Oil pressure heading local heating process for reducing energy consumption

Abstract

The application relates to the technical field of metal plastic working, and particularly discloses an oil pressure upsetting head local heating billet forging process capable of reducing energy consumption, which comprises the following steps: firstly, determining an effective deformation volume according to a target upsetting head forming volume and an effective volume of a billet mold cavity, and calculating a theoretical deformation length, so as to determine a total local heating length; secondly, dividing an end portion of a blank into a main plastic deformation zone, a gradient transition deformation zone and a low-temperature constraint zone, heating the main plastic deformation zone to a first temperature, heating the gradient transition deformation zone to a second lower temperature, and limiting the diffusion of heat to the low-temperature constraint zone; thirdly, placing the blank into the billet mold, and completing upsetting, filling and shaping through axial pressure of an oil pressure head, and correcting subsequent heating parameters according to a pressure-displacement curve. The application can reduce invalid heating length, reduce energy consumption, make the gradient transition deformation zone block deformation diffusion in the early stage and limitedly supplement material in the later stage, so as to improve the problems of underfilling, cracks, flash and bulging in the later stage.

Description

Technical Field

[0001] This invention relates to the field of metal plastic forming technology, and in particular to a hydraulic upsetting head local heating forging process that reduces energy consumption. Background Technology

[0002] Hydraulic upsetting is a common plastic forming process used for machining metal bars, rods, pins, tie rods, and end-bearing components. It typically involves first heating the end of the blank or a certain length to a temperature suitable for plastic deformation. The blank is then placed into a die or fixture, and hydraulic pressure is applied axially along the blank using a hydraulic press head. This causes the blank end to be upset, filled, and shaped within the die cavity, resulting in an upset head structure with a thickened end. Existing publicly available documents already describe methods involving heating the end before upsetting. Axial upsetting techniques, such as CN106040913A which discloses a method for heating and upsetting the ends of reinforcing bars, involve heating and maintaining the temperature of the reinforcing bar ends using heating electrodes, and then applying upsetting force along the length of the reinforcing bar to form an enlarged upset head within an upsetting fixture. CN106670368A discloses a hot round steel end upsetting device, which also addresses the forming requirements of large-sized ends of long rod-shaped round steel bars, reducing raw material specifications and production costs through end upsetting. Therefore, end heating or hot end upsetting is already a common technical approach in the thickening and forming of bar stock ends.

[0003] However, the aforementioned end-heated upsetting or hot round steel end-heating technologies mainly focus on how to complete end heating, clamping, and axial upsetting. They lack further zonal control regarding the effective deformation volume of the billet end actually participating in the filling of the mold cavity, the matching relationship between the total length of local heating and the material replenishment capacity, and the differences in the role of different axial temperature sections in the early and late stages of upsetting. In actual hydraulic upsetting forging production, to ensure sufficient filling of the mold cavity, a long area of ​​overall heating or near-uniform temperature heating is often used. This method easily causes softening of non-target deformation areas, leading to increased ineffective heating energy consumption, oxidation burn-off, and increased flash, and may also cause bulging in the later stage of the billet. If the heating length is simply shortened to reduce energy consumption, it is easy to cause insufficient filling of the outer edge, root cracks, or folds due to insufficient high-temperature ductile metal at the end. At the same time, existing processes mostly rely on experience to determine the heating length and heating temperature, lacking feedback correction for pressure-displacement changes during the forming process, making it difficult to judge in time the state of insufficient material replenishment in the gradient transition area or premature softening in the later stage, resulting in a difficulty in achieving both energy saving effect and forming stability. Summary of the Invention

[0004] The technical problem to be solved by this invention is that the existing end-heated upsetting process is difficult to balance energy saving and forming quality. Overall heating of a long area is prone to high energy consumption, flash and bulging. Simply shortening the heating length is prone to underfilling, cracks or folds. Moreover, there is a lack of feedback correction based on the forming process. Therefore, a hydraulic upsetting head local heating forging process with reduced energy consumption is proposed.

[0005] To achieve the above objectives, this application adopts the following technical solution: a hydraulic upsetting head local heating forging process with reduced energy consumption, comprising the following steps:

[0006] S1: Determine the effective deformation volume of the billet end that needs to participate in plastic flow based on the forming volume of the target upsetting head and the effective volume of the mold cavity, and determine the theoretical deformation length based on the effective deformation volume and the original cross-sectional area of ​​the billet.

[0007] S2: Determine the total length of local heating at the end of the billet based on the theoretical deformation length. Within the total length of local heating, divide the section near the end of the billet into the main plastic deformation zone, divide the section behind the main plastic deformation zone into the gradient transition deformation zone, and form a low-temperature constraint zone behind the gradient transition deformation zone.

[0008] S3: Local gradient heating is applied to the end of the billet, so that the main plastic deformation zone is heated to the first temperature, the gradient transition deformation zone is heated to the second temperature which is lower than the first temperature, and the heat is restricted from continuing to diffuse to the low temperature constraint zone. This allows the gradient transition deformation zone to have a higher deformation resistance than the main plastic deformation zone in the early stage of hydraulic upsetting, and to generate limited material replenishment in the direction of the diameter expansion forming section after the filling resistance of the mold cavity increases.

[0009] S4: Place the billet after local gradient heating into the mold, so that the main plastic deformation zone corresponds to the expansion forming section of the mold cavity, so that the gradient transition deformation zone is at least located in the mold entrance constraint section of the mold cavity, and so that the low temperature constraint zone is supported or clamped by the clamping and positioning part.

[0010] S5: Upsetting, filling, and shaping of the blank end within the mold cavity;

[0011] S6: Collect pressure signals and displacement signals of the hydraulic upsetting head during the process, form a pressure-displacement curve, and correct the total length of local heating of the subsequent billet, the second temperature or the length of the gradient transition deformation zone based on the pressure-displacement curve.

[0012] Preferably, the effective deformation volume is determined based on the target upsetting head solid volume, transition fillet volume, allowable flash volume, and oxidation burn-off compensation volume; when the billet is a solid round bar, the theoretical deformation length is determined according to the ratio of the effective deformation volume to the original cross-sectional area of ​​the billet.

