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外文翻译--一个激光束加工（LBM方法）数据库的切割瓷砖 英文版.pdf

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外文翻译--一个激光束加工（LBM方法）数据库的切割瓷砖  中文版.doc

外文翻译--一个激光束加工（LBM方法）数据库的切割瓷砖  英文版.pdf

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目       录

摘 要I

AbstractII

1 绪论1

1.1 序言1

1.2设计主要任务2

2 进给系统设计3

2.1总体方案设计3

2.1.1 概述3

2.1.2 机械系统设计3

2.2 伺服电机设计5

2.2.1 伺服电机概述5

2.2.2 伺服电机选择6

2.3 滚珠丝杠副介绍10

2.3.1 滚珠丝杠副概述10

2.3.2 滚珠丝杠副特点11

2.3.3 滚珠丝杠副结构11

2.4 滚珠丝杠副设计12

2.4.1 设计滚珠丝杠副原理12

2.4.2滚珠丝杠副选择13

2.4.3 滚珠丝杠副预紧14

2.4.4滚珠丝杠副校核15

2.5 滚珠丝杠副密封与润滑17

2.6 滚轴丝杠副支撑选择及轴承选用18

2.6.1 支撑方式选择18

2.6.2 轴承选择19

2.6.3 轴承配合与润滑20

2.7 联轴器简介20

2.8 联轴器基本要求21

2.9 联轴器选择22

2.10 联轴器校核23

2.10.1 转矩校核23

2.10.2 销抗剪强度校核24

3 导轨设计25

3.1 导轨概述25

3.2 导轨分类25

3.3 导轨选型与长度计算25

3.4 导轨副技术要求26

3.5导轨的间隙调整27

4 防护罩设计29

4.1 基本要求29

4.2 选择设计29

4.3 其他设计30

4.3.1  基本要求30

4.3.2  支撑架设计31

总 结32

致 谢33

参考文献34

摘 要

　　　数控车床进给系统是指能分别沿着X 向和Y向做进给运动的系统，是许多机电一体化设备的基本部件，如数控车床的纵—横向进刀机构、数控铣床和数控钻床的X-Y工作台、激光加工设备的工作台、电子元件表面贴装设备等。模块化的X-Y数控工作台，通常由导轨座、移动滑块、工作、滚珠丝杠螺母副，以及伺服电动机等部件构成。其中伺服电动机做执行元件用来驱动滚珠丝杠，滚珠丝杠螺母带动滑块和工作平台在导轨上运动，完成工作台在X、Y方向的直线移动。导轨副、滚珠丝杠螺母副和伺服电动机等均以标准化，由专门厂家生产，设计时只需根据工作载荷选取即可。控制系统根据需要，可以选取用标准的工作控制计算机，也可以设计专用的微机控制系统。

　　　该设计从确定小型数控车床的方案入手，设计进给系统的装配图和主要零件图。确定数控车床数控系统后，详细论述进给传动系统各组成部分，以及各部分的计算和选用。

　关键词：数控车床; 进给系统; 装配图; 零件图

　　　　　数控车床进给系统的具体参数如下：

　　　　　 X方向行程:100mm      

　　　　　 Y方向行程:1500mm

        工作台面的参考尺寸:240260mm

        工作台和工件最大物重质量60kg

        工作台表面滑动摩擦系数为0.5

        平均切削力:500N

        快进进给速度:1000mm/min

        最高运动速度:10000mm/min

        脉冲当量0.001mm

        定位精度: 0.02mm

工作寿命:每天8小时，工作8年，250天/年

1 绪论

1.1 序言

数控技术是用数字信息对机械运动和工作过程进行控制的技术，是现代化工 业生产中一门新型的，发展十分迅速的高新技术。数控装备是以数控技术为代表 的新技术对传统制造业和新型制造业的渗透，形成的一种机电一体化技术。这一 技术使生产过程中的生产效率、产品成本及工人劳动强度等方面问题得以明显改 善，特别是针对对市场化生产的小批量、多品种特点，有无可比拟的优势。数控机床是采用了数控技术的机床。即能按照程序逻辑，一步步处理生产过程的机床。数控技术也叫计算机数控技术，目前它是采用计算机实现数字程序控制的技术。这种技术用计算机按事先存贮的控制程序来执行对设备的运动轨迹和外设的操作时序逻辑控制功能。由于采用计算机替代原先用硬件逻辑电路组成的数控装置，使输入操作指令的存贮、处理、运算、逻辑判断等各种控制机能的实现，均可通过计算机软件来完成，处理生成的微观指令传送给伺服驱动装置驱动电机或液压执行元件带动设备运行。

