A forging method for large and complex TC18 titanium alloys

Abstract

This invention belongs to the field of forging hot working and relates to a forging method for large and complex TC18 titanium alloys. The method includes: selecting a surface parallel to the triangular region of the forging as the parting surface for pre-forging and final forging; preparing a spindle-shaped rough shape using bar stock; the two ends of the spindle-shaped rough shape are mutually perpendicular flat plates; the rear end of the horizontal plate of the spindle-shaped rough shape has a groove, leaving shoulders on both sides at the end; pre-forging the spindle-shaped rough shape to obtain a pre-forged part: specifically, a groove is added to the upper surface of the horizontal plate, and the inner surface of the groove between the two shoulders becomes a concave curved surface; a high boss with a semi-elliptical cross-section is formed on the vertical plate of the spindle-shaped rough shape above the parting surface, and a front reinforcing rib is formed on the part near the connection area of ​​the two plates; U-shaped grooves are added on the left and right sides of the high boss in the height direction; the part of the vertical plate below the parting surface is formed by conformal molding; pre-forging the spindle-shaped rough shape to obtain a pre-forged part; and die forging the pre-forged part to obtain the forging.

Description

Technical Field

[0001] This invention belongs to the field of forging hot working and relates to a forging method for large and complex TC18 titanium alloys. Background Technology

[0002] TC18 titanium alloy possesses high strength, high toughness, and good hardenability, making it widely used in the aerospace field. Meanwhile, with the continuous improvement of domestic forging equipment capabilities, aerospace aircraft structural components are gradually evolving from the original assembly of multiple welded parts to integrated systems. The structures of forgings are also exhibiting greater diversity and complexity. As the difficulty of forging and the requirements for microstructure and performance increase, higher demands are being placed on forging forming and processing methods.

[0003] A new type of forging combining a torsion arm and a rocker arm joint for landing gear, the structure of which is (see...) Figure 1 The forging process combines a triangular region (1) with a high-bore region (2). Its characteristics include: triangular region 1 is thin and wide with ribs, while high-bore region 2 is large and tall, with the width L1 of the triangle exceeding the height L2 of the high-bore. This type of forging exhibits significant cross-sectional variations. Furthermore, the deformation and forging temperature during the TC18 titanium alloy forging process have a substantial impact on the product's microstructure and properties. If no pre-forging is designed or the pre-forging is poorly designed, unidirectional forging can easily lead to uneven deformation and temperature field, resulting in substandard microstructure and properties, ultimately causing the forging to be scrapped. Summary of the Invention

[0004] Purpose of the invention: This invention provides a forging method for large and complex TC18 titanium alloy die forgings that meets the requirements for forging forming. It also provides a design method for pre-forgings that improves the uniformity of the microstructure and the small amount of surface deformation in the high boss area. Furthermore, the use of a circular arc design concept improves the utilization rate of forging materials, reduces production costs, and meets the requirements for key components used in the landing gear of next-generation aircraft.

[0005] Technical solution:

[0006] A forging method for large and complex TC18 titanium alloys is provided, comprising:

[0007] The surface parallel to the triangular region of the forging is selected as the parting surface for pre-forging and the parting surface for final forging;

[0008] A spindle-shaped rough shape is prepared using bar stock; the two ends of the spindle-shaped rough shape are mutually perpendicular flat plates; the rear end of the horizontal plate of the spindle-shaped rough shape has a groove, so that the ends have two shoulder sections.

[0009] The spindle-shaped rough is pre-forged to obtain a pre-forged part: Specifically, a groove is added to the upper surface of the horizontal plate, and the inner surface of the groove between the two shoulders becomes a concave curved surface; the vertical plate of the spindle-shaped rough forms a high boss with a semi-elliptical cross section above the parting surface, and a front reinforcing rib of the high boss is formed near the connection area of ​​the two plates; U-shaped grooves are added to the left and right sides of the high boss in the height direction; the part of the vertical plate below the parting surface is formed accordingly.

[0010] The spindle-shaped rough shape is pre-forged to obtain a pre-forged part;

[0011] The pre-forged part is die-forged to obtain the forging part.

