Forming Technology of Large-diameter, Thin-walled and Weldless Tube of TC4 Al­loy

Qi Jun Li Qi Wang Cao Gen Yao Qun Shan Si Yuan Huang

Aerospace Research Institute of Material and Processing Technology ,Beijing 100076

In this paper, effect of parameters of spin forming on large-diameter, thin-wall and weld less tube of TC4 alloy was analyzed by finite element anal­

ysis. In addition, the spinning technology for manufacturing the TC4 tube was optimized and the microstructure and the properties of original

material were investigated. Results show that the TC4 alloy tube with high precision is successfully manufactured by spin forming technology.

After spinforming and heat treatment, the microstructure and property can be improved.

Keywords: TOI alloy, large-diameter ,thin-walled ,weld less, spinforming

I. Introduction

In order to achieve the goal of light weight, large dimension and high strength materials, the large-diam­eter and thin-wall and weldless TC4 alloy tube was widely applied in the space flight system. At present, there are few references about the manufacturing tech­nology of the large-diameter, thin-wall and weldless TC4 alloy tube. Due to the large resistance to deforma­tion, it is difficult to manufacture the TC4 alloy tube by usual technology. The spinforming is an advanced technology for manufacturing the TC4 alloy tube. However, there are many factors affect the spinform­ing of TC4 alloy especially for the tube. In the back­ground of the TC4 alloy tube (the size <1>6 70;i0

· 5 X 400

X 2;i0·

2 mm) served as a component in aerospace, the spinforming technology of a TC4 alloy was investiga­ted.

2. Experimental

2. I Materials The TC4 alloy plate, with a thickness of 10 -

12mm and diameter of </>1150-1200 mm, was punched into a tube.

2. 2 Test Technology

On the basis of finite element model <FEM) simu­lation spinforming process, the technological parameter of spinforming and the technology of temperature con­trol was investigated to make sure the forming and pre­cision of the work piece. Because the spinforming cau­ses the TC4 alloy to fracture in room temperature, the hot spinforming must be carried out, which can enhance the deformation capability and reduces the resistance to deformation and the components snapping back. At present, the hot spinforming is the main spinning tech­nology for manufacture titanium components. Figure 1

shows the hot forming chart of TC4 alloy in some strain by thermal simulation experiment. Hot forming region is preferable from 800 to 900"C. During this re­gion, dynamic recrystallization is easy to occur for TC4

alloy and also the flow stress is low.

"' -3 c - -4

-5 -6

-7+-'-"'=.-~~T'-'-'--"=..."-'--."'-',,__,_-'.-'--'--;

700 750 800 850 900 950 T,"C

preferable hot fonning region

Figure I. The hot forming chart of TC4 alloy

Heat treatment was conducted in order to stabilize the microstructure and reduce the relaxation of residual stress after spinning deformation. The microstructure of the alloy after heat treatment was analysis.

3. Results and Discussion

3. I Analysis of Technological Parameter Figure 2 shows the axial displacement of different

ratio of feeding. According to Figure 2, the influence of the ratio of feeding on the metal flow can be observed. When the ratio of feeding is quite small, the contact material region between roller and raw materi.al is very small and the distribution of deformation is inhomoge­neous in thickness direction. It is easy to produce the band and follow slight bulge. While the ratio of feeding is large, the axial displacement in front of roller is also large, causing pile up and bulge, the metal axial flow is blocked; The metal axial flow is steady when the ratio

of feeding is 0. 6 mm/ r. Figure 3 shows the axial displacement of the ratio

of thinning. The corresponding curve with the axial dis­placement is indicated as Figure 4.

It is clear from Figure 3-Figure 4 that the axial displacement increases with the increase of the ratio of thinning. This indicates that the increase of the ratio of thinning can increase the axial flow. Also, the distribu­tion of the axial displacement in thickness direction

changes with the ratio of thinning changed While during 20 %- 40 % , the distribution is even, while more than

• 2008 • Proceedings of the 12'h World Conference on Titanium

2.993e-001

2.609e-001

2.225e-001

1.840e-001

J.456e-001

J.072e-00 1

6.872e-002

3.029e-002

-8. l 47e-003

-4.658e-002

-8.501 e-002

( a ) 0.2mm/ r ratio

6.712e-001

5.986e-001

5.260e-001

4.533e-001

3.807e-001

3.081e-001

2.354e-001

l .628e-00 1

9.016e-002

J.752e-002

-5.5 11 e-002

( b ) 0.6mm/r ratio

l.051 e+OOO

8.654e-00 1

6.794e-001

4.934e-001

3.074e-001

l.214e-001

-6.455e-002

-2 .505e-00 1

-4.365e-001

-6.225e-00 1 ( c) 1.4mm/ r ratio

Figure 2. The axial displacement of different ratio of feeding

60 % , the axial displacement concentrates in the outer layer and deformation of metal in inner layer is difficult because of bulge.

