Impact of processing conditions and sizing on the thermomechanical and morphological properties of polypropylene/carbon fiber composites fabricated by material extrusion additive manufacturing

For the 3D printed composites, fiber alignment is affected by the direction of melt-flow during extrusion of filaments and subsequently through the printing nozzle. The resulting fibers orientation and the fiber-matrix compatibility have a direct correlation with mechanical properties. This study investigates the impact of processing conditions on the state of the carbon fiber types and their orientation on the mechanical properties of 3D-printed composites. Short and long carbon fibers were used as starting reinforcing materials, and the state of fibers at the beginning and on the printed parts were evaluated. Strong anisotropy in terms of mechanical properties (flexural and impact properties) was observed for the samples printed with different printing orientations. Interestingly, the number of voids in the printed composites was found to be correlated with the fiber types. The present work provides a step towards the optimization of tailored composite properties by additive manufacturing.     

Printability,shape-memory,and mechanical properties of PHB/PCL/CNFs composites

Shape-memory polymers have attracted attention as smart implant materials in recent years because they are lightweight, low-cost, easily processable, and because they undergo large deformation. Here, cellulose nanofibers (CNFs) were used as a reinforcement for polyhydroxybutyrate (PHB)/polycaprolactone (PCL) composites to improve mechanical properties. The composites were investigated by rheological tests, differential scanning calorimetry, dynamic mechanical analysis, mechanical property tests, and shape-memory tests. The printability of PHB/PCL/CNFs composites was demonstrated by using them to print interconnected porous structures with a gyroid surface. The results showed that the PHB/PCL (80:20) composites with 1 wt% CNF displayed the best comprehensive mechanical and shape-memory properties. As a functional verification, a model of the self-opening hand was fabricated by 3D printing, and its deformation and recovery capabilities were evaluated.     

Characterization of PA-12 specimens fabricated by projection sintering at various sintering parameters

Large area projection sintering (LAPS) promises to be a new method in the field of additive manufacturing. Developed in the Mechanical Engineering Department, University of South Florida, LAPS uses long exposure times over a broad area of powder to fuse into dense, reproducible materials. In contrast, LS, a common powder-based additive manufacturing, uses a focused beam of light scanned quickly over the material. Local regions of concentrated high-energy bursts of light lead to higher peak temperatures and differing cooling dynamics and overall crystallinity. The mechanical properties of laser sintered specimens suffer because of uneven particle fusion. LAPS offers the capacity to fine-tune fusion properties through enhanced thermodynamic control of the heating and cooling profiles for sintering. Further research is required to identify the relationship between LAPS build settings and part properties to enable the fabrication of custom parts with desired properties. This study examines the influence of LAPS sintering parameters on chemical structures, crystallinity, mechanical, and thermal properties of polyamide-12 specimens using powder X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, small-angle X-ray scattering, scanning electron microscopy, and microhardness testing. It was observed that higher crystallinity was imparted to specimens that were sintered for a shorter time and vice versa.     

Fabrication process of smooth functionally graded materials through a real-time inline control of the component ratio

Functionally graded materials (FGMs) play an essential role in tissue engineering because of their satisfactory histocompatibility and excellent mechanical performance. While traditional manufacturing methods allow production of simple FGMs, precise control of composition and customized property at transition between the dissimilar materials is still a challenge. Here, an extrusion-based functionally graded additive manufacturing (FGAM) platform was developed to generate smooth graded parts by thrusting out monolithic cylindrical filaments with high viscosity. Furthermore, the rheological properties, hydrodynamic behavior, and mixed homogeneity of the non-Newtonian fluids were studied. Therefore, the appropriate solid contents, alternative energy-efficient mixers, and optimized printing parameters were proved to be beneficial for an outstanding deposition effect of the suspension. Ultimately, an object with smooth gradient was successfully manufactured. The validity of this strategy was verified via optical microscopy combined with an image processing method to gauge homogeneity and a scanning electron microscope to investigate graded composition and microstructure.     

