Digital Design And Manufacturing Theoretical Method And Practice Of Weft Knitting Fabric

Weft knitting fabric formation effect is affected by yarn,structure and knitting technology parameters.After relaxed,the size,density,loop form of the fabric changed.For lack of theoretical research,especially the study of loop transformation caused by knitting technology variation and different structures combination,the quantitative relationship between the parameters of knitting design and product technical parameters was hard to set up.The accuracy of design by the way knitting fabric design and produce with the mixed product and manufacture procedure parameters for now,is heavily depending on the artificial experience and proofing over and over.To solve the problem mentioned above,this paper researched on the digital design and manufacturing theoretical method and practice of weft knitting fabric.An intermediate state hypothesis of weft knitting fabric formation was set up in this paper.It was based on the fact that yarn was knitted with continuous deformation,and the yarn state could be defined according to parameters at the loop formation moment.This hypothesis simplified the process that knitting fabric formation loop by loop,course by course,for the goal of that calculated relaxed knitting fabric state by design parameters.It set up the quantitative relationship between the parameters of knitting design and product technical.It also provided the theory gist for relaxed state calculated.Based on the hypothesis,the geometrical model of intermediate state and the mechanical model were set up.A yarn modeled by 19 singe yarns of circular section twisting in three layers.Their paths were modeled using non-uniform rational B-splines.The geometrical model of knitting fabric was set up using three knitting structure basic elements and three auxiliary elements.They were knit,arc,float,set-up,bind-off and link unit.Five knitting structure geometrical model were also set up using structure elements.The singe yarn was modeled by a rod elements chain with no friction joint.The stress,strain,mass,friction,contaction and equilibrium equation were also studied.MATLAB and Abaqus/Explicit were employed to calculate geometrical model and relaxed state of knitting fabric based on the theories mentioned above.Two types of tuck structures,rib structure with two different yarns,four types structures of single knit fabric were simulated.Compared to the knitting products,simulation results could predict the loop transformation,distortion and fabric shrinkage.The prediction results were in line with the reality.A CAD/CAM system with a simulation interface was design and developed based on the modeling method of knitting fabric formation.In this system,pattern design subsystem,action order subsystem,yarn using subsystem and simulation subsystem were designed.The related algorithm including pattern edit,patter data analysis,data compression,etc.The CAD/CAM system using flexible technical file format developed with Visual Studio 2015,and it has been used in several types of knitting machine and corporations.This paper focus on the problem that the low accuracy of design usually exits in knitting fabric digital design and manufacturing.Modelling the knitting fabric formation process,and the model could calculate the relaxed state of knitting fabric.The prediction results were consistent with knitting product.Based on the model,CAD/CAM systems have been developed and used in different machine types and corporations.The research on theoretical method and practice in this paper was meaningful for knitting fabric digital design and manufacture.