Design And Study Of Bilateral Powder Nozzle For Broad Beam Laser Cladding

With the development of laser processing technique,laser cladding has been widely used in industry.Generally,in industrial application,the area and thickness of molten objects are relatively large.In this case,the method of multi-channel overlap is usually applied.The times of overlap will impact the quality of cladding layer.However,compared with narrow beam laser cladding,the width of broad beam laser cladding is significantly larger.When they act on workpieces with the same area,broad beam laser cladding effectively decreases the times of overlap and the trend of cracking so that cladding layer with good properties is obtained.Then broad beam laser cladding often adopts the method of lateral powder feeding,which has two problems at present: low powder utilization and high sensitivity to feeding position.In order to solve these two problems,this thesis focuses on the design,simulation,optimization and experiment of the nozzle Main research contents and results are as follows:(1)When the feeding angles,incidence angles of powder,widths of the nozzle and convergence angles of flow channel of the nozzle are different,the powder convergence is simulated by FLUENT.The results show that with the increase of feeding angle and the convergence angles of flow channel of the nozzle,the powder distribution becomes more uniform and the distribution zone is narrower,which presents good convergence.Secondly,the smaller the incidence angle and width of the nozzle are,the more uniform the powder distribution becomes and the narrower the distribution zone.(2)Based on results of FLUENT,the structure of previously designed nozzle is optimized and a new nozzle with contractive flow channel is designed.First,the availability of the nozzle is validated.Then the tests of unilateral powder feeding and bilateral powder feeding are performed with the designed nozzle.When the feeding angles are different,the results of cladding experiments show that 60° is the optimal feeding angle.Besides,when the feeding angle is less than 42°,in aspect of macro profile of clad layer and powder utilization rate,the method of unilateral powder feeding is superior to that of bilateral powder feeding.When the feeding angle is more than 42°,the method of bilateral powder feeding is superior to that of unilateral powder feeding.(3)An experiment on the unilateral and bilateral powder-feeding cladding in different scanning speed directions is conducted to study the reversibility of the scanning speed direction The results show that when the direction of scanning speed is changed,the cladding layer and the powder utilization rate of bilateral powder feeding is higher and the adaptability is better.Compared with the unilateral powder feeding,the bilateral powder feeding has a more reversible movement direction and can improve the cladding efficiency in a large area of laser cladding.Besides,the adaptability experiment on the unilateral and bilateral powder feeding is carried out in the case of single-layer cladding and multi-layer cladding with variable focus,the utilization rate of the powder is higher and the sensitivity to the powder-feeding position weak.Therefore,the bilateral powder-feeding has a weaker sensitivity to the powder-feeding position than the unilateral powder-feeding and can be applied to multi-layer cladding and cambered surface laser cladding.(4)In order to increase the width of the cladding layer without changing the structure of the nozzle,the two symmetrical powder nozzles are adjusted to stagger by 0,2mm,4mm or 6mm to regulate the width of clad layer.The results show that the width of the clad layer increases gradually and the powder utilization rate decreases slightly with the increasing stagger distance of the two nozzles.(5)The technology of unilateral and bilateral powder-feeding cladding is applied on the ball valve respectively.The ball valve with unilateral powder-feeding cladding is poor in surface smoothness,has a low utilization rate of powder and is easily oxidized.The ball valve with bilateral powder-feeding cladding shows a smooth glossy surface and a high utilization rate of the powder.