Backward extrusion forming die and forming method for thin-wall high-cylinder forge piece

Abstract

The backward extrusion forming die comprises a forming moulding bed, a cushion block, a guide ring and a forming punch, a cavity with an opening in the top is designed in the forming moulding bed, a cushion block through hole communicated with the cavity is formed in the bottom of the forming moulding bed, and the cushion block and the cushion block through hole are installed in a matched mode. An annular groove is formed in the upper end face of the forming moulding bed, an annular step is arranged on the lower end face of the guide ring, the annular groove and the annular step are installed in a matched mode, a punch installation hole is formed in the guide ring and used for installing the forming punch in a clearance fit mode, and a cavity in the forming moulding bed coincides with the central axis of the punch installation hole of the guide ring. The cushion block through hole coincides with the central axis of the cavity. According to the invention, a matching structure of the forming moulding bed and the guide ring is introduced on the free forging equipment, and step positioning and clearance fit are utilized, so that accurate positioning and centering of the forming punch and the blank are realized, the uniformity of the wall thickness is effectively controlled, and the applicable equipment range of the backward extrusion process is expanded.

Description

Technical Field

[0001] This invention belongs to the field of forging forming technology, and specifically relates to a reverse extrusion forming die and forming method for thin-walled high-cylinder forgings. Background Technology

[0002] Thin-walled cylindrical forgings typically refer to structural parts with a wall thickness to inner diameter ratio of no more than 1 / 10 and a height to inner diameter ratio of no less than 2. The core challenge in forming these parts lies in ensuring uniform wall thickness, preventing instability during deformation (such as bulging or denting), reducing internal defects (such as porosity or cracks), and ensuring good material density.

[0003] Currently, the commonly used manufacturing processes in this field mainly include free forging combined with assisted forming, radial-axial ring rolling (RAFM), extrusion forming, and die forging. Among them, free forging combined with assisted forming is mostly used for small-batch production with lower precision requirements; radial-axial ring rolling is currently the mainstream method for high-precision forming; extrusion forming is suitable for non-ferrous metals and thin-walled cylindrical parts with a large length-to-diameter ratio; while die forging is more suitable for products with complex structures and high batch requirements.

[0004] However, existing technologies still have certain limitations. Especially in reverse extrusion molding, the key issues lie in controlling wall thickness uniformity and suppressing deformation instability. Therefore, under sufficient forming force, accurate positioning between the die and the billet is particularly crucial. Conventional reverse extrusion processes typically rely on the equipment's guiding mechanism to ensure the positional relationship between the die and the billet, thereby controlling wall thickness uniformity. However, free forging equipment, lacking high-precision guiding capabilities, struggles to achieve satisfactory reverse extrusion molding. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a reverse extrusion forming die and forming method for thin-walled high-cylinder forgings. By introducing a matching structure of forming die and guide ring on a free forging equipment, and utilizing step positioning and clearance fit, precise positioning and alignment of the forming punch and the blank are achieved, effectively controlling the uniformity of wall thickness and expanding the applicable equipment range of the reverse extrusion process.

[0006] The main technical solution adopted in this invention is as follows:

[0007] A reverse extrusion forming die for thin-walled high-cylinder forgings includes a forming die, a pad block, a guide ring, and a forming punch. The forming die has a cavity with a top opening. The bottom of the forming die has a through hole in the pad block communicating with the cavity, and the pad block is fitted into the through hole. An annular groove is formed on the upper surface of the forming die, and an annular step is formed on the lower surface of the guide ring. The annular groove and the annular step are fitted together. A punch mounting hole is formed on the guide ring for clearance-fitting the forming punch. The central axis of the cavity in the forming die coincides with the central axis of the punch mounting hole in the guide ring, and the through hole in the pad block coincides with the central axis of the cavity.

[0008] Preferably, the annular groove has an inverted trapezoidal cross-section, the annular step has a trapezoidal cross-section, and the annular groove and the annular step are fitted together with a clearance fit.

[0009] Preferably, a stepped groove is formed on the lower end face of the guide ring.

[0010] Preferably, the cavity wall is designed with a draft angle to facilitate demolding.

