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三轴联动激光切雕一体机设计【原创含7张CAD图带开题报告】

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三轴联动激光切雕一体机设计【含7张CAD图带开题报告】

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充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-1459919609I三轴联动激光切/雕一体机设计THE DESIGN OF THE THREE AXIS LINKAGE LASER CUTTING / ENCARVING MACHINE摘要激光切割和雕刻加工是以数控技术为基础,激光作为加工媒介,使待加工材料在激光的照射下,被照射部位温度瞬间升高,发生熔化和气化,从而达到去除材料的目的。为了提高三轴联动激光切/雕一体机的加工精度并尽可能的降低制造成本,应用现代CAD/CAE 技术来设计和分析三轴联动激光切/雕一体机的相关零部件十分必要。本课题基于既定的性能指标,设计了一种基于同步带和滚柱丝杠传动的三轴联动激光切/ 雕一体机的机械结构。在整个设计过程中,首先对三轴联动激光切 /雕一体机的发展状况进行了调研;其次根据设定好的性能指标,对机器进行整体的设计计算,并对关键零部件进行了校核;然后使用 SolidWorks 建模软件对三轴联动激光切 /雕一体机进行了三维建模、整机装配以及运动仿真工作;最后再利用 ANSYS 完成对三轴联动激光切/ 雕一体机关键部件的静力学分析。主要完成工作如下:1)进行了充分的市场调研,对三轴联动激光切/雕一体机的多种设计方案进行了详细的对比分析之后,确定了三轴联动激光切/雕一体机的总体方案。2)根据所学知识设计三轴联动激光切/雕一体机,并使之达到设定的性能指标。3)使用 SolidWorks 建模软件对三轴联动激光切/雕一体机进行了三维建模、整机装配以及运动仿真工作。4)利用 ANSYS 对三轴联动激光切 /雕一体机的关键部件进行了静力学分析,校核了方案的可行性和合理性。最后采购相关的零部件,进行了机器的实物装配。关键词 三轴联动;激光切/雕;运动仿真;静力学 分析 充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-1459919609II充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-1459919609IIIAbstractLaser cutting and encarving are based on numerical control technology, and laser is used as the processing medium, so that the material to be processed is irradiated by laser, the temperature of the irradiated part rises instantaneously, melting and gasification, so as to achieve the purpose of removing material. In order to improve the machining precision of the three axis linkage laser cutting / encarving machine and reduce the manufacturing cost as much as possible, it is necessary to apply modern CAD/CAE technology to design and analyze the related parts of the three axis linkage laser cutting / encarving machine.Based on the established performance index, this paper designs a mechanical structure of three axis linkage laser cutting / encarving machine based on synchronous belt and roller screw drive. In the whole design process, the development of the three axis linkage laser cutting / encarving machine is investigated. Secondly, according to the set performance index, the machine is designed and calculated as a whole, and the key parts are checked. Then the SolidWorks modeling software is used to carry out the three axis linkage laser cutting / encarving machine. Three dimensional modeling, assembly and motion simulation work, and finally the static analysis of the key components of the three axis laser cutting / carving machine is completed by using ANSYS. The main work is as follows:1) After a full market investigation and a detailed comparison and analysis of the various design schemes of the three axis linkage laser cutting / encarving machine, the overall scheme of the three axis linkage laser cutting / encarving machine is determined.2) Design a three axis linkage laser cutting / engraving machine based on the knowledge, and achieve the set of performance indicators.3) Using the SolidWorks modeling software, the 3D modeling, assembly and motion simulation of the three axis linkage laser cutting / encarving machine were carried out.4) Using ANSYS to analyze the key components of the three axis linkage laser