Analysis and homogenization of residual stress in aerospace ring rolling process of 2219 aluminum alloy using thermal stress relief method

International Journal of Mechanical Sciences 157–158 (2019) 111–118

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International Journal of Mechanical Sciences journal homepage: www.elsevier.com/locate/ijmecsci

Analysis and homogenization of residual stress in aerospace ring rolling process of 2219 aluminum alloy using thermal stress relief method Qiong Wu a, Jian Wu a, Yi-Du Zhang a,∗, Han-Jun Gao a, David Hui b,∗ a b

State Key Laboratory of Virtual Reality Technology and Systems, School of Mechanical Engineering and Automation, Beihang University, Beijing, 100191, PR China Department of Mechanical Engineering, University of New Orleans, New Orleans, LA 70148, USA

a r t i c l e Keywords: Rolling theory Rolling residual stress Stress homogenization Thermal stress relief

i n f o

a b s t r a c t Substantial amount of material is removed during the manufacturing process of large ring parts, thereby causing the ring parts to become a thin-walled structure with reduced rigidity. The influence of internal and external factors leads to machining deformation, which is ubiquitous in the actual production process in the aerospace industry. Studies showed that the main factor that causes this type of machining deformation is the initial residual stress inside the blank. The initial residual stress must be homogenized to solve the machining deformation problem. Large and uneven residual stress is easily produced during rolling. The research object in this study is a 2219 aluminum-alloy aerospace rolling ring. First, the mechanical model for the rolling process is established to analyze the mechanical behaviors of the diameter and axial directions. The reasonable parameters for the rolling process are determined according to continuous and penetration conditions. Second, a finite element model was established to simulate the rolling process and the Thermal Stress Relief process. This process was conducted to explore and verify the effect of Thermal Stress Relief treatment on the reduction of residual stress and homogenization of the rolling process. Corresponding rolling and Thermal Stress Relief experiments were conducted to verify the simulation results. The experimental results are highly consistent with the simulation results when the treatment time of Thermal Stress Relief was changed. The Thermal Stress Relief of the rolling ring can effectively reduce and homogenize residual stress. This study is significant for the reduction and homogenization of large residual stress.

1. Introduction Aerospace technology continues to change with industrial development. The aerospace industry promotes optimal working speed, thrustto-weight ratio, power-to-weight ratio, lightweight aircraft, and other parameters to address instances of severe working environments. Thin wall parts are widely used in aerospace field, and the removal rate of materials is even as high as 95% [1–3]. Thin walls, which are structural parts measured at a few millimeters, encounter difficulties during processing. These difficulties include machining deformation. International studies showed that residual stress is the main factor that affects the deformation and failure of part processing [4,5]. Deformation and fatigue life will be affected if excessive residual stress exists in the workpiece after formation [6]. The diameter of large rings used in space launch vehicles measures approximately 5 m and develops to 10 m. Wall thickness is usually measured at 0.1–0.2 m, which is the characteristic of thin-walled parts. The ring parts tend to deform under the influence of residual stress when the rolled parts of large thin-walled ring are processed; this process causes difficulty in the subsequent weld-

∗

ing process of multi-ring parts [7]. Thus, deformation has become a key problem in the aerospace manufacturing industry. Han and Hua [8] studied the plastic deformation and mechanical properties of a 20CrMnTi alloy rolling ring using finite element method. Johnson and Needham [9] studied the effect of rolling force on plastic deformation. Park et al. [10] studies the rolling process of contour rings, which were used to produce large “L” section rings on building machinery. To optimize the rolling process, Han et al.[11] established a 3D elastic-plastic finite element model of the rolling ring for simulation. Li and Fu [12] used DEFORM finite element software to examine the selection of technological parameters of 2-m rings. Zhao and Xu [13] proposed an efficient simulation method to reduce the long simulation time of DEFORM for the rolling parts of large rings on the premise of guaranteeing accuracy. Zhang et al. [14] introduced a 5-m diameter axial NC ring rolling mill developed by Xian Heavy Machinery Research Institute; this machine is the largest aluminum ring rolling equipment in China. Wuxi-Parker Company rolled out rings of 2219 aluminum alloy that measure nearly 9 m by filling the gap of more than 5 m rings for domestic aluminum materials [15].

