PEEK熔融沉积成形温度对零件拉伸性能的影响

作为一种高性能聚合物,聚醚醚酮(PEEK)具有耐高温、耐化学腐蚀、高强度等优点,但由于材料熔点高,采用传统制造方法难以实现复杂结构功能零件的低成本快速制造。针对该问题,利用高温型熔融沉积成形(FDM)设备开展了以PEEK为研究对象的FDM工艺实验研究。结果表明:通过合理控制打印机喷嘴温度、底板温度及成形室温度,可改善单层的线间搭接及层间的融合状态,从而使PEEK零件的最高拉伸强度达到77 MPa,接近传统注塑成形的力学性能指标,为难加工材料复杂结构成形过程中的控形与控性提供了新的解决方法。     

熔融沉积成型彩色打印技术研究

针对FDM的梯度渐变色打印,提出了一种对梯度渐变效果进行预测和评价的方法。利用Visual C++提供的MFC应用程序开发平台编写软件模拟两种颜色的梯度渐变,通过在软件上改变色彩细分量得到梯度渐变效果不同的图像,实现了对梯度渐变效果的预测。为了实现彩色打印,设计了一种彩色打印机。首先进行梯度渐变色打印实验,用软件分析在与模拟对应的色彩细分量下打印出的零件和模拟结果的梯度渐变效果,验证了模拟结果的正确性,实现了对梯度渐变效果的评价。然后进行多色打印实验,实现了彩色3D打印,为彩色3D打印技术的进一步发展提供了参考。     

FDM快速成形系统的控制系统研究

从FDM的快速成形的工艺原理出发，设计了新型FDM快速成形系统的硬件和软件，并对决定控制系统性能的硬件和软件进行了分析。     

熔融沉积成型彩色3D打印机的研究

当前基于FDM的3D打印机大部分只能使用一种颜色的耗材,因此打印件颜色单一。为了解决这一问题,在深入研究FDM 3D打印机工作原理的基础上,设计一套彩色3D打印机挤出装置,对普通切片软件进行了二次开发,编写了与挤出装置相匹配的彩色切片插件,并进行了样机的试制与调试。通过打印试验,验证了所设计的挤出装置及彩色切片插件达到了设计要求,实现了彩色打印,为彩色3D打印技术的进一步研究提供参考。     

融积成型技术在石膏型精密铸造上的应用

介绍了应用融积成型技术与石膏型精密铸造工艺相结合,成功地铸造出薄壁、复杂结构件的生产实例。这在国内尚属首例。希望能为铸造行业有效地引入快速成型技术提供有益的借鉴。     

TA15应变速率敏感指数对变形温度、应变和应变速率的响应规律

通过TA15多组试样的热物理模拟压缩试验获得了温度1073～1323K、应变速率0.01～10 s-1下的真应力-真应变数据,以此作为计算应变速率敏感指数(m值)的底层材料模型.以一组拟合图和3-D曲面揭示了应力、温度、应变速率和应变量共同作用诱导多种变形机制变化及同时存在将引起应变速率敏感系数m值的剧烈响应.通过m值的正负判断了变形稳定区与失稳区,为建立TA15合金高温变形时的加工图并合理制定锻造工艺,为有效控制及提高构件性能和质量提供了依据.     

曲面立体熔丝沉积成型的层厚选择与精度分析

分析FDM快速成型制造曲面立体时的加工原理误差与残余加工量.以圆球曲面成型为例,对变层厚切片的加工精度和残余加工量及定层厚切片的加工精度和残余加工量进行理论分析与计算,并进行比较.结果表明:采用变层厚切片加工可以减少因加工原理误差造成的后处理加工量,保证加工精度和成型效率.     

FDM工艺中的支撑自动生成技术研究

在FDM工艺中,基于其成型特点,在加工过程中需要添加支撑。支撑结构的合理性对成型件的精度和加工效率都有很大的影响。提出的基于扫描线的支撑自动生成技术生成支撑的速度快且无遗漏,在此基础上还能快速完成路径优化,实际应用效果较好。     

基于熔融沉积技术的快速熔模铸造工艺实践

确定新产品的熔模铸造工艺需要反复试验验证,设计周期长,成本高。利用熔融沉积技术(FDM)打印ABS模样,采用常规方法用蜡制造浇冒系统模样,二者黏接组成模组。涂挂试验配方的涂料实现挂砂,通过高压釜脱蜡和焙烧炉脱ABS两步过程,获得完整的型壳。焙烧、浇注、冷却后,进行喷砂清理,采用三维扫描仪检测产品尺寸。实现了基于熔融沉积技术(FDM)的快速熔模铸造生产铸钢件。     

基于神经网络和遗传算法的熔融沉积成型多目标优化

在建立了熔融沉积成型工艺参数和目标函数的基础上,论述了人工神经网络和遗传算法在熔融沉积快速成型工艺参数优化中的应用.首先利用人工神经网络建立熔融沉积快速成型工艺参数与成型件尺寸精度、翘曲变形之间关系的数学模型,然后用遗传算法对工艺参数优化.根据多目标函数优化问题的单目标化思想,对优化后的单目标进行了分解,得到最优工艺参数条件下的成型件尺寸精度、翘曲变形,从而为建立和控制熔融沉积快速成型工艺参数提供了一种行之有效的途径.     

