Design af formværktøj til titaniumlegeret tee i klasse 5

Through the process calculation of Grade 5 titanium alloy tee, a reasonable hot extrusion forming scheme was analyzed and formulated, the die design of the tee’s multi-directional extrusion forming was completed, and a multi-directional forging process for titanium alloy tees was explored.

1. Overview

Titanium and titanium alloys are low density materials with high specific strength. In addition, it has good creep resistance in high corrosion and high temperature environment, and has good welding performance, which is applied in various fields of industry. The element composition of the formed titanium alloy tee required in this paper is Ti-6Al-4V (UNS designation R56400), also sometimes called TC4, Ti64 or ASTM Grade 5, which is typical α+β Two-phase alloy, which contains 6% α Stable element Al and 4% β Stable element V. It can show good mechanical properties during hot pressure processing, and can use quenching and failure to strengthen the alloy; After heat treatment, its strength can be greatly improved, which is 50% – 100% higher than that of annealing; In addition, it can work continuously in high temperature environment (400 ℃ – 500 ℃).

2. Selection of Grade 5 titanium alloy extrusion process plan

The Grade 5 titanium alloy extrusion workpiece is shown in Figure 1.

Fig. 1 Three-dimensional and two-dimensional diagram of Grade 5 titanium alloy extrusion workpiece
According to Figure 1, the following two forming schemes are preliminarily determined:

• Option 1: radial extrusion. The blank is made into tube material, which is embedded with elastic medium, and placed in the die chamber. The third end is extruded by radial extrusion, and the tee is made by mechanical processing after unloading.
• Option 2: Three-direction extrusion. The blank is made into a T-shaped bar, which is placed in the die chamber, and is initially formed by the three-way reverse extrusion method using a three-way press. After unloading, it is machined to make a tee.

The tee material is Grade 5, and the blank is made of Grade 5 powder after being compacted in the mold cavity. In Scheme 1, when the third end is formed by radial extrusion, the deformation of the material is large, the degree of work hardening is high, and the requirements for equipment and die strength are high. Scheme 2 adopts three-way reverse extrusion, the deformation of the three ports is relatively small, and the forming is easier, and the punch and die can be effectively protected. After comprehensive consideration, Scheme 2 should be adopted.

3. Part extrusion process analysis

3.1 Determination of blank heat treatment scheme
Grade 5 is a titanium alloy used in the annealed state. The microstructure and properties of titanium alloy with different phase combinations can be obtained by performing stress relief annealing, recrystallization annealing and solution aging treatment on Grade 5 respectively, as shown in Table 1.

Table.1 Corresponding relationship between heat treatment temperature and microstructure and properties of Grade 5 alloy

Type of heat treatment	Stress relief annealing	Recrystallization annealing	Solution aging treatment
Organization and performance characteristics	α and β Two phases coexist, but β The phase content is relatively small, accounting for about 10% (mass fraction)	Equiaxed α Phase+ β Phase, good comprehensive performance	Vicinite structure has the advantages of high rupture strength and high fracture toughness
Heat treatment temperature	100 ℃ below the recrystallization temperature (750 ℃ for TC4)	80 ℃ – 100 ℃ above recrystallization temperature	α＋β／β 40 ℃ – 100 ℃ below the transition temperature (TC4 α＋β／β The phase transition temperature is 980 ℃ – 990 ℃)

According to this, the Grade 5 blank can be annealed at 550 ℃ – 650 ℃ and air cooled; Recrystallization annealing 750 ℃ – 800 ℃, air cooling or furnace cooling to 590 ℃, air cooling; Vacuum annealing 790 ℃ – 815 ℃.

3.2 Selection of lubricant during extrusion
The hot extrusion forming of Grade 5 can adopt two lubrication methods: one is the naked extrusion with glass powder, the other is the extrusion with copper or steel ladle. Because the use of copper or ladle sleeve will block the flow of metal in the extrusion cylinder, and metal adhesion will also occur, which will damage the surface of the pipe, so glass powder is used as lubricant in this paper.
3.3 Selection of parting surface
It can be seen from Figure 1 that the tee forming die can be divided horizontally or longitudinally along the center line. In contrast, the transverse parting is convenient for loading and unloading, while the longitudinal parting is easy to leave the pipe in the die chamber and not easy to take out when unloading, so the transverse parting is selected.
3.4 Selection of initial extrusion temperature, heating method and heating time
With the increase of temperature, the deformation resistance of the billet decreases. From the deformation resistance of Grade 5 alloy, the law of allowable deformation degree changing with temperature, and from the perspective of reducing energy consumption and making full use of alloy plasticity, the higher the initial extrusion temperature is, the better the initial extrusion temperature is. The initial extrusion temperature should be β 14 ℃ – 28 ℃ below the transition temperature (980 ℃ – 990 ℃). In this paper, 950 ℃ is used as the extrusion temperature of the blank, and the heating method is induction heating, which can effectively reduce the temperature of the blank. The heating time is 3min-5min.