[0013] Preferably, the total length of the local heating is 1.05 to 1.30 times the theoretical deformation length.

[0014] Preferably, the total length of the local heating is 1.10 to 1.18 times the theoretical deformation length.

[0015] Preferably, the total length of local heating is composed of the length of the main plastic deformation zone and the length of the gradient transition deformation zone, and the low-temperature constraint zone is not included in the total length of local heating; wherein, the main plastic deformation zone accounts for 60% to 85% of the total length of local heating, and the gradient transition deformation zone accounts for 15% to 40% of the total length of local heating.

[0016] Preferably, the main plastic deformation zone accounts for 68% to 78% of the total length of local heating, and the gradient transition deformation zone accounts for 22% to 32% of the total length of local heating.

[0017] Preferably, the first temperature is 900°C to 1100°C, and the second temperature is 80°C to 250°C lower than the first temperature; the second temperature is the temperature representing the temperature measurement position within the gradient transition deformation zone.

[0018] Preferably, the first temperature is 960°C to 1030°C, and the second temperature is 120°C to 180°C lower than the first temperature; the temperature measurement position is located near the rear end of the gradient transition deformation zone, or is the detection position corresponding to the second heating unit.

[0019] Preferably, the hydraulic upsetting head includes a pre-upsetting stage, a die filling stage, and a pressure holding and shaping stage; in the pre-upsetting stage, the hydraulic head advances axially at a speed of 20 mm / s to 60 mm / s; in the die filling stage, the hydraulic head continues to press the billet at a speed of 3 mm / s to 15 mm / s; in the pressure holding and shaping stage, the hydraulic head holds pressure for 2s to 20s after reaching the final forging position.

[0020] An upsetting die forging is formed from metal bar, rod or shaft blank through end local gradient heating, die positioning and hydraulic upsetting die forging, and its end has a thickened upsetting structure.

[0021] The technical effects and advantages of this invention are as follows:

[0022] In this invention, the effective deformation length that the billet end actually needs to participate in plastic flow is first determined based on the effective volume of the mold cavity and the target upsetting volume. Then, the local heating area is divided into a main plastic deformation zone and a gradient transition deformation zone, with a low-temperature constraint zone remaining behind it. In this way, the main plastic deformation zone can preferentially complete upsetting and mold filling at a higher temperature, the gradient transition deformation zone can hinder the backward diffusion of high-temperature metal in the early stage of forming, and can provide limited material replenishment when the resistance of the mold cavity increases in the later stage of forming, while the low-temperature constraint zone restricts the softening and bulging of non-target areas. Thus, while reducing the ineffective heating length and heating energy consumption, it avoids underfilling, cracking or folding caused by insufficient plastic metal in ordinary local heating, and can also alleviate the problems of increased flash, oxidation burn-off and bulging of the billet in the later stage caused by heating at the same temperature or overall heating.

[0023] Meanwhile, the pressure-displacement curve provides feedback on the hydraulic upsetting process. When an abnormally steep pressure rise occurs near the final forging position, it indicates insufficient material replenishment in the gradient transition deformation zone. When the pressure is low but the flash or bulge increases, it indicates that the local heating length or second temperature is too high, thus providing a basis for correcting the heating length, second temperature, or gradient transition deformation zone length of the subsequent billet. This feedback method can reduce the fluctuations caused by setting heating parameters solely based on experience, enabling the process to maintain relatively stable forming quality under different material batches, mold temperatures, and transfer times, thereby balancing energy saving, filling integrity, and batch processing stability. Attached Figure Description

[0024] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0025] Figure 1 This is a schematic diagram of the process for reducing energy consumption in hydraulic upsetting head local heating forging according to the present invention;

[0026] Figure 2 This is a schematic diagram showing the division of the local gradient heating region at the end of the billet according to the present invention;

[0027] Figure 3 This is a schematic diagram of the structure of the local heating device of the present invention in conjunction with the billet;

[0028] Figure 4 This is a cross-sectional schematic diagram of the present invention, showing the process of hydraulic upsetting after the blank is placed into the mold.

[0029] Figure 5 This is a schematic diagram illustrating the pressure-displacement curve feedback correction during the hydraulic upsetting process of the present invention;

[0030] Figure 6This is a schematic diagram of the axial temperature distribution of the billet after local gradient heating according to the present invention.

[0031] Figure 7 This is a schematic diagram comparing the pressure-displacement curves of the hydraulic upsetting head under different heating methods according to the present invention.

[0032] Legend: 1. Pressure detection unit; 2. Hydraulic pressure head; 3. Clamping and positioning part; 4. Tire mold; 5. Tire mold inlet constraint section; 6. Diameter expansion forming section; 7. Tire mold cavity; 8. Temperature detection unit; 9. First heating unit; 10. Second heating unit; 11. Temperature limiting unit. Detailed Implementation

[0033] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0034] like Figures 1 to 4 As shown, the present invention provides a hydraulic upsetting head local heating die forging process with reduced energy consumption, which is applicable to metal bars, rods, shafts, pins, tie rods and other blanks whose ends need to be formed with thickened heads.

[0035] The main components include: pressure detection unit 1, hydraulic pressure head 2, clamping and positioning part 3, mold 4, mold inlet constraint section 5, diameter expansion forming section 6, mold cavity 7, temperature detection unit 8, first heating unit 9, second heating unit 10, temperature limiting unit 11, and control unit, etc.

[0036] Based on the effective volume of the mold cavity 7 and the target upsetting volume, the process determines the effective deformation length at the end of the billet that needs to participate in plastic flow, and forms the main plastic deformation zone, gradient transition deformation zone and low temperature constraint zone on the basis of the effective deformation length.

[0037] The main plastic deformation zone is used to undertake the main upsetting and mold filling functions; the gradient transition deformation zone has a blocking effect in the early stage of forming, which is used to limit the excessive diffusion of the main plastic deformation zone to the rear of the billet, and generates limited plastic flow in the later stage of forming as the resistance in the mold cavity 7 increases, which is used to replenish metal to the main plastic deformation zone; the low temperature constraint zone is used to limit the plastic bulging of non-target areas, so that the metal flow is concentrated in the mold cavity 7.

