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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.

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  1. 1. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461239 | P a g eAlternative Method of Forming Hard To Form Metal by usingLASER: A ReviewMs. Sweety patel1, Prof. R.I.Patel21M.E. (CAD/CAM) Student, Government Engineering College, Dahod Gujarat.2Professor and Head of Mechanical Engineering department Government Engineering College, Dahod Gujarat.AbstractThis paper gives a review for a newtechnique to give shape to metal by laser sourceis presented. Typically metal forming by Laser iscontactless method in which laser beam is used asenergy source and by inducing temperatureinduced stress in material, we can form materialin various shapes. The main benefit of laserforming lies in its capability to form low ductilitymetal and with high accuracy of forming whichnormally not possible in conventional formingprocess which uses mechanical tool and die. Inthis paper various experimental result andobservation of laser forming technique ispresented so that one can easily analyze the laserforming technique and its capability andlimitations. The important parameters whichaffect process results are laser beam diameter,sheet thickness, laser input power, scan velocityand material properties. By suitably choosingabove parameters two dimensional and threedimensional geometry had been formed fromsheet metal.Key words- Laser forming, temperature inducedstress, Scanning velocity.I. INTRODUCTIONForming metal by Laser is novel techniquefor sheet metal part which has advantage of higheraccuracies and no hard mechanical tool required. Intypical laser bending of sheet metal, as shown infig.1 workpiece is clamped and a beam of laserscanned along a predetermined path and because ofthat the surface temperature at that locationincreases very rapidly. This will result in steeptemperature difference between the irradiated areaand surrounding area that not directly heated. Thisuneven heating produce thermal stress within theworkpiece. When this stresses become higher thanthe temperature dependent yield strength of thematerial, due to plastic deformation, metal sheetbend along the scanned laser beam path as shown infig.1. Because of small laser spot diameter and laserenergy input can be controlled accurately, thisprocess gives higher accuracy. Also this process canbe automated and controlled very easily. Thisprocess is very suitable for metals like titaniumwhich has very low ductility at room temperatureand normally difficult to form using conventionalforming methods. In laser bending process there isno springback effect and process is gradual in natureso we can achieve very high positional accuracy.FIGURE 1: Simple Line diagram of Laser bendingset upFig. 2.Typical experimental setup of laser bendingof metal sheet.[9]Direction and amount of bending can becontrolled by altering process parameters such aslaser input power, scan speed, laser beam diameterand sheet thickness. These changes in processLaser head
  2. 2. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461240 | P a g eparameters can be grouped to define three importantlaser bending mechanisms that are discussed indetail in following sections.Laser Bending MechanismsLaser bending can be classified by mechanisms usedfor achieving deformation. These mechanisms aredifferentiated from each other by parameters used;such as, Laser beam diameter, sheet thickness, laserinput power and scan speed. These mechanisms areclassified as,A. Temperature Gradient MechanismB. Buckling MechanismC. Upsetting MechanismThese mechanisms are discussed in detail infollowing sub-sectionsA. Temperature Gradient Mechanism (TGM)In Temperature Gradient Mechanism, laserand material parameters are chosen in such amanner that a steep temperature gradient can beformed across the thickness of the sheet material.Temperature Gradient Mechanism (TGM)dominates when the beam diameter is much smallerthan the sheet thickness. The beam travels along aline often called as the bending line. As the beam isirradiated on the work piece surface, the surfacetemperature begins to rise at a very rapid rate. Asharp temperature gradient is established across thethickness that produces differential thermalexpansion at the top surface and compressivestresses at the bottom surface. Expansion of thematerial at the top surface causes the sheet to bendaway from the laser beam as seen from Figure 3.(a).After the laser scan is complete, temperature of thetop surface begins to drop rapidly.The materialexpanded at the upper surface layer begins tocontract and the plate starts bending towards thelaser beam as shown in Figure 2.Fig. 3 Sequence of Temperature GradientMechanism[9]This mechanism dominates under theconditions corresponding to a small (≤ 1) modifiedFourier number which is expressed as,F = λ·d / (h²·u) ,where, λ is Thermal diffusivity(m2/sec), d is the laser beam diameter at the sheetsurface (m), h is the sheet thickness (m) and u isscan velocity (m/sec).Along with bending in y-axis direction, the materialalong the x-axis also produces thermal expansionduring heating bending the workpiece in threedimensions.B. Buckling Mechanism (BM)Buckling Mechanism (BM) asbending/distortion that occurs in thin sheets or in asituation where ratio of thermal conductivity tosheet thickness is large [see Figure 1.4]. In bucklingmechanism, the temperature gradient across thethickness is much smaller. This is usually achievedby reducing the scan velocity and the sheetthickness. A local elastic buckling and plasticdeformation takes place when the speed of the laserscan is maintained low in order to provide moreenergy input. The beam diameter is also maintainedmuch higher than the sheet thickness. The ratio ofthe diameter of the heated area to the sheet thicknessis in the order of 10 in BM while for TGM it is inthe order of unity. The use of large beam diameterresults in larger heated area and the small thicknessresults in small temperature gradient. BM dominatesfor a large value of the Fourier number.
