激光选择性烧结金属粉末快速成形的研究

描述了激光选择性烧结金属粉末快速成形设备的粉末供给和铺平压实系统及动作，探讨了烧结过程参数对烧结质量的影响，粘结剂含量、孔隙率和缺陷尺寸与烧结件压缩强度之间的关系，并指出影响激光选择性烧结的重要因素是烧结粉末的特性、激光参数的设置等。     

激光选择性烧结金属粉末快速成形的研究

描述了激光选择性烧结金属粉末快速成形设备的粉末供给和铺平压实系统及动作,探讨了烧结过程参数对烧结质量的影响,粘结剂含量、孔隙率和缺陷尺寸与烧结件压缩强度之间的关系,并指出影响激光选择性烧结的重要因素是烧结粉末的特性、激光参数的设置等。     

青铜-镍粉末直接选择性激光烧结的研究

简要分析了选择性激光烧结的成形机制及其工艺和材料影响因素。详细分析了青铜一镍粉末直接选择性激光烧结的材料组分以及磷元素对烧结成形质量的影响。具体讨论了粉床温度、粉层厚度、激光功率以及激光扫描速率和方向等工艺参数对烧结件致密度和强度等机械性能的影响     

选择性激光烧结成形温度场的研究进展

选择性激光烧结技术与传统铸造工艺相结合,为快速制造某些难以用传统方法获得的铸件提供了有利途径.对于各种粉末材料在选择性激光烧结成形过程中温度场的模拟与预测,是合理选择其烧结工艺参数的基础.本文中综述了聚合物粉末、聚合物覆膜金属/陶瓷粉末和金属粉末在选择性激光烧结过程中的热物性参数变化规律及其相应的成形温度场分布,以利于激光选择性烧结各类粉末材料而精确成形零部件.     

多组分铜基金属粉末选区激光烧结致密化机理

研究了选区激光烧结专用多组分铜基金属粉末(组分包括纯Cu,预合金CuSn,CuP)的烧结性能.结果表明,通过合理控制激光工艺参数(特别是激光功率和扫描速率),能顺利实现粉末烧结成形,且无明显的"球化"效应和翘曲变形.扫描电镜和X射线衍射分析证实,此组粉末体系的激光烧结是基于液相烧结机制,其中熔点较低的CuSn充当粘结金属,熔点较高的Cu充当结构金属;而添加元素P则起稀释剂的作用,能避免Cu颗粒表面氧化.研究了粉末体系中粘结金属含量对粉末烧结致密化和烧结件微观组织的影响.结果表明,在一定范围内粘结金属含量的提高有利于改善烧结致密度;但若粘结金属过量,则会因"球化"效应而降低致密度.     

青铜-镍粉末直接选择性激光烧结的研究

简要分析了选择性激光烧结的成形机制及其工艺和材料影响因素。详细分析了青铜-镍粉末直接选择性激光烧结的材料组分以及磷元素对烧结成形质量的影响。具体讨论了粉床温度、粉层厚度、激光功率以及激光扫描速率和方向等工艺参数对烧结件致密度和强度等机械性能的影响。     

FGH95粉末激光直接烧结的微观组织及力学性能

基于直接激光金属烧结快速成形(DLMS)技术,进行了FGH95镍基高温合金粉末的烧结成形试验,主要分析了激光烧结工艺参数对烧结制件的微观组织和拉伸强度的影响.分析结果表明:制件组织结构由胞状枝晶组成,γ1相其比例及大小受工艺参数影响较大.较高的激光功率、较快的扫描速度以及合适的扫描间距组合可获得较高的拉伸强度,制件拉伸强度最高可达730 MPa.     

多组分铜基金属粉末选择性激光烧结成形的工艺研究

对多组分铜基金属粉末(组分包括纯Cu,预合金CuSn和CuP)进行了选择性激光烧结试验,其成形机制为粉末部分熔化状态下的液相烧结机制.研究了激光功率、光斑直径、扫描速率、扫描间距、铺粉厚度等工艺参数对粉末激光烧结致密化的影响.为便于整体调控激光烧结过程,本文将各工艺参数综合为"能量体密度"这一个参数,结果表明,增加激光功率或减小扫描速率能增加液相生成量,且利于液相的铺展和流动,进而提高润湿性和烧结性;扫描速率越高,则越易引起"球化"现象.减小铺粉厚度有利于获得较好的层间结合,并提高烧结致密度;若铺粉厚度过小,会降低铺粉均匀性,进而有损层间结合性.减小扫描间距使烧结线从断续分布转变为较为平整的结合状态,进而提高烧结致密度.当能量体密度增至一临界值(约0.15 kJ/mm3)时,烧结致密度有显著提高;但若增至过高(大于0.30 kJ/mm3),烧结致密度则呈下降趋势.     