[0012] The preparation of spindle-shaped rough shapes using bar stock includes:

[0013] Step 1: Select bar stock as billet;

[0014] Step 2: First, upset the billet, square it, and shape it into a cuboid; the upsetting ratio should be less than or equal to 3;

[0015] Step 3: Flip the rectangular blank, divide the rectangular blank into sections, use one end as a triangular forming area and the other end as a high-protrusion forming area; flatten and widen the triangular forming area to form a spindle-shaped horizontal plate; flatten the rectangular blank vertically in the width direction; widen it until one end cannot enter the mold cavity.

[0016] Step 4: Rotate the billet 90°, place the high boss forming area vertically into the mold, upset and widen the triangular forming area, form the triangular area, and then press a groove in the middle of the end of the triangular area to leave shoulders on both sides of the end of the triangular area.

[0017] Step 5: Remove the blank from the mold, flatten the high-protrusion forming area to form a spindle-shaped vertical plate, and finally shape it into a spindle-shaped blank.

[0018] The longitudinal section of the reinforcing rib is triangular. The height of the triangle does not exceed the designed height of the boss, and the width of the triangular rib does not exceed 1 / 3 to 1 / 2 of the designed width of the part. The two sides of the rib width need to be drafted and then transitioned with large R rounded corners.

[0019] The U-shaped groove should have a draft angle of 1° to 10°; the depth h of the U-shaped groove should be less than 1 / 3 of the diameter of the U-shaped groove; and the radius R of the convex circle of the U-shaped groove should be greater than or equal to the radius R1 of the concave circle.

[0020] The heat treatment parameters for die forging include:

[0021] One-time annealing: heating to 830℃, furnace cooling to 760℃, electric furnace uniformity is ±10℃;

[0022] Secondary annealing: The forging is heated to 616℃, and the uniformity of the electric furnace is ±5℃.

[0023] The volume of the billet is 1.1 to 1.25 times the volume of the forging.

[0024] During heat treatment, the effective thickness of the forging should be less than or equal to 250 mm. For forgings with an effective thickness greater than 150 mm, air cooling after removal from the furnace is adopted; for forgings with an effective thickness less than or equal to 150 mm, air cooling after removal from the furnace is adopted. For forgings with an effective thickness greater than 250 mm, machining is adopted to reduce the thickness of the forging before the first annealing.

[0025] During heat treatment, the transfer time of the forging after exiting the furnace should be less than or equal to 2 minutes.

[0026] The beneficial effects are:

[0027] This invention presents a forging method for large and complex TC18 titanium alloy die forgings to meet the requirements of key components for next-generation aircraft landing gear. It also provides a design method for pre-forgings to improve the uniformity of microstructure and the small amount of surface deformation in the high boss area. Furthermore, the use of a circular arc design concept improves the utilization rate of forging materials and reduces production costs. Attached Figure Description

[0028] Figure 1 This is a simplified diagram of the structural features of the forging of the present invention.

[0029] Figure 2 This is a simplified structural diagram of the present invention.

[0030] Figure 3 This is a simplified diagram of the pre-forged part structure of the present invention.

[0031] Figure 4 For the present invention Figure 3 EE section view.

[0032] Figure 5 This is a simplified diagram of the U-shaped groove in the longitudinal section of the sidewall of the high boss of the present invention.

[0033] Figure 6 This is a flowchart of the forging process of the present invention.

[0034] Figure 7-1 This is a simulation diagram of the cross-sectional deformation of the pre-forged part of the present invention.

[0035] Figure 7-2 This is a simulation diagram of the longitudinal section deformation of the pre-forged part of the present invention.

[0036] Figure 8-1 This is a simulation diagram of the cross-sectional deformation of a conventional pre-forged part.

[0037] Figure 8-2 This is a simulation diagram of the longitudinal section deformation of a conventional pre-forged part. Detailed Implementation

[0038] A forging method for large and complex TC18 titanium alloy billets, consisting of pre-forging and final forging, is proposed, along with a pre-forging design method to improve the uniformity of the forging microstructure. The method comprises steps 1 to 6, as detailed below.

[0039] Step 1: Design the forging part according to the shape of the part. Usually, the parting surface is selected to be parallel to the triangle to facilitate the forming of the forging part.