[0038] To achieve the aforementioned localized gradient heating, a localized heating device is provided, such as... Figure 3As shown, the local heating device includes a first heating unit 9, a second heating unit 10, and a temperature limiting unit 11. The first heating unit 9 is located on the outer side of the end of the billet and corresponds to the main plastic deformation zone. It is used to heat the main plastic deformation zone to a first temperature suitable for hydraulic upsetting. The second heating unit 10 is located behind the first heating unit 9 and corresponds to the gradient transition deformation zone. It is used to heat the gradient transition deformation zone to a second temperature lower than the first temperature. The temperature limiting unit 11 is located behind the second heating unit 10 and close to the low-temperature constraint zone. It is used to limit the heat from continuing to transfer to the rear section of the billet, so that the low-temperature constraint zone maintains a high deformation resistance during hydraulic upsetting.

[0039] The first heating unit 9 and the second heating unit 10 can be a ring induction coil, a resistance heating jacket, a segmented flame nozzle, or other structures capable of heating different sections of the billet along the axial direction. In order to facilitate the formation of a stable axial temperature gradient, a ring induction coil is preferred. When a ring induction coil is used, the first heating unit 9 and the second heating unit 10 are arranged at intervals along the axial direction of the billet. They can be connected to independent power output terminals or to different power control channels of the same power supply. By making the input power, energizing time, or equivalent heating intensity of the first heating unit 9 greater than that of the second heating unit 10, the temperature of the main plastic deformation zone is higher than that of the gradient transition deformation zone.

[0040] The second heating unit 10 is not used to fully heat the gradient transition deformation zone to the same temperature as the main plastic deformation zone, but to enable the gradient transition deformation zone to obtain limited plasticity. Limited plasticity means that the gradient transition deformation zone still has a higher deformation resistance than the main plastic deformation zone in the early stage of hydraulic upsetting, which can limit the main plastic deformation zone from spreading backward. When the mold cavity 7 is gradually filled and the hydraulic upsetting pressure increases, the gradient transition deformation zone can generate a small amount of plastic flow to supplement metal in the direction of the diameter expansion forming section 6.

[0041] The temperature limiting unit 11 can be a heat insulation sleeve, a cooling jacket, a heat-resistant baffle, or a temperature limiting ring with a cooling channel. The temperature limiting unit 11 can be fixed on the bracket of the local heating device or on the base of the heating station, and maintain a gap with the outer periphery of the billet that does not affect the axial movement of the billet. The temperature limiting unit 11 does not actively heat the billet. Its function is to block or weaken the heat after the second heating unit 10 from continuing to diffuse into the low-temperature constraint area. After using the temperature limiting unit 11, the low-temperature constraint area is less likely to soften prematurely during the heating stage, so that the material itself can form an axial deformation boundary during the subsequent hydraulic upsetting.

[0042] It should be noted that, Figure 3 The local heating device shown represents the local gradient heating station before the billet enters the mold 4. Figure 4The mold 4 and hydraulic press head 2 shown represent the hydraulic upsetting station after the billet has been locally heated. They can be set as independent stations or as adjacent stations on the same production line.

[0043] Temperature detection unit 8 is used to detect the temperature of the main plastic deformation zone and the gradient transition deformation zone. Temperature detection unit 8 can be an infrared thermometer, a dual-color thermometer, a thermal imager, or a thermocouple. In mass production, a non-contact infrared thermometer or thermal imager is preferred to avoid the detection component affecting the blank entering the mold. During the process debugging stage, a temporary thermocouple can also be used for calibration. Temperature detection unit 8 is provided with at least two temperature measurement positions corresponding to the main plastic deformation zone and the gradient transition deformation zone to obtain the first temperature and the second temperature respectively.

[0044] The pressure detection unit 1 is used to collect pressure signals during the hydraulic upsetting process. The pressure detection unit 1 can be set in the oil circuit of the hydraulic equipment, or it can be set in the hydraulic head 2 or the force-bearing part of the hydraulic equipment. The control unit can be a PLC, an industrial computer, or a controller with data acquisition function. The control unit is connected to the temperature detection unit 8, the pressure detection unit 1, the first heating unit 9, and the second heating unit 10 respectively. It is used to record temperature and pressure data, and obtain the displacement signal of the hydraulic head 2 through the stroke detection component of the hydraulic equipment or the control unit, thereby forming a pressure-displacement curve. Based on the pressure-displacement curve, it is determined whether the heating length, second temperature, or pressing parameters of the subsequent billet need to be corrected.

[0045] like Figure 5 As shown, when the material replenishment capacity in the later stage of the gradient transition deformation zone is insufficient, the control unit generates a pre-correction measured pressure-displacement curve based on pressure and displacement signals. This curve will show a rapid and sharp increase in pressure relative to the reference curve just before the final forging position. Combined with the detection results of underfilling at the outer edge or corner of the upsetting head after demolding, it can be determined that the material replenishment capacity in the later stage of the gradient transition deformation zone is insufficient. In this case, the corrected curve of the subsequent billet can be made closer to the reference curve relative to the pre-correction measured curve by increasing the second temperature, increasing the length of the gradient transition deformation zone, or appropriately adjusting the total length of local heating. Figure 5 The reference curve in the figure is used to represent the pressure-displacement variation trend under the target forming state, the measured curve before correction is used to represent the actual forming response under the initial parameters, and the curve after correction is used to represent the forming response after parameter correction.