  3. 3. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461241 | P a g eThe sheet may bend towards or away from the laserbeam. direction of bending can be manipulated byfollowing methods;1. Elastic prebending by external forces2. Plastic prebending3. Relaxation of residual stresses4. Counter bending due to temperature gradientBending can be achieved at a higher rate (10º / step)using buckling mechanism, as compared to TGM(1º- 5º / step).C. Upsetting Mechanism (UM)In this mechanism, parameters are chosenin such a way that the heat penetration is ashomogenous as possible. The process parameters aresimilar to that of BM except the heat zone is muchsmaller. Due to nearly homogenous heating of thesheet and restrictions in thermal expansion from thesurrounding material, the sheet is compressed with anearly constant strain across the thickness. Thisleads to shortening of the material across its lengthand increase in the thickness if the material does notbuckle. UM is more difficult to achieve as comparedto TGM and BM. Fig. 5. shows the workingprinciple of the UM.Fig.5 The upsetting mechanism[9]Factors Affecting Laser Bending ProcessIn order to optimize the results of the laserforming process i.e. the bending angle, factors thataffect its magnitude must be studied. A significantamount of research has been conducted on thefactors that affect the bending angle and overallperformance of the process . Following are theimportant process parameters and materialproperties that significantly affect the laser bendingprocess.A. Laser PowerAs shown in Figure 1.6., bending angleincreases with an increase in the laser input poweras the energy density increases, while otherparameters remain unchangedFig.6. - Effect of laser power on the bending angle .Material: AISI1010, laser input power =200 – 260W, laserbeam diameter = 2 – 3 mm,scan velocity = 2 – 4 mm/s,pulse duration = 7 – 11 ms [9]Fig 4. - The Buckling Mechanism[9]
  4. 4. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461242 | P a g eB. Beam DiameterLaser beam diameter or spot size is anotherparameter used to regulate the bending angle. As thelaser beam diameter increases, energy density willdecrease given that the laser input power and scanvelocity are unchanged. Decrease in energy densitywill result in decreasing the bending angle. Figure .7shows the relationship between beam diameter andbending angle obtained via experiment results.Fig.7- Effect of beam diameter on the bending angle. Process parameters; Material: AISI1010, laserinput power =200 – 260W, scan velocity = 2 – 4mm/s, pulse duration = 7 – 11 ms[9]C. Scan Velocitybending angle is inversely proportional tothe scan velocity. As scan speed increases, incidentheat flux absorbed by the workpiece surface perunit time will decrease for constant laser inputpower and beam diameter. Thus, lowering attainablesurface temperature and reducing the bending angle.Fig.8 - Effect of scan velocity on the bending angle .Process parameters; Material: AISI1010, laser inputpower =200 – 260W, laser beam diameter = 2 – 3mm, scan velocity = 2 – 4 mm/s, pulse duration = 7– 11 ms[9]D. Number of ScansIn laser bending process, the value ofbending angle achieved per laser scan (pass) rangesfrom 0.1° to 5° depending on the processparameters. When steeper angles are required, themulti-scan system (up to 20-30 scans for 55° anglefor low carbon steel) is used. Figure 1.8 shows therelationship between the number of scans and thebending angle .Fig .9 - Relationship between bending angle andnumber of scans. Process parameters: Material =Low carbon steel, laser input power = 170 W, laserbeam diameter = 1.2 mm, scan velocity = 3 mm/sec,workpiece thickness = 1.2 mm[9]According to Figure 8, bending anglevaries linearly as the workpiece is scanned multipletimes. Linear variation of bending angle overmultiple scans is usually observed for the materialswhose properties do not vary significantly afterHowever, for the materials that are sensitive to thelaser radiation, bending angle may show non-linearvariation.E. Material Properties.Different materials respond differently tothe laser treatment. Yield strength is an importantproperty that decides the material’s response to laserbending. Larger bending angles could be achievedwith materials having low yield strength. Figure2.11 illustrates the effect of yield strength on thebending angle. Materials with low yield strengthwill require less heat to deform plastically. Hence,more bending angle is achieved for given set ofparameters, while Materials with high yield strengthneed to be formed at a higher temperature byincreasing the laser input power or decreasing thescan velocity.Fig.10 - Relationship between material yieldstrength and bending angle in degrees.[9]As the temperature gradient in a material isa function of its thermal conductivity, for materialshaving high thermal conductivity, heat input by thelaser will be rapidly dispersed throughout thematerial, hence, producing smaller temperaturegradient. This results in reduction of the bendingangle.