[0040] Preferably, based on the characteristics of the part, the forging allowance, draft angle, and fillet size are determined. For high bosses and areas that are difficult to fill in the die forging, a variable allowance design approach can be adopted to design the forging.

[0041] Step 2: Forging Billet Preparation Process. The billet preparation process includes steps one through five, the details of which are as follows:

[0042] Step 1: Select bar stock as the billet. The volume of the billet is 1.1 to 1.25 times the volume of the forging.

[0043] Step 2: The billet is first upset, squared, and shaped into a cuboid. The ratio of the diameter to the length of the bar (i.e., the upsetting ratio) is less than or equal to 3; the shape and size of the shaped cuboid billet can be inserted into the mold cavity.

[0044] Step 3: Material division, flattening, and widening of one end. Divide the material according to 1.1 to 1.25 times the volume of the triangular area of ​​the forging; flatten the rectangular block perpendicularly in the width direction; widen it until one end cannot enter the mold cavity.

[0045] Step 4: Rotate the billet 90° and place it vertically into the mold. Upset and widen the triangular area, then press out the groove in the middle of the triangular area, leaving the shoulder dimensions on both sides.

[0046] The membrane cavity can be designed as a cylinder, cuboid, or cube. The four sides of the cylinder, cuboid, or cube have a draft angle of 1° to 3°, which makes it easy to demold. At the same time, the volume of the membrane cavity is 1.1 to 1.25 times the volume of the high boss 2 of the forging.

[0047] Step 5: Remove the billet from the mold, rotate it 90°, flatten the high-protrusion area 2, and shape it into a spindle shape (see...). Figure 2 (Rough shape and size)

[0048] Step 3: Pre-forging Design. Pre-forging design includes the following four characteristic elements (see...). Figure 3 The high boss has a semi-elliptical cross-section, designated as A (see EE section view). Figure 4 A) The transition area between the boss and the triangle has reinforcing ribs (B); C) The side wall of the high boss is designed with a U-shaped groove that runs through the height direction (C); D) One end of the triangle is designed with an arc shape (D).

[0049] The pre-forging is designed according to the shape and size of the final forging. Usually, the maximum projected area of ​​this type of forging is parallel to the triangle, so the parting surface is selected to be parallel to the triangle. The horizontal length and width of the pre-forging are narrower than those of the final forging. The metal stored in the characteristic parts must meet the forming requirements of the forging, and the metal flow must meet the deformation requirements of the material.

[0050] Furthermore: the plane of the parallel triangle is selected as the parting surface, and the cross-section of the high boss part is designed as a semi-ellipse.

[0051] Objective: To increase the height of the boss and thus increase the deformation of the boss area in the forging; at the same time, the side wall of the pre-forged part does not require demolding, and the forging can be naturally demolded, thereby improving design efficiency.

[0052] Furthermore: Reinforcing ribs are added to the transition area between the high boss and the triangular area. The characteristics of the reinforcing ribs are: the longitudinal section is triangular, the height of the triangle does not exceed the designed height of the boss, and the width of the triangle does not exceed 1 / 3 to 1 / 2 of the designed width of the part. The two sides of the rib width need to be drafted and then transitioned with large R rounded corners to avoid defects such as clamping and folding in the forging.

[0053] The typical design method for this part is a large radius fillet transition; the design of reinforcing ribs significantly improves the problem of the difference in deformation between the core and the surface of the high boss area;

[0054] Furthermore: the high boss sidewall is designed with a U-shaped groove running through the height direction, and the sidewall groove should have a draft angle of 1° to 10°; the sidewall is excavated with a U-shaped groove (see...). Figure 5 To ensure that the forgings do not have defects such as clamping or folding, the U-shaped groove should not be too deep, where h < 1 / 3b and R ≥ R1;

[0055] Objective: To improve the microstructure differences caused by surface deformation dead zones or small deformation amounts.

[0056] Furthermore, the middle part of one end of the triangular area is designed to be arc-shaped.

[0057] The purpose of the arc design is to reduce the material consumption of forgings in the triangular area, improve the uniformity of the microstructure, and improve the microstructure differences caused by excessive deformation due to the large amount of metal flowing into the burrs in this area.

[0058] Step 4: Place the formed blank into the cavity of the pre-forging die for pre-forging.

