基于选择性激光烧结生物陶瓷复合粉体的工艺研究

主要研究了复相陶瓷Al2O3-ZrO2-SiO2单层烧结工艺,采用Nd:YAG激光器通过选择性激光烧结(SLS)成型复相陶瓷Al2O3-ZrO2-SiO2,实现了在不添加粘结剂、不作任何后处理的情况下激光束完全熔化样品。采用试验设计法系统地分析了激光烧结各项工艺参数对单层烧结质量的影响。利用SEM、XRD分析了不同工艺参数下单层烧结的显微结构以及对试样性能的影响,并通过试验确定最优工艺参数。而后,分别研究了t-ZrO2相对复合粉体的增韧效果与莫来石对改善零件强度所起的作用,对改善零件整体寿命和可靠性有着重要的意义。     

Fabrication and characterization of three-dimensional poly(ether- ether- ketone)/-hydroxyapatite biocomposite scaffolds using laser sintering

The ability to have precise control over porosity, scaffold shape, and internal pore architecture is critical in tissue engineering. For anchorage-dependent cells, the presence of three-dimensional scaffolds with interconnected pore networks is crucial to aid in the proliferation and reorganization of cells. This research explored the potential of rapid prototyping techniques such as selective laser sintering to fabricate solvent-free porous composite polymeric scaffolds comprising of different blends of poly(ether-ether-ketone) (PEEK) and hydroxyapatite (HA). The architecture of the scaffolds was created with a scaffold library of cellular units and a corresponding algorithm to generate the structure. Test specimens were produced and characterized by varying the weight percentage, starting with 10 wt% HA to 40 wt% HA, of physically mixed PEEK-HA powder blends. Characterization analyses including porosity, microstructure, composition of the scaffolds, bioactivity, and in vitro cell viability of the scaffolds were conducted. The results obtained showed a promising approach in fabricating scaffolds which can produce controlled microarchitecture and higher consistency.     

Development and application of new composite materials as EDM electrodes manufactured via selective laser sintering

The cost of a part manufactured by electrical dischargeEDM machining (EDM) is mainly determined by electrode cost. The production of electrodes by conventional machining processes is complex, time consuming, and can account for over 50 % of the total EDM process costs. The emerging additive manufacturing (AM) technologies provide the possibility of direct fabrication of EDM electrodes. Selective laser sintering (SLS) is an alternative AM technique because it has the possibility to directly produce functional components, reducing the tool-room lead time and total EDM costs. The main difficulty of manufacturing an EDM electrode using SLS is the selection of an appropriate material, once both processes require different material properties. The current work focused on the investigation of appropriate materials that fulfill EDM and SLS process demands. Three new metal-matrix materials composed of Mo–CuNi, TiB₂–CuNi, and ZrB₂–CuNi were developed and characterized. Electrodes under adequate SLS conditions were manufactured through a systematic methodology. EDM experiments using different discharge energies were carried out, and the performance evaluated in terms of material removal rate and volumetric relative wear. The results showed that the powder systems composed of Mo–CuNi, TiB₂–CuNi, and ZrB₂–CuNi revealed to be successfully processed by SLS, and the EDM experiments demonstrated that the new composite electrodes are promising materials. The work also suggests important topics for future research work on this field.     

基于正交实验的多孔金属激光烧结成型工艺的研究

文章介绍了正交实验设计法的特点及其对实验研究的科学指导作用。正交实验设计法可以用少数几个代表性的实验代表全面实验。采用正交试验设计和直观分析的方法,对影响激光烧结多孔金属的各因素进行研究,从而找出了最佳工艺参数。     

Fabrication of porous bioactive structures using the selective laser sintering technique