cutting / encarving machine, the feasibility and rationality of the scheme were checked. Finally, the relevant parts were purchased, and the physical assembly of the machine was carried out.Keywords three axis linkage laser cutting / encarving motion simulation statics analysis充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-1459919609I目 录摘要 .IAbstract .II1 绪论 .11.1 三轴联动激光切/雕一体机的原理 .11.2 三轴联动激光切/雕一体机的发展现状 .11.3 本课题研究的内容及意义 .22 三轴联动激光切/雕一体机的总体方案设计 .32.1 三轴联动激光切/雕一体机的总体方案 .32.2 激光器的选型 .42.2.1 激光器的发展历程 .42.2.2 激光器的选型 .43 三轴联动激光切/雕一体机传动系统设计及计算 .63.1 电机的选型 .63.1.1 X 向电机的选型 .63.1.2 Y 向电机的选型 .63.1.3 Z 向电机的选型 .73.2 同步带副的设计 .83.2.1 X 向同步带副的设计 .83.2.2 Y 向同步带副的设计 .103.3 滚珠丝杠副的设计 .123.4 导轨的设计 .163.4.1 X 向导轨的设计 .163.4.2 Y 向导轨的设计 .173.5 联轴器的选型 .174 三轴联动激光切/雕一体机控制系统的设计 .194.1 系统硬件的设计 .194.2 系统的控制软件 .205 基于 ANSYS 的静力学分析 .225.1 ANSYS 简介 .225.2 直线导轨副静力学分析 .225.2.1 X 向横梁静力学分析 .225.2.2 X 向直线导轨静力学分析 .235.3 滚珠丝杠副静力学分析 .25充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-1459919609II6 基于 SolidWorks 的整机 3D 建模及装配 .276.1 同步带副的建模 .276.2 滚珠丝杠副的建模 .276.3 直线导轨的建模 .296.4 联轴器的建模 .296.5 三轴联动激光切/雕一体机的装配及干涉检验 .307 基于 SolidWorks 的运动仿真 .367.1 仿真的意义 .367.2 运动仿真 .368 实物装配 .398.1 三轴联动激光切/雕一体机的实物装配 .398.2 三轴联动激光切/雕一体机的加工参数 .40结论 .42致谢 .43参考文献 .44充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-145991960911 绪论1.1 三轴联动激光切/ 雕一体机的原理激光虽然也是光,但它和普通的光存在着显著的不同,激光一般只在最初极短的一段时间内依赖自发的辐射,而此后的过程则是完全通过激辐射决定的,因此激光本身的颜色十分纯正,几乎是没有发散的方向性的,三轴联动激光切/雕一体机的激光器具有极高的发光强度。三轴联动激光切/雕一体机的工作原理是利用激光器产生激光,然后利用光学镜片的反射和聚焦,最终将聚焦后的光束照射到被加工物上,光能迅速转变为热能,在极短的时间里使得被照射部位温度上升,使其发生物理变化,从而在材料的表面雕刻或切割出设定的形状,从而达到加工目的。激光制造技术是一种具有巨大发展潜力的高柔性、绿色制造技术 1。作为现代特种加工技术的一种,激光加工方式并不是传统的接触式加工,而是通过激光照射的非接触式加工。这种非接触式的加工方式跟传统的接触式加工相比,由于不存在接触摩擦力,加工速度更快,也不存在加工工具的损耗,而且加工精度更高、材料变形更小。就理论而言,激光加工方式可以加工多种材料,但具体的加工参数受到激光器功率的限制 2。功率高的激光器可以在极短的时间内对加工位置释放大量能量,加工材料被照射部位温度会急剧升高,被照射部位的材料会被迅速去除,达到加工目的。激光切割与雕刻技术是将激光束汇聚到待加工材料表面,利用汇聚后激光的能量将加工材料表面熔化或气化形成痕迹以达到雕刻材料表面的目的 3。激光切割与雕刻是激光加工方式的一种,属于热加工方式,加工效果不但受激光功率的影响,而且与加工速度和深度等都有密切关系。激光雕刻与切割主要是在被加工材料的表面进行,可以分为位图雕刻(切割)及矢量雕刻(切割)两类。1.2 三轴联动激光切/ 雕一体机的发展现状激光加工领域是一个极具发展前景的领域,激光被机械从业人员称为“最快的刀” ,是20 世纪最为重大的发明之一。经过各国科学家的不懈努力,激光加工技术日渐成熟,发展速度极快,被广泛应用于机械制造领域。随着激光加工优势的日益凸显,包括我国在内的各个工业大国都将激光加工技术的发展视为未来发展战略的重要一环。以美国为首的西方发达工业国家是激光加工的首创者,他们的研究时间长,经验丰富,技术成熟,是激光加工领域的领导者。例如加拿大的 VIRTEK 公司研发出了激光三维精雕系统(3D laser engraving system) ,在模具制造业中发挥着极为重要的作用。我国在激光研究领域起步晚,在激光加工领域属于追赶者。虽然在近年来国家加大了对相关领域的投入,使我国在激光加工领域取得了长足的进步,但我们也要看到我国在激光精密加工领域的严重不足,相关的技术水平与国外存在着的巨大差距,这使我国充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-14599196092在一些核心元器件的制造领域仍要受到国外厂商的掣肘,对我国的工业发展极为不利。这次中美之间爆发的大规模贸易冲突更使我们清楚的认识到核心技术受制于人的后果,国家号召相关部门与企业瞄准技术前沿,攻克技术难关。我国的相关企业也充分认识到了自身的不足,加大了相关领域的研发力度,这一点是十分值得欣慰的。相信在科研人员的努力之下,我国在激光加工领域一定会奋起直追,达到世界先进水平。1.3 本课题研究的内容及意义本课题旨在设计一台三轴联动激光切/雕一体机,三轴联动激光切 /雕一体机是一台用于雕刻和切割包括玉石、亚克力、塑胶、玻璃、竹木、皮革等材料在内的各种材质的激光雕刻和切割设备。随着现代加工发展对精密化与微细化的要求越来越高,传统的机械加工方式已经无法满足现代工业发展的需求。而激光加工方式作为一种现代加工方式,光斑直径可小到微米量级,且激光束容易控制,易于与精密机械、精密测量技术和电子计算机相结合,因而激光十分适合用于精密微细加工 4。三轴联动激光切/雕一体机设计的主要内容有:三轴联动激光切 /雕一体机的总体方案设计、传动系统设计计算及校核、机架的设计等,并按照国家标准绘制相关图纸。本课题要求设计的主要性能参数:最大幅面为 1000mm600mm,雕刻速度为400mm/s,激光功率为 60W,采用同步带传动方式,最小成形字符 11mm,最大切割厚度 7mm。在激光加工领域内,由于我们国家在相关方面的研究积累不足,发达国家不论是在设备的研发,还是市场经验的积累,都领先我们国家,我们要意识到自身跟发达国家的差距是非常巨大的。因此,我们需要根据实际情况,把握市场需求,研制出一套实用经济的设备。因此,本课题的研究具有一定的实际意义。