Extrusion method for deep-hole thin-wall titanium alloy forge piece

Abstract

This invention discloses an extrusion method for deep-hole thin-walled titanium alloy forgings. This method solves the forging filling problem, reduces material extrusion deformation, reduces the extrusion pressure on the die, increases die life, and improves product quality, while also preventing surface cracking caused by excessive deformation. The method involves a first extrusion forming a flange at one end and a boss at the other, with the boss forming a Φb step between the boss and adjacent parts. A second extrusion forming involves the material flowing radially outward in the upper half of the Φb step, forming the upper half of the forging's central hole and expanding the upper half of the Φb step to form a Φb+c step. The second extrusion provides a reference and material reserve for the third extrusion forming. Finally, the third extrusion forming involves the material flowing radially outward in the lower half of the Φb step, forming the lower half of the forging's central hole and expanding the lower half of the Φb step to obtain the finished forging.

Description

Technical Field

[0001] This invention relates to the field of metal forging and plastic forming technology, and in particular to an extrusion method for deep-hole thin-walled titanium alloy forgings. Background Technology

[0002] 1. TC4 titanium alloy, as a dual titanium alloy with titanium as the base and the addition of elements such as aluminum and vanadium, is suitable for parts subjected to alternating load stress. It has high strength and toughness, which means that a greater external force needs to be applied during the extrusion process to make it plastically deformed. High strength also means that the material is difficult to plastically deform, which increases the difficulty of extrusion forming and requires more precise control of the deformation amount and metal flow distance during the forming process.

[0003] 2. During the extrusion process, TC4 titanium alloy is prone to work hardening, that is, as extrusion proceeds, the hardness of the material gradually increases, and the stress environment of the die deteriorates, requiring a more reasonable process and die structure design.

[0004] 3. The stator housing shaft is used in the connection between the rotor and motor of low-altitude aircraft, and is a critical component of the aircraft, subjected to relatively harsh stress environments. The stator housing shaft forging blank ( Figure 1 TC4 titanium alloy is typically used for forgings, which are thin-walled, deep-cup shaped forgings. Due to the difficult plastic forming characteristics of TC4 titanium alloy and the structural characteristics of the product, forging is challenging, and the working conditions of the die are harsh. Specifically, during the extrusion process of TC4 titanium alloy, the heating process of the billet, the amount of metal deformation, lubrication, and other parameters must be strictly controlled to ensure that the forging is fully filled and to avoid surface cracking due to excessive deformation. Furthermore, because the product has high deformation resistance, the forging die must withstand significant stress during extrusion, which can easily cause the die to crack, chip, etc., leading to the scrapping of both the forging and the die.

[0005] The stator housing shaft forging has an inner hole depth of 95mm and a diameter of Φ28-37mm, with a wall thickness of only 11mm at the thinnest point, resulting in an inner hole-to-diameter ratio of 2.9. Firstly, the forging is a thin-walled, deep-hole forging, which is difficult to form. Furthermore, the forging material is TC4 titanium alloy. Traditional forward and reverse extrusion processes result in a long metal flow distance. During forging, due to the thin circumferential structure, heat loss is rapid, and the temperature drops significantly, leading to poor metal fluidity and further increasing the difficulty of filling the mold, making it difficult to achieve full filling. Secondly, to ensure the metal can be extruded into the inner hole, the material's deformation resistance must be overcome. The upper die must withstand significant deformation resistance, and this repeated stress during mass production causes stress concentration at the bottom of the upper die core. This easily leads to die bottom cracking, reducing the die life to less than 100 pieces, making mass production difficult. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an extrusion method for deep-hole thin-walled titanium alloy forgings. This method can solve the problem of forging filling, reduce material extrusion deformation, reduce the extrusion pressure on the die, improve die life, improve product quality, and solve the problem of surface cracking caused by excessive deformation of forgings.

[0007] The objective of this invention is achieved as follows: An extrusion method for deep-hole thin-walled titanium alloy forgings, the extrusion method comprising the following steps: One-time extrusion molding produces a flange at one end of the forging and a boss at the other end, with a Φb step formed between the boss and the adjacent parts; In the secondary extrusion molding, the material flows radially outward in the upper half of the Φb step, forming the upper half of the center hole of the forging, and expanding the upper half of the Φb step of the forging to form the Φb+c step. The secondary extrusion molding provides a benchmark and material reserve for the tertiary extrusion molding. The material is formed by three extrusion molding processes. The material flows radially outward in the lower half of the Φb step, forming the lower half of the center hole of the forging. This expands the lower half of the Φb step of the forging, resulting in the finished forging.

