Reverse extrusion forming method for cylindrical thin-walled forgings

Abstract

The invention discloses a backward extrusion forming method for a cylindrical thin-wall type forge piece, which comprises the following steps of: heating an alloy bar blanked according to specifications to 20-80 DEG C below a phase transformation point, then loading the alloy bar into a blank making die preheated to 200-300 DEG C, and carrying out centering blank making to obtain a blank of which the upper end surface is provided with a circular positioning blind hole; the blank is heated to 20-80 DEG C below the phase transformation point and then is put into an extrusion die preheated to 200-300 DEG C to be centered and put into the die; starting a press machine to downwards press a convex die of the extrusion die, so that an extrusion head of the convex die downwards and quickly extrudes the blank along a positioning blind hole in the upper end face of the blank at the speed of 85-95mm / s to the distance of one third of the height of the blank, and extruding the blank to form a guide positioning hole with a certain depth; and then the extrusion head slowly extrudes the blank along the guide positioning hole at the speed of 35-45 mm / s until the male die and the female die of the extrusion die are completely closed, and the blank is reversely extruded into the shell forge piece. The method is mainly used for manufacturing aviation shell forgings.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of forging forming method, in particular to a kind of cylindrical thin-walled type forging reverse extrusion forming method. BACKGROUND

[0002] The shell forging of aviation is generally cylindrical thin-walled structure, and the ratio of height and diameter (the ratio of height and diameter) is about 1, that is, the numerical value of height and diameter is close, and the shell forging belongs to thin-walled high cylinder forging, and when free forging is used, forming quality is poor, and the following defects are prone to occur: core deviation, uneven structure, unstable performance, low material utilization, etc., which increases the cost of forging production.

[0003] Chinese patent specification CN103302123A published on September 18, 2013 discloses a process for reverse extrusion of long cylindrical sleeve by non-standard low-speed press, and the technical solution is as follows: (a) blanking and heating; (b) pressing: the heated bar is placed in the die bore of the pressing die, the press is lowered, the press head is connected to the press through the connecting rod and then presses the blank, the press is returned after the pressing is completed, and the blank in the die bore is ejected by the ejector rod of the pressing die; (c) shallow punching: the pressed blank is placed in the die bore of the shallow punching die, the press is lowered, the shallow punching punch is connected to the press through the connecting rod and then shallow punches the blank, the press is returned after the shallow punching is completed, and the blank in the die bore is ejected by the ejector rod of the shallow punching die; (d) reverse extrusion: the shallow punched blank is placed in the die bore of the reverse extrusion die; the press is lowered, the reverse extrusion punch is connected to the press through the connecting rod and then reverse extrudes the blank, the reverse extrusion of the blank is completed, the press is returned after the reverse extrusion is completed, and the workpiece after the reverse extrusion is ejected from the die bore by the ejector rod of the reverse extrusion die; the press is a non-standard low-speed press, and the working speed is not greater than 40 mm / s.

[0004] The technical solution of the patent mainly uses low-speed reverse extrusion process to form long cylindrical sleeve, but if the technical solution is used to form thin-walled high cylinder shell forging, complex special equipment and molds are needed, which results in large investment, and the production process is too complicated and the production efficiency is not high; moreover, if the center lines of the mold and the blank are not accurately matched, the pressing speed of the punch is not well controlled, and the following defects are prone to occur during reverse extrusion forming: core deviation, uneven structure, unstable performance, etc. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a centering scheme to realize the reverse extrusion forming method of cylindrical thin-walled type forging, which makes the forming quality of the forging better through centering blank making and centering reverse extrusion.

[0006] To solve the above technical problems, the reverse extrusion forming method of cylindrical thin-walled type forging according to the present application has the following steps:

[0007] Centering of blanking: a blanking die is provided, which is composed of a tire membrane, a cover plate and a pressing block; the blanking die is mounted on the base of a press and preheated to 200-300℃, then the titanium alloy bar stock cut according to the specifications is heated to 20-80℃ below the phase transition point and loaded into the blanking die so that the outer circumferential surface of the bar stock is matched with the inner circumferential surface of the tire membrane, the upper end surface of the bar stock is placed at the center positioning hole of the cover plate and is in contact with the bottom end surface of the punch of the pressing block, and the blanking die is assembled in the centering manner; the press is started to press down the pressing block so that the punch of the pressing block punches the upper end surface of the bar stock along the center positioning hole of the cover plate, and a cylindrical blank with a circular positioning hole in the upper end surface is obtained;