[0011] Preferably, the circumferential surface of the through hole of the pad is tapered, which mates with the corresponding tapered surface on the pad to achieve installation guidance.

[0012] Preferably, the bottom of the cavity and the bottom of the molding die are connected by a continuous conical transition.

[0013] A method for reverse extrusion forming of thin-walled high-cylinder forgings using a free forging equipment, the specific steps of which are as follows:

[0014] Step 1: Heat the billet in the furnace to the forging temperature, hold it at that temperature, and then place the billet into a precast billet mold for upsetting to obtain the precast billet;

[0015] Step 2: Place the preform into the reverse extrusion molding die, and press down the forming punch to perform reverse extrusion molding;

[0016] Step 3: Flip and demold to obtain the formed forging.

[0017] Preferably, in step 1, the dimensions of the preform blank are consistent with the cavity dimensions of the forming mold.

[0018] Preferably, the specific steps of step 2 are as follows:

[0019] Step 2-1: Assemble the forming mold onto the pad block, and then assemble the forming punch and guide ring with clearance.

[0020] Step 2-2: The preform obtained in Step 1 is placed into the forming mold of the reverse extrusion molding die. Then, the assembled guide ring and forming punch are placed on the forming mold, and the annular groove on the upper end face of the forming mold and the annular step on the lower end face of the guide ring are used for positioning and centering.

[0021] Steps 2-3: Control the forming punch to move at a uniform speed of 10-15mm / s to back-extrude the preform to the target size, and control the final forging temperature ≥850℃ throughout the process.

[0022] Preferably, the formed forging after being flipped and demolded is subjected to normalizing and spheroidizing annealing heat treatments in sequence.

[0023] Beneficial effects: This invention provides a reverse extrusion forming die and forming method for thin-walled high-cylinder forgings, which has the following advantages:

[0024] (1) In this invention, the forming mold and the guide ring are positioned by using annular steps and annular grooves, and the guide ring and the forming punch form a clearance fit, which can effectively ensure that the forming punch and the blank are always in a precise center position, and the forming punch is rigidly constrained during the movement, thereby strictly maintaining its movement direction vertically downward, fundamentally eliminating the risk of uneven wall thickness of parts, abnormal wear of molds, or even damage caused by skew or misalignment, and effectively controlling the uniformity of wall thickness.

[0025] (2) The present invention utilizes a pre-made blank mold to pre-process the blank into a shape and size consistent with the final mold cavity, so that when the blank is placed into the mold, it can be automatically and accurately positioned at the center of the cavity by its own shape, providing ideal initial conditions for the final molding.

[0026] (3) The present invention utilizes the positioning and clearance fit between the annular step and the annular groove to overcome the limitation of the lack of guiding mechanism in free forging equipment, expands the applicable equipment range of the reverse extrusion process, and has a simple process flow, suitable for small batch and multi-specification production, and has high economy and flexibility. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the pre-fabricated billet processing in step 1 of Example 1;

[0028] Figure 2 This is a schematic diagram of the assembly of the mold and the pad block in step 2-1 of Example 1;

[0029] Figure 3 This is a schematic diagram of the assembly of the forming punch and the guide ring in step 2-1 of Example 1;

[0030] Figure 4 This is a schematic diagram of the reverse extrusion molding die assembly in step 2-1 of Example 1;

[0031] Figure 5 This is a schematic diagram of the reverse extrusion molding die forming process in step 2-2 of Example 1;

[0032] Figure 6 The image shows a micrograph (low magnification) of the molded sample from Example 1.

[0033] Figure 7 The image shows a high-magnification micrograph of the molded sample from Example 1.

[0034] Figure 8 A photograph of the grain size of the molded sample from Example 1;

[0035] Figure 9 This is a photograph of the non-metallic inclusions in the molded sample of Example 1.

