CN116186934A

CN116186934A - Bolt structure optimization design method

Info

Publication number: CN116186934A
Application number: CN202310177221.5A
Authority: CN
Inventors: 柳欢欢; 邓滨佼; 廖世辉
Original assignee: Chongqing Changan Automobile Co Ltd
Current assignee: Chongqing Changan Automobile Co Ltd
Priority date: 2023-02-28
Filing date: 2023-02-28
Publication date: 2023-05-30

Abstract

The invention relates to a bolt structure optimization design method, which comprises the following steps: selecting a bolt connection structure comprising a connection piece and a connected piece, and carrying out reliability analysis on the bolt connection structure to obtain a plurality of reliability analysis results; if a result item which does not meet the pre-designed target value exists in the reliability analysis result, determining that the bolt structure needs to be optimized, and screening and determining at least one key parameter of the result item which affects the fact that the pre-designed target value is not met in the bolt structure; taking a result item which DOEs not meet a pre-designed target value as a response, taking a key parameter as a factor, and respectively carrying out DOE test design on each response, wherein the DOE test design comprises the following steps: responding to the target value setting, selecting factors associated with the target value setting and setting corresponding factor levels; and (3) carrying out DOE test by combining all responses, all response target values, all selected factors and all set factor levels, and obtaining the optimal solution of each factor when the responses are the pre-designed target values.

Description

Bolt structure optimization design method

Technical Field

The invention relates to the field of design of automobile bolt connection structures, in particular to a bolt structure optimization design method.

Background

The bolts are indispensable parts in the whole vehicle production process. The whole vehicle bolt comprises a standard part bolt and a non-standard part bolt, wherein the standard part is a bolt with strong industrial universality, and all aspects of structure, size, drawing and the like are completely standardized; the nonstandard parts are parts which need to be designed in structure and size according to actual conditions.

For the whole vehicle bolt, the standard component can be selected from a bolt standard component library; the nonstandard parts are mainly bolts which are required to be structurally designed according to the fact that standard parts cannot be adopted according to actual connection structures.

The automobile bolt structure may be divided into a coupling member and a coupled member. At present, no design and optimization method aiming at the automobile bolt structure exists. The connecting piece adopts standard component bolts, the non-standard component bolts are different from each other, and no systematic design method exists; the coupled members are typically sheet metal or metal members, and are typically not considered when using bolted couplings.

The automobile bolt structure needs to ensure that the connection is not opened in the use process of the automobile, namely certain installation pretightening force is ensured between the joint surfaces under the action of external load, so that the phenomena of sliding, loosening, breakage and the like of the bolt connection are avoided.

The mounting pretension of the bolt is mainly generated by applying a suitable tightening torque. Therefore, the tightening torque is an important indicator for managing the bolt pretightening force for the bolt structure. The tightening torque needs to be designed reasonably, and the torque is too large, so that the connection structure is possibly damaged, and the reliability of the connection structure cannot be guaranteed due to too small torque. In the prior art, no design method specifically aims at the tightening torque of the bolt.

In the prior art, a method for structural design of a bolt, such as a method for optimizing bolt pretightening force and bolt structural design by finite element, has a patent application number of CN201210278894.1. The method uses an improved model and method of two-dimensional FEA to adapt to various bolt structure modeling. The complex nonlinear factors such as contact, friction, pretension and the like in the threaded connection are considered. Step-by-step loading pre-tightening force and external force; according to the stress state of the thread, a change curve of the maximum stress along with the external force and a change condition of the maximum stress along with the pretightening force in the thread are defined; and determining the optimal pretightening force of the threaded connection according to whether the contact surface is separated into a judging criterion or not. And calculating the optimal design and the optimal parameter value of the bolt structure according to the maximum bearing external force of the bolt structure and the required pretightening force requirement.

Firstly, the method adopts a two-dimensional model for analysis, and is unfavorable for reflecting the actual characteristics of the bolt connection structure relative to a three-dimensional model. Secondly, the method can pay attention to the stress change condition of the threaded contact surface through finite element software, the threaded contact surface is removed by bolt connection, and meanwhile, the contact surface between the bolt head and the connected piece, the contact surface between the connected pieces, the stress strain of the bolt polish rod part and the like are also required to be paid attention. In addition, the method only can obtain the optimal pretightening force of the bolt connecting structure, the tightening torque required to be applied for realizing the optimal pretightening force is not specifically described, the installation pretightening force of the bolt is mainly applied through the tightening torque, and the optimal pretightening force is not convenient for guiding production practice. Most importantly, the method is used for structural design of the bolts, and specific structural parameters of the bolts are not involved, and the coupled parts are not included.