基于随机开关喷孔数量的3D错位打印研究及应用

3D打印机打印过程是逐层堆砌打印,在实际的工业生产中,打印机喷头经常会出现部分喷孔堵塞,无法喷墨的情况,导致打印的零部件在层叠加方向上堵塞喷孔的部位始终无法喷洒粘接剂造成断裂面而成型失败。目前只能清理喷孔后再重新打印或更换喷头解决上述问题,但是会造成喷头使用寿命减短、生产效率降低、成本增加等问题。通过随机开关部分喷孔和打印头偏移相结合的方式可以有效的避免因少量喷孔堵塞而导致的打印零部件断裂报废的问题,也可延长喷头使用寿命。从而使得3D打印在生产制造领域使用的更加得心应手。     

面向3D打印体积极小的拓扑优化技术

与传统制造所生产的产品相比,3D打印产品的成本仍相对较高.因此,如何能在不牺牲打印物体表面质量的前提下通过模型优化来减少打印材料消耗,对于降低打印成本至关重要.针对这一问题,借鉴传统渐进结构优化方法,结合Von Mises应力计算,给出一种面向3D打印体积极小的拓扑优化算法.该算法通过模型力学计算所得的最大Von Mises应力与材料允许应力之比来引导模型体积减小进化,直至最大Von Mises应力达到允许应力值为止.同时,引入多分辨率技术,由粗网格再到细网格进行优化计算,有效地提高了计算效率.与现有其他给定结构模式的方法相比,该优化结果能更好地体现模型荷载受力的传递路径.     

DMS2015-33: Generative interface structure design for supporting existing objects

Increasing availability of high quality 3D printing devices and services now enable ordinary people to create, edit and repair products for their custom needs. However, an effective use of current 3D modeling and design software is still a challenge for most novice users. In this work, we introduce a new computational method to automatically generate an organic interface structure that allows existing objects to be statically supported within a prescribed physical environment. Taking the digital model of the environment and a set of points that the generated structure should touch as an input, our biologically inspired growth algorithm automatically produces a support structure that when physically fabricated helps keep the target object in the desired position and orientation. The proposed growth algorithm uses an attractor based form generation process based on the space colonization algorithm and introduces a novel target attractor concept. Moreover, obstacle avoidance, symmetrical growth, smoothing and sketch modification techniques have been developed to adapt the nature inspired growth algorithm into a design tool that is interactive with the design space. We present the details of our technique and illustrate its use on a collection of examples from different categories.     

A3菌产絮凝剂培养动力学及靛蓝废水脱色研究

从土壤中筛选出1株产微生物絮凝剂的菌株A3,利用均匀设计安排试验,用曲线拟合创建数学模型的方法研究了其产絮凝剂的培养基条件和利用A3菌产絮凝剂对靛蓝废水进行脱色处理,获得A3菌最佳絮凝剂生产条件和最佳靛蓝废水脱色工艺.结果表明,A3菌产絮凝剂的最佳培养条件为葡萄糖添加量2.2%、酵母膏添加量0.51%、pH 7.6、温...     

CMYK到L*a*b*色彩空间转换的研究

为了满足色彩复制一致性和预期性要求,寻找一种精确实用的L*a*b*与CMYK转换方法尤为重要。本文利用数理统计的二元线性回归方法在建立CMY到L*a*b*的转换模型的基础上,验证了网点呈色平面规律同样适用四色印刷,并通过最小二乘及数值分析的方法拟和各四色平面方程系数建立了CMYK到L*a*b*转换模型。随后对模型进行精度验证并修正,分析误差产生的原因,最终得到比较精确的模型。     

基于开源LAMP架构的Web打印技术

通过对现有B/S架构打印方法进行分析对比,针对它们的缺陷提出了一种基于开源LAMP架构的跨平台、精确、有效的Web打印新技术,并详细介绍了其原理,最后给出了具体的实现方法.