充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-145991960932 三轴联动激光切/雕一体机的总体方案设计2.1 三轴联动激光切/ 雕一体机的总体方案三轴联动激光切/雕一体机的结构形式多种多样,本课题要求设计的主要性能参数:最大幅面为 1000mm600mm,雕刻速度为 400mm/s,激光功率为 60W,采用同步带传动方式,最小成形字符 11mm,最大切割厚度 7mm。经过反复比较,结合设计的要求,最终确定下面的设计方案:本方案中采用的是固定龙门式结构,激光器在同步带的带动下精确灵活的加工工件,并且运动载荷小,机构简单,造价低,适合选用。三轴联动激光切/雕一体机主要由控制系统、步进电机、XY 向同步带副、XYZ 向导轨、Z 向滚珠丝杠副、联轴器等部分组成。三轴联动激光切/雕一体机的基本结构如图 2-1、2-2 所示。图 2-1 结构原理图 图 2-2 结构原理图三轴联动激光切/雕一体机的 Y 轴方向是由两个平行直线导轨副和同步带副构成,X轴方向由一个横梁、直线导轨副和同步带副构成,X 轴方向的横梁垂直置于在 Y 轴方向的两个平行的直线上;Z 轴方向由两个与丝杠平行的导轨构成。三轴联动激光切/雕一体机的激光器安装在 X 方向导轨上,并由同步传动带带动在 X方向导轨上运动,由滚柱丝杠带动在 Z 轴方向上运动; X 方向的横梁的两端分别通过滑块连接在 Y 方向的两个直线导轨上,并且通过同步带带动在 Y 方向上运动,从而完成雕刻和切割加工。充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-145991960942.2 激光器的选型2.2.1 激光器的发展历程激光器能发射激光的装置。激光的英文 laser 这个词是由最初的首字母缩略词LASER 演变而来,LASER 的意思是“受激辐射光放大器 ”英文的单词的缩写简略。 “受激辐射”的概念是研发激光器的理论依据。20 世纪 40 年代,在电磁辐射和其他微观粒子的研究中量子力学理论被广泛应用,这为激光器的研制工作提供了充分的条件。1953 年微波量子放大器的诞生,加速了激光器的研制。随后科学家又把这一原理应用到了光波频率的研究中,为激光器的问世奠定了基础。1960 年,世界上第一台激光器在美国诞生,激光器的大门由此被打开。此后,各种新型的激光器层出不穷,激光器的研制也成为激光研究领域的热点。2.2.2 激光器的选型从 1960 年休斯顿实验室的科学家梅曼采用脉冲氙灯抽运掺铬的红宝石,制成红宝石激光器以来,激光技术的发展蒸蒸日上,因其具备较好的方向性、单色性、相干性和高亮度等特点,在工业、农业、通信、娱乐、医疗、科研和国防等领域逐步产生深远影响。激光技术日渐成为了信息时代高新技术产业链中的关键一环,并成为一股重要的驱动力量,带动了人民生活的快速变化,推动着科研水平、国民经济建设、国防安全的战略性前进 5。目前市场上激光器的种类多种多样,常用激光器的分为以下几类:(1)CO 2 激光器CO2 激光器是一种常见的气体激光器,在气体激光器中的应用最为广泛。CO 2 激光器中,主要的工作物质由 CO2、氮气、氦气三种气体组成。其中 CO2 是产生激光辐射的气体,氮气及氦气为辅助性气体。加入其中的氦,可以加速 010 能级热弛预过程,因此有利于激光能级 100 及 020 的抽空。氮气加入主要在 CO2 激光器中起能量传递作用,为CO2 激光上能级粒子数的积累与大功率高效率的激光输出起到强有力的作用 6。CO 2 激光器具有以下特点:1)CO 2 激光器是以 CO2、N 2 和 He 三种气体混合在一起作为工作物质的,相对于固体工作物质而言,气体工作物质均匀性良好;2)CO 2 激光器的单色性好;3)CO 2 激光器的谱线范围非常宽;4)CO 2 激光器能够的输出功率较大;5)CO 2 激光器的泵浦方式灵活方便。(2)准分子激光器准分子激光器,一般是利用相对论电子束或者横向的快速脉冲放电实现分子的激励,准分子激光器的输出波长非常短。充值后即可下载预览所包含的全套带图纸源文件压缩包,需要其他课题加 Q-14599196095准分子激光器具有以下特点:1)准分子的寿命极短;2)由于其荧光谱为一连续带,故可以实现波长可调谐运转;3)由于激光跃迁的下能级(基态)的离子迅速离解,激光下能级基本为空的,极易实现粒子数反转,因此量子效率很高,接近 100%,且可以高重复频率运转。(3)Nd:YAG 激光器Nd:YAG 激光器是应用最广泛的一种固体激光器。Nd:YAG 激光器具有以下特点:1)Nd:YAG 激光器的体积小,使用方便;2)Nd:YAG 激光器的加工的范围广泛,广泛使用于金属行业。根据实际应用的情况知道,CO 2 激光器非常适合用于非金属材料的加工;而准分子激光器在精密加工领域的应用十分广泛; Nd:YAG 激光器在金属材料的加工方面的优势十分明显。综合考虑实际的设计情况,本设计选择 CO2 激光器。此激光器的主要性能参数如表 2-1 所示:表 2-1 激光器性能参数表关键元件 激光波长 功率 额定电流 额定电压 冷却方式 光斑模式CO2 封离式激光管450mm 60W 2A 12V 水冷 点状图 2-3 CO2 封离式激光管essandureulationsnedremainsMPawayalues.diateds contributis particularthis case,limitsinvestigedgesre carriedsing.was introduced by Aloke et al. 3. They assumed that the laserlasertoenhance the thermal stresses for driving a propagating crackARTICLE IN PRESSContents lists available at ScienceDirectOptics and LasersOptics and Lasers in Engineering 48 (2010) 1019field. Hardjadinata and Doumanidis 11 introduced a new solidE-mail address: bsyilbas.sa (B.S. Yilbas).adjacent to the hole was plastically deformed and contained thealong a pre-ordained path using simultaneous CO2laser. Lasercleaving of a soda-lime glass substrate was investigated by Kuoand Lin 10. They introduced uncoupled thermal-elastic analysisbased on the finite element method (FEM) to model the stress0143-8166/$-see front matter fax: +99638602949.of the heat affected zone and on the resulting residual stresses. Aphysical model for thermal effects during laser cutting of holescontrol fractures for the