Disclosure of Invention

The invention aims to provide a method for optimizing design and torque of a bolt structure by combining a DOE method with MDESIGN bolt analysis software. The method can systematically solve the problems of parameter design and optimization of the existing bolt structure by combining the connecting piece and the connected piece; meanwhile, reasonable bolt tightening torque can be obtained, and production practice is guided.

The aim is realized by the following technical scheme:

the invention provides a bolt structure optimization design method, which comprises the following steps:

selecting a bolt connection structure comprising a connection piece and a connected piece, and carrying out reliability analysis on the bolt connection structure to obtain a plurality of reliability analysis results;

if a result item which does not meet the pre-designed target value exists in the reliability analysis result, determining that the bolt structure needs to be optimized, and screening and determining at least one key parameter of the result item which affects the fact that the pre-designed target value is not met in the bolt structure;

taking a result item which DOEs not meet a pre-designed target value as a response, taking a key parameter as a factor, and respectively carrying out DOE test design on each response, wherein the DOE test design comprises the following steps: responding to the target value setting, selecting factors associated with the target value setting and setting corresponding factor levels;

and (3) carrying out DOE test by combining all responses, all response target values, all selected factors and all set factor levels, and obtaining the optimal solution of each factor when the responses are the pre-designed target values.

And (3) carrying out reliability analysis on the bolt connection structure again based on the optimal solution of each factor, and verifying whether the optimal solution of each factor meets the design requirement of the bolt connection structure based on the new reliability analysis result to finish optimization.

Preferably, the step of performing reliability analysis on the bolt coupling structure includes:

inputting various parameters of a connecting piece and a connected piece in a bolt connecting structure by using a bolt analysis module in MEDSIGN analysis software, setting boundary conditions, establishing a bolt analysis model, and calculating to obtain a reliability analysis result;

the parameters of the coupling piece in the input bolt coupling structure comprise: the parameters of the coupled piece in the input bolt coupling structure comprise: gasket parameters and sheet metal part parameters;

the bolt parameters include: bolt selection, nominal diameter, screw pitch, boring diameter, outer diameter of a bolt head bearing surface, inner diameter of a bolt head bearing surface, thread length, screw diameter and screw length;

the nut parameters include: nut diameter, nut width across edges, nut bearing surface outer diameter, nut bearing surface inner diameter, nut thickness and diagonal length;

the gasket parameters include: gasket type, gasket inner diameter, gasket outer diameter, gasket thickness, average surface roughness;

sheet metal part parameters include: material type, thickness, bearing surface outer diameter and bearing surface inner diameter;

the set boundary conditions include: the process, temperature, external load, and tightening torque of the bolt structure.

Preferably, the result items in the reliability analysis result include at least: the bolt clamping force, the anti-yielding safety coefficient, the bolt head anti-compression safety coefficient, the nut head anti-compression safety coefficient and the anti-sliding safety coefficient.

Preferably, the method comprises, when the DOE test is performed,

generating a DOE test plan according to the selected factors and the set factor levels which are associated with the results which do not meet the pre-designed target values;

performing reliability analysis on the bolt connection structure according to the generated DOE test plan by utilizing MEDSIGN software to obtain an analysis result of the DOE test design;

performing factor regression analysis and precision check based on the analysis result of the DOE test design to obtain a regression equation of response and factor;

and optimizing the response by combining the set response target value based on a regression equation of the response and the factors, and obtaining an optimal solution of each factor when the response is a pre-designed target value.

Preferably, the verification is specifically: and after obtaining the optimal solutions of the factors, carrying out bolt reliability analysis again, verifying whether the optimal solutions of the factors meet the design requirement of the bolt connection structure based on the new reliability analysis result, if the new bolt reliability analysis result items meet the pre-designed target value, completing the optimization of the bolt structure design, and if the new reliability analysis result has a result item which does not meet the pre-designed target value, carrying out the optimization again.

