Laser Forming of Fibre Metal Laminates - Lasers and Laser ... · Laser Forming of Fibre Metal Laminates S. P. EDWARDSON1*, P. FRENCH1, G. DEARDEN1 K. G. WATKINS1, W. J. CANTWELL2

Laser Forming of Fibre Metal Laminates

S. P. EDWARDSON1*, P. FRENCH1, G. DEARDEN1

K. G. WATKINS1, W. J. CANTWELL2

1Laser Group, 2Impact Research Centre, Department of EngineeringUniversity of Liverpool, Liverpool, L69 3GH, UK

The laser forming process has been shown to be a viable method ofshaping metallic components, as a means of rapid prototyping and ofadjusting and aligning. Although the process does compete withconventional forming processes, applications are being discoveredwhere laser forming alone can achieve the desired results. Theapplication reported in this work demonstrates how the process can beused to form recently developed high strength fibre metal laminatematerials. These materials due to their construction and high strength aredifficult to form once constructed using conventional techniques. Fibremetal laminates are of particular interest to the aerospace industry, wherethe high strength yet lightweight construction of parts made with thesematerials offers significant weight reductions and hence a reduction inoperational costs of new large commercial aircraft such as the AirbusA380. In addition a more recent application under investigation for thesematerials is in the construction of street furniture (e.g. litter bins) andairline cargo containers utilising their excellent blast resistancecapabilities to save lives in the event of terrorism.

Keywords: Laser Forming, Bending, Fibre Metal Laminates, Metal LaminateComposite, FML, MLC, GLARE

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____________________________*Corresponding author: [email protected]

Lasers in Eng., Vol. 15, pp. 233-255 © 2005 Old City Publishing, Inc.Reprints available directly from the publisher Published by license under the OCP Science imprint,Photocopying permitted by license only a member of the Old City Publishing Group

1. INTRODUCTION

This investigation is primarily concerned with the process of laserforming or laser bending of metal sheet material with a high power laserbeam. Laser forming has become a viable process for the shaping of

metallic components, as a means of rapid prototyping and of adjusting andaligning. The laser forming process is of significant value to industries thatpreviously relied on expensive stamping dies and presses for prototypeevaluations. Relevant industry sectors include aerospace, automotive,shipbuilding and microelectronics. In contrast with conventional formingtechniques, this method requires no mechanical contact and thus promotesthe idea of “Virtual Tooling.” It also offers many of the advantages ofprocess flexibility associated with other laser manufacturing techniques,such as laser cutting and marking [1]. Laser forming can produce metallic,predetermined shapes with minimal distortion. The process is similar to thewell established torch flame bending used on large sheet material in the shipbuilding industry but a great deal more control of the final product can beachieved [2]. The laser forming process is realised by introducing thermalstresses without melting into the surface of a work piece as a de-focusedlaser beam is passed over it. These internal stresses induce plastic strains,bending or shortening the material, or result in a local elastic plasticbuckling of the work piece depending on the mechanism active [3].

The range of materials that can be laser formed is considerable. As thereis only localised heating involved below the melting temperature goodmetallurgical properties can be retained in the irradiated area [4, 5].Materials of particular interest are specialist high strength alloys [6]. Theseinclude titanium and aluminium alloys. These materials are widely used inthe aerospace industry where the implementation of laser forming as areplacement of existing manufacturing processes is under investigation [7,8, 9, 10] as well as other industry areas [11, 12, 13, 14]. The applicationreported in this work demonstrates how the laser forming process can beused to form recently developed high strength Fibre Metal Laminate materials.These materials, due to their construction and high strength, are difficult toform once constructed using conventional techniques. Fibre Metal Laminates(FML), sometimes referred to as Metal Laminate Composite materials (MLC),are of particular interest to the aerospace industry, were the high strength yetlightweight construction of parts made with these materials offers significantweight reductions and hence a reduction in operational costs of new largecommercial aircraft such as the Airbus A380 and the proposed ultra-efficientBoeing 7E7. Other industries where these materials are of interest includeautomotive, in particular the high performance sports car and racing sectorssuch as Formula One. A more recent application under investigation for thesematerials is in the construction of street furniture (e.g. litter bins) and airline

234 EDWARDSON, et al.

cargo containers utilising their excellent blast resistance capabilities to savelives in the event of terrorism.