fast laser machining of lamina plates.They accommodated the simultaneous scoring technique toaffected zone and residual stress distribution during laser cuttingof the thin sheet plates was carried out by Li and Sheng 2. Theyanalyzed the effects of cutting speed and laser power on the sizeand the model developed was integrated with a probabilisticfracture model to assess the failure probability during thecutting process. Brugan et al. 9 introduced a new methoddetermining the stress levels and fracture during the laser cuttingof ceramics was investigated by Li and Sheng 1. They introduceda hybrid model to predict the fracture initiation while a numericalapproach adopting a plane stress model was employed for thestress analysis. The numerical study for predictions of heatfunction method while accommodating stress evolution duringthe heating and cooling cycles. A model study incorporating theablation process and the thermal stress evolution during the lasercutting of ceramics was carried out by Akarapu and Seqall 8.They used a fixed grid algorithm to model the ablation processwith high temperature, the temperaturlaser processed region attains high vthermal stress generation in the irrahigh cooling rates after the procesformation in this region. This situationcutting of sharp edges or corners. Ingenerated in the edges and cornersthe parts produced. Consequently,stress fields in laser cutting of sharpessential.Considerable research studies welaser cutting and the thermal procest developed in theThis, in turn, results inregion. In addition, thees to the stressly true for laserthe residual stressthe practical usage ofation of thermal andand corners becomesout to examine theThe plane stress modelthermal field induced by the heat source tends to close thesurfaces of the cut in the vicinity of the tip. The elastic thermalstress model was used to predict the stress field during the laserprocessing of ceramics by Modest and Mallison 5. Theypredicted the elastic stress fields as developed and decayedduring the laser processing. The laser cutting technique by acontrolled fracture was introduced by Tsai and Chen 6. Theyused the Nd:YAG laser to scribe a groove crack on the surface ofthe substrate material while using a defocused CO2laser beam togenerate the thermal stresses. A high-speed laser cutting ofthermoplastic films was investigated by Coelho et al. 7. Theysolved the heat transfer equation analytically by the Greenand a precision of operation. Since the laser processing is involvede gradienthe stress intensity factors were negative, which meant that theLaser cutting of sharp edge: Thermal strB.S. YilbasC3, A.F.M. Arif, B.J. Abdul AleemME Department, KFUPM, Dhahran 31261, Saudi Arabiaarticle infoArticle history:Received 22 November 2008Received in revised form28 February 2009Accepted 1 March 2009Available online 20 August 2009Keywords:LaserCuttingSheet metalThermal stressabstractLaser cutting of sharp edgefinite element method is usedtechnique is used to measthickness is used in the simaround the edges are examiis found that temperatureThis, in turn, lowers the coolingresidual stress is about 90of 280MPa, which occurs athe experimental data.1. IntroductionLaser