According to the invention, the automobile bolt structural design and torque optimization method is feasible, the qualification of the bolt structural design parameters can be accurately estimated, and various parameters of the connecting piece and the connected piece can be designed; meanwhile, the tightening torque of the bolt structure can be optimized, and industrial production is guided. The method provided by the invention can systematically design the automobile bolt structure, and is suitable for the situation that the bolt connection structure exists in parts in the industries of automobiles, aviation, machinery, bridges and the like, or the problem of optimizing the bolt structure in similar products.

Drawings

FIG. 1 is a flow chart of a technical scheme related to the invention;

FIG. 2 is a block diagram of an automotive bolt according to an embodiment of the present invention;

FIG. 3 is a Pareto chart of the effect between the bolt clamping force E and the factor according to an embodiment of the present invention;

FIG. 4 is a main effect diagram, an interaction diagram and a residual diagram of a bolt clamping force E according to an embodiment of the present invention;

FIG. 5 is a Pareto plot of the effect between the anti-slip safety factor F and the factor according to an embodiment of the present invention;

fig. 6 is a main effect diagram, an interaction diagram and a residual diagram of an anti-slip safety factor F according to an embodiment of the present invention.

Detailed Description

In order to clearly demonstrate the technical solution of the present invention, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

The invention is not limited to the specific details, but may be practiced in other similar ways than those described herein, and therefore the scope of the invention is not limited to the examples described below.

A method for designing and optimizing the structure of an automobile bolt and torque mainly combines a DOE method with MDESIGN bolt analysis software to systematically design and optimize the structure of the automobile bolt.

The method mainly comprises the following steps:

11. and (5) analyzing reliability of the bolts.

111. And (5) primarily selecting bolts. The primary choice of couplings (bolts and nuts) is made according to the car bolt construction. And determining whether a standard component or a non-standard component is adopted, and referring to a VDI design manual, determining bolt selection and obtaining a target value of the bolt clamping force.

112. And analyzing the reliability of the bolts of the bolt connection structure through a bolt analysis module in MEDSIGN analysis software. The bolt reliability analysis process comprises the following steps: inputting various parameters of a connecting piece and a connected piece in the bolt connecting structure, setting boundary conditions, establishing a bolt analysis model, and calculating to obtain an analysis result.

The boundary conditions include: the process, temperature, external load, tightening torque, etc. of the bolt structure. After the structural position of the automotive bolts is usually determined, the tightening torque of the coupling is of primary concern.

The invention can optimize the tightening torque.

Based on the analysis result, whether or not to perform the optimal design for the coupling or the coupled member is considered.

12. And (5) key parameter identification.

121. The response to be verified is determined, as well as the design target value of the response.

After the reliability analysis of the bolts is performed, a plurality of reliability analysis results can be output. These analysis results include: bolt clamping force, anti-yielding safety coefficient, anti-fatigue safety coefficient, anti-compression safety coefficient, anti-sliding safety coefficient, bolt utilization rate and the like. If a result item which does not meet the pre-designed target value appears, the structural parameters or boundary conditions of the connecting piece or the connected piece need to be optimally designed; the boundary condition is mainly the tightening torque.

The analysis results described above may have a single result or a plurality of results therein as the response to be optimally validated. The design target value of the response is mainly determined according to the VDI design manual and the experience of the engineer.

122. The key parameters can be identified through specific results of bolt reliability analysis, and the key parameters are determined according to actual conditions and aiming at the bolt connection structure which does not meet the design target value.

The key parameters are related parameters of the connecting piece and the connected piece (a gasket and a sheet metal clamped by a bolt).

The coupling generally refers to a bolt and a nut, and the coupled member generally refers to a washer, a component or a sheet metal part coupled or clamped by the bolt; key parameters include, but are not limited to: bolt parameters, nut parameters, washer parameters, sheet metal parameters, etc.

The bolt parameters are as follows: bolt selection, nominal diameter, screw pitch, boring diameter, outer diameter/inner diameter of a bearing surface of a bolt head, thread length, screw diameter, screw length and the like.