4. Calculation of original size and mass of blank

After drawing the three-dimensional diagram of the workpiece through UG7.0, the workpiece volume V=543821.145397477mm³ can be obtained from the tool “measuring body”, and the blank length can be calculated according to formula (1).

In the formula:

• L * is the blank length, mm;
• S is the area of the workpiece end face, mm², S=π (R²-r²), R and r are the outer radius and inner radius of the workpiece end face respectively; L is the length of the workpiece, mm; D is the blank diameter, mm.

Calculate the machining allowance V₀ (cm³) according to formula (2):

In the formula:

• D₁ and D₂ are the diameters of the left and right ends, upper and lower ends of the workpiece respectively, mm;
• Δ h₁、 Δ H₂ is the trimming allowance of left and right ends, upper and lower ends, mm; L₁ * and L₂ * are the lengths of the left and right ends, upper and lower ends of the blank respectively.

Substitute the corresponding data into formula (2) to obtain V₀=196433.85m³.

Considering the loss rate of induction heating, the volume V * (cm³) of the blank is calculated according to formula (3):

Including: δ Is the loss rate of induction heating, taking δ= 1.0%。 Then the blank mass m (kg) is obtained from the following formula:

Including: ρ Is the density of titanium alloy Grade 5, ρ= 4.51 × 10^-6kg/mm^3.
Substitute the relevant parameters into Formula (3) and Formula (4), and calculate the volume of the blank V ^*=747657.545 mm³, and the mass of the blank m *=3.37 kg.

5. Design of hot extrusion die

5.1 Punch process design
Combined with the shape of the workpiece, in consideration of the simple processing and the convenience of assembly and replacement, the punch is designed as a inclined punch; The lathe is used for processing, the matching with the fixed plate of the male and female die is H7/m6, the length of the male die is L_convex=160mm, and the material is superalloy GH4049. The punch structure is shown in Figure 2.
5.2 Die process design
The concave die is a combined concave die, which is processed by a milling machine and a wire cutting machine. It should be noted that when installing the female die on the mold base, the data of the pressure center should be considered to locate it; In addition, the design of the contour size of the die should consider its strength, rigidity and repair modulus when it is used. Here, the superalloy GH4049 is selected to make the concave die, and HRC58-HRC62 is hardened. The structure of the female die is shown in Figure 3.
5.3 Structural design of lower base plate
The material selected for the lower base plate is T10A. Its structure is shown in Figure 4.
5.4 Design of punch fixing plate

When clamping, the punch adopts the punch fixing plate, which can effectively prevent the offset of the punch in the extrusion process. The material is T10A, and the heat treatment hardness is hardened HRC55-HRC45. Its structure is shown in Figure 5.

Figure 2 Punch structure

Fig. 3 Die structure

Figure 4 Structure of lower base plate

Figure 5 Structure of punch fixing plate
5.5 Upper formwork design
The upper formwork shall have sufficient thickness and weight, large contact area, and be able to reasonably distribute the load acting on the mold to the press slider and work table. Its structure is shown in Figure 6.
5.6 Design of mold base and other parts

Because the force of the four-guide pillar mold base is relatively uniform and balanced, the stability and guidance accuracy are high, and the structure of the guide pillar mold is relatively complete, which can meet the design requirements of the Grade 5 titanium alloy tee, the four-guide pillar mold base is selected. The guide post and guide sleeve are made of 20 steel, and the heat treatment (carburizing) hardness is HRC58-HRC62. The upper and lower mold bases are made of HT200. The discharge device of flexible discharge plate is adopted. The clearance between the edge of discharge plate and the inner cavity of base plate is kept. The material is T10A, and the elastic discharge body is polyurethane elastomer.

Fig. 6 Upper formwork structure
5.7 Assembly structure of extrusion die

When the blank is sent in, the left and right discharging plates which play a guiding role are used as the guiding parts to make the blank enter the mold cavity. The three-way press simultaneously extrudes the blank and reversely extrudes the workpiece. After the workpiece is produced, the three punches are withdrawn backward. The discharger pushes the material out of the convex and concave dies. After the workpiece is taken out, the inner hole is punched through mechanical processing, and all data meet the dimensional requirements. The processing is completed. The assembly structure of the tee extrusion die is shown in Figure 7.

Fig. 7 Assembly structure of tee extrusion die
1 – Lower formwork; 2,8-heat insulation board; 3 – Lower base plate; 4-pack; 5 – female die; 6 – Heating ring; 7 – Upper formwork; 9 – Upper base plate; 10,11-punch; 12-support rod; 13 – Discharging plate; 14-Polyurethane elastomer

6. Conclusion

Through the calculation and analysis of the titanium alloy tee workpiece, the production problems of the alloy pipe such as large deformation resistance, strong work-hardening and easy cracking have been solved, and the extrusion die design of the titanium alloy tee has been completed, which is believed to provide a reference for the future titanium alloy pipe forming die design.

Source: China Titanium Tee Manufacurer: www.titaniuminfogroup.com