processing of sheet metals finds wide application inindustry. The high energy focused beam provides a fast processingjournal homepage: analysisthermal stress development in the cutting section is examined. Theto predict temperature and stress fields while the X-ray diffraction (XRD)the residual stress around the cut edges. A mild steel sheet with 5mmand the experiment. The morphological and metallurgical changesusing the optical microscopyand scanning electron microscopy (SEM). Ithigh at the sharp edge when the laser beam is located in this region.rate and reduces von Mises stress in this region. The magnitude of theat the sharp corner while the maximum von Mises stress is in the orderfrom sharp corner. In addition, the residual stress predicted agrees withtherefore,evaporative heat transfer taking place at the free surface has notsignificant affect on temperature field in the vicinity of thesolidliquid interface. Since the thermal stress is only developedwithin the solid phase of the substrate material during the cuttingprocess, the transient heat diffusion equation based on the Fouriermodel, with the appropriate boundary conditions, can be applic-able to describe temperature field in the solid. Temperature fieldcan be coupled with the thermo-mechanical response of thematerial to determine the thermally induced stresses in thecutting section during the laser processing. The transient heatdiffusion equation can be written in the Cartesian coordinatesystem asrDEDtrkrT So(1)where E is the energy gain by the substrate material,r(k(rT) (q/qx)(k(qT/qx)+(q/qy)(k(qT/qy)(q/qz)(k(qT/qz) (x, yand z are the axes (Fig. 1a), and Sois the volumetric heat sourceterm. The laser heating source is assumed to be Gaussian at thesurface (x,y)-plane with the Gaussian diameter a and the beamis absorbed in the absorption depth along the y-axis within thesurface region. The volumetric source isSo Iod1C0 rfeC0dzeC0x2y2=a2(2)Iois laser peak intensity, d is the absorption depth, rfis thetccooling period (ms)trpulse rise time (ms)tfpulse fall time (ms)u laser cutting speed (m/s)dU strain energy (J)duTvector for virtual displacements (m)dV external work (J)w workpiece thickness (m)x,y,z space coordinatesGreek Symbola vector of coefficients of thermal expansion (1/K)eth thermal strain vectord absorption coefficient (1/m)r density (kg/m3)surface reflectivity, and x and z are the axes. However, the laserheating situation can be represented through consecutive pulsesresembling the duty cycle of the laser output power. In this case,the temporal variation of the laser pulse shape is resemblesalmost the actual laser pulse shape used in the experiment (50%duty cycle), which is in trapezium shape in time domain. The laserpulse parameters used in the simulations are given in Table 1while Fig. 1b shows the temporal variation of consecutive laserpulses. The time function (f(t) representing the consecutivepulses isft0; t 01; trttp0; t tp0; tpttp tc8:9=;(3)where tris the pulse rise time, tfis the pulse fall time, tpis thepulse length, tcis the end of cooling period. f(t) repeats when thesecond consecutive pulse begins, provided that time t tf+tccorresponds to the starting time of