Carbon-Nanofiber-Reinforced Syntactic Foams: Compressive Properties and Strain Rate Sensitivity

The current study is focused on exploring the possibility of reinforcing syntactic foams with carbon nanofibers (CNFs). Syntactic foams are hollow, particle-filled composites that are widely used in marine structures and are now finding applications in other modes of transportation due to their high stiffness-to-weight ratio. The compressive properties of syntactic foams reinforced with CNFs are characterized over the strain rate range of 10^?4 to 3,000 s^?1, which covers seven orders of magnitude. The results show that despite lower density with respect to neat epoxy, CNF/syntactic foams can have up to 7.3% and 15.5% higher quasi-static compressive strength and modulus, respectively, for the compositions that were characterized in the current study. In addition, these properties can be tailored over a wide range by means of hollow particle wall thickness and volume fraction, and CNF volume fraction. The compressive strength of CNF/syntactic foams is also shown to generally increase by up to a factor of 3.41 with increasing strain rate when quasi-static and high-strain-rate testing data are compared. Extensive microscopy of the CNF/syntactic foams is conducted to understand the failure and energy absorption mechanisms. Crack bridging by CNFs is observed in the specimens, which can delay final failure and increase the energy absorption capacity of the specimens. Deformation of CNFs is also noticed in the material microstructure. The deformation and failure mechanisms of nanofibers are related to the test strain rate and the structure of CNFs.     

FDM工艺中支撑添加技术的研究

在FDM成型系统中,零件原型的制作是靠热喷头挤出熔丝逐层堆积成型的,因此,在零件制作过程中支撑结构的生成是不可避免的.本文详细阐述了支撑结构生成中要考虑的因素.在向下特征体支撑自动生成算法中,为简化布尔运算,采用了基于直线扫描的自动支撑生成算法,在局部支撑自动生成算法中,提出了各种特征区域的识别方法,并把三维的布尔运算简化成二维的布尔运算来处理干涉问题.实践证明,该方法简化了运算,确保支撑无遗漏.最后通过大量的实验,总结出不同支撑生成方法的优缺点及对支撑不足区域的解决办法.     

熔融沉积成型工艺参数及数控加工后处理对表面精度的影响

为了提高熔融沉积成型(Fused Deposition Modeling,FDM)成型件的表面质量,提出利用数控加工对FDM成型件进行表面加工的后处理方法,研究打印速度、挤出速度和分层厚度等工艺参数对成型件的成型误差和表面粗糙度的影响,在此基础上,研究数控加工对其加工误差和表面粗糙度的影响。结果表明:FDM成型件表面粗糙度较大,最大达到24.434μm,合理设置打印速度、挤出速度和分层厚度可以有效降低FDM成型件的成型误差;数控加工可以有效降低FDM成型件的表面粗糙度值,表面粗糙度降低到1.979~2.446μm。     

喷涂机器人油漆沉积率优化建模与仿真

油漆沉积率模型是自动编程工艺参数选取的重要依据,为了建立符合实际工况的漆膜模型,采用喷涂机器人喷涂时椭圆型雾锥的实验数据,将贝叶斯归一化神经网络法和遗传算法分别用于漆膜模型的拟合。经过对比分析,采用2种算法得出模型都具有较高的精度,但遗传算法收敛速度更快,并可得出油漆沉积率方程的具体表达式,更适合油漆沉积率建模。     

Additive Manufacturing of PLA and CF/PLA Binding Layer Specimens via Fused Deposition Modeling

As one of the most popular additive manufacturing techniques, fused deposition modeling (FDM) is successfully applied in aerospace, automotive, architecture, and other fields to fabricate thermoplastic parts. Unfortunately, as a result of the limited nature of the mechanical properties and mass in raw materials, there is a pressing need to improve mechanical properties and reduce weight for FDM parts. Therefore, this paper presents an experiment of a special polylactic acid (PLA) and carbon fiber (CF)/PLA-laminated experimental specimen fabricated using the FDM process. The mechanical properties and mass analysis of the new composites for the PLA and CF/PLA binding layer specimen are investigated experimentally. Through the experimental analysis, one can conclude that the mass of laminated specimen is lighter than the CF/PLA specimen, and the tensile and flexural mechanical properties are higher than the pure PLA specimen.     