2. MATERIALS

The materials investigated in this study are composite laminates orlayered structures. FML or MLC consist of thin sheets of aluminium bondedand alternated with thin sheets of fibre reinforced composite (figure 1). Thefirst FML was ARALL (Aramid Reinforced ALuminium Laminates)developed at the Delft University of Technology, a combination ofaluminium and aramid/epoxy [15]. Although the material showed promise,adoption by the aerospace industry for which it was developed was slow.With the development of GLARE (GLAss REinforced), an aluminium glassfibre laminate, a commercial breakthrough came when Airbus decided touse the material on its 650 seat A380. GLARE was intended to be analternative to aluminium in aircraft structures. Research has shown it hasbenefits over both aluminium and glass fibre reinforced composites,especially in fatigue and impact. By the selection of different types oflaminate components, together with the possibility to vary the volumefraction of the composite and fibre orientation, a wide range of materialproperties of the resultant product can be produced [15, 16]. The FMLmaterials used in this investigation have been developed in the MaterialsScience Division of the University of Liverpool, work is ongoing to develop

LASER FORMING OF FIBRE METAL LAMINATES 235

FIGURE 1Schematic of the FML lay-ups used in the investigation.

materials (or material combinations) that require much shorter manufacturingtimes and have superior impact resistance. Four types of materials wereinvestigated of different lay-ups or construction, a schematic of theconstruction, lay-ups and nomenclature for the FML used is shown in figure 1.

The first material used was a laminate of 0.3mm aluminium 2024 alloy anda glass reinforced polyamide. The polymer is a thermoplastic which has amelting point of approximately 280ºC. The second material was a laminate of0.3 mm aluminium 2024 and a self-reinforced polypropylene; this polymer isalso a thermoplastic which has a lower melting point of approximately 165ºC.The third material was a laminate of 0.3mm aluminium 2024 and a glass fibrereinforced polypropylene, the polymer here has a similar melting point to theprevious material. Unlike the other materials used where the fibre orientationsare orthogonal and bi-directional, it was possible with this last material to setthe fibre orientations as bi-directional (standard) or in a single direction so asto investigate the effect of material anisotropy. A fourth GLAREthermosetting type material was also investigated after work was completedon the previous three material combinations. This material was a 2/1 lay-upcombination of 0.9mm Al2024 and glass fibre reinforced epoxy. The reasonsfor investigating this lay up combination involving a thermosetting polymerwill be discussed later.


FIGURE 24/3 Polyamide based FML as Received Section.

The materials were manufactured using Teflon coated steel mouldswhere the laminates are laid up, using a polypropylene bonding interlayer tobond the pre-preg composite material to the aluminium. The moulds werethen heated and a pressure applied to the upper surface to melt the bondinglayers. A mounted and polished section of a 4/3 glass reinforced polyamidebased FML is shown in figure 2.

FML materials can be formed conventionally into components. Howeverdue to their high strength and laminated construction, difficulties can arisesuch as a limited minimum bend radius and the need for a metal layer withinthe laminate in order to deform it. The materials have considerableanisotropy and its axes change direction as any forming operation proceeds.Also, in laminated parts the layers can slip over one another. Another factoris the large residual stresses that remain between each layer aftermanufacturing, this can produce considerable distortion in a formed part.

The aim of this study was to demonstrate the potential of laser forming asa manufacturing tool for FML materials, either as a means of directmanufacture or a means of alignment and distortion removal.

3. EXPERIMENTAL

This investigation consists of an initial feasibility study to determinewhether or not laser forming could be used to bend FML materials, a moredetailed study of the laser forming characteristics and an investigation into theimplications of laser forming on the material structure, including thermocoupleanalysis. A coupon size of 80x40mm was used throughout these studies and thebend line was always across the shortest width (i.e. a 40mm long bend) in themiddle of the coupon. Energy parameters consistent with the temperaturegradient mechanism (TGM) were used throughout this study. This mechanismproduces a bend towards the laser [3]. An additional investigation was alsoperformed to demonstrate the capability of the process to form larger morecomplex structures from 200x100mm coupons of FMLs.