[0008] Centering of die assembly: an extrusion die is provided, which is composed of a concave membrane and a convex membrane; the extrusion die is loaded into a press and preheated to 200-300℃, the above-mentioned blank is heated to 20-80℃ below the phase transition point and loaded into the extrusion die so that the upper end surface with the positioning hole is upward, the extrusion head of the convex die is moved so that the bottom surface is just placed in the positioning hole of the upper end surface of the blank, and the centering assembly of the concave membrane, the convex die and the blank is completed;

[0009] Reverse extrusion forming in the centering manner: the press is started to press down the convex die so that the extrusion head of the convex die is quickly extruded downward at a speed of 85-95 mm / s along the positioning hole in the upper end surface of the blank to a distance of one third of the height of the blank at an extrusion force F, and the blank is extruded to have a guide positioning hole with a certain depth, then the extrusion head is slowly extruded along the guide positioning hole at a speed of 35-45 mm / s until the convex die and the concave die are completely closed, and the blank is reverse extruded into a shell forging;

[0010] The above-mentioned α+β two-phase titanium alloy is preferably TC11.

[0011] In the reverse extrusion process, the blank is subjected to the extrusion force F of the extrusion head, which is calculated as follows:

[0012]

[0013] In the formula:

[0014] σ s The yield strength of the titanium alloy at the extrusion temperature is 25-38 MPa;

[0015] V1 is the pressing speed of the extrusion head of the convex die when extruding the blank, unit: mm / s;

[0016] V2 is the upward flowing speed of the metal in the blank along the circular ring gap between the die cavity of the concave die and the extrusion head when the metal is extruded, unit: mm / s;

[0017] S1 is the cross-sectional area of the extrusion head of the convex die, unit: mm 2;

[0018] and,

[0019] In the formula: S2—the cross-sectional area of ​​the annular part of the shell forging, unit: mm 2 .

[0020] The α+β two-phase titanium alloy shell forging manufactured by the reverse extrusion forming method described in this invention is a thin-walled high-cylinder shape with an open top surface and a sealed bottom surface. Its outer diameter ranges from Φ280mm to Φ295mm, its wall thickness is from 25mm to 35mm, its height-to-diameter ratio on the outer surface is from 0.95 to 1.05, and its height-to-diameter ratio on the inner cavity is from 0.95 to 1.05.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The reverse extrusion forming method for thin-walled cylindrical forgings described in this invention, during the centering and blanking process, ensures that the punch of the blanking die press block, through cooperation with the central positioning hole of the cover plate, punches the bar stock to obtain a blank with a positioning blind hole on the upper end face. In addition, the height of the punch is designed to be the sum of the thickness of the central positioning hole of the cover plate and the depth of the positioning blind hole, thereby ensuring that the center line of the positioning blind hole is aligned with the center line of the blank, providing a high-quality blank for achieving centering and reverse extrusion.

[0023] During the centering reverse extrusion forming process, since the billet temperature is high at the beginning of the extrusion, the extrusion head of the extrusion die punch is first rapidly extruded downwards along the positioning blind hole on the upper end face of the billet at a speed of 85 mm / s to 95 mm / s to one-third of the billet height. This ensures that the center line of the extrusion head is aligned with the center line of the positioning blind hole and does not deviate from the center. In addition, the wall thickness of the extruded annular part is relatively thin, and the heat dissipation is faster. The billet is extruded with guide positioning holes of a certain depth. At this time, the billet temperature drops, and the billet is slowly extruded at a speed of 35 mm / s to 45 mm / s until the punch and die are completely closed. Since the extrusion head will continue to extrude the billet along the aforementioned guide positioning hole, the punch and die are finally aligned and closed. This ensures that the entire reverse extrusion process is carried out in a centered state, thereby obtaining a shell forging that is not eccentric, has a uniform structure, stable performance, and good forming quality.

[0024] During the reverse extrusion process, the relationship between the extrusion force F exerted on the billet by the extrusion head and the billet's reduction velocity and upward flow velocity is as follows:

[0025]

[0026] This allows the force to be predetermined based on the speed, and the speed can be controlled during extrusion based on the force, which is beneficial for the stable execution of the reverse extrusion process and the production of shell forgings with uniform structure, excellent performance, and no defects.

[0027] and,

[0028] As can be seen from the above formula, the speed at which the billet is squeezed upward can be known based on the billet's pressing speed, which is beneficial for controlling the entire reverse extrusion process and obtaining high-quality forgings.

[0029] Furthermore, this invention does not require a dedicated extrusion press or complex extrusion die device. The reverse extrusion forming of thin-walled high-cylinder shell forgings can be achieved using a simple die on a forging press, saving the cost of dedicated equipment and dies, simplifying the process, improving production efficiency, and reducing manufacturing costs. Attached Figure Description

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 This is a schematic diagram of the bar stock centering and mold assembly.