[0008] Preferably, the deep-hole thin-walled titanium alloy forging is a stator housing shaft forging, with an inner hole depth of 95 mm, an inner hole diameter of 28-37 mm, and a minimum wall thickness of 11 mm.

[0009] Preferably, the pressure of each extrusion is controlled below 350T.

[0010] Preferably, the volume of the diameter expansion dimension in the secondary extrusion molding and tertiary extrusion molding is controlled at 10%-15% of the volume of the extrusion center hole.

[0011] Preferably, during one-time extrusion molding, a titanium rod with a diameter of Φa is selected as the blank according to the minimum size of the shaft end of the finished forging. After the forging is heated, it is placed in the blank positioning position of the cavity of the lower die of the one-time extrusion molding die. The upper die of the one-time extrusion molding die presses down once, and a second step with a size of Φb is formed on the surface of the forging. A groove is extruded from the flange end of the forging. During secondary extrusion molding, after the forging is heated, the lower half of the second step is placed in the lower die of the secondary extrusion molding die as a positioning reference. The upper die of the secondary extrusion molding die presses downward once. The material in the center of the upper half of the Φb step is pressed radially outward by the upper die of the secondary extrusion molding die, expanding the upper half of the Φb step of the forging. After the upper half of the Φb step is expanded, a third step with a size of Φb+c is formed between it and the lower half. During the three-stage extrusion molding process, after the forging is heated, the third step is placed into the lower die of the three-stage extrusion molding die as a positioning reference. The upper die of the three-stage extrusion molding die then extrudes once, and the material at the center of the Φb step flows radially outward.

[0012] Preferably, the lower mold cavity of the primary extrusion molding die consists of a boss cavity, a central cavity, and a flange cavity from bottom to top. The diameter of the central cavity is smaller than the corresponding outer diameter of the finished forging. The upper mold of the primary extrusion molding die has a flange pressure block, and the flange pressure block has a groove pressure block in the middle.

[0013] Preferably, the upper die of both the secondary extrusion molding die and the tertiary extrusion molding die has an upper die core. The upper die core is used to extrude and form the center hole of the forging. The diameter of the upper die core of the secondary extrusion molding die is smaller than the maximum diameter of the groove, and the diameter of the upper die core of the tertiary extrusion molding die is smaller than the diameter of the upper die core of the secondary extrusion molding die.

[0014] Due to the adoption of the above technical solution, the present invention has the following beneficial effects: This invention relates to a forming process design for forging TC4 titanium alloy stator housing shafts. It includes primary, secondary, and tertiary extrusion processes, as well as the design of the extrusion die cavity and structure. It is primarily applied to the forging process of TC4 titanium alloy stator housing shafts for low-altitude aircraft. This process creatively solves problems such as the difficulty of forming deep-hole, thin-walled titanium alloys, surface cracking of forgings, and short die life, while ensuring product quality and performance. It improves die life and production efficiency, reduces manufacturing costs, and meets the requirements of mass production. Attached Figure Description

[0015] Figure 1 Schematic diagram of the finished TC4 titanium alloy stator housing shaft forging; Figure 2 This is a process flow diagram of the present invention; Figure 3 This is a schematic diagram of the billet deformation process; Figure 4 This is a schematic diagram of the extrusion process. Detailed Implementation

[0016] An extrusion method for deep-hole thin-walled titanium alloy forgings, the extrusion method comprising the following steps: One-time extrusion molding forms a flange at one end of the forging and a boss at the other end. The boss and the adjacent parts form a Φb step (second step). The first extrusion molding provides a reference and material reserve for the second extrusion molding. The reference provided by the first extrusion molding includes the outer circle of the lower half of the forging (excluding the boss) and the outer circle of the flange. The material reserve is the storage bin of the intermediate hole in the second extrusion molding (material required for diameter expansion).

[0017] In the secondary extrusion molding, the material flows radially outward in the upper half of the Φb step, forming the upper half of the center hole of the forging. The upper half of the Φb step of the forging is expanded to form the Φb+c step. The secondary extrusion molding provides a reference and material reserve for the tertiary extrusion molding. The reference provided by the secondary extrusion molding includes the outer circle of the flange and the outer circle of the upper part of the forging (excluding the flange). The material reserve is the storage bin of the middle hole in the lower half of the tertiary extrusion molding.

[0018] The material is formed by three extrusion molding processes. The material flows radially outward in the lower half of the Φb step, forming the lower half of the center hole of the forging. This expands the lower half of the Φb step of the forging, resulting in the finished forging.

