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Alternative TitleResearch on the Produce Metal Parts Key Technology by Laser Rapid Prototyping Methods
Thesis Advisor王越超 ; 刘伟军
Keyword激光快速成形 数值模拟 扫描方式 工艺参数 Logistic回归模型
Call NumberTH166/K48/2012
Degree Discipline模式识别与智能系统
Degree Name博士
Degree Grantor中国科学院沈阳自动化研究所
Place of Conferral沈阳
Abstract激光快速成形技术是在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覆(On-axis Laser Cladding)技术发展起来的一项先进制造技术。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。本文针对制约金属零件激光快速成形技术发展的“变形开裂”重大技术难题,研究长期剧烈热循环作用下零件内应力演化规律和零件变形开裂机理,发展非稳态温度场和应力场数值模拟分析方法和实验测试方法,揭示零件激光沉积成形制造过程中的非稳态热力耦合行为、非稳态温度场和应力场的演化规律、内应力形成机理以及零件变形与开裂形成机理,取得一系列的成果,具体研究内容如下: 1. 根据有限元法中的单元生死技术,利用APDL 语言编程实现对多道多层激光金属沉积成形过程三维温度场和应力场的数值模拟,并对熔池与粉末、激光与粉末的相互作用进行能量补偿,更加准确地计算成形过程中温度场和应力场的动态变化,得到成形过程中模型温度场、温度梯度、热应力场和残余应力的分布规律。并使用相同的工艺参数进行了验证实验,并得到误差很小的实验结果。 2. 使用ANSYS有限元软件分析研究了不同扫描方式和工艺参数对激光快速成形方法制备金属零件过程的热力耦合场及残余应力场分布规律的影响,得到了不同扫描方式及不同工艺参数下试样和基板的温度、热应力变化规律及残余应力分布,并且使用与验证实验相同的参数进行实验验证。 3.在Linux环境下,使用VC++和Fortran语言,对激光快速成形方法制备金属零件过程中所涉及的基本现象的微观组织机理进行了仿真,主要内容有熔化,凝固,相变,断裂等。主要目的是深入研究快速成型过程中合金组织形成规律及内部缺陷形成机理,一定程度的为内应力控制的研究提供了理论基础。 4.进行单道的激光快速成形实验,通过宏观和微观的判定方法对样件质量进行评价,得到各工艺参数对样件质量的影响。并对实验得到的样件进行深入的研究,如:利用游标卡尺测量成形试样的高度;利用扫描电镜分析成形试件沉积层的显微组织特征;使用X-射线衍射仪测定沉积层表面的物相分布;利用能谱仪分析沉积层合金元素的化学成分偏析情况;使用显微硬度计对沉积层的硬度分布进行测试和分析。通过Logistic回归模型,重新对工艺实验进行设计,并对实验结果进行归纳和分析,得到最佳的工艺参数。
Other AbstractLaser metal 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. 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. In order to solve the important problem that deformation and fracture of the metel part manufacturing with Laser metal deposition, study on the internal stress changing rule and mechanism of deformation and fracture of part which under long term violent thermal cycling, and developing method of the numerical simulation and the experiment measurement of non-steady state thermo-mechanical coupling field. The research results including: 1.In order to control the thermal stress of forming process, based on “element birth and death” technology of finite element method, a numerical simulation of three-dimensional temperature field and stress field during multi-track & multi-layer laser metal deposition process is developed with ANSYS parametric design language (APDL). The dynamic variances of temperature field and stress field of forming process are calculated with the energy compensation of interaction between molten pool - powder and laser-powder. The temperature field, temperature gradient, thermal stress field and distribution of residual stress are obtained. Finally, it’s verified that the analysis results are consistent with actual situation by the experiments with same process parameters. 2.Study on the effects of different scanning methods and parameter processing on thermal-stress couple field and residual stress distribution during direct laser metal deposition process. In this paper, according to the “element life and death” technique of finite element method, with APDL, we simulated the effects of difficult scanning method and parameter processing in different layers reciprocating scanning method to thermal-stress couple field and residual stress distribution during whole process. The dynamic regularities of thermal stress, temperature and residual stress distribution under different scanning methods are studied in detail. With the same process parameters, the samples fabricated by laser metal deposition show good agreement with the simulation results. 3.Metal micro-dynamics was simulated in Linux With "VC++" and "Fortran" .It including melt, solidification, fracture, phase transition, etc. It provides the theoretical basis for internal stress and residual stress controlling. 4. Research on the LMD process (e.g. laser power, scanning velocity, powder addition speed, ration of overlap etc). Evaluating the sample quality by macro-quality criteria and quality criteria, to obtain the effect of parameter processing. By virtue of analysis equipment, detailed experimental operations were conducted: the forming height of samples are measured by using slide calipers; the microstructure characteristics of the as-deposited parts were analyzed by Scanning Electron Microscope (SEM); the phase distribution of clad surface was tested by X-Ray; the micro-segregation of chemical composition of clad was measured by Energy Dispersive Spectroscopy (EDS); the hardness distribution of clad was detected by sclero-meter.
Contribution Rank1
Document Type学位论文
Recommended Citation
GB/T 7714
孔源. 激光快速成形方法制备金属零件关键技术研究[D]. 沈阳. 中国科学院沈阳自动化研究所,2012.
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