Corresponding authors. E-mail addresses: [email protected] (Y.-D. Zhang), [email protected] (D. Hui).

https://doi.org/10.1016/j.ijmecsci.2019.04.040 Received 20 December 2018; Received in revised form 18 April 2019; Accepted 19 April 2019 Available online 20 April 2019 0020-7403/© 2019 Elsevier Ltd. All rights reserved.

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International Journal of Mechanical Sciences 157–158 (2019) 111–118

∑

Many scholars have studied the influence of initial residual stress on machining deformation. Lin et al.[16] and Heinz et al. [17] showed that the initial residual stress [18] in the ring piece greatly influences the field processing and production of the entire ring piece. FEM simulation and experimental study are used to predict the residual stress of aluminum alloy [19,20]; machining deflection due to original residual stress can be forecasted and validated by the experiment and the model for finite element analysis [21]. H. Dong showed that the deformation distribution resulting from FEM is consistent with the experiment result [22]. X. Cerutti and K. Mocellin introduced a new parallel finite element tool to predict distortion induced by initial residual stresses during machining [23]. Wang et al. [24] systematically studied the measurement of initial residual stresses and the distortion of a windshield frame part. Residual stress reduction is the core of the controlling the deformation of parts. Liu et al. [25] studied the variation of residual stress in welded structural parts under different loading methods. Fergani et al. [26] studied the use of different manufacturing processes to reduce residual stress in additive manufacturing. The use of vibration to reduce residual stress in molding of metal parts has a positively effect in Munsi’s research [27]. A novel, multistage interrupted artificial aging treatment [28] was designed to reduce residual stresses in quenched Al–Zn–Mg– Cu alloy thick plates. Croucher [29] studied the influencing factors of the treatment process of deep cold and rapid heat method; this study indicated that a large temperature difference positively affects the homogenization of residual stress. Fredj and Sidhom [30] conducted heat aging treatment on AISI304 stainless steel to reduce surface residual stress. Kobayashi verified the effectiveness of thermal aging in reducing residual stress by comparing ultrasonic vibration and thermal aging [31]. Many studies examined residual stress reduction. However, only few studies explored the reduction and homogenization of residual stress by thermal stress R, especially for ring rolled parts that can easily produce large and non-uniform residual stress during the forming process. Therefore, the process parameters of ring rolling process should be analyzed and the effect of thermal aging on residual stress distribution should be studied.

𝐹𝑦 = 𝑇1𝑦 + 𝑃1𝑦 + 𝑃2𝑦 = −𝑇1 sin(𝜉1 𝛼1 ) − 𝑃1 cos(𝜉1 𝛼1 ) + 𝑃2 𝑐𝑜𝑠(𝜉2 𝛼2 ) = 0, (2)

where P1 and P2 represent the positive pressure of driving roller and core roller on the ring member, respectively; T1 represents the friction of the drive roller against the ring; 𝛼 1 and 𝛼 2 represent the contact angle between two rollers and ring parts, respectively; 𝜉 1 𝛼 1 and 𝜉 1 𝛼 2 represent the positions where the driving roller and the core roller act on the joint force of the ring parts. The two coefficients are greater than 0 and less than 1. Coulomb friction exists between the ring and the roller. Friction angle is 𝛽. Thus, 𝑇1 = 𝜇𝑃1 ,

(3)

𝜇 = tan 𝛽.

(4)

The combined action position of driving roller and core roller is the center of contact arc segment. Thus, 𝜉1 = 12 and 𝜉2 = 12 . Then, 𝛼1 + 𝛼2 , 2 ( ) 𝑃1 𝛼1 + 𝛼2 ≤ cos . 𝑃2 2

𝛽≥

(5) (6)

Eqs. (5) and (6) represent the continuous rolling conditions of the ring. The value and direction of the positive pressure depends on the size of the system and the feeding speed. 2.2. Analysis of penetration condition during rolling Continuous rotation is a precondition for ring rolling as long as the ring does not slip. Considerable plastic deformation is forced on the whole ring that needs to be rolled. The penetration model of the ring is shown in Fig. 2. The projection of the roller contact arc in the X-axis direction is L, ℎ +ℎ and the average ring thickness is ha , and ℎa = 02 . The penetration condition obtained using slip line theory:

2. Theory

𝐿 1 ≥ , ℎ𝑎 8.7

2.1. Analysis of rolling of ring parts in diameter direction

where h0 represents the initial ring thickness and h represents the final ring thickness.

