Theoretical Study of the Technological Process of Machining the Outer Edge of Screw Elements of Agricultural Machinery

Despite previous studies of the grinding of the outer edge of screw elements, the dynamics of grinding and sharpening of the outer edge of the screw element were not considered, taking into account the vibrations of the workpiece, tool, elements of basing and fastening of the workpiece, and the tool holder of the machine tool. In addition, previous studies are related to grinding the outer edge of the screw element with a small feed of the through cutter (0.1…0.3 mm/rev), respectively, the length of the working edge of the cutter involved in the cutting process is several times smaller than when grinding the outer edge of the screw element. This leads to a significant increase in the cutting force, and accordingly to the vibrations of the tool and the workpiece. And the instantaneous value of the cutting force and its influence on the dynamic parameters of the process of grinding the outer edge of the screw element determine the quality of the machined surface and require further theoretical and experimental research. A theoretical study of the technological process of machining the outer edge of screw elements of agricultural machinery has been conducted. During the process of turning and sharpening the outer edge of the screw element, the cutting tools are moved along the axis of rotation of the screw element with a feed equal to the pitch of the turns, the rotational movement of the screw element, geometric parameters, their deviations, and the material of the initial workpiece determine the parameters of the quality of shaping the outer edge of the screw element. In addition, the quality of the machined surface is determined by: the accuracy of the machining system (which includes the tool, workpiece positioning and clamping elements, and the machine tool), variable cutting force parameters, workpiece deformation, tool wear, and the rigidity and vibration resistance of the workpiece machining system elements. It has been established that increasing the width of the cut part of the screw element's turn and the distance between the top of the sharpened edge of the screw element to the center of the circular cutting plate of the cutter leads to an increase in the area of the part of the screw element's material that is cut, and, accordingly, the cutting force, while increasing the radius of the cutting insert of the cutter leads to a decrease in the value of the specified parameters. A significant increase in the area of the part of the material of the screw element that is cut, and therefore the cutting force, is observed when the distance between the tip of the edge of the screw element that is sharpened approaches to the center of the circular cutting insert of the cutter to the value of the radius of the cutting insert of the cutter with the ratio of the radius of the cutting insert of the cutter to the distance between the tip of the edge of the screw element that is sharpened less than 1.1. At the same time, increasing the radius of the cutter's cutting plate leads to an increase in the sharpening angle of the screw element's edge, and increasing the distance between the tip of the sharpening screw element's edge to the center of the circular cutter's cutting plate leads to a decrease. Therefore, rational ratios of the radius of the cutter's cutting plate to the distance between the tip of the edge of the sharpening screw element to the center of the circular cutter's cutting plate in the cutter design are values from 1.4 to 1.8, which allow reducing the area of the part of the material of the screw element that is cut from 1.54 to 2.21 times, providing a sharpening angle of the edge of the screw element from 47 degrees to 57 degrees. The width of the cut part of the screw element's turn has a minor effect on the angle of sharpening of the screw element's edge. Also, to provide a different angle of sharpening of the edge of the screw element, as well as to change the load on the cutter, the distance between the top of the sharpening edge of the screw element to the center of the circular cutting plate of the cutter must be adjustable.