The nut parameters are as follows: nut diameter, nut width across the edge, nut bearing surface outside diameter/inside diameter, nut thickness, diagonal length, etc.

The gasket parameters are as follows: gasket type, gasket inner/outer diameter, gasket thickness, average surface roughness, etc.

The sheet metal part parameters are as follows: material type, thickness, bearing surface outer diameter/inner diameter, etc.

The invention can design single parameter or multiple parameters for the bolt structure parameters.

And determining structural parameters or boundary conditions to be optimized as factors, and setting factors and factor levels according to VDI design manuals, engineering experience and actual conditions of whole vehicle development.

13. DOE test design.

131. And performing DOE test design according to the identified key parameters.

Determining response and target values of the response, mainly the number of the responses, the size of the target values and the value range; determining factors and the levels of the factors, wherein the factors mainly comprise the quantity of the factors, the selection of the levels and the value range.

132. DOE data analysis was performed.

And generating a DOE test plan according to the selected factors and the selected levels. And (3) carrying out bolt connection structure analysis according to the generated DOE test plan by utilizing MEDSIGN software to obtain an analysis result of the DOE test design.

133. Regression analysis and accuracy check are performed. And obtaining a regression equation.

Performing factor regression analysis on the data to obtain a factor regression analysis result; and judging the significance relation between the fitting model and each coefficient according to the factor regression result, eliminating one factor item at a time if the factor item with the P value larger than 0.05 exists, and then carrying out factor regression analysis again until the factor item with the P value larger than 0.05 does not exist, so as to obtain a response standardized effect Pareto diagram and a residual diagram.

If the P values are smaller than 0.05, the effect is obvious; on the contrary, the effect is not significant.

If the bending value is greater than 0.05, the model bending is not remarkable; on the contrary, the model is obviously bent, and RSM response surface analysis is needed.

If the values of R-Sq/R-Sq (adjustment)/R-Sq (prediction) are close and the values are larger than 99%, the model fitting is better; otherwise, the model fitting is poor, the reliability of the result is reduced, and the fitting is needed again.

And obtaining a regression equation between the response and the factor according to the fitting result.

14. Optimizing design.

And carrying out response optimization on the key parameters, setting target optimization for response, and defining target values and upper and lower limits of the response optimization.

If only one response is optimized, the weight of the response is set to 1; if two or more responses are optimized, weights are assigned according to the actual conditions of the vehicle development.

And obtaining a parameter optimization result, and determining a bolt structural design and a torque design scheme.

15. And verifying the target value.

Substituting the parameter optimization result obtained by the optimization design 14 into a bolt reliability analysis model, calculating to obtain an analysis result, and verifying the accuracy of the bolt structural design and the torque optimization scheme.

If the scheme cannot be implemented or the analysis result does not meet the target value requirement, the fourth step of optimization design is carried out again.

The following describes specific examples of structural design and torque optimization of the coupling bolts of the front pillars and the vehicle bodies of the vehicles. The embodiment shows a method for structural design and torque optimization of an automobile bolt, and mainly uses analysis software as follows: MDESIGN and Minitab, the analysis flow is shown in figure 1, and specifically comprises the following steps:

21. and (5) analyzing reliability of the bolts.

211. And (5) primarily selecting bolts. This embodiment is mainly directed to front pillar and vehicle body mounting point bolt, and this position bolt easily appears screw thread smooth tooth problem, can refer to fig. 2.

The bolts are three M10 outer hexagon bolts and nuts, and the connecting device is characterized in that the number of connected pieces is small, the clamped length is small, the flatness of the contact surface is low, and the like; the screw tightening torque is typically empirically designed, in this case an initial tightening torque of 81.5n·m.

212. And analyzing the reliability of the bolts of the bolt connection structure through a bolt analysis module in MEDSIGN analysis software.

The process of analyzing the reliability of the bolts of the bolt connection structure comprises the following steps: inputting various parameters of a connecting piece and a connected piece in the bolt connecting structure, setting boundary conditions, establishing a bolt analysis model, and calculating to obtain an analysis result.

