Uniform wall thickness control method for radial forging hollow component

Abstract

The invention relates to a method for controlling the uniform wall thickness of a radially forged hollow component. The method comprises the following steps: selecting a pipe blank and a core rod for hollow forging, wrapping the surface of one end of the pipe blank, painting an inner hole with an anti-oxidation coating, heating the pipe blank and lubricating the inner hole of a hot blank with glass powder, adopting proper rolling reduction during forging, configuring a blank feeding speed and a rotating angle of a precision forging machine during forging, controlling a forging sequence, and finishing and straightening at a high temperature. The high-precision hollow pipe blank and the core rod are adopted, and in order to achieve uniform deformation, friction is reduced from the temperature uniformity, anti-oxidation and lubrication modes of the blank; in order to ensure that metal flows are consistent, requirements are put forward from the aspects of forging deformation sequence and deformation parameter configuration; bending caused by forging and high-temperature normalizing is eliminated through radial warm forging, a key technology for controlling the wall thickness difference of the radial forging 40CrNi4Mo1V steel hollow component is formed, the wall thickness difference of a blank forging piece of the hollow component is smaller than or equal to 5 mm, the out-of-roundness of an inner hole is smaller than or equal to 3 mm, and the rough machining condition is met.

Description

Technical Field

[0001] This invention belongs to the field of material forming and relates to a method for controlling the uniform wall thickness of radially forged hollow components, specifically a method for controlling the uniform wall thickness of radially forged 4Ni-Cr-Mo-V steel hollow components. Background Technology

[0002] High-pressure load-bearing component blanks are manufactured using 4Ni-Cr-Mo-V ultra-high strength and toughness steel. The blanks are hollow stepped in shape, with an inner hole of φ60mm, an outer diameter of φ315-φ240mm, and a length of 8000mm. See the attached instruction manual for the final shape. Figure 1 The component blanks have a wall thickness difference ≤3mm, an inner hole curvature ≤3mm, and mechanical property requirements of Rp0.2≥1350MPa and -40℃KV≥25J. However, the hot forming process using multi-fire solid forging, i.e., free forging or free forging blanking + precision forging forming process, produces solid forging blanks, which are then machined into hollow component blanks through drilling and other machining processes. The first-pass performance satisfaction rate is only 42.9%, indicating insufficient performance reserves. Therefore, an advanced hollow extrusion forging composite forming technology is adopted to leverage the advantages of hot extrusion and hollow precision forging deformation to prepare hollow component blanks with uniform microstructure, refined grains, and continuous streamline distribution. This forming technology meets the mechanical property reserve requirements, but the preparation process requires two-fire hollow forging on a precision forging machine. The forged hollow component blanks have problems such as inner hole curvature, non-roundness, large wall thickness difference, and hole deviation. The shape is shown in the attached instruction manual. Figure 2 The inner hole bending reaches 8mm, the out-of-roundness Dmax-Dmix reaches 15mm, and the wall thickness difference Hmax-mix reaches 25mm.

[0003] In subsequent processing of hollow component blank forgings, the wavy bending of the inner hole affects the direction of the drilling tool, causing the drilling to deviate with the hole. The large difference in wall thickness of the forging leads to a large machining allowance correction of the outer circle, affecting the machining accuracy and material utilization rate. After machining, it is difficult to achieve the accuracy requirements of wall thickness difference ≤3mm and inner hole curvature ≤3mm. Summary of the Invention

[0004] This invention provides a method for controlling the uniform wall thickness of radially forged hollow components. The technical problem to be solved is that the manufacturing of 4Ni-Cr-Mo-V ultra-high strength and toughness steel hollow component blanks by hollow forging presents technical difficulties such as inner hole bending, non-roundness, large wall thickness difference, and hole deviation. This invention solves the wall thickness difference problem in the hollow forging process during extrusion forging and achieves the processing accuracy of hollow component blanks.

