OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 5 No. 4 2023 At the same time, there are a number of disadvantages in the design of twist drills: a decrease in the rake angle along the cutting edge (CE) up to negative when approaching the center; rake angles at the periphery are too large. To reduce and, if possible, completely eliminate these disadvantages, a design solution for a drill with a gash in the center has been proposed. The gash is made either to reduce the area with negative rake angle values [3] or with a positive rake angle along the entire gash [4]. Also in tool production, there are solutions with the gash along the entire cutting edge [5]. However, the implementation of such a design is possible only at small rake angles, which can lead to increased cutting forces and accelerated drill wear [6]. To reduce the rake angle at the periphery, a drill design with two conical sections with different generatrix angles j is used. At the periphery, the cone has a smaller angle, for example, for 2j it is equal to 118°, the second conical section has an angle of 70° [7]. As a result, for this drill design, the rake angle at the periphery can be reduced by 7–8°, which will relieve the load on the areas most susceptible to wear. As a result of reducing the angle j, the chip thickness decreases, the chips width increases and heat dissipation drastically improves, which allows increasing the tool life by more than 3 times [1]. However, this design has a flaw in the form of an uneven change in the width of the cut layer and the formation of a stress concentrator in the transition zone. These problems can be resolved by using a twist drill with a toroidal flank surface instead of a conical one. 3D analysis algorithms provide more complete and accurate rake angle data along the drill cutting edge compared to analytical models [8]. Currently, modeling of specialized automated algorithms is used to estimate the geometric parameters of various classes of cutting tools. Therefore, the rationale for the choice of geometric parameters of the class of drills being considered in this work is formed based on the CAD new designs of drills with a toroidal flank surface. In addition, some critically important operational parameters of drills, such as stresses in the cutting wedge, which are difficult to obtain experimentally, can be easily predicted using the finite element method (FEM) [9–11]. When computer modeling metalworking processes, two main problems arise while developing models using FEM. The first is the material model, which should adequately reflect the deformation under loading with different intensities and directions of stresses applied to the structure in a wide range of typical operating conditions and take into account the nature of internal stress in the structure [12–14]. The second is related to the modeling and numerical implementation of changes in the configuration of the cutting part during the shaping process depending on the state of the technological system [15, 16]. Computer modeling of machining processes is complicated due to multiple areas of contact between the cutting wedge and the material being processed [17, 18]. These problems cannot be solved using standard FEM [19]. Currently, many studies focused at solving these problems regularly appear in the computer modeling of cutting processes [20, 21]. Although many studies have been conducted on the use of FEM to predict operational parameters in machining a wide range of workpiece materials [22], currently there does not exist a unified FEM model that could be used for toroidal flank drills. The literature review shows that although today there are several types of drill designs with a spherical or toroidal flank surface, however there are neither its comprehensive studies nor recommendations on its cutting part geometry and parameters used to assess its efficiency. In addition, no CAD systems for drills with a toroidal flank surface and established mechanisms for computer modeling of the stress state of the cutting part are available at the present time. In this regard, the main purposes of this study are reducing the range of changes in the rake angle and the sharpening angle of the cutting wedge along the cutting edge from the periphery to the center, and lowering the equivalent stresses in the cutting wedge through the use of drills with a toroidal flank surface with rational geometric parameters. To achieve these purposes, the following tasks should be solved: 1) to develop a CAD system for drills with a toroidal flank surface; 2) to investigate changes in the value of the rake angle and the sharpening angle of the cutting wedge depending on the radius of the generatrix of the toroidal flank surface; 3) to study changes in equivalent stresses in the cutting wedge depending on changes in the radius of the generatrix of the toroidal flank surface.
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