制造业是作为衡量一个国家经济的重要指标，体现了一个国家或一个民族的科技实力，是一个时代科学技术发展最明显的突出体现。尤其是在最近几十年了，发达的资本主义国际凭借其先进的制造技术，利用其强大的科技和财政实力获得了巨大的经济利益。我国的制造业起步晚、基础差，但近二十年来，我国投入了巨大的人力物力，并取得了骄人的成绩。但同时也要看到，我们国家的制造业和西方发达资本主义国家的制造业还有差距，而且在某种层度上说，差距还很大，这就要求我们国家还要付出更大的努力去提高我国的制造业在世界制造业中的地位，使我国的制造业对我国的经济发展能够发挥更大的作用，为人民和人类带来更大的帮助。

数控车床、车削中心，是一种高精度、高效率的自动化机床。配备多工位刀塔或动力刀塔，机床就具有广泛的加工艺性能，可加工直线圆柱、斜线圆柱、圆弧和各种螺纹、槽、蜗杆等复杂工件，可咨询：宁波众鑫数控机床厂。具有直线插补、圆弧插补各种补偿功能，并在复杂零件的批量生产中发挥 了良好的经济效果。传统的机械加工都是用手工操作普通机床作业的，加工时用手摇动机械刀具切削金属，靠眼睛用卡尺等工具测量产品的精度的。现代工业早已使用电脑数字化控制的机床进行作业了，数控机床可以按照技术人员事先编好的程序自动对任何产品和零部件直接进行加工了。数控加工广泛应用在所有机械加工的任何领域，更是模具加工的发展趋势和重要和必要的技术手段。

数控车床又称为 CNC车床，即计算机数字控制车床，是目前国内使用量最大，覆盖面最广的一种数控机床，约占数控机床总数的25%。数控机床是集机械、电气、液压、气动、微电子和信息等多项技术为一体的机电一体化产品。是机械制造设备中具有高精度、高效率、高自动化和高柔性化等优点的工作母机。控机床的技术水平高低及其在金属切削加工机床产量和总拥有量的百分比是衡量一个国家国民经济发展和工业制造整体水平的重要标志之一。数控车床是数控机床的主要品种之一，它在数控机床中占有非常重要的位置，几十年来一直受到世界各国的普遍重视并得到了迅速的发展。

1.2设计主要任务

进给系统机械传动结构是伺服进给系统的主要组成部分，主要由传动机构、运动变换机构、导向机构、执行件组成，它是实现成形加工运动所需的运动及动力的执行机构。由于数控机床的进给运动是数字控制的直接对象，被加工工件的最终位置精度和轮廓精度都与进给运动的传动精度、灵敏度和稳定性有关。进给系统是数控加工的关键环节，是数字控制的直接对象，被加工工件的最终坐标位置精度和轮廓精度都与传动结构有关。脉冲当量是0.001mm，快进速度是1000mm/min，X轴行程：100mm ，Y轴行程： 150mm。合理设计进给系统的结构；完成进给部件（包含滚珠丝杠螺母副、燕尾槽导轨、导轨防护罩等）的结构设计及总图和零件图；完成主传动系统的设计计算；完成二万字的毕业论文及5000字的译文。

