Optimization of printing parameters for improvement of mechanical and thermal performances of 3D printed poly(ether ether ketone) parts

Many processing parameters can be adjusted to optimize the fused filament fabrication (FFF) process, a popular and widely used additive manufacturing techniques for plastic materials. Among those easily adjusted parameters are the nozzle temperature, printing speed, raster orientation, and layer thicknesses. Using poly(ether ether ketone) (PEEK) as the base material, a design of experiments analysis was performed on the main FFF parameters. A response surface methodology was applied to analyze the results and to maximize the output responses. Results have shown that the nozzle temperature is the most influential parameter on tensile properties and the crystallinity degree of printed PEEK by FFF process. Parts produced with optimized FFF parameters were then subjected to an annealing treatment to induce a relaxation of residual stress and to enhance crystallinity. The best properties for 3D printed PEEK parts were achieved with annealed parts prepared at 400°C with a printing speed of 30 mm/s, 0.15 mm layer thickness and raster orientation of [0°/15°/−15°]. The resulting parts have mechanical properties comparable to those of injected PEEK.     

Tough thiourethane thermoplastics for fused filament fabrication

Fused filament fabrication (FFF) is the most common form of additive manufacturing. Most FFF materials are variants of commercially available engineering plastics. Their performance when printed can widely vary, thus there is an increasing volume of research on alternative materials with thermal and mechanical performance optimized for FFF. In this work, thiol–isocyanate polymerization is used for the development of a one‐pot synthesis for polythiourethane thermoplastics for tough three‐dimensional (3D) printing applications. The thiol–isocyanate reaction mechanism allows for rapid polymer synthesis with minimal byproduct formation and few limitations on reaction conditions. The resulting elastomer has high toughness and a low melting point, making it favorable for use as a 3D printing filament. The elastomer outperforms commercial filaments in tension when printed. Considering the rapid advancement of additive manufacturing and the limitations of many engineering polymers with the 3D printing process, these results are encouraging for the development of bespoke 3D printing thermoplastics. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45574.     

Fracture and mechanical properties of lightweight alumina ceramics prepared by fused filament fabrication

Fused filament fabrication (FFF), as one of the additive manufacturing technology, provides cost-effective and relatively fast preparation of 3D objects of desired dimensions and design. In this work, a composite filament containing 50 vol. % of sub-micron alumina powder was successfully used for the manufacturing of samples with prismatic design. The influence of the layer thickness (0.1–0.3 mm) on the final bulk density and mechanical properties were investigated. Sintering at 1600 °C for 1 h results in relative densities ranging from 80 to 89 % and the flexural strength reached 200–300 MPa depending on the layer thickness used for the printing.     

Semi‐Crystalline Polymer Blends for Material Extrusion Additive Manufacturing Printability: A Case Study with Poly(ethylene terephthalate) and Polypropylene

Semi‐crystalline polymers are an important class of materials for engineering applications due to their high modulus and barrier properties. Traditional manufacturing methods process semi‐crystalline polymers via rigid molds and well‐controlled temperature and pressure environments to handle the significant change in specific volume occurring during crystallization; however, material extrusion additive manufacturing does not use these features. This often leads to warpage‐induced build failure in fused filament fabrication (FFF). To enable FFF of semi‐crystalline polymers, this work investigates characteristics of immiscible polymer blends (e.g., disparate crystallization behavior and phase separation) to mitigate warping failure during printing. A series of poly(ethylene terephthalate)/polypropylene/polypropylene–graft–maleic anhydride blends are explored and the effect of thermal and morphological characteristics on printability is analyzed. It is shown that these blends can be extruded into filament and printed into a 3D structure. Extrapolations indicate that phase‐separated blends with increased total crystallization half‐time are beneficial for FFF printing.     

Effect of the nanoparticles on the morphology and mechanical performance of thermally blown 3D printed HIPS foams

Cellular polymer nanocomposites can combine high mechanical performance with low density. However, the manufacturing of porous nanocomposites into complex shapes can represent a challenge. Therefore, this article deals with the preparation, characterization, and 3D printing of porous nanocomposites. The filaments were extruded from the polymer nanocomposite filled by thermal chemical blowing agent, and then processed by 3D printing into the required shapes. In-situ and post-treatment foaming strategies were investigated and compared. The nanoparticles (NPs) significantly affected the processing, structure, thermal and mechanical properties of polymeric foams. The NPs, serving as a nucleating agent, allowed preparation of smaller pores and led to finer and more homogeneous foams. At the same time, they reinforced foam walls and thus improved mechanical properties. Moreover, NPs catalyzed decomposition of the blowing agent grains at lower temperature which brought about faster and more efficient foaming. This study showed the straightforward approach to prepare mechanically robust lightweight 3D printed materials.     