The precondition of ring rolling is the continuous entry of ring parts [32]. The mechanical model is shown in Fig. 1. The effect of guide roller was not considered in this model. To achieve continuous entry during ring rolling, the pulling force must be greater than or equal to its impedance force and the feeding direction must be balanced. The force analysis of ring rolled parts on the basis of the mechanical model is given as: ∑ 𝐹𝑥 = 𝑇1𝑥 + 𝑃1𝑥 + 𝑃2𝑥 = 𝑇1 cos(𝜉1 𝛼1 ) − 𝑃1 sin(𝜉1 𝛼1 ) − 𝑃2 sin(𝜉2 𝛼2 ) ≥ 0,

(7)

2.3. Analysis of rolling process parameters Contact arc length projection L can be expressed as: √ √ 2▵ℎ √ 𝐿=√ , 1 1 + + 𝑅1 − 1𝑟 𝑅 𝑅 1

2

where Δh represents the quantity per revolution and Δh = h0 − h.

(1)

KD h x

R1 y

α1 P1

O1

T1 P2 α 2 L

R2

/

O2 r

n1 h0

R

Fig. 1. Force analysis model of ring rolling.

Fig. 2. Penetration analysis model of ring rolling. 112

(8)

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International Journal of Mechanical Sciences 157–158 (2019) 111–118

The reasonable range of rolling feed is obtained according to geometric relation 𝛼1 = 𝑅𝐿 , 𝛼2 = 𝑅𝐿 and ha = h + ▵h/2 ≈ h0 = R − r, and 1

2𝑇𝑎 cos

2

combining with Eq. (5) and Eq. (7): ( ) 2𝛽 2 1 1 1 1 ▵ ℎ ≤ ▵ ℎmax = + + − , (1∕𝑅1 + 1∕𝑅2 )2 𝑅1 𝑅2 𝑅 𝑟 ( ) 1 1 1 1 ▵ ℎ ≥ ▵ ℎmin = 6.55 × 10−3 (𝑅 − 𝑟)2 + + − , 𝑅1 𝑅2 𝑅 𝑟

𝑇𝑎 = 𝜇𝑎 𝑃𝑎 = 𝑃𝑎 tan 𝛽𝑎 ,

▵ℎ . ▵𝑡

(10)

𝑅𝑎 = 𝑆𝑎 sin(𝛾∕2),

(11)

2𝑛1 𝑅1 𝛽 2 , 𝑅(1∕𝑅1 + 1∕𝑅2 )

𝛼𝑎 ≈

𝑣 ≥ 𝑣min = 6.55 × 10−3 (𝑅0 − 𝑟0 )2

𝑛1 𝑅1 𝑅0

) 1 1 + . 𝑅1 𝑅2

(13)

𝐻 ≥ 𝐻min

17.5𝛽𝑅1 1+

𝑅1 𝑅2

,

( ) 𝑅 𝑟𝑎0 𝐻0 = 0.183 1 + 1 , 𝑅2 𝑅1

𝐿𝑎 , 𝑅𝑎

▵ ℎ𝑎 =

To achieve effective rolling, ▵hmax ≥ ▵hmin meet the stiffness condition of the ring. The thickness condition of the ring is obtained as follows: 𝐻 ≤ 𝐻max =

(19) (20)

where La and Ra represent the contact arc length projection and the equivalent rolling radius of the axial conical rollers, respectively; 𝛾 represents the top angle of the axial conical rollers; Sa represents the distance from the vertex of the axial roller to the rolling contact line. The feed requirement of the cone roller is given as follows (va represents the feed of the conical rollers) under the condition that sliding displacement does not occur between the cone roller and the ring member:

(12) (

(17)

where Ta represents the friction of the roll against the ring, Pa is the positive pressure of the roll on the ring, and 𝛼 a represents the contact angle between the ring piece and the roll. According to Fig. 3, the geometric relationship is described as follows: √ 𝐿𝑎 = 𝑆𝑎 ℎ𝑎 tan(𝛾∕2), (18)

Given that R and r are constantly changing during rolling, Eqs. (9) and (10) cannot be conveniently calculated. For large ring rolling parts, the size of the roll is smaller than that of the ring parts. Thus, these equations are simplified to obtain the reasonable feed range of the core roller in diameter direction as follows (n1 represents the rotating speed of the driving roller): 𝑣 ≤ 𝑣max =

(16)

