Speed change mechanism process control method based on load step control

Abstract

The invention relates to a speed change mechanism process control method based on load step control, which comprises the following steps of: performing screw axial pre-tightening force influence factor analysis, finite element model construction based on a load step control method, simulation result comparative analysis and the like in the assembly process of a speed change mechanism; the optimal assembly sequence can be obtained through effective comparison, and the control port variation is minimum, so that the deformation of the speed change mechanism caused by assembly loading is reduced, a process control analysis method of the speed change mechanism is obtained, and the assembly precision and stability of products are improved.

Description

Technical Field

[0001] The invention relates to a process control method of a speed change mechanism based on load step control, and belongs to the field of mechanical industry. Background Art

[0002] The speed change mechanism is the core component of the transmission system and the key to the transmission of power and motion in the transmission system. With the increasing demand for lightweight, the size and weight of the speed change device have been significantly reduced, but a large number of precision parts are integrated inside, which greatly increases the assembly complexity of the speed change device and poses a severe challenge to the high-precision assembly standards.

[0003] The assembly of mechanical parts determines the quality of the product. Different assembly sequences determine different process errors. The appropriate assembly sequence will reduce process errors and improve the stability and durability of the product. The end face of the speed change mechanism is fixed by multiple screws. The assembly process involves the assembly sequence of the screws. Different assembly sequences will cause different runouts of the end face of the speed change mechanism. At the same time, the load during the assembly process will also cause different degrees of deformation of the housing. The deformation caused by the screws that are assembled first will affect the subsequent assembly, resulting in significant differences in the final quality and performance of the product.

[0004] Therefore, by analyzing the influencing factors of the axial preload of the screws in the assembly process of the speed change mechanism, constructing a finite element model based on the load step control method, and comparing and analyzing the simulation results, the optimal assembly sequence can be effectively compared and the change in the control port can be minimized, thereby reducing the deformation of the speed change mechanism caused by the assembly load, obtaining the process control analysis method of the speed change mechanism, and improving the assembly accuracy and stability of the product. Summary of the invention

[0005] The purpose of this invention is to solve the problems of chaotic assembly sequence, insufficient precision and lack of theoretical guidance encountered in the current speed change mechanism assembly process, and propose a speed change mechanism process control scheme based on load step control that is widely applicable and easy to operate. This method aims to determine the optimal assembly sequence of the assembly process and reduce process deviation, thereby ensuring that the speed change mechanism can achieve higher quality.

[0006] The technical implementation scheme adopted by the present invention is: a speed change mechanism process control method based on load step control, including: analyzing the influence of micro-wear and plastic deformation on preload force in view of the screw tightening force problem; calculating the axial preload force of the screw based on the torque method, and analyzing the relationship between the axial preload force and the friction coefficient; setting up a speed change mechanism simulation model based on the finite element method to simulate the actual assembly state; using the load step control method to gradually increase the preload force, analyzing the influence of different assembly sequences on the port runout of the speed change mechanism, obtaining the optimal assembly sequence with the least influence, and obtaining the speed change mechanism process control scheme.

[0007] The present invention adopts a torque control method to determine the tightening force of the screw. The first step of using the torque method for tightening operations is to set a target torque value, and then use a tightening tool to apply this target torque to the fastener, so as to indirectly determine the required axial preload according to the size of the target torque. During the tightening process, the torque output by the tightening tool is mainly converted into three parts: overcoming the friction between the threads, overcoming the friction of the supporting surface, and the axial preload. The control logic of the torque control method is relatively intuitive and easy to understand, so it is suitable for application scenarios of various tightening tools.

[0008] Furthermore, based on the non-rotational loosening theory, the relationship between the axial preload and multi-cycle load in the tightening process under fretting wear conditions is analyzed.

[0009] Furthermore, based on the elastic deformation theory, the influence of the plastic elongation deformation of the fastener on the axial preload of the screw is analyzed.

[0010] Furthermore, the torque method is used to analyze the screw tightening, the relationship between the tightening torque and the axial preload is obtained, and the screw preload in the actual assembly process is calculated.