[0059] Preferably, steps 2 and 4 further include: heating the billet or blank to 30°C to 40°C below the phase transformation point; the heating coefficient for cold material is 0.6 to 0.8 min / mm, and the heating coefficient for hot material returning to the furnace is 0.3 to 0.4 min / mm;

[0060] Preferably, steps 2 and 4 further include: heating with an electric furnace at ±10°C;

[0061] Step 5: Place the pre-forged part in the cavity of the final forging die for final forging.

[0062] Preferably, step 5 further includes: heating the pre-forged part to 30°C–40°C below the phase transformation point, and maintaining...

[0063] The temperature coefficient is 0.6–0.8 min / mm, then the temperature is raised to 15–25℃ above the phase transformation point, with a holding coefficient of 0.3–0.4 min / mm. Hot material is not allowed to be returned to the furnace. An electric furnace with a temperature range of ±5℃ is preferred, with material temperature controlled by a monitoring instrument. Before loading, ensure the heating furnace equipment is in good working order. During loading, the billets are supported, leaving a 60–100 mm gap between them for heating. Purpose: To ensure the billets are fully and evenly heated, avoiding any impact on heating efficiency due to improper furnace conditions or loading.

[0064] Preferably, steps 2, 4, and 5 further include: during forging, the deformation amount per firing cycle is within...

[0065] 20%–50%; final forging temperature greater than or equal to 720℃; cooling method is air cooling.

[0066] Preferably, steps 4 and 5 further include: placing the billet or pre-forged part at 100℃~150℃.

[0067] Preheating is performed in an electric furnace for 10–40 minutes. After preheating, the coating is evenly sprayed onto the entire surface of the blank or pre-forging part using titanium-5 as the spraying agent. This aims to reduce metal flow resistance. During forging, the upper and lower die cavities are covered with 5–10 mm thick insulating cotton or cloth, using high-silica fiber cloth. This aims to reduce the metal cooling rate, ensuring the forming process of the pre-forging and final forging; and simultaneously reducing the microstructure differences between the surface and core of the metal blank caused by different cooling rates. The die preheating temperature is 250℃–450℃.

[0068] Step 6: Perform heat treatment on the forging from Step 5;

[0069] Further, step 6 includes: primary annealing: heating to a temperature of 820℃~850℃, furnace cooling to 740℃~760℃, cooling method: air cooling or wind cooling.

[0070] Preferably, the uniformity of the electric furnace is ±10℃.

[0071] Preferably, the forging transfer time after exiting the furnace is less than or equal to 2 minutes;

[0072] Preferably, the effective thickness of the forging should be less than or equal to 250 mm. For forgings with an effective thickness greater than 150 mm, furnace-exit air cooling is used; for those less than or equal to 150 mm, furnace-exit air cooling is used. For forgings with an effective thickness greater than 250 mm, the thickness is reduced by machining before the first annealing.

[0073] Furthermore, step 6 also includes: secondary annealing: heating the forging to a temperature of 500℃~650℃, and cooling by air cooling.

[0074] Preferably, the uniformity of the electric furnace is ±5℃;

[0075] Preferably, step 6 further includes: placing the charging plate and forgings within the effective qualified area of ​​the electric furnace; selecting the number of forgings based on the outer dimensions and weight of the forgings, the effective qualified area of ​​the electric furnace, and the heating power of the electric furnace; leaving a gap of 50 to 100 mm between the forgings; placing the forgings on the charging plate, which has ventilation holes or supports and padded the forgings to prevent deformation of the forgings during heating, which would result in uneven machining allowance of the forgings.

[0076] Example

[0077] Forging of rear rocker arm joint for a certain type of machine (see...) Figure 1 The material is TC18, the forging dimensions are 1287×887×538 mm, the single-sided allowance is 8-10 mm, and the maximum projected area is 0.596 m². 2 Phase transition point: 872℃; the forging method of this patent, such as... Figure 6 As shown, it includes the following steps:

[0078] Step 1: Design the forging part according to the shape of the part, and select the parting surface parallel to the triangle.

[0079] Step 2: Forging Billet Preparation Process. The billet preparation process includes steps one through five, the details of which are as follows:

[0080] Step 1: Select Bar stock is used as the billet. The volume of the billet is 1.1 to 1.25 times the volume of the forging.