4.337e-001

3.854e-001

3.371e-001

2.888e-001

2.405e-001

J.922e-00 1

1.439e-00 1

9.56 1e-002

4.73 le-002

-9.930e-004

-4.930e-002

( a) 20% ratio

6.712e-001

5.986e-001

5.260e-001

4.533e-001

3.807e-001

3.0Sle-001

2.354e-001

1.628e-001

9.016e-002

J.752e-002

-5 .51 1 e-002

( b ) 40% ratio

8.480e-001

7.337e-001

6.195e-001

5.053e-00 1

3.91 le-001

2.768e-00 1

l.626e-OOI

4.837e-002

-6.586e-002

-1 .801e-001

-2 .943e-001

( c ) 60% ratio

Figure 3. The axial displacement of different ratio of thinning

Figure 4 also demonstrates the situation of bulge with different ratio of the thinning. When rollers axially

9. Aerospace Applications • 2009 •

----60% 1.0 ---- 40%

20% E E 0.8

-::::-i:i E 0.6 " u

"' 0. "' :; 0.4

-;;; ·x "' 0.2

0.0 0.5 1.0 1.5 2.0 2.5 3 .0 thickness direction/ mm

Figure 4. Corresponding curve with the axial displacement

compress blank, the metal piles up in the deformational region, which lead to the deformation of bulge. While

the ratio of thinning is from 20 % to 40 % , the spin­forming process can be normally carried out because that the bulge remains slight and stable. While more than 60 % , peeling happens because of seriously bulge (Figure 5) .

Figure S. Peeling

The results of FEM simulation show that it is suitable for spinforming and process control when the

ratio of feeding is 0. 6mm/ r and the ratio of thinning is in the region of 20 %~40%.

3. 2 Analysis of Spinning Technology

The experiment is carried out by multi-passes

spinforming. During the following pass of hot spin­

forming, the work piece will contract and enclasp the

mandrel. In adition, the metal axial flow is blocked in

unformed section and forming section and bulge occurs (Figure 6) in front of roller, which lead to the reverse

Figure 6. Bulge

flow of metal and plump up ( Figure 7) in the back of roller. Therefore, the auxiliary spinning technology was

used to expand the diameter of work piece between passes of spinfoming, causing the work piece to sepa­

rate from the mandrel. The metal axial fluidity is corre­spondingly enhanced. At last , the typical quality prob­lem such as indirect extrusion and bulge , which appears easily during multi-passes spinforming of the large di­ameter and thin wall T C4 alloy tube, was solved.

Figure 7. Plump up

3. 3 Result Analysis on Temperature Control The temperature control is one of the key aspects

which affect the spinforming of the large diameter and thin wa ll T C4 alloy tube. Because the size of the raw

materials of spinning tube is large , it is difficult to maintain high temperature for the entire work piece and ensure the uniform of temperature. For stabilize the temperature of deformation region , the technology of district temperature control is used during the de­formed region, the deformation region ( including region of contact in front of roller) and undeformed region.

Meanwhile, the temperature of mandrel was controlled before spinforming in order that the temperature of mandrel distributed unifomly and the inflationis con­sistent The heat transfer ra te of material is also re­duced, which is advantage for temperature control of

the materials. Figure 8 shows the large diameter and thin wall

T C4 alloy tube with good quality by spinforming tech­

nology( ct>670;i0· 5 X 400 X 2;i0

· 2 mm).

Figure 8. Weldless tube of TC4 alloy

The tube is cut off and precisely machined in the in­

ner surf ace and the outer surface. Finally, the large-diame­

ter and thin-wall and weldless TC4 alloy tube with high

• 2010 • Proceedings of the 12'h World Conference on Titanium

precision is successfully manufactured (Figure 8) .

3. 4 Analysis of Microstructure and Properties

Table 1 shows the properties of samples in differ-

ent conditions. It is clear that the strength changes slightly and plasticity increase markedly. This results show that the hot spinforming improved the properties

of TC4 alloy.

Table 1. The results of testing properties

Test sta tus Ultimate tensi le strength

ab b/ MPa

Raw material 940

heat treatment 780"C / l h 952

Figures 9~ 10 show microstructure of raw materi­al and the materials after spinning, respectively. The microstructure of the TC4 alloy changes after spin­forming. Firstly, the a+~ sheet structure of raw mate­rial disappears, the a lamellar structure and ~ structure among a lamellar structure are fell to pieces. Secondly, the grain size becomes smaller and many a+ ~ equiaxed structure come into being. While grains refining, many grains are stretched along the axial direction(Figure 10 (b)) especially for crphase. These stretched structure

distribute regularly along the axial direction and the corresponding result is the formation of fibrous-stre­amlined structure. These microstructure characteristics are advantageous for improve the properties of the raw

material.

Figure 9. The microstructure of the raw material

4. Conclusions

(1) The multi-passes hot spinforming technology

is a suitable technology for manufacturing TC4 alloy tube, the large-diameter, thin-wall and weldless TC4

alloy tube with high precision. ( 2 ) The auxiliary spinning technology and the

technology of district temperature control can effec­

tively solve the model quality problem such as indirect extrusion and bulge and the difficulty of temperature

control. The large-diameter and thin-wall and weldless

TC4 alloy tube and precision control was successfu lly

manufactured by means of spinforming.

(3) After spinforming and treat treatment, the grain

size of TC4 alloy become small, the a+~ equiaxed micro-

the properties in room temperature

Yield strength ao. ,/MPa Ductility a/%

897 13

898 17. 3

structure is formed and the properties are enhanced. This condition is suitable for engineering application.

(a ) Tangential metallurgical microstructure

( b) Axial metall urgical microstructure

Figure 10. Microstructure of the materials after spinforming

(Annealing 780°C/lh)

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