Research On The Technology Of Single-sided Two Needles Stitching Equipment For 3D Reinforced Composites

Three-dimensional stitching technique can improve the interlaminar properties and damage tolerance of composite materials,and it has been gradually applied to the integral forming of complex structural parts of advanced aircraft.The traditional double-sided stitching technology is limited by the stitching platform,so it's difficult to stitch complex curved surface structural parts.This paper is based on the traditional industrial sewing machine,according to the requirements of complex curved surface structure of integral forming connection technology to analysis and design of single-sided two needles stitching principle prototype which is the lead mechanism and the thread hooking mechanism are positioned at the one side of the stitching piece.The influence of the angle between two needles on the stable forming of the coil is studied by adjusting the angle between two needles.The shear strength of the composites was enhanced by stitching technique,the influence of the stitching parameters on the tensile strength of the composites stepped joint was studied.According to the forming principle of single-sided two needles stitching coil.The relationship between the motion of the conventional needle and a catcher is analyzed to find out the catcher lags behind of the conventional needle stroke.Analysis the parameters of the cam and crank connecting rod according to the characteristics of the crank slider mechanism.Establish the relationship between supply and demand of stitching thread which is a cycle of thread consumption is equal to the release amount of thread bobbin.The thread tension is controlled by adjusting the thread picking mechanism to avoid the thread breakage and floating line on the surface of the thread relaxation phenomenon.The conventional needle mechanism and the catcher needle mechanism are designed into the same size.The needle bar mechanism comprises cam,crank connecting rod and slider mechanism,etc.Chosen synchronous belt drive to realize the linkage of double needles mechanism.Adjust the thread tension by thread picking mechanism.Completed the design and manufacture of the single-sided two needles stitching principle prototype.The multi axis motion controller is used to control the movement of each axis.And debugging it to achieve its basic stitching action.The catcher needle replaces the rotary shuttle,then cooperate with the conventional needle mechanism motion.The angle between two needles is certain.Different angles between two needles influence on the coil forming probability.Design the direction of slider slots relative to the wall can be adjusted to change the movement direction of the needle rod.The influence of the angle between two needles on the stable forming of coil is studied.Through debugging it to find the suitable anglerange is 45°-60 °.According to the characteristics of the prepreg,a pre-punching stitching operation scheme is proposed.Preparation of semi-cured Kevlar fiber thread replaced twisting process to strengthen the connection of the prepreg material.Pre-puncture operation enhanced the fiber puncture at the pinhole and then the shear strength increased by 9.12%.Continuous thread can effectively inhibit the failure of sliding mode crack propagation and shear strength increased by 38.26%.Stitching method and stitch density are affected shear strength due to the thread content.The resin flows along the fiber tear to form the resin enrichment film due to the resin infiltrated the Kevlar fiber thread.It can help to prevent interlayer sliding failure and increase the shear strength.