[0081] Step 2: The billet is first upset, squared, and shaped into a cuboid. The ratio of the diameter to the length of the bar (i.e., the upsetting ratio) is less than or equal to 3; the shape and size of the shaped cuboid billet can be inserted into the mold cavity.

[0082] Step 3: Material division, flattening, and widening of one end. Divide the material according to 1.1 to 1.25 times the volume of the triangular area of ​​the forging; flatten the rectangular block perpendicularly in the width direction; widen it until one end cannot enter the mold cavity.

[0083] Step 4: Rotate the billet 90° and place it vertically into the mold. Upset and widen the triangular area, then press out the groove in the middle of the triangular area, leaving the shoulder dimensions on both sides.

[0084] The membrane cavity can be designed as a cylinder, cuboid, or cube. The four sides of the cylinder, cuboid, or cube have a draft angle of 1° to 3°, which makes it easy to demold. At the same time, the volume of the membrane cavity is 1.1 to 1.25 times the volume of the high boss 2 of the forging.

[0085] Step 5: Remove the billet from the mold, rotate it 90°, flatten the high-protrusion area 2, and shape it into a spindle shape (see...). Figure 2 (Rough shape and size)

[0086] Step 3: Pre-forging Design. Pre-forging design includes the following four characteristic elements (see...). Figure 3 The high boss has a semi-elliptical cross-section, designated as A (see EE section view). Figure 4 A) The transition area between the boss and the triangle has reinforcing ribs (B); C) The side wall of the high boss is designed with a U-shaped groove that runs through the height direction (C); D) One end of the triangle is designed with an arc shape (D).

[0087] The pre-forging is designed according to the shape and size of the final forging. Usually, the maximum projected area of ​​this type of forging is parallel to the triangle, so the parting surface is selected to be parallel to the triangle. The horizontal length and width of the pre-forging are narrower than those of the final forging. The metal stored in the characteristic parts must meet the forming requirements of the forging, and the metal flow must meet the deformation requirements of the material.

[0088] Furthermore: the plane of the parallel triangle is selected as the parting surface, and the cross-section of the high boss part is designed as a semi-ellipse.

[0089] Objective: To increase the height of the boss and thus the deformation of the forging; at the same time, the sidewalls of the pre-forged part do not require demolding, allowing the forging to be naturally demolded, thereby improving design efficiency.

[0090] Furthermore: Reinforcing ribs are added to the transition area between the high boss and the triangular area. The characteristics of the reinforcing ribs are: the longitudinal section is triangular, the height of the triangle does not exceed the designed height of the boss, and the width of the triangle does not exceed 1 / 3 to 1 / 2 of the designed width of the part. The two sides of the rib width need to be drafted and then transitioned with large R rounded corners to avoid defects such as clamping and folding in the forging.

[0091] The typical design method for this part is a large radius fillet transition; the design of reinforcing ribs significantly improves the problem of the difference in deformation between the core and the surface of the high boss area;

[0092] Furthermore: the high boss sidewall is designed with a U-shaped groove running through the height direction, and the sidewall groove should have a draft angle of 1° to 10°; the sidewall is excavated with a U-shaped groove (see...). Figure 5 To ensure that the forgings do not have defects such as clamping or folding, the U-shaped groove should not be too deep, where h < 1 / 3b and R ≥ R1;

[0093] Objective: To improve the microstructure differences caused by surface deformation dead zones or small deformation amounts.

[0094] Furthermore, the middle part of one end of the triangular area is designed to be arc-shaped.

[0095] The purpose of the arc design is to reduce the material consumption of forgings in the triangular area, improve the uniformity of the microstructure, and improve the microstructure differences caused by excessive deformation due to the large amount of metal flowing into the burrs in this area.

[0096] The design effect of this invention was compared using simulation software:

[0097] Figure 7-1 and Figure 7-2 : Simulation effect diagram of deformation from pre-forging to final forging of this invention

[0098] Figure 8-1 and Figure 8-2 Simulation diagram of deformation from conventional pre-forging design to final forging.

[0099] Step 4: Place the formed blank into the cavity of the pre-forging die for pre-forging.

[0100] Step 5: Place the pre-forged part in the cavity of the final forging die for final forging.

