Effect Of Oxidation And Workpiece Angle On Laser Repair Of Cast Iron

Cast iron is a widely used engineering material in industry.It has the advantages of low cost,good casting performance and easy cutting.Nodular cast iron is the main material for the production of large parts such as turbine outer cylinder,engine outer cylinder and crankshaft of internal combustion engine.It has high economic and social benefits to use laser repair technology to repair the damaged area.However,due to the large overall size of large-scale iron castings and inconvenient transportation,when laser repairing large-scale parts,local parts of the area to be repaired can not be protected by atmosphere,which will inevitably lead to oxidation problems.Oxidation will produce pores and oxide inclusions in the deposit layer,reducing the performance of the repair area.At the same time,due to the random location of the defect area to be repaired,it is difficult to ensure that the area to be repaired and the laser cladding head remain vertical at all times,so it is necessary to consider multi angle repair.In the process of laser multi angle repair of nodular cast iron,with the change of inclination angle between the substrate and the horizontal plane and the relative position between the laser cladding head and the substrate,the morphology of the cladding layer and the remelting area will be affected,thus affecting the forming quality and dilution ratio of the repair area.In the process of repairing the vertical upward elevation angle of laser cladding head,the alloy powder is easy to rebound into the cladding head and damage the optical fiber.In this paper,based on the application of qt400,the oxidation control in open environment and the characteristics of laser multi angle repair of the cladding layer of nodular cast iron are studied.The main research results are as follows:(1)The mechanism of porosity in laser remelting cast iron was studied.In the laser remelting of nodular cast iron and gray cast iron without air curtain protection and air curtain protection,there is no pore formation in the molten pool of nodular cast iron,while there is pore formation in the molten pool of gray cast iron.Combined with the thermogravimetry differential thermal analysis and oxygen nitrogen hydrogen analysis of nodular cast iron and gray cast iron,it is confirmed that the three elements of oxygen,nitrogen and hydrogen in gray cast iron are higher than those in nodular cast iron.After vacuum heat treatment,the laser remelting of nodular cast iron and gray cast iron under the protection of air curtain,it is found that there is no pore formation in remelting area.The results show that the formation of porosity in laser remelting gray cast iron is due to a large amount of gas adsorbed in flake graphite of gray cast iron.(2)The quality of laser repair of nodular cast iron was improved in two aspects: oxidation control of molten pool and oxidation control of deposited area.In the aspect of pool oxidation control,the self-designed air curtain protection device can effectively solve the problem of pool oxidation in the process of laser repair in the open environment.Through experiments,the air flow process parameters of the air curtain protection device to achieve the best effect of atmosphere protection are obtained as follows: protection air flow is 5 L / min,carrier gas flow is 5 L / min,air curtain protection air path width is 4 mm,air curtain protection air.The flow rate is 15 L / min,and the oxygen content in the atmosphere above the molten pool is 0.07%.In the oxidation control of the deposited area,the oxidation of the substrate surface at high temperature can be effectively reduced when the side blowing pipe diameter is large,and the area protected by atmosphere is also large,but the oxidation of the substrate surface at high temperature cannot be completely prevented.(3)When there is an angle between the laser cladding head and the substrate,because of the asymmetry of the spot and the powder spot,the remelting area will be deeper in the uphill area.When the laser cladding head is vertical to the substrate,the inclination of the substrate has little effect on the laser repair of cast iron.(4)When laser cladding nodular cast iron,the slow scanning speed will cause the explosion of graphite to produce large droplet splash,which will damage the protective lens of the cladding head during overhead welding.During overhead welding,the powder that is not captured by the cladding will not fall back into the molten pool after bouncing,resulting in the reduction of powder utilization rate during overhead welding,and the reduction of powder utilization rate during cast iron repair will cause the increase of dilution rate and hardness of cladding layer.Based on the influence of working air flow and workpiece angle on laser repair quality,this paper studies the forming process and quality control in the process of laser multi angle repair in open condition,which can realize laser repair of nodular cast iron qt400 in open condition.The research results can provide theoretical support for laser multi angle repair of nodular cast iron.