| Slab stack rolling is a new manufacturing process for the production of composite plates in the world.It has many advantages such as high quality,uniform structure and stable performance,which has shown broad application prospects in nuclear power,petrochemical,transmission pipeline and other fields.However,due to the large influence of human factors and unstable welding quality,manual arc welding with large bevel has relatively low efficiency under normal condition.Therefore,robot automatic welding is the inevitable trend of large-scale application of blank forming technology.Multi-layer and multi-pass bead planning of bevel with horizontal narrow gap is an important key technology of robot automatic welding.The following problems currently exist:(1)effect of weld pool drain on weld formation due to the lack support of base metal;(2)effect of different swing frequency,swing angle,wire feeding speed,etc.on weld formation in multilayer and multi-pass welding process;(3)influence of different bead sequences and bead planning methods on weld formation.In view of the above problems,this paper has carried out research on the multi-layer and multi-pass bead planning of the horizontal narrow gap welding assembly blank.An arc scanning model of a narrow-gap swing welding torch was obtained,and the influence of factors such as wire feed speed,swing angle,and arc length correction factor on the weld formation was revealed.We have Introduced the rugged topography coefficient of the weld seam to evaluate the actual weld seam,and proposed a new plan for bead planning combining the theory of parallel growth and equal height and area.Firstly,a quantitative analysis of the currently used horizontal narrow gap swing welding torch was carried out.Based on the analysis of its influence on the weld pool,a continuous swing arc model and a wire offset arc model were constructed for the continuous swing welding mode and the wire offset welding mode.Besides,the mathematical relationship between the swing angle and the final welding forming width of the arc was explored,and the model was verified by experiments.(1)For the continuous swing arc model,the arc radius is 3 mm,and the predicted value of the model differs from the actual situation by about 10%.(2)For partial welding under the wire,the arc radius is 3.37 mm,and the model prediction value is within 5% of the actual situation.(3)In view of partial welding on the welding wire,due to the influence of gravity,equipment,and front bead,the predicted value of the model is greatly different from the actual situation.Thus,in the actual bead planning,the above model needs to be further modified.Further analysis through the arc model has found that when the width of the weld is greater than 16 mm,the heat of the arc is not enough to melt the edge of the groove,and it is easy to form unfused defects on the side wall.At this time,the welding gun needs to be shifted downward and upward.The establishment of the above arc model has laid a foundation and provided theoretical support.for the determination of important parameters such as the planned bead swing angle and the welding gun up / down offset.Secondly,the single-variable method is used to perform the influence of speed of wire feed and swing angle in welding parameters on weld formation of backing weld,partial welding under the wire of the lower bead and partial welding in the filled bead.It is found that the closer the dz value of the bump profile of the weld to zero,the closer the weld profile to the planar shape,the better the arc accessibility of the lower layer / lower track,and the easier it is to avoid the side walls from not melting or the occurrence of defects between the welds.When the negative value of dz is larger,the shape of the weld is more convex,and the arc heat source is less accessible to the side wall or the depression between the channels,and the more prone to unfused defects.Therefore,the dz value should close to zero when planning the bead.Furthermore,in order to facilitate the bead planning,according to the welding seam forming law,the morphology of the seam of the backing weld,partial under welding and partial over welding was simplified.The backing weld was approximated as a bow.Besides,the lower partial welding and the upper partial welding are approximately trapezoidal.In order to accurately carry out the bead planning,the deposition coefficient has been researched and found that the deposition coefficient k1 of the backing weld equals0.3585+0.07*Vf,k2 of lower partial welding equals 1.15 and k3 of the upper partial welding equals 1.12.In addition,the research has also found that the best combination of parameters for continuous swing angle is ±25° or +35°combined with-15° when making the bottom welding,and the seam bump value is between-1 mm and 1 mm.The optimal swing angle for the lower partial welding is-45°,and the seam bump value is between-1 mm and 0.While the optimal swing angle for the upper partial welding is +25° or +35°,and the seam bump value is between-1 mm and 1mm.According to this,the optimal parameter interval of the welding wire swing angle of each bead is formed: the optimal amplitude for continuous swing of backing weld is around 50°,the optimal angle below the wire is between [-50°,-40°],and the optimal angle above the wire is between [25°,35°].This above research on the influence law of weld formation provides important theoretical support and data support for the specific selection of weld bead planning parameters.Furthermore,based on the above research,a multi-layer and multi-pass bead planning method based on the horizontal narrow gap of the swing arc is proposed: the “parallel growth” bead planning theory is proposed,and the principle of multi-layer and multi-bead planning with parallel growth of equal height and area is adopted.Each layer of welding bead has a welding sequence of welding from bottom to top.The backing weld adopts continuous swing welding,the lower side fills with the welding wire downward deflection,the upper side fills with the welding wire upper deflection,and the middle uses the filled methods of welding wire with continuous swing or without swing.While the cover surface is planned as a cover surface welding method in which the welding wire is biased downward,the welding wire is not biased,and the welding wire is biased from bottom to top.The order of the continuous or unbiased middle welding bead is completely determined by the width of the groove and the planned parameters.Based on the above research results,a final multi-layer multi-pass bead planning procedure for horizontal narrow gap of composite billet based on the swing arc is formed.Firstly,according to the bevel size,welding process requirements,the width and height range of the cover surface,welding speed,wire feed speed range and other constraints,etc.,the number of welding passes and welding layers were planned based on the principle of parallel growth of layer by layer with the same height and area.Secondly,according to the arc model and the welding seam forming rule,the bead of each layer of the underlayer,filling and cover surface was planned one by one,and welding parameters,such as the wire feeding speed,deflection angle,welding speed,welding gun height,welding gun vertical offset,and arc length correction coefficient,etc.were determined.Finally,according to the above-mentioned bead planning program,a multi-layer and multi-pass bead planning for a bevel with the thickness of 20 mm and horizontal narrow gap was carried out and the actual welding verification was performed.A total of 14 layers were planned for 7 layers.The final weld seam was well formed,and the number of layers or lines was clear.There were basically no unfused defects of side walls.The experimental results have shown that the bead planning algorithm formed in this subject basically meets the requirements,laying a foundation and providing theoretical support for the subsequent practical application of rolled assembling. |
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