Research On Weld Bead Profile Model Based On Axisymmetric Drop Shape Analysis

Arc additive manufacturing is a wire feed additive manufacturing technology that uses welding arc as heat source and metal wire as raw material.It has shown better application prospects due to its advantages of higher molding efficiency and lower cost,and has been widely used in aerospace,national defense,automobile,biology,medical equipment and other fields.Generally,the main steps of additive manufacturing include establishing three-dimensional solid model through CAD software,exporting the STL file with an appropriate angle and step size,slicing the model into a set of 2.5D layers along the building direction,planning deposition paths with designated process parameters and post-processing.Before the path planning of slicing and inter-layer stacking,it is necessary to master the weld bead section morphology under different welding parameters.Therefore,accurate modelling of single bead profile and subsequent multi-bead overlapping effects plays an important role in improving the surface quality and forming precision of additive manufactured parts.Generally,the deposition process in arc additive manufacturing is a multi-physics field coupling effect,and the weld pool,as an important carrier,contains important process characteristic information,and is closely related to the forming quality and accuracy of the workpiece.It is difficult to accurately grasp the essence of the welding process by fitting the actual weld profile only with common mathematical function curves（parabolic function,cosine function,arc function）.The surface tension is the key factor affecting the flow behavior of the weld pool during the welding process,which determines the final forming effect of the weld profile.Therefore,it is necessary to establish the weld profile model from the perspective of surface tension.In this paper,a single-layer single-bead weld bead profile model based on Axisymmetric Drop Shape Analysis（ADSA）is proposed in the process of arc additive manufacturing,and orthogonal tests are designed to explore the influence of welding process parameters on surface tension;Then,according to the quantitative relationship between the geometric dimensions of weld bead profile during multi-bead overlapping,the recursive sequence is derived from the ADSA single-layer single-bead weld profile based on simple physical assumptions,and the single-layer multi-bead recursive weld profile model is constructed.The attributes of the model are emphatically analyzed and tested.Finally,based on the spatial coordinate transformation of weld contour,a recursive weld contour overlap model based on improved ADSA is proposed to improve the large error problem of traditional recursive models in valley areas.The relationship and difference between the attributes of the two models before and after the improvement are emphatically analyzed and compared.Finally,the accuracy and applicability of the model are verified through experiments.The main work completed in this paper includes:（1）A single-layer single-bead weld bead profile model was established for WAAM based on axisymmetric drop shape analysis（ADSA）.The prediction accuracy of the proposed model is then compared with the commonly encountered profile models such as parabola,cosine,and arc model.The results show that the ADSA model is capable of describing actual weld bead profiles with better accuracy.Orthogonal test is used to analyze the influences of welding process parameters on the coefficients of ADSA weld bead model,i.e.the radius of curvature at origin R₀and the surface tension coefficientγ.It provides a theoretical basis for revealing the influence of welding process parameters on surface tension,and also helps to improve the forming accuracy of arc additive products.（2）Based on the traditional recursive bead profile model,a single-layer multi-bead recursive weld bead profile model based on ADSA is established.That is,a recursive sequence is derived to build the overall weld bead profile curve based on the known single pass ADSA model contour curve and simple physical assumptions according to the quantitative relationship between the geometric dimensions of weld bead profile during multi-bead overlapping.The influence of the relative height,relative waviness,wetting angle and convergence of the model with the overlapping ratio OR was investigated,and compared with the traditional parabolic contour recursive model.Finally,the accuracy of the model was verified through experimental analysis.The research results provide a new idea and method for predicting weld profile.（3）Based on the spatial coordinate transformation of weld contour,a recursive weld contour overlap model based on improved ADSA is proposed to improve the large error problem of traditional recursive models in valley areas.The recursive sequence is derived from the ADSA single-layer single-bead profile by contour coordinate transformation to build the overall weld bead profile curve.The relationship and difference between the two model attributes before and after the improvement are analyzed and compared.Finally,the accuracy of the model is verified by experiments.This study reveals the evolution of the morphology of the multi pass overlap deposition layer and improves the molding quality and accuracy.