Forming Characteristics And Path Planning Of Curved Layer Wire And Arc Additive Manufacturing For Vehicle Die Cavity

The forging die needs to be repaired through surfacing welding to extend the service life because of surface wear or fatigue cracking.Especially for the vehicle die,the requirements of the repairing cost and performance are critical for the large application amount.With the additive remanufacturing technology,the failure area was filled via the horizontal slicing method,with which the uniform reinforcement layer with consistent material and performance cannot be achieved.However,the problem could be fixed through the curved layer additive manufacturing method along the die cavity surface.With the theory analysis,numerical simulation and experimental verification,the weld pool dynamic and bead forming characteristics under different welding position on the die cavity surface were analyzed.The single bead geometry and multi-bead optimal overlapping model with arbitrary local angle of the free surface were developed.The contour line-based path planning method with a varied overlapping distance for global horizontal welding on the partitioned surface was presented.The forming characteristics and thermal properties were discussed,which facilitated the research on the curved layer wire and arc additive remanufacturing technology.The research work is as follows:Firstly,based on the geometrical features of the free surface,the weld pool dynamics model on different position was developed,and the effect of the heat source,arc pressure,gravity and surface geometry on the fluid flow and forming appearance were investigated.For the flat welding position,the weld pool was symmetrical along the welding direction,and the weld bead was consistent.For the horizontal welding position,the weld pool and bead skewed for the sideways dragging effect of the gravity,but the fluid flow and the bead forming process were stable for the surface tension and viscosity of the melting metal.For the vertical down welding position,the fluid flowed forward and spread out,and hence the width increased and the weld pool fluctuated drastically.For vertical up welding position,excessive fluid in front of the weld pool flowed to the tale,and the welding hump appeared for the faster cooling speed at the middle of the weld pool,so that the forming morphology was extremely irregular.For the horizontal-welding curved layer additive manufacturing,the geometrical model of the single bead for the flat welding was developed,and the varying parabolic profile of two bead overlapping was established,then the optimal overlapping ratio was obtained.The arbitrary bead geometry could be obtained through the proposed model,and the welding layer surface was smooth with the optimal overlapping ratio,which decreased with the increasing of the width-height ratio.Subsequently,the modified model for the horizontal welding position was deduced,and the maximum bead offset was considered to compensate the overlapping ratio on arbitrary tilt angle of the surface.It could be used to obtain the flat layer surface for the die cavity repairing,and offer the offset distance for the path planning.The horizontal welding position could be guaranteed along the contour line,but the spacing of the contour line was not even on the die cavity surface.The geometrical properties of the vehicle die cavity surface were analyzed,and the key variables described the surface were calculated.The points cloud representing the surface was partitioned to several segments with the fuzzy clustering method(FCM),of which the normal and curvature were similar to each other.Then,a skeleton points extraction method of the surface segments,a contour line across the segment center point generating method and a projection method of the spatial point onto the NURBS surface were developed,which could be the basis of the welding path planning.Based on the requirement of horizontal welding and the simple surface segments,the topology of the path and the segment boundary on the surface was discussed.The fitting method of NURBS curve based on the accumulative chord length for the welding path,and the discretization method based on the equal arc height were established.The path planning based on the contour line across the surface segment center was conducted with the varied overlapping distance according to the arbitrary local tilt angle and welding parameters.The deviation of Z coordinates of the points on the generated path were less than 1.2 mm,with which the horizontal welding position and even cladding layer surface and thickness could be achieved.The curved layer additive manufacturing experiment with the ordinary continuous path and the proposed segments path were conducted.The surface flatness and evenness of the additive layer was measured.For the continuous path,the welding position was inconstant on different region of the complex surface,and thus the forming appearance,layer flatness and evenness was different.For the proposed segments path,the horizontal welding position could be guaranteed at any position of the surface,and thus the additive layer flatness and evenness was better.The metallography and evolution of the microstructure was observed,and the thermalstructure FEM model was established.For the segments path method,the thermal distribution was uniform on different region of the whole surface,the stress caused by the welding thermal was smaller without the significant anisotropy,and the distortion of the part was smaller.The research work in this paper is significant to application of the curved layer additive manufacturing technology on the vehicle die cavity repairing.