[0046] like Figure 4As shown, the mold 4 has a mold cavity 7, which includes a mold inlet constraint section 5 and a diameter expansion forming section 6. The mold inlet constraint section 5 is used to limit the radial expansion of the rear section of the billet and to keep at least the front part of the gradient transition deformation zone under constraint. The diameter expansion forming section 6 is used to constrain the metal at the end of the billet to form the target upsetting head shape. The clamping and positioning part 3 is located on the rear side of the mold 4 or the rear side of the mold inlet constraint section 5, and is used to support or clamp the billet so that the low temperature constraint zone remains axially stable during the hydraulic upsetting process. The hydraulic pressure head 2 is located on one side of the tail of the billet and advances along the axis of the billet to apply axial pressure to the billet, so that the end of the billet is upset and filled in the mold cavity 7.

[0047] The process of this invention can be implemented according to the following steps.

[0048] Step 1: Determine the billet parameters and target upsetting head parameters

[0049] Select the blank to be processed, and obtain the blank's material, diameter, initial end length, surface oxidation state, outer diameter, height, transition fillet size, allowable flash amount, and effective volume of the mold cavity 7. The effective volume of the mold cavity 7 can be calculated based on the mold design drawing, or determined by three-dimensional modeling, coordinate measuring machine measurement, wax injection measurement, or filling volume measurement.

[0050] In this step, the effective volume of the mold cavity 7 is not only roughly estimated based on the target upsetting head shape, but also includes the transition part that needs to be filled near the mold inlet constraint section 5, the rounded corner part of the diameter expansion forming section 6, the step part, and the allowable flash space. This can avoid the subsequent local heating length being too short, resulting in underfilling of the outer edge or corner of the diameter expansion forming section 6.

[0051] Step 2: Determine the effective deformation volume and the theoretical deformation length.

[0052] The effective deformation volume Ve is determined based on the solid volume of the target upsetting head, the volume of the transition fillet, the volume of the allowable flash, and the volume of oxidation loss compensation. When the billet is a solid round bar, the original cross-sectional area A0 of the billet is calculated according to the billet diameter, and the theoretical deformation length L0 is determined according to Ve / A0.

[0053] The theoretical deformation length L0 represents the axial length of the billet that needs to participate in plastic flow under ideal conditions. However, in actual production, there are heating transfer temperature drops, oxidation burn-off, die corner replenishment, and flash loss. Directly using L0 as the heating length is usually too small. Therefore, this invention further sets a compensation amount based on L0.

[0054] Step 3: Determine the total length of local heating

[0055] The total length of local heating, Lh, is determined to be 1.05 to 1.30 times the theoretical deformation length, L0. For commonly used carbon steel, medium-diameter bars, and general flange-shaped or stepped upsetting heads, the total length of local heating, Lh, is preferably determined to be 1.10 to 1.18 times L0.

[0056] When Lh is less than 1.05 times L0, although the heating energy consumption is low, the amount of high-temperature plastic metal is insufficient. The gradient transition deformation zone in the later stage of forming cannot provide effective material replenishment, which easily leads to underfilling or fine cracks at the root. When Lh is more than 1.30 times L0, the non-target area is heated for too long, and the later part of the billet softens significantly, which easily causes the flash to increase and bulging near the low-temperature constraint zone.

[0057] Step 4: Divide the main plastic deformation zone and the gradient transition deformation zone.

[0058] like Figure 2 As shown, within the total length Lh of local heating, the section near the end of the billet is divided into the main plastic deformation zone, and the section behind the main plastic deformation zone is divided into the gradient transition deformation zone. The total length Lh of local heating is composed of the length of the main plastic deformation zone and the length of the gradient transition deformation zone. The low-temperature constraint zone is not included in the total length Lh of local heating.

[0059] The main plastic deformation zone accounts for 60% to 85% of the total local heating length Lh, preferably 68% to 78%; the gradient transition deformation zone accounts for 15% to 40% of the total local heating length Lh, preferably 22% to 32%.

[0060] The main plastic deformation zone is used to form the main body of the upsetting head. This area has a high temperature and low deformation resistance, and can preferentially generate axial compression and radial flow under the action of the hydraulic pressure head 2. The gradient transition deformation zone does not fully participate in plastic flow in the early stage of upsetting, but maintains a relatively high deformation resistance in the early stage of forming, limiting the diffusion of the main plastic deformation zone to the rear of the billet. When the diameter expansion forming section 6 is gradually filled and the forming pressure increases, the gradient transition deformation zone generates limited plastic flow again, feeding material to the main plastic deformation zone. The low temperature constraint zone is located behind the gradient transition deformation zone and is not actively heated. It is used to form the axial deformation boundary.

[0061] Step 5: Perform local gradient heating

[0062] like Figure 3 As shown, the first heating unit 9 is positioned to correspond to the main plastic deformation zone, the second heating unit 10 is positioned to correspond to the gradient transition deformation zone, and the temperature limiting unit 11 is positioned behind the second heating unit 10 and close to the low temperature constraint zone. The first heating unit 9 and the second heating unit 10 are then activated to heat the billet in zones.

[0063] For steel billets, the first temperature of the main plastic deformation zone is controlled at 900℃ to 1100℃, preferably 960℃ to 1030℃; the second temperature of the gradient transition deformation zone is 80℃ to 250℃ lower than the first temperature, preferably 120℃ to 180℃ lower; the second temperature can be the temperature representing the temperature measurement position within the gradient transition deformation zone, preferably the temperature near the rear end of the gradient transition deformation zone or the corresponding detection position of the second heating unit 10; when the first temperature is too low, the deformation resistance of the main plastic deformation zone is large, and cracks are prone to occur during hydraulic upsetting; when the first temperature is too high, oxidation loss increases significantly, and unit energy consumption increases; when the second temperature is too high, the gradient transition deformation zone softens prematurely, which easily causes the billet to bulge in the rear section; when the second temperature is too low, the gradient transition deformation zone cannot be replenished in the later stage of forming, and the outer edge of the diameter expansion forming section 6 is prone to underfilling.

[0064] During the heating process, the billet can rotate around its own axis. For steel bars with a diameter of 25mm to 40mm, the rotation speed can be controlled between 5r / min and 30r / min. The rotation of the billet is used to improve the temperature uniformity in the circumferential direction and avoid local overheating or insufficient temperature in the billet. After the main plastic deformation zone reaches the first temperature, a short temperature equalization time of 5s to 40s can be performed. If the temperature equalization time is too short, the temperature of the billet core will be insufficient. If the temperature equalization time is too long, the heat will diffuse to the gradient transition deformation zone and the low temperature constraint zone, weakening the axial temperature gradient.