On reducing anisotropy in 3D printed polymers via ionizing radiation

The mechanical properties of materials printed using fused filament fabrication (FFF) 3D printers typically rely only on adhesion among melt processed thermoplastic polymer strands. This dramatically limits the utility of FFF systems today for a host of manufacturing and consumer products and severely limits the toughness in 3D printed shape memory polymers. To improve the interlayer adhesion in 3D printed parts, we introduce crosslinks among the polymer chains by exposing 3D printed copolymer blends to ionizing radiation to strengthen the parts and reduce anisotropy. A series polymers blended with specific radiation sensitizers, such as trimethylolpropane triacrylate (TMPTA) and triallyisocyanurate (TAIC), were prepared and irradiated by gamma rays. Differential scanning calorimetry (DSC), tensile testing, dynamic mechanical analysis (DMA) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were employed to characterize the thermomechanical properties and the chemical structure of the various polymers. TAIC was shown to be a very effective radiation sensitizer for 3D printed sensitized polylactic acid (PLA). The results further revealed that crosslinks induced by radiation temperatures near T_g of shape memory systems have prominently enhanced the thermomechanical properties of the 3D printed polymers, as well as the solvent resistance. This enables us to deliver a new generation of inexpensive 3D printable, crosslinked parts with robust thermomechanical properties.     

微孔发泡模内表面装饰复合成型工艺参数对泡孔结构与力学性能影响

微孔发泡模内表面装饰复合成型工艺是高表观质量、轻量化塑料制品的重要成型方法,成型制品的泡孔结构与力学性能对其最终质量具有决定性影响.以典型拉伸样条为例,采用数值模拟的方法,通过对比分析不同工艺参数条件下平均气泡半径、密度和力学性能的变化规律,研究该工艺过程中主要工艺参数对泡孔结构及其力学性能的影响.结果表明,注射速率、...     

多浇口顺序控制技术在消除仪表盘熔接痕中的应用

传统注射成型生产的汽车仪表盘上存在大量的熔接痕,严重地影响了仪表盘的力学性能和外观质量,针对这一问题,提出了热流道顺序控制注射成型技术,介绍了热流道顺序控制成型技术的成型原理,根据该原理对模具的浇注系统进行了优化设计。通过Moldflow模拟分析,研究了各个熔接痕和气泡形成的原因,并对各个浇口的开启时间进行了优化。研究发现通过优化浇口的开启时间,可以有效地控制熔体的充模顺序和流动路径,从而消除熔接痕和气泡,提高仪表盘的质量和使用档次。     

Resin transfer molding (RTM) process of a high performance epoxy resin. II: Effects of process variables on the physical,static and dynamic mechanical behavior

The effects of processing variables on the mechanical behavior and the void content of one‐part epoxy based glass fabric composites produced by resin transfer molding (RTM) were investigated. The variables studied included injection pressure, injection temperature, and fabric structure. Image analysis was used to measure the void content in the composites. Variations in injection pressure and temperature were found to have a significant effect on the quality and the mechanical performance of composites. The optimized physical and mechanical performance of the composites was obtained by processing the resin at 160°C under 392 kPa pressure. Molding of highly permeable EF420 fabric required a shorter mold filling time, but resulted in reduced flexural strength and storage modulus in the resulting composites as compared with that of the composites containing 1581 fabric.     

不同填充率下FDM 3D打印预制件建模及力学性能分析

以拉伸、压缩、弯曲、扭转4种受载情况下的熔融沉积型三维（FDM 3D）打印预制件为研究对象,以填充率、填充单元结构类型为分析参数,通过确定3D打印预制件填充率的影响因素,建立了填充率与格子形填充单元几何参数的通用解析式,据此构建不同填充率下3D打印预制件的三维几何模型;然后对不同受载类型3D打印预制件进行有限元仿真分析,明确填充率对不同载荷工况下3D打印预制件力学特性的影响规律。仿真和实验结果表明,填充率对3D打印预制件所受拉伸应力、压缩应力、弯曲应力均有较大影响,而扭转情况下影响较小,据此进一步确定了一定受载情况下3D打印预制件的较优填充率;基于本文提出的不同填充率下预制件三维模型建立方法,可有效实现对预制件的力学性能仿真分析,对减少产品试验验证次数、降低研发成本具有积极作用。     

