Development of Three-Dimensional Hot Bending and Direct

Journal of Advanced Control, Automation and Robotics (JACAR), 1 (1): 18-24, 2015

ISSN 2186-9154

Applied Science and Computer Science Publications

Corresponding Author: Kazuo Uematsu. Application Technology Research Lab., Nippon Steel & Sumitomo Metal

Corporation, 20-1 Shintomi Futtsu, Chiba, Japan, Tel: +81(0)70-3514-8038, Fax: +81(0)439-80-

2743, E-mail: [email protected]

18

Development of Three-Dimensional Hot Bending and Direct Quench Using

Robot

Kazuo Uematsu, Atsushi Tomizawa, Naoaki Shimada and Hiroshi Mori

Abstract: To achieve both weight reduction and crash safety improvement in automobile bodies, we

have developed Three-Dimensional Hot Bending and Direct Quench (3DQ) technology, the first in the

world. In this paper, we describe the overview and the effect of 3DQ with robot.

Keywords: 3DQ, automobile body, hot bending, quench

I. INTRODUCTION

In recent years, the automobile industry has been

focusing on two issues: development of lighter

vehicles to improve fuel economy, in an effort to

prevent global warming; and improvement in crash

safety. Three-Dimensional Hot Bending and Direct

Quench (3DQ) Mass Processing Technology has been

developed as a means of satisfying these two conflicting

needs. The technology enables materials with a hollow

tubular structure, a major component of a vehicle body,

to gain ultra high-tensile strength and the manufacture of

components in three-dimensional complex shapes. 3DQ

machine is based on the numerical control using the

servo motor. There are various three-dimensional shapes

and cross-sectional shape and thickness of the hollow

member in automobile body, it is necessary to develop a

3DQ machine corresponding to them. In this report, the

study of simplifying the 3DQ machine, improving the

shape accuracy and equipment rigidity is described.

II. BACKGROUND AND PURPOSE OF

DEVELOPMENT

Fig.1 shows the forming method for high-tensile

automobile components. Cold stamping is widely used

to form open cross-section structure components, of

which tensile strength up to 980MPa. Furthermore, hot

stamping technology was adopted in Europe for

components with open cross-section structures with a

high-tensile strength of 1470MPa or more from around

1992[1][2]. Its application has expanded to the Japanese

market as well. On the other hand, tube hydroforming

technologies has been developed around 1990, in an

effort to meet high-level demands from automobile

manufacturers [3][4]. As shown in Fig.2, the automobile

components with a hollow tubular structure have

advantages in rigidity because of continuous closed

section. In addition, it has an advantages in weight by

flangeless. Tube hydroform is cold forming, so the

maximum tensile strength achieved was 980MPa[5]. In

contrast, newly developed 3DQ technology has enabled

the manufacture of automobile components with a

hollow tubular structure of as high as 1470MPa high-

tensile strength made by steel. It has produced effects

that are hard to achieve with conventional hydroforming

and other cold forming methods.

～Ｍａ４Ｍａ～

Hollow tubular

structure

Open cross-section structure

High strength

High

rigidity

Cold stamping Hot stamping

Hydroforming

3DQ

～Ｍａ４Ｍａ～

Hollow tubular

structure

Open cross-section structure

High strength

High

rigidity

Cold stamping Hot stamping

Hydroforming

3DQ

Fig. 1 Forming method for high-strength automobile

components

III. PROCESS PRINCIPLE OF 3DQ

I

最大５0％の軽量化

Spot Welding

(Intermittent)

Electric Resistance Welding

(Continuous)

Flange Flangeless Fig. 2 Comparison of the press and spot-weld structure

and the hollow tubular structure


19

Conventional high frequency bending method used for

piping is shown in Fig.3 [6][7].

Feed

BendingRadius

BendingArm

Water Quench deviceSupport Roller

Induction Coil

Work Piece

Fig. 3 Conventional high-frequency-heating and bending

method

While high-frequency heating, the work piece tip is

constrained by the arm, it is intended to carry out the

bending of the two-dimensional single radius by

pivoting the arm.

