选择性激光烧结用聚合物粉末材料研究进展

选择性激光烧结(SLS)是一项重要的3D打印技术,目前已广泛应用于各个高新技术领域。本文首先介绍了三种聚合物粉末的制备方法及原理,主要包括机械粉碎法、溶剂沉淀法和相分离法,并分析总结了三种制备方法的优缺点。其次,重点论述了聚合物粉末特性对SLS工艺的影响,如粉末材料的粒径大小、表面形貌以及材料的表面张力。最后,分析总结了SLS工艺参数对烧结制件性能的影响因素。本文的研究内容可为从事聚合物粉末SLS技术的相关生产技术人员和科研人员提供参考借鉴。     

树脂基复合成型材料的选择性激光烧结

介绍选择性激光烧结及烧结技术的基本原理,探讨了树脂基复合成型材料选择性激光烧结工艺及参数。     

用于选择性激光烧结功能件的基体聚合物烧结材料的研究

选取PC、ABS和HIPS三种典型的无定形聚合物粉末材料作为基体聚合物烧结材料，对其烧结及后处理性能进行了研究。经比较，有较好后处理效果的PC和有较好原始力学性能的HIPS均可作为新材料的基体聚合物烧结材料。并提出了进一步提高烧结功能件力学性能的方法，对今后用于制作功能件的SLS粉末材料的开发具有指导意义。     

选择性激光烧结的研究进展

选择性激光烧结是一种增材制造快速成型技术。本文简要介绍了选择性激光烧结技术的原理,综述了目前的研究现状。     

选择性激光烧结用尼龙1212粉末的制备

为得到适用于选择性激光烧结的原材料,降低选择性激光烧结用尼龙1212生产成本,用溶剂沉淀法制备了尼龙1212粉末,讨论了溶剂种类、溶解温度、成核温度等因素对尼龙1212粉末粒度和形貌的影响。通过显微镜、扫描电子显微镜、粒度分析、差示扫描量热法等对制备的尼龙1212进行了表征,结果表明采用溶剂沉淀法可有效地制备出分散良好且粒径在20～80μm范围内的尼龙1212球形粉末,其最佳制备工艺条件为：乙醇作溶剂、溶解温度为160℃,将成核温度控制在130℃。对自制尼龙1212和市售选择性激光烧结用尼龙1212进行了松装密度、熔体流动速率、拉伸及弯曲等性能表征,发现两者的粉末性能和制件性能接近,其中自制尼龙1212的弯曲强度和弯曲弹性模量略高于市售尼龙1212,已达到了选择性激光烧结对原材料的要求,能烧结出光滑制件,其尺寸精度可达到±0.1 mm。     

选择性激光烧结用复合尼龙粉的制备与性能

采用溶剂沉析法制备了低熔点复合尼龙12基料,对其改性处理后获得适合于选择性激光烧结用的复合尼龙粉末。通过正交实验的方法对复合尼龙粉末的烧结工艺进行研究,得到优化的烧结工艺参数,探讨了烧结工艺参数对成型件烧结成型性能的影响,对复合尼龙粉及其烧结成型件进行了SEM分析,发现尼龙12烧结件的烧结精度和力学性能都得到了很大的改善。     

聚合物选择激光烧结成型的研究进展

选择激光烧结是一种新型的快速成型技术。简要论述了选择激光烧结成型原理、研究现状、聚合物成型原料的选择、影响因素、发展前景等。     

选择性激光烧结用尼龙粉体的老化及回收研究进展

从选择性激光烧结原理出发,分析了选择性激光烧结用尼龙粉体老化机理、老化粉体物理化学性能的变化特征、老化粉体性能变化对选择性激光烧结工艺和制件性能的影响及老化粉体回收利用措施.综合研究分析,提出老化粉体回收的进一步研究应从分子尺度出发,改变其分子量,从根本上恢复材料的烧结性能.     

