碳化硅零件的激光选区烧结及反应烧结工艺

为了获得高密度、高性能、复杂结构的碳化硅陶瓷件,提出采用机械混合法制备含有黏结剂和乌洛托品固化剂的碳化硅复合粉体,对复合粉体进行激光选区烧结（SLS）形成陶瓷素坯,并对素坯进行气氛烧结和渗硅处理,使其与基体发生反应烧结,最终形成复杂陶瓷异形件。实验证明：若激光功率为8.0 W、扫描速率为2 000 mm/s、扫描间距为0.1 mm、单层厚度为0.15 mm,获得的 SLS 陶瓷样品密度和强度最好。对SLS试样进行合理的中温碳化和高温渗硅,所得碳化硅陶瓷烧结体的抗弯强度最高可达 81 MPa,相对密度大于86%。     

一种新型材料3D打印性能及应用研究

本文提出了一种用于激光选区烧结(Selective Laser Sintering,SLS)成形的新型粉末材料KZF。研究了其适合进行SLS成形的粉末制备工艺,基于不同的激光加工工艺参数,得出了最优工艺参数。在最优工艺参数下SLS成形KZF粉生坯体具有较高的初始强度,得出了成形KZF生坯所需粘接剂的最低含量,和具有的强度值。研发了SLS成形的KZF生坯件的后处理材料、配方及工艺规范,研究了经确定最佳后处理规范后的KZF SLS成形件的力学性能以及微观组织的影响,确定了提高KZF生坯强度的材料及含量,经后处理后的KZF粉SLS成形件的弯曲强度提升幅度最大达273倍。本文为制造复杂形状的KZF成形件提供了一种新的思路与方法,并扩大了SLS成形材料的应用范围。     

一种新型材料3D打印性能及应用研究

本文提出了一种用于激光选区烧结(Selective Laser Sintering,SLS)成形的新型粉末材料KZF。研究了其适合进行SLS成形的粉末制备工艺,基于不同的激光加工工艺参数,得出了最优工艺参数。在最优工艺参数下SLS成形KZF粉生坯体具有较高的初始强度,得出了成形KZF生坯所需粘接剂的最低含量,和具有的强度值。研发了SLS成形的KZF生坯件的后处理材料、配方及工艺规范,研究了经确定最佳后处理规范后的KZF-SLS成形件的力学性能以及微观组织的影响,确定了提高KZF生坯强度的材料及含量,经后处理后的KZF-SLS成形件的弯曲强度提升幅度最大达273倍。本文为制造复杂形状的KZF成形件提供了一种新的思路与方法,并扩大了SLS成形材料的应用范围。     

氮化硅陶瓷球冷等静压过程有限元模拟及试验验证

利用Abaqus软件对氮化硅陶瓷球的冷等静压(CIP)成形过程进行了数值模拟,分析了氮化硅陶瓷球在CIP成形过程中致密度的变化和粉末颗粒的流动规律,研究了其应力分布,并进行了试验验证,结果表明:在CIP成形过程中,致密化曲线可分为4个阶段,相对密度的分布存在环形密度差现象,试验证明该工艺可以改善氮化硅陶瓷球压坯密度和组织结构分布的均匀性。     

新的激光快速成形方法及应用

针对目前主要激光快速成形方法的优缺点,提出一种基于三维实体边界分割的激光快速成形新方法.该方法将叠层实体制造(LOM)法主要进行激光二维轮廓线扫描和选择性激光烧结(SLS)法能够加工多种覆膜粉末材料的优点有机结合,能够克服SLS法加工效率低,成形件致密度、硬度、精度和表面粗糙度等性能较低的缺点.利用自主开发的快速成形系统,采用热像仪测温与Ansys模拟激光能量输入模型相结合的方法对工艺参数进行确定,对基于三维实体边界分割激光快速成形方法进行应用研究,实现三维实体的快速成形及金属零件的快速铸造,并通过无模具快速铸造的手段获得金属齿轮铸件.     

预烧结温度对多孔氧化锆陶瓷孔隙率和力学性能的影响

将氧化锆亚微米粉干压、冷等静压成型后在8501 100℃下进行预烧结,制得了多孔氧化锆陶瓷,研究了预烧结温度对陶瓷孔隙率、硬度和抗弯强度的影响;然后对多孔氧化锆陶瓷进行铣削试验,获得了适合铣削的多孔氧化锆陶瓷的预烧结温度。结果表明:随着预烧结温度升高,氧化锆陶瓷的孔隙率降低,硬度和抗弯强度增加;当预烧结温度高于1 000℃后,陶瓷颗粒间会形成烧结颈,将大幅提高陶瓷的力学性能;适合铣削的多孔氧化锆陶瓷的预烧结温度为1 050℃。     