内容简介：
Journal of Materials Processing Technology 84 (1998) 4755A laser beam machining (LBM) database for the cutting ofceramic tileI. Black *, S.A.J. Livingstone, K.L. ChuaDepartment of Mechanical and Chemical Engineering, Heriot-Watt Uni6ersity, Riccarton, Edinburgh EH14 4AS, UKReceived 13 December 1997AbstractThis paper covers the cutting of commercially-available ceramic tiles using a CO2laser cutting machine, with the object ofproducing a laser beam machining (LBM) database that contains the essential parameter information for their successfulprocessing. Various laser cutting parameters were investigated that would generate a cut in ceramic tile which required minimalpost-treatment. The effects of various shield gases, of multi-pass cutting and of underwater cutting were also examined. 1998Elsevier Science S.A. All rights reserved.Keywords:CO2; Laser cutting; Ceramic materials; Advanced manufacturing processes1. Introduction and backgroundManual methods of cutting ceramic tiles are verysimilar to that for glass, i.e. scribing the materials withtungsten-carbide tipped cutter, followed by the applica-tion of a bending moment along the scribed line toinitiate controlled fracture. However, manual tech-niques are limited to straight-line cutting and relativelylarge-radius cuts. Internal and undercut profiles arenearly impossible to produce with scoring alone (withthe possible exception of internal circles); more sophis-ticated methods having to be applied to achieve theseprofiles.Traditionally,diamond-saw,hydrodynamic(water jet) or ultrasonic machining are used to createcomplex geometries in ceramic tiles, but these processesare very time consuming and expensive. For example,typical diamond-saw cutting speeds are in the order of20 mm min11, while ultrasonic drilling of Al2O3takes over 30 s per hole 2.The most critical factor arising from use of a CO2laser to cut ceramic tiles is crack damage, which isessentially caused by a high temperature gradientwithin the ceramic substrate during the cutting process.These cracks reduce the strength and are sources forcritical crack growth, which may result in partial orcomplete failure of the tile substrate 3. Thus a reduc-tion of process-induced crack formation is paramountfor the realistic commercial use of lasers to cut ceramictiles.2. Laser cutting parametersLaser machining of any material is a complex processinvolving many different parameters that which all needto work in consort to produce a quality machiningoperation 4, parameters such as: (i) laser power input;(ii) focal setting; (iii) assist gas type and pressure;(iv) nozzle configuration; (v) workpiece thickness; and(vi) optophysical properties.Previous research within the authors department1,5,6 has also demonstrated the criticality of the aboveparameters in efficient laser cutting.2.1.Laser powerLaser power depends on the type of laser used. Forthe work reported in this paper, a Ferranti MF400CNC laser cutter was employed, rated at a poweroutput of 400 W. However, due to upgrading, themaximum beam power achievable was between 520 and* Correspondingauthor.Fax:+441314513129;e-mail:i.blackhw.ac.uk0924-0136/98/$ - see front matter 1998 Elsevier Science S.A. All rights reserved.PIIS0924-0136(98)00078-8I. Black et al./Journal of Materials Processing Technology84 (1998) 475548530 W in continuous wave (CW) cutting mode. Thelaser also had the ability to work in pulse mode (PM)and super-pulse mode (SPM; Fig. 1). To determine theequivalent power output during pulsing operation, apower verses pulsing chart was used in conjunctionwith the following basic equation 9:Pr=Pl/Psf=1/(Pl+Pr)Although the laser cutter could operate between fre-quencies of 50 and 5000 Hz, a value of 500 Hz wasrecommended in previous work 1,5. Since this settingproved to be successful, only limited investigation intoother frequencies was carried out (at 250 Hz, 750 and100 Hz).2.2.Cutting speedThe CNC table used with the Ferranti MF400 lasercutter had a maximum feed rate of 10000 mm min1.Previous work 6 indicated that feed rates above 6000mm min1proved to be unstable for any standardisedtesting. The optimum cutting speed varied with thepower setting and, more importantly, with the thicknessof the