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ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 3, July, 2014

© 2014 IJMERR. All Rights Reserved

Review Article

MECHANISM OF LASER ASSISTED BENDINGFIXTURE- AN OVER VIEW

B N Nagendra Kumar1, Shailesh P S2*, Ramesh Babu K2 and Arvind Rao M Yadwad1

*Corresponding Author: Shailesh P S � shylesh_mysore@yahoo.com

Laser beam forming is a novel technique developed for the joining of metallic components. Inthis study, an overview of the laser beam forming process,the basic mechanisms of the laserbeam forming process, some recent researchstudies and the need to focus more researcheffort on designing a manually operated fixture for laser forming process is presented.

Keywords: Laser forming, Mechanisms, Bending angle, 3D model of Solid Works software

INTRODUCTION

LASER Beam Forming (LBF) is a non-contactforming process and is based on the flamebending process which was traditionally usedfor ship construction. Laser Beam Formingcan be regarded as a flexible manufacturingprocess with great potential for sheet metalforming. It is considered as a novelmanufacturing method for forming andshaping of metallic components. It is athermo-mechanically forming process thatenables component parts (sheet metals, rodsand pipes) to be formed without externalforces and does not require the use of diesas found in most traditional forming methods.The LBF process is achieved by irradiatingthe surface of the material with a defocusedlaser beam, there by inducing rapid localized

1 Department of Mechanical Engineering, NIE, Mysore, Karnataka, India.2 Department of Tool Engineering, G.T & T.C, Mysore, Karnataka, India.

heating followed by cooling as the laserenergy is either moved to the adjacent areaor switched off. The process can beconsidered as a green technology as nofumes are evolved during the process. Theschematic of the process is presented inFigure 1. As a consequence of the thermalinduced forming process, no spring backoccurs in the material after the laser formingprocess. Three major process variables thatare significant during the LBF process arethe material parameters which include; thecoefficient of thermal expansion, the thermalconductivity, the material density, latent heat,the mechanical elastic and plastic parameters(Young’s modulus, Poisson’s ratio, flow stressvs. strain curves) and the rate of laserabsorption.

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The parameters of the laser and thisinclude; the laser power, the beam diameter,the feed rate and the beam wavelength whichdepend on the type of laser in use. And lastlythe geometric parameters of the samplebeing formed which include the sheetthickness and width. The major advantageof the LBF process over flame bending iscontrollability. With LF, it is possible toaccurately control the power and geometryof the heat source. LBF process also offersmany of the advantages of process flexibilityand automation associated with othermanufacturing techniques, such as lasercutting, drilling, welding and marking. Themajor benefit of LF, from a metal formingperspective, is that spring back is completelyeliminated. Materials such as steels and otherlight alloys such as Aluminium, Magnesiumand Titanium have a high coefficient ofthermal expansion. These materials signi-ficantly deform when heated with the laserbeam. The temperature gradient developedduring the process compels the material toexpand non-uniformly, which in turn leads tonon-uniform thermal stresses. Plasticdeformation results when the thermalstresses.

THE MECHANISMS OF THE LASER

BEAM FORMING PROCESS

The laser beam forming process is achievedby introducing thermal stresses into thesurface of a workpiece with a high powerlaser beam. These internal stresses induceplastic strains that result in local elastic/plasticbuckling. The process is principally used atthe macro level to form metallic sheetmaterial. The principle behind the process offorming sheet material uses a laser beam that

is guided across the sheet surface. The pathof the laser is dependent on the desiredforming result. In the simplest case, it maybe a point and in another case it may be astraight line, rotating and wavering beamacross the whole part. The degree of defor-mation is often dependent on the formingmechanisms being employed. During thelaser beam forming process, photons travelto form a beam of light. The beam, which maynot be visible, comes out from the laser cavityand is directed towards the material processstation. Based on the laser wavelength, thebeam travels either via optical fibers ordirectly through optics to the workpiece.There are five different types of mechanismsidentified in LBF process and are herebydiscussed.

The Temperature Gradient Mechanism(TGM)

This mechanism is widely used to form sheetmaterial out of plane towards the source ofthe laser beam. The temperature gradientmechanism develops from processingconditions, one of which is rapid heating ofthe work piece surface in order to generatehigh temperature gradients in the workpiece.The thermal expansion of the heated surfacebrings about the initial bending of the sheetaway from the heat source or towards thecold side of the workpiece during the heatingprocess.

The Buckling Mechanisms (BM)

The buckling mechanism occurs in relativelythin sheets where the ratio of the beamdiameter of the heated area to the sheetthickness is relatively high that is, it could bein the order of 10 or above. This is when the

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laser beam diameter is large compared tothe sheet thickness and the processing speedis low resulting in a small temperaturegradient across the sheet thickness.

The Point Mechanism

The point mechanism is the dividing linebetween the two previously discussedmechanisms, that is, the TGM and BM. Thepoint source mechanism creates a heatedzone in the World Academy of Science,Engineering and Technology 71 2012. Usingshort pulses of the laser to introduce athermal gradient, yet the mechanism remainsa point source since the beam is stationarywhen heating the component. Longer pulsesenables heating through thicker materials,and may be mistaken for another type ofmechanism for instance buckling, howeverthe beam and workpiece are also stationarywhen in contact. Micro components may beformed with the Point source Mechanism.