the second pulse. The samemathematical arguments can apply for the other consecutivepulses after the second pulse.In the case of a moving heat source along the x-axis with aconstant scanning speed u (Fig. 1), energy gain by the substratematerial yieldsrDEDt rEtC0ruEx(4)where qE/qt (q(CpT)/qt) and qE/qx (q(CpT)/qx)orrDEDt rCpTtC0ruCpTx(5)Combining Eqs. (1) and (5) yieldsrCpTt rkrTruCpTx So(6)It should be noted that in the cutting analysis, the reflection ofthe laser beam from the cut edges are omitted, since internalreflection is absorbed by the cutting surface. Therefore, thereflection loss from the irradiated laser beam only occurs fromthe free surface of the substrate material. Moreover, at the freesurfaces of the workpiece (the irradiated surface), the convectiveboundary is assumed and at the rear side of the workpiece, theconvective and radiative boundary condition is considered.Therefore, the corresponding boundary condition isAt the free surface (in xy plane at z 0) a convectiveboundary is assumed, therefore, the corresponding boundarycondition isAt z 0 at the surface!TzhkTsC0 Towhere h is the heat transfer coefficient and Tsand Toare thesurface and reference temperatures, respectively. In addition, at adistance far away from the surface in the xy plane temperaturebecomes the same as the reference temperature. This yields theboundary condition ofAt x and y 1!T T1To;SpecifiedARTICLE IN PRESSz = 0u - Laser cutting velocityWorkpiecexyz B.S. Yilbas et al. / Optics and Lasers in Engineering 48 (2010) 101912Duty Cycle = 0.50.00.51.01.50.00TIME (ms)RELATIVE INTENSITYtB= Begining of Heating CycletE= Ending of Heating CycletBtEtrtftptcz = waLaser heat sourceLaser cut edgew0.50 1.00 1.50 2.00 2.50Fig. 1. (a) A typical laser cutting situation and coordinate system. w is theworkpiece thickness. (b) Two consecutive pulses with a 50% duty cycle. It shouldbe noted that 50% duty cycle is used in the cutting experiments.Table 1Laser pulse parameters used in the simulations.Duty cycle Laser pulselength, tp(ms)Cooling period,tc(ms)Pulse rise time,tr(ms)50% 0.5 0.5 0.065The thermo-mechanical phenomenon of laser cutting isidealized as a sequentially coupled unidirectional problem. Forthe thermo-mechanical coupling situation which does not exhibita high degree of nonlinear interaction, the load transfer method ismore efficient and flexible due to that one can perform the twoanalyses independently from each other 20. Therefore, a loadtransfer thermal stress analysis is performed involving a nonlinearPulse fall time,tf(ms)Pulse intensity(W/m2)C2109Guassian parameter,a (m)C210C040.0325 1 2.997For structural response, the finite element formulation is basedon the principle of virtual work. From the principle of virtual work(PVW), a virtual (very small) change of the internal strain energy(dU) must be offset by an identical change in external work due tothe applied loads (dV). Considering the strain energy due tothermal stresses resulting from the constrained motion of a bodyduring a temperature change, PVW yieldsfdugTZvolBC138TDC138BC138dvfugfdugTZvolBC138TDC138fC15thgdv (7)Noting that the du T vector is a set of arbitrary virtualdisplacements common in all of the