[0036] In the figure: forming mold 1, annular groove 1-1, cavity 1-2, draft angle 1-21, conical surface 1-22, pad block through hole 1-3, conical surface 1-31, pad block mounting hole 1-4, pad block 2, guide ring 3, annular step 3-1, step groove 3-2, punch mounting hole 3-3, forming punch 4, precast blank 5, precast blank mold 6. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application are clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0038] Example 1:

[0039] This embodiment provides a method for reverse extrusion forming of thin-walled high-cylinder forgings using a free forging equipment, used to manufacture forgings made of D406A material. The rough machining target dimensions of the forging are: outer diameter φ430mm, inner diameter φ387mm, and height 415mm, with a dimensional tolerance of ±1mm. Φ300mm round steel is used as the raw material, with a blank size of Φ300mm × 374mm and a weight of 208Kg. The specific forming steps are as follows:

[0040] Step 1: Pre-forming the billet: Load billet 5 into the furnace and heat it to the forging temperature of 1180℃. After holding at this temperature, place billet 5 into the pre-forming billet mold 6, as follows... Figure 1 As shown, upsetting is performed on the billet. In this embodiment, the forging temperature is set according to the billet material, and the holding time can be calculated based on the effective wall thickness of the billet × 0.5 min / mm.

[0041] In step 1, the dimensions of the preform must be consistent with the dimensions of the cavity in the forming mold. That is, when the preform is placed into the forming mold, its dimensions must match the cavity dimensions. The height of the preform is determined by the weight of the blank; it is only necessary to ensure that the radial dimension of the preform matches the radial dimension of the cavity in the forming mold, thereby ensuring the coaxiality consistency between the blank and the cavity.

[0042] Step 2: Reverse Extrusion Molding: Place the preform 5 into the reverse extrusion molding die, and perform reverse extrusion molding using the upper anvil and lower pressing punch 4. The specific steps are as follows:

[0043] Step 2-1 Mold Assembly: As shown Figure 2 As shown, place the pad block 2 on the lower anvil of the free forging equipment, then assemble the forming die 1 onto the pad block 2, and then proceed as follows. Figure 3 As shown, the forming punch 4 and the guide ring 3 are fitted with a clearance. In this embodiment 1, the forming punch 4 and the guide ring 3 have a clearance fit with a single-sided clearance of 0.5-1mm.

[0044] Step 2-2 Precast billet positioning and centering: (e.g.) Figure 4 As shown, the preformed blank 5 obtained in step 1 is placed into the cavity 1-2 of the forming mold 1. Then, the guide ring 3 with the forming punch 4 assembled is placed on the forming mold 1. The annular groove 1-1 on the upper end face of the forming mold 1 and the annular step 3-1 on the lower end face of the guide ring 3 are used for positioning. The upper anvil is pressed down slightly, and the gap between the forming punch 4 and the guide ring 3 is observed and confirmed to be uniform, so as to ensure the alignment of the forming punch 4 and the cavity 1-2 of the forming mold 1.

[0045] In this embodiment 1, the dimensions of the preform 5 are consistent with the dimensions of the cavity 1-2, thereby ensuring that the central axes of the preform 5 and the cavity 1-2 coincide. The forming punch 4 and the punch mounting hole 3-3 on the guide ring 3 are fitted with clearance to ensure that their central axes coincide. At the same time, the guide ring 3 is fitted with the annular groove 1-1 of the forming mold 1 through the annular step 3-1 at its lower end, ensuring that the axis of the guide ring 3 and the cavity 1-2 coincide. Through this series of axis coincidence relationships from the inside to the outside (from the mold to the punch), the coaxiality between the forming punch 4 and the preform 5 is ultimately guaranteed.

[0046] Step 2-3 Reverse extrusion molding: as follows Figure 5 As shown, the driving equipment uses a pressing punch to achieve extrusion forming, ensuring a final forging temperature ≥850℃ throughout the process. To reduce frictional wear between the forming die 1 and the precast blank 5, a lubricant can be applied to the contact surface between them.

[0047] Step 3: Flipping and Demolding. In this embodiment, after the reverse extrusion is completed, the upper anvil is raised, the guide ring 3 is removed, and the forming mold 1 containing the forging and the forming punch 4 are flipped 180° using a lifting device. After the forming mold 1 leaves the original pad 2, a universal pad is replaced, and the forming forging is smoothly ejected from the forming mold 1 by pressing down with the upper anvil. This flipping and demolding method can overcome the limitation of free forging equipment without an ejection mechanism, realize the complete demolding of the forging, and avoid the deformation of the forging caused by forced ejection.