  5. 5. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461243 | P a g eF. Absorption of the Laser BeamAny light, including the laser radiation,striking on the surface of a material is eitherabsorbed, reflected, transmitted or re-radiated .‘Absorption Coefficient’ is a measure of the radiantenergy absorbed into a material and ‘Absorptivity’ isa material property that characterises how easily amaterial can absorb a radiation.Fig.10 – Schematic of variation of absorptivity withwavelength for metals, alloys and organic materials.[9]As evident from Fig.10, absorption of thelaser beam by the workpiece surface depends on twoimportant parameters, i.e. wavelength of the laserbeam and type of the material in use. Metals mostlyreflect the laser beams having high wavelength.Hence, the Nd: YAG laser (wavelength of 1.06 μm)is more suitable for processing metals as comparedto the CO2 laser, which has a wavelength of 10.6μm. To minimise reflection of the laser beam,coatings such as graphite are used to improve theabsorption. A number of researchers have studiedthe effect of absorptive coatings . Depending on thebase material, efficiency of the process can beimproved up to 80% with the use of absorptivecoatings.However, it is suggested in previousresearch that coatings such as graphite will bedamaged after few scans because of hightemperature and laser beam shock waves. Ablationof coating will result in reduction of the bendingangle over multiple scans; however, it can beimproved again by respraying.II. REVIEWTo get better result of laser formingprocess, here different model and experimentalresults of laser forming are analyzed, so we canselect optimum parameters for better control overprocess. Therefore this paper concentrate on thereview of laser forming parameters.K.C. Chan and J.Liang et al.[1] had formed lowductility Ti₃Al based intermetallic alloy with CO₂laser. They reveled that bending take place becauseof differential thermal expansion of the theintermetallic alloy across the thickness. The finalbending angle found to be strongly related to laserpower, the scanning velocity and number ofirradiations. But linear relationship found betweenlaser bending angle and input line energy found onlywhen line energy found between minimum andmaximum limit. when line energy is belowminimum value, called threshold value, bendingangle is zero. But when line energy above maximumvalue, excessive melting occurs and which is notsuitable for laser forming. So we conclude that forbetter control of the process, the process must beoperated within certain line energy limit based onprocess parameters.Lubiano and Jorge et al[2], studied laserbending of thin metal sheets by means of a lowpower CO₂ laser, for three different materials 304stainless steel, 1100 Aluminium and 1010 Carbonsteel. They had scanned sheets for several times andresults were plotted as bending angle Vs.number ofscansin fig 1.11. they observed that as the opticalpower of the laser beam increases, keeping thescanning speed and number of scans constant, thebending angle also increases in all three materials.But 1100 aluminium apperars to be more sensitiveto laser power relative to 1010 steel,while 304stainless steel is less sensitive to both laser powerand scan speed.Fig.12 2θ-scan speed results for three differentmaterials at 80 W after 15 scans[2].1100 aluminum and 1010 steel both show adecreasing-increments behavior of the bendingangle (i.e. 2θ) evolution as the number of laser scansincrease beyond the initial scans. The strain due tothe as-received rolled condition of the sheets and in-situ strain-hardening during bending are not
  6. 6. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461244 | P a g eannealed by the laser heat flux due to its short livedthermal cycles and high thermal diffusivity of 1100aluminum and 1010 steel. On the other hand, 304stainless steel, shows an increasing-incrementsbehavior of the bending angle instead. Strain-hardening is prone to occur in the latter material,however, stress relief and partial annealing mayoccur due to higher magnitude and longer time-scalethermal cycles. This is thought to be caused by 304stainless steel low thermal diffusivity and possiblyfaster nucleation kinetics, due to a high density ofstacking faults and twins, which may facilitatepartial recrystalization.Watkins, J.Magee et al [3] present study ofaluminium and titanium alloys, mainly used inaerospace industry, for non contact forming usingthermal source with laser. They reviews themechanisms involved in laser forming of 2-D sheetmaterials and material of particular interest includehigh strength alloys like titanium and aluminiumalloys. Also they present forming of 3-D geometryfrom flat sheet. They demonstrated method of todevelop large primitive 2-D shape. By using datafrom parametric and metallurgical study theyformed flat rectangular sheet of 450*225*0.8 mmdimension made from AA2024T₃ into a part-cylinder of radius 900mm as shown