above terms, the conditionrequired to satisfy above equation reduces toKC138fugfFthgwhereKC138ZvolBC138TDC138BC138dv element stiffness matrixfFthgZvolBC138TDC138fC15thgdv element thermal load vectorfC15thgfagDT thermal strain vectorfagvector of coefficients of thermal expansionvon Mises stress can be computed from the stress tensor, whichis defined ass 32sijsijq(8)where sijare the components of the stress deviator tensor.4. Finite element simulationInitially the substrate material is assummed to be at a referencetemperature (To), therefore, the initial condition becomesAt t 0 ! T T1To;SpecifiedThe finite difference method is used to discretize Eq. (6). Explicitscheme is used to compute temperature field. The grid indepen-dent tests are conducted to secure the grid independent results.3. Modeling of thermal stressestransient thermal analysis followed by a static stress analysis. Thetwo fields are coupled by applying results from one analysis asloads in another analysis. Utilizing the ANSYS APDL programminglanguage, separate thermal and stress analysis files were createdusing a single finite element mesh with different element types.The computation process was to read in the first physics file forthermal analysis and to solve. Then, the next physics field wasread for stress analysis specifying the loads to be transferred, andsolved the second physics. In the current work, the nodaltemperatures from the thermal analysis are applied as bodyforce loads in the subsequent stress analysis. For thermalanalysis, the given structure is modeled using thermal element(SOLID70). SOLID70 has a 3-D thermal conduction capability. Theelement has eight nodes with a single degree of freedom,temperature, at each node. The element is applicable to a 3-D,steady state or transient thermal analysis. Since the modelcontaining the conducting solid element is also to be analyzedstructurally, the element is replaced by an equivalent structuralThe moving heat source is modeled as a moving source at thenozzle and co-axially with the laser beam is used. Focal lens of127mm is used to focus the laser beam. The laser cuttingparameters are given in Table 3.JEOL JDX-3530 scanning electron microscope is used to obtainphotomicrographs of the cross section and surface of the work-pieces after the tests. The Bruker D8 Advance having MoKaradiation is used for XRD analysis. A typical setting of XRD wasARTICLE IN PRESScycle0300600900120020DISTANCE ALONG Y-AXIS (cm)TEMPERATURE (K)x = 3.22 cm : z = 0 cm and Laser Beam is at Bx = 6.52 cm : z = 0 cm and Laser Beam is at O050010001500200020DISTANCE ALONG Y-AXIS (cm)TEMPERATURE (K)x = 3.30 cm : z = 0 cm and Laser Beam is at Bx = 6.30 cm : z = 0 cm and Laser Beam is at O21 21 22 22 2321 21 22 22 23Fig. 2. Temperature variation along the y-axis at two locations on the cut edge.