基于熔融沉积技术的燃机叶片快速熔模铸造工艺优化研究

针对熔融沉积技术应用于熔模铸造燃机叶片时存在的因材料熔融膨胀流动而导致型壳胀裂、表面品质和尺寸精度难以保证等问题,分别进行了3D打印ABS材质的实心、空心叶片模样用于熔模铸造的实验,研究了熔模铸造过程中的蜡质浇注系统设计、涂挂工艺参数、脱蜡和脱ABS材料工艺流程优化技术。通过对铸件尺寸精度的检测表明,ABS材质空心叶片模样的铸件产品尺寸精度优于实心叶片产品。     

Layer Thickness-Dependent Hardness and Strain Rate Sensitivity of Cu–Al/Al Nanostructured Multilayers

Cu–Al/Al nanostructured metallic multilayers with Al layer thickness hAlvarying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The results showed that the hardness increased drastically with decreasing hAldown to about 20 nm, whereafter the hardness reached a plateau that approaches the hardness of the alloyed Cu–Al monolithic thin films. The strain rate sensitivity(SRS, m),however, decreased monotonically with reducing hAl. The layer thickness-dependent strengthening mechanisms were discussed, and it was revealed that the alloyed Cu–Al nanolayers dominated at hAlB 20 nm, while the crystalline Al nanolayers dominated at hAl[ 20 nm. The plastic deformation was mainly related to the ductile Al nanolayers, which was responsible for the monotonic evolution of SRS with hAl. In addition, the hAl-dependent hardness and SRS were quantitatively modeled in light of the strengthening mechanisms at different length scales.     

Analytical Modeling of Strain Rate Distribution During Friction Stir Processing

Friction Stir Processing (FSP) is becoming an acceptable technique for modifying the grain structure of sheet metals. One of the most important issues that hinder the widespread use of FSP is the lack of accurate models that can predict the resulting microstructure in terms of process parameters. Most of the work that has been done in the FSP field is experimental, and limited modeling activities have been conducted. In this work, an analytical model is presented that can predict the strain rate distribution and the deformation zone in the friction stir processed zone as a function of process parameters. In the model, the velocity fields within the processed zone are determined by incorporating the effects of both the shoulder and the pin of the tool on the material flow. This is achieved by introducing state variables and weight functions. The model also accounts for different interfacial conditions between the tool and the material. The effects of different process parameters and conditions on the velocity fields and strain rate distributions are discussed. The results clearly show that the model can successfully predict the shape of the deformation zone and that the predicted strain rate values are in good agreement with results reported in the literature. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Baltimore, MD, June 25-28, 2007.     

Determination of Strain Rate Sensitivity of Micro-struts Manufactured Using the Selective Laser Melting Method

Micro-lattice structures manufactured using the selective laser melting (SLM) process provides the opportunity to realize optimal cellular materials for impact energy absorption. In this paper, strain rate-dependent material properties are measured for stainless steel 316L SLM micro-lattice struts in the strain rate range of 10^?3 to 6000 s^?1. At high strain rates, a novel version of the split Hopkinson Bar has been developed. Strain rate-dependent materials data have been used in Cowper–Symonds material model, and the scope and limit of this model in the context of SLM struts have been discussed. Strain rate material data and the Cowper–Symonds model have been applied to the finite element analysis of a micro-lattice block subjected to drop weight impact loading. The model output has been compared to experimental results, and it has been shown that the increase in crush stress due to impact loading is mainly the result of strain rate material behavior. Hence, a systematic methodology has been developed to investigate the impact energy absorption of a micro-lattice structure manufactured using additive layer manufacture (SLM). This methodology can be extended to other micro-lattice materials and configurations, and to other impact conditions.     

Dependence of Strain Rate Sensitivity on the Slip System: A Molecular Dynamics Simulation

The strain rate of deformation might affect mechanical properties of metallic materials, especially at elevated temperatures. Due to the nature of dislocation slip, it is anticipated that strain rate sensitivity (SRS) depends on the slip system. While the dependency of SRS on the temperature and strain rate of the deformation is well recognized, its dependence on the slip system is not well understood. Accordingly, the molecular dynamics simulation was used to investigate the dependence of strain rate sensitivity of pure Al single crystals on the slip system. In this study, the embedded atom method (EAM) potential for Al was employed. SRS and shear strength of the material were studied in four different slip systems and at two temperatures of 300 and 500 K. It was found that SRS of the material depends on the slip system in addition to the temperature, and SRS was higher in less compact systems with more difficult slip. The dislocation theories were used to rationalize the simulation results.