in fig.12Important to note that the shallow radius ofcurvature is almost at the spring back limit ofconventional forming operations. The system usesCO₂ laser, CNC tables and pneumatic clampingsystem.Fig. 13 Demonstrator Part [3].They also formed saddle shape from rectangularsheet to demonstrate 3D forming. In fig 13 scanstrategy and in fig 14 formed 3-D saddle shape isshown.Fig. 14: Scan strategy to laser form the saddleshape, 800W , 20mm/s [3]Fig. 15 3-D Contour plot of laser formed saddleshape[3].Laser forming has emerged as a process with strongpotential for application in aerospace, rapidprototyping and adjustment of misalignedcomponents. This process advantage has arise due toprogressive nature of laser forming process that canbe used to achieve adjustment of misaligned part.A.R. Majed and F.Ahmadi et al [4] present studyof bending of needle having 0.63 mm outer diameterand 0.19 mm thickness with pulsed Nd-YAG laser.Laser bending of tubes haing following advantagesover mechanical bending of tubes. Neither hardbending tool nor external force required, wallthickness reduction seems to be avoided and lesserovalization results. It can be seen that the material inthe intrados moves outward in the radial directionand shortned in the longitudinal direction asindicated by distorded mesh in finite elementanalysis. Maximum thickening of less than onepercent occur at intradoce while there is noappreciable thinning at the extradose. The laser localheating causes large thermal expansion and lowyield stress on the upper surface under hightemperature subsequently the heated region of thematerial produces compressive plastic strain. Thematerial of the heated region of the tube becomesshorter than that of the unheated region after coolingand thus the difference in length enables the tube tobend.
  7. 7. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461245 | P a g eZhang, G.Chen et al[5] present method ofnumerical simulation of pulsed laser bending.The aim of this work is to develop an efficientmethod for computing pulsed laser bending. Duringpulsed laser bending, thousands of laser pulses areirradiated onto the target. Simulations of thethermomechanical effect and bending resulted fromall the laser pulses would exceed the currentcomputational capability. The method developed inthis work requires only several laser pulses to becalculated. Therefore, the computation time isgreatly reduced. Using the new method, it is alsopossible to increase the domain size of calculationand to choose dense meshes to obtain more accurateresults. The new method is used to calculate pulsedlaser bending of a thin stainless-steel plate. Resultscalculated for a domain with a reduced size are ingood agreement with those obtained by computingall the laser pulses. In addition, experiments ofpulsed laser bending are performed. It is found thatexperimental data and computational results areconsistent. A new efficient method for computingpulsed laser bending is developed. The totalcomputation time is greatly reduced and results arefound to agree with those obtained using aconventional computation method. Experimentalstudies are also carried out to verify the simulationresults. It is found that the calculated results agreewith the experimental values. For most pulsed laserbending processes, the newly developed method isthe only possible way to compute bending within areasonable amount of time.C.Carry, W.J.Cantwell et al [6] presentexperimental results of graphite coating on lasersheet bending. Due to the optical nature of lasermaterial processing it is often necessary to reducethe reflectivity of surface to be processed or toprotect the surface from irradiation of laser. In manycases graphite is used for coating in spray form, toachieve this. Graphite is normally selected for itshigh absorptivity qualities, ease of application,availability and for economic reasoans. The methodof application greatly varies the resultant graphitelayer and therefore level of absorption ad types ofinteraction. Trying to apply thick layer at oncereduces surface roughness, which in turn increasereflectivity reduces the advantages of the graphitecoating. Also graphite layer buildup process isnonlinear process with initial layer having sub 10micron thickness and additional layers being 15-20micron thick.M.Gollo, S.Ding et al [7], present that the processof laser bending requires numerous experiments topinpoint parameters that produce the highestbending angle of sheet metals. The effects of laserpower, beam diameter, scan velocity, pass number,pulse duration, sheet metal thickness and proposedparameter for material properties on bending anglewere investigated. The Taguchi method and analysisof variance (ANOVA) were applied to find outsignificant parameters in laser bending. An equationthrough regression analysis was introduced topredict the bending angle with respect to theseparameters. The optimum laser bending angle wasalso determined by using