3.1 Experimental Set-upAn Electrox 1.5 kW CO2 laser, wavelength 10.6µm, operated in a

continuous wave mode was used for the forming process. The laser beamwas fed via turning mirrors to a set of X-Y-Z CNC tables for beammanipulation. The FML coupons were guillotine cut to the correct dimensions


and the upper surfaces were cleaned with acetone. They were then sprayedwith graphite in order to increase the absorption of the 10.6µm radiation. Thecoupons were clamped 30mm from the scan line along one edge duringprocessing using an aluminium clamp as can be seen in figure 3.

A laser range finder was used to record height data either side of theirradiation line and hence determine the bend angle after each pass. Thesensor can be seen to the right of the processing head in figure 3.Combined with Galil software/PC based control of the CNC axes andshutter, the system was fully automated, producing bend angle output tofile after each pass. The thermocouple analysis of a multi-pass strategyusing a single Al foil was performed using K type thermocouples, whichhave a range of -200 to 1370ºC. The thermocouples were attached to thebottom surface of the foil on the centreline of the laser irradiation lineusing adhesive pads. An Agilent 34970A data acquisition unit was used torecord the temperature data from the thermocouples, acquiring data at upto 250 readings per second. In order to verify the material integrity, the


FIGURE 3Experimental Set-up.

laser formed samples were cut using a band saw, mounted, polished andphotographed using an optical microscope. The materials could not beetched due to the presence of the composite.

4. RESULTS & DISCUSSION

4.1 Feasibility StudyThe initial concept for the use of laser forming with FML materials was

specifically based around the development of new thermoplastic based fibrereinforced composites with high melting temperatures. In that it was thoughtthat it may be possible to form the material as if it were the equivalentthickness of metallic solid, generating a semi-uniform thermal gradientthrough the thickness (TGM) [3], this can be seen in figure 4.

Initial tests on 1.38mm thick 2/1 glass reinforced polyamide based FMLusing 800W, a 5mm beam diameter and 80mm/s processing speed producedexcessive melting of the upper 0.3mm Al 2024 layer, with little or no heattransfer into the lower layers. This led to the conclusion that due to theextreme differences in thermal properties between each of the layers in anFML lay-up it is not possible to set-up a uniform thermal gradient through


FIGURE 4Treating the section as a metallic solid results in a buckling of the Upper Layer due to non-TGM parameters and excessive heating.

the thickness. However, as the TGM causes a plastic compression just of theupper surface layers of a solid metallic section, it was thought that byforming by TGM the upper aluminium layer alone, a moment could begenerated sufficient to bend the material section (figure 5).

Initial tests of this theory found that it was difficult to set up the TGMacross the 0.3mm thickness. The material tended to buckle (BucklingMechanism [3] ) and as the upper layer was constrained the buckle tended tobe away from the laser and hence delamination occurs. Figure 4 shows theresults of a 2/1 glass reinforced polyamide based FML processed at 300W,3mm beam diameter and 90mm/s.

By tuning the processing parameters for a high thermal gradient acrossthe thickness of the upper aluminium layer, it was possible to produce asignificant bend in the 1.38mm 2/1 glass reinforced polyamide based FMLwithout any melting or damage (figure 5). Figure 6 shows the results ofincreasing numbers of passes using two different processing parameters,hence demonstrating the feasibility of using laser forming to bend FMLmaterials. Additionally, what can be noted from this is the relatively smallenergy input required to bend the material.

4.2 Laser Forming Characteristics of FML MaterialsA number of studies were conducted in order to determine the laser forming

characteristics of laminated materials. The first study was a repeatability test in


FIGURE 5Laser forming the upper layer alone results in a positive bend, no melting and no obviousdamage.

order to confirm the initial results. Figure 7 shows the results of laser formingthree 2/1 glass reinforced polyamide based FML coupons at 200W, 90mm/sand a 2.5mm beam diameter. The results show a good repeatability of theprocess. In addition it can be seen that there is a consistent linear increase inbend angle with increasing number of passes up to 20 passes.

