Study On CMT Arc Additive Manufacturing Process For Crossing Features And Inclined Structure

The arc additive manufacturing technology is based on the forming principle of discrete/stacking.It takes electric arc as the heat source to melt welding wire and deposits threedimensional solid parts layer by layer,which has the advantages of high material utilization rate,low cost and great manufacturing freedom.Based on CMT arc additive manufacturing technology,ER316 L stainless steel wire with excellent comprehensive performance is used as the material.Based on the common complex structural parts in the fields of car body,and aviation,the elements are extracted,and the additive forming technology of the extracted cross structure and inclined structure should be studied.The microstructure and mechanical properties of the inclined wall are analyzed.Finally,the hollow structural parts of trapezoidal platform with the characteristics of cross and inclined suspension are verified and the forming parts with good morphology are obtained.The dimension defects of welding begins and ends of single cladding layer are tested.In order to have a good shape,the current,time and gradient time at the beginning of the welding should be smaller.The current at the ending of the welding should be smaller,time and gradient time should be longer.Then the L-shaped,T-shaped and cross-shaped structural parts were studied respectively,supplemented by the molten pool visual analysis.It shows that good forming can be realized when L-shape adopts right angle and fillet transition,T-shape intersection adopts cladding layer width 50% ratio lap,cross shape adopts double T-shape lap(distance is 50% of cladding layer width)or double L-shape fillet lap(fillet radius is 50% of cladding layer width).The experiments of inclined wall structure is carried out.The effects of different process parameters on the effective inclined angle,shape size and surface roughness of the inclined wall were studied.When the off-lap distance is 1.8mm,the maximum effective inclined Angle is 46.2°.It is concluded that within the parameters of noncollapse forming,the precision of forming inclined parts is higher under the parameters of small offset distance,small interlayer temperature,large travel speed and small wire feeding speed.At the same time,the collapse problem of inclined wall is analyzed by using molten pool vision method.It is found that the accumulated heat input per unit time and the gravity of metal liquid are the main factors affecting the tilt forming.Then,the microstructure and mechanical properties of the formed inclined wall structural parts were analyzed,and it was found that the microstructure of the bottom,middle and top of the inclined wall were cellular crystal,dendritic crystal and axial crystal respectively.The microhardness of the upper and outer parts of the inclined wall was greater than that of the bottom and inner parts,while the microhardness of the inclined wall changed little under different offset distances.In the case of smaller layers temperature,larger travel speed and smaller wire feeding speed,the microstructure is smaller and the continuity of dendrite growth is better.Meanwhile,the microhardness and tensile properties also increase slightly,but the increase amplitude is very small,and there is no obvious change on the whole.Trapezoid table hollow structure is manufactured,The bending angle error of the forming part is small,the minimum error is 0.2°,the maximum error is 0.6°,the height error is 1.33 mm,the top square side length error is 0.83 mm,the bottom square side length error is 1.72 mm,the standard deviation of the four trapezoidal planes is 0.526 mm,0.478 mm,0.391 mm,0.406 mm.