塑料粉末选择性激光烧结收缩实验研究

针对塑料粉末材料激光烧结过程中成形质量不高的问题,设计实验,分析了收缩对成形精度的影响,得到了制件的收缩规律,给出了改善选择性激光烧结制件精度的具体方式.     

选区激光烧结WC-10%Co颗粒增强Cu基复合材料的显微组织

利用选区激光烧结工艺制备了WC-10%Co颗粒增强Cu基复合材料,其中WC-Co和Cu的质量比为30:70.X射线衍射和扫描电镜分析证实,粉末激光成形是基于液相烧结机制,其中Cu,Co充当粘结相,WC充当增强相;而激光作用的非平衡性导致形成亚稳相CoC0.25.WC增强颗粒具有3种典型形态(未熔且团聚、部分熔化且部分团聚、熔化且弥散),表明粒径较大的WC以颗粒重排为主要成形机制,而粒径较小的WC则以溶解-析出为主导机制.烧结试样显微硬度平均值HV0.1为3898 MPa,且分布平稳.     

Microstructural evolution during direct laser sintering of multi-component Cu-based metal powder

A multi-component Cu-based metal powder was chosen for direct laser sintering. The powder consists of a mixture of high-purity Cu powder, pre-alloyed CuSn and CuP powder. Liquid phase sintering with complete melting of the binder （CuSn） but non-melting of the cores of structural metal （Cu） proves to be a feasible mechanism for laser sintering of this powder system. The microstructural evolution of the sintered powder with variation of laser processing parameters was presented. High sintering activities and sound densification response were obtained by optimizing the laser powers and scan speeds. Using a high laser power accompanied by a high scan speed gives rise to baUing effect. At a high laser power with a slow scan speed the sintering mechanism may change into complete melting/solidification, which decreases the obtainable sintered density. The role of additive phosphorus in the laser sintering process is addressed. Phosphorus can act as a fluxing agent and has a preferential reaction with oxygen to form phosphatic slag, protecting the Cu particles from oxidation. The phosphatic slag shows a concentration along grain boundaries due to its light mass as well as the short thermal cycle of SLS.     

Fabrication and microstructure characterization of selective laser‐melted FeAl intermetallic parts

Selective laser melting was considered in this study with the goal to manufacture dense parts with mechanical properties comparable to those of bulk materials, directly from FeAl intermetallic powder. Based on a series of single line scans, the processing window was first explored, paying attention to the melting mechanisms. Then, FeAl samples were produced using various selected parameters according to the previously established processing map. These samples were investigated in terms of microstructure, surface roughness, densification and microhardness. Observations revealed that these characteristics are strongly dependent on the processing parameters. Finally, interesting FeAl specimens with a relatively high density (98% of the theoretical value), high microhardness and smooth surface were obtained using a laser power of 90 W and a scanning speed of 0.2 m/s, corresponding to a continuous melting mechanism of the powder bed.     

Physico-chemical behaviour of Poly (Ether Ketone) (PEK) in High Temperature Laser Sintering (HT-LS)

Laser sintering (LS) of polymers has high potential for growth as a manufacturing technique into a wide range of applications provided the range of engineering polymers available for LS expands and machines and LS process conditions are optimised for such materials.This study is the first investigation into laser sintering of both virgin and used polyether ketone (PEK) powder using a bespoke high temperature (HT) polymer laser sintering machine (known commercially as EOSINT P800). The physico-chemical results reveal that, in spite of polymer degradation, used PEK has a viable processing window for LS manufacturing which, combined with optimisation of specific parameters can successfully lead to manufacture of good quality parts. The proposed sintering mechanism of both, virgin and used powders is supported by the experimental data. The incorporation of 30% used HP3 PEK powder led to an approximately 17% drop in tensile strength.     