Preparation of alumina/polystyrene core-shell composite powder via phase inversion process for indirect selective laser sintering applications

Indirect selective laser sintering (SLS) is one of the promising additive manufacturing (AM) methods that can process conventionally difficult or even impossible materials such as ceramics. In this work, an innovative phase inversion technique is used to fabricate spherical alumina particles coated with a thin layer of polystyrene (PS). Then, indirect SLS is used to fabricate green parts from the 6 wt% PS coated alumina particles via a Nd:YAG laser. The assessed SLS process parameters were the scan speed, laser power, scan spacing, pulse frequency, and pulse width. The characterization of the AL₂O₃/PS core-shell composite particles was described using techniques including SEM (for morphology), FT-IR (for chemical bonding at the interfaces), TGA (for mass loss), and DSC (for glass transition temperature, T_g). 3D green parts were then fabricated using proper process parameters as a proof of the feasibility of using SLS technique for AL₂O₃/PS core-shell composite powder. The results showed that using a Nd:YAG laser with less absorption by alumina and PS provides greater penetration through a powder bed. In addition, the possibility of sound connections among particles in every direction was observed due to the uniformity of the coating process in spite of a minimal amount of binder. In addition, green part density measurements show high values compared to previously reported results.     

Effects of raw material ratio and post-treatment on properties of soda lime glass-ceramics fabricated by selective laser sintering

A reliable method for fabricating soda lime glass-ceramics by selective laser sintering was demonstrated. The effect of the ratio of glass powder to epoxy resin and sintering process on the properties and microstructure of glass-ceramics was investigated. Research shows that: with the improvement of glass powder proportion, sintering shrinkage rate declined and mechanical strength could be improved gradually. When the mass ratio of glass powder and epoxy resin powder was 18:1 and heat-holding at 740 °C for 3 h, the shrinkage rate of the sample was 21.11% and the bending strength reached 95.45 MPa. Therefore, this research laid a foundation for 3D printing to fabricate high performance and complex structure glass-ceramics.     

Direct selective laser sintering of hexagonal barium titanate ceramics

A direct selective laser sintering (SLS) process was combined with a laser preheating procedure to decrease the temperature gradient and thermal stress, which was demonstrated as a promising approach for additive manufacturing of BaTiO₃ ceramics. The phase compositions in BaTiO₃ ceramics fabricated by SLS were investigated by X-ray and neutron diffractions. The surface morphologies and cross-section microstructures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A dense hexagonal h-BaTiO₃ layer was formed on the surface and extended to a depth of 500 μm, with a relative density higher than 97% and absence of pores or microcracks. SLS resulted in the formation of the high-temperature phase, h-BaTiO₃, which was retained at room temperature possibly due to the high cooling rate. The grain boundaries of SLSed h-BaTiO₃ ceramics consist of a Ti-rich secondary phase. Compared with that of the pressureless sintered t-BaTiO₃ ceramics, the Vickers hardness of SLSed h-BaTiO₃ is 70% higher.     

聚合物基导热复合材料的研究进展

阐述了聚合物基导热复合材料的导热机制。综述了国内外导热胶粘剂、导热橡胶和导热塑料等研究进展。介绍了提高复合材料导热性能的途径,并在此基础上,展望了聚合物基导热复合材料的应用前景和未来的发展方向。     

Additive manufacturing of zirconia parts by indirect selective laser sintering

Thermally induced phase separation (TIPS) was used to produce spherical polypropylene–zirconia composite powder for selective laser sintering (SLS). The influence of the composition of the composite starting powder and the SLS parameters on the density and strength of the composite SLS parts was investigated, allowing realizing SLS parts with a relative density of 36%. Pressure infiltration (PI) and warm isostatic pressing (WIPing) were applied to increase the green density of the ZrO₂–PP SLSed parts. Infiltrating the SLS parts with an aqueous 30 vol.% ZrO₂ suspension allowed to increase the sintered density from 32 to 54%. WIPing (135 °C and 64 MPa) of the SLS and SLS/infiltrated complex shape green polymer–ceramic composite parts prior to debinding and sintering allowed raising the sintered density of the 3 mol Y₂O₃ stabilized ZrO₂ parts to 92 and 85%, respectively.     