(9)

where ▵hmax and ▵hmin represent the maximum and minimum feed per revolution of the roll, respectively. R and r represent the radius of the outer and inner surfaces of the initial blank, respectively. Core roll feed speed v is obtained as follows: 𝑣=

𝛼𝑎 𝛼 − 2𝑃𝑎 sin 𝑎 ≥ 0, 2 2

2𝜋𝑅𝑣𝑎 . 𝑛1 𝑅1

(21)

Similar to rolling in diameter direction, axial rolling must satisfy the following penetration condition:

(14)

𝐿𝑎 1 ≥ , 𝑏0 − 𝑣𝑎 𝑡 8.74

(15)

(22)

where ba represents the initial height of the blank and t means rolling time. Finally, a reasonable range of axial feed (▵ha ) is obtained as follows:

where Hmax and Hmin represent the maximum and minimum values of final ring thickness H, respectively; H0 represents the initial thickness of ring, and ra0 represents the initial average radius of the ring.

▵ ℎ𝑎 ≤▵ ℎmax,𝑎 = 2𝛽𝑎2 𝑆𝑎 sin 𝛾,

2.4. Analysis of ring rolling parts in axial direction

▵ ℎ𝑎 ≥▵ ℎmin,𝑎 =

Two axial conical rollers were added to the rolling process of ring parts to improve the quality of axial rolling, which must also satisfy the entry conditions [33]. The mechanical model of axial rolling is shown in Fig. 3. Similar to the entry condition in the diameter direction, axial entry condition is obtained as follows (set the Coulomb friction coefficient 𝜇a and friction angle 𝛽 a ):

0.0131(𝑏0 − 𝑣𝑎 𝑡)2 , 𝑆𝑎 tan(𝛾∕2)

(23)

(24)

where ▵hmax ,a and ▵hmin ,a represent the maximum and minimum feed per revolution of the axial roll, respectively. The reasonable range of rolling process parameters in radial and axial direction was determined through the mechanical analysis of ring rolling process. This result provided the basis for simulation and experimental verification. Fig. 3. Axial force analysis model of ring rolling.

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Table 1 Physical properties of 2219 aluminum alloys. Parameter Units 2219 Al-alloys

Young’s modulus GPa 73

Density Kg/m 2840

Poisson’s ratio

Yield strength

0.3

MPa 350

3

3. Material and methods 3.1. Material of rolled ring part Aluminum alloy is widely used in various industries because of its superior performance. Military and civilian products cannot be produced without the use of aluminum alloy. The demand for aluminum alloy is high given the rapid advancements in fields such as aerospace technology and national defense science and technology. Space with more than 10 m of large ring rolled piece using aluminum alloy material and 2219 aluminum alloy is used to enhance the performance of large ring rolling. This material has good thermal deformation and heat treatment properties. The physical properties and chemical compositions of aluminum alloys used in this experiment are shown in Tables 1 and 2. The plastic deformation of 2219 aluminum alloy occurred after the elastic limit, and a large number of slip bands appeared in each grain. In the process of plastic deformation, most of the work done by external forces is transformed into heat energy, and the remaining small part still remains in the metal to form residual stress. The material properties at different temperatures are shown in Table 3.

Fig. 4. Analysis of rolling simulation in SIMUFACT.

which is inconsistent with the real situation. FORGE is also a powerful tool that focuses on simulation of form. FORGE provides best-in-class forge simulation and has an easy-to-use work environment. Considering that thermal stress release simulation will be carried out after rolling, SIMUFACT performs well in multi-process simulation, and SIMUFACT can easily extract residual stress results in each process. Therefore, a powerful SIMUFACT software is adopted in forming simulation. The simulation model and process are shown in Fig. 4. In the simulation, the element type is Hexahedral element. The element size is 5 mm, and the total number of elements is 10,688. Mesher is the Ringmesh. In SIMUFACT, mold friction is assumed to be ideal coulomb friction. The initial temperature of ring rolling process is 380◦ C. At this temperature, the initial residual stress of the blank is relatively homogeneous, within the range of −10∼10 MPa. The size of the final ring obtained by rolling is Φ200×Φ160×120 mm. The results of stress, strain, and temperature changes of the ring rolled parts are obtained by setting up the model of blank ring parts and simulating the calculated process parameters. Stress relief annealing model was adopted. For a closed system with a constant temperature for heat transfer with the environment, the spontaneous change of the system state is always in the direction of the decrease of free energy. When the free energy reaches the minimum, the system reaches an equilibrium state. During Thermal Stress Relief period, the former non-uniform state of the system was eliminated and the residual stress decreased.

