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CN-122021150-A - Prediction method for linear degree degradation of guide rail of machine tool induced by loosening of assembly pretightening force

CN122021150ACN 122021150 ACN122021150 ACN 122021150ACN-122021150-A

Abstract

The invention discloses a prediction method for linear degree degradation of a machine tool guide rail induced by loosening of assembly pretightening force. And 2, constructing a pretightening force relaxation dynamic simulation model under the transverse vibration load. And 3, calculating deformation distribution of the machine tool guide rail joint surface along the length direction at the corresponding moment. And 4, processing the deformation distribution curve of the guide rail at each moment by adopting an envelope method, calculating the straightness of the guide rail, and analyzing the evolution rule of the straightness at m moments. And 5, based on the data of the straightness changing along with time, establishing a nonlinear mapping model of straightness and time, and verifying a prediction result through a test. The invention can effectively predict and improve the precision retention of the key component joint surface of the machine tool.

Inventors

  • LIU ZHIFENG
  • XIAO XINWEI
  • LI YING
  • ZHAO YONGSHENG
  • Bai tengfei
  • XU JINGJING

Assignees

  • 北京工业大学

Dates

Publication Date
20260512
Application Date
20260125

Claims (6)

  1. 1. The method for predicting the linearity degradation of the guide rail of the machine tool by loosening the assembly pretightening force is characterized by comprising the following steps of: Step 1, establishing a refined finite element model of a machine tool guide rail system considering thread contact nonlinearity, simulating a pre-tightening process under a given torque based on a torque-pre-tightening force mapping relation, and obtaining initial pre-tightening forces of n threaded fasteners under elastic interaction ; Step 2, constructing a pre-tightening force relaxation dynamic simulation model under transverse vibration load, acquiring relaxation rule curves of the pre-tightening force of n threaded fasteners under vibration excitation along with time by adopting an explicit dynamics analysis method, and building a time-varying process characterization model ; Step 3, extracting pretightening force values of m characteristic time nodes as static boundary conditions, calculating deformation distribution of a machine tool guide rail joint surface along the length direction at corresponding time, and obtaining guide rail deformation curve clusters at different time through multiple simulation ; Step 4, processing the deformation distribution curve of the guide rail at each moment by adopting an envelope method, and calculating the straightness of the guide rail Analyzing the evolution rule of the straightness under m moments; Step 5, based on the data of the straightness change along with time, establishing a nonlinear mapping model of straightness and time And verifying the prediction result through a test.
  2. 2. The method for predicting the linearity degradation of the guide rail of the machine tool induced by the relaxation of the assembly pre-tightening force according to claim 1, wherein in the step 1, a refined finite element model of the guide rail system of the machine tool considering the nonlinearity of the thread contact is established, the model comprises the real geometric profile and the friction contact characteristic of a thread pair, and the initial pre-tightening force distribution under the elastic interaction is solved based on the physical relationship of the torque-pre-tightening force: 。
  3. 3. the method for predicting the linearity degradation of the guide rail of the machine tool induced by the relaxation of the assembly pretightening force according to claim 1, wherein in the step 2, the dynamic response of the guide rail system of the machine tool under the transverse vibration load is simulated by a finite element explicit dynamics method, a pretightening force relaxation rule curve is obtained, and a time-varying process characterization model based on double exponential decay is established, wherein the time-varying process characterization model comprises the following steps: 。
  4. 4. The method for predicting the linearity degradation of the guide rail of the assembly pre-tightening force relaxation-induced machine tool according to claim 1, wherein in the step 3, a time node pre-tightening force value with a certain interval is extracted from a pre-tightening force relaxation curve and is applied to a static structure model of the guide rail as a boundary condition, k equidistant nodes in the length direction of a joint surface of the guide rail are selected, and the deformation in the vertical direction is solved as follows: 。
  5. 5. The method for predicting the linearity degradation of the guide rail of the machine tool induced by the relaxation of the assembly pretightening force according to claim 1, wherein in the step 4, an envelope method is adopted to process curve clusters of the deformation of the guide rail, and the linearity values at different moments are calculated as follows: ; Wherein, the Representation of Straightness values at the moment; Representation of Position of guide rail at moment Maximum deformation at; Representation of Position of guide rail at moment Minimum amount of deformation at that point.
  6. 6. The method for predicting the linearity degradation of the guide rail of the machine tool induced by the relaxation of the assembly pre-tightening force according to claim 1, wherein the establishing a nonlinear mapping model of the linearity and the time in the step 5 is fitted by adopting a double-exponential decay model: ; Wherein, the The straightness of the combination surface of the guide rail is shown; Time is indicated.