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.     

Preparation and indirect selective laser sintering of alumina/PA microspheres

Indirect selective laser sintering (SLS) is a promising additive manufacturing technique to produce ceramic parts with complex shapes in a two-step process. In the first step, the polymer phase in a deposited polymer/alumina composite microsphere layer is locally molten by a scanning laser beam, resulting in local ceramic particle bonding. In the second step, the binder is removed from the green parts by slowly heating and subsequently furnace sintered to increase the density. In this work, polyamide 12 and submicrometer sized alumina were used. Homogeneous spherical composite powders in the form of microspheres were prepared by a novel phase inversion technique. The composite powder showed good flowability and formability. Differential scanning calorimetry (DSC) was used to determine the thermal properties and laser processing window of the composite powder. The effect of the laser beam scanning parameters such as laser power, scan speed and scan spacing on the fabrication of green parts was assessed. Green parts were subsequently debinded and furnace sintered to produce crack-free alumina components. The sintered density of the parts however was limited to only 50% of the theoretical density since the intersphere space formed during microsphere deposition and SLS remained after sintering.     

Preparation of Ti2AlC through in-situ selective laser forming and reaction sintering

This paper proposes the preparation of Ti₂AlC complex parts through the combination of in-situ selective laser forming (ISLF) and reaction sintering. By studying the impaction of scan speed and laser power on the phase composition and microstructure of the formed test specimen, it was found that the test specimen mainly consisted of Ti3Al, TiAl, TiC, and graphite reacted incompletely. When the laser power was fixed, the lower the scan speed, the higher the TiC content. The TiC phase developed from nanoparticles to coarse dendritic structures gradually. When the laser power is further increased, the dendritic structure does not increase significantly. The process optimization found that when the laser power was 40 W and the scan speed was 100 mm/s, the density of the formed test specimen was 80.308%, which was mainly because the difference between the diffusion coefficients of Ti and Al resulted in Kirkendall pores, causing the incomplete densification of the formed part.     

Statistical evaluation of laser energy density effect on mechanical properties of polyamide parts manufactured by selective laser sintering

Selective laser sintering (SLS) is a rapid manufacturing technology that builds layer‐by‐layer solid object from particulate materials. Nowadays there are materials that are used to produce prototypes and end‐user parts. Powders might be made from metals, ceramics, polymers, and composites. The union or fusion of the particles is made by the energy provided by a heated environment and a laser beam. Parts are built based on data extracted from its CAD design. The process has many variables that directly affect the mechanical properties of the parts. One important and direct processing parameter is laser energy density. This work evaluated the effect of the variation of the energy density in the mechanical properties of a polymeric material by changing laser beam speed and average power. The analyzed variables were stress at 10% of elongation, flexural modulus, and density of the samples built with polyamide 2200 (PA2200‐EOSINT) using a CO₂ laser (10 W). Specimens obtained by combination of different laser powers (2.7, 3.4, and 4.1 W) and laser scan speeds (39.0, 44.5, and 50.0 mm/s) were submitted to flexural tests. Additionally, volumetric density was calculated with mass and physical dimensions of specimens, and micrograph were taken using scanning electron microscope to analyze the changes of the sintering degree. The results indicated that laser power had more influence over density and mechanical properties than scan speed. The microstructures presented good correlation with the statistical results. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Monitoring the effects of selective laser sintering (SLS) build parameters on polyamide using near infrared spectroscopy

Near infrared spectroscopy has been used to monitor the effects of changing build parameters on the sintering process of selective laser sintering components. The surface roughness of the parts produced has been studied whilst modifying laser scan speed and laser power build parameters. Near infrared spectroscopy is shown to be a powerful tool in detecting subtle variations in the coalescence of particles that form the surface topology of the component. Principal component analysis (PCA) performed on the diffuse reflectance spectra obtained from the surface of the components shows a strong correlation between near infrared (NIR) spectra and build parameters. Using the chemometric model produced from the PCA analysis it is possible to calculate build parameters for unknown components, making NIR a useful aid for quality control of additive manufacturing technologies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011