Numerical simulation of temperature field during selective laser sintering of polymer-coated molybdenum powder

The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the temperature field during length-alterable line-scanning and laser sintering of polymer-coated molybdenum powder was presented. Finite element method （FEM） was used to simulate the temperature field during laser sintering process. In order to verify the simulated results, a measuring system was developed to study the laser sintering temperature field. Infrared meter was introduced to measure the surface temperature of sintering powder; the temperature of its inside part was measured by thermocouple. The measured results were compared with the numerical simulation results; the conformity between them is good and the relative error is less than 5%.     

Selective laser sintering of polymer-coated Al2O3／ZrO2／TiC ceramic powder

A type of polymer-coated Al2O3/ZrO2/TiC ceramic powder was prepared. The laser sintering mechanism of polymer-coated Al2 O3/ZrO2/TiC powder was investigated by studying the dynamic laser sintering process.It is found that the mechanism is viscous flow when the sintering temperature is between 80 ℃ and 120 ℃, and it is melting/solidification when the temperature is above 120 ℃. The process parameters of selective laser sintering were optimized by using ortho-design method. The results show that the optimal parameters include laser power of 14 W,scanning velocity of 1 400 mm/s, preheating temperature of 50 ℃ and powder depth of 0.15 mm. A two-step posttreatment process is adopted to improve the mechanical properties of laser sintered part, which includes polymer debinding and high temperature sintering. After vacuum sintering for 2 h at 1 650 ℃, the bending strength and fracture toughness of Al2O3/ZrO2/TiC ceramic part reach 358 Mpa and 6.9 Mpa · m1/2 , respectively.     

包覆不锈钢粉末激光烧结深度的影响因素

制备一种用于激光烧结成形的包覆不锈钢粉末。应用数值模拟预测结合实际测量方法,研究激光功率、激光束扫描速度、预热温度及铺粉密度等参数对激光烧结深度的影响。结果表明,随着预热温度、铺粉密度与激光功率增加,烧结深度增加;随着扫描速度增加,烧结深度降低。但当扫描速度不超过2 mm/s时,烧结深度随扫描速度的增加反而增大。提出一种利用数值模拟预测结果进行激光烧结工艺参数选择的方法。     

Ni-CuSn混合粉末选区激光烧结试验

通过对双组分Ni-CuSn混合粉末进行激光烧结试验,表明此组粉末体系成形机制是粉末半熔化状态下的液相烧结机制。详细讨论了激光工艺参数对成形机制及烧结质量的影响,结果表明,将激光功率和扫描速率控制在适宜的范围内,才可实现预期的成形机制,并获得较好的烧结质量。对烧结件显微组织分析表明,组分M和CuSn间存在较为明显的熔点差、及两者之间较高的固溶度,是保证液相烧结机制、获得较高烧结致密度的前提。     

Selective laser sintering of single-phase powder Cr-V tool steel

Presented is positive experience from selective laser sintering (SLS) of cylindrical steel specimens (3.0% C, 3.0% Cr, 1.0% Si, 12.0% V, Fe balance) 30 mm long and 5 mm in diameter by rapid prototyping. It was demonstrated that monolithic steel material could be successfully fabricated by this technology. Differential thermal analysis (DTA), scanning electron microscopy (SEM), and x-ray diffractometry (XRD) were used to study the microstructure, phase, and chemical composition of the source material and obtained specimens. Low-melting cementite-based eutectic was found to provide the liquid phase sintering of powder tool steel. The porosity of the green sintered specimens did not exceed 5%. The mean hardness value of sintered specimens was 825 HV.     

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.     

磷元素对铜基金属粉末选区激光烧结作用机理

对不同CuP含量的多组分铜基金属粉末(Cu-CuSn-CuP)进行了选区激光烧结实验。利用X射线衍射和扫描电镜研究了添加元素P对烧结致密度及显微组织的影响。研究表明:P元素能在烧结过程中充当脱氧剂而与Cu反应生成CuPO3;但当P过量时,则会因熔体过热倾向明显而加剧氧化;适量增加P元素能改善烧结件层间结合性;而P元素过量则会因生成过多磷渣而降低润湿性及致密度;P元素亦能充当稀释剂而降低熔体粘度及表面张力,从而改善烧结致密度及组织均匀性;但若P元素过量时,则会因熔体粘度过低而导致球化现象。实验结果证实,该组铜基金属粉末体系中CuP的最佳含量为15%。     

选择性激光烧结翘曲变形模拟

建立了烧结过程的温度场、弹性应力应变场的有限元计算模型,开发了C++模拟软件,模拟了选择性激光烧结(SLS)过程的温度、残余热应力的演化,以及最终的翘曲变形.提出的改进移动热源加载算法提高了计算速度.研究结果表明:激光烧结过程中温度场不均匀,导致了热应力的产生,进而使制件变形,制件的上下部分收缩不一致,从而向上翘曲.随...     

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.     