Description

Prediction method for linear degree degradation of guide rail of machine tool induced by loosening of assembly pretightening force Technical Field The invention belongs to the technical field of precision assembly and precision maintenance of high-end equipment, and particularly relates to a prediction method for linear degree degradation of a guide rail of an assembly pretightening force relaxation-induced machine tool. Background In the long-term service process of the high-precision numerical control machine tool, the time-varying relaxation behavior of the assembly pretightening force is one of key factors causing the accuracy degradation of the straightness of the guide rail. The bolt connection is used as a core assembly form of the machine tool guide rail, pretightening force attenuation is generated under the action of alternating loads such as vibration, temperature change and the like, the joint surface of the guide rail and other parts is caused to deform, and further linearity precision is induced to be gradually degraded. At present, most of researches on machine tool precision degradation are focused on geometric error compensation or static characteristic analysis, and no in-depth researches on the mapping relation and evolution mechanism between the dynamic time-varying process of assembly pretightening force relaxation and guide rail straightness degradation are yet available. The existing research method has obvious defects in the aspect of representing the straightness degradation of the guide rail induced by pretightening force relaxation, namely, the experimental method can acquire straightness change data through long-term monitoring, but has long test period and high cost, and a quantitative mapping relation between pretightening force relaxation and straightness degradation is difficult to establish, and the finite element simulation method can simulate pretightening force relaxation process, but generally adopts a simplified bolting model or ignores thread contact nonlinear characteristics, and is developed based on pretightening force distribution equality, so that the problem of uneven distribution of pretightening force of a fastener with threads under elastic interaction cannot be fully considered, and the prediction precision of long-term evolution behavior of straightness is not high enough. Therefore, it is needed to establish a prediction method capable of accurately representing the internal association between the assembly pretightening force relaxation and the linearity degradation of the guide rail, and an effective technical means is provided for predicting and improving the precision retention of the guide rail joint surface of the machine tool. Disclosure of Invention Aiming at the problems in the prior art, the method for predicting the linearity degradation of the machine tool guide rail induced by the relaxation of the assembly pretightening force is provided, so that the accuracy retention of the machine tool guide rail joint surface in the long-term service process is accurately predicted and evaluated. In order to achieve the aim of the invention, the invention discloses a prediction method for the linearity degradation of a guide rail of a machine tool induced by loosening of an assembly pretightening force. The method comprises the following steps: Step 1, establishing a refined finite element model of a machine tool guide rail system considering thread contact nonlinearity, simulating a pre-tightening process under a given torque based on a torque-pre-tightening force mapping relation, and obtaining initial pre-tightening forces of n threaded fasteners under elastic interaction 。 Step 2, constructing a pre-tightening force relaxation dynamic simulation model under transverse vibration load, acquiring relaxation rule curves of the pre-tightening force of n threaded fasteners under vibration excitation along with time by adopting an explicit dynamics analysis method, and building a time-varying process characterization model。 Step 3, extracting pretightening force values of m characteristic time nodes as static boundary conditions, calculating deformation distribution of a machine tool guide rail joint surface along the length direction at corresponding time, and obtaining guide rail deformation curve clusters at different time through multiple simulation。 Step 4, processing the deformation distribution curve of the guide rail at each moment by adopting an envelope method, and calculating the straightness of the guide railAnd analyzing the evolution rule of the straightness under m moments. Step 5, based on the data of the straightness change along with time, establishing a nonlinear mapping model of straightness and timeAnd verifying the prediction result through a test. In the step 1, a refined finite element model of a machine tool guide rail system considering thread contact nonlinearity is established, the model comprises a true geometric profile and frict