signal-to-noise (S/N) ratiomethod. The influence of various processparameters on bending angle in the laser bendingprocess has been investigated in this paper. ANOVAwas used for the experimentation. Factors which aredetected to have most significant effects on bendingangle are found to be: i) Pass number, ii) Materialparameter, iii) Sheet thickness, iv) Scan velocity, v)Beam diameter. Other factors which have less effecton the bending angle under this condition are asfollows: i) Laser power, ii) Pulse duration. Thecorrelation between factors and bending angle wasderived by using a regression analysis. Anoptimized parameter combination for the maximumbending angle has been obtained by using theanalysis of S/N ratios.M-L Chen, J Jeswiet, P J Bates, and G Zak etal[8], Present in this experimental study, the two-dimensional laser bending of the low-carbon steelsheet demonstrated that a 940Nm diode laser is aneffective tool for laser forming of carbon steelsheets. No additional surface coating is required.The buckling mechanism may be the main sourcecontributing to the large angle of bend as well as themixed bending up and bending down for the laserbeam width to sheet thickness aspect ratio close to4; both temperature gradient and bucklingmechanisms contributed to the lower bend anglesfor a laser beam width to sheet thickness aspect ratioless than 2. This laser beam width study showed thatthe maximum bend angle depends mainly on thematerial thickness, not the power intensitydistribution across the bend line for the given laserbeam profile and material thickness range testedhere. However, a more evenly distributed laser beamis preferred to a sharp one for obtainingapproximately the same bend angle but with lessmaterial property and surface appearance changes.For obtaining the same bend angle, less laser lineenergy is required if a higher laser scan speed isapplied, except for the extreme high-line energylevel. Laser bending is more effective in the initialnumber of passes. So, a multi-path bend strategymay be preferred for maximizing the total bendangle as well as reducing the bend surfacemorphologychange.III. CONCLUSIONTo get the better results of force formingprocess, various models and experiments publishedby previous authors are critically examined and
  8. 8. Ms. Sweety patel, Prof. R.I.Patel / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp. 1239-12461246 | P a g eretrieved to optimize the parametric control over theforming process. The contributions and conclusionsare as follow.Bending angle increased with the laserpower and pulse duration, and decreased with thelaser scan speed. There was an optimum spotdiameter for which bending angle was themaximum. Bending angle increased with theincrease in overlap, and decreased with the increaseof gap at a constant laser power. However, for theconstant line energy, there was an optimum valuefor both overlap and gap corresponding to themaximum bending angle. Bending angle increasedwith the increase of pulse width at constant laserpower, but it showed a decreasing trend atconstant pulse energy. It increased with theincrease of pulse energy in both overlapping anddiscrete spots laser forming. Moreover, for thesame pulse energy it was seen to be more in case ofoverlapping spots.ACKNOWLEDGMENTIt is a privilege for me to have beenassociated with Professor R.I. Patel, Head ofmechanical engineering department, Governmentengineering college, Dahod, during this paper work.I express my sincere thanks to him for valuableguidance and constant inspiration.REFERENCES[1] K.C. Chan, J. Liang, “ Laser bending of aTi Al-based intermetallic alloy”, MaterialsLetters 49 _2001.pp.51–55[2] Gigliola Lubiano, Jorge A. Ramos,“Laser Bending of Thin Metal Sheets byMeans of a Low Power CO2 Laser”[3] K. G. Watkins, S. P. Edwardson, J. Magee,G. Dearden, P. French,” Laser Forming ofAerospace Alloys”, AerospaceManufacturing Technology ConferenceSeptember 10-14, 2001Washington StateConvention & Trade Center Seattle,Washington, USA[4] A.R. majed, F.Ahmadi, M.Farzin,“Experiment and finite element simulationof laser bending of tubes”,Iranianconference on manufacturingengineering(ICME2009), march 3-5,2009,Birjanal, Iran[5] X. R. Zhang, G. Chen1, X. Xu2,”Numerical Simulation of Pulsed LaserBending”, Vol. 69,p-p 254-263, MAY2002, Transactions of the ASME[6] C.Carry, W.J. Cantwell, ”Effect of laserinteraction with graphite coating”, LaserAssisted net shape Engineering 5,proceedings of the LANE 2007.[7] M. Hoseinpour Gollo, S. Ding,“Experimental analyses of bending angleby a pulsed Nd:YAG laser in sheet metalforming process”, Scientific Research andEssays Vol.7(3), pp. 279-287, 23 January,2012[8] M-L Chen, J Jeswiet, P J Bates, and G Zak,” Experimental study on sheet metalbending with medium-power diode laser”,Proc. IMechE Vol. 222 Part B: J.Engineering Manufacture.[9] Darpan Prakash Shidid ,“Theoretical andExperimental Analyses of Titanium SheetMetal Bending by Nd:YAG” March 2011