Fig.4 shows principle of 3DQ process. The straight

tube is fed downstream supported by the support roller

or the support guide. As shown in Fig.5, the straight

pipe with various cross sections, such as round, square

and odd-shaped, are available. Then, this pipe is heated

by the induction heater rapidly. The heat temperature is

more than Ac3 for quenching. Bending or twisting

moment is applied to the pipe by the robots or the

movable roller dies, this is the different point from the

conventional high-frequency bending method. As the

yield stress of the heated portion is low, deformation by

this moment is concentrated in this heated potion. Then,

the bent portion is quenched by water cooling and the

tensile strength is raised as high as 1470MPa or more.

By performing this process consecutively, the products

which have complex 3-dimensional bent shape and ultra

high tensile strength are obtained.

3DQ technology has the following characteristics:

- Tensile strength of 1470MPa or more in components is

realized.

- High shape fixability results in high forming precision

(minimal springback).

- Residual stress is low for products.

- There is no concern about delayed fracture caused by

residual stress of products.

- Forming of hollow tubular structures becomes possible,

because flanges needed for welding assembly of

stamped products can be omitted, the number of

components can be reduced and additional welding can

be omitted.

- Processing in complex bended shapes enables the

production of complex components in one piece.

- Partial quenching allows strengthening of only the

areas of an automobile component that need to have

high-tensile strength.

- The number of dies can be reduced significantly (die-

less forming).

Quenched

product

(≧1470MPa)

Heated

portion

(50MPa)

Straight tube

(600MPa)

Quenched

product

(≧1470MPa)

Heated

portion

(50MPa)

Straight tube

(600MPa)

Straight tube

(600MPa)

Fig. 4 Principal of 3DQ process

Fig. 5 Various shaped tubes for 3DQ

IV. FEATURES OF PRODUCTS BY 3DQ

Fig.6 shows hardness distribution of the product by

3DQ. Vickers hardness of 450HV, which is equivalent

to tensile strength 1470MPa, is obtained in all portions

of the product, and the micro structure of the product is

uniform martensitic structure, as shown in Fig.7. It is

easy to obtain partial quenched products by 3DQ. Fig.8

shows the example of hardness distribution of partial

quenched product of which the heating pattern was

controlled. Fig.9 and Fig.10 shows the results of the

axial crash test for the partial quenched specimen. The

Heated

portion

(50MPa)


20

test condition is shown in Table 1. The partial quenched

specimen shows higher energy absorption than the

specimen which is not quenched. Fig.10 shows the

deformation of the specimen in this test. The specimen

which is not quenched deforms sequentially from top of

the products, whereas the partial quenched specimen

deforms preferentially at the portion which is not

quenched. For the bent products, the partial quenching

would be effective in the control of crash deformation

pattern and the improvement of energy absorption. Fig.11 shows the example of the twisted products

by 3DQ, which were formed from rectangular shape

pipe. There were no defects, such as wrinkle, in this

product.

硬度測定位置

ビッ

カス

硬度

]

外面

中央

内面

硬度測定位置

ビッ

カス

硬度

]

外面

中央

内面

Position

Outer

Center

Inner

Vic

kers

hard

ness

Fig. 6 Hardness distribution of products by 3DQ

(40mmX40mm, Thickness=1.8mm)

Fig. 7 Micro structure of product by 3DQ

(40mmX40mm, Thickness=1.8mm)

Table.1 Axial crash test condition

Dimension of the cross

section of the specimen for

axial crash test

Weight of

the

impactor

(kg)

Speed of

the

impactor

(m/s) Width

(mm)

Height

(mm)

Thickness

(mm)

70 50 1.8 430 7-10

E

=

=

）

Fig. 9 Energy absorption of the partial quenched

specimen by 3DQ in axial crash test

Fig. 10 Appearance of the partial quenched specimen by

3DQ in axial crash test

Fig. 11 Examples of twisted parts by 3DQ

0.2mm from outer surface

Thickness center

0.2mm from inner surface

長手方向距離

ビッ

カス

硬度

焼き入れ焼き入れ

長手方向距離

ビッ

カス

硬度

長手方向距離

ビッ

カス

硬度

焼き入れ焼き入れ

Longitudinal position

Quenched Quenched

Vic

kers

hard

ness

Fig. 8 Hardness distribution of partial quenched

product by 3DQ


21

V. 3DQ MACHINE

Fig.12 shows movable roller die type 3DQ machine.