名词解释

<正>三维印刷成形法(3DP,Three Dimension Printing)三维印刷(3DP)工艺与SLS工艺类似,采用粉末材料成形,如陶瓷粉末、金属粉末。所不同的是材料粉末不是通过烧结连接起来的,而是通过喷头用粘接剂(如硅胶)将零件的截面"印刷"在材料粉末上面。用粘接剂粘接的零件强度较低,还需后处理。先烧掉粘接剂,然后在高温下渗入金属,使零件致密化,提高强度。目前,该工艺已被美国的Soligen公司以DSPC(Direct Shell Production Casting)名义商品化,用以制造铸造用的陶瓷壳体和芯子。精密模锻精密模锻是在一般模锻基础上发展起来的一种少及无切削的加工工艺。与一般模锻相比,它能获得表面质量好,     

ZrO2对激光烧结Al2O3/SiO2/ZrO2显微组织和显微硬度的影响

在Nd:YAG激光器低功率烧结的条件下,基于选择性激光烧结工艺（SLS）成形复相陶瓷Al2O3/SiO2/ZrO2材料,利用扫描电子显微镜（SEM）、X射线衍射分析仪（XRD）和显微硬度计分别对激光烧结层加入ZrO2前后的表面形貌和断口形貌、表面物相、表面显微硬度进行了分析。结果表明,部分四方相ZrO2(t-ZrO2)相变成单斜相ZrO2(m-ZrO2),应力诱导微裂纹增韧作用和Al2O3弥散强化共同作用在某种程度上提高了烧结试样的断裂韧性,对于改善零件整体寿命和可靠性有着重要的意义。     

冷等静压工艺对纳米WC-8Co硬质合金性能的研究

以纳米WC-8Co粉末和VC、Cr3C2、TaC晶粒长大抑制剂作为YG8硬质合金原料,采用金属模压预成型+冷等静压处理获得压坯,后经真空烧结制备WC-8Co硬质合金.研究冷等静压工艺对硬质合金收缩率、致密度、硬度的影响,结果表明经冷等静压处理的生坯烧结后的硬质合金具有低收缩率、高致密度和硬度的特点.     

选择性激光烧结激光能量密度与温度补偿规律研究

选择性激光烧结（SLS）成型预热温度从成型缸中间到缸壁呈降低趋势,由于预热温度不均匀,导致SLS成型件密度不均匀。针对这一问题,通过增加激光能量密度对预热温度不足进行了补偿。通过试验建立了激光能量密度差△E与预热温差△T的经验公式,并比较了温度补偿前后烧结件的机械强度。实验结果表明,通过增加激光能量密度对预热温度不足进行补偿,提高了产品机械强度。     

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.     

Manufacturing AISI304 metal parts by indirect selective laser sintering combined with isostatic pressing

In order to improve the lower relative densities and mechanical performance of metal parts manufactured by indirect selective laser sintering (SLS), cold isostatic pressing (CIP) technology is introduced into SLS combined with hot isostatic pressing (HIP). In the process of SLS/CIP/HIP, the degreasing of SLS green parts was carried out according to the thermal gravity curve of the binder. Then, airproof canning made of RTV-2, CH₃COOCH₂CH₃, Si(OEt)₄, and Bu₂Sn(OCOC₁₁H₂₃)₂ prepared for CIP was manufactured. Finally, the densifications and mechanical performance of the metal parts were analyzed. The results show that the degreasing process is rational, airproof canning made of RTV-2, CH₃COOCH₂CH₃, Si(OEt)₄, and Bu₂Sn(OCOC₁₁H₂₃)₂ is suitable for CIP, and the relative densities of AISI304 metal parts manufactured by SLS/CIP/HIP reach 98%, with their tensile strengths, yield strengths, Young’s modulus, and elongation percentages being 577.5 MPa, 306 MPa, 93.15 GPa, and 32.05%, respectively. Consequently, dense metal parts with better mechanical performance can be manufactured by SLS/CIP/HIP, and the process has a vital contribution to the development of SLS.     

Moulage par injection de poudres métalliques. Expérimentation,modélisation et simulation

Metal injection moulding. Experiment, modelling and simulation. The metal injection moulding process is used to produce small and complex metallic components. The first step is the injection of a mixture composed by a metallic powder and a thermoplastic binder. The binder is eliminated by a thermal or catalytic debinding. The last step is the sintering in order to obtain a part with the correct size and required mechanical properties. The metal injection moulding process is analysed using both experiments and computational modelling. A numerical approach for biphasic mixtures has been developed to analyse the flow of the feedstock during injection. The solution of the Navier–Stokes equations is made by an implicit finite element method. The mould filling simulation uses an Eulerian formulation with a VOF method. The simulation gives the density field in order to detect the segregation zones leading to an anisotropic shrinkage. The modelling of the solid state sintering is based on a viscoplastic model. The results obtained by experiments and numerical simulations are compared and reveal a good agreement. Furthermore, the components obtained after injection, debinding and sintering have the correct size and required mechanical properties.     

