螺纹成形件设置孔直径计算的特点

L. Danylova, Serhii Lapkovskyi, Vasyl Prykhodko
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Despite the advantages of self-tapping screws, their widespread use is restrained by several disadvantages: the strength of the connection using screws is lower than in the connection using a stud or bolt, screws with an increased pitch have unsatisfactory locking performance, with a diameter of more than 10 mm torque instability and thread profile deformation are observed. Improving the quality of threaded joints by ensuring the optimal size of the hole for threading is the topic of this publication. The calculation of the setting diameter for thread-forming parts with a large step has its own characteristics and must be decided taking into account friction, strength and tolerance. The main causes of surface defects in the installation of thread-forming fasteners are those related to geometry - rolling in a filled contour, which leads to an axial displacement of the surface layers of the metal. Determining the optimal value of the diameter of the hole for screwing the thread-forming part, on the one hand, as large as possible, but not more than the permissible value, is the purpose of this work. The nomenclature of thread-forming fastening elements is constantly expanding, while the ratio of the height of the profile to the step is a variable value even within the limits of one standard. Therefore, the calculation method should be universal, taking into account the conditions of friction, strength, tolerances. Thread forming processes are described as plane deformation processes. Physically, the mechanism of plastic deformation of metals is presented in the form of shifts in planes where the tangential stresses have reached their maximum value. For plane deformation, the trajectories of maximum tangential stresses in two orthogonal directions are described by slip lines, or characteristics. The slip line method allows you to calculate contact stresses and deforming forces, fully determine the fields of stresses and velocities in the sections of deformable metal, and also analyze local phenomena, which are usually fundamental in solving technological problems. The characteristics of plane plastic deformation allow you to find a solution using a graphical method. The use of this method allows you to determine the appearance of the slip line field, or its geometric characteristics, which establish the relationship between the maximum tangential stress and normal hydrostatic pressure, i.e., the deforming force, as well as determine the appearance and geometric parameters of the formed profile, the height of which is limited by the permissible amount of overflow of the profile. Analyzing the geometric parameters of the deformation zone of the threaded turn of the part, the diameter of the hole for the thread-forming fastening part was theoretically justified. 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This visualization allows you to choose a value of filling the profile even greater than one, when a sufficiently large size of the “crater” of the thread does not allow the profile to overflow. This makes it possible to increase the height of the thread profile and the contact area, as well as to expand the tolerance for the hole in the part. As a result, we have an increase in the strength of the connection and the reliability of the assembly process.","PeriodicalId":32423,"journal":{"name":"Mechanics and Advanced Technologies","volume":" ","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Peculiarities of calculating the diameter of the hole for setting the thread-forming part\",\"authors\":\"L. 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引用次数: 0