[0019] During a single extrusion molding process, a titanium rod with a diameter of Φa is selected as the blank based on the minimum dimension (boss dimension) of the shaft end of the finished forging. After the forging is heated, it is placed in the blank positioning position (corresponding to the boss) of the cavity of the lower die of the single extrusion molding die. The upper die of the single extrusion molding die presses downward once, and a second step with a dimension of Φb is formed on the surface of the forging. A groove is extruded from the flange end of the forging.

[0020] During secondary extrusion molding, after the forging is heated, the lower half of the second step is placed into the lower die of the secondary extrusion molding die as a positioning reference. The flange and boss assist in positioning. The upper die of the secondary extrusion molding die presses downward once. The material in the center of the upper half of the Φb step is pressed radially outward by the upper die of the secondary extrusion molding die, expanding the upper half of the Φb step of the forging. After the upper half of the Φb step is expanded, a third step with a size of Φb+c is formed between it and the lower half.

[0021] During the three-stage extrusion molding process, after the forging is heated, the third step is used as a positioning reference and placed into the lower die of the three-stage extrusion molding die for positioning. The flange and boss assist in positioning. The upper die of the three-stage extrusion molding die extrudes once, and the material at the center of the Φb step is extruded radially outward.

[0022] The lower mold cavity of the primary extrusion molding die consists of a boss cavity, a central cavity, and a flange cavity from bottom to top. The diameter of the central cavity is smaller than the corresponding outer diameter of the finished forging. The upper mold of the primary extrusion molding die has a flange pressure block, and the flange pressure block has a groove pressure block in the middle.

[0023] Both the secondary and tertiary extrusion molding dies have an upper die core. This upper die core is used to extrude and form the center hole of the forging. The diameter of the upper die core in the secondary extrusion molding die is smaller than the maximum diameter of the groove, while the diameter of the upper die core in the tertiary extrusion molding die is smaller than the diameter of the upper die core in the secondary extrusion molding die. After the billet is cut, the end face needs to be chamfered, and the billet is pre-coated before heating to reduce friction. Specifically: This invention addresses the challenges of forming stator housing shaft forgings, particularly the high difficulty in forming the upper die core and its susceptibility to breakage. It innovatively provides a diameter-expanding composite extrusion method. Extensive production verification has shown that this process not only solves the forging filling problem and reduces material extrusion deformation, but also reduces the extrusion pressure on the die, increases die life, improves product quality, and resolves surface cracking caused by excessive deformation in the forgings.

[0024] A novel composite extrusion method for expanding diameter breaks through the traditional forward and reverse extrusion processes for this type of forging. The stator housing shaft forging employs a three-stage extrusion sequence. The first extrusion primarily forms the flange portion of the forging, provides a positioning surface for the second forming, and serves as a storage bin for the intermediate hole in the second forming. The second extrusion primarily forms the upper half of the center hole in the forging and provides a positioning surface for the third extrusion, as well as a storage bin for the lower half of the center hole. The third extrusion primarily forms the dimensions and the lower half of the center hole. (e.g.) Figure 3 ) This process has been validated in batches on a 630T extrusion press, producing qualified forgings. The single life of the die can reach more than 2,000 pieces, and the comprehensive life (die can be sunk for repair) reaches more than 6,000 pieces. The forgings are fully filled, have qualified dimensions, and no folds on the surface. The single extrusion pressure of the forgings is less than 350T, which is 50% lower than the traditional positive extrusion pressure, and the die life is increased by more than 10 times.

[0025] The following is combined Figure 3 , 4 The present invention will now be described in further detail.

[0026] First, based on the minimum dimension of the forging shaft end, a titanium rod with a diameter of Φa is selected. After heating the Φa titanium rod as required, it is placed in the lower die cavity at the blank positioning position (dimension Φa+0.2). The upper die presses downwards in the first stage to meet the requirements of the first blank drawing, forming a second step with a dimension of Φb at the shaft end. The lower half of the first forging step dimension Φb is used as the positioning dimension and placed in the lower die for the second stage. The upper die for the second stage begins to press downwards, and the material in the extrusion center of the upper die begins to flow towards the upper part of the Φb step, expanding the upper half of the Φb step in the first forging. A third step with a dimension of Φb+c is formed at the shaft end, where the volume of the expanded dimension c is less than 10%-15% of the volume of the extrusion center hole of the upper die (the volume composed of %d and e). The step dimension Φb+c of the second stage is used as the positioning dimension and placed in the lower die for the third stage. The upper die for the third stage begins to press downwards, and the material in the extrusion center of the upper die begins to flow towards the lower part of the Φb step, where the volume of the expanded dimension c is less than 10%-15% of the volume of the extrusion center hole of the upper die (the volume composed of %d and e).