[0005] To solve the above technical problems, the present invention provides a method for controlling the uniform wall thickness of radially forged hollow components, characterized by the following steps: selecting a hollow forging tube blank and mandrel—wrapping one end of the tube blank—applying an anti-oxidation coating to the inner hole—heating the tube blank and lubricating the inner hole of the hot blank with glass powder—using an appropriate reduction during forging—configuring the blank feeding speed and rotation angle of the precision forging machine during forging—forging in order from small diameter to large diameter—high-temperature finishing and straightening.

[0006] Beneficial effects: This invention significantly improves the uniformity of wall thickness in hollow component blank forgings, creating processing conditions for the preparation of ultra-high strength and toughness steel hollow component blank forgings.

[0007] By using the wall thickness difference control technology for hollow forging components, the wall thickness difference of 4Ni-Cr-Mo-V steel hollow forgings is controlled within 5mm, and the out-of-roundness of the inner hole is controlled within 3mm. This meets the machining accuracy requirements of inner hole curvature ≤3mm and wall thickness difference ≤3mm for hollow component blanks, thus avoiding machining difficulties caused by large wall thickness differences. No abnormalities were found during the production of 5 samples. Attached Figure Description

[0008] Figure 1 Schematic diagram of a high-pressure load-bearing component blank;

[0009] Figure 2 Schematic diagram showing non-circular inner hole and large wall thickness deviation;

[0010] Figure 3 : Schematic diagram of the clamping end wrapping;

[0011] Figure 4 : The meaning of radial hollow forging sequence;

[0012] Figure 5 Schematic diagram for wall thickness detection of hollow component forgings. Detailed Implementation

[0013] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below.

[0014] The present invention proposes a method for controlling the uniform wall thickness of radially forged hollow components, comprising the following steps: selection of tube blanks and mandrels for hollow forging; wrapping one end of the tube blank surface; applying anti-oxidation coating to the inner hole; heating the tube blank and lubricating the inner hole of the hot blank with glass powder; using an appropriate reduction amount during forging; configuring the blank feeding speed and rotation angle of the precision forging machine during forging; controlling the forging sequence; and high-temperature finishing and straightening.

[0015] S1. Selection of tube blanks and mandrels for hollow forging

[0016] The tube blank for hollow forging uses hollow tube material with outer diameter D * inner diameter d * length L, with a diameter accuracy of ±2mm and a wall thickness difference of ≤5mm. The mandrel material is 45Cr5MoSiV1, and after phosphate treatment, the hardness is HRC45-48. The mandrel diameter accuracy is ±0.2mm, and the surface finish Ra is ≤3.2um.

[0017] S2, One end of the tube blank is wrapped with...

[0018] To prevent uneven forging temperatures caused by rapid heat transfer between the billet and the manipulator jaws, the billet clamping section in the first and second forging processes is wrapped with insulating cotton. The outer surface of the wrapped section is then coated with a layer of glass powder mixed with water (approximately 1:10 ratio), followed by a 25-30mm thick layer of aluminosilicate fiber blanket. The wrapping length is within 350mm. See the attached diagram for details on the wrapping process. Figure 3 The clamping section of the manipulator is wrapped with a thickness of 25-30mm and a length of 350mm from the end to prevent uneven temperature due to heat transfer at the clamping point after the clamp is released when forging.

[0019] S3. Apply anti-oxidation coating to the inner hole.

[0020] The inner hole of the billet is coated with an anti-oxidation coating. Before heating, the billet is placed in a heating furnace at 150-200℃ to preheat it. After holding it at that temperature for at least 0.5 hours, it is taken out and coated with an anti-oxidation coating of G20 grade alloy steel suitable for forging temperatures of 950-1250℃. Then, the inner holes at both ends of the billet are sealed after the aluminum silicate fiber blanket is bundled.

[0021] S4. Tube blank heating and hot billet inner hole glass powder lubrication

[0022] The tube blank is heated in a furnace at a temperature of 1210±10℃ for 3.5h / 100mm (wall thickness). To increase the uniformity of the deformation of the inner hole of the blank and reduce the friction between the mandrel and the inner hole, the inner hole is hot-sprayed with glass powder for lubrication after the tube blank is heated.

