Study On Laser Joining With Trailing Rolling Technology Of Cfrp And Aluminium Alloy

Carbon fiber reinforced plastics(CFRP)are widely applied in aerospace,automobile industry,and new energy equipment due to the low density,high specific strength and specific modulus,and strong corrosion resistance.Aluminium alloys are promising materials in the development of automobile lightweight,among which the6061 aluminum alloy has a large proportion in complete vehicles.With the further development of lightweight process of automobile industry,the joining of CFRP and6061 aluminium alloy will be involved.Laser joining is a non-contact and efficient joining method,whose advantages over mechanical joining,adhesive bonding,and plastic deformation joining are fast,small heat affected zones and easy to automate.At present,existing researches of laser joining of CFRP and aluminium alloy are all carried out with small-sized specimens.The laser joining of large-sized sheets which is commonly applied in automobile production has not been reported.The resin on CFRP which use continuous carbon fiber as reinforce phase is little and can not fully fill the micro structures or grooves on aluminium alloy surface in laser joining process,weakening the mechanical properties of CFRP-aluminium alloy joints.Thus,developing laser joining technology of continuous carbon fiber reinforced CFRP and aluminium alloy sheets has a great significance of promoting its application in automobile industry.We have first designed and manufactured laser joining with trailing rolling device,comprising cylinder system,pressure conduction system,laser head system,and pre-clamping roller system.Among them,cylinder system is the core and directly connected to the machine tool.Pressure conduction system,laser head system,and pre-clamping roller system are installed in different parts of cylinder system.The main roller and pre-clamping roller system can follow the laser beam for a long distance movement to achieve joining with trailing rolling.Pressure is applied by moving the machine tool in the z-axis direction,and the roll pressure can be adjusted according to the variable of the compression spring in the pressure conduction system.When the height of weld seam varies,the cylinder in the cylinder system can ensure good contact between the roller and weld seam,keeping the pressure acting on the weld seam constant.In addition,when the sizes of the joining sheets are small or the thermal deformation is not obvious,the pre-clamping roller system may not be needed.Then the study of laser joining with trailing rolling of continuous carbon fiber reinforced CFRP and aluminium alloy has been conducted,which also testified the feasibility of laser joining with trailing rolling device.CFRP with size of 60 mm×25mm×2 mm and 6061 aluminium alloy with size of 60 mm×30 mm×2 mm were used to investigate the effect of laser power and joining speed on the mechanical properties of joints and full process window has been obtained.With the pre-treatment methods of femtosecond laser texturing on 6061 aluminium alloy surface and presetting matrix resin at interface,the highest shear strength of joints was 32.58 MPa.On this basis,CFRP and 6061 aluminium alloy both with size of 220 mm×70 mm×2 mm were used to investigate the effect of roll pressure on the mechanical properties of joints.The result indicated that CFRP and 6061 aluminium alloy could not be adjoined tightly with each other when the roll pressure was low,while the melted PA6 resin was squeezed out of the bonding interface when the roll pressure was high.The joints were well formed and the highest shear load per unit length of weld seam was 134.49N/mm at proper roll pressure.