[0065] Step 6: Transfer the blank and complete the mold positioning.

[0066] After local heating is completed, the blank is transferred from the local heating position to the mold 4. The time for transfer and positioning is preferably no more than 15 seconds, and more preferably no more than 8 seconds. If the transfer time is too long, the surface temperature of the main plastic deformation zone will drop, causing the actual forming temperature to be lower than the set temperature, which in turn leads to an increase in forming pressure.

[0067] After the billet is placed into the mold 4, the main plastic deformation zone is aligned with the diameter expansion forming section 6, and the gradient transition deformation zone is located at least in the front part of the mold entrance constraint section 5, while the rear part of the gradient transition deformation zone is close to the clamping and positioning part 3, so that the low temperature constraint zone is supported or clamped by the clamping and positioning part 3. This positional relationship can ensure that the main plastic deformation zone enters the diameter expansion forming section 6 first to fill, the gradient transition deformation zone is in a controlled feeding position, and the low temperature constraint zone will not bulge out radially due to pressure.

[0068] Step 7: Perform staged hydraulic upsetting.

[0069] The hydraulic head 2 applies pressure from one side of the billet tail along the billet axis. The hydraulic upsetting process is divided into the pre-upsetting stage, the mold filling stage, and the pressure holding and shaping stage.

[0070] During the pre-upsetting stage, the hydraulic head 2 advances axially at a speed of 20 mm / s to 60 mm / s, causing initial axial compression in the main plastic deformation zone and material accumulation near the mold entrance. The speed should not be too low during this stage, as this will lead to an increase in the temperature drop of the billet; nor should it be too high, as this will easily cause unstable metal flow.

[0071] During the mold filling stage, the hydraulic pressure head 2 reduces its advancing speed and continues to press the billet at a speed of 3 mm / s to 15 mm / s, so that the main plastic deformation zone is stably filled along the expansion forming section 6. As the resistance inside the mold cavity 7 increases, the gradient transition deformation zone produces limited plastic deformation under the action of higher axial pressure, and feeds material into the main plastic deformation zone. If the speed is too fast during this stage, folds are easily formed at the root of the upsetting head or the step area; if the speed is too slow, the temperature drop of the billet increases and the forming pressure rises.

[0072] After the hydraulic pressure head 2 reaches the final forging position, pressure holding and shaping are performed. The pressure holding time is 2s to 20s, preferably 5s to 8s. If the pressure holding time is less than 2s, the corners and outer edges of the expansion forming section may not be adequately filled. If the pressure holding time is too long, the improvement on the filling rate is limited, and the production cycle is reduced, and the mold heating time is increased.

[0073] Step 8: Collect forming data and correct subsequent parameters

[0074] like Figure 5 As shown, the pressure signal during the hydraulic upsetting process is collected by the pressure detection unit 1, and the displacement signal of the hydraulic head 2 is obtained by the stroke detection component or control unit of the hydraulic equipment. The control unit forms a pressure-displacement curve. The actual temperature of the main plastic deformation zone and the gradient transition deformation zone is recorded by the temperature detection unit 8. After demolding, the outer diameter, height, mold filling rate, flash thickness, cracks, folds and bulging of the constraint zone of the upsetting head are detected.

[0075] When the pressure-displacement curve rises sharply before the final forging position, and there is underfilling at the outer edge or corner of the upsetting head, it indicates insufficient material replenishment in the gradient transition deformation zone. The power of the second heating unit 10 can be appropriately increased, the second temperature can be increased, or the length of the gradient transition deformation zone can be appropriately increased. When the flash of the formed part increases significantly or bulging occurs near the low-temperature constraint zone, it indicates that the total local heating length is too large or the second temperature is too high. The power of the second heating unit 10 can be appropriately reduced, or the total local heating length Lh can be shortened. When the forming pressure is too high but the mold filling rate is qualified, the second temperature or the length of the gradient transition deformation zone should be adjusted first, rather than directly increasing the first temperature, to avoid overheating of the main plastic deformation zone.

[0076] Through the above feedback corrections, the present invention can adapt to material batch differences, mold temperature changes, mold wear and heating transfer time fluctuations, so that the local heating parameters are kept within a range that is both energy-saving and stable in forming.

[0077] This embodiment also provides an upsetting die forging, which is processed by the above-mentioned energy-saving hydraulic upsetting local heating die forging process. The upsetting die forging is formed from metal bar, rod or shaft blank after end local gradient heating, die positioning and hydraulic upsetting die forging, and its end has a thickened upsetting head structure.

[0078] Example 1: To illustrate the implementation of the process of the present invention in the end flange-shaped upsetting head of carbon steel bar stock, a solid round bar of 45 steel was used as the billet for the test. The billet diameter was 30 mm. The target upsetting head was an end flange-shaped structure with an outer diameter of 48 mm and a height of 18 mm. The diameter expansion forming section 6 was provided with an R3 mm transition fillet. The rated pressure of the hydraulic equipment was 1000 kN, the heating method was a two-stage annular induction heating, and the test environment temperature was 22°C to 26°C.

[0079] Based on the target upsetting head volume, transition fillet volume, allowable flash volume, and oxidation loss compensation volume, the effective deformation volume is calculated to be 36.5 cm³. 3 The original cross-sectional area of ​​the billet was 706.9 mm². 2 The theoretical deformation length is 51.6 mm, and the total length of local heating is 58 mm, which is about 1.12 times the theoretical deformation length. Among them, the length of the main plastic deformation zone is 42 mm, and the length of the gradient transition deformation zone is 16 mm.