摘要

技术的有效性取决于从实施中获得的总技术效果。提高技术效率指标的方法之一是在产品设计中使用螺纹成形紧固件的基础上引入装配螺纹成形工艺。螺纹成型螺钉、销、衬套拧入光滑的孔中,并通过切割或变形形成螺纹轮廓。通过消除预螺纹操作来降低劳动强度,并且由此产生的连接具有高的操作和技术指标。在电子设备和器件的生产中,根据技术要求,不希望形成芯片,使用螺纹挤压螺钉。尽管自攻螺钉具有优点,但其广泛使用受到几个缺点的限制:使用螺钉的连接强度低于使用双头螺栓或螺栓的连接,螺距增加的螺钉具有不令人满意的锁定性能,直径超过10mm的扭矩不稳定和螺纹轮廓变形。本出版物的主题是通过确保螺纹孔的最佳尺寸来提高螺纹接头的质量。具有大台阶的螺纹成形零件的设定直径的计算有其自身的特点,必须在考虑摩擦、强度和公差的情况下确定。螺纹成形紧固件安装过程中表面缺陷的主要原因是与几何形状有关的——在填充轮廓中滚动,这会导致金属表面层的轴向位移。这项工作的目的是确定用于螺纹形成部件的孔的直径的最佳值,一方面,尽可能大,但不超过允许值。螺纹成形紧固元件的名称不断扩大,而轮廓高度与台阶的比率是一个可变值,即使在一个标准的限制范围内也是如此。因此,计算方法应该是通用的,考虑到摩擦、强度和公差的条件。螺纹成形过程被描述为平面变形过程。从物理上讲,金属塑性变形的机制表现为切向应力达到最大值的平面中的位移。对于平面变形,最大切向应力在两个正交方向上的轨迹用滑移线或特征来描述。滑移线法可以计算接触应力和变形力,完全确定可变形金属截面中的应力和速度场,还可以分析局部现象,这通常是解决技术问题的基础。平面塑性变形的特性使您可以使用图形方法找到解决方案。使用这种方法可以确定滑移线场的外观或其几何特征,从而建立最大切向应力和法向静水压力(即变形力)之间的关系,并确定成形轮廓的外观和几何参数,其高度受到型材的允许溢流量的限制。通过对零件螺纹车削变形区几何参数的分析,从理论上论证了螺纹成形紧固件的孔直径。这种计算方法是以软件和数学的形式实现的。这些建议与自攻螺钉端部的几何参数有关。由于零件的孔直径的优化,该工作的结果将提高与螺纹成形紧固零件的连接质量。在解决塑性理论中压头浸入刚塑性区域的问题和分析变形最大区域的塑性区的基础上,建立了成形轮廓的几何参数和外观。使用滑动线的方法可以直观地计算和分析几何图形,观察可变形轮廓形状的变化,从轮廓高度与螺纹节距的比率、材料和滑动系数。当螺纹的“弹坑”尺寸足够大而不允许轮廓溢出时,这种可视化允许您选择填充轮廓的值,甚至大于1。这使得可以增加螺纹轮廓的高度和接触面积,并扩大零件中孔的公差。因此,我们提高了连接的强度和组装过程的可靠性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Peculiarities of calculating the diameter of the hole for setting the thread-forming part
The effectiveness of technologies is determined by the total technical effect obtained from their implementation. One of the ways to improve technology efficiency indicators is the introduction of assembly-thread-forming processes based on the use of thread-forming fasteners in product designs. Thread-forming screws, pins, bushings are screwed into smooth holes and form a threaded profile by cutting or deformation. The reduction in labor intensity is achieved by eliminating the operation of preliminary threading, and the resulting connections have high operational and technical indicators. In the production of electronic equipment and devices, where, according to technical requirements, the formation of chips is undesirable, thread-extruding screws are used. Despite the advantages of self-tapping screws, their widespread use is restrained by several disadvantages: the strength of the connection using screws is lower than in the connection using a stud or bolt, screws with an increased pitch have unsatisfactory locking performance, with a diameter of more than 10 mm torque instability and thread profile deformation are observed. Improving the quality of threaded joints by ensuring the optimal size of the hole for threading is the topic of this publication. The calculation of the setting diameter for thread-forming parts with a large step has its own characteristics and must be decided taking into account friction, strength and tolerance. The main causes of surface defects in the installation of thread-forming fasteners are those related to geometry - rolling in a filled contour, which leads to an axial displacement of the surface layers of the metal. Determining the optimal value of the diameter of the hole for screwing the thread-forming part, on the one hand, as large as possible, but not more than the permissible value, is the purpose of this work. The nomenclature of thread-forming fastening elements is constantly expanding, while the ratio of the height of the profile to the step is a variable value even within the limits of one standard. Therefore, the calculation method should be universal, taking into account the conditions of friction, strength, tolerances. Thread forming processes are described as plane deformation processes. Physically, the mechanism of plastic deformation of metals is presented in the form of shifts in planes where the tangential stresses have reached their maximum value. For plane deformation, the trajectories of maximum tangential stresses in two orthogonal directions are described by slip lines, or characteristics. The slip line method allows you to calculate contact stresses and deforming forces, fully determine the fields of stresses and velocities in the sections of deformable metal, and also analyze local phenomena, which are usually fundamental in solving technological problems. The characteristics of plane plastic deformation allow you to find a solution using a graphical method. The use of this method allows you to determine the appearance of the slip line field, or its geometric characteristics, which establish the relationship between the maximum tangential stress and normal hydrostatic pressure, i.e., the deforming force, as well as determine the appearance and geometric parameters of the formed profile, the height of which is limited by the permissible amount of overflow of the profile. Analyzing the geometric parameters of the deformation zone of the threaded turn of the part, the diameter of the hole for the thread-forming fastening part was theoretically justified. The methodology of this calculation is implemented in the form of software and mathematics. These recommendations are related to the geometric parameters of the end part of the self-tapping screw. The results of the work will improve the quality of the connection with the thread-forming fastening part due to the optimization of the diameter of the hole of the part. On the basis of solving the problem of the plasticity theory about the immersion of the indenter into the rigid-plastic region and the analysis of the plastic zone in the region of the largest deformations, the geometric parameters and the appearance of the formed profile are established. The method of using sliding lines allows you to calculate and analyze the geometry visually, to observe the change in the shape of the deformable profile from the ratio of the height of the profile to the pitch of the thread, the material and the coefficient of sliding. This visualization allows you to choose a value of filling the profile even greater than one, when a sufficiently large size of the “crater” of the thread does not allow the profile to overflow. This makes it possible to increase the height of the thread profile and the contact area, as well as to expand the tolerance for the hole in the part. As a result, we have an increase in the strength of the connection and the reliability of the assembly process.
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