Research On Rotary Bending Straightening Process For Small And Medium-sized Shaft And Pipe Parts

Shaft and pipe parts are an important metal product.Affected by factors such as heat treatment process,uneven material properties and processing technology,it is very common for the straightness of shaft and pipe parts to exceed the standard.Excessive straightness will greatly reduce the service life of shaft and pipe parts,and even cause accidents in severe cases.Straightening is a necessary process,and the straightening equipment is also a necessary processing equipment.For small and medium-sized shaft and pipe parts,the most widely used straightening process is the pressure straightening.However,the pressure straightening operation is complicated and the straightening efficiency is low.In view of the limitation of the pressure straightening process,a new straightening process by rotary bending for small and medium-sized shaft and pipe parts was proposed in this paper.In the rotary bending straightening process,workpiece fibers undergo multiple reciprocating tension and compression loadings,and exhibit complex material properties.Considering the Bauschinger effect,yield plateau and the variation of elastic modulus,the expressions of the constitutive model in the multi-direction stress state and the unidirectional stress state was given,and the constitutive model was implemented in ABAQUS.This lays the foundation for the analysis and numerical simulation of the rotary bending straightening process.Rotary bending springback is simplified as multiple reciprocating bending springbacks in the plane in the traditional analysis.Considering the three key factors of the Bauschinger effect,nonlinear elastic behavior and stress inheritance,an analytical model of multiple reciprocating bending springback was established.Multiple reciprocating bending experiments were carried out to verify the analytical model.Based on the analytical model,the effect of the three key factors on springback was explored.The results show that the proposed analytical model can accurately predict the springback of multiple reciprocating bending,and the three factors have non-negligible effects on the springback results.The proposed analytical model lays a foundation for the traditional analysis of the rotary bending straightening process and the accurate analysis of other processes involving multiple reciprocating bending springback.Strain paths of any fiber during rotary bending and reciprocating bending were analyzed.The results show that strain paths of the two bending modes are quite different.Considering strain paths in the rotary bending process,an analytical model of rotary bending springback was established.In order to improve the fitting accuracy of hysteresis curves,a new chord modulus model was proposed.Based on the analytical model,springback characteristics of rotary bending were revealed.The analytical model was verified by the rotary bending springback experiment.The results show that the proposed analytical method can accurately predict the rotary bending springback,and the traditional analytical method have a large error in predicting the rotary bending springback.The proposed analytical model lays the foundation for the accurate analysis of the rotary bending straightening process,and can provide a reference for the accurate analysis of other processes involving rotary bending springback.The rotary bending straightening process of shaft and pipe parts was introduced.The change law of curvature during unloading process was analyzed,and an analytical model of the rotary bending straightening process for shaft and pipe parts was established.Based on the analytical model,the reason that the parameter setting of the rotary bending straightening process is independent of the initial deflection was analyzed.The straightening mechanism of the rotary bending straightening process was revealed,and the feasibility of the proposed process was verified.Based on the implemented material model,the finite element model of rotary bending straightening of shaft and pipe parts was established,the effect of different process parameters on the straightening results was explored,and the stress and straightening force in the straightening process were analyzed.The results show that the rotary bending straightening process has a good straightening effect for shaft and pipe parts with equal cross-sections and multi-diameter shafts.The rotary bending straightening experimental prototype was designed and manufactured,and the feasibility of the proposed process was verified based on experiments.The results show that the proposed straightening process has good straightening accuracy,and the straightness after straightening is within 0.15 mm.The trend of the experimental results is consistent with the numerical simulation results,which verifies the validity of the finite element model.The proposed straightening process does not need to detect the initial deflection of workpieces,and can realize continuous and omni-directional straightening of shaft and pipe parts.The proposed straightening process improves the straightening efficiency and is suitable for mass straightening of small and medium-sized shaft and pipe parts.