Structural Optimization And State Control Of Carbon Fiber Braided Carriers During End Face Vertical Braiding

Carbon fiber is a new type of composite material with excellent properties such as high strength,high modulus,high temperature resistance and corrosion resistance.Carbon fiber braiding products are often called carbon fiber preforms,which have the advantages of good flexibility,no kinking,no rotation,and strong contouring ability.The carbon fiber preforms are reinforced with RTM,VARTM and other techniques to obtain the final braiding products.Based on the present technology,the carbon fiber is braided into various shapes of preforms,such as I-beam,F-beam,conical sleeve and variable cross-sections.Through being reinforced by RTM,carbon fiber preforms become various structural parts such as plates,beams and shafts,which are used in various industrial fields.However,there are still many problems to be solved in the existing braiding processing methods,such as errors between actual values and theoretical values of the structural parameters,and material damage during the braiding process.Only by continuously improving the braiding process and combining the new composite materials,the braiding products can be more excellent,and the braiding technology can be pushed to the next industrial application peak.The braiding carrier is a very important actuator in the carbon fiber braiding process.It has the functions of carrying carbon fiber,adjusting the length of carbon fiber,and controlling the tension of carbon fiber.In addition,the trajectory of the carrier is inextricably linked to the released law of carbon fiber.The carbon fiber tension applied by the carrier has a direct influence on the carbon fiber damage and the braiding parameter error.Therefore,the braiding carrier plays a decisive role in the quality of the braiding products.During the braiding process,the braiding carrier will adjust the released length and control the tension of the carbon fiber according to the needs of the braiding task.The carbon fiber and the ceramic ring produce sliding friction at the outlet of the top of the carrier,which causes damage to the surface of the carbon fiber.In addition to this,the carbon fiber forms a carbon fiber catenary between the carrier outlet and the braiding point.The clockwise braided carbon fiber and the counterclockwise braided carbon fiber rub against each other in the catenary segment,which causes secondary damage on the surface of the carbon fiber.At the same time,the carbon fiber forms a bending angle due to frictional force,thereby causing a braiding angle error.The regulation of carbon fiber tension by braiding carrier has become an important research point of carbon fiber braiding technology.It is of great significance for the future development of carbon fiber braiding technology.In order to obtain a better braiding product,this paper sets the widely used end-face vertical carbon fiber braiding machine as the research equipment.Firstly,model is analyzed for the tension regulation of the carbon fiber braiding carrier.Then,the structural optimization and state control are performed based on the above model.Finally,the optimization effect is judged based on the friction of the carbon fiber and the braiding angle error before and after optimization.The main contents are as follows:1)In order to obtain the working condition of the carbon fiber braiding carrier,firstly determine the structure and principle of the end face vertical carbon fiber braiding machine;then calculate and analyze the important parameters of the braiding process;finally analyze the regularity and relative position of the carrier movement under the common three carrier arrangements.2)In order to obtain the released law of carbon fiber,the trajectory of the carrier slider is segmented to calculate the mathematical model of the ideal trajectory of the slider.The released law of the carbon fiber from the carrier can be calculated based on the relative position of the carrier,the slider,the outlet,and the braiding task parameters.Considering that there is a certain collision between the carrier slider and the braiding track during the actual working process,the structural model of the braiding track is established,and the critical situation is calculated separately when the carrier slider collides with the arc track and the linear track.Collision analysis is performed using multi-body dynamics,and Adams is used for dynamic simulation verification.The results show that the length of the carbon fiber catenary and the length of the carbon fiber wound around the surface of the mandrel can be calculated according to the trajectory model of the slider and the structural parameters of the mandrel.Finally,the released law of the carbon fiber from the carrier is obtained.Comparing the calculation results of the ideal trajectory model with the collision trajectory model,it is known that the collision between the slider and the track has little influence on the movement path of the carrier,and there is no interference in the regulation of the carbon fiber length.The slight difference caused by the collision can be negligible in the subsequent calculation process.However,the collision will cause a large acceleration of the carrier,which will adversely affect the stability of the carrier movement and the working environment.3)Based on the released law of the carbon fiber from the carrier,a mathematical model of the carrier is established for controlling the tension of carbon fiber.In order to obtain accurate results,the spatial position and fit relationship of each component of the carrier are substituted into the model.Then the relationship between the carbon fiber unwinding point,the rotation angle of the lever and the released length of the carbon fiber is obtained,finally a carbon fiber tension control model is established.The Minakov theory is used to calculate the carbon fiber tension values on both sides of the pulley,so as to obtain the influence of the carrier on the distribution of the carbon fiber tension.The results show that the carbon fiber tension changes periodically after the braiding work enters a stable state.In the single spring adjustment state,the carbon fiber tension value fluctuates within a small range,which can satisfy the steady state of the carbon fiber tension,and avoid the large tension change caused by the length fluctuation in the non-woven state.After entering the double spring adjustment state,the carbon fiber tension value is greatly increased,thereby tightening the carbon fiber to reduce the braiding angle error.The carrier adjusts the carbon fiber length to release and tighten.If the working state of the carrier changes,the carbon fiber tension value on both sides of the pulley will be replaced.4)Based on the model of carbon fiber tension controlled by carrier,key structural parameters of carrier are selected for optimization.Through analysis,it is found that the carbon fiber tension in the braiding process is mainly affected by the starting angle of the three control states,the length of the lever,the elastic coefficient of the spring 1,the pre-compression amount of spring 1,the elastic coefficient of the spring 2 and the pre-compression amount of spring 2.Because the ant-lion algorithm can globally search and converge fast,it is used to optimize the above eight parameters.In the optimization process,different optimization objectives can be set according to the processing tasks and the braiding materials.By setting the three optimization objectives such as the overlap time of the carbon fiber tension state,the carbon fiber tension value and the carbon fiber fluctuation frequency,the structural parameters of the carrier are respectively obtained,which satisfy the processing requirements.In the calculation process,multiple optimization objectives can be merged into one comprehensive optimization objective by introducing optimization weights.And the optimization direction of the optimization is adjusted by changing the weight values.Finally,a new structure of braiding carriers is obtained,which satisfies the processing requirements.5)Based on the law of the braiding carrier movement,the spatial structure model and force model of carbon fiber catenary are established.During the braiding process,the clockwise braiding carbon fiber and the counterclockwise braiding carbon fiber come into contact at the catenary segment,then the friction is generated due to the relative motion.Friction will cause the monofilaments on the surface of the carbon fiber to break.When the number of broken monofilaments is large,a relatively pronounced fluffing phenomenon occurs.The structure of catenary is calculated by using the "Frontal Approach" model proposed by J.H.van Ravenhorst.In order to obtain a more accurate calculation result,the coordinates of the carriers' outlet are set as the initial values of the iterative calculation.For the three common carrier arrangements such as 1F1 E,2F2E and 1F3 E,the spatial structure model and force model of carbon fiber catenary are established respectively.Finally,the optimization effect of the carrier structure is verified by the calculation of the friction of the carbon fiber and the braiding angle error.This paper models and optimizes the tension control of the carbon fiber braiding carrier.The principle and the change of controlling carbon fiber are obtained in the braiding process.Finally,the optimization effect of the carrier structure is judged by calculating the friction of the carbon fiber and the braiding angle error,which provides a theoretical basis for the optimization and improvement of the braiding process and equipment.