基于3D打印技术制造柔性传感器研究进展

与传统的涂覆、沉积等加工手段相比,使用3D打印技术可制造复杂立体功能结构的传感器,将3D打印与柔性传感技术结合可以促进未来生物医疗、人工智能等领域的发展。本文介绍了国内外基于3D打印技术制造柔性传感器的最新进展,其中包括聚酰亚胺等多种基底材料、纳米金属等多种打印传感材料;按照熔融沉积、黏弹性墨水沉积、粉末烧结熔化、还原光聚合和材料喷射的制造原理分别阐述了多种传感器的材料选择、成型特点,并对制造方法进行总结分析。虽然3D打印制造柔性传感器件存在着缺乏行业标准及多种类打印材料等问题,但经过不断创新与发展,3D打印将成为柔性传感领域极佳的制造手段。     

Characterization and enhancement of quasi-static and shear mechanical properties of 3D printed lightweight SiOC lattices: Effects of structural design and parameters

Ceramic structures have attracted extensive attention due to their excellent high temperature properties, low density and function application after structural design. Herein, six different ceramic lattices based on struts and triply periodic minimal surfaces (TPMS) sheet lattices were designed and fabricated by digital light processing (DLP) using polymer precursor. The effects of unit cell size, relative density and other parameters on the compressive and shear properties of the structure were studied in detail. A structure optimized from Gyroid was put forward, which realized excellent mechanical properties under 15% low relative density (0.25 g/cm³). Results also suggested that the TPMS sheet lattices were more suitable for bearing under low relative density and the struts-based lattices were more sensitive to the parameters change, 20% is an important node where the mechanical properties of the structure decline significantly. Design of the structure in the loading direction can effectively improve the mechanical properties. This study provides a new basis for structural design under low relative density, which will aid in the further improvement of traditional structures and the development of the application of ceramic materials in mechanical structures.     

基于流动模拟的瓶底注射成型浇注系统优化设计

以开水瓶底塑料件为例,利用Pro／E的外挂程序Plastic Advisor模块分析塑料件的最佳浇口位置,选取不同的浇口数目,通过对塑料件注射成型过程的流动模拟,预测塑料熔体注射成型的填充性、填充时间、压力降、熔体流动前沿温度、熔接痕、气穴、材料消耗量及塑料件质量等,并对不同注射成型方案的流动模拟结果进行比较、选优,获得最佳注塑模浇注系统设计方案,为模具设计与制造提供可靠的设计数据,减少了试模时间,降低了制造成本。     

基于DSC法的混杂纤维增强树脂基复合材料拉挤工艺研究

为提高碳纤维/玻璃纤维混杂增强树脂基复合材料(以下简称混杂纤维复合材料)拉挤型材的固化质量和力学性能,通过差示扫描量热分析(DSC)法,得出了相同配方条件下复合材料的4种不同升温速率下的固化DSC曲线,运用T–β外推法初步确定了三段式加热拉挤成型方法的温度工艺参数范围。在此基础上,选择直径为10 mm的混杂纤维棒材作为研究对象,变化不同的拉挤温度和速度制备型材,并对其分别进行力学性能试验,研究拉挤工艺参数对复合材料力学性能的影响,从而根据力学性能表征进一步明确适合于本配方的生产工艺参数。结果表明,通过以上方法所得到的混杂纤维复合材料拉挤工艺参数能够满足制备混杂纤维复合材料型材的要求;与传统的经验方法相比,采用该方法更为高效和准确。     

Experimental study of PLA thermal behavior during fused filament fabrication

Fused filament fabrication (FFF) is an additive manufacturing technique that is used to produce prototypes and a gradually more important processing route to obtain final products. Due to the layer-by-layer deposition mechanism involved, bonding between adjacent layers is controlled by the thermal energy of the material being printed, which strongly depends on the temperature development of the filaments during the deposition sequence. This study reports experimental measurements of filament temperature during deposition. These temperature profiles were compared to the predictions made by a previously developed model. The two sets of data showed good agreement, particularly concerning the occurrence of reheating peaks when new filaments are deposited onto previously deposited ones. The developed experimental technique is shown to demonstrate its sensitivity to changing operating conditions, namely platform temperature and deposition velocity. The data generated can be valuable to predict more accurately the bond quality achieved in FFF parts.     

