DEVELOPMENT OF A DATABASE FOR SPRINGBACK PREDICTION IN TUBE BENDING MACHINES TOBB ETU TOBB ETU Department of Mechanical Engineering, Ankara, 2010 Senior Students : Recep Muhammet Görgülüarslan, Engin Metin Kaplan Advisor : Asst. Prof. Mehmet Ali Güler ABSTRACT DESIGN FINITE ELEMENT ANALYSIS DEFORMATION ANALYSIS SPRINGBACK ANALYSIS This project has achieved the following results after all work of literature review, design of the tooling, and development of analytical equations and FEM simulations of tube bending and springback prediction. • The design of toolings and FE simulation models for rotary draw bending and push rolling bending techniques were developed by using the dynamic explicit FE code LS-DYNA. The deformation analysis of these simulation models with different tube dimensions and tooling setup were proved to have good agreement with analytical methods, and published experimental data. • The FE simulation model for springback of the bent tube was developed, the FE results were validated with the ana- lytical and experimental results in the literature, and the effect of geometric and material parameters on springback angle was investigated. • Springback database for rotary draw bending and push rolling bending methods were developed for different materials and different tube geometries. Tube bending is a manufacturing process which is performed by bending machines to bend the circular hollow tubes into certain angle and provides permanent forming. It is used in various industries such as automotive, aerospace, boilers and heat exchangers, etc. One of the easiest ways of having high quality tube formed end-products is using CNC tube bending techniques. The most common problems encountered during tube bend- ing operations are thickness reduction, ovalisa- tion, wrinkling and springback. Especially; springback, is an undesirable condition that causes some difficulties in the assembly process. The main objective of this study is to develop a springback database in tube bending techniques by using finite element method (FEM). For this purpose, tube bending and springback simulation models for rotary draw and push rolling bending processes are developed, and the simulation results are validated with the analytical results, previous simulation and experimental results. 1. DESIGN OF ROTARY DRAW BENDING TOOLING 2. DESIGN OF PUSH ROLLING BENDING TOOLING The design of the tooling is crucial for a good bending quality. Also, obtaining desired dimen- sions and geometries is a necessity to develop finite element models of bending processes, and achieve good simulation results. Therefore, the geometry of the tooling must be designed. Rotary draw tube bending, which is used for bending tubes in small radius, is the most flexible, versatile and precise bending method among the types of tube bending process. The tooling of this method includes bend die, clamp die, pressure die, and wiper die. Also, mandrel is used in worst cases. The tooling is designed in respect of the design parameters and the deformation results are validated with the previouss studies. Push rolling bending process is used for bend- ing the tube in large radius, spirals, and tube sec- tios of different diameters. The tooling of the method consists of a bend die and three roll dies. The best design for tooling is determined by com- paring the simulation results of different die ge- ometries. The finite element models of bending processes were developed by using the dynamic explicit FE code LS- DYNA. Firstly, simulation model of bending is developed since the springback simulation model can be created after bending simulation. The CAD data of the bending process is meshed by using the program ANSA before preparing the simulation model. After the simulations are performed, the strain, thickness and thinning distribution results of bent tubes, which are obtained from simulations are vali- dated with the analytical results calculated, and both simu- lation and experimental results in the literature. Springback prediction by analytical methods may not give satisfactory results due to the several parameters involved such as geometrical, mechanical and forming pa- rameters. It is therefore necessary to use the finite element method to predict the springback angle. The springback simulations can be performed after the bending simulations since the initial stresses on bent tube are necessary for springback. A parametric study is performed in order to de- termine the effect of material and geometrical properties on springback angle of bent tube. Furthermore, springback da- tabase for different materials and different tube geometries were developed in respect of the finite element analysis. Max. Thickness Element Min. Thickness Element Feeding Axes Effect of Elastic Modulus on Springback 0 0,5 1 1,5 2 2,5 0 10 20 30 40 50 60 70 80 90 100 Bend Angle Springback Angle E = 160 GPa E = 210 GPa E = 260 GPa CONCLUSIONS Springback Comparison with Experimental Results 0 1 2 3 4 5 0 10 20 30 40 50 60 70 80 90 100 Bend Angle Springback Angle Khodayari Experiment FEM Results Push Rolling Bending Wall Thickness Comparison 1,50 1,52 1,54 1,56 1,58 0 200 400 600 800 1000 1200 Tube Length (mm) Wall Thickness (mm) 4 m/s 8 m/s 10 m/s 12 m/s Rotary Draw Bending Thickness Reduction Comparison -20 -10 0 10 20 90 120 150 180 210 240 270 Position on the cross-section (degree) Thickness Reduction (%) FEM Analytical Khodayari Experiment Agarwal FEM Rotary Draw Bending Strain Comparison 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2 0 100 200 300 400 500 Tube Length (mm) Effective Strain Analytical FEM Simulation FEM Shr FEM Agarwal Springback Database for Different Materials 0 1 2 3 4 5 6 7 0 10 20 30 40 50 60 70 80 90 100 Bend Angle (Degree) Springback Angle (Degree) Aluminum 2024 T3 Steel SS 304 Steel AISI 1010 Aluminum AlMgSi0.5 Steel A 573-81 65
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DEVELOPMENT OF A DATABASE FOR SPRINGBACK PREDICTION IN TUBE BENDING MACHINES
TOBB ETU TOBB ETUDepartment of Mechanical Engineering, Ankara, 2010Senior Students : Recep Muhammet Görgülüarslan, Engin Metin Kaplan
Advisor : Asst. Prof. Mehmet Ali Güler
ABSTRACT DESIGN FINITE ELEMENT ANALYSISDEFORMATION ANALYSIS SPRINGBACK ANALYSIS
This project has achieved the following results after all work of literature review, design of the tooling, and development of analytical equations and FEM simulations of tube bending and springback prediction. • The design of toolings and FE simulation models for rotary draw bending and push rolling bending techniques were developed by using the dynamic explicit FE code LS-DYNA. The deformation analysis of these simulation models with different tube dimensions and tooling setup were proved to have good agreement with analytical methods, and published experimental data. • The FE simulation model for springback of the bent tube was developed, the FE results were validated with the ana-lytical and experimental results in the literature, and the effect of geometric and material parameters on springback angle was investigated. • Springback database for rotary draw bending and push rolling bending methods were developed for different materials and different tube geometries.