[0080] The first heating unit 9 heats the main plastic deformation zone to 980℃, and the second heating unit 10 heats the gradient transition deformation zone to 820℃. The temperature difference between the first and second temperatures is 160℃. The billet rotates at 12r / min during heating, and after reaching the set temperature, it is uniformly heated for 12s. After leaving the heating station, it is placed into the mold within 6s. During the hydraulic upsetting, the pressing speed in the pre-upsetting stage is 35mm / s, and the pre-upsetting stroke is 12mm. The pressing speed in the mold filling stage is 8mm / s. After reaching the final forging position, the pressure is held for 6s.

[0081] According to the above process parameters, 30 pieces were continuously trial-produced to obtain the Sample of Example 1. The Sample of Example 1 was used in subsequent experimental cases to detect and compare the heating energy consumption of a single piece, the maximum forming pressure, the mold filling rate, the flash thickness, and the forming defects.

[0082] Example 2: To illustrate the applicability of the process of the present invention to materials with high deformation resistance and stepped upsetting head structure, a solid round bar of 40Cr was used as the blank for the experiment. The blank diameter was 35mm, the target upsetting head was a stepped thickened head with a maximum outer diameter of 56mm and a total height of 20mm. Since the deformation resistance of 40Cr material is higher than that of 45 steel, the total length of local heating was taken as 1.18 times the theoretical deformation length.

[0083] The effective deformation volume is calculated to be 55.8 cm³. 3 The theoretical deformation length is 58.0 mm, and the total local heating length is determined to be 68 mm; among which, the length of the main plastic deformation zone is 49 mm, and the length of the gradient transition deformation zone is 19 mm. The first heating unit 9 heats the main plastic deformation zone to 1020℃, and the second heating unit 10 heats the gradient transition deformation zone to 860℃. The billet rotates at 10 r / min, the temperature is uniformized for 15 s, and the mold transfer time is controlled within 8 s.

[0084] During hydraulic upsetting, the pressing speed is 30 mm / s in the pre-upsetting stage and 6 mm / s in the die filling stage, with a holding pressure of 8 seconds after final forging. Thirty samples were continuously produced according to the above process parameters, resulting in Sample 2. Sample 2 was used to verify the applicability of the process of this invention to materials with high deformation resistance and stepped upsetting head structures.

[0085] Example 3: To illustrate the effect of pressure-displacement curve feedback correction on batch forming stability in this invention, a Q355 solid round bar was used as the blank for the experiment. The blank diameter was 28 mm, the target upsetting head was a mushroom-shaped thickened head with a maximum outer diameter of 44 mm and a height of 17 mm, the initial local heating total length was set to 52 mm, of which the length of the main plastic deformation zone was 37 mm, the length of the gradient transition deformation zone was 15 mm, the first temperature was 960 °C, and the second temperature was 790 °C.

[0086] Ten prototypes were fabricated according to the initial parameters. During the fabrication process, the pressure-displacement curve showed that the pressure slope of some billets increased significantly about 2 mm before the final forging position. After demolding and inspection, it was found that some prototypes with initial parameters had slight underfilling at the outer edge of the upsetting head. Based on this result, the length of the gradient transition deformation zone was adjusted from 15 mm to 17 mm, the second temperature was adjusted from 790℃ to 830℃, and the total length of local heating was adjusted accordingly to 54 mm, while other parameters remained unchanged.

[0087] After adjusting the parameters based on the feedback correction results, 30 more samples were continuously produced to obtain the feedback-corrected samples. The initial parameter samples and the feedback-corrected samples were used in subsequent experimental cases to verify the effect of the pressure-displacement curve feedback correction on the maximum forming pressure, mold filling rate, and number of qualified parts in one go.

[0088] Comparative Example 1: In order to compare with the overall heating process of a longer area, the same 45 steel billet, mold 4 and hydraulic parameters as in Example 1 were used for the test. The difference is that Comparative Example 1 did not use local gradient heating, but heated the entire 150mm range of the end of the billet to 980°C and then performed hydraulic upsetting.

[0089] Thirty samples were continuously produced using the aforementioned long-area overall heating process, resulting in Comparative Example 1. Comparative Example 1 was used to compare energy consumption, mold filling rate, flash thickness, and forming defects with Sample 1 of Example 1.

[0090] Comparative Example 2: In order to compare with the ordinary single-area local heating process, the same 45 steel billet, mold 4 and hydraulic parameters as in Example 1 were used for the test; the difference is that Comparative Example 2 only performed single-area local heating on the end 44mm of the billet, the temperature was 980℃, and no gradient transition deformation zone was set.

[0091] Thirty pieces were continuously trial-produced using the above-mentioned ordinary single-area local heating process, resulting in two comparative sample pieces. These two sample pieces were used to verify the effect of shortening the heating length without setting a gradient transition deformation zone on the mold filling rate, forming pressure, and forming defects.

[0092] Comparative Example 3: In order to compare with the local heating process at the same temperature, the same 45 steel billet, mold 4 and hydraulic parameters as in Example 1 were used for the test. The difference is that Comparative Example 3 heated the entire 58mm range of the end of the billet to 980°C, without forming the main plastic deformation zone and the temperature difference between the gradient transition deformation zone.

[0093] Thirty pieces were continuously produced using the same local heating process described above, resulting in three comparative samples. These three samples were used to verify the effects of no axial temperature gradient on flash, bulging, and mold filling state under the same total local heating length.

[0094] Comparative Example 4: In order to verify the necessity of pressure-displacement curve feedback correction, the same Q355 billet, mold 4 and initial heating parameters as in Example 3 were used for the test. The difference is that Comparative Example 4 did not adjust the length of the gradient transition deformation zone and the second temperature according to the pressure-displacement curve, but instead continuously used the initial parameters for trial production.

[0095] 30 prototypes were continuously produced using the above-mentioned fixed initial parameters to obtain 4 comparative sample pieces. These 4 comparative sample pieces were used to compare with the sample pieces after feedback correction in Example 3 to verify the impact of pressure-displacement curve feedback correction on batch forming stability.