Toughening PVC with Biocompatible PCL Softeners for Supreme Mechanical Properties,Morphology, Shape Memory Effects,and FFF Printability

In this article, a first of its kind blend of polyvinyl chloride (PVC) and biocompatible polycaprolactone (PCL) is introduced by melt mixing and then 3D printed successfully via Fused Filament Fabrication (FFF). Experimental tests are carried out on PCL-PVC blends to assess thermo-mechanical behaviors, morphology, fracture toughness, shape-memory effects and printability. Macro and microscopic tests reveal that PVC-PCL compounds are miscible due to high molecular compatibility and strong interaction. This causes extraordinary mechanical properties specially for PVC-10 wt% PCL. In addition to the desired tensile strength (45 MPa), this material has a completely rubbery behavior at ambient temperature, and its total elongation is more than 81%. In addition, due to the high formability of PVC-PCL at ambient temperature, it has capability of being programed via different shape-memory protocols. Programming tests show that PVC-PCL blends have an excellent shape-memory effect and result in 100% shape recovery. SEM results prove a high improvement of PVC printability with the addition of 10 wt% PCL. Toughened PVC by PCL is herein added to the materials library of FFF 3D printers and expected to revolutionize applications of PVC compounds in the field of biomedical 3D and 4D printing due to its appropriate thermo-mechanical properties, supreme printability, and excellent biocompatibility.     

Determination of robust material qualities and processing conditions for laser sintering of polyamide 12

Material aging of Polyamide 12 (Laurinlactam) is a very common problem in laser sintering (LS). For stable process conditions, recycled material used in previous processes should be refreshed with 30–50% virgin powder material. However, even by following these refreshing strategies, material quality drops to an insufficient level after several process cycles which leads to poor part quality showing orange peel or poor mechanical properties when processed. In order to avoid this, a quality assurance system has been established to provide recommendations for robust process conditions and material qualities. A detailed study on aging processes in LS comparing two different machines was performed in order to analyze correlations between material quality, process parameters and part properties. Energy input allowing for robust processing conditions should be in a range between 0.325 and 0.42 J/mm³ showing almost identical values for both machines. Optimal material quality ranges was found to be machine specific, while the lower limit lies between 20 and 25 cm³/ 10 min for both machines used. Additionally, material aging characteristics in an oven and a LS machine were compared, in order to simulate material aging in the LS process by simple experiments in an oven. POLYM. ENG. SCI., 54:1540–1554, 2014. © 2013 Society of Plastics Engineers     

Optimization of the spark plasma sintering processing parameters affecting the properties of polyimide

The present study deals with the optimization of polyimide (PI) mechanical properties, obtained by Spark Plasma Sintering (SPS), by using a method combining Design of Experiments (DOE) with physical, structural, and mechanical characterizations. The effects of SPS parameters such as temperature, pressure, dwell time, and cooling rate on the density, mechanical properties, and structure of PI were investigated. The experimental results revealed that the mechanical properties of the material were optimized by raising the sintering temperature up to 350°C. The optimized SPS processing parameters were a temperature of 350°C, a pressure of 40 MPa, and a dwell time of 5 min. Under these conditions, a relative density of 99.6% was reached within only a few minutes. The corresponding mechanical properties consisted of Young's modulus of 3.43 GPa, a Shore D hardness of 87.3, and a compressive strength of 738 MPa for a maximum compressive strain of 61.8%. Moreover, when working at 320°C and at 100 MPa, an increase in the dwell time was necessary to enhance the properties. Contrary to the other parameters, the cooling rate appeared to be a non‐significant parameter. Finally, correlations between the PI structure and the mechanical properties were made to demonstrate the densification mechanisms. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41542.     

FDM 3D打印工艺参数对PLA制件力学性能的影响

采用五因素四水平正交试验设计,对16组不同工艺参数(打印层厚、填充密度、打印温度、填充速度、外壳厚度)的FDM 3D打印聚乳酸(PLA)制件力学性能进行了测试和结果分析,确定了影响PLA制件力学性能的主要因素,其中,外壳厚度对制件力学性能影响最为明显,打印温度影响最小,同时分析得到了在打印层厚0.15 mm,填充密度40%,打印温度210℃,填充速度60 mm/s,外壳厚度1.6 mm条件下可获得力学性能最佳的制件。最后对试验数据进行回归分析,拟合得到了FDM打印工艺参数与PLA制件力学性能指标的数学模型;通过对不同打印工艺参数的试样进行试验验证,表明该模型拟合误差小(5%以内),可靠性高,可用来对FDM 3D打印制件的加工提供参考。     

High temperature strength of an ultra high temperature ceramic produced by additive manufacturing

In this study hafnium diboride was fabricated using the additive manufacturing technique robocasting. Parts have been successfully produced with complex shapes and internal structures not possible via conventional manufacturing techniques. Following pressureless sintering, the monolithic parts reach densities of 94–97% theoretical. These parts exhibit bending strength of 364 ± 31 MPa at room temperature, and maintain strengths of 196 ± 5 MPa up to 1950 °C, which is comparable to UHTC parts produced by traditional means. These are the highest temperature mechanical tests that a 3D printed part has ever undergone. The successful printing of the high density HfB₂ demonstrates the versatile range materials that can be produced via robocasting using Pluronic pastes.