3.2. Process parameters of ring rolling The rolling process of ring is divided into: (1) upsetting; (2) stretch forming; (3) punching hole; (4) enlarging the hole; (5) ring rolling; (6) cooling. The technological parameters of ring rolling are obtained on the basis of the theoretical analysis in Section 2 as shown in Table 4. 3.3. Simulation of ring rolling and thermal stress relief The commonly used simulation software in the ring rolling process are DEFORM and SIMUFACT. Compared with SIMUFACT, the DEFORM guide roller has a troublesome movement design. In DEFORM, the center of the drive roll, core roll, and ring piece is always in a straight line, Table 2 Chemical composition of 2219 aluminum alloy (%). Cu

Mn

Ti

Zr

V

Mg

Zn

Fe

Si

Al

5.8–6.8

0.2–0.4

0.02–0.1

0.1–025

0.05–0.15

≤0.02

≤0.1

≤0.3

≤0.2

The rest

Table 3 Material properties of 2219 aluminum alloy at different temperatures. Temperature (°C)

24

100

150

175

205

230

260

370

450

Young’s modulus (GPa) Yield strength (MPa)

73 350

71 346

68 342

66 335

63 328

61 323

59 318

45 297

32 280

Table 4 Process parameters of ring rolling. Ring rolling parameters

Ring part

Ring rolling parameters

Ring part

Initial outer diameter of ring Initial inner diameter of ring Initial axial height of ring Final outer diameter of ring Final inner diameter of ring Final axial height of ring Coefficient of friction

160 mm 120 mm 160 mm 200 mm 160 mm 120 mm 0.6

Linear speed of drive roller Linear speed of core roller Feed speed of axial cone roll Linear speed of axial conical roll Initial temperature of blank Environmental temperature Roll temperature

0.4–0.6 m/s 0.05–0.5 mm/s 0.01–0.5 m/s 0.4–0.6 m/s 380 °C 20 °C 150 °C

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Fig. 5. Flow chart of simulation of ring rolling process.

Fig. 6. Thermal Stress Relief rolling rings.

Thermal Stress Relief simulation was performed on the rolled ring, and the heating temperature was set at 170 °C. Heating time was divided into three groups of 2 h, 4 h, and 8 h to explore the homogenization effect of Thermal Stress Relief on residual stress. The detailed Settings of simulation of Thermal Stress Relief are as follows: (1) establish a new project, Type is set to Heating, Forging is set to Hot; (2) the default Suggested Solver; (3) import the finite element model after rolling, and maintain the original material properties and mesh division; (4) set the heating temperature and time according to the above three conditions; (5) complete the simulation calculation and extract the residual stress results. The simulation process of ring rolling and Thermal Stress Relief treatment is shown in Fig. 5. Fig. 7. Thermal Stress Relief treatment experiment.

3.4. Experiments of ring rolling and thermal stress relief is 4 h; (4) the Thermal Stress Relief treatment time of the fourth ring is 8 h. Fig. 7 shows Thermal Stress Relief treatment using precision high temperature furnace heating (SLX11-40). Heating temperature is set to 170 °C. The heating steps of the heating furnace are controlled by the program. The heating furnace is heated rapidly in the early stage. In the later stage, the heating furnace is closed and the workpiece is cooled with the furnace. The heating time of the workpiece is controlled in 3 groups at 2 h, 4 h, and 8 h.

The rings were rolled according to the rolling parameters in Table 4. The experimental rings were then obtained. After rolling, the surface quality of the ring parts became smooth, and the ellipticity of the ring parts is small at about 1 mm. The ellipticity meets the engineering requirements, which indicates that the parameter design is reasonable and the experimental piece is feasible and reliable. The residual stress of ring rolling is large, which is homogenized and weakened by Thermal Stress Relief (Fig. 6). Rolling out a total of four rings in the experiments, and the dimensional parameters of the four rings are Φ200 × Φ160×120 mm: (1) the first ring as the reference group, without Thermal Stress Relief; (2) the Thermal Stress Relief treatment time of the second ring is 2 h; (3) the Thermal Stress Relief treatment time of the third ring

3.5. Measurement of residual stress in rings The residual stress on the surface of the ring was measured by Prism electronic speckle interferometric drilling equipment manufactured by 115

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Fig. 8. Measurement of residual stress in ring (1-Ring, 2-Fixed block, 3-Industrial camera, 4-Laser generator, 5-Measuring points).

the Stress-Tech Group of Finland. The equipment is based on borehole method combined with digital imaging and Electronic Speckle Pattern Interferometry (ESPI), which has high precision and can easily measure various stress states. The measurement process of residual stress is shown in Fig. 8(a). Each ring member measures four points. The position of measurement is shown in Fig. 8(b). The X and Y directions were measured simultaneously. The surface radial depth of each measurement point was 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, and 1.2 mm.

