Research On The Key Technology Of Laser Additive Remanufacturing Of Shearer Spiral Blade

Due to the complex and harsh working environment,the spiral drum bears the impact and alternating load of coal and rock.The cutting pick,gear seat,blade,end plate and other parts are worn seriously,which is easy to cause damage and failure,and the failure frequency is high.The traditional cutting rewelding and surfacing welding technology are aimed at restoring the size and morphology,but the bonding force between the repaired area and the substrate is not strong,and the repaired layer is easy to fracture and peel off,which seriously affects the production efficiency of enterprises.To overcome the shortcomings of traditional repair technology and extend the safe service period of fully mechanized mining equipment and its key parts,in this paper,based on the complex structural characteristics of the spiral blade,the systematic experimental research and analysis of shearer spiral blade laser additive remanufacturing were carried out.The multi-parameter analytical models for cladding layer geometric characteristics of complex substrate were established.The influence of process parameters on the forming quality and thermal characteristics of multi-layer cladding layer were investigated.The microstructure characteristics and defect formation mechanism of spiral blade cladding layer were analyzed,and the inhibiting measures of defects were proposed.The comparative experimental researches on the life extension mechanism of the cladding layer were carried out,which laid a theoretical and technical foundation for the successful application of the laser additive remanufacturing technology to the damaged spiral blade.The main research contents are as follows:(1)To avoid the effect of the overlap phenomenon among powder particles on laser energy attenuation rate in the laser-powder interaction zone,the number of effective powder particles was introduced.Based on the laser energy attenuation rate,the laws of energy and mass conservation,the laser beam distribution characteristics and the cladding forming theroy of horizontal and inclined substrate,the multi-parameter analytical models of geometric characteristics of Fe Cr alloy cladding layer were estanlished.The effects of process parameters on the geometric characteristics of Fe Cr alloy cladding layer were analyzed.The results showed that the analytical models calculation values fit well with the experimental measurements.The powder density was positively correlated with the cladding height and the cladding area and negatively correlated with the mixing area and the peak shift.The tilt angle of the nozzle was the most important factor affecting the variation of cladding width.(2)The prediction models of minimum cladding height and deposition efficiency of multi-layer Fe Cr alloy cladding layer were established based on response surface methodology.The significance of each variable,the interaction effect mechanism and the prediction accuracy of the model were discussed and verified by ANOVA.The MORPSO algorithm was adopted to solve the multi-objective optimization model of cladding layer.The difference of temperature field and stress field of multi-layer cladding structures with different laser energy densities as well as the thermal cycling characteristics and stress evolution characteristics of interlayer cladding nodes were analyzed.It was found that the higher powder feeding rate and smaller Z-axis increment could improve the deposition efficiency of multi-layer Fe Cr alloy cladding layer.The optimal process parameters of E=33 J/mm~2,Q_m=500 mg/s and?h=0.8 mm was determined.During the laser scanning process,the X-direction stress at both ends was one of the main reasons for the collapse defect in the middle of the cladding layer.(3)The phase composition,phase transformation and volume fraction change of Fe Cr alloy cladding layer during solidification were analyzed.The evolution laws of microstructure morphology,dendrite growth and transformation of single cladding and multi-layer cladding were investigated.The trends of pore,cracks and surface spheroidized defects in Fe Cr alloy cladding layer with process parameters were revealed.The inhibiting measures of defects were proposed and verified.The results showed that the primary and secondary dendrite arms and the mean primary dendrite spacing of the cladding layer were coarsening and increasing with the increase of laser energy density from 20 J/mm~2 to 40 J/mm~2.The forming quality of cladding layer could be improved with the appropriate increase of laser energy density and Z-axis increment.The pore,cracks and surface spheroidized defects could be effectively inhibited by reducing the residual stress generation by preheating powder and substrate.(4)The life extension mechanism of tensile strength,hardness,residual stress and wear resistance of Fe Cr alloy were systematically researched.The influence of laser energy density on the mechanical properties were discussed.The remaining life evaluation model for cladding layer based on nonlinear thermal-fatigue damage was established.The reinforced Ti C particles were introduced to further improve the wear resistance of the repaired area,and the microstructure,phase composition and wear resistance of the Ti C/Fe Cr composite cladding layer with different mass fraction of Ti C particles were studied and analyzed.The results showed that the tensile strength and rockwell hardness of the cladding layer firstly increased and then decreased with the increase of laser energy density.Meanwhile,the larger temperature gradient lead to the increase of the residual stress on the surface of the cladding layer.The wear resistance of Fe Cr alloy cladding layer and Ti C/Fe Cr composite cladding layer is 2 times and 5?9 times as much as that of34Cr Ni Mo6,respectively,which can effectively improve the wear resistance of spiral blade.(5)To ensure that the laser head and the normal vector of machining points were coincided,based on the curve interpolation theory,the non-uniform rational B-spline surface fitting method and the attitude modeling of the robot,the pose control method of laser head of curved substrate processing was proposed.The experimental research on multi-area repair of the blade end of shearer screw blade blade was carried out.The experimental results showed that the forming size of the repaired area was basically the same as the predicted size,the forming quality was good,and there were no cracks and serious deformation defects,which verified the effectiveness of the laser head pose control and the feasibility of the laser additive remanufacturing technology to repair the failed drum.The paper has 93 figures,18 tables,182 references.