Hydroxyapatite, a ceramic with which natural bone inherently bonds, has been incorporated into a polymer matrix to enhance the bioactivity of implant materials. In order to manufacture custom-made bioactive implants rapidly, selective laser sintering has been investigated to fabricate hydroxyapatite and polyamide composites and their properties investigated. One objective of this research was to identify the maximum hydroxyapatite content that could be incorporated into the matrix, which was sintered at various parameters. The study focused on investigating the control of porosity and pore size of the matrix by manipulating the selective laser sintering parameters of the laser power and laser scan speed. The interception method was used to analyse the internal porous morphology of the matrices which were cross-sectioned through the vertical plane. Most notably, all structures built demonstrated interconnection and penetration throughout the matrix. Liquid displacement was also used to analyse the porosity of the matrices. The laser power showed a negative relationship between porosity and variation in parameter values until a critical power value was reached. However, the same relationship for laser scan speed matrices was inconsistent. The effects of the laser power and laser scanning speed on the features of porous structures that could influence cell spreading, proliferation, and bone regeneration are presented.     

Investigation into manufacturing injection mold via indirect selective laser sintering

Cooling system of an injection mold is important for the promotion of production rate and the quality of injection plastic components. Conformal cooling channels are newly developed temperature-adjusting method to promote the efficiency of cooling system. They can be made in the injection mold inserts via the method of indirect selective laser sintering combined with traditional powder metallurgy. This work discussed some processes such as thermal transmission, powders removing, and metal melt infiltration during the manufacturing of the mold inserts in detail. The result showed that redundant powders outside of laser-scanned areas might be sintered together with the sintered parts owing to the accumulation of laser energy during sintering process. This was solved by switching the temperature to initial level after one layer had been sintered. A limit length corresponding to some certain power vacuum system was found when the removal of unsintered powders in the cooling channels was carried out. Therefore, some subsidiary channels leading the cooling channels outside were made to help the removal of powders within the cooling channels. Dripping method was adopted during metal melt infiltration process, which was proven to be relevant for maintaining of the final shape of infiltrated inserts.     

316L不锈钢多孔结构的选区激光烧结成型工艺研究

研究了一种新型的制备金属多孔结构技术-选区激光烧结,着重说明该技术的基本原理和工艺过程,并利用此制备技术对316L不锈钢粉末进行了激光烧结制备多孔材料的实验研究.利用SEM分析了316L不锈钢多孔试样的微观孔隙特征,并测定其孔隙率.结果表明,在较高的扫描速率下可获得孔径分布均匀、孔隙贯通性良好的多孔结构;随扫描速率逐渐提高,试样孔隙率和弹性模量呈上升趋势.     

SLS烧结实验的优化设计

激光功率、扫描速度、铺粉厚度、预热温度及扫描间距是影响SLS成型质量的主要因素.通过激光快速成型机AFS-450制作专门的样件,采用正交试验和方差分析,对SIS成型工艺参数进行优化设计.确定了ABS粉末最佳的烧结参数,即预热温度为100℃、扫描速度为2000mm/s、激光功率为24W、铺粉厚度为0.2mm.     

Research on manufacturing Cu matrix Fe-Cu-Ni-C alloy composite parts by indirect selective laser sintering

The property of alloy parts can be adjusted conveniently if alloy element powders are used for manufacturing alloy parts by indirect selective laser sintering (SLS), but there have been no reports in this field. Fe, Cu, Ni, C composite powders of two compositions were obtained through a 3D blending way in this paper. Green parts of above composite powder were manufactured by indirect SLS. Then, Cu matrix Fe-Cu-Ni-C alloy composites were produced after green parts had been depolymerized, high temperature sintered and infiltrated by molten Cu. The post-processing of green parts, microstructure and mechanical properties of alloy composites were investigated. The results show: Ni, Cu and C diffuse into γ-Fe when green parts are being sintered at high temperature and the distributing non-uniformity of alloy elements is eliminated basically; at room temperature, alloy composite microstructures are composed of lower bainite, α-Cu precipitated out of γ-Fe and Fe-Ni after they have been solution treated at 930°C and held at 350°C for 1 h later; the yield strength of alloy composites is near to 400 MPa and the elongation is under 3%. It can be used for manufacturing injection mold or other functional parts by indirect SLS.     