A study was also conducted to determine the effect of increasingnumbers of layers for each of the thermoplastic based materials tested, usingthe same energy input parameters for each lay-up. In order to determine the


FIGURE 6Laser Forming of 1.38mm 2/1 Glass Reinforced Polyamide based FML.

FIGURE 7Repeatability Test, 1.38mm 2/1 Glass Reinforced Polyamide based FML.

effect of the bottom layer on achievable bend angle when forming 2/1structures it was possible to manufacture 1/1 lay-ups (figure 1) without abottom aluminium layer. Figure 8 shows the results for glass reinforcedpolyamide based FML. A comparison was also made with the laser formingof a single 0.3mm Al 2024 foil at the same energy input parameters. Thethickness of the 3/2 and 4/3 lay-ups are 2.35mm and 3.1mm respectively.

It can be seen in figure 8 that as would be expected the achievable bendangle falls with increasing number of layers, for the 3/2 lay-up themaximum bend angle after 10 passes is 2º. This is consistent with theincrease in material strength and increasing ratio of depth of material toavailable depth of plasticized zone. Hence, the moment generated in theupper surface produces less overall bend. The limiting effect of the lowerlayers can clearly be seen when comparing the 1/1 and 2/1 forming results.The results of this study for the second material type, a self-reinforcedPolypropylene are shown in figure 9.

Here a slightly higher energy fluence was used; 150W, 1.5mm beamdiameter and 90mm/s. It can be seen that in this material using these energyinput parameters a considerable bend angle can be formed after 10 passes inthe 2/1 lay-up, of 20.6º, and in the 3/2 and 4/3 lay-ups more forming is seen


FIGURE 8The Effect of Increasing No. of Layers on the Laser Forming of Glass Reinforced Polyamidebased FML.

when compared to the forming of glass fibre reinforced polyamide basedFML (figure 8). This bend angle increase may be due to the optimisation ofthe forming parameters and/or an indication of a difference in strengthbetween the materials and hence formability.

Figure 10 shows results for the study on glass-reinforced polypropylene


FIGURE 9The Effect of Increasing No. of Layers on the Laser Forming of Self-Reinforced Polypropylenebased FML.

FIGURE 10The Effect of Increasing No. of Layers on the Laser Forming of Glass-ReinforcedPolypropylene based FML .

based FML. The fibre orientations for this study were as standard, bi-directional and orthogonal. As can be seen a comparison was made with thesingle 0.3mm Al 2024 foil, a 1/1 lay-up and the other standardconfigurations. As with figures 8 & 9 the results shown in figure 10 showthe decrease in achievable bend angle with increasing number of layersused. For the same energy parameters used in figure 8 there is less overallforming indicating an increase in material strength between the self-reinforced polypropylene and the glass fibre reinforced polypropylene basedFMLs. It can also be seen in figures 8, 9, and 10 that the bend angle rate perpass falls off with increasing number of passes. This may be due to acombination of the factors that influence the laser forming of solid metalliccomponents such as strain hardening, plus an indication of a mechanicallimit where the non-uniformity of the mechanical properties through thematerial thickness allows for a certain amount of distortion, before thebending strength of the material increases as the lower layers are placedunder increasing tensile load.

Figure 11 shows results for the effect of fibre reinforcement orientation onachievable bend angle using a 2/1 glass fibre reinforced polypropylene basedFML. The fibre orientations are reported relative to the scan line direction. Ascan be seen in figure 11, the orientation of the reinforcement fibres has a largeeffect on the achievable bend angle and hence the bending strength of thematerial. The largest bend angle 21.2º is formed after 10 passes with the fibres


FIGURE 11The Effect of Fibre Orientation on the Laser Forming of Glass-Reinforced Polypropylene based FML.

parallel to the bending line thus offering little or no additional bending strengthto the material. This study gives an insight into the effect of material anisotropyon the laser forming process. This effect could be used to improve theformability of a material in a particular orientation.

