新型塑料颗粒3D打印机技术方案的研究

针对如何使用工程塑料颗粒(PLA等)来完成熔融快速成型进行了研究,设计了一套小型螺杆挤出机构,与Delta并联结构的FDM打印机结合,实现快速成型的目的;应用STAR-CCM+软件进行仿真研究,数值分析主要集中在进料端塑料颗粒的DEM(离散元模型)仿真,和出料端的CFD(计算流体动力学)分析;进料端的研究目的是解决颗粒进料顺畅度问题,分析不同漏斗对进料效率影响,以确保设计合理的进料漏斗;考虑螺杆挤出的压力波动因素,及加热温度对融料的流动影响因素,出料端的温度控制影响到打印效果。通过对挤出机构关键参数的设计,结合验证机的实验;给出新型塑料颗粒3D打印机的初步方案。     

基于FDM的低熔点金属牙模制备方法研究

对熔融沉积成形过程中丝材的受力情况进行了分析,分别建立了丝材进给力和挤出阻力数学模型以及有温度场影响情况下的力学模型;通过ANSYS Workbench软件对喷头温度场分布情况和挤出阻力进行有限元分析与计算,并对一定打印温度下的进给力和挤出阻力进行计算比较,得出在230℃~240℃范围内满足打印条件的结论。通过熔融沉积成型技术以低熔点金属材料制备具有一定精度的牙模,通过不同打印温度和不同分层厚度的制备实验发现:在240℃时初始层成型质量较好,同时分层厚度越小得到的牙模越精细。考虑到成型时间和成型质量,最终选择打印温度240℃、分层厚度0.2mm作为牙模制备的参数设置。     

色母粒影响聚乳酸成型质量的实验研究

针对不同添加剂(色母粒等)的聚乳酸(PLA)材料,在熔融沉积式(FDM)打印机成型质量不同的问题上,对FDM打印机成型过程涉及的工艺参数进行归纳研究,提出了一种根据PLA添加剂(色母粒等)不同而进行调整FDM成型工艺参数的方法。基于材料力学的理论知识,建立了PLA材料成型过程的数学模型,选取了某厂家同批次的6种PLA材料,用正交试验方法验证了不同添加剂(色母粒等)的PLA材料对成型质量的影响。实验结果表明,添加剂色母粒对聚乳酸成型质量有较大影响,使用不同色母粒添加剂的聚乳酸时,必须适当调整成型工艺参数,以保证成型质量,并能够有效指导PLA材料在桌面版3D打印机的应用。     

PLA材料在熔融沉积过程中的温度场分析

采用有限元的方法进行3D打印过程的模拟,建立了熔融沉积成型(FDM)有限元仿真模型,对PLA材料在FDM成型过程中进行了温度场分析,得到了在不同方向、不同时间的温度变化曲线。温度的变化对成型件的精度有重要影响。     

振动诱导聚合物塑化过程中熔体温度分布的预测

在振动力场诱导聚合物塑化成型作用下,建立了聚合物熔融挤出过程中的熔体温度分布模型,研究了模头温度、振动力场的振幅、频率等工艺参数对挤出过程中熔体温度的影响。提出了基于多项式和高斯RBF核函数变换的两种非线性岭回归模型(PT-RR和GRBF-RR),并对具有非线性、非等温、强耦合特征的熔融过程熔体温度分布进行研究。该建模方法实现了多变量输入样本的高维特征空间非线性映射与重构,充分挖掘了多影响因素之间的耦合信息。仿真实验结果表明了PT-RR和GRBF-RR模型的有效性,其回归预测值与实验测量值之间的相关系数均值分别为0.9940和1。由于GRBF-RR模型取得了满意的模型精度,本文基于对GRBF-RR模型的数值模拟分析了各影响因素对熔体温度分布的交叉耦合影响,表征了聚合物熔融挤出成型过程中熔体温度分布的规律。该项研究可为提高精密挤出制品质量及优化配置各工艺参数提供决策依据。     

熔融沉积成型3D打印机混色装置的研究

当前基于熔融沉积成型的桌面级3D打印机的大部分打印头装置只能打印一种颜色的耗材,打印出来的物体颜色单一,为了解决这一问题,在分析了整个3D打印头装置的基础上,运用TRIZ理论对3D打印头进行了创新设计,设计出一种双进料单挤出的打印头装置,该打印头装置能将两种颜色的耗材融化混合,并从同一喷嘴挤出,实现混色打印。运用UG有限元模块对所设计机构进行了温度场的模拟分析,最终对装置进行了试验,验证了温度场分析的正确性,达到了混色要求,为3D打印机混色装置的进一步研究提供了理论依据。     

工艺参数对FDM成型方法圆筒制件的精度影响

熔融沉积快速成型(Fused Deposition Modeling,FDM)是基于热源融化丝状材料的3D打印技术,以圆筒制件为模型,使用FDM成型方法进行3D打印,以分层厚度、填充密度、填充速度、挤出头温度为影响因素,获得了不同工艺参数下的壁厚误差和表面粗糙度Ra值。     

含能材料3D打印机喷嘴参数对挤出速度的影响

在熔融沉积(FDM)成型机的基础上,设计了一种适用于含溶剂的含能材料挤出成型的气压式喷头。利用了正交实验原理及有限元软件ANSYS/FLOTRAN,探讨了喷头的关键尺寸对挤出速度的影响规律,得出了各因素对挤出速度的影响程度,并建立了挤出速度与流道关键尺寸之间的指数预测模型,研究结果表明,最主要的影响参数为喷嘴直径大小,其次为成型段长度,入口收缩角等因素影响较小。所得指数预测模型与CFD计算值结果误差在8%左右,即可根据指数预测模型,通过调节压力大小来获取较为精确的挤出速度。     

多点进料的宽幅片材机中间接管流道有限元模拟

针对宽幅片材挤出成型提出了多点进料的设计思想.首先对机头进行改型处理,尽量保证中间接管的入口流量一致,然后利用有限元模拟中间接管的流场,得出出口的流速和压力分布,进而探讨多点进料的可行性.     

义齿陶瓷浆料微流挤压成型头研究

挤出头内部结构直接影响陶瓷浆料微流挤压成型的最终效果,因此通过使用ANSYS软件对挤出头出口横截面的流速和流道内部压力场的分布情况进行了数值模拟,利用流体力学理论,对挤出过程的关键部件挤出头的流道形状进行了设计,并找出4种不同流道形状挤出头内部压力场和出口流速的分布规律,该研究为解决陶瓷浆料挤压成型工艺的难点问题提供了理论依据,具有重要的参考价值。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.