Fabrication of porous polymeric matrix drug delivery devices using the selective laser sintering technique

New techniques in solid freeform fabrication (SFF) have prompted research into methods of manufacturing and controlling porosity. The strategy of this research is to integrate computer aided design (CAD) and the SFF technique of selective laser sintering (SLS) to fabricate porous polymeric matrix drug delivery devices (DDDs). This study focuses on the control of the porosity of a matrix by manipulating the SLS process parameters of laser beam power and scan speed. Methylene blue dye is used as a drug model to infiltrate the matrices via a degassing method; visual inspection of dye penetration into the matrices is carried out. Most notably, the laser power matrices show a two-stage penetration process. The matrices are sectioned along the XZ planes and viewed under scanning electron microscope (SEM). The morphologies of the samples reveal a general increase in channel widths as laser power decreases and scan speed increases. The fractional release profiles of the matrices are determined by allowing the dye to diffuse out in vitro within a controlled environment. The results show that laser power and scan speed matrices deliver the dye for 8-9 days and have an evenly distributed profile. Mercury porosimetry is used to analyse the porosity of the matrices. Laser power matrices show a linear relationship between porosity and variation in parameter values. However, the same relationship for scan speed matrices turns out to be rather inconsistent. Relationships between the SLS parameters and the experimental results are developed using the fractional release rate equation for the infinite slab porous matrix DDD as a basis for correlation.     

Development of lunar regolith composite and structure via laser-assisted sintering

Aiming at the exploration and resource utilization activities on the Moon, in situ resource utilization and in situ manufacturing are proposed to minimize the dependence on the ground transportation supplies. In this paper, a laser-assisted additive manufacturing process is developed to fabricate lunar regolith composites with PA12/SiO₂ mixing powders. The process parameters and composite material compositions are optimized in an appropriate range through orthogonal experiments to establish the relationship of process–structure–property for lunar regolith composites. The optimal combination of composite material compositions and process parameters are mixing ratio of 50/50 in volume, laser power of 30 W, scanning speed of 3500 mm/s, and scanning hatch space of 0.2 mm. The maximum tensile strength of lunar regolith composites reaches 9.248 MPa, and the maximum depth of surface variation is 120.79 μm, which indicates poor powder fusion and sintering quality. Thereafter, the mechanical properties of laser-sintered lunar regolith composites are implemented to the topology optimization design of complex structures. The effectiveness and the feasibility of this laser-assisted process are potentially developed for future lightweight design and manufacturing of the solar panel installed on the lunar rover.     

Densification of alumina components via indirect selective laser sintering combined with isostatic pressing

To improve the final density of ceramic parts via indirect selective laser sintering (SLS), cold/hot isostatic pressing (CIP/HIP) technologies were introduced into the process. The proposed approach in the present study combined spray drying with mechanical mixing by which we prepared a kind of compound powder consisting of polyvinyl alcohol (PVA, 1.5 wt%), epoxy resin E06 (8 wt%), and alumina so as to get a good fluidity for SLS. At the first step, SLS parts reached the highest relative density of about 32 % when the laser energy density was 0.094 J/mm², which facilitated the next operation and improvement of final density. Then, a soft polymer canning was prepared for CIP around the surface of SLS alumina ceramic parts using pre-vulcanized natural rubber latex RTV-2, gelation and film. Following that, we experimented on different CIP maximum pressure which had different effects on densification of SLS alumina parts, the whole process in CIP was divided into three stages of I, II, and III. Based on thermal gravity curve of epoxy resin E06, ignoring the impacts of the only 1.5 wt% PVA on degreasing, green bodies were degreased and furnace-sintered. Finally, the relative density of alumina parts reached 95.94 % after HIP process. Field emission scanning electron microscopy was used to analyze the densification evolvement in each stage of process and the fracture mechanism. The study showed a positive and practical approach to manufacture ceramic matrix and ceramic components with complex shape by indirect SLS technology.     