[0096] Experimental Example 1: To verify the relationship between the total length of local heating and the theoretical deformation length, an experiment was conducted using 45 steel φ30mm billet from Example 1, the same mold 4, and the same hydraulic press equipment. During the experiment, the first temperature was maintained at 980℃, the second temperature at 820℃, the pressing speed during the pre-upsetting stage was 35mm / s, the pressing speed during the mold filling stage was 8mm / s, and the holding time was 6s. Only the ratio of the total length of local heating Lh to the theoretical deformation length L0 was changed. 20 pieces were produced for each group.

[0097] The energy consumption of a single piece of heating is read by the power metering module of the induction heating power supply; the maximum forming pressure is read by the pressure detection unit 1; the mold filling rate is calculated based on the ratio of the measured projected area of ​​the outward contour of the upsetting head to the theoretical projected area; the flash thickness is measured at four equally divided positions on the circumference and the average value is taken; cracks, folds and bulges are confirmed by visual inspection and local section inspection. The test results are shown in Table 1.

[0098] Table 1. Test results of molding quality and energy consumption under different Lh / L0 conditions: 1.00 52 0.68 792 96.3 0.38 4 pieces were underfilled, 1 piece had a fine crack 1.05 54 0.71 745 97.8 0.48 2 pieces with minor underfill 1.12 58 0.77 690 98.9 0.66 1 piece with a slight dent 1.18 61 0.83 675 99.0 0.78 No obvious forming defects 1.30 67 0.93 660 99.1 1.03 2 pieces with slightly bulging bellies 1.38 71 1.05 648 99.2 1.28 5 pieces with bulging bellies and oversized trim. ;

[0099] As can be seen from Table 1, when Lh / L0 is below 1.05, the total length of local heating is insufficient, the mold filling rate is significantly low, and underfilling and fine cracks appear. When Lh / L0 is close to or above 1.30, the mold filling rate can be improved only slightly, but the heating energy consumption per piece, flash thickness and bulging defects increase significantly. Therefore, it can be seen that controlling Lh / L0 between 1.05 and 1.30 can balance molding quality and energy saving effect, with the comprehensive performance around 1.10 to 1.18 being better.

[0100] Experimental Example 2: To verify the division ratio between the main plastic deformation zone and the gradient transition deformation zone, the 45 steel φ30mm billet from Example 1 was used as the test object. In the test, the total length of local heating was kept at 58mm, the first temperature was 980℃, and the second temperature was 820℃. The pressing parameters were the same as in Example 1, only the ratio of the length of the main plastic deformation zone to the total length of local heating was changed. 20 pieces were produced in each group, and the testing method was the same as in Experimental Example 1. The test results are shown in Table 2.

[0101] Table 2. Test results of forming quality and energy consumption under different proportions of the main plastic deformation zone: 55% 32 26 0.73 96.6 0.49 3 pieces with incomplete filling at the outer edge 60% 35 23 0.74 97.8 0.55 1 piece with minor underfill 72% 42 16 0.77 98.9 0.66 1 piece with a slight dent 80% 46 12 0.80 98.7 0.82 1 piece with flash that is too large 88% 51 7 0.84 98.5 1.06 Three pieces have oversized frills, and two pieces have bulging bellies. ;

[0102] As can be seen from Table 2, when the proportion of the main plastic deformation zone is less than 60%, the amount of metal in the high-temperature main deformation zone is insufficient, and the outer edge of the expansion forming section 6 is prone to underfilling. When the proportion of the main plastic deformation zone is higher than 85%, the gradient transition deformation zone is too short, and the metal in the later section is prone to participate in plastic flow too early, resulting in increased flash and bulging. Therefore, it is more appropriate for the main plastic deformation zone to account for 60% to 85% of the total length of local heating, of which 68% to 78% can better balance the filling rate and flash control.

[0103] Experiment Example 3: To verify the effect of the temperature difference between the first temperature and the second temperature on the feeding effect, the 45 steel φ30mm billet in Example 1 was used as the object for the experiment. In the experiment, the total length of local heating was kept at 58mm, the length of the main plastic deformation zone was 42mm, the length of the gradient transition deformation zone was 16mm, the first temperature was 980℃, and only the second temperature was changed. 20 pieces were produced in each group. The detection method was the same as in Experiment Example 1. The test results are shown in Table 3.

[0104] Table 3. Test results of molding quality and energy consumption under different differences between the first and second temperatures: 50 930 0.85 660 99.0 1.12 3 pieces with bulging bellies and oversized trim. 80 900 0.82 668 98.9 0.92 1 piece with a slightly bulging belly 120 860 0.79 681 98.9 0.73 No obvious forming defects 160 820 0.77 690 98.9 0.66 1 piece with a slight dent 250 730 0.73 752 97.7 0.46 2 pieces with minor underfill 300 680 0.70 815 95.9 0.35 4 pieces were underfilled, 2 pieces had fine cracks ;

[0105] As can be seen from Table 3, when the temperature difference between the first and second temperatures is less than 80℃, the temperature of the gradient transition deformation zone is too high, the early-stage restraint effect is weakened, and the billet bulge and flash are too large in the later stage. When the temperature difference is higher than 250℃, the temperature of the gradient transition deformation zone is too low, the later-stage material replenishment capacity is insufficient, the maximum forming pressure increases, and underfilling and fine cracks appear. Therefore, it is reasonable for the second temperature to be 80℃ to 250℃ lower than the first temperature, and the area around 120℃ to 180℃ can better balance the material replenishment capacity and the restraint effect.

[0106] Experimental Example 4: To compare the overall effect of the process of the present invention with conventional heating methods, samples from Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were tested. The test items included single-piece heating energy consumption, maximum forming pressure, mold filling rate, average flash thickness, number of qualified parts in one go, and main defects. The test method was the same as that of Experimental Example 1. Qualified parts were judged comprehensively according to the outer diameter and height of the upsetting head, mold filling state, cracks, folds, bulges, and appearance quality requirements. The test results are shown in Table 4.