Investigation into the selective laser sintering of styrene–acrylonitrile copolymer and postprocessing

The amorphous polymer of polystyrene (PS) has been widely used in the selective laser sintering (SLS) process. However, PS is not suitable to make parts with thin-wall or delicate structures because of the poor mechanical properties of its SLS parts. Therefore, styrene–acrylonitrile copolymer (SAN), another kind of amorphous polymers, was investigated as an SLS material. The effects of laser energy density on the relative density, mechanical properties, and dimensional accuracy of the SLS parts were studied, and the properties of PS and SAN SLS parts were compared. The postprocessing method of infiltrating with epoxy resin was used to reinforce the green SAN SLS parts. The results show that there is little difference in the relative density between the SAN and PS SLS parts, while the flexural strength of the SAN SLS specimens is obviously higher than that of the PS SLS specimens at the same energy density. After the postprocessing, the flexural strength, flexural modulus, and impact strength of the SAN SLS specimens increase by 133%, 4394%, and 254%, respectively, and the SLS parts maintain relatively high-dimensional accuracy although slight shrinkage occurs due to epoxy resin cure. SAN can be used to fabricate SLS parts with more complex and delicate structures.     

Development of a feedstock formulation based on polypropylene for micro-powder soft embossing process of 316L stainless steel micro-channel part

To exploit the potential of micro-system technology, the micro-powder embossing process, a rapid manufacturing production technology of microstructured die mould, was currently being investigated. Present work focused on establishing a suitable binder system for micro-powder embossing process. Multi-component binder systems, comprising of different weight percentages of paraffin wax, stearic acid and polypropylene were investigated. The compatibility between binder constituents was studied by thermogravimetric analysis (TGA) showing a partial miscibility between both components. The feedstock comprised of 316L stainless steel powder, and a wax-based thermoplastic binder was used to achieve a feedstock with 60 to 68 vol.% powder loading. The degradation temperature of binders was determined by using TGA and flow behaviour through rheometer. Homogeneity of the feedstock was verified by using TGA and scanning electron microscopy. Then, hot embossing was done, and it was found that the feedstock having solid loading up to 68 vol.% were successfully embossed, and components were without physical defects. The polymeric part was driven off by thermal debinding using a thermal cycle designed on the basis of a thermogravimetric study of the binder. Finally, the vacuum sintering of the parts allows high quality parts to be obtained.     

尼龙粉末激光烧结的数值模拟与实验分析

激光选区烧结热传导对成型物有着直接影响。基于点热源热传导理论,建立了尼龙粉末材料的激光高斯热源热传导方程,通过理论和实验分析,得到了尼龙粉末（PA6）材料的有效热传导系数和密度比热系数,为后续工艺优化提供了理论基础。     

A macroscale FEM-based approach for selective laser sintering of thermoplastics

A numerical approach to model the selective laser sintering (SLS) of polypropylene is proposed. A 3D thermal model was developed and thus enables the prediction of the temperature fields and the extension of the sintered area in the powder bed taking into account the phase change during multiple laser passes. Powder–liquid, liquid–solid and solid–liquid phase changes were modelled during the SLS and the subsequent cooling processes. Then, a 3D thermomechanically coupled model was set up based on the temperature results of the thermal model in order to predict the distortion of the produced parts after cooling down. Different pre-heating temperatures were considered, highlighting their influence on the final part properties.     

选择性激光烧结金属件精度和密度的研究

金属件成形精度和密度是快速成形技术在工业应用中的关键问题之一。通过对覆膜金属粉末选择性激光烧结 ,研究了激光烧结工艺参数激光功率、扫描速度、扫描间距、单层层厚 ,烧结体厚度对金属件成形精度和密度的影响关系 ,并得出了一个分析 X、Y轴方向尺寸误差的定性公式 ,给出了烧结工艺参数优化的方法 ,而且优化了一组烧结工艺参数 ,用此工艺参数成功烧制出金属原型件     

Process optimization for PA12/MWCNT nanocomposite manufacturing by selective laser sintering

Nanocomposites produced through the addition of carbon nanotubes to a polymeric matrix can improve the material properties. The mobility of the polymer chains is usually affected, and this is also related to the properties. Parts produced with the free-form fabrication process using the selective laser sintering (SLS) technique can be used in different high-performance applications as they do not require expensive tools for their manufacture. A specific field of interest is the aerospace industry which is characterized by a low production volume and the need for materials with a high performance to weight ratio. In this study, the free-form fabrication by SLS of parts made from nanocomposites comprised of polyamide 12 and multiwalled carbon nanotubes (MWCNTs) was investigated. Specimens were manufactured by SLS to identify the appropriate processing parameters to achieve high mechanical properties for aerospace applications. Laser energy density was adjusted to improve the material density, flexural modulus, and stress at 10 % elongation. Design of experiments was used to identify and quantify the effects of various factors on the mechanical properties. The results obtained showed that there was a limit to the amount of MWCNTs which could be mixed with the polyamide powder to improve the mechanical properties since a higher content affected the laser sintering process.