Tube bending is a manufacturing process which is performed by bending machines to bend the circular hollow tubes into certain angle and provides permanent forming. It is used in various industries such as automotive, aerospace, boilers and heat exchangers, etc. One of the easiest ways of having high quality tube formed end-products is using CNC tube bending techniques. The most common problems encountered during tube bend-ing operations are thickness reduction, ovalisa-tion, wrinkling and springback. Especially; springback, is an undesirable condition that causes some difficulties in the assembly process. The main objective of this study is to develop a springback database in tube bending techniques by using finite element method (FEM). For this purpose, tube bending and springback simulation models for rotary draw and push rolling bending processes are developed, and the simulation results are validated with the analytical results, previous simulation and experimental results.
1. DESIGN OF ROTARY DRAW BENDING TOOLING
2. DESIGN OF PUSH ROLLING BENDING TOOLING
The design of the tooling is crucial for a good bending quality. Also, obtaining desired dimen-sions and geometries is a necessity to develop finite element models of bending processes, and achieve good simulation results. Therefore, the geometry of the tooling must be designed.
Rotary draw tube bending, which is used for bending tubes in small radius, is the most flexible, versatile and precise bending method among the types of tube bending process. The tooling of this method includes bend die, clamp die, pressure die, and wiper die. Also, mandrel is used in worst cases. The tooling is designed in respect of the design parameters and the deformation results are validated with the previouss studies.
Push rolling bending process is used for bend-ing the tube in large radius, spirals, and tube sec-tios of different diameters. The tooling of the method consists of a bend die and three roll dies. The best design for tooling is determined by com-paring the simulation results of different die ge-ometries.
The finite element models of bending processes were developed by using the dynamic explicit FE code LS-DYNA. Firstly, simulation model of bending is developed since the springback simulation model can be created after bending simulation. The CAD data of the bending process is meshed by using the program ANSA before preparing the simulation model. After the simulations are performed, the strain, thickness and thinning distribution results of bent tubes, which are obtained from simulations are vali-dated with the analytical results calculated, and both simu-lation and experimental results in the literature.
Springback prediction by analytical methods may not give satisfactory results due to the several parameters involved such as geometrical, mechanical and forming pa-rameters. It is therefore necessary to use the finite element method to predict the springback angle. The springback simulations can be performed after the bending simulations since the initial stresses on bent tube are necessary for springback. A parametric study is performed in order to de-termine the effect of material and geometrical properties on springback angle of bent tube. Furthermore, springback da-tabase for different materials and different tube geometries were developed in respect of the finite element analysis.
Max. Thickness Element
Min. Thickness Element
Feeding Axes
Effect of Elastic Modulus on Springback
0
0,5
1
1,5
2
2,5
0 10 20 30 40 50 60 70 80 90 100
Bend Angle
Spr
ingb
ack
Ang
le
E = 160 GPa E = 210 GPa E = 260 GPa
CONCLUSIONS
Springback Comparison with Experimental Results
0
1
2
3
4
5
0 10 20 30 40 50 60 70 80 90 100
Bend Angle
Spr
ingb
ack
Ang
le
Khodayari Experiment FEM Results
Push Rolling Bending Wall Thickness Comparison
1,50
1,52
1,54
1,56
1,58
0 200 400 600 800 1000 1200
Tube Length (mm)
Wal
l Thi
ckne
ss (m
m)
4 m/s 8 m/s 10 m/s 12 m/s
Rotary Draw Bending Thickness Reduction Comparison
-20
-10
0
10
20
90 120 150 180 210 240 270
Position on the cross-section (degree)
Thic
knes
s R
educ
tion
(%)
FEM Analytical Khodayari Experiment Agarwal FEM
Rotary Draw Bending Strain Comparison
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
0,18
0,2
0 100 200 300 400 500
Tube Length (mm)
Effe
ctiv
e S
train
Analytical FEM Simulation FEM Shr FEM Agarwal
Springback Database for Different Materials
0
1
2
3
4
5
6
7
0 10 20 30 40 50 60 70 80 90 100
Bend Angle (Degree)
Spr
ingb
ack
Ang
le (D
egre
e)
Aluminum 2024 T3 Steel SS 304 Steel AISI 1010Aluminum AlMgSi0.5 Steel A 573-81 65
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