固变量沿锚固长度分布的表达式,算例验证了有效性。分析表明:距离自由端约为0.6倍锚固长度位置处的粘结应力等于平均粘结应力。对于压纹CFRP筋,当锚长≤12.5倍筋材直径时,粘结应力沿埋长分布较为均匀,其不均匀性系数在1.02―1.05之间;当埋长>12.5倍且≤20倍筋材直径时,粘结应力沿埋长分布较为不均匀,其不均匀性系数在1.05―1.14之间。     

复合材料固化工艺的直热模具温度场均匀性分析

针对复合材料固化成型工艺的直热模具温度场均匀性进行了研究。建立模具温度场和复合材料固化反应温度场的耦合传热学模型,并对该模型进行有限元建模仿真分析。针对影响模具表面温度均匀性的主要因素,即电加热管的间距和功率,设计正交试验优化,优化后模具表面最大温差为3.5℃,达到行业标准。此外,对影响温度场均匀性的其他因素,即加热管与模具的接触热阻、复合材料层合板厚度进行了探讨,接触热阻的存在使得模具表面最大温差达到7.24℃,模具加热到指定温度多用时800 s,降低了效率。研究层合板对模具温度均匀性的影响时发现未加入复合材料时模具表面最大温差为4.44℃,加入层合板耦合后最大温差为3.5℃;厚度为毫米级时,层合板对直热模具表面温度均匀性影响不大。      

电磁流量计矩形与鞍状线圈磁场的数值仿真

讨论了电磁流量计矩形和鞍状线圈所产生磁感应强度的分布情况。运用毕奥-萨伐尔定律和叠加原理,通过数值仿真得到励磁线圈在测量管道内电极横截面上的磁场分布情况。提出磁感应强度的方向平行程度和大小均匀程度2个指标,并用其来判别感应磁场分布的均匀程度。依据以上2个指标,分别对不同尺寸的矩形和鞍状励磁线圈所产生的感应磁场进行计算分析和优化。     

衰荡光腔温度控制研究

研制出一套光腔衰荡光谱中的温度控制系统。首先,设计了内壁带有硅胶加热片的控温箱体,将光腔置于箱体中并模拟内部温度分布;然后,对箱体进行有限元分析及参数化扫描,得到最优化情况下加热片的分布及功率大小,保证光腔通光部分温度的均匀性;根据仿真结果完成实际控温箱体和加热片的加工,以比例积分微分（PID）控制算法为核心,设计包括温度采样模块、控制模块、驱动电路模块等在内的硬件电路系统,开发相应的控制算法,精密控制光腔内部的温度变化,实现衰荡光腔通光部分8 h内温度变化标准差不超过0.01 ℃。     

Numerical simulation and experimental investigation on the induction hardening of a ball screw

To improve the distribution of the hardened layer and avoid potential defects, the effects of induction hardening parameters on the hardened layer were researched using the finite element method (FEM). A FEM model of single coil induction hardening was built, and temperature curves on the surface region of a ball screw were attained by numerical simulation. The hardenability and phase transformation of 55CrMo steel were researched by experiment. The simulation and experimental results show that the temperatures Ac1 and Ac3 rise with increasing heating rate. Non-uniformity of temperature at the groove region can lead to non-uniformity of austenitization and hardness. High temperature can result in cracks, coarse grain size and overheating defects at the groove tip. Martensite produced during cooling transforms into tempered martensite due to the residual heat, and the remaining austenite transforms into martensite at a low cooling rate. A 5010-type ball screw cannot attain a hardened layer with the thickness of 2.5 mm at the groove bottom without defects at the groove tip by single coil induction hardening. Multiple induction coils with a certain gap would be helpful to improve the uniformity of temperature and hardness.     

能量天平永磁体系统的温度场分析

提出基于COMSOL有限元仿真的方法对永磁体系统的温度场进行分析。通过分析,得到永磁体在不同工作模式下的温度上升曲线。仿真结果表明永磁体磁盘在两种工作模式下存在10^-4 K量级的温度差异,由于钐钴永磁体磁盘存在-3×10^-4 K^-1的温度系数,温度对磁链差的测量影响在10^-8量级。为改善能量天平永磁体系统中悬挂线圈的发热问题,提出调整悬挂线圈电流,增大辐射面辐射系数,改变天平支撑结构3种方案,以改善温度波动引入的普朗克常数测量不确定度。     