workpiece.2.3.Shield gas type and pressureCompressed air, argon, nitrogen and oxygen wereused as shield gases during cutting, with pmax:4 bar.Different shield gases were used to examined their effecton cut quality after processing, since the shield gas notonly cools and cut edges and removes molten material,but also generates a chemical reaction with the sub-strate material 7. The results of this chemical reactiondiffer for each type of shield gas used. For test purposesp was varied in steps of 0.5 bar from 1 to 2.5 bar, thenin steps of 0.2 bar from 2.6 bar to the maximumattainable gas pressure.2.4.Nozzle configurationThe nozzle diameter contributes directly to the maxi-mum achievable gas pressure and hence to the massflow rate of the gas was important for the economics ofcutting, especially when using cylinders of argon andnitrogen. Only circular profiles for the nozzle exits wereavailable (0.6 mm5Ns520 mm), but this uniformnozzle exit geometry allowed cutting in any direction.2.5.Nozzle height and focal positioningThe height at which the nozzle was set was governedby the position of the focal point. The Ferranti MF400laser cutter only possessed a long focal length of 110Fig. 1. Cutting modes.mm (originally a short focal length of 46 mm wasavailable before upgrading) and this length could bealtered by 95 mm. If the nozzle height was incorrectlyset the beam would clip the nozzle and reduce theequivalent power output to the workpiece 6. For thebulk of the testing the focal height was set so the focalpoint was on the job, i.e. on the top surface of theworkpiece. This condition obviously governed the posi-tion of the nozzle above the workpiece.3. Experimental procedureSix types of Si/Al2O3-based ceramic tiles were exam-ined (Table 1), originating from different countries.Note that the composition of the tiles varied, as did thethickness, but all possessed a surface glaze and in thecase of the 7.5, 8.6 and 9.2 mm Spanish tiles the glazewas double layered.3.1.Set-up procedureSince there was a need for standard testing condi-tions, the following procedure was implemented beforethe start of testing: (i) the beam power was validated tospecification, i.e. 520530 W developed at full power(CW), although this dropped to around 50 W afterTable 1Types of ceramic tile usedts(mm)Tile typeBody colour3.7BrazilianWhite4.7WhitePeruvianLight redItalian5.2SpanishRed5.74Spanish7.5RedRedSpanish8.69.2RedSpanishI. Black et al./Journal of Materials Processing Technology84 (1998) 475549about 1 h of testing; (ii) the nozzle and the focal lenswere checked to ensure that they were in good condi-tion, i.e. clean and undamaged; (iii) the shield gaspressure regulator and shield gas tanks were turned onto prevent damage to the focal lens; (iv) the laser beamwas centred within the nozzle using a square test, alower energy input in PM being used to cut a square ona mild steel, the sparking density that resulted fromcutting being checked to see if it was equally distributedabout the cut line; and (v) the focal point was set for itsdesired positioning, i.e. on the job.3.2.TestingA straight-line test (SLT) was used to evaluate thevariablelaserparametersforfullthrough-cutting(FTC). Angular cutting was configured to investigatehow the material reacted during cutting of tight geome-try. Circular testing and square testing were devised todetermine the effects resulting from cutting variousgeometries.The SLT allowed for the combined testing of twoseparate parameters on one testpiece, upon completionthe results being present automatically in a cuttingmatrix in the form of the resulting cuts. P and V arethe most important laser parameters, as they dictate theamount of energy input per unit length of cut, thereforethey were paired for the SLT, as were p and NSwhichgovern the mass flow rate of the shield gas.For the P/V test runs, the power was held constantwhile the cutting speed was increased along the cut(Fig. 2(a). The length of cut at constant cutting speedhad to be of sufficient magnitude to accommodate theacceleration or deceleration of the CNC table betweenfeed changes: previous work 6 indicated that 50 mmwas adequate. Interpreting the results was made easierdue to their tabular format, with the