Procedia Engineering 81 ( 2014 ) 280 – 285

1877-7058 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of the Department of Materials Science and Engineering, Nagoya University doi: 10.1016/j.proeng.2014.09.164

ScienceDirectAvailable online at www.sciencedirect.com

11th International Conference on Technology of Plasticity, ICTP 2014, 19-24 October 2014, Nagoya Congress Center, Nagoya, Japan

Quantitative design methodology for flat ring rolling process Wujiao Xu*, Qiaoli Wang, Xue Zhou, Xiaobing Yang

College of Material Science and Engineering, Chongqing University, Chongqing, China, 400044

Abstract

For a specific ring rolling, the quantitative design of the rolling billet and feeding strategy is the most important factor to obtain the ideal process. This research focuses on developing the quantitative design methodology for the flat ring rolling in a systematic way. The paper is organized in two parts: billet constraint and feeding interval in the flat ring rolling. In the first part, the constraint conditions for both the piercing process and ring rolling are taken into consideration, deducing the limiting wall thickness and the limiting height of the billet for a specific ring rolling. And for the second part, the expansion of ring outer diameter, the rolling force and rolling temperature, the form error occurrence together with the gripping and penetration condition are included to generate the feeding interval. In the feeding interval created, the response of ring material to the processing parameters must also be considered. So for a specific ring rolling, we established the processing map of the material used. Based on that, a desirable feeding strategy that could obtain a higher efficiency of power dissipation was determined by means of the subroutine VUAMP in ABAQUS. Practical ring rolling experiment was carried out and the microstructure of the finished ring was also observed. The experiment shows that the deformed ring was rolled to the final dimension in a stable manner without macroscopic or microscopic defects, which indicated that the quantitative design of the flat ring rolling process is reasonable.

© 2014 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of Nagoya University and Toyohashi University of Technology

Keywords: Quantitative design; Ring rolling; Constraint; Feeding interval; Processing map

1. Introduction

A ring rolling process is an advanced metal forming process to manufacture varieties of seamless rings. It has evolved over 150 years, with the significant research work in this area in the past 50 years (Julian et al., 2005).

* Corresponding author. Tel.: +86-13368186252; fax: +0086-23-65111493. E-mail address: xuwujiao_cq@163.com

© 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of the Department of Materials Science and Engineering, Nagoya University

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281 Wujiao Xu et al. / Procedia Engineering 81 ( 2014 ) 280 – 285

Johnson and Needham (1968) have investigated the rolling process of different diameter rings on a model two-high rolling mill and the rolling force and torque were obtained by the machine. Mamalis et al. (1976) measured the pressure distribution of the rolls on the ring by using special rolls. U. Coppers (1987) developed analytical equations for the kinematics of the ring rolling process to guide the design of rolling schedules. Hua et al. (1996) derived gripping and penetration condition which must be satisfied in ring rolling process to guarantee the deformation of the ring. Li (2008) proposed a control method of guide rolls by the hydraulic adjustment mechanism. Zhou et al. (2011) investigated the effects of rolls size on the radial-axial ring rolling process by using finite element analysis. Jenkouk et al. (2012) explored the integrated close-loop control of ring rolling process.

However, there are still quite a number of key challenges faced with to limit the achievement of an ideal ring rolling process, i.e., design of rolling schedule, form error in the cross section and ring, control of temperature and residual stress, attainment of desired material properties, energy use and so on. For a specific ring rolling, the quantitative design of the rolling billet (including the pre-form) and feeding strategy is the most important factor to obtain the ideal process. This paper mainly focuses on developing the quantitative design methodology for the ring rolling process in a systemic way. The rest of this paper is organized as following. Section 2 studies the billet constraint, deducing the limiting wall thickness and the limiting height of the billet for a specific flat ring rolling. Section 3 presents feeding interval and the processing map of the material to determine a desirable feeding strategy by means of subroutine VUAMP in ABAQUS. Section 4 verifies the reliability and validity of the quantitative design methodology for the flat ring rolling process experimentally. Section 5 contains the conclusions.

Nomenclature

H0 height of the ring billet D0 diameter of the ring billet h piercing depth d piercing diameter V volume of the ring R1 radius of main roll R2 radius of idle roll R instantaneous outer diameter of the ring r instantaneous inner diameter of the ring

friction coefficient b instantaneous radial feed amount per revolution

B0 wall thickness of the ring billet R mean working radius of axial roll

2. Billet constraint

2.1. Constraint conditions for piercing process

Generally, a ring billet is obtained after upsetting and piercing process. In the piercing process shown in Fig. 1, to avoid the instable process and occurrence of piercing defects, the following constraint conditions (Hong et al., 2007) must be satisfied:

0

01DH

, (1)

031

51

Ddmm

, (2)

282 Wujiao Xu et al. / Procedia Engineering 81 ( 2014 ) 280 – 285

043

32

Hh . (3)

According to the geometry relationship, the volume of the ring billet can be expressed as:

hHdHDV 02

020 44 . (4)

Combining Eqs. (1) - (4), the constraint can be expressed as:

332

2

0 098.111

4 Vm

VH. (5)

Thus, for a specific ring, the height of the ring billet has a maximum value. Once the billet height exceeds the limit, the desirable ring billet will hardly be achieved and defects will even occur during the piercing process.