[0032] Figure 2 This is a schematic diagram of the centering and blanking process.

[0033] Figure 3 This is a schematic diagram of the blank reverse extrusion centering mold assembly.

[0034] Figure 4 This is a schematic diagram of the reverse extrusion forming of the shell forging.

[0035] Figure 5 This is a cross-sectional view of the shell forging formed by reverse extrusion along its centerline. Detailed Implementation

[0036] Implementing the reverse extrusion forming method for thin-walled cylindrical forgings described in this invention requires equipment such as a forging furnace, a press, and a robotic arm. The specific implementation method is illustrated below using an α+β two-phase titanium alloy with the Chinese material designation TC11 as an example.

[0037] The main chemical element contents (by weight percentage) of the alloy are as follows: Al 5.8%–7.0%, Mo 2.8%–3.8%, Zr 0.8%–2.0%, Si 0.20%–0.35%, Fe ≤0.25%, C ≤0.10%, N ≤0.05%, H ≤0.012%, O ≤0.15%, other elements individually ≤0.10% and their total ≤0.40%, with the balance being Ti.

[0038] Testing revealed that the phase transformation point of the alloy used in this embodiment is 1008℃. The process steps for forging this alloy from bar stock into a shell forging are as follows:

[0039] Step 1: Centering and billet preparation

[0040] like Figure 1 As shown, a blanking mold 10 is first provided, which consists of a mold 11, a cover plate 12, and a pressing block 13. The mold 11 is annular and has a slope on the upper part of its outer circumference. The cover plate 12 is disc-shaped with a central positioning hole and a raised ring with a slope on the edge of its lower end face. The cover plate 12 covers the upper end face of the mold 11, and the slope of its raised ring presses against the slope on the upper part of the outer circumference of the mold 11. The pressing block 13 consists of a circular pressing plate 13a and a cylindrical punch 13b located in the center of the bottom surface of the pressing plate 13a. The punch 13b of the pressing block 13 can cooperate with the central positioning hole of the cover plate 12. After the mold 11, cover plate 12, and pressing block 13 of the blanking mold 10 are assembled, they can be aligned, that is, the center lines of the three are concentric.

[0041] The blanking mold 10 is mounted on the base of the press and preheated to 200℃~300℃. Then, the TC11 alloy bar 14a, cut to specifications, is heated to 20℃~80℃ below its phase transformation point and placed into the blanking mold 10, so that the outer circumferential surface of the bar 14a mates with the inner circumferential surface of the die 11. The upper end face of the bar 14a is positioned at the center positioning hole of the cover plate 12 and contacts the bottom end face of the punch 13b of the pressure block 13. The blanking mold 10 is then aligned and assembled. The press is started to press down the pressure block 13, causing its punch 13b to punch the upper end face of the bar 14a along the center positioning hole of the cover plate 12, resulting in the desired shape. Figure 2 The cylindrical blank 14 shown has a circular positioning blind hole on its upper surface; in order to ensure that the center line of the positioning blind hole is also aligned with the center line of the blank 14, the height of the punch 13b is designed to be the sum of the thickness of the center hole of the cover plate 12 and the depth of the positioning blind hole.

[0042] Step 2: Centering and Mold Assembly

[0043] like Figure 3 As shown, this step requires the use of an extrusion die 20, which consists of a concave die 21 and a convex die 22. The concave die 21 is annular and its die cavity 21a has a draft angle. The convex die 22 consists of a disc-shaped die base 22b and a cylindrical extrusion head 22a with a draft angle. The extrusion head 22a of the convex die 22 can cooperate with the die cavity 21a of the concave die 21 to perform the extrusion operation.

[0044] The extrusion die 20 is installed into the press and preheated to 200℃~300℃. The billet 14 is heated to 20℃~80℃ below the phase transformation point and then installed into the extrusion die 20 with its upper end face with the positioning hole facing upward. The extrusion head 22a of the punch 22 is moved so that its bottom surface is just placed in the positioning hole on the upper end face of the billet 14, thereby realizing the centering assembly of the concave die 21, the punch 22 and the billet 14.