[0023] Before forging, the inner hole of the heating tube blank is hot-sprayed with 844-7 glass powder with a softening point of 750℃-780℃ for lubrication treatment, to ensure that the glass powder effectively softens the inner hole of the heat tube blank at a temperature above 920℃. The amount of glass powder added is calculated based on an adhesion of 1-2mm to the inner hole. During forging, the blank is rotated after being inserted into the mandrel, so that the molten glass powder adheres to the surface of the inner hole with a 90% adhesion rate.

[0024] S5. Use appropriate reduction during forging.

[0025] The gap δ between the forging mandrel and the inner hole of the billet should be between 25mm and 50mm. Heating the billet and bending it makes inserting the mandrel difficult; a minimum gap of 25mm is required. The forging inner hole should not deform and fold (inward folding). The maximum gap is 50mm. After the inner hole and mandrel are properly fitted, the inner hole deformation should reach more than 25%, eliminating inner hole out-of-roundness and meeting the performance requirements for deformation. The wall thickness H of the forged part after forging should, based on the forging deformation, have a reduction B ≥ δ / 1.08 + 25H / 75, eliminating inner hole out-of-roundness and meeting the performance requirements for deformation.

[0026] S6. During forging, properly configure the billet feed speed and rotation angle of the precision forging machine.

[0027] The billet rotation angle is configured according to the billet feed speed. Each hammer strikes at least once at each point in the finishing section to achieve inner hole rounding. The billet rotation angle is r, the hammer length in the finishing section is L, the billet feed speed is N (mm / min), the hammer strike frequency is K (times / min), and the number of strikes to achieve finishing at each point is V = (L*K) / (4*N). The rounding is performed downwards to an integer, and the rotation angle is r = 90 / V.

[0028] S7. Forging sequence control: Forging should proceed from small diameter to large diameter.

[0029] To avoid uneven deformation and wall thickness differences caused by the mismatch between the step cross-section change and the hammer head deformation section, the hollow component blanks should be forged in a precision forging machine in the following order: forge the smaller dimensions first, then forge the larger dimensions. See [link to forging sequence]. Figure 4 .

[0030] S8. After warm forging, finishing, and straightening, low-temperature annealing is performed.

[0031] During the annealing process, after the 840℃ normalizing process is completed and the surface temperature reaches 600℃-750℃ during the air cooling stage, warm forging and straightening are performed on the precision forging machine using an R180 flat hammer head. The finishing reduction is 3mm, and the finishing forging batch is 240 times / min. After the finishing warm forging, the product is put into the furnace for subsequent annealing treatment.

[0032] High-precision hollow tube blanks and mandrels are used to create conditions for achieving uniform wall thickness. Uniform deformation during the hollow forging process of precision forging machine is achieved by controlling the oxidation of the blank, lubrication, deformation parameter configuration, and forging sequence. This solves the problem of inconsistent metal flow during the forming process. Radial warm forging finishing and straightening improves the wavy shape of the inner hole caused by subsequent straightening by the straightening machine, and solves the technical problems of large wall thickness deviation and inner hole deviation in radial hollow forging.

[0033] This invention enables the production of large hollow component blanks of various specifications with outer diameters of 250-400mm, hole diameters of 60mm-150mm, and lengths ≤8000mm, laying the foundation for improving rough machining accuracy and increasing material utilization. It allows for controlling the wall thickness difference of radial hollow forgings within a 5mm range, smoothly realizing the machining of hollow component blanks and avoiding machining difficulties caused by large wall thickness differences.

[0034] Example:

[0035] Specifications and dimensions of blank forgings for pressure-bearing hollow components:

[0036] Φ320*3350+Φ290*2650+Φ270*900+Φ250*3800 / Φ60, unit mm. Drawing output:

[0037] 1. Preparation of tube blank materials;

[0038] The rough-machined tube blank is formed by extrusion of electroslag remelted steel ingot. The tube blank size is φ515 / φ160×2750mm, and the wall thickness difference is ≤3mm.

