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激光金属沉积成形过程热行为的研究
Alternative TitleResearch on Thermal Behavior during Laser Metal Deposition Shaping Processing
龙日升1,2
Department现代装备研究室
Thesis Advisor刘伟军
ClassificationTG665
Keyword激光金属沉积成形 扫描方式 基板预热 组织性能分析 工艺实验研究
Call NumberTG665/L79/2009
Pages113页
Degree Discipline机械电子工程
Degree Name博士
2009-01-15
Degree Grantor中国科学院沈阳自动化研究所
Place of Conferral沈阳
Abstract激光金属直接快速成形技术是在80年代末期出现的快速原型技术(Rapid Phototyping, RP)基础上结合同步同轴送料激光熔敷(On-axis Laser Cladding)技术发展起来的一项先进制造技术。它涉及机械、激光、计算机辅助设计(CAD)、计算机辅助制造(CAM)、计算机数字控制(CNC)、材料科学等领域的关键技术。它突破了传统快速成形工艺方法和成形材料的局限,是目前快速成形诸多方法中研究最多、最有发展前途的新型制造技术。它基于材料累加思想,能够在无需任何刀具和模具的情况下由CAD模型直接驱动沉积成形金属零件,从而大大缩短了新产品的研发周期并节省了大量的资源。中国科学院沈阳自动化研究所开展了该技术的研究,并研制开发了激光金属沉积成形系统(Laser Metal Deposition Shaping, LMDS)。本文介绍了金属零件激光直接快速成形技术的原理和特点,分析了当前金属零件激光快速成形过程数值模拟研究的热点和发展趋势。结合激光金属沉积成形系统的研究需要和遇到的实际问题,阐述了激光、金属粉末和基板三者之间的相互作用,利用有限元的方法数值模拟了各种影响成形精度和效率的因素对激光金属沉积成形系统过程热行为的影响,包括不同扫描方式、不同基板预热温度等,并利用激光金属沉积成形系统系统进行了验证。具体的研究内容如下: 1. 阐述了激光与金属粉末之间的相互作用。激光快速成形过程中,高功率激光束与基板金属交互作用产生熔池,同步送入的金属粉末在熔池内被迅速熔化然后迅速凝固。熔池内的冶金动力学过程包括传热、传质、对流及气-液界面冶金反应和固-液界面扩散等与工艺质量的好坏密切相关,直接影响成形零件内气体和夹渣物的吸收、聚集和逸出,进而影响成形零件的微观组织、成分变化及其它物理冶金性能。基于熔池内传质、传热及流动对成形层的组织和性能的决定性作用,建立了激光金属沉积成形过程的数学模型和有限元模型。 2. 利用有限元分析中的“单元生死”技术,通过APDL语言编程建立了激光金属沉积成形系统过程三维多道多层的数值模拟模型,得到了激光金属沉积成形系统过程中试样和基板内的温度、温度梯度以及热应力分布规律。 3. 研究了沿长边平行往复扫描、沿短边平行往复扫描以及层间正交变向平行往复扫描等不同扫描方式对激光金属沉积成形系统过程热行为的影响,得到了不同扫描方式下试样和基板的温度、温度梯度和热应力变化规律,并结合快速凝固理论对这一过程中出现的现象进行解释。 4. 为了实现基板的预热,根据热传导理论自主设计开发了用于激光金属沉积成形系统过程的基板预热系统。该系统由基板预热器、智能PID控制器以及计算机串口温度检测和反馈控制等部分组成,具有结构简单、功能完善、可靠性高等特点。它既可以通过智能PID控制器实现对基板预热温度的控制,也可以通过计算机串口实现对基板预热温度的实时检测、记录以及反馈控制,从而使基板预热温度在室温~600℃之间连续调节。此外,它的计算机串口温度检测模块还可以用来实现对激光金属沉积成形系统成形过程基板温度的实时监测,为数值计算提供较为准确的边界条件以及用来检验和校正数值模型的正确性与可靠性。 5. 利用数值模拟的方法研究了基板预热温度分别在室温、200℃、300℃、400 ℃、500 ℃、600 ℃时对激光金属沉积成形系统过程温度、温度梯度以及热应力的影响。在相同的条件下,利用激光金属沉积成形系统系统和基板预热系统进行了实际成形实验。对成形实验得到的试样进行了深入的研究,包括:成形试样的成形高度和表面质量与基板预热温度的关系;成形试样的利用扫描电镜分析成形试件沉积层的显微组织特征;利用能谱仪分析沉积层合金元素的化学成分偏析情况。 6. 建立了集数值模拟和成形加工于一体的软件平台。它既可以实现简单零件变模型尺寸、变热物性参数和变工艺参数的数值模拟,也可以直接驱动激光金属沉积成形系统完成简单零件的快速成形。这为研究各工艺参数如激光功率、扫描速度、送粉速率、光斑尺寸以及基板预热温度等对激光金属沉积成形系统过程的影响提供了一个平台。
Other AbstractLaser metal directive rapid shaping is a new advanced manufacturing technology developed from the rapid prototyping technique which appeared in the late 1980s and the synchronous coaxial-feeding laser cladding technique. It is the integration of several techniques, including mechanical engineering, CAD/CAM/CNC, material science etc., and it breaks through the limitation of the traditional rapid prototyping technology and shaped material. For its fabricating ability of fully-dense metal parts, laser metal directive rapid shaping is the most researched and the most developing future in the rapid prototyping means. Based on the material accumulation idea, metal parts can be fabricated directly from CAD models automatically and rapidly without any part-specific tooling. At the same time, the development cycle of new product can be significantly shortened and lots of resources can be saved, too. The research of laser additive direct deposition is conducted by Chinese Academy Sciences Shenyang Institute of Automation since the late 1990s, and a promising rapid manufacturing system called “Laser Metal Deposition Shaping, LMDS” has been successfully constructed and developed. In this paper, the principles and characteristics of laser metal directive rapid shaping are introduced; the hotspots and developing trends of numerical simulations during metal rapid fabricating are analyzed. For the actual demands and encountered problems of LMDS, the interactions among laser, metal powder and substrate are elaborated. The effects of those factors which influence the fabrication efficiency and quality of parts on thermal behavior during LMDS processing are numerically simulated by using FEM, including different scanning methods, different substrate preheating temperatures and different process parameters etc. The results are verified by LMDS system. The specific research details are listed as following: 1. Expatiate on the interaction between laser and metal powder. During the laser rapid prototyping processing, the molten pool on substrate is generated by the high-power