In this embodiment, the parameters of the input coupling (bolt and nut) are as follows in table 1:

parameters (parameters)	Unit (B)	Numerical value
			Nominal diameter	mm		10
Pitch of thread	mm	1.25
			Bore diameter	mm	11
Outer diameter of bearing surface of bolt head	mm	16
			Inner diameter of bearing surface of bolt head	mm	10.7
Length of thread	mm	19
			Screw diameter	mm	10.6
Screw length	mm					5
			Width of nut opposite edge	mm	21
Inner diameter of nut bearing surface	mm	14
			Nut bearing surface outer diameter	mm	20.5
Nut thickness	mm	11

TABLE 1

The parameters of the input coupled elements are as follows in table 2:

material name	Density (g/cm 3)	Modulus of elasticity (MPa)	Poisson's ratio
				A380	2.7	70000	0.33
QT450	7.2	170000	0.3
				Standard	7.85	210000	0.3

TABLE 2

The set boundary conditions include: the process, temperature, external load, tightening torque, etc. of the bolt structure.

Analysis results were obtained by analysis by the bolt analysis module in the MDESIGN analysis software, as shown in table 3 below:

calculation item	Results	Target value	Remarks
				Tightening torque/N.m	81.5
Bolt clamping force/KN	49.3	≤44.5KN	Telescope for looking big
				Yield coefficient of safety	1.06	≥1
Compression-resistant safety coefficient of bolt head	0.87	≥1	Not meeting the target
				Compression-resistant safety coefficient of nut head	2.71	≥1
Anti-slip safety factor	4.02	≥1

TABLE 3 Table 3

As can be seen from the calculation results in table 3, the compression safety factor of the bolt head does not satisfy the requirement, and therefore, the compression safety factor of the bolt head is required to be the main response.

22. And (5) key parameter identification.

221. The response to be verified is determined, as well as the design target value of the response.

In this embodiment, from the analysis results in table 3, the compression safety coefficient of the bolt head does not meet the requirement, so the key parameters identified are the bolt clamping force and the compression safety coefficient of the bolt head.

The compression safety coefficient F of the bolt head is equal to or greater than 1 according to the VDI design manual in order to ensure that the compression is not generated.

In order to ensure that the bolt clamping does not loosen, the requirement of the bolt clamping force E is larger than the minimum clamping force required by the bolt clamping; in order to ensure that no crushing occurs, the bolt clamping force E should be less than the bolt allowable installation preload.

According to the preliminary analysis result, in the embodiment, the minimum clamping force required by the bolt is 6.67KN; the target value of the bolt clamping force was 44.5KN in combination with the VDI design Manual. Therefore, the optimized bolt clamping force E should be as close to the target value 44.5KN as possible on the basis of being greater than the minimum clamping force 6.67 KN.

222. The key parameters can be identified through specific results of bolt reliability analysis, and the key parameters are determined according to actual conditions and aiming at the bolt connection structure which does not meet the design target value. According to engineering experience, two problems that the bolts at the mounting points of the front support and the vehicle body are easy to occur are that the bolts are clamped loose or the contact surfaces of the heads of the bolts are crushed. The outer diameter of the bearing surface of the bolt head, the inner diameter of the bearing surface of the bolt head and the tightening torque are determined as key parameters which are factors related to the response, and the key parameters are used as input.

23. DOE test design.

231. And performing DOE test design according to the identified key parameters. Determining factors and levels, wherein the factors comprise the number of the factors and the value of the levels; the response and the target of the response are determined.

The response and target values for this example are shown in table 4 below:

response to	Name of the name	Target value
			E	Bolt clamping force (N)	≤44453.0
F	Compression safety coefficient of bolt head (mm)	≥1

TABLE 4 Table 4

The factors and levels for this example are shown in table 4 below:

TABLE 5

232. DOE data analysis.

And generating a DOE test plan according to the selected factors and the selected levels. This example uses a 3-factor 2 level full-factor test, with 2 center points inserted.

Specifically, the DOE test plan was generated by the MINITAB software, requiring 10 bolt reliability analyses. The test plan and analysis results are shown in table 6 below, where E is the bolt clamping force and F is the bolt head compression safety factor.

TABLE 6

233. And carrying out regression analysis and precision check simultaneously to obtain a regression equation of the response and the factor.

Because the main response of this embodiment is the bolt head compression safety factor F, the factor regression analysis is performed on the response F and the factor A, B, C, and the result of the factor regression analysis, that is, the effect Pareto diagram of the bolt head compression safety factor F in fig. 3, is obtained.

