Research On Preparation And Laser Connection Techniques Aiming At Achieving Composite Fibers Consisted Of Carbon Fiber And Thermoplastic Resin

To date,one of most important issues in the manufacturing industry is lightweight design.In that regard,compared with metal(iron,stainless steel or aluminum),continuous carbon fiber reinforced thermoplastic polymer(CCFRTP)has attracted great attention for its excellent properties such as low density,high strength to weight ratio,excellent corrosion resistance,anti-fatigue performance and anti-deformability,as well as the flexibility of large structures.At present,the research of the preparation of CCFRTP and the process of joining them using laser welding technique are still in the initial stage.In this paper,a novel structure of the continuous carbon fiber(CF)with thermoplastic resin(PA12)are proposed,and the resin layer of CFRTP surface are melted by YSL-10000 fiber laser.The effects of different parameters on the electrostatic adsorption,tube extrusion and the melting process are investigated and the conclusions can be drawn as follows:First,the continuous CF and thermoplastic engineering plastic resin powder Nylon 12(PA12)are used as the model,and carbon fiber is fixed on the electrostatic fluidized bed to absorb certain resin powder by electrostatic absorption.Orthogonal experimental design method is used to obtain the optimal parameters,amongst which the most important one is the absorbing time,followed by fiber type,fiber splitting numbers,airflow pressure and static voltage.When the resin powder is 70?m in diameter,the optimal parameters are as follows: the absorbing time 1 min,static voltage 30 kV,airflow pressure 0.14 MPa,fiber type 3k,and the fiber bundle is split into 4 bundles equally.Second,the extruding process is conducted on an industrial single screw machine with high pressure and temperature to make resin powder melt and plasticize,and then a thermoplastic resin tube will be coated on the moving carbon fiber,followed by extrusion at low temperature.In the tube extrusion experiment,the weight percentage of carbon fiber can be tuned by tuning the thickness of coating layer,which is in the range of 34%~71%.When the speed of carbon fiber exceeds 16 m/min or that of the screw is lower than 80r/min,the coating resin layer would be incomplete due to a lack of PA12 powders coated on the carbon fiber,thereby resulting in the exposure of some carbon fibers.Therefore,the speed of the moving fiber and rotating screw are to be controlled to achieve a coating layer with a certain thickness.In addition,through exploration on laser melting resin matrix of thermoplastic composite,the optimal welding parameters for molding PA12/CCF pipe are listed as follows: Axis rotation speed: 13r/min;Laser power: 150 W;Laser beam spot diameter: 4.9 mm(+70 defocus);Laser moving speed: 0.5mm/min.The resin on the PA12/CCF material's surface is completely melted and consolidates into a neat and smooth layer with a uniform thickness and high molding quality.When the laser output time exceeds 2min,the length of the PA12/CCF sample plastic pipe increases from 3.35 cm to 6.70 cm.To achieve a PA12/CCF sample plastic pipe with a respectively thick wall and high molding quality,the materials can be welded at maximum twice.At last,another thermoplastic composite material(PEEK/CCF)is prepared,which is very thin(0.8mm)and has a large tensile strength in the direction of continuous carbon fiber.The PA12/CCF sample is soft and can be easily bended.However,the PEEK/CCF sample is easily broken in the vertical direction,making it difficult to be processed into complex structures by using laser fusion bonding technique.The continuous carbon fiber improves the rigidity and strength of PEEK material.Nevertheless,the tensile strength of PEEK/CCF is greatly reduced indicated by the tensile test after laser-scanning of the surface resin matrix.