Thermal Stress Relief simulation is carried out on the basis of rolling simulation. The residual stress at the measured position was extracted. The result of residual stress after Thermal Stress Relief treatment is shown in Fig. 10. Fig. 10 shows that the residual stress of ring parts without Thermal Stress Relief is large and the maximum residual stress in the X direction is −128 MPa. The maximum residual stress in the Y direction is −119 MPa. Residual stress decreased significantly after 2 h, 4 h, and 8 h of Thermal Stress Relief, but the residual stress did not disappear. The reduction of residual stress was most significant in 2 h of Thermal Stress Relief. The average residual stress in the X direction changed from −124.4 MPa to −63.6 MPa, which indicates a decrease of 48%. The decrease of Thermal Stress Relief residual stress at 4 h and 8 h decreased gradually at 57% and 61%. The variation trend of residual stress in the Y direction is the same as that in the X direction at 53%, 62% and 68%, respectively. The simulation results show that the Thermal Stress Relief is effective in reducing and homogenizing the residual stress. The degree of reduction decreases with the increase of Thermal Stress Relief.

4. Result and discussion 4.1. Simulation results of ring rolling and thermal stress relief Multi-process continuous simulation was conducted using the SIMUFACT finite element simulation software. The residual stress of ring rolling was obtained according to the previous simulation method, as shown in Fig. 9.

Fig. 9. Simulation results of residual stress after ring rolling (Section view and Axonometric drawing).

. Fig. 10. Simulation results of residual stress for different Thermal Stress Relief time.

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Fig. 11. Experimental results of residual stress for different Thermal Stress Relief time.

Fig. 12. Average values and standard deviations of residual stress.

4.2. Experimental results of ring rolling and thermal stress relief

tions of ring parts treated with Thermal Stress Relief is significantly smaller than that without Thermal Stress Relief. The simulation results showed that residual stress in the X direction decreased from −124.44 MPa to −47.91 MPa, which is equivalent to a decrease of about 61%. The residual stress in the Y direction decreased from −111.55 MPa to −35.57 MPa, which is equivalent to a decrease of nearly 68%. The experimental results showed that the residual stress in the X direction decreased from −87 MPa to −60 MPa, with a decrease of about 31%. The residual stress in the Y direction decreased from −70 MPa to −35 MPa, with a decrease of about 50%. The experimental results are consistent with the simulation results. The reduction effect of residual stress is significant. The average value of residual stress did not change significantly after 2 h, 4 h, and 8 h of Thermal Stress Relief treatment. Thermal Stress Relief can significantly reduce residual stress, but it will not eliminate the residual stress. Duration has little effect on the reduction of residual stress. The standard deviation of residual stress gradually decreased with the increase of Thermal Stress Relief time. The experimental results show that the standard deviation of residual stress in the X direction decreased from 37.9 to 15.9, which is equivalent to nearly 58%. The standard deviation of the residual stress in the Y direction decreased from 58.5 to 26.1, which is equivalent to nearly 55%. The data show good homogenization of residual stress. Thermal Stress Relief, as the most common means of residual stress homogenization.