This type machine is the first developed, and is suitable

for manufacturing large diameter pipe components.

However, this type machine has problems of complex

structure, low shape accuracy and high cost. Therefore,

the development to apply robot to 3DQ has been made

to solve their problems.

Fig.13 shows single arm type 3DQ machine. This

system has very simple structure, and since it is not

necessary to add a special twist mechanism by joint

flexibility of the robot, while a twisting process also

allows a feature of 3DQ, simplicity and compactness of

the equipment of the machine structure is realized. This

system is suitable for small to middle sized pipe and

simple shaped components. This type is the most

versatile system of 3DQ.

Fig.14 shows dual arm type 3DQ machine. In the

single arm type, when bending complex components,

the robot becomes possible to carry out complex

operations at high speed, there is a tendency that the

amount of movement and the acceleration increases.

Therefore, the track deviation is likely to occur due to

vibrations and delays due to the repeated frequent

acceleration and deceleration. So dual arm type 3DQ

system that combines the dual arm robot and the single

arm robot has been developed for complex shaped

components as U-shape. In the dual arm type 3DQ

machine, three robots are cooperative controlled. One is

"the coil robot", which is fitted with a cooling unit and

the supporting roll and the heating coil, and is a single-

arm robot only in this system. One is "the bend robot"

which grips the end of pipe in downstream of process

and bend the pipe. Another is "the feed robot" which

grips the end of pipe in upstream of process and feeds

the pipe. The later two are each arm of the dual arm

robot. By optimizing the operation of each robot,

acceleration of them can be greatly reduced, as shown in

fig.15, and it leads to improve dimensional accuracy of

the product.

Fig.16 shows parallel link robot type 3DQ machine.

In the case of bending large-diameter pipe, high forces

and high rigidity is required for the robot to perform

bending operations. Therefore parallel link robot which

has high rigidity and corresponds to the high load has

been developed, and the parallel rink type 3DQ machine

has been developed using parallel link robot. Since

parallel link robot has six degrees of freedom of

x,y,z,θx,θy and θz, additional torsion device is not

needed. Fig.17 shows a comparison between the serial

link robot and a parallel link robot of equivalent

performance. The height of the parallel link robot is 1/3

of serial link robot and greatly downsizing is realized.

As shown in Fig.18, x and y-direction rigidity of the

parallel link robot is equivalent to the serial link robot,

and z direction rigidity is 10 times. As shown in Fig.19,

the positioning accuracy is doubled in the x-direction,

10 times in the y direction, is five times in the z-

direction. By combining and cooperative control the

movable roller die and the parallel link robot and the

single arm robot, components of large diameter pipe can

be processed.

Fig. 12 Movable rollers die type 3DQ machine

Fig. 13 Single arm robot type 3DQ machine

Fig. 14 Dual arm robot type 3DQ machine


22

0

0.2

0.4

0.6

0.8

1

1.2

Single arm

type

Coil robot Bend robot Feed robot

Acc

ele

rati

on

ra

tio

Dual arm type Fig. 15 Comparison of acceleration of robot

Fig. 16 Parallel link robot type 3DQ machine

Measure Point

Measure Point

(a) Serial link robot (b) Parallel link robot

Fig. 17 Comparison of serial link robot and parallel link

robot

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

X Y Z

Dis

pla

cem

en

t ra

tio

un

de

r lo

ad

ing

Serial link

Parallel link

Fig. 18 Rigidity comparison of serial link and parallel

link robot

0

0.2

0.4

0.6

0.8

1

1.2

X Y Z

Po

siti

on

ing

va

ria

ble

ra

tio

Serial link

Parallel link

Fig. 19 Positioning reproducibility comparison of serial

link and parallel link robot

VI. GENERATION OF ROBOT TRAJECTORY

AND ITS ACCURACY

Fig.20 shows a typical flow of forming procedures

by the robot type system. The designated products CAD

data is compiled to a robot arm trajectory curve data in

three-dimension. The compiling program is based on a

precise plastic deformation analysis, and the robot is

able to precisely trace the trajectory. As the result, the

3DQ system provides high reliable quantities in forming

work. However actually, the calculation and actual

plastic deformation of pipe are not match because the

robot arm or quenched pipe will deform elastic and

plastic deformation does not occur in pin-point. So it

might be needed that robot path is corrected according

to measured dimensional difference of processed pipe

and CAD data. Repeatability of robot trajectory is

extremely high, so once it is determined, the

dimensional accuracy variance of the component

produced by 3DQ is small, as shown in Fig.21.