2.2. Constraint conditions for ring rolling process

The gripping and penetration conditions are the constraint conditions which must be fulfilled (Hua et al. 1996) to guarantee the rolling deformation of the ring during flat ring rolling process.

According to the practical condition, the gripping condition in the radial rolling zone can be modified as:

Fig. 1. Schematic illustration of piercing process. Fig. 2. Billet constraint.

Fig. 3. (a) Ring product (b) designed ring billet.

rRRR

RR

ab 1111

11

tan114.1

212

21

2

. (6)

283 Wujiao Xu et al. / Procedia Engineering 81 ( 2014 ) 280 – 285

The penetration condition can be expressed by the minimum feed amount per revolution as follows:

rRRRrRb 11111055.6

21

23

. (7)

Thus, according to Eqs. (6) and (7), the inequality following can be obtained:

21

0 11tan13

RR

aB

. (8)

The inequality determines the limiting wall thickness of ring billet. Only when it is satisfied, the ring rolling process can proceed.

Similarly, in the axial rolling zone of a radial-axial ring rolling process, the constraint can be expressed as:

2tan13

0aRH

. (9)

Thus, the limiting height of ring billet in ring rolling process is determined by the gripping and penetration condition in axial rolling zone.

For a specific ring rolling, the limiting heights of ring billet in both piercing and ring rolling process can be determined according to Eqs. (5) and (9), as described in Fig. 2, while the limiting wall thickness is obtained by Eq. (8). For a ring product shown in Fig. 3(a), the ring billet is accordingly designed as illustrated in Fig. 3(b).

3. Quantitative design of feeding strategy

3.1. Feeding interval

There are multi-factors related with feed rate affecting the stability of ring rolling process. To obtain a stable ring rolling process and ring with desirable geometry and high quality, the feeding constraints of multi-factors including the expansion speed of outer diameter (Xu et al., 2012), the rolling force (Hua et al., 2001) and rolling temperature, the form error occurrence (Xu et al., 1990) and gripping and penetration condition (Hua et al., 1996) are calculated to generate a feeding interval, as shown in Fig. 4. The feeding interval illustrates the instantaneous extreme values of feed rate quantitatively, which could avoid instability of the flat ring rolling process and form error occurrence.

3.2. Processing map

To consider the response of ring material to the processing parameters, the processing map of steel 42CrMo based on dynamic materials model is established for a specific ring rolling process. By means of the processing map, the flow instability regions and ideal hot working domains are identified. Meanwhile, a relatively optimized deformation path with high efficiency of power dissipation is obtained (Xu et al. 2013), as shown in Fig. 5.

284 Wujiao Xu et al. / Procedia Engineering 81 ( 2014 ) 280 – 285

Fig. 4. Feeding interval in flat ring rolling process. Fig. 5. Processing map of steel 42CrMo.

Fig. 6. 3D FE model for flat ring rolling. Fig. 7. Designed feed rates.

3.3. Feeding design

A flat ring rolling model for the ring shown in Fig. 3 is established under ABAQUS environment, which is illustrated in Fig. 6. A coupled thermal-mechanical simulation with dynamic explicit solution is applied and the ring is correspondingly meshed with coupled thermal-mechanical element C3D8RT. The ring of steel 42CrMo is rolled with the initial temperature of 1125 . In this model, a subroutine VUAMP (Xu et al., 2013) in ABAQUS is developed to control the feed rates of the idle roll and the upper conical roll. The bisection method is adopted to search the reasonable feed rates from the feeding interval established, until the temperature and strain rate of the deformed ring get close to the optimized deformation path discussed in the processing map section. Thus, a desirable feeding strategy with a high efficiency of power efficiency is obtained, which is shown in Fig. 7.

Fig. 8. Simulated and experimental results (a) ring outer diameter (b) axial height. Fig. 9. Microstructure of the deformed ring.

285 Wujiao Xu et al. / Procedia Engineering 81 ( 2014 ) 280 – 285

4. Experiment verification and discussion

Practical ring rolling experiment with the designed billet and feeding strategy was carried out. The ring was rolled stably to the final dimension without obvious macroscopic defects. The variations of ring outer diameter and axial height in experiment as well as in simulation were shown in Fig. 8, which also prove that the FEM model is valid. The final microstructure of the deformed ring was observed, which is indicated in Fig. 9. There are basically no coarse grains or microscopic defects existed and the grains are distributed homogeneously. Therefore, the quantitative design of the flat ring rolling process is reasonable.

5. Conclusions

In this paper, quantitative design methodology for flat ring rolling process was developed in a systemic way. According to the constraints during the piercing process and ring rolling process, the limiting wall thickness and the limiting height of the ring billet were deduced for a specific ring rolling, which supply guideline for the design of ring billet. In the ring rolling process, a feeding interval considering multi-factors was generated. After that, the processing map of the ring material was established to get a relatively optimized deformation path. Thus based on the deformation path and the feeding interval, a desirable feeding strategy that could obtain a higher efficiency of power dissipation was determined by means of the subroutine VUAMP in ABAQUS. Practical ring rolling experiment with the designed ring billet and feeding strategy was carried out and the microstructure of the deformed ring was observed. The ring was rolled stably to the final dimension without obvious macroscopic or microscopic defects and the homogeneous microstructure was obtained, which indicates that the quantitative design of the flat ring rolling process is valid and reasonable.

Acknowledgements

The authors would like to thank for the support of Ministry of Science and Technology Sino-German Cooperation Project (2010DFA51860).

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