[0048] Step 4: Heat treatment: The formed forging after being turned over and demolded undergoes normalizing + spheroidizing annealing to refine the grains, homogenize the microstructure, and reduce hardness. The specific steps of this Example 1 are as follows:

[0049] Normalizing process: Load the furnace at ≤850℃, heat to 930℃, hold for 3 hours, then remove from the furnace and air cool;

[0050] Spheroidizing annealing heat regime: Load the furnace at ≤400℃, heat to 810℃, hold for 4 hours, cool in the furnace to 740℃, hold for 24 hours, cool in the furnace to 680℃, hold for 5 hours, cool in the furnace to 550℃, and then air cool after being removed from the furnace.

[0051] Step 5: Rough machining: After heat treatment, the formed forging is rough machined to a final size of φ430mm (outer diameter) × φ387mm (inner diameter) × 415mm (height), with a dimensional tolerance of ±1mm.

[0052] The specific structure of the reverse extrusion molding die used in this embodiment 1 is as follows: Figure 2-5 As shown, the device includes a forming mold 1, a pad 2, a guide ring 3, and a forming punch 4. The forming mold 1 has a cavity 1-2 with a top opening. The bottom of the forming mold 1 has a pad through hole 1-3 communicating with the cavity 1-2, and the pad 2 is fitted with the pad through hole 1-3. The upper end face of the forming mold 1 has an annular groove 1-1, and the lower end face of the guide ring 3 has an annular step 3-1. The annular groove 1-1 and the annular step 3-1 are fitted together. The guide ring 3 has a punch mounting hole 3-3 for clearance fitting of the forming punch 4. The central axis of the cavity 1-2 in the forming mold 1 coincides with the central axis of the punch mounting hole 3-3 in the guide ring 3, and the pad through hole 1-3 coincides with the central axis of the cavity 1-2.

[0053] In this embodiment 1, the cross-section of the annular groove 1-1 is an inverted trapezoidal structure, and the cross-section of the annular step 3-1 is a trapezoidal structure. The annular groove 1-1 and the annular step 3-1 are installed with a clearance fit, and the coaxiality of the two is ensured by using the principle of conical centering.

[0054] In this embodiment 1, a stepped groove 3-2 is provided on the lower end face of the guide ring 3. This structural design forms a load-bearing interface for reverse demolding on the one hand, and reserves material flow space for the reverse extrusion molding process of the billet on the other hand, thereby effectively avoiding forming defects caused by material overfilling.

[0055] To facilitate demolding, the walls of the cavity are designed with a draft angle. In this embodiment 1, the draft angle is preferably 1°, and the inner diameter of the cavity gradually increases from bottom to top.

[0056] In this embodiment 1, the through holes 1-3 of the pad block are tapered in the circumference, which cooperate with the corresponding tapered surface on the pad block 2 to achieve installation guidance, and at the same time facilitate the pad block 2 to detach from the molding mold 1 when demolding.

[0057] In this embodiment 1, the bottom of the cavity 1-2 and the bottom of the forming mold 1 are connected by a continuous conical transition, thereby providing guidance for the placement of the preform 5.

[0058] Based on the acceptance standard GJB3325A-2019, the mechanical properties of the forgings obtained in Example 1 were tested, and the specific test results are shown in Table 1.

[0059] Table 1 shows the mechanical performance test results of Example 1.

[0060]

[0061] As shown in Table 1, the thin-walled high-cylinder forgings obtained in Example 1 meet and exceed all standard requirements: their room temperature tensile properties (tensile strength, specified plastic extension strength, elongation after fracture, and reduction of area) are significantly higher than the lower limit of the standard; their Charpy impact absorption energy and fracture toughness are excellent, with average values ​​far exceeding the standard requirements; their Brinell hardness is moderate and lower than the upper limit; in terms of microstructure, the low-magnification and high-magnification structures are uniform and dense, without defects, with a grain size of grade 7, and non-metallic inclusions are well controlled. In summary, the mold and forming method of this invention successfully produced thin-walled high-cylinder forgings with high strength, excellent plasticity and toughness, and a uniform microstructure on a free forging machine, verifying the effectiveness and reliability of this technical solution in achieving high-precision reverse extrusion forming on a free forging machine.