cutting matrixshowing clearly any trends or patterns occurring due tothe changes in parameter settings. The SLT also al-lowed a large number of cuts to be carried out over ashort time-frame. This proved advantageous, as thelaser tended to drift from its initial settings with time.Precautions had to taken to avoid localised heating inthe tile from continuous close proximity cutting, as achange in tile body temperature would invalidate anyresulting data. Initially, a 20 mm separation betweencuts was used and this proved sufficient. In order tostudy how close the cuts could be made to each other,the separation between cuts was reduced by incrementsof 2 mm from an initial 20 mm spacing.During the SLT the other laser parameters had to beheld constant 6. For P versus V, f was held at 500 Hzwith NS=1.2 mm and p=3 bar. The beam focal pointremained on the job. The results from the P/V cuttingmatrix determined the fixed values for the cutting speedand pulse settings for the succeeding SLT. For the NS/pFig. 2. Testing configuration: (a) straight-line testing; (b) angulartesting; (c) circular testing; (d) square testing.cutting matrix, the nozzle size remained constant alongthe x-axis (refer to Fig. 2(a) while p was increased insteps of 0.2 bar from 2 bar in the y-axis (the cutseparation remained constant at 20 mm). A new matrixwas created subsequently for each nozzle size.Angular testing (Fig. 2(b) was used to investigatehow the cut material reacted to sustained exposurefrom the laser beam during the machining of tightgeometries (i.e. where several cuts are made in closeproximity to each other). The proximity test mentionedfor SLT determines how close parallel lines can be cutto each other, whereas angular testing is used to deter-mine how the cutting of acute angles effects the cutquality. The angles cut from a workpiece were reducedfrom 45 to 10 and the corresponding surface finishquality (SFQ) was noted.I. Black et al./Journal of Materials Processing Technology84 (1998) 475550Table 2Multi-pass cutting parametersPlCutting modePsNo. of passesLast cutCW60FTC9000100SPMFTC100Table 3Grading of SFQGrading1No cracking in surface glaze, solid sharp cut edgeMinimal glaze cracking (WcB2 mm) with slight2loss of sharpness in cut edgeMedium cracking (2 mmBWcB4 mm) and slight3damage to unglazed tile substrateSignificant damage to glaze coating (Wc6 mm),4heavy damage to unglazed substrate causing flakingin the glazed surface5Same as 4 but with the formation of cracks in thetiles main body leading to structural failure in apart of the tile (usually at the end of a cut orwithin 8 mm of the tile edge).There are two reasons for conducting square andcircular testing (Fig. 2(c) and (d): first, to determinethe optimum method of laser-beam introduction tointernal cut profiles; and secondly, to determine if therewas any limitation in the dimension of the size ofsquare or hole cut. If not correctly introduced, the laserbeam would cause an internally-cut profile to fail at thepoint of introduction, due to the brief but excessivethermal gradient induced from cutting (i.e. thermalshock). Therefore, utilising methods of beam introduc-tion, such as trepanning, onto a profile enabled com-plex geometries to be investigated. What also becameapparent during testing was the importance of theposition of beam extraction from the cut profile and theposition of the beam starting point relative to thegeometry, i.e. whether it was at a corner or on astraight edge.3.3.Multi-pass and underwater cuttingMulti-pass cutting was begun with a low power(P=100 W) laser beam. The first pass produced a welldefined blind kerf in the substrate, followed by a secondpass to cut deeper and so on. The process was repeateduntil the kerf was about 20 mm deep and then the laserpower was switched to 500 W and do the final FTC.The objective of multi-pass cutting was to reduce ther-mal overload by use of less input energy per unitlength. The parameters used in this test are given inTable 2.Underwater cutting was conducted with the objectiveof reducing the influence of heat around the cut areaand also to examined the effect on cut quality throughaccelerated heat dissipation using water 8. The ce-ramic tile was placed under water