The results of all these studies show that the effectiveness of laserforming to produce sharp single bends in these materials decreases withincreasing number of layers. However there is sufficient available distortionper scan line even in 4/3 lay-ups for multiple scan line large radii bends andeven the capability to use the process to align and remove distortion post-conventional forming. It can be seen that the 2/1 lay-up shows the bestpotential for the use of laser forming as a direct manufacturing tool.

4.3 Implications of Laser Forming on Material IntegrityIt has been shown that laser forming can be used to produce significant

bends in FML materials, in particular 2/1 lay-ups. It is necessary todetermine what effect this process has on the material integrity, in particularthe effect on the thermoplastic composite material which has a relativelylow melting temperature. It has been described earlier that the approachtaken to laser form these laminated structures relies on forming the top thinlayer and as such a very small energy input is used. In order to determinehow much heat is transmitted through the upper aluminium layer to thecomposite material a thermocouple study was performed. A thermocouplewas mounted on the bottom surface of a 0.3mm Aluminium foil under thescan line, the foil was then processed using the empirically determineenergy parameters. Figure 12 shows the thermocouple results for 6 passes at200W, 90mm/s and a 2.5mm beam diameter.

As can be seen in figure 12 the peak temperature seen at the bottom surfaceduring forming is approximately 65ºC. Due to the thin section and high thermalconductivity of the aluminium the heat is rapidly dissipated after each pass. Inaddition it can be seen that thermal equilibrium is reached after the second passwith no further increase in peak temperature for subsequent passes. At thetemperatures recorded on the bottom surface and hence the temperatureexperienced by the first composite layer, there should be little or no effect onthe structure of the composite. This is backed up by optical microscopy of theirradiated area, an example of which is seen in figure 13.

This shows the irradiated zone of a 2/1 polyamide based FML after 5passes at 200W, 90mm/s and a beam diameter of 2.5mm. It can be seen thatthe composite layer appears undamaged, with no delamination and no


reduction in the distance between the upper and lower aluminium layers, allother samples processed at optimum parameters are consistent with thisresult shown in figure 13. It can be also noted from figure 13 that athickening is present in the irradiated zone of the upper layer. This isperhaps consistent with the TGM theory [3] in that as the material is


FIGURE 12Thermocouple Output for a 0.3mm Al 2024 Foil.

FIGURE 132/1 Polyamide FML after 5 passes, 200W, 90mm/s, 2.5mmØ.

shortened laterally in the upper surface layers, to account for the volume ofmaterial, there is a thickening of the section. The effect observed in the FMLsamples is very pronounced when compared to laser formed solid metalliccomponents, this could be due to the thin section of the upper layer or a uniqueeffect due to the constraints of the lower layers. Further study would reveal this.

An effect on the FML structure when processing with non-optimum


FIGURE 14Upper layer cracked due to non-optimum excessive heating.

FIGURE 15Delamination due to failure in bonding layer.

(TGM) parameters is shown in figure 14. This 4/3 polyamide based FMLwas processed using 5 passes at 300W, 90mm/s and a 3mm beam diameter.It can be seen that the upper layer is cracked, this is thought to be due toexcessive heating through the section leading to a sufficient reduction inyield stress and hence ultimate tensile strength, such that due to the limitingstrength of the lower layers, the generated compression of the upperaluminium layer in the irradiated zone is more than can be carried by theAl2024 at that temperature and thus a crack forms. Figure 15 shows how thelaser forming process on laminated materials relies on the ability to transmitthe generated moment through to the lower layers. In other words theprocess relies on the strength of the bonds between the layers. In figure 15 itcan be seen that bonding between the upper and the composite layers has failedand delamination has occurred. On closer inspection it was discovered that thepolypropylene interlayer had folded back on itself in the mould prior to curingfor this sample and thus an incomplete bond was formed.

