Research On Laser Shock Flexible Micro Forming Of Laminated Metal Composite Sheets

Owning to the superior mechanical,physical and chemical properties,laminated metal composite sheets have been applied in many fields.The research about the forming processes of laminated metal composite sheets has become a hot point.Currently,these researches are all focused on conventional quasi-static forming processes.A new technique on laser shock flexible micro forming(LSFMF)of laminated metal composite sheets was investigated in this dissertation.This process used laser shock soft punch as the flexible punch to realize the micro forming of laminated metal composite sheets under single pulse laser.The main work and results are as following:Firstly,three-layer nickel-copper-nickel metal composite sheet was selected as the experiment materials.The feasibility of this process was analyzed,and the effect law of process parameters on formability was researched.The morphology,cross section,forming depth,and thickness thinning ratio of formed parts were achieved by a VHX-1000 C hyperfocal three-dimensional microscope.The results revealed that the forming depth increased with laser energy and number of laser pulse increasing,and decreased with the thickness of soft punch increasing.The thickness reduction of external nickel layer was larger than middle copper layer,and that of middle copper layer was larger than internal nickel layer.An Axio CSM 700 true color confocal microscope was utilized to obtain the surface morphology and roughness value of formed parts.Surface roughening happened in formed parts and surface quality became worse with laser energy increasing.A HXD-1000TMSC/LCD Vickers indentation test machine was used to measure the micro-hardness.It showed that work hardening happened in formed parts,and the distribution of the amplification of micro-hardness was similar to thickness thinning ratio.Unlike conventional plastic forming processes,the formation of three-layer nickel-copper-nickel metal composite sheets did not suffer from delamination failure any more under LSFMF.Next,two-layer copper-nickel metal composite sheet was selected as the experiment materials for research,and the effect law of layer stacking sequence was discussed mainly.The results showed that,the forming depth increased with laser energy increasing,number of laser pulse increasing and thickness of soft punch decreasing.Surface roughening was happened in formed parts and roughness increased with laser energy increasing.Deformation of two-layer copper-nickel metal composite sheets was dominant by external layer.Unlike conventional plastic forming processes,it was found layer stacking sequence didn't have considerable effect on forming behavior of two-layer copper-nickel metal composite sheets under LSFMF.Another advantage of LSFMF was discovered that two-layer copper-nickel metal composite sheets were formed without any delamination till fracture under this forming process.Then,five types of micro molds with different diameters were utilized to perform the feature size effect experiment,and two-layer copper-nickel metal composite sheet was also selected as the experiment materials.It was revealed with increasing feature size,the forming depth increased,thickness thinning ratio and surface roughness first increased and then decreased.With feature size increasing,the effect of layer stacking sequence on forming depth,thickness thinning ratio,and surface roughness became increasingly larger.The difference of the thickness thinning ratio of external layer and entire sheet,and forming depth and surface roughness between Cu-Ni formed parts and Ni-Cu formed parts increased with increasing feature size,and the deformation extent was larger when the copper layer was set as the external layer.The distribution of the amplification of micro-hardness was similar to thickness thinning,but it seemed that the difference of micro-hardness between two different layer stacking sequences was not considerably influenced by feature size.Finally,ANSYS/LS-DYNA software was used to establish the finite element model of LSFMF of two-layer copper-nickel metal composite sheets,and the formability was studied furtherly,including forming depth,thickness thinning ratio,equivalent plastic stress and equivalent plastic strain.The results showed adopted the method that establish two layer metal materials independently and combine them through contact pair could obtain preferable results.The profile of the formed parts and the effect of laser energy on forming depth were in agreement with experiment results.Regardless of the layer stacking sequence,with specimen thickness increasing,forming depth decreased,thickness thinning ratio decreased,and equivalent plastic strain also decreased.With the thickness percentage of copper increasing,forming depth increased.Equivalent plastic stress and equivalent plastic strain were the largest in bottom area,and became increasingly smaller in the area which was more far away from bottom.The laser shock flexible micro forming of laminated metal composite sheets studied in this dissertation could remedy the drawbacks in conventional forming processes,and it has expansive prospects for development in micro manufacturing.Besides,the forming mechanism revealed in this dissertation have certain guiding significance for the research on laminated metal composite sheets forming process and laser shock flexible micro forming process,and it could also promote the development of size effect theory.