Towards selective laser sintering of objects with customized mechanical properties based on ANFIS predictions

Recently, the adaptive network-based fuzzy inference system (ANFIS) has been used extensively in modeling of manufacturing processes to save both optimization time and manufacturing costs. ANFIS is a powerful iterative tool for optimizing non-linear and multivariable manufacturing operations. In the present study, ANFIS is used to predict the optimum manufacturing parameters in selective laser sintering (SLS) of cement-filled polyamide 12 (PA12) composite. For this purpose, a set of cement-filled PA12 test specimens is manufactured by SLS technique with 8 different values of laser power (4.5–8 Watt) and 8 different weight fractions of white cement (5 %–40 %). Mechanical characterization of cement-filled PA12 is carried out to evaluate the ultimate tensile strength (UTS), compressive strength, and flexural properties. The experimental data are then divided into two groups; one group for training the ANFIS model and the other group for checking the validity of the identified model. The built ANFIS model was validated experimentally and comparison with experimental results revealed mean relative errors of 2.92 %, 3.84 %, 4.75 %, and 3.31 % in the predictions of UTS, compressive strength, flexural modulus, and flexural yield strength, respectively.

     

Optimizing process parameters for selective laser sintering based on neural network and genetic algorithm

Selective laser sintering (SLS) is an attractive rapid prototyping (RP) technology capable of manufacturing parts from a variety of materials. However, the wider application of SLS has been limited, due to their accuracy. This paper presents an optimal method to determine the best processing parameter for SLS by minimizing the shrinkage. According to the nonlinear and multitudinous processing parameter feature of SLS, the theory and the algorithms of the neural network are applied for studying SLS process parameters. The process is modeled and described by neural network based on experiment. Moreover, the optimum process parameters, such as layer thickness, hatch spacing, laser power, scanning speed, work surroundings temperature, interval time, and scanning mode are obtained by adopting the genetic algorithm based on the neural network model. The optimum process parameters will be benefit for RP users in creating RP parts with a higher level of accuracy.     

选择性激光烧结主要成型材料的研究进展

简要介绍了选择性激光烧结的原理以及特点,比较和分析了几种选择性激光烧结主要成型材料的特点和国内外的研究现状,展望了选择性激光烧结材料的展前景.     

Effect of delay time on part strength in selective laser sintering

Selective laser sintering (SLS) is one of the most popular layered manufacturing processes used for making functional prototypes of polymers and metals. It is a powder-based process in which layers of powder are spread and laser is used to sinter selected areas of preheated powder. In the present work, experimental investigations have been made to understand effect of delay time on SLS prototypes. Delay time is the time difference for laser exposure between any two adjacent points on successive scanning lines on a layer. Tensile specimens of polyamide material as per the ASTM standard are fabricated on SLS machine keeping delay time range constant for the entire specimen. Specimens are fabricated for different ranges of delay time and tested on universal testing machine for tensile strength. An optimum value of delay time range is obtained experimentally. As delay time depends on part build orientation, an algorithm has been developed and implemented to find out optimum part build orientation for improving tensile strength. The obtained results from developed code are validated experimentally for tensile specimen. Case study for a typical 3D part is also presented to demonstrate the capabilities of developed algorithm.     

Surface microgeometry after selective laser sintering of metal powder

A multifactorial model is proposed for the surface microgeometry after selective laser sintering of metal powder. The dependence of the microgeometry on the following dominant factors is established: the laser power, the speed of the laser beam, and the scanning increment.     

Fuzzy set based cost model of additive manufacturing with specific example of selective laser sintering

A fuzzy set based cost model for additive manufacturing is proposed. The model is illustrated through an example of selective laser sintering (SLS), a commonly used additive manufacturing (AM) process. Initially, a deterministic cost model is developed. It is then converted to a fuzzy set based model by considering uncertainty in build time estimation and cost components. For the specific case of SLS, a build time estimation procedure is developed as a part of the cost model. A method to evaluate the reliability of the cost estimate in AM and its significance is also introduced. The cost model is illustrated through two examples of products manufactured by SLS.

     

激光选区烧结成型材料的研究和应用现状

介绍激光快速成型的原理及SLS对材料性能的要求,概括激光选取烧结成形技术中各种材料的研究和应用现状,分析SLS技术产业化存在的问题及可能解决的途径。