The Upsetting Mechanism

The upsetting mechanism develops whenuniform heating of a localized zone isachieved through the thickness of the sheetmetal. The process parameters may besimilar to the buckling mechanism, exceptthat the diameter of the heat source is thesame as the plate thickness or larger than it.As a result of the near homogenous heatingof the sheet in the localized zone, andprevention of thermal expansion by thesurrounding material, the sheet is subjectedto near uniform compressive strain throughthe thickness of the material. At cooling, theregion contracts, and deformation occurs inthe sheet. This mechanism finds applicationsin spatial sheet metal forming and profileforming.

Coupling Mechanism

Coupling Mechanism (CM) is the combinationof the Temperature Gradient mechanism(TGM) and Upsetting Mechanism (UM). Theprocess parameter for the CM lies betweenthat of TGM and UM. From a TGM analysis,the plastic compressive deformation does notoccur at the bottom surface and for UM,plastic compressive deformation at the topsurface of the materials is nearly same asthe plastic compressive deformation at thebottom surface of the material. On the otherhand with Coupling Mechanism, plasticdeformation occurs at both the top and thebottom surface of the material but greater atthe top surface.

CURRENT RESEARCH WORK

Recent research attempts conducted on laserbeam forming of thin metal sheets reviewedin this section. First of such attempts is theresearch work conducted by designing 3Dmodel with the help of solid works software.To design a fixture that lifts the worktableupwards after laser beam scan pass to bendthin metal sheets up to 90° with the help ofexternal forces, following mechanisms areincorporated in the fixture. They are

1. Spring assisted bell crank levermechanism

2. Peauciller mechanism

Bell Crank Lever Mechanism

A bell crank is a type of crank that changesmotion through an angle. The angle can beany angle from 0 to 360 degrees, but 90degrees and 180 degrees are most common.The name comes from its first use, changingthe vertical pull on a rope to a horizontal pull

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on the striker of a bell, used for calling staffin large houses or commercial establish-ments.

A typical 90 degree bellcrank consists ofan “L” shaped crank pivoted where the twoarms of the L meet. Moving rods (or cablesor ropes) are attached to the ends of the Larms. When one is pulled, the L rotatesaround the pivot point, pulling on the otherarm.

A typical 180 degree bellcrank consists ofa straight bar pivoted in the center. When onearm is pulled or pushed, the bar rotatesaround the pivot point, pulling or pushing onthe other arm. Changing the length of thearms changes the mechanical advantage ofthe system. Many applications do not changethe direction of motion, but instead to amplifya force “in line”, which a bellcrank can do ina limited space. There is a tradeoff betweenrange of motion, linearity of motion, and size.

Peauciller Mechanism

The Peaucellier-Lipkin linkage invented in1864, was the first planar straight linemechanism the first planar linkage capableof transforming rotary motion into perfectstraight-line motion, and vice versa. It isnamed after Charles-Nicolas Peaucellier(1832-1913), a French army officer, and YomTov Lipman Lipkin (1846-1876), a LithuanianJew and son of the famed Rabbi IsraelSalanter. Until this invention, no planarmethod existed of producing straight motionwithout reference guide ways, making thelinkage especially important as a machinecomponent and for manufacturing. Inparticular, a piston head needs to keep a goodseal with the shaft in order to retain the driving

(or driven) medium. The Peaucellier linkagewas important in the development of thesteam engine.

With the help of this mechanism we havedesigned a manually operated fixture to bendthin metal sheets. For this purpose, the fixtureis designed in solid works software 2013 togenerate 3D model. Three types of 3D modeland calculations are demonstrated in thisarticle.

Figure 1: Schematic of the LaserBeam Forming Process

Figure 2: Shows Top View of the FixtureSpring Assisted Bell Crank Lever

Figure 3: Shows Front View of the Fixtureof Spring Help of Assisted Bell Crank

Mechanism

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Figure 4: Shows Work Table Lift withthe Peauciller Mechanism

CONCLUSION

Laser beam forming alternatively is a flexiblemanufacturing process that forms metalsheets by means of thermal stresses inducedby external heat instead of external forcecommon in mechanical forming process.Empirical evidences from the reviewedliterature suggests laser beam forming as aviable process for the production of sheetmetal prototypes, spring back free and non-contact process. Further more, the processhas demonstrated potential uses in manydifferent engineering applications. An over-view of the Laser Beam Forming process ahas been presented in this study as it is beenapplied in the industry, with special attentionto the LBF of titanium and its alloys.

REFERENCES

Journals

1. Amir H Rochi and M Hoseinpour (2012),“External Force Assisted Laser FormingProcess for Gaining High BendingAngles”. Journal of ManufacturingProcess, Gollo Tarbiat ModaresUniversity, Tehran, Iran, Vol. 14, pp. 269-276.

2. Ferdinand Bammer, Thomas Schumi,Andreas Otto and Dieter Schuöcker(2011), “Laser Assisted Bending forEfficient Light-weight-production”, ISSNpp. 1330-3651.

3. Gigliola lubiano and Jorge A Ramos(xxxx), “Department of Mechanical &Metarllurgical Engineering”, PortificiaUniversity, Chile. Laser bending of thinmetal sheets by means of a low powerCO2 laser.

Book

1. Design of machine elements, third editionby V B Bhndari. ISBN-13: 978-0-07-068179-8.