[0011] Furthermore, the model is constructed based on CATIA three-dimensional modeling software to form a finite element model of the transmission mechanism.

[0012] Furthermore, the finite element model is constructed based on material properties and contact conditions of actual parts and assembly processes.

[0013] Furthermore, the middle point of the end face of the finite element model is set as a reference point, and the change of the reference point is observed as a reference value for the change of the port runout.

[0014] Furthermore, different assembly and tightening sequences of screws are set based on the load step control method, and a process analysis model of the speed change mechanism is constructed.

[0015] Furthermore, the reference point displacement variation curves under different assembly sequences are analyzed, and the tightening sequence with the smallest runout is analyzed from multiple angles.

[0016] Furthermore, the tightening scheme for process control of the speed change mechanism is obtained by combining the total deformation diagram and stress cloud diagram of the simulation model.

[0017] The advantages of the present invention compared with the prior art are: analyzing the influence of different factors on the axial preload when the fastener and the connected parts are assembled under load, using the load step control method to control the tightening sequence of different screws, restoring the real assembly production process, and ensuring the controllability and stability of the assembly process. Setting the port center as the reference point can intuitively and accurately express the port runout value under different tightening sequences, providing strong data support for subsequent adjustments and optimizations. Comprehensively considering various factors in the assembly process, such as the material, size, tightening torque of the screws, and the influence of the assembly sequence on the port runout, a process control method for obtaining the optimal screw tightening sequence for the speed change mechanism assembly process is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the overall flow chart of the present invention;

[0019] Figure 2 This is a position diagram of the screw tightening sequence based on load step control of the present invention. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] like Figure 1 As shown, the present invention provides a process control method for a speed change mechanism based on load step control, and its process mainly consists of 6 steps:

[0022] 1. Analysis of the influence of fretting wear and plastic deformation on screw preload: Analyze the influence of sliding friction between fasteners and connected parts on axial preload, as well as the influence of plastic deformation of fasteners during the tightening process on axial preload.

[0023] 2. Analysis of preload change based on non-rotational loosening theory: Summarize the changes in screw preload caused by deformation during the tightening process.

[0024] 3. Calculation of screw preload based on torque method: Tighten the fastener by controlling the torque and analyze the relationship between the torque and the screw preload.

[0025] 4. Construction of finite element model of speed change mechanism: Construct a finite element model of the speed change mechanism for simulation analysis.

[0026] 5. Load step and other property settings: Set general properties such as materials and contact conditions, and set the loading order of different load steps for finite element simulation.

[0027] 6. Analysis of process control results of speed change mechanism: Analyze the reference point displacement change curve, stress cloud diagram and total deformation diagram of the model to obtain the optimal process control solution.

[0028] During the tightening process, sliding friction occurs between the fastener and the supporting surface of the connected component, which causes fretting wear on the contact surface. Therefore, when experiencing multiple cyclic loads, it is important to pay attention to the non-rotational loosening problem caused by this wear.

[0029] The degree of fretting wear is expressed by the fretting wear amount W, which is proportional to the axial preload F during the tightening operation and the number of cyclic loads N. The specific relationship can be expressed as:

[0030] W=K w FN

[0031] Where K w Indicates the wear coefficient.

[0032] In each cycle, the reduction of preload is proportional to the wear depth. Assuming the elastic coefficient is Z, we have:

[0033]

[0034] Assume that the contact area between the fastener and the connected part during tightening is S, where δ is the ratio of the wear amount W to the contact area S, then:

[0035]

[0036] Furthermore, assuming that the load is 0 and the preload is F0, the equation can be obtained:

[0037]

[0038] It can be seen from the above formula that in order to reduce the influence of wear on the preload, the wear coefficient k can be reduced. w , increase the contact area or reduce the elastic coefficient Z.

