Preliminary Study On Precision Forming Technology Of Sprocket Of Coal Mine Scraper Conveyor

The existing coal mine scraper conveyor sprocket(hereinafter referred to as the sprocket)is generally manufactured from thick-walled tubular free forgings or castings with teeth by cutting,and the obtained sprocket teeth are easily broken.In order to improve the mechanical properties and material utilization of sprocket,based on the analysis of precision forming process of large module spur gear and spline shaft similar to sprocket structure,a new precision forming process of sprocket is proposed.In this paper,a sprocket with a teeth number of 7,a module of 59.2mm,a tooth width of 230 mm,and a hub width of 424 mm is used as the research object,the single-way and two-ways upsetting one-step forming process and the die forging are designed.Two kinds of tubular billets and one kind of solid billets are used for numerical simulation.The load stroke curve,equivalent stress,equivalent strain and metal flow velocity field are analyzed.The results show that the inner wall of the forging is easy to fold during the forming process of the tubular blank,and the blank preparation is difficult;although the forming force of the solid blank is large,the shortage of the tubular blank can be avoided.The forging process of solid blank forming sprocket can be divided into four stages: extrusion free deformation,upsetting extrusion,upsetting filling and corner filling.The two-ways upsetting extrusion needs up and down driving,which is difficult to achieve under production conditions,and the maximum forming load is only reduced by 4.5%.Based on the results of numerical simulation,the die forging physical simulation experiment was manufactured,and the blank material was pure lead.The results of physical simulation is in good agreement with numerical simulation,and the forging with clear tooth profile is obtained,which proves the feasibility of one-step forming of sprocket.It is difficult to fill the upper corner of sprocket in the later stage of die forging,and the forming force increases sharply.The expanding space is set in the upper corner of the die.The metal is stored in the expanding space in the upsetting extrusion stage,and the metal flowing into the expanding space is refluxed to the upper corner in the demoulding stage by using the pushing action to achieve the upper corner filling.In order to solve this problem,the shape of the expansion space is optimized,and the geometric parameters of the expansion space(expansion angle ?,expansion range b in the direction of tooth width,expansion range h in the direction of tooth height)are optimized.The numerical simulation results show that the expanding space of die can not only ensure the full filling of forging corners,but also reduce the forming force by at least 33%.The results show that the larger of ? and b,the smaller of forming force and the larger of push out force.The forming effect is better when the ? value is 7°-13°,the b value is(1/4-1/2)B,and the h value is(1/7-1/4)H.The optimal combination of process parameters is ? = 7°,b = 110 mm,and h = 14 mm.In this study,a large module and large size precision forming of sprocket is completed by using die forging method for the first time.The die structure is not complex,the equipment action is simple,and it is feasible and practical.It has a certain reference value for promoting the industrialization of precision forming process of sprocket.