[0039] 2. Selection of forged mandrel

[0040] The tube blank is forged into a hollow component blank through a two-stage forging process. The first stage of hollow forging uses a φ110mm mandrel, and the second stage uses a φ60mm mandrel. The mandrel is made of 4Cr5MoSiV1 material, with a phosphated surface treatment, a surface hardness of HRC46, and a surface roughness of 1.6µm.

[0041] 3. Preheating of the tube blank

[0042] The billet is preheated in a furnace at 180℃ for 1.5 hours. After removal, the inner hole of the billet is coated twice with G20 anti-oxidation paint, and both ends of the inner hole are sealed with aluminum silicate asbestos. A layer of glass powder mixed with water (approximately 1:10 ratio) is applied to the outer surface of one end within a 400mm radius. Then, a 30mm thick layer of aluminum silicate fiber blanket is wrapped around it. The billet is then loaded into the furnace for preheating at a furnace temperature ≤550℃. It is held at 500℃-550℃ for 3 hours, then heated to 700℃-800℃ for further preheating, and held at this temperature for at least 5 hours. Finally, the heating temperature is 1210℃, and the holding time is 6.0 hours. After holding, a single-fire hollow forging is performed.

[0043] 4. Hollow forging in one firing process

[0044] After the billet is removed, 8 kg of 844-7 glass powder is sprayed into the inner hole, and the mandrel is coated with MoS2 lubricant. After the billet is inserted into the Φ110mm mandrel, it rotates 360° twice and then undergoes hollow forging. The forging parameters are 180 forgings / min, billet feed speed of 1.2m / min, and billet rotation angle of 12.8°. One end is forged into a φ380mm×2800mm section, and the remaining part is forged into a φ420mm section, with a total length of approximately 4600mm.

[0045] 5. Hollow forging in two stages

[0046] When the tube blank cools to 180℃, 12Kg of 844-7 glass powder is sprayed into the inner hole, and the mandrel is coated with MoS2 lubricant. The tube blank is then inserted into a Φ60mm mandrel. After the manipulator clamps and wraps the section, the tube blank rotates 360° twice, and then hollow forging is performed. The forging parameters are 180 forgings / min, a billet feed speed of 1.2m / min, and a billet rotation angle of 12.8°. First, one end of the φ380mm section is forged into a φ250mm×2800mm section, and then successively forged into a Φ270*900mm section. Then, the φ420mm section is forged into Φ290*2650mm and Φ320*3350mm sections. The total length is approximately 8000mm.

[0047] 6. Warm forging finishing during annealing process

[0048] After the annealing and normalizing process at 840℃ is completed, the surface temperature is taken out during the air cooling stage and reaches below 750℃. The surface is then straightened by warm forging with an R180 flat hammer on a precision forging machine. The finishing reduction is 3mm, and the finishing forging batch is 240 times / min. After the finishing warm forging, the surface is put into the original furnace for subsequent annealing processes.

[0049] 7. Forging wall thickness inspection

[0050] Five hollow component blanks were inspected, covering six generatrices along their total length. Inspection points were taken at 60° intervals along the same cross-section. The maximum wall thickness difference was 4.2 mm. Inspection details are attached. Figure 5 Positions 1 and 6, 2 and 5, and 3 and 4 are 180° apart, and the wall thickness difference between the corresponding points is the wall thickness difference.

[0051] 8. Hollow forgings meet rough machining conditions. After rough machining, the maximum bending of the inner hole is 2.5mm and the maximum wall thickness difference is 2.3mm, which meets the requirements for precision forging of blanks.

[0052] This invention uses "high-precision hollow tube blanks and mandrels" to create conditions for achieving uniform wall thickness in hollow components. It reduces friction and increases centering uniformity by addressing issues related to "temperature uniformity, oxidation prevention, and lubrication methods" in the blank. Then, through "forging deformation sequence and deformation parameter configuration," it ensures consistent inner hole roundness and metal flow during the hollow forging process in a precision forging machine. "Radial warm forging" eliminates bending caused by forging and high-temperature normalizing, and improves the wavy shape of the inner hole caused by straightening. This invention provides a method for controlling the uniform wall thickness of radially forged 4Ni-Cr-Mo-V steel hollow components, solving technical problems such as large wall thickness deviation, inner hole deviation, and non-roundness in radially forged hollow component blanks. It achieves a wall thickness difference of ≤5mm and an inner hole roundness of ≤3mm in hollow component blanks, meeting the requirements for rough machining.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles 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 method for controlling the uniform wall thickness of radially forged hollow components, characterized in that, The steps are as follows: Select a hollow forging tube blank and mandrel — Wrap one end of the tube blank surface — Apply an anti-oxidation coating to the inner hole — Heat the tube blank and lubricate the inner hole of the hot blank with glass powder — Use an appropriate reduction during forging — Configure the blank feeding speed and rotation angle of the precision forging machine during forging — Forge in order from small diameter to large diameter — High-temperature finishing and straightening.