[0039] During the tightening process, the plastic deformation of the fastener will also cause the change of the preload force. Assume that the stiffness of the fastener and the connecting part are K B and K C , then the stiffness ratio can be expressed as K B / K B K C , recorded as φ. The relationship between axial preload and load can be divided into two end curves separated by a yield point. The first section is the elastic deformation stage. In this stage, as the load increases, the change of preload is relatively slow; the second section is the yield stage. In this stage, as the load increases, the change of preload is large. Let the coordinate of the yield point be (W A ,F A ), then:

[0040]

[0041] Where μ represents the thread friction coefficient, F y Indicates the maximum tensile load. Therefore, the maximum tensile load value needs to be set during the tightening process to avoid plastic deformation entering the yield stage.

[0042] Furthermore, the torque method is used to calculate the axial preload force, and the preload force is controlled by controlling the torque. The calculation formula is:

[0043]

[0044] In the formula, d is the thread diameter, α is the flank angle, P is the pitch, d is the thread diameter. w —Equivalent friction diameter of the support surface, μ w —Support surface friction coefficient.

[0045] Furthermore, a finite element simulation model of the speed change mechanism is constructed, the mesh is divided, the material properties of the parts, the contact friction properties and other conditions are set, and the positions of the screws are numbered, such as Figure 2 shown.

[0046]

[0047] Based on the load step control method, 6 groups of different tightening sequences are set according to the different tightening sequences of the screws, and the changes of the reference point port are observed. Since the finite element analysis model is idealized and has no positional error, and the screws are also simplified into a cylindrical structure, the actual thread structure is not modeled. Binding constraints are used at the threaded connection to replace the actual thread surface contact, and the screw preload is set using the system's built-in Bolt-load load. In the actual tightening process of the screw group, the later pre-tightened screws will have a certain impact on the previously pre-tightened screws, causing the pre-tightening force of the previously pre-tightened screws to change slightly, and there is a mutually coupled action relationship between the structure and the force. Therefore, in the present invention, the vertex of the brake port is selected to establish a reference point, and the changes in the displacement of the reference point in the three coordinate directions during the tightening process are output in the final simulation results, and it is believed that the smaller the fluctuation of the displacement change on each coordinate, the better.

[0048] Different tightening sequences cause different degrees of deformation of the projectile. The total deformation of the screw tightening process, as well as the stress cloud diagram, reference point displacement change curve, stress change curve, and preload change curve can be observed. The extreme value and change process of the reference point displacement change can be analyzed to obtain the method for selecting the optimal screw tightening sequence, realize the process control of the speed change mechanism, and reduce the error caused by deformation during the assembly process.

[0049] The above implementation method is provided only for the convenience and purpose of describing the present invention, and is not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A speed change mechanism process control method based on load step control, the characteristics of which include: An analysis method of the effect of fretting wear and plastic deformation on screw preload based on non-rotational loosening theory; Process control analysis method of screw tightening sequence on port runout based on load step control method.

2. The method for analyzing the effect of micro-wear and plastic deformation on screw preload based on non-rotational loosening theory as described in claim 1 is mainly characterized in that: under the action of multiple cyclic loads of micro-wear, the influence of sliding friction between the fastener and the connected part on the axial preload is analyzed, and the influence of wear on the preload is reduced by reducing the wear coefficient and increasing the contact area. Under plastic deformation, the influence of plastic deformation of the fastener during the tightening process on the axial preload is analyzed to obtain the coordinate value of the yield point and set the maximum tensile load value.

3. The process control analysis method of the screw tightening sequence based on the load step control method for the port runout as described in claim 1 is mainly characterized by: constructing a finite element simulation model of the speed change mechanism, dividing the grid, setting conditions such as part material properties and contact friction properties, numbering the positions of the axial screws on the end face of the speed change mechanism, and setting multiple groups of different tightening sequences, adding the axial preload of the screw based on the load step control method, setting the midpoint of the port as the reference point, observing the total deformation of the screw tightening process as well as the stress cloud map, the reference point displacement change curve, the stress change curve, and the preload change curve, so as to obtain the optimal screw tightening sequence with the least impact on the assembly process.

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