[0027] Secondly, during the second and third extrusions, the inner core of the upper die extrudes the inner hole and is subjected to axial and circumferential radial extrusion forces. During the extrusion process, as long as the positioning of each process is reliable and the anisotropy of metal flow is relatively uniform, the deformation resistance borne by the die is reduced, thereby improving the die life.

[0028] The main innovation of this extrusion method is as follows: 1. In view of the special characteristics of TC4 material forming, the deformation amount of the three extrusions is reasonably allocated to solve the problems of difficult forming of thin-walled deep holes and surface cracking of TC4 titanium alloy, thus ensuring the surface quality of the forging.

[0029] 2. Traditional forward and reverse extrusion molding processes have the following disadvantages for this type of titanium alloy product: titanium alloy materials have high plasticity and deformation resistance, the forward and reverse extrusion molding process has a long metal flow distance, the surface of the forging is prone to tearing, and the inner core of the mold cannot withstand this deformation resistance, resulting in fracture and affecting the service life of the mold.

[0030] 3. By adopting the diameter expansion extrusion process, radial flow of metal can be achieved, reducing the metal flow distance during the TC4 titanium alloy extrusion process, reducing deformation resistance, improving the stress environment of the die, and preventing die breakage during forging, thereby increasing die life and reducing die cost.

[0031] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for extruding deep-hole thin-walled titanium alloy forgings, characterized in that, The extrusion method includes the following steps: One-time extrusion molding produces a flange at one end of the forging and a boss at the other end, with a Φb step formed between the boss and the adjacent parts; In the secondary extrusion molding, the material flows radially outward in the upper half of the Φb step, forming the upper half of the center hole of the forging, and expanding the upper half of the Φb step of the forging to form the Φb+c step. The secondary extrusion molding provides a benchmark and material reserve for the tertiary extrusion molding. The material is formed by three extrusion molding processes. The material flows radially outward in the lower half of the Φb step, forming the lower half of the center hole of the forging. This expands the lower half of the Φb step of the forging, resulting in the finished forging.

2. The extrusion method for a deep-hole thin-walled titanium alloy forging according to claim 1, characterized in that: The deep-hole thin-walled titanium alloy forging is a stator housing shaft forging. The inner hole depth of the stator housing shaft forging is 95mm, the inner hole diameter is 28-37mm, and the minimum wall thickness is 11mm.

3. The extrusion method for a deep-hole thin-walled titanium alloy forging according to claim 2, characterized in that: The pressure of each extrusion is controlled below 350T.

4. The extrusion method for a deep-hole thin-walled titanium alloy forging according to claim 1, characterized in that: The volume of the diameter expansion dimension in secondary and tertiary extrusion molding is controlled at 10%-15% of the volume of the extrusion center hole.

5. The extrusion method for a deep-hole thin-walled titanium alloy forging according to claim 1, characterized in that: During a single extrusion molding process, a titanium rod with a diameter of Φa is selected as the blank based on the minimum size of the shaft end of the finished forging. After the forging is heated, it is placed in the blank positioning position of the cavity of the lower die of the single extrusion molding die. The upper die of the single extrusion molding die presses downward once, and a second step with a size of Φb is formed on the surface of the forging. A groove is extruded from the flange end of the forging. During secondary extrusion molding, after the forging is heated, the lower half of the second step is placed in the lower die of the secondary extrusion molding die as a positioning reference. The upper die of the secondary extrusion molding die presses downward once. The material in the center of the upper half of the Φb step is pressed radially outward by the upper die of the secondary extrusion molding die, expanding the upper half of the Φb step of the forging. After the upper half of the Φb step is expanded, a third step with a size of Φb+c is formed between it and the lower half. During the three-stage extrusion molding process, after the forging is heated, the third step is placed into the lower die of the three-stage extrusion molding die as a positioning reference. The upper die of the three-stage extrusion molding die then extrudes once, and the material at the center of the Φb step flows radially outward.

6. The extrusion method for a deep-hole thin-walled titanium alloy forging according to claim 5, characterized in that: The lower mold cavity of the primary extrusion molding die consists of a boss cavity, a central cavity, and a flange cavity from bottom to top. The diameter of the central cavity is smaller than the corresponding outer diameter of the finished forging. The upper mold of the primary extrusion molding die has a flange pressure block, and the flange pressure block has a groove pressure block in the middle.

7. The extrusion method for a deep-hole thin-walled titanium alloy forging according to claim 5, characterized in that: Both the secondary extrusion molding die and the tertiary extrusion molding die have an upper die core. The upper die core is used to extrude and form the center hole of the forging. The diameter of the upper die core of the secondary extrusion molding die is smaller than the maximum diameter of the groove, and the diameter of the upper die core of the tertiary extrusion molding die is smaller than the diameter of the upper die core of the secondary extrusion molding die.

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