and the nozzle wasalso dipped in water, the shield gas pressure preventingany water from entering the nozzle jet chamber.4. Cut qualityMaterial properties, laser parameters and workpiecegeometry have a significant effect on the final result ofthe laser cutting process. Cut quality is essentially char-acterisedbysurfaceroughnessanddrossheight,whereas crack length dictates the strength reduction inthe substrate (Fig. 3). The overall SFQ at the glazesurface was classified according to the grading scalegiven in Table 3. Therefore, the quality of the cutsurface and edge were measured with respected to:(i) surface roughness; (ii) surface finish and; (iii) drossadherence.Fig. 3. Quality criteria for the laser cutting of ceramic tiles.I. Black et al./Journal of Materials Processing Technology84 (1998) 475551Fig. 4. Measurement of Rafor the cut surface.4.1.Surface roughnessIt was important to measure surface roughness asthis allowed the cut quality to be gauged alongsidevalues obtained from previous work 1 and valuesrecorded for other manufacturing processes. Due to thelarge number of cuts being made it was necessary toreduce the number of cuts to be analysed. Thereforecuts with SFQB2 were not measured.The surface roughness of the cut edge was character-ised by the formation of striation lines left by thecutting process Ravalues were measured from thecentre-line of the cut edge (Fig. 4). Measurements weretaken over a 12.5 mm traverse of the stylus with acut-off value of 2.5 mm, i.e. five readings were takenover the traverse, which ensured that the stylus trav-elled over a reasonable number of striation lines.4.2.Dross adherenceDross adherence directly effected the Ravalue of thecut and the ability to remove internally-cut geometries.A micrometer was used to measure the dross height atthree intervals along the cut section. The dross heightremained fairly constant (approximately 1 mm) with alltypes of cutting. Since this value was deemed to be ofno practical importance, it was not recorded in thedatabase.5. ResultsTable 4 contains the current LBM database for cut-ting ceramic tiles that was compiled from the results ofthe work reported in this paper. The first part of thetable contains the parameters and results for substratescut in atmosphere, while the results for underwatercutting are shown in the second part.5.1.Parameter effects5.1.1.Cutting speedFor the thinner tiles (tsB7 mm) the P/V cuttingmatrix showed a wide region of FTC with SFQ=1. Inthe case of the Brazilian tile (ts=3.7 mm) FTC wasobtained with cutting speeds of up to 2200 mm min1and down to Pr=0.5 (with reduced speeds) at f=500Hz. This region diminished with the increase in tilethickness and also with the redness of the body colour(generally the thicker tiles are darker in body colour).Fig. 5 shows how the maximum cutting speed for FTCvaries with ts. The exponential relationship obtainedconcurs with previous work 6 for different materialssuch as steel, wood and perspex. The cutting matrixalso showed that once the cutting speed exceeded valuesfor attainable FTC, scribing or blind cutting results.5.1.2.PulsingPulsing the laser for all but the thick Spanish tileswas not required, as the CW setting produced cuts witha good SFQ grading. Successful FTC was obtained atPr0.4 in the Brazilian tile, but Vmaxwas so low that,in a practical sense, the settings were not viable. On thethick Spanish tiles pulsing of the beam was required, asCW caused cracking in the glaze. This was probablydue to an excess of energy input per unit length of cutcausing thermal shock as the thermal expansion rate ofthe glaze differed sufficiently from that of the parenttile. Since pulsing the laser reduced the energy input byapproximately 25 W for every 0.1 drop in Pr at f=500Hz, the surface glaze cracking virtually disappeared atPr=0.6 and optimum cutting speed, although tinycracks (of the order of 0.5 mm wide) at the cut edge stillremained.5.1.3.Gas pressureThis parameter has a great effect on the quality andthe rate at which cuts could be made successfully.Previous work 2 had shown that high gas pressureswere required to achieve FTC on thick substrates (ts7 mm). This was borne out by the results obtained fromthep/Nscuttingmatrix.Highqualitycutswereachieved