Direct laser sintering of a copper-based alloy for creating three-dimensional metal parts

Direct laser sintering of metal, as one of the important developments in rapid prototyping technologies, is discussed in this paper. A special copper-based alloy is used for this rapid prototyping process. Experiments on the sintering conditions of this material had been conducted in a self-developed high temperature metal sintering machine. The mechanism of laser sintering for this kind of material was disclosed by SEM analysis of microstructures of sintered parts. The density, surface roughness and mechanical properties of the laser sintering parts due to variation of process parameters were measured and analysed. The effect of process parameters to the accuracy of sintered parts was also investigated. Thus, optimum parameters were obtained for direct laser sintering of three-dimensional metal parts.     

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.     

Investigating on casting mold (or core) making with coated sand by the selected laser sintering

1 .Introduction Based on the parameters and cross-section's information from a CAD model, the selected laser sintering (SLS) uses a laser beam to sinter selectively powdered solid materials (plastic, wax, ceramic, metal, etc.), and the solidified material is built up layer by layer to formthepart needed} As there are still some problems in material and technology, it is difficulty to sinter or produce directly     

基于选择性激光烧结覆膜金属纳米复合粉末材料的研究进展

综述了选择性激光烧结金属粉末材料和纳米粉末材料的研究进展。介绍了选择性激光烧结覆膜Al-Fe-Ni合金系金属纳米复合粉末材料的开发思路。提出了选择性激光烧结覆膜Al-Fe-Ni合金系金腻纳米复合粉末材料的主要成分与制备方法，并对前景进行了展望。     

Preparation of Mo/Cu composites by SLS method and its post-treatment techniques

A multi-component polymer-coated molybdenum powder was chosen for selective laser sintering（SLS）. The powder was prepared by coating polymer on Mo particles and frozen by grinding techniques. The laser sintering activities and sound densification response were obtained by optimizing the process parameters. The post-treatment process of SLS samples was developed, which was high temperature sintering Mo framework combined with Cu impregnation. Then, the Mo/Cu composites are gained. The microstructure evolution of post-treatment samples was investigated by scanning electron microscopy. Mo grains frequently string together. The microstructural characterization of Mo/Cu composites is homogeneous compound structure of adhesive phase Cu linked with Mo grains. There is little ellipsoidal Mo grains singly existing around Cu phase. Between Mo grains and Cu zone, there is a medium changing zone with width of 10-20 nm. Post-treatment mechanism is Mo framework sintering of solid phase and Cu impregnation of melting/solidification. The mechanical and thermal properties concluding tensile strength, elastic modulus, elongation and linear expansion of Mo/Cu composites were studied.     

Fe-C混合粉末激光烧结成形试验

在激光选区成形机上对一定比例的、未添加低熔点粘结剂Fe-C混合粉末进行了烧结工艺试验研究,分析了工艺参数对金属粉末烧结成形的影响,分析了激光功率、扫描间隔、扫描速度与烧结层厚的关系,建立了扫描间隔与烧结层厚之间的关系公式并由试验数据给予了论证.通过烧结件微观结构分析了Fe-C粉末在激光作用下的烧结机制及烧结过程出现的球化现象.获取了合理的烧结工艺参数并烧结出具有一定精度、致密性和复杂的Fe-C金属件.     

基于选择性激光烧结方法的金属零件快速制造技术研究

主要研究了通过选择性激光烧结高分子原型件制造金属零件的工艺。通过采用真空压差铸造工艺。结合铸造型壳的制造，成功制造出金属零件。对基于SLS技术的精密铸造过程中的精度控制进行了研究分析，并提出了解决办法。     

激光快速成形过程中粉末与熔池交互作用的数值模拟

建立了描述激光快速成形过程中气/粉两相流送粉、粉末与熔池交互作用及激光熔覆成形温度场的联合模型.采用有限单元生死技术模拟了熔池形成和自由界面形状演化及熔覆层的沉积过程:根据界面温度与粉末粒子动量损失状况模拟了熔池对粒子的捕捉以及工件对粉末的反射,并采用Lagrangian粒子追踪模型实现了对粉末颗粒的跟踪.在此基础上,模拟了激光快速成形过程中316L不锈钢粉末、激光与熔池的交互作用过程.计算结果与实验结果吻合.     

VIGA法制备的M2052锰铜合金粉末及其SLM打印件的性能

采用真空感应熔炼气雾化法(VIGA)制备了M2052锰铜合金粉末,分析了M2052锰铜粉末的物性和显微组织;用选区激光熔化3D打印技术(SLM)制备锰铜试样,并分析热处理前后SLM成型的锰铜合金的组织与性能。结果表明,VIGA法能够有效地控制金属粉末形状,制备的15~53 μm粒度区间的锰铜粉末收得率高,松装密度高,具有较好的球形度,有效满足SLM用金属粉末的要求。由SLM制备的锰铜打印件横纵向具有不同的微观组织,随熔池内部延伸逐渐变为胞状晶,沿焊接界面形成柱状晶,离熔池越远柱状晶越细。与铸态合金相比,SLM方法制备的锰铜合金具有明显的力学性能差异,SLM打印件的抗拉强度为611 MPa,规定塑性延伸强度为504 MPa,远远高于铸态母合金的454 MPa和172 MPa。其原因是打印件细晶强化效果明显,但微裂纹的存在对塑性不利。