[0062] The reverse extrusion forming die and forming method of the present invention are applicable to thin-walled high-cylinder forgings of different specifications and shapes, and meet the quality control requirements in industrial production.

[0063] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A backward extrusion forming die for a thin-walled high-cylinder forged product, characterized by, The application relates to a reverse extrusion forming die, which comprises a forming die, a cushion block, a guide ring and a forming punch, wherein an open-top cavity is arranged in the forming die, a cushion block through hole is arranged at the bottom of the forming die and communicates with the cavity, the cushion block is installed in cooperation with the cushion block through hole, an annular groove is arranged at the upper end surface of the forming die, an annular step is arranged at the lower end surface of the guide ring, the annular groove and the annular step are installed in cooperation, punch installation holes are arranged on the guide ring and used for gap cooperation installation of the forming punch, the center axis of the cavity in the forming die coincides with that of the punch installation holes of the guide ring, and the center axis of the cushion block through hole coincides with that of the cavity.

2. The inverse extrusion forming die for a thin-walled high-cylinder forged piece according to claim 1, characterized by The cross section of the annular groove is in an inverted trapezoidal structure, the step cross section of the annular step is in a trapezoidal structure, and the annular groove and the annular step are installed in cooperation.

3. The inverse extrusion forming die for a thin-walled high-cylinder forged piece according to claim 1, characterized by A step groove is arranged on the lower end surface of the guide ring.

4. The inverse extrusion forming die for a thin-walled high-cylinder forged piece according to claim 1, characterized by A demolding slope is arranged on the wall surface of the cavity, so that demolding is facilitated.

5. The inverse extrusion forming die for a thin-walled high-cylinder forged piece according to claim 1, characterized by The circumferential surface of the cushion block through hole is a conical surface which cooperates with a corresponding conical surface on the cushion block to realize installation and guidance.

6. The inverse extrusion forming die for a thin-walled high-cylinder forged piece according to claim 1, characterized by The bottom of the cavity is connected with the bottom end of the forming die through a continuous conical surface.

7. A method of backward extrusion forming thin-walled high-cylinder forgings in a free forging apparatus, characterized by, The reverse extrusion forming die is used for forming a thin-wall high-cylinder forged piece, and the specific steps are as follows: Step 1: a blank is heated in a furnace to a forging temperature, and after heat preservation, the blank is placed into a prefabricated blank die to be upset to obtain a prefabricated blank; Step 2: the prefabricated blank is placed into the reverse extrusion forming die, and a forming punch is pressed downward to perform reverse extrusion forming; Step 3: the forming die is turned over to be demolded to obtain a formed forged piece.

8. The method according to claim 7, wherein, In step 1, the size of the prefabricated blank is consistent with the size of the cavity of the forming die.

9. The method according to claim 7, wherein, The specific steps of step 2 are as follows: Step 2-1: the forming die is assembled on the cushion block, and then the forming punch and the guide ring are gap assembled; Step 2-2: the prefabricated blank obtained in step 1 is placed into the forming die of the reverse extrusion forming die, and then the assembled guide ring and the forming punch are placed on the forming die, and the annular groove at the upper end surface of the forming die and the annular step at the lower end surface of the guide ring are used for positioning and centering; Step 2-3: the forming punch is controlled to move at a uniform speed of 10-15 mm / s, the prefabricated blank is reverse extrusion processed to a target size, and the final forging temperature is controlled to be greater than or equal to 850 DEG C.

10. The method of claim 7, wherein the method is a method of reverse extrusion forming of a thin-walled high-cylinder forged product of a free forging apparatus, characterized by, The formed forged piece after the turning over demolding is sequentially subjected to normalizing and spheroidizing annealing heat treatment.

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