And obtaining a significance relation between the fitting model and each coefficient through a factor regression analysis result, eliminating one factor item at a time aiming at the factor item with the P value larger than 0.05, and carrying out factor regression analysis again until the factor item with the P value larger than 0.05 does not exist.

After factor items with the P value larger than 0.05 are deleted in sequence, a standardized effect Pareto (berla) diagram of the obtained bolt head compression safety coefficient F is shown in fig. 4; and simultaneously carrying out residual analysis to obtain a residual image, see fig. 5.

From the obtained normalized effect Pareto plot and residual plot results, it follows that: all P values are smaller than 0.05, and the effect is obvious; the bending value is 0.023 and less than 0.05, the central point is obvious, the model is a nonlinear model, and RSM response surface regression analysis is required.

And carrying out RSM response surface regression analysis on the response F to obtain a main effect diagram, see FIG. 6.

The regression equation for the response F is given as follows:

F＝-2.367+0.3715A-0.3094B+0.02796C+0.005354A*A+0.001284A*B-0.003902A*C+0.002105B*C

24. optimizing design.

And (3) performing response optimization on the response F, wherein the target of the response F is set to be a target, the target value is 1.5, the lower limit is 1, the upper limit is 1.9, the weight is set to be 1, and the importance is 1.

The range of values of the variable A, B, C is set in step 231.

The optimal solution result is obtained as follows: a=17.97 mm, b=10.7mm, c=75 Nm.

The optimization scheme is as follows: the outer diameter of the bearing surface of the bolt head is 18.6mm, and the inner diameter is 10.7mm; tightening torque 75NM.

25. And verifying the target value.

Substituting the obtained parameter optimized result scheme into a bolt reliability analysis model, and calculating to obtain the analysis result shown in the following table 7.

Calculation item	Results	Target value	Remarks
				Tightening torque/N.m	75
Bolt clamping force/KN	43.2	≤44.5KN	Telescope for looking big
				Yield coefficient of safety	1.21	≥1
Compression-resistant safety coefficient of bolt head	1.66	≥1
				Compression-resistant safety coefficient of nut head	3.1	≥1
Anti-slip safety factor	3.41	≥1
				Shear safety coefficient	18.7	≥1.5

TABLE 7

The compression safety coefficient of the bolt head is 1.66, and other results meet the targets, so that the bolt structure design and torque optimization scheme are feasible.

In the embodiment of the invention, the bolt structure design and tightening torque optimization method can accurately evaluate the qualification of the bolt structure design parameters, and can optimize the related parameters of the connecting piece and the connected piece aiming at the automobile bolt structure which does not meet the design requirement; meanwhile, the tightening torque can be optimized aiming at the bolt structure, and industrial production is guided.

The method is suitable for the condition that the bolt connection structure exists in parts in the industries of automobiles, aviation, machinery, bridges and the like, or the problem of optimizing the bolt structure in similar products.

Claims

1. The bolt structure optimization design method is characterized by comprising the following steps of:

and (3) carrying out DOE test by combining all responses, all response target values, all selected factors and all set factor levels, obtaining the optimal solution of each factor when the responses are the pre-designed target values, and verifying.

2. The method for optimizing a bolt structure according to claim 1, wherein the step of performing reliability analysis on the bolt coupling structure comprises:

3. The bolt structure optimization design method according to claim 1, wherein the result items in the reliability analysis result at least include: the bolt clamping force, the anti-yielding safety coefficient, the bolt head anti-compression safety coefficient, the nut head anti-compression safety coefficient and the anti-sliding safety coefficient.

4. The method for optimizing a bolt structure according to claim 1, wherein, when the DOE test is performed,

5. The method for optimizing a bolt structure according to claim 1, wherein the verification is specifically: and after obtaining the optimal solutions of the factors, carrying out bolt reliability analysis again, verifying whether the optimal solutions of the factors meet the design requirement of the bolt connection structure based on the new reliability analysis result, if the new bolt reliability analysis result items meet the pre-designed target value, completing the optimization of the bolt structure design, and if the new reliability analysis result has a result item which does not meet the pre-designed target value, carrying out the optimization again.