Thermal analysis of magnetic shields for induction heating

For the design of magnetic shields for induction heating, it is useful to analyse not only the magnetic field reduction but also the temperature behaviour of the shield. The latter is heated by its electromagnetic losses and by thermal radiation from the workpiece. A coupled thermal-electromagnetic axisymmetric finite element model is used to study the temperature of a shield for an axisymmetric induction heater, highlighting the effect of the radius, length, thickness and material of the shield on its temperature and magnetic shielding factor. Also the effect of frequency and workpiece dimensions is investigated. The model is validated by measuring magnetic induction, induced currents in the shield and temperature of the shield on the experimental setup. The temperature is unacceptably high for shields close to the excitation coil, especially if the shield length is lower than the workpiece length. Although the study is carried out for one specific induction heater geometry, the paper indicates the effect of parameters such as geometry, material and frequency on shield temperature so that the results are also useful for other induction heating configurations.     

Heating/cooling channels design for an automotive interior part and its evaluation in rapid heat cycle molding

Rapid heat cycle molding (RHCM) is a recently developed innovative injection molding technology. Rapid heating and cooling of the injection mold is the most crucial technique in RHCM because it not only has a significant effect on part quality but also has direct influence on productivity and cost-efficiency. Accordingly, Heating and cooling system design plays a very important role in RHCM mold design. This study focuses on the heating/cooling system design for a three-dimensional complex-shaped automotive interior part. Heat transfer simulation based on finite element analysis (FEA) was conducted to evaluate the thermal response of the injection mold and thereby improve heating/cooling channels design. Baffles were introduced for heating/cooling channels to improve heating/cooling efficiency and uniformity of the mold. A series of thermal response experiments based on full factorial experimental design were conducted to verify the effectiveness of the improved heating/cooling channels design with baffles. A mathematical model was developed by regression analysis to predict the thermal response of the injection mold. The effects of the cavity surface temperature on weld mark and surface gloss of the part were investigated by experiments. The results show that the developed baffle-based heating/cooling channels can greatly improve thermal response efficiency and uniformity of the mold. The developed mathematical model supplies an efficient approach for precise predication of mold thermal response. As the cavity surface temperature raises to a high enough level, automotive interior parts with high gloss and non-weld mark surface can be obtained.     

Analysis of thermal cycling efficiency and optimal design of heating/cooling systems for rapid heat cycle injection molding process

Rapid heat cycle molding (RHCM) is a molding process that the mold cavity is rapidly heated to a high temperature before plastic melt injection, and then cooled quickly once the cavity is completely filled. Heating/cooling efficiency and temperature uniformity of the RHCM system are two key technical parameters to ensure a high productivity and high-quality products. In this study, a numerical model to analyze the heat transfer in heating and cooling phases of RHCM was built. The effect of heating/cooling medium, layout and structure of the heating/cooling channels, mold structure, etc., on heating/cooling efficiency and temperature uniformity was studied and discussed by analyzing the thermal responses of the molding system in RHCM process. Based on the simulation results, the optimization design of the RHCM mold with hot-fluid heating was performed. Then, a new RHCM mold structure with a floating mold cavity was proposed to improve the heating/cooling efficiency and temperature uniformity. The effectiveness of this new mold structure was also verified by numerical experiments. At last, a RHCM production line with steam heating and water cooling was constructed for a thin-wall plastic part. In testing production, the molding systems can be heated and cooled rapidly with a molding cycle time of about 72 s. The production results show that the aesthetics of the molded parts was greatly enhanced and the weld mark on the plastic part’s surface was completely eliminated.     

用于心磁传感器测试系统的三轴向亥姆赫兹线圈的设计与仿真

心磁检测对于心脏相关疾病的诊断具有独特优势，在用于测量心脏磁场的传感器(下称心磁传感器）的研制过程中，需要在模拟心磁的磁场环境下进行测试工作。基于此，设计了一个用于心磁传感器测试系统的亥姆赫兹线圈，它可以产生磁感应强度为pT级的动态磁场，模拟心磁环境，以满足心磁传感器测试的需求。根据亥姆赫兹线圈的磁场产生原理，使用磁屏蔽筒对环境磁场进行屏蔽，通过计算确定了线圈尺寸、线圈匝数、导线长度及导线横截面直径等参数。使用COMSOL Multiphysics仿真软件对亥姆赫兹线圈产生的静态磁场的分布均匀性以及通入线圈电流变化时磁场的动态特性进行仿真分析。仿真结果表明，所设计的亥姆赫兹线圈满足设计要求，能够产生磁场强度为100 pT左右、均匀度小于5%、波形实时性好的类心脏磁场波形，为心磁传感器的测试提供了良好的测试环境。所设计的亥姆赫兹线圈能够用于心磁传感器的测试工作，为心磁传感器的实际应用奠定了基础。