Study On Laser Cladding Forming Of Overhung Closed Structure With Coaxial Inside-beam Powder Feeding

As a common structure in engineering,hanging closed structure has been widely used in aerospace,ship,nuclear power,mining,metallurgy,mold,engine and other fields.It has unique advantages and important significance to adopt 3D printing technology to directly form hanging closure structure without mold.It has been reported that the metal 3D printing method is used to directly shape the large dip overhanging structure,which usually results in the melting pool collapse,surface steps and other defects,and it is more difficult to form a fully closed structure.The laser cladding technology with laser powder feeding inside the laser cladding can effectively improve the collapse of the molten pool and other problems.Based on the laser cladding technology of powder feeding in laser,the forming process of the closed structure with large inclination suspension is studied deeply.Aiming at the problems of thinning,warping and deviation of cladding layer from predetermined track in high dip machining,an oblique laser feeding powder cladding forming method was proposed.When the inclination Angle of structural parts increases to a certain Angle,different nozzle deflection Angle is used for cladding accumulation.By adjusting and optimizing the processing parameters,the cladding layer can grow smoothly according to the busbar position of the structure parts,and the forming of the overhanging structure parts can be realized.At first,this paper studied the molten pool suspension deposition process,the basis of the analysis of the variable Angle cases cladding flare deformation condition,the results showed that feeding cladding head light within within 25° to 90° can realize normal accumulation,between the cladding layer and cladding layer is relatively smooth,does not affect the subsequent processing situation.The mechanical model of the inclined surface molten pool subjected to laser radiation during melting and resolidification was established.Theoretical analysis shows that when laser cladding is carried out on an inclined plane with a certain inclination,the distance of displacement of the molten pool flowing down the substrate surface is proportional to the square of the loading time.With the decrease of the deflection Angle of the powder feeding nozzle to the forming base surface,the influence of the powder flow pressure becomes more obvious,and the displacement value increases accordingly.The higher the power is,the higher the temperature is and the larger the displacement is.The flow process of molten pool was simulated by FLIENT,and it was determined that the deposition of molten pool within 2s to 4s was relatively stable and the transverse height was less affected by the convection generated by the impact of powder gas,so a better deposition morphology could be obtained.Has formed the vertical plane of single path point to sedimentation experiment results validate the above theory,summarizes the processing parameters(laser power,load time,nozzle deflection Angle),the influence law of the molten pool sedimentation effect,the results show that the loading time of 2 s to 4 s pool sedimentation phenomenon is relatively stable,and the sedimentary displacement was positively related with laser power,load time,and negatively correlated with nozzle deflection Angle.In the power of 870 w,nozzle deflection Angle of 30°,can get better sedimentary morphologyAiming at the difficulties in the forming process of arch closed structure,the method of region successive accumulation is proposed.According to the relative position relation between the formed part and the nozzle in the processing process,the closed component is divided into non-interference area,interference-prone area and closure area.The normal forming method and the hanging deposition method of molten pool are respectively adopted for processing.The normal layering method can eliminate the surface step effect of parts,and the overhanging deposition method can avoid the interference of nozzle and restrain the trend of oblique growth of molten pool.The process parameters were changed synchronously to ensure the growth of the melting pool along the design track.The mathematical model of closed structure closure zone is established,and the condition of closed structure closure is analyzed.The arched closed structure was formed by combining the normal forming method with the hanging deposition method.The size and performance of the formed parts were tested.There was a certain error between the size of the formed structural parts and the design size,with the error value within 8%.The morphology at the closure of the structure was good,and the wall thickness at the closure was larger than the d sign size.The overhanging branches of structural parts have uniform microstructure and larger grain size along the direction of height,which is obvious in the overhanging deposition area.The overall hardness is relatively average,and the hardness of the two structural parts fluctuates regularly within the range of 590hv-700hv.