(3.3 cm, 22.8 cm)Location By-axis(6.6 cm, 20 cm)(1.65 cm, 20 mm)Location OLocation Ax-axis (cm)z-axis (cm)Cutting DirectionB.S. Yilbas et al. / Optics and Lasers in Engineering 48 (2010) 1019 13cutting edge resulting in a specified temperature greater than thesubstrate melting temperature. Using the specified laser speedand the finite element mesh size, time step was calculated for thethermal analysis. At each incremental time step, the specifiedtemperature for the heat source was moved to the next adjacentset of nodes using APDL DDELE and D commands 16. DDELEcommand deletes degree of freedom constraints. However,deleting a constraint in ANSYS is not the same as setting it tozero. Deleting a constraint has the same effect as deactivating,releasing, or setting the constraint free.The mechanical and thermal properties used in the currentsimulations are given in Table 2. It should be noted that theconditions for the current simulations resemble the actualexperiments carried out in the present study.5. ExperimentalThe laser used in the experiment is a CO2laser (LC-aIII-Amada)and delivering nominal output power of 1800Wat the pulse modewith adjustable frequencies. Nitrogen emerging from a conicalTable 2Thermal and mechanical properties of mild steel used in the simulations.k (W/mK) 63Cp (J/kgK) 420r (kg/m3) 7860a (m2/s) 1.6134E-5Tm(K) 1700aT(1/K)C210C0615n 0.29E (GPa) 210Table 3Laser cutting parameters.Feed rate (m/s) Power (W) Frequency (Hz) Nozzle gap (mm) Duty0.1 1800 1000 1.5 50%element (such as SOLID45) for the structural analysis. SOLID45 isused for the 3-D modeling of solid structures. The element isdefined by eight nodes having three degrees of freedom at eachnode: translations in the nodal x, y, and z directions. The elementhas plasticity, creep, swelling, stress stiffening, large deflection,and large strain capabilities.Nozzle diameter (mm) Focus diameter (mm) N2pressure (kPa)1.5 0.3 600Fig. 3. The cutting geometry used in the simulations and the experiment. Thethickness is 5mm.ARTICLE IN PRESSB.S. Yilbas et al. / Optics and Lasers in Engineering 48 (2010) 10191440kV and 30mA. It should be noted that the residual stressmeasured using the XRD technique provides the data in thesurface region of the specimens. This is because of the penetrationdepth of MoKa radiation into the coating, i.e. the penetrationdepth is in the order of 1020mm. The measurement relies on thestresses in fine grained polycrystalline structure. The position ofthe diffraction peak undergoes shifting as the specimen is rotatedby an angle c. The magnitude of the shift is related to themagnitude of the residual stress. The relationship between theFig. 4. (a) Temperature distribution around the cut edges when laser beam is at locationlocation O.peak shift and the residual stress (s) is given 21s E1usin2cdnC0 dodo(9)where E is Youngs modulus, n is Poissons ratio, c is the tilt angle,and diare the d spacing measured at each tilt angle. If there are noshear strains present in the specimen, the d spacing changeslinearly with sin2c.B. (b) Temperature distribution around the cut edges when laser beam is atresults in higher the stress gradients. In addition, change in thetemperature gradient along the y-axis results in the shift of thelocations (A and B, Fig. 3) along the cutting edge. It should benoted that the x- and y-axes locations are the locations of the laserbeam axis. Consequently, the maximum temperature is limitedwith the melting temperature of the substrate material.Temperature rises rapi
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