in the thinner tiles (tsB6 mm) at gas pressuresof 2 bar but in the double-glazed, thicker tiles values ofSFQB3 were not achieved unless p3 bar. At lowpressures (pB2.5 bar), the maximum cutting speeds forFTC dropped drastically, as the gas failed in its role ofdross clearer. Vmaxfor Brazilian tile in CW droppedfrom 2200 mm min1at p=3.8 bar to 1500 mm min1at p=3 bar. An increase in surface-glaze cracking alsobecame apparent at low gas pressures. This led to theconclusion that the shield gas was acting as a coolantand thus helping to minimise the large thermal gradientcreated by the beam.I. Black et al./Journal of Materials Processing Technology84 (1998) 475552Table 44 LBM database for ceramic tilesAtmospheric cuttingRa(mm)V (mm/min)Tile typets(mm)BodyShield gasSFQGlaze typeNs(mm)Geometricp (bar)Pl-Pscutcolour1.21.51Brazilian3.7WhiteWhiteStraightCW5001000C. air32535253511.21.53180205001000C. air31.21.51253516040500900C. air253511.21.53Internal18020400600C. air1.21.515Angular16040300500C. air32535253511.21.53Radial18020300500C. air31.21.51Peruvian4.72535WhiteWhiteStraightCW500700C. air125351.21.5318020500700C. air31.21.51253516040500700C. air253511.21.53Internal18020300500C. air31.21.5152535Angular16040250450C. air125351.21.53Radial18020250450C. air31.21.51Italian5.21725Light redWhiteStraightCW500700C. air1.21.5118020500700C. air3172511.21.51725316040500700C. air1.21.51Internal18020300500C. air317251725151.21.53Angular16040200400C. air31.21.511725Radial18020200400C. air203011.21.5Spanish5.74Red3WhiteStraightCW300550C. air1.21.5118020300400C. air32030203011.21.5316040300450C. air31.21.512030Internal18020200350C. air2520301.21.53Angular16040200300C. air31.21.512030Radial18020200350C. air163721.21.5Spanish7.5Red3Clear/whiteStraightCW200370C. air31.21.52163718020200350C. air1637121.21.5316040200350C. air31.21.52163714060200350C. air1.21.512Internal14060200300C. air31637351.21.516373Angular14060200250C. air1.21.513Radial16040200300C. air3163791211.2Spanish8.5Red2.8WhiteStraight1002503070Argon2.81.219111002003080Argon121311.22.81003003040Argon1.211502503080Argon2.8101411.22.8Internal1002007080Argon2.81.211502505070Argon31.21.52.2StraightCW150250Argon2.21.21.534618020150250Argon48241.21.52.218030150250Argon2.21.21.5246918040150250Argon247111.21.52.218050150250Argon2.21.21.5391116020150250Argon1.21.5316030150250Argon2.2101131.21.511132.216040150250Argon1.21.5214020150200Argon2.21012101431.21.52.214040150200Argon2.21.21.53101414060150200Argon7911.2Spanish8.5Red3.5WhiteStraight15025050C. air3.51.21100250783050C. air101211.23.51002005070C. air3.51.212Angular1002006080C. air315181.23.5StraightCW70160Nitrogen3.51.219121502504060Nitrogen81011.23.51002503050NitrogenNitrogen3.51.219111002002050I. Black et al./Journal of Materials Processing Technology84 (1998) 475553Table 4 (continued).Atmospheric cuttingts(mm)Tile typeBodyGlaze typeGeometricRa(mm)Pl-PsV (mm/min)Shield gasp (bar)Ns(mm)SFQcutcolourAngular1502504060Nitrogen3.51.2341002503040Nitrogen3.51.234StraightCW80100Oxygen3.51.231002005060Oxygen3.51.2110111002503050Oxygen3.51.219111502503080Oxygen3.51.211012Angular1502507080Oxygen3.51.213100-25050Oxygen3.51.213RedWhiteStraight15020040100SpanishC. air9.23.51.2110131002003040C. air3.51.219101002502030C. air3.51.21101215025030100C. air3.51.211012Angular1502004080C. air3.51.2141002003040C. air3.51.2141002502030C. air3.51.2141502504080C. air3.51.214Underwater CuttingRedWhite10 acute100-200508.5OxygenSpanish3.51.212100-25050Oxygen3.51.21215025050Oxygen3.51.212RedWhite10 acute100-20050OxygenSpanish3.59.21.21210025050Oxygen3.51.21215025050Oxygen3.51.212Note: focal point on the job; data for angular cut only.5.1.4.Gas typeCompressed air as recommended by previous work1 proved adequate in the removal of molten materialwithout any adverse effects from its exothermic proper-ties, over the full range of tile thicknesses. Cutting usingthe inert gases argon and nitrogen produced betterresults, especially with the latter as it acted as anefficient coolant 9. High-quality cuts with SFQ=1were produced in the thicker tiles at an optimum cut-ting speed of 360 mm min1in CW mode. However,when using the required high gas pressures, a cylinderof nitrogen or argon was used