Residual stress after rolling was measured. The results of residual stress of different Thermal Stress Relief time were compared as shown in Fig. 11. The measurement results show that the residual stress of the ring without Thermal Stress Relief is large and the distribution is uneven. The maximum residual stress in the X direction is −152 MPa. Residual stress fluctuates violently. The maximum residual stress in the Y direction is −173 MPa, and the difference in residual stress is 157 MPa. Residual stress was homogenized and significantly reduced after 2 h, 4 h, and 8 h of Thermal Stress Relief, but the residual stress did not disappear. The change in Thermal Stress Relief time had little impact on the size of residual stress because depth was measured at 1.2 mm only. Moreover, the surface can be heated at a short time. Thus, residual stress value does not change significantly. After the entire ring piece is heated evenly, stress is rebalanced and the residual stress of the surface becomes homogeneous. 4.3. Discussion of experiment and simulation of thermal stress relief of ring For different Thermal Stress Relief processes, residual stresses at different surface depths in the Xand Y directions are shown in Figs. 10 and 11. For example, the average value and standard deviation of the residual stress in the X direction of the 2 h heating time experimental ring, which are calculated from the 6 data measured at 6 different depths (Fig. 11(a)) of the same ring, are −55.21 MPa and 26.5, respectively. Similarly, the average values and standard deviations of other Thermal Stress Relief processes can be obtained, as shown in Fig. 12. This process is conducted to clearly observe the variation trend of residual stress. The comparison between the simulation results and the experimental results show that the average residual stress in the Xand Y direc-

5. Conclusions Numerous studies showed that the main factor in the machining deformation of large ring parts is the initial residual stress inside the blank. The fundamental solution to machining deformation is to equalize initial residual stress. The research object of this study is a typical aerospace in 2219 aluminum alloy rolling ring. The parameter design, residual stress measurement, and ring residual stress homogenization of the ring rolling 117

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are considered. The residual stresses of the ring control the machining deformation. The main conclusions are as follows.

[6] Wu Q, Li DP. Analysis and X-ray measurements of cutting residual stresses in 7075 aluminum alloy in high speed machining. Int J Precis Eng Manuf 2014;15(8):1499–506. [7] Xu KH, Zhang WX, Yang DJ. Development of 9 m super-large diameter 2219 aluminum alloy integral ring . Forg Technol 2016;41(10):92–7. [8] Han X, Hua L. Plastic deformation behaviors and mechanical properties of rolled rings of 20CrMnTi alloy in combined radial and axial ring rolling. Mater Des 2014;58:508–17. [9] Johnson W, Needham G. Plastic hinges in ring indentation in relation to ring rolling. Int J Mech Sci 1968;10(6) 487IN11489-488IN16490. [10] Park M, Lee C, Lee J, et al. Development of L-sectioned ring for construction machines by profile ring rolling process. Int J Precis Eng Manuf 2016;17(2):233–40. [11] Han X, Hua L, Zhou G, et al. FE simulation and experimental research on cylindrical ring rolling. J Mater Process Technol 2014;214(6):1245–58. [12] Li HW, Fu JH. Numerical simulation and experimental study on thermal rolling expansion of large ring parts . Shanxi Metall 2007(4):19–21. [13] Zhao CX, Xu SQ. Simplification of finite element model of rolling process of large ring parts . Forg Equip Manuf Technol 2007;42(5):90–2. [14] Zhang SL, He YM, Yang DX. Determination of main parameters of 5m diameter axial nc ring rolling mill . Heavy Mach 2007(2):12–14. [15] Xu KH, Zhang WX, Yang DJ. Research and development of integral ring parts of 9m-class super-large diameter 2219 aluminum alloy . Forg Press Technol 2016;41(10):92–7. [16] Lin ZC, Lai HY, Lin HY, et al. The study of ultra-precision machining and residual stress for nip alloy with different cutting speeds and depth of cut. J Mater Technol 2000;97:200–10. [17] Heinz A, Haszler A, Keidel C, et al. Recent development in aluminum alloys for aerospace applications. Mater Sci Eng A 2000;280:102–7. [18] Sadrtdinov RA, Geitsan VB, Rybalko VG, et al. Studying the stressed state of a pipe wall with nonuniform residual stresses during bending. Russ J Nondestr Test 2012;48(1):59–68. [19] Huang X, Jie S, Li J. Finite element simulation and experimental investigation on the residual stress-related monolithic component deformation. Int J Adv Manuf Technol 2015;77(5–8):1035–41. [20] Tanner DA, Robinson JS. Residual stress prediction and determination in 7010 aluminum alloy forgings. Exp Mech 2000;40(1):75–82. [21] Wei Y, Wang XW. Computer simulation and experimental study of machining deflection due to original residual stress of aerospace thin-walled parts. Int J Adv Manuf Technol 2007;33(3–4):260–5. [22] Dong HY, Ying-Lin KE. Study on machining deformation of aircraft monolithic component by FEM and experiment. Chin J Aeronaut 2006;19(3):247–54. [23] Cerutti X, Mocellin K. Parallel finite element tool to predict distortion induced by initial residual stresses during machining of aeronautical parts. Int J Mater Form 2014;8(2):1–14. [24] Wang ZJ, Chen WY, Zhang YD, et al. Study on the machining distortion of thin-walled part caused by redistribution of residual stress. Chin J Aeronaut 2005;18(2):175–9. [25] Liu ZC, Jiang C, Li BC, et al. A residual stress dependent multiaxial fatigue life model of welded structures. Fatigue Fract Eng Mater Struct 2017;41(4). [26] Fergani O, Berto F, Welo T, et al. Analytical modelling of residual stress in additive manufacturing. Fatigue Fract Eng Mater Struct 2016. [27] Munsi ASM Y, Waddell AJ, Walker CA. The influence of vibratory treatment on the fatigue life of welds: a comparison with thermal stress relief. Strain 2010;37(4):141–9. [28] Sun Y, Jiang F, Zhang H, et al. Residual stress relief in Al–Zn–Mg–Cu alloy by a new multistage interrupted artificial aging treatment. Mater Des 2016;92(23):281–7. [29] Croucher T. Uphill quenching of aluminum: rebirth of a little-known process. Heat Treat 1983;15(10):30–4. [30] Fredj NB, Sidhom H. Effects of the cryogenic cooling on the fatigue strength of the AISI 304 stainless steel ground components. Cryogenics 2006(46):439–48. [31] Kobayashi A, Sugihashi M, Yagasaki A. Influence of ultrasonic stress relief on stainless steel 316 specimens: a comparison with thermal stress relief. Mater Des 2013;46(4):713–23. [32] Hua L, Qian D. Ring rolling forming theory and technology for bearing. J Mech Eng 2014;50(16):70. [33] Pan S, Qian DS, Hua L. Φ 9 m super large diameter axial ring rolling forming simulation and experiment . J Eng Plast 2012;12(3) 19-24 + 53.