Robots of a general-purpose type available in the

market are used for 3DQ, which allows very compact

configuration and standardization of the equipment.

Whereas, by conventional mechanical forming methods,

the equipment design tends to be different according to

individual object parts, use of the general purpose robots

makes it possible to standardize the equipment and

shorten the construction lead time. In addition, because

the 3DQ method does not use dies and it is very easy to

input a new set of trajectory data to the robot, it is also

suitable for manufacturing wide varieties of products in

small quantities.

1244

187

Prototyped model


23

Design of automotive part

(CAD data)

Generation of robot path

Forming by 3DQ machine

Dimensional accuracy?

Mass production Correct data

OK NG

Fig. 20 Typical flow of 3DQ process using robot

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

A B C

Dif

fern

ce f

rom

ca

d d

ata

(mm

)

Measuring position Fig. 21 Example of dimensional accuracy of 3DQ

components

VII. FUTURE OF 3DQ

Fig.22 shows the example of automobile

components prototyped by 3DQ. By application of 3DQ

to the automobile components, it is expected to

contribute to reduction in weight and improvement in

crash safety for automobile. Currently 3DQ components

has been applied to the door impact beams and seat parts,

and are expected to be applied to the body structure

components in the near future.

VIII. CONCLUSION

The 3DQ technology has been developed. This

technology is a consecutive forming method that allows

three-dimensional complex hot bending and quenching

at the same time. This technology enables to produce the

automobile components which have the ultra high

tensile strength (1470MPa or more) and hollow tubular

structure.

The features of 3DQ technology are as follows:

- High shape fixability results in high forming precision

(minimal springback).

- Residual stress is low level for products.

- There is little risk about delayed fracture caused by

residual stress of products.

- Products of hollow tubular structures can be obtained,

so flanges needed for welding assembly of stamped

products can be omitted and integration of components

is possible and additional welding can be omitted.

- Processing in complex bended shapes enables the

production of complex components in one piece

including twisted products.

- Partial quenching allows strengthening of only the

areas of an automobile component that need to have

high-tensile strength.

- The number of dies can be reduced significantly (die-

less forming.)

Several type of 3DQ machines are developed. It is

desirable to select optimal system to match the pipe

diameter and components shape.

The 3DQ products would be widely applied to the

automobile components and would be effective in the

improvement of energy absorption and the control of

deformation pattern during crash deformation.

ACKNOWLEDGEMENTS

The authors would like to thank the project

members in Nippon Steel & Sumikin Pipe Co., LTD.

and Yaskawa Electric Corporation, Ltd.

REFERENCES [1] N.Kojima, T.Nishibata, K.Uematsu, M.Uchihara, K.Imai,

K.Akioka and K.Kikuchi, “The effect of process factors on performance of hot stamped parts”, Trans. JSAE. 38(2007), pp.321-326.

[2] T.Asai and J.Iwata, “Hot stamping drawability of steel”, Proc. IDDRG (2004), pp.344-354.

[3] M.Kojima and S.Inoue, “Tubes and hydroforming for car industry in Japan”, Proc. JSTP 195 International Joint Symposium(2000), pp244-258.

A

B C

Single arm robot, n=30

Fig. 22 Example of prototyped automobile components

by 3DQ


24

[4] A. Tomizawa, “The state of the hydroforming technology

in Japan”, Tube Hydro 2009(2009), pp.1-12.

[5] Y.Hasegawa, H.Fujita, T.Endo, M.Fujimoto, J.Tanabe

and M.Yoshida, “Development of front pillar for

visibility enhancement”, Honda R&D Technical Review,

Vol.20 No.2(2008), pp106-113.

[6] H.Asao, K.Okada, H.Yonemura and S.Fujishima,

Journal of JSPE, vol.50, No.3 (1984), pp.531-533.

[7] K.Kobatake, T.Ichise, H.Sekiguchi and K.Osakada,

Journal of JSTP, Vol.28, No.313 (1987), pp.158-

165.

Documents

Development of Three-Dimensional Hot Bending and Direct