4.4 Laser Forming of More Complex FML ComponentsIt has been demonstrated in the previous sections that it is possible to

laser form Fibre Metal Laminate materials. For 2/1 lay-ups a considerablesingle bend angle is possible, for 3/2 and 4/3 lay-ups bend angles of only afew degrees are possible in a reasonable number of passes. This limits themanufacturing capability of the laser forming of FML components.However it is possible to form large radii bends using a series of steppedsingle bends of no more than a few degrees each. An example of thisstrategy is shown in figure 16; this part-cylinder was formed from a200x100mm 2/1 glass reinforced polyamide based FML coupon, using 12scan lines at 10mm intervals, using just 2 passes per line at 150W, 90mm/sand a 1.5mm beam diameter. From figure 6, 2 passes at these energyparameters results in a bend angle of ~2.8º. Considerably more forming hasbeen achieved in coupon shown in figure 17 using the same strategy on aself reinforced polypropylene based FML. It can be seen in figure 9 thatthese parameters give ~5º after 2 passes per line.

As discussed earlier there is sufficient available distortion per scan lineeven in 4/3 lay-ups for this multi-line strategy and even the capability to usethe process to align and remove distortion post conventional forming. It canbe seen however that the 2/1 lay-up shows the best potential for the use oflaser forming as a direct manufacturing tool. As mentioned, there is arequirement for a metal layer to be within the FML to form the material


successfully i.e. a minimum of a 3/2 lay up [16], laser forming thereforeoffers a useful tool to produce bends in 2/1 lay-up FMLs. It may also bepossible to use a 3D laser forming approach [8] to form FML materials.However as can be seen in figure 10, the inherent effect of materialanisotropy may add an unwanted additional complication to a 3D problem.Work is ongoing, however, by a number of research groups [8, 13] including


FIGURE 16200x100mm Part-Cylinder formed from Glass Reinforced Polyamide based FML.

FIGURE 17240x80mm Part-Cylinder formed from 2/1 Self Reinforced Polypropylene based FML.

the University of Liverpool on systems that use predictive and adaptiveapproaches to 3D laser forming independent of residual stress history andnon-uniform material behaviour.

4.5 Laser forming of thermosetting based FML materialsAfter the success of laser forming the thermoplastic based FMLs it was

decided to verify the results using a GLARE type material (GLARE 3) [16],this material is a laminate of 2024 aluminium and glass fibre reinforcedepoxy, a thermosetting material.

As shown earlier, the laser forming process when applied to laminatestructures relies on the bending of the upper layer alone, therefore in orderto aid the process for this study, it was decided to increase the thickness ofthe Al2024 metal layers to 0.9mm, improving the laser formability of thematerial as it were by increasing the achievable moment. The materialinvestigated was a 2/1 lay-up of glass fibre reinforced epoxy and 0.9mmAl2024. The fibre directions were bi-directional and orthogonal. Thesamples were again 40x80mm.

As with the work presented earlier on the thermoplastic FMLs an initialfeasibility study was performed. The first energy parameters investigatedwere taken from the successful work on the other materials, 150W, 1.5mmbeam diameter and a speed of 90mm/s. As may be expected there was little


FIGURE 18Laser forming 2/1 GLARE type materials, initial feasibility test.

or no forming, perhaps due to the increased thickness and hence strength ofthe upper layer. It was therefore decided to increase the laser power to 300Wand leave the other parameters the same, this produced a usable result. Thisresult and the result of a repeatability test can be seen in figure 18.

Here it can be seen that it is possible to laser form this thermosettingGLARE type material to the same extent as the thermoplastic FMLs. A limitcan be seen in the data at approximately 6° which corresponds to a point weresome delamination occurs, this is consistent with the problem of a minimumachievable bend radius for these materials [16]. In addition the energyparameters used caused some surface melting, therefore it was decided toincrease the beam diameter to 3mm for a further study to establish optimumprocessing parameters where delamination does not occur. The result of thisstudy at various processing speeds can be seen in figure 19.