1 The mechanical model of rolling stability is established, and the mechanical behavior of the ring in the diameter and axial direction is analyzed. A series of rolling process parameters, such as feed speed range and driving roller speed, are obtained according to the continuity and penetration conditions. This result provides the basis for simulation and experiment. 2 The simulation of rolling process and Thermal Stress Relief process was completed in SIMUFACT. The heating times were changed for comparison. The simulation results on the surface show that the residual stress gradually decrease (up to 68%) with the increase of Thermal Stress Relief, but the rate of decrease gradually decreases. The degree of homogenization of residual stress under Thermal Stress Relief did not change significantly with heating time because it can be easily heated for a short time within the surface layer of 1.2 mm. 3 The experiments of rolling process and Thermal Stress Relief process were completed. Different heating times were compared. The experimental results are highly consistent with the simulation results. The residual stress gradually decreases (90.3 MPa maximum) with the increase of Thermal Stress Relief time, but the reduced rate gradually decreases. The homogenization degree of residual stress under the Thermal Stress Relief is outstanding. 4 The simulation and experimental results show prominent residual stress homogenization effect. Thermal Stress Relief, as the most common means of residual stress homogenization. Acknowledgments This work was supported by the Beijing Municipal Natural Science Foundation #1 under Grant number 3172021; State Key Laboratory of Virtual Reality Technology Independent Subject #2 under Grant number BUAA-VR-16ZZ-07; National Defense Basic Scientific Research program of China #3 under Grant number JCKY2018601C002; and National Natural Science Foundation of China #4 under Grant number 51875024. Conflicts of interest No potential conflict of interest was reported by the authors. References [1] Izamshah R, Mo JPT, Ding S. Hybrid deflection prediction on machining thin-wall monolithic aerospace components. Proc Inst Mech Eng Part B J Eng Manuf 2011;226(4):592–605. [2] Raja I. Deflection prediction on machining thin-walled monolithic aerospace component. Proc Inst Mech Eng Part B J Eng Manuf 2011;226(4):592–605. [3] Wu Q, Li DP, Zhang YD. Detecting milling deformation in 7075 aluminum alloy aeronautical monolithic components using the quasi-symmetric machining method. Met - Open Access Metall J 2016;6(4):80. [4] Heinz A, Haszler A, Keidel C, et al. Recent development in aluminium alloys for aerospace applications. Mater Sci Eng A 2000;280(1):102–7. [5] Srivatsa SK, Aviation GE. Modeling of Residual Stress and Machining Distortion in Aerospace Components; 2010. Cdn.intechopen.com.

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