Process energy analysis and optimization in selective laser sintering

Additive manufacturing (AM) processes are increasingly being used to manufacture complex precision parts for the automotive, aerospace and medical industries. One of the popular AM processes is the selective laser sintering (SLS) process which manufactures parts by sintering metallic, polymeric and ceramic powder under the effect of laser power. The laser energy expenditure of SLS process and its correlation to the geometry of the manufactured part and the SLS process parameters, however, have not received much attention from AM/SLS researchers. This paper presents a mathematical analysis of the laser energy required for manufacturing simple parts using the SLS process. The total energy expended is calculated as a function of the total area of sintering (TAS) using a convex hull based approach and is correlated to the part geometry, slice thickness and the build orientation. The TAS and laser energy are calculated for three sample parts and the results are provided in the paper. Finally, an optimization model is presented which computes the minimal TAS and energy required for manufacturing a part using the SLS process.     

A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing,microstructure, and properties

Manufacturing businesses aiming to deliver their new customised products more quickly and gain more consumer markets for their products will increasingly employ selective laser sintering/melting (SLS/SLM) for fabricating high quality, low cost, repeatable, and reliable aluminium alloy powdered parts for automotive, aerospace, and aircraft applications. However, aluminium powder is known to be uniquely bedevilled with the tenacious surface oxide film which is difficult to avoid during SLS/SLM processing. The tenacity of the surface oxide film inhibits metallurgical bonding across the layers during SLS/SLM processing and this consequently leads to initiation of spheroidisation by Marangoni convection. Due to the paucity of publications on SLS/SLM processing of aluminium alloy powders, we review the current state of research and progress from different perspectives of the SLS/SLM, powder metallurgy (P/M) sintering, and pulsed electric current sintering (PECS) of ferrous, non-ferrous alloys, and composite powders as well as laser welding of aluminium alloys in order to provide a basis for follow-on-research that leads to the development of high productivity, SLS/SLM processing of aluminium alloy powders. Moreover, both P/M sintering and PECS of aluminium alloys are evaluated and related to the SLS process with a view to gaining useful insights especially in the aspects of liquid phase sintering (LPS) of aluminium alloys; application of LPS to SLS process; alloying effect in disrupting the surface oxide film of aluminium alloys; and designing of aluminium alloy suitable for the SLS/SLM process. Thereafter, SLS/SLM parameters, powder properties, and different types of lasers with their effects on the processing and densification of aluminium alloys are considered. The microstructure and metallurgical defects associated with SLS/SLM processed parts are also elucidated by highlighting the mechanism of their formation, the main influencing factors, and the remedial measures. Mechanical properties such as hardness, tensile, and fatigue strength of SLS/SLM processed parts are reported. The final part of this paper summarises findings from this review and outlines the trend for future research in the SLS/SLM processing of aluminium alloy powders.     

To evaluate the change in release from solid dispersion using sodium lauryl sulfate and model drug sulfathiazole

The solubility of drugs remains one of the most challenging aspects of formulation development. There are numerous ways to improve the solubility of drugs amongst which the most promising strategy is solid dispersion. Different ratios of sulfathiazole: PVP-K29/32: sodium lauryl sulfate (SLS) were prepared (1:1:0.1, 1:1:0.5, 1:1:1) and various methods were employed to characterize the prepared solid dispersions, namely modulated differential scanning calorimeter, X-ray powder diffraction, Fourier Transformed Infrared Spectroscopy and dissolution studies. Lack of crystallinity was observed in internal and external systems suggesting a loss of crystallinity, whereas the physical mixtures showed a characteristic peak of sulfathiazole. In vitro dissolution results clearly showed that the incorporation of a relatively small amount of surfactants (5, 20 or 33% w/w) into a solid dispersion can improve its dissolution rates compared to binary solid dispersion (SD) alone and pure sulfathiazole. In all ratios solid dispersion internal shows a higher dissolution rate compared to a physical mixture and solid dispersion external which suggests that the way that the surfactant is incorporated into the solid dispersion plays an important role in changing the solubility of a drug. The solubilization mechanism is mainly responsible for this higher dissolution rate when we incorporate the SLS in SD.     

一种支持移动IPv6和QoS的新型服务管理模型

提出了一种新型的服务管理体系结构模型 ,它基于移动IPv6 ,并且在服务传输期间支持QoS。在这种体系结构中 ,为了支持服务请求和绑定注册等操作 ,扩展了服务定位协议和AAA协议。另外 ,这里提出了一新观点 :将所有的服务 ,如DHCP、带宽代理和AAA服务等都考虑成服务代理 ,它们可以向目录代理注册服务。最后 ,给出了实现时的一些信令交互     

SLS快速成形机软件系统的开发

介绍了新软件的结构体系和主要功能,详细阐述了基于VC平台的SLS快速成形机软件系统的开发过程,并对软件开发中的若干技术问题进行了探讨.     

Viscoelastic Properties and Creep-Fatigue Behavior of PA2200/HA Composites Manufactured by Selective Laser Sintering

Porous(polyamide/hydroxyapatite)composites were manufactured via SLS(selective laser sintering)process.Specimens with different PA2200/HA contents(100/0;95/5;90...     

无底柱分段崩落法端壁倾角与步距关系模拟优化

针对某铁矿进一步加大结构参数,利用自主研发的无底柱分段崩落法放矿计算机模拟系统,对试验方案进行了模拟,获得不同端壁倾角和不同步距间的关系;同时通过实验室物理放矿试验确定了最优步距。试验取得的成果可为该铁矿18 m×20 m结构参数下实现试验矿块的安全、高效、低成本回采的目标提供技术支撑。     

SLS快速成形机CNC系统抗干扰设计

针对新型选择性激光烧结快速成形机CNC系统的开发，分析了外部和内部的电磁和激光器噪声，从线路设计、电源处理、隔离、屏蔽、滤波、接地等方面提出了一系列抗干扰措施。     

QBONE中带宽代理的应用

介绍了Internet3组织建立的区分服务实验床－－QBONE以及带代理（BandWidth Broker）。提出了一种应用带宽代理实现端到端的资源预留的模式。     

Fundamentals of Selective Laser Melting of alloyed steel powders

The successful fabrication of dense iron-based parts by selective laser melting (SLM) is still limited to a narrow range of materials. This study aims at gaining an understanding of the effect of elements such as oxygen, carbon, silicon, titanium and copper on the quality of two-dimensional and three-dimensional iron-based objects. The results are related to the effect of the elements on physical phenomena such as laser absorption, heat transfer, wetting and spreading of the melt, oxidation, Rayleigh instability and Marangoni convection.