quickly.5.1.5.Nozzle sizeThis parameter was related directly to p (i.e. thesmaller is the nozzle size the higher is the obtainablepressure). Table 5 shows the maximum achievableshield gas pressure with the corresponding nozzle sizeswhen using compressed air. Nozzles with diametersgreater than 1.5 mm were ignored as pmaxwas insuffi-cient. The smaller nozzle diameters produced bettercuts with higher cutting speeds.5.1.6.Focal point positioningDuring testing the focal point of the beam remainedon the job, i.e. on the surface. Cuts with an adequateSFQ grading were achieved with this setting. Investiga-tion showed that by lowering the focal point into thejob the dross adherence decreased and in raising thefocal point away from the job FTC was lost as thebeam de-focused. Therefore, for practical reasons, thefocal point remained on the job.5.1.7.Multi-pass cuttingThicker tiles were cut successfully by the multi-passmethod without degradation of cut quality. Due to thelow power of the laser beam, the temperature gradientin the tile was greatly reduced, thus material damagewas minimised. This method can also be used to pro-cess thicker ceramics without any fracture. However,multi-pass cutting has a distinct disadvantage in being avery time-consuming process and would prove uneco-nomic on a commercial basis.5.2.Material effectsThe darker-bodied tiles were denser and heavier andduring cutting they retained more heat than the white-body tiles. Analysing how this effected the cutting wasnot possible, as the thickness of tile also increased withdarkening of the body colour, the increase in thicknessmasking any of the compositional effects of the mate-rial. In some of the tiles the material composition wasnot homogeneous. Whether this was due to the specificI. Black et al./Journal of Materials Processing Technology84 (1998) 475554Fig. 5. Vmaxagainst tsfor ceramic tiles of different origin.tile manufacturing processes is unknown, but the resultson cutting were a loss of FTC even at optimum cuttingspeed.Glaze damage was a significant factor in assessing cutquality. In all but the thicker tiles glaze damage wasminimal even at poor parameter settings. For example,with the 7.5 mm Spanish tile SFQ53 for most of thecuts with compressed air, although nitrogen producedbetter values. The problem with this latter type was thatthe tile had a double-layered glaze. No cracking ap-peared in the lower white glaze (similar to the othertiles) but the upper clear glaze splintered and flaked ifthe energy input or heat retention in the tile was toohigh. Barbero, Kaufman and Idelsohn 10 have shownthat the surface glaze usually possesses a different linearexpansion rate to that of the underlying substrate.Therefore the large thermal gradient caused by the laserbeam causes the lower substrate to expand at a differ-ent rate, resulting in cracking of the glaze.Another significant factor was control of the amountof energy input and heat dispersion from the cut. Theeffects of poor parameter settings were either loss ofFTC (which was corrected easily), or thermal shock inthe tile or the surface glaze (i.e. cracking in the glaze).The laser cutting process readily promoted thermalshock during cutting, so it was vital to control thiseffect with the correct selection of parameters. Thethermal properties of ceramic tile were primarily thecause of the problem, as generally a tile has a poorthermal conductivity (0.9 W mK15k51 W mK1)and a relatively low co-efficient of expansion (2106K15a55106K1).The glassy film (or dross) that covered the cut edgethickened with an increase in tile substrate and reduc-tion in cutting speed. The increase in dross due to tilethickness was obvious: more tile melted, therefore moredross resulted. The thickness of the dross film alsovaried through the cut. There were two apparent rea-sons for this.(a) First, the width of the beam diverged after thefocal point (which was on the job), thus causing anout-of-flatness in the cut which resulted in a larger kerfwidth at the bottom. Therefore, more of the parent tilematerial was melted lower down in the cut. Dependingon the laser focal length and positioning of the focalpoint, the
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