2. The method for controlling the uniform wall thickness of radially forged hollow components according to claim 1, characterized in that: Hollow tube blanks for hollow forging are made of hollow tube material with outer diameter D * inner diameter d * length L.

3. The method for controlling the uniform wall thickness of radially forged hollow components according to claim 1, characterized in that: Used for forging hollow components made of 4Ni-Cr-Mo-V steel.

4. The method for controlling the uniform wall thickness of radially forged hollow components according to claim 1, characterized in that: The mandrel is made of 45Cr5MoSiV1, and its hardness is HRC45-48 after phosphating. The diameter accuracy of the mandrel is ±0.2mm, and the surface finish Ra≤3.2um.

5. The method for controlling the uniform wall thickness of radially forged hollow components according to claim 1, characterized in that: The diameter accuracy of the raw material tube blank is ±2mm, and the wall thickness difference is ≤5mm.

6. The method for controlling the uniform wall thickness of radially forged hollow components according to claim 1, characterized in that: For the surface wrapping of one end of the tube blank, specifically: the tube blank clamping section of the first and second forging manipulators is wrapped with heat insulation cotton, and the outer surface of the wrapped section is coated with a layer of glass powder mixed with water at a ratio of about 1:10, and then wrapped with a 25-30mm thick layer of aluminum silicate fiber blanket.

7. The method for controlling the uniform wall thickness of radially forged hollow components according to claim 1, characterized in that: The inner hole of the billet is coated with an anti-oxidation coating. Before heating, the billet is placed in a heating furnace at 150-200℃ to preheat it. After holding it at that temperature, it is taken out and coated with an anti-oxidation coating suitable for alloy steel with a forging temperature of 950-1250℃. Then, the inner holes at both ends of the billet are sealed after the aluminum silicate fiber blanket is bundled.

8. A method for controlling the uniform wall thickness of radially forged hollow components according to any one of claims 1-8, characterized in that: Before forging, the inner hole of the heating tube blank is hot-sprayed with 844-7 glass powder with a softening point of 750-780℃ for lubrication treatment. The amount of glass powder added is calculated based on an adhesion of 1-2mm to the inner hole. During forging, the tube blank is rotated after being inserted into the mandrel. The tube blank is then heated in the furnace at a temperature of 1210±10℃.

9. A method for controlling the uniform wall thickness of radially forged hollow components according to any one of claims 1-8, characterized in that: The gap δ between the forging mandrel and the inner hole of the billet is between 25mm and 50mm. After the inner hole and the mandrel are fitted together, the deformation of the inner hole reaches more than 25%. The reduction amount B ≥ δ / 1.08 + 25H / 75, where H is the wall thickness of the forging after forging. In the finishing section, each point is hit at least once by each hammer to achieve the rounding of the inner hole. The billet rotation angle r, the length of the hammer head in the finishing section L, the billet feeding speed N, the hammer head hitting frequency K, and the number of times V = (L*K) / (4*N) is used to achieve finishing at each point. The rounding is then carried out downwards to an integer.

10. A method for controlling the uniform wall thickness of radially forged hollow components according to any one of claims 1-8, characterized in that: After the annealing and normalizing process at 840℃ is completed, the surface temperature is taken out during the air cooling stage and is below 750℃. It is then warm forging, finishing and straightening on a precision forging machine. After finishing and warm forging, it is put into the original furnace for subsequent annealing processes.

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