Research on Technology of Laser Induced Forming of Integral Panel with Crossed Reinforcing Bars of 5A06 Aluminum Alloy

Author:Fu Shou Chong

Supervisor:wang yang

Database:Doctor

Degree Year:2018

Download:8

Pages:163

Size:10094K

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Lightweight panel had the property of high strength and rigidity though the weight was small.So the lightweight panel was used widely in the aerospace industry as it could decrease the weight of the aircraft.Though the lightweight panel had many advantages,the panel was very hard to form because of the complicated structure which restrict the application of the lightweight panel such as the lightweight panel with stiffeners.The forming of the lightweight panel with traditional forming technology was with low efficiency and high cost,and so a new forming technology was needed urgently to form the lightweight panel efficiently.Laser induced forming technology was a dieless forming technology which used a high energy density laser beam to induce strong temperature gradient and plastic strain in the heat zone,so the plate would bend to a certain angle.Laser induced forming technology had the property of high efficiency and low cost,so it would be a good choice to form the lightweight panel.The integral panel with crossed reinforcing bars(PWCRB)made of 5A06 aluminum alloy was a type of lightweight panel,and in this paper the laser induced forming technology of this type of integral panel was investigated.In order to investigate the forming behaviour of the PWCRB under laser induced forming,in this paper,the thermal elastic-plastic constitutive model was established and the finite element model for laser induced forming was established based on the thermal elastic-plastic constitutive model.The laser induced forming experiments of 5A06 aluminum alloy sheet were carried out: the temperature distribution was tested using infrared thermal imager and thermocouples.The deformation of the sheet was measured using a 3D scanner.Built on the experiments,the finite element model was verified.The schematic of edge effect in the laser induced forming process was interpreted through numerical simulation of the 5A06 aluminum alloy sheet.The laser induced forming process of the PWCRB was investigated numerically,and the analyses of the temperature distribution as well as the stress and strain distribution were carried out.The results showed that the plastic strain along the scanning line induced the edge effect.When the deformation was the same,the spot size had the largest influence on the deformation of the panel,followed by the laser power and the scanning speed.Based on the heat transfer equation of a semi-infinite solid,an analytical model of influence of process parameters on the maximum temperature was established.The mechanism of the influence of process parameters on the deformation of the panel was analyzed.The influence of the width of the PWCRB on the deformation was simulated.The results revealed that the total equivalent thermal moment perpendicular to the scanning line increased with the increasing of the width of the panel which induced the increase of the edge effect of the panel.The numerical simulations of the influence of different position of the panel along the scanning line on the deformation of the panel were carried out.The results indicated that the deformation of the plate around the stiffener had the largest influence on the deformation of the panel,especially the inner plate.The numerical simulations subjected to the unexpected twisting phenomenon of the panel were carried out.The distribution of the temperature as well as the stress and strain was discussed.The results revealed that large compressive stress and bend stress existed in the middle stiffener and increased as the process continued.The equivalent model of the cross section of the panel was established as well as the buckling critical loads of different stiffeners,and the result revealed that the buckling critical load of the middle stiffener was less than that of the marginal stiffener.So when the load suffered by the middle stiffener excessed the buckling critical load of the middle stiffener,the middle stiffener would first suffer lateral-torsional buckling which induced the unexpected twisting phenomenon of the panel.The corresponding consistency-deformation scanning strategy(CDSS)was proposed and was proved to be effective to avoid the unexpected twisting phenomenon of the panel.In the laser induced forming process of the PWCRB,the absorptivity of the panel was very small,and graphite was used to coat on the panel to increase the absorptivity of the panel.The corrosion phenomenon of the surface of the panel was observed when the panel was coated with graphite solution with water as the sovent.In order to investigate the reason of the corrosion,the energy spectrum analyses of the corrosion surface of the panel were carried out.The results revealed that the electrochemical corrosion phenomenon happened.The corrosion of the surface of the panel was avoided by coating graphite solution with absolute ethyl alcohol as the sovent.In the laser induced forming process of the panel,in order to ensure the accuracy of the panel,a precision model which took the deformation of each scanning position as the criteria was established.So a theoretical foundation was provided to ensure the forming accuracy in the laser induced forming of the panel.On the basis of the consistency-deformation scanning strategy(CDSS)and the precision model,the experimental investigations were carried out.The rules of the consistency-deformation in different positions of the panel were analyzed and the precision of the panel was tested using 3D scaner.Taking the consistency-deformation of different stiffeners as the optimized target,the processing parameters were optimized.The results showed that the panel with different dimension could be formed with the consistency-deformation scanning strategy.