laser beam, and the metal powder which sent simultaneously into in the pool is rapidly melting and then rapidly solidified. The kinetics of metallurgical processes within molten pool, including heat transfer, mass transfer, convection, gas-liquid metallurgical reaction and solid-liquid interface proliferation etc., are closely related to the goodness and badness of technological quality. They have direct impacts on the absorption, accumulation and escaption of the gas and slag inside the shaped parts. Ulteriorly, it affects the microstructure, composition changes and other physical metallurgical performance of the formed parts. Based on the decisive role of formed layers, the mass transfer, heat transfer and flow-forming within molten pool to the organization and performance of shaped layers, the mathematical and finite element model have been formed. 2. According to the “element life and death” technique of finite element method (FEM), a three-dimensional multi-track & multi-layer numerical model for LMDS is developed with ANSYS parametric design language (APDL). The regularities of temperature, temperature gradient and thermal stress in sample and substrate are obtained. 3. The effects of long edge reciprocating scanning method, short edge reciprocating scanning method and direction orthogonal changing in different layers reciprocating scanning method to thermal behavior during whole LMDS process are studied. The dynamic distribution regularities of thermal stress and temperature under different scanning methods are researched in detail. Combining with the rapid solidification theory, the phenomena arisen in the process are interpreted. 4. In order to realize the preheating of substrate, based on thermal conduction theory, the substrate preheating system for LMDS has been constructed by self-development. It consists of substrates preheater, intelligent PID controller and computer serial temperature measurement & feed-back control components. The system holds integrated structure, perfect function and high reliability. The preheating temperature of substrate can be controlled through intelligent PID controller, or through computer serial preheating temperature real-time detecting, recording and feed-back control. The preheating temperature of substrate can be continuously regulated from room temperature to 600℃. Moreover, its computer serial temperature detection module can also be used to achieve the substrate temperature LMDS forming process real-time monitoring, to provide more accurate numerical boundary conditions and used to test and calibration accuracy of the numerical model and reliability. 5. Using numerical simulation method, the effects of preheating temperature at room temperature, 200℃, 300℃, 400℃, 500℃ and 600℃ on temperature, temperature gradient and thermal stress during LMDS process are researched. Under the same conditions, the actual experiments are conducted by using LMDS system and substrate preheating system. By virtue of analysis equipment, detailed experimental operations were conducted: the relationship between forming height, surface quality of samples and preheating temperature are researched; the microstructure characteristics of the as-deposited parts were analyzed by Scanning Electron Microscope (SEM); the micro-segregation of chemical composition of clad was measured by Energy Dispersive Spectroscopy (EDS). 6. Provide a set of software platform which combines numerical simulation with forming. It can be used to simulate the shaping process of those simple parts which have variable model size, variable thermal parameters and variable process parameters, and it can also direct-drive laser deposition of metal parts forming completed simple Rapid Prototyping. This study various process parameters such as laser power and scanning speed, powder feed rate, spot size, the impact on the process of LMDS provides a platform.
Language中文
Contribution Rank1
Document Type学位论文
Identifierhttp://ir.sia.cn/handle/173321/384
Collection智能产线与系统研究室
Affiliation1.中国科学院沈阳自动化研究所
2.中国科学院研究生院
Recommended Citation
GB/T 7714
龙日升. 激光金属沉积成形过程热行为的研究[D]. 沈阳. 中国科学院沈阳自动化研究所,2009.
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