It can be seen here that the rate of forming per pass is governed by theenergy input, the slower the traverse speed for the same power and spot size,

the higher the energy input and hence the higher the bend angle per pass. At40mm/s it can be seen that the bend angle data is reasonably linear untilapproximately 5°. At this point (pass 5) there is a significant increase inbend angle rate per pass, as with the previous study (figure 18) this alsocorresponds to a point where some delamination of the upper layer away


FIGURE 19Laser forming 2/1 GLARE type materials at various processing speeds.

from the lower layers can be observed in the sample. In this case thedelamination appears to reduce the bending stiffness of the section as seenby the upper layer, thus allowing more deformation to occur for the givenenergy parameters. At approximately 13° (pass 7) the sample fails. Theupper layer completely delaminated on the free end of the plate (the otherend was still attached and in the edge clamp), the lower layers sprung backflat, as they were only elastically constrained and the upper Al2024 layerremained bent. Although this result demonstrates that it is possible todamage the material using laser forming, it can also be seen that as with theprevious sections there is sufficient available distortion per scan line formultiple scan line large radii bends and even the capability to use theprocess to align and remove distortion post-conventional forming. This wasobserved at 60mm/s, that providing the plate was not bent to more than 5° ina single location, no delamination or damage occurred.

In order to demonstrate the concept of multiple scan line large radii bends inthis material, a demonstration part was produced. As with the previous sectiona 240x80mm coupon was used and processed using 300W, 3mm beamdiameter, a processing speed of 40mm/s. 21 lines, 10mm step between the linesand 2 pass per line were used. From figure 19 it can be seen that these energy


FIGURE 20Laser forming a multiple scan line large radii bend, 2/1 GLARE type material, 240x80mm.

parameters would give approximately 2.5° per line, well below the 5° damagethreshold. The completed demonstration part is shown in figure 20, it can beseen that this technique employing a number of smaller bends can produce alarge overall distortion. One possible drawback with this technique however, isthe fact that only the upper metal layer is plastically deformed, the lower layersare merely elastically constrained at such a large bending radius, thus addingpossible un-wanted residual stresses between the layers. A solution to this issueand to the problem of a minimum bend radius is the (laser) pre-forming of eachmetal layers to a near required shape prior to bonding, then final alignment andadjustment with a laser forming technique.

5. CONCLUSIONS

It has been shown that it is possible to laser form Fibre Metal Laminatematerials without damage to the material or structure. The process is realisedby laser forming by the TGM the upper aluminium layer alone. The resultshave shown that the effectiveness of laser forming to produce sharp singlebends in these materials decreases with increasing number of layers. Howeverit was shown that there is sufficient available distortion per scan line even in4/3 lay-ups for multiple scan line large radii bends and even the capability touse the process to align and remove distortion post-conventional forming. Ithas been shown that the 2/1 lay-up shows the best potential for the use of laserforming as a direct manufacturing tool. As it is a requirement that a metal layerneeds to be within the material to conventionally form the material successfully(i.e. a minimum of a 3/2 laminate), laser forming offers a useful tool to producebends in 2/1 FML materials.

An insight into the effect of material anisotropy on the laser formingprocess was also presented. This effect could be used to improve theformability of a material in a particular orientation.

It was also shown that the technique could be used to form thermosettingGLARE type materials. A large part-cylinder was formed using a series ofsmall bends. An improvement to the laser formability of the material wasmade by increasing the thickness of the metal layers, so as to increase themoment generated by laser forming the upper layer alone.

Further study is planned on using laser forming to pre-bend the metallayers prior to curing to achieve larger available deformation and possiblymore complex 3D structures.


ACKNOWLEDGEMENTS

The authors acknowledge the contributions to this study by Mr JonathanHoward and Miss Heather Tjia.

Thanks are also given to Derek Riley of BP Amoco for the kind donationof the self reinforced polypropylene.

The authors are also grateful for the funding provided by the EPSRC.

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Laser Forming of Fibre Metal Laminates - Lasers and Laser ... · Laser Forming of Fibre Metal Laminates S. P. EDWARDSON1*, P. FRENCH1, G. DEARDEN1 K. G. WATKINS1, W. J. CANTWELL2