New Ferro Powder for Selective Laser Sintering of Dense Parts

The paper describes a new powder composition specially developed for selective laser sintering (SLS). The aim is to obtain a ferro powder that can be sintered without need for a (sacrificial) polymer binder and that results in quasi dense parts that do not need any post-processing like furnace sintering, infiltration or HIP. The powder is a mixture of different types of particles (Fe, Cu, Ni and Fe₃P). The composition and mixture ratio are justified by using phase diagrams. The powder has been tested using an own developed Nd: YAG SLS machine. The influence of process parameters (laser power, scan velocity, scan spacing and scan strategy) and the microstructural characteristics have been investigated. Attention is devoted to the binding mechanism (liquid phase sintering, through melting) and to the quality of resulting parts (density, balling effect,…).     

Densification mechanism and microstructural evolution in selective laser sintering of Al-12Si powders

The role of processing parameters on the densification mechanism and microstructural evolution in laser sintered Al-12Si powder has been explored. It was established that both the densification mechanism and microstructural evolution in laser sintered Al-12Si powder were controlled by the specific laser energy input. Analysis of the cross-section of laser sintered microstructures of Al-12Si powders indicated that the tops of the grains in the previous layer are partially re-melted and then undergo epitaxial growth in the next layer where the heat affected zones (HAZ) grain boundaries and solidification grain boundaries (SGBs) are continuous along the fusion boundary.     

Selective laser sintering mechanism of polymer-coated molybdenum powder

A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine （HLRP-350I）. The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting/solidification when the temperature is above 160 ℃.     

MICROSTRUCTURES OF LASER SINTERED MICRON/ NANO-SIZED Cu-W POWDER

研究了激光烧结工艺条件下微/纳米Cu-W粉体致密化的过程及对显微组织的影响. 结果表明,合理增加激光功率或降低扫描速率, 可提高烧结致密度及组织均匀性; 降低扫描间距至0.15 mm, 可改善烧结表面光洁度; 铺粉厚度降至0.15 mm, 可提高烧结层间结合性. 经工艺优化, 最高成形致密度达到95.2%, 且在烧结组织中形成一系列规则的W环/Cu芯结构; 并探讨了该结构的成形机制.     

Effect of total applied energy density on the densification of copper–titanium slabs produced by a DMLF process

The effect of process parameters (laser scan step, scan speed and furnace initial temperature) on the densification degree of copper–titanium single layer slabs produced by a DMLF process is presented here. For each parameter, varied at three levels, specimens were made. An increasing powder densification degree for increasing initial temperature and decreasing scan step and speed was found, when performed at 63 mTorr of oxygen partial pressure in an argon rich atmosphere. However, decrease in densification at large energy densities (50 J/mm³) occurred. Total applied energy density and powder densification results were fitted to an exponential asymptotic curve using least square error criterion. Reduction in densification at a high energy density plus observation of the asymptotic behavior of the fitted model, are likely because the oxidation of the material inhibits sintering/partial melting of the powder.     

Development and characterisation of direct laser sintering Cu-based metal powder

Direct laser sintering of metal powder is a promising manufacturing process to produce rapid moulds (or rapid tooling) because complex three-dimensional (3-D) metal parts can be created directly from computer-aided design (CAD) data without machining or use of additional tooling. However, material and process are still the crucial issues that restrict its wider adoption although the technology has been introduced more than 7 years. This paper characterises a self-developed Cu-based metal powder used for direct laser sintering. The material system is Cu-based alloy metal powder, which consists of two metal powders: high-purity Cu powder and pre-alloyed SCuP metal powder. The scanning electron microscope (SEM), XRD and energy dispersive X-ray (EDX) analyses show that the bonding mechanism of this process is liquid-phase sintering. The pre-alloyed SCuP metal powder with lower melting point (645 °C) acts as the binder during laser sintering, while the Cu powder with higher melting point (1083 °C) acts as the structure. The element phosphorus in the powder can act as flux to protect the Cu oxidisation. A case study on fabricating the inserts of a mobile phone cover mould was also carried out. The inserts were created in ambient atmosphere at room temperature. The total sintering time is 40 h. Sixty five percent relative theoretical density and average surface roughness R_a 14–16 μm were achieved with negligible distortion and curling. Epoxy infiltration was employed as post-process to improve the density and the strength of the sintered tooling. The mould inserts were used to inject ABS-PC mobile phone cover after polishing. No defects were found after moulding of 500 components.