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

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 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 ,weldless, spinforming

alloy and also the flow stress is low. I. Introduction

In order to achieve the goal of light weight, large dimension and high strength materials, the large-diam­ eter and thin-wall and weldless TC4 alloy tube was hot "'c -3 preferable widely applied in the space flight system. At present, - -4 fonning region there are few references about the manufacturing tech­ -5 nology of the large-diameter, thin-wall and weldless -6

TC4 alloy tube. Due to the large resistance to deforma­ -7+-'-"'=.-~~T'-'-'--"=..."-'--."'-',,__,_-'.-'--'--; tion, it is difficult to manufacture the TC4 alloy tube 700 750 800 850 900 950 T,"C by usual technology. The spinforming is an advanced technology for manufacturing the TC4 alloy tube. Figure I. The hot forming chart of TC4 alloy However, there are many factors affect the spinform­ Heat treatment was conducted in order to stabilize ing of TC4 alloy especially for the tube. In the back­ 0 5 the microstructure and reduce the relaxation of residual ground of the TC4 alloy tube (the size <1>6 70;i · X 400 stress after spinning deformation. The microstructure 0 2 X 2;i · mm) served as a component in aerospace, the of the alloy after heat treatment was analysis. spinforming technology of a TC4 alloy was investiga­ ted. 3. Results and Discussion

2. Experimental 3. I Analysis of Technological Parameter Figure 2 shows the axial displacement of different 2. I Materials ratio of feeding. According to Figure 2, the influence of The TC4 alloy plate, with a thickness of 10 - the ratio of feeding on the metal flow can be observed. 12mm and diameter of 1150-1200 mm, was punched When the ratio of feeding is quite small, the contact into a tube. material region between roller and raw materi.al is very small and the distribution of deformation is inhomoge­ 2. 2 Test Technology neous in thickness direction. It is easy to produce the On the basis of finite element model

2.993e-001 4.337e-001

2.609e-001 3.854e-001

2.225e-001 3.371e-001

1.840e-001 2.888e-001

J.456e-001 2.405e-001

J.072e-00 1 J.922e-001

6.872e-002 1.439e-00 1

3.029e-002 9.56 1e-002

-8. l 47e-003 4.73 le-002

-4.658e-002 -9.930e-004

-8.501 e-002 -4.930e-002

( a ) 0.2mm/ r ratio ( a) 20% ratio 6.712e-001 6.712e-001 5.986e-001 5.986e-001 5.260e-001 5.260e-001 4.533e-001 4.533e-001 3.807e-001 3.807e-001 3.0Sle-001 3.081e-001 2.354e-001 2.354e-001 1.628e-001 l .628e-001 9.016e-002 9.016e-002 J.752e-002 J.752e-002 -5.51 1e -002 -5.5 11 e-002 ( b ) 40% ratio ( b) 0.6mm/r ratio 8.480e-001 l.051 e+OOO 7.337e-001 8.654e-00 1 6.195e-001 6.794e-001 5.053e-001 4.934e-001 3.91 le-001 3.074e-001 2.768e-001 l.214e-001 l.626e-OOI -6.455e-002 4.837e-002 -2.505e-001 -6.586e-002 -4.365e-001 -1 .801e-001 -6.225e-001 ( c) 1.4mm/ r ratio -2.943e-001 ( c) 60% ratio Figure 2. The axial displacement of different ratio of feeding Figure 3. The axial displacement of different ratio of thinning 60 %, the axial displacement concentrates in the outer layer and deformation of metal in inner layer is difficult Figure 4 also demonstrates the situation of bulge because of bulge. with different ratio of the thinning. When rollers axially 9. Aerospace Applica tions • 2009 •

----60% flow of metal and plump up ( Figure 7) in the back of 1.0 ---- 40% 20% roller. Therefore, the auxiliary spinning technology was E E 0.8 used to expand the diameter of work piece between -::::- passes of spinfoming, ca using the work piece to sepa­ i:i E 0.6 rate from the mandrel. The metal axial fluidity is corre­ "u 0."' spondingly enhanced. At last , the typical quality prob­ :;"' 0.4 lem such as indirect and bulge , which appears -;;; ·x easily during multi-passes spinforming of the large di­ "' 0.2 ameter and thin wall T C4 alloy tube, was solved.

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 spin­ forming process can be normally carried out because that the bulge remains slight and stabl e. While more than 60 % , peeling happens because of seriously bulge (Figure 5). 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 wall 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 Figure S. Peeling the temperature of deformation region , the technology The results of FEM simulation show that it is of district temperature control is used during the de­ suitable for spinforming and process control when the formed region, the deformation region ( including region ratio of feeding is 0. 6mm/ r and the ratio of thinning is of contact in front of roller) and undeformed region. Meanwhile, the temperature of mandrel was controlled in the region of 20 %~40%. before spinforming in order that the temperature of 3. 2 Analysis of Spinning Technology mandrel distributed unifomly and the inflationis con­ sistent The heat transfer rate of material is also re­ The experiment is carried out by multi-passes duced, which is advantage for temperature control of spinforming. During the following pass of hot spin­ the materials. forming, the work piece will contract and enclasp the Figure 8 shows the large diameter and thin wall mandrel. In adition, the metal axial flow is blocked in T C4 alloy tube with good quality by spinforming tech­ unformed section and forming section and bulge occurs 0 5 0 2 nology( ct> 670;i · X 400 X 2;i · mm). (Figure 6) in front of roller, which lead to the reverse

Figure 8. Weldl ess tube of TC4 alloy

The tube is cut off and precisely machined in the in­ ner surface and the outer surface. Finally, the large-diame­ Figure 6. Bulge 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). ent conditions. It is clear that the strength changes slightly and plasticity increase markedly. This results 3. 4 Analysis of Microstructure and Properties show that the hot spinforming improved the properties Table 1 shows the properties of samples in differ- of TC4 alloy.

Table 1. The results of testing properties the properties in room temperature

Test status Ultimate tensi le strength Yield strength ao. ,/MPa a/% ab b/ MPa

Raw material 940 897 13 heat treatment 780"C / l h 952 898 17. 3

Figures 9~ 10 show microstructure of raw materi­ structure is formed and the properties are enhanced. This al and the materials after spinning, respectively. The condition is suitable for engineering application. microstructure of the TC4 alloy changes after spin­ forming. Firstly, the a+~ sheet structure of raw mate­ rial 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-stre­ amlined structure. These microstructure characteristics are advantageous for improve the properties of the raw (a) Tangential metallurgica l microstructure material.

( b) Axial meta ll urgical microstructure Figure 9. The microstructure of the raw material Figure 10. Mi crostructure of the material s after spinforming (Annealing 780°C/lh) 4. Conclusions

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