Fundamental Research on a Novel Double-Pulse Laser Micro Sintering Technology

选择性激光烧结(SLS)是一种能够快速、灵活地制造复杂金属零件的添加制造工艺。用来制造微米级部件或具有微米级特征的部件的SLS工艺可称为激光微细烧结(LMS)。与LMS相关的一个挑战是，很难实现完全致密的金属部件。通过这一奖项，将研究一种新的双脉冲激光微烧结工艺(DP-LMS)。这种新工艺有可能增强致密化(减少内部空洞)，从而改善LMS生产的零件的机械性能。研究的重点是了解材料在DP-LMS过程中的瞬时响应，并随后建立相关的过程-结构-性能关系。所获得的知识也可能与涉及金属粉末烧结的其他材料加工和合成工艺相关。DP-LMS工艺的成功实施具有巨大的潜力，可以积极影响那些可能受益于快速灵活地制造微米级复杂部件的应用，如MEMS或微型医疗设备。预计研究生和本科生都将参与这项研究，工艺原理和/或新发现将直接纳入当前的制造课程和将向公众提供的视频。具体的研究目标是：(1)验证在DP-LMS过程中，适当地发送两个脉冲可以有效地帮助材料在不增加表面粗糙度的情况下进行致密化的假设；(2)从根本上了解DP-LMS过程中目标材料的传热、相变、熔体流动和致密化过程；(3)建立DP-LMS过程的工艺-结构-性能关系。研究内容包括：(1)利用快速热分析、快速成像和发射光谱技术对DP-LMS过程进行现场研究，以测量目标温度、表面形貌变化和等离子体性质。(2)发展了一个基于连续介质力学的模型，以了解目标材料在DP-LMS过程中的热、流体传输和相变。该模型将通过任务1中的实验测量来验证。和(3)通过光学显微镜和电子显微镜、X射线衍射和硬度测试来表征烧结材料的组织和力学性能。

Selective laser sintering (SLS) is an additive manufacturing process capable of rapidly and flexibly producing complex metallic parts. An SLS process, which is set up to manufacture micron sized components or components with micron scale features, can be called 'laser micro sintering' (LMS). One challenge associated with LMS is that fully dense metallic components are difficult to achieve. Through this award a novel double-pulse laser micro sintering process (DP-LMS) will be investigated. This new process has the potential to enhance the densification (reduce internal voids), and hence improve the mechanical properties of parts produced by LMS. The research focuses on understanding the material's transient responses during the DP-LMS process, and subsequently establishing the relevant process-structure-property relationships. The knowledge gained is also potentially relevant to other material processing and synthesis processes involving metal powder sintering. Successful implementation of the DP-LMS process has great potential to positively impact applications that may benefit from rapid and flexible fabrication of complex components with micron scale aspects such as MEMS, or micro medical devices. It is expected that both graduate and undergraduate students will be involved in the research, and that process principles and/or new findings will be incorporated directly into a current manufacturing classes and a video that will be made available to the public. The specific research objectives are: (1) to test the hypothesis that during DP-LMS, suitably sending the two pulses can effectively help material densification with little increase of its surface roughness; (2) fundamentally understand the heat transfer, phase change, melt flow, and densification process in the target material during DP-LMS; and (3) establish the process-structure-property relationships for the DP-LMS process. The research tasks include: (1) in-situ study of the DP-LMS process using fast pyrometry, fast imaging, and emission spectroscopy to measure target temperatures, surface morphology variations, and plasma properties. (2) Development of a continuum-mechanics based model to understand the thermal and fluid transport and phase changes in the target material during the DP-LMS process. The model will be validated by the experimental measurements in task 1. And (3), characterization of the sintered material microstructures and mechanical properties through optical and electron microscopy, X-ray diffraction and hardness testing.