[0101] Step 6: Perform heat treatment on the forging from Step 5;

[0102] Further, step 6 includes: primary annealing: heating to 830°C, furnace cooling to 760°C, cooling method: air cooling.

[0103] Furthermore, step 6 also includes: secondary annealing: heating the forging to a temperature of 616°C and cooling it by air cooling.

[0104] The forgings produced using the above method all meet the standard requirements in terms of physical and chemical properties. The results of the physical and chemical properties are shown in Table 1. In the design of this pre-forging, the reliability of the pre-forging in the cavity of the final forging die was also considered, which meets the usage requirements of key components for the landing gear of the new generation of aircraft. The material utilization rate of the forging is improved, the production cost is reduced, and a new design idea and method are provided for the production of this type of forging. At the same time, it provides reliability for subsequent batch production.

[0105] Table 1. Mechanical test results of forgings

[0106]

[0107]

Claims

1. A forging method for large and complex TC18 titanium alloys, characterized in that, include: The surface parallel to the triangular region of the forging is selected as the parting surface for pre-forging and the parting surface for final forging; A spindle-shaped rough shape is prepared using bar stock; the two ends of the spindle-shaped rough shape are mutually perpendicular flat plates; the rear end of the horizontal plate of the spindle-shaped rough shape has a groove, so that the rear end head has two shoulder sections. The spindle-shaped rough is pre-forged to obtain a pre-forged part: Specifically, a groove is added to the upper surface of the horizontal plate, and the inner surface of the groove between the two shoulders at the rear end of the horizontal plate becomes a concave curved surface; a high boss with a semi-elliptical cross section is formed on the vertical plate of the spindle-shaped rough above the parting surface, and a front reinforcing rib is formed on the part near the connection area of ​​the two plates. U-shaped grooves in the height direction are added on the left and right sides of the high boss; the part of the vertical plate below the parting surface is formed accordingly. The pre-forged part is die-forged to obtain the forging part, and the forging part is heat-treated; The preparation of spindle-shaped rough shapes using bar stock includes: Step 1: Select bar stock as billet; Step 2: First, upset the billet, square it, and shape it into a cuboid; the upsetting ratio should be less than or equal to 3; Step 3: Flip the rectangular blank, divide the rectangular blank into sections, use one end as a triangular forming area and the other end as a high-protrusion forming area; flatten and widen the triangular forming area to form a spindle-shaped horizontal plate; flatten the rectangular blank vertically in the width direction; widen it until one end cannot enter the mold cavity. Step 4: Rotate the billet 90°, place the high boss forming area vertically into the mold, upset and widen the triangular forming area, form the triangular area, and then press a groove in the middle of the end of the triangular area to leave shoulders on both sides of the end of the triangular area. Step 5: Remove the blank from the mold, flatten the high-protrusion forming area to form a spindle-shaped vertical plate, and finally shape it into a spindle-shaped blank.

2. The method according to claim 1, characterized in that, The U-shaped groove has a draft angle of 1° to 10°; the depth h of the U-shaped groove is less than 1 / 3 of the diameter of the U-shaped groove; and the radius R of the convex circle of the U-shaped groove is greater than or equal to the radius R1 of the concave circle.

3. The method according to claim 1, characterized in that, The heat treatment parameters for forgings include: First annealing: Heat to 820-850℃, furnace cool to 740-760℃, furnace cooling method: air cooling or wind cooling, electric furnace uniformity is ±10℃; Secondary annealing: Heat the forging to 500-650℃, and cool it after it is taken out of the furnace by air cooling. The uniformity of the electric furnace is ±5℃.

4. The method according to claim 1, characterized in that, The volume of the billet is 1.1 to 1.25 times the volume of the forging.

5. The method according to claim 3, characterized in that, During the first annealing, the effective thickness of the forging should be less than or equal to 250 mm. For forgings with an effective thickness greater than 150 mm, furnace air cooling is used; for those less than or equal to 150 mm, furnace air cooling is used. For forgings with an effective thickness greater than 250 mm, the thickness of the forging is reduced by machining before the first annealing.

6. The method according to claim 3, characterized in that, During heat treatment, the transfer time of the forging after exiting the furnace should be less than or equal to 2 minutes.

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