[0045] Step 3: Centering and reverse extrusion forming

[0046] The press is started, pressing the punch 22 downwards so that its extrusion head 22a, with an extrusion force F, rapidly extrudes the blank 14 along the positioning hole on the upper end face of the blank 14 at a speed of 85 mm / s to 95 mm / s, to a distance of one-third of the blank 14's height. The blank 14 is extruded to form a guide positioning hole of a certain depth. Then, the extrusion head 22a is slowly extruded along the guide positioning hole at a speed of 35 mm / s to 45 mm / s. As the extrusion head 22a continues to extrude downwards, the metal inside the blank 14 flows upwards along the annular interlayer formed between the die cavity 21a and the extrusion head 22a, until the extrusion head 22a is completely inserted into the blank 14, causing the punch 22 and the die 21 to completely close. Figure 4 As shown, the billet 14 is reverse-extruded into a shell forging 30. (As illustrated...) Figure 5 As shown, the shell forging 30 is a thin-walled high cylinder with an open top and a sealed bottom. Its wall thickness is 25mm to 35mm, and its outer diameter ratio (the ratio of height to diameter) is 0.95 to 1.05. The inner diameter ratio is also 0.95 to 1.05.

[0047] During the reverse extrusion process, the extrusion force F exerted on the billet 14 by the extrusion head 22a is calculated using the following formula:

[0048]

[0049] In the formula:

[0050] σ s —The yield strength (MPa) of the alloy at the extrusion temperature is taken as 25MPa to 38MPa;

[0051] V1—The pressing speed (mm / s) of the extrusion head 22a of the punch 22 for extruding the blank 14;

[0052] V2—The speed (mm / s) at which the metal in the billet 14 flows upward along the annular interlayer formed between the die cavity 21a and the extrusion head 22a when it is extruded;

[0053] S1 — Cross-sectional area of ​​the extrusion head 22a of the punch 22 (mm²) 2 );

[0054] and, Where: S2—the cross-sectional area of ​​the annular part of the shell forging 30 (mm²) 2 ).

Claims

1. A method of reverse extrusion forming of a cylindrical thin-walled forged piece, characterized by, It comprises the following steps: Centering and blanking: a blanking die is provided, which is composed of a membrane, a cover plate and a press block; the blanking die is mounted on the base of a press and preheated to 200-300 DEG C, and then the titanium alloy bar stock cut according to the specifications is heated to 20-80 DEG C below the phase transition point and loaded into the blanking die so that the outer circumferential surface of the bar stock is matched with the inner circumferential surface of the membrane, the upper end surface of the bar stock is positioned at the center positioning hole of the cover plate and is in contact with the bottom end surface of the punch of the press block, and the blanking die is assembled in the centering manner; the press is started to press down the press block so that the punch of the press block punches the upper end surface of the bar stock along the center positioning hole of the cover plate, and a cylindrical blank with a circular positioning hole in the upper end surface is obtained; Centering and die assembling: an extrusion die is provided, which is composed of a concave membrane and a convex membrane; the extrusion die is loaded into a press and preheated to 200-300 DEG C, and then the blank is heated to 20-80 DEG C below the phase transition point and loaded into the extrusion die so that the upper end surface with the positioning hole faces upward, the extrusion head of the convex die is moved so that the bottom surface is just placed in the positioning hole in the upper end surface of the blank, and the centering assembly of the concave membrane, the convex die and the blank is completed; Centering and backward extrusion forming: the press is started to press down the convex die so that the extrusion head of the convex die is quickly extruded downward at a speed of 85-95 mm / s along the positioning hole in the upper end surface of the blank to a distance of one third of the height of the blank under the extrusion force F, and the blank is extruded to have a guide positioning hole with a certain depth, and then the extrusion head is slowly extruded along the guide positioning hole at a speed of 35-45 mm / s until the convex die is completely combined with the concave die, and the blank is backward extruded into a shell forging.

2. The method of claim 1, wherein: The α+β two-phase titanium alloy is TC11.

3. The method of claim 1 or 2, wherein In the backward extrusion process, the blank is subjected to the extrusion force F of the extrusion head, which is calculated according to the following formula: In the formula: σ s - the yield strength of the titanium alloy at the extrusion temperature is comprised between 25 MPa and 38 MPa; V1 is the pressing speed of the extrusion head of the convex die, unit: mm / s; V2 is the upward flowing speed of the metal in the blank along the circular ring interlayer formed between the die cavity of the concave die and the extrusion head when the metal is extruded, unit: mm / s; S1 - cross-sectional area of the extrusion head of the male die, in mm 2 ; And, In the formula: S2 - annular cross-sectional area of the shell forging, unit: mm 2 .

4. The method of claim 1 or 2, wherein: The backward extrusion formed α+β two-phase titanium alloy shell forging is a thin-walled high-cylindrical shape with an open top surface and a sealed bottom surface, the outer diameter size ranges from Φ280 mm to Φ295 mm, the wall thickness is 25-35 mm, the height-to-diameter ratio of the outer circumferential surface is 0.95-1.05, and the height-to-diameter ratio of the inner cavity is 0.95-1.05.

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