[0107] Table 4. Test results of hydraulic upsetting head forming effect under different heating methods: Example 1 0.77 690 98.9 0.66 29 / 30 1 piece with a slight dent Comparative Example 1 1.52 622 99.1 1.36 30 / 30 High energy consumption and large flash. Comparative Example 2 0.60 812 94.8 0.34 22 / 30 underfill, cracks Comparative Example 3 0.93 668 98.8 1.18 26 / 30 The belly is bulging and the edge is too large. ;

[0108] As shown in Table 4, compared with overall heating over a longer area, the present invention significantly reduces the energy consumption of heating a single part and reduces the flash thickness. Compared with ordinary local heating in a single area, although the energy consumption of the present invention is slightly higher, the mold filling rate and the number of qualified parts in one go are significantly improved. Compared with local heating at the same temperature, the present invention reduces energy consumption and flash thickness while maintaining a high filling rate, and reduces bulging near the low-temperature constraint zone. These results indicate that the energy-saving effect of the present invention is not achieved by simply shortening the heating length, but by the synergistic effect of the main plastic deformation zone, the gradient transition deformation zone, and the low-temperature constraint zone.

[0109] Experiment Example 5: To verify Figure 5The pressure-displacement curve feedback correction method shown is used to test the initial parameter prototype, the feedback-corrected prototype, and the prototype of Comparative Example 4 in Example 3. The test items include the second temperature, the length of the gradient transition deformation zone, the maximum forming pressure, the mold filling rate, the number of qualified parts at one time, and the main defects.

[0110] During the experiment, the pressure signal during the hydraulic upsetting process was recorded by the pressure detection unit 1, and the displacement signal of the hydraulic head 2 was obtained by the stroke detection component of the hydraulic equipment. The control unit generated the pressure-displacement curve. After demolding, the mold filling rate and defect status were detected. The results are shown in Table 5.

[0111] Table 5. Test results of pressure-displacement curve feedback correction effect: Initial parameter prototype 790 15 738 96.9 7 / 10 Partial underfill at the outer edge Feedback and correction 830 17 696 98.8 29 / 30 1 piece with slight uneven flash Continuous production with fixed initial parameters 790 15 733 96.7 24 / 30 Underfilled, 1 folded piece ;

[0112] As can be seen from Table 5, after using the pressure-displacement curve feedback correction, the maximum forming pressure decreased, the mold filling rate increased, and the number of qualified parts increased. This result shows that the pressure-displacement curve can not only record the hydraulic upsetting process, but also reflect whether the material feeding capacity of the gradient transition deformation zone is sufficient, and can be used as a basis for correcting the second temperature and the length of the gradient transition deformation zone.

[0113] It should be noted that, Figure 5 The reference curves in the table are used to represent the target forming state or the stable forming curve of the previous batch of qualified blanks, and are not the individual test states in Table 5. Figure 5 The measured curves before correction correspond to the initial parameters in Table 5. Figure 5 The corrected curve in Table 5 corresponds to the feedback correction in Table 5. The fixed initial parameters in Table 5 are used as a comparison state without feedback correction.

[0114] Experiment Example 6: To further verify the actual formation of the local gradient heating region and the influence of different heating methods on the load change of the hydraulic upsetting head, temperature distribution detection and pressure-displacement curve comparison were carried out respectively. Temperature distribution detection was based on the local gradient heating process conditions of Example 1 to verify whether a continuous axial temperature gradient was formed between the main plastic deformation zone, the gradient transition deformation zone and the low temperature constraint zone. Pressure-displacement curve comparison was based on the process conditions of Example 1, Comparative Example 2 and Comparative Example 3 to compare the differences in forming pressure with the displacement of hydraulic upsetting head 2 under different heating methods.

[0115] During temperature distribution detection, before the billet is locally heated and transferred into the mold, the surface temperature of the billet is collected using an infrared thermal imager or a multi-point temperature measurement method along the axial direction, and the results are as follows: Figure 6The axial temperature distribution curve shown indicates that the temperature is higher at the end of the billet and gradually decreases towards the rear. A continuous axial temperature gradient is formed between the main plastic deformation zone, the gradient transition deformation zone, and the low-temperature constraint zone. The low-temperature constraint zone is not actively heated by the first heating unit 9 and the second heating unit 10. Although its front end is heated by heat conduction from the adjacent heating zone, its temperature drops rapidly along the billet axis and is lower than the second temperature of the gradient transition deformation zone, thus not reaching the temperature range that allows it to fully participate in thermoplastic deformation.

[0116] During pressure-displacement curve detection, the pressure signal during the hydraulic upsetting process is recorded by the pressure detection unit 1, and the displacement signal of the hydraulic head 2 is obtained through the stroke detection component or control unit built into the hydraulic equipment, resulting in the following... Figure 7 The comparison curves shown indicate that: in ordinary single-area local heating processes, due to insufficient local high-temperature metal, the pressure usually rises rapidly before the final forging position; in isothermal local heating processes, due to the long isothermal heating zone, the pressure is low in the early stage, but the metal is prone to non-target flow in the later stage; the local gradient heating process adopted in this invention has a relatively stable pressure-displacement curve, and the pressure rise before final forging is moderate, indicating that the gradient transition deformation zone can provide limited material replenishment in the later stage.

[0117] The above temperature distribution and pressure-displacement curve results can be corroborated by the data from Experimental Examples 1 to 5, indicating that the temperature distribution formed by local gradient heating in this invention is not simply a reduction in heating length, but rather a change in metal flow and feeding state through a controlled temperature gradient, thereby improving the mold filling quality while reducing energy consumption.

[0118] In summary, this invention determines the total length of local heating by utilizing the effective deformation volume, forms a controlled temperature gradient through the main plastic deformation zone, the gradient transition deformation zone, and the low-temperature constraint zone, achieves stable mold filling through staged hydraulic upsetting, and corrects the heating parameters of subsequent billets using pressure-displacement curves. Compared to overall heating over a longer area, this invention reduces ineffective heating in non-deformation areas. Compared to ordinary local heating in a single area, this invention improves mold filling rate and reduces cracks. Compared to local heating at the same temperature, this invention reduces flash and non-target bulging. This process achieves a good balance between energy saving and forming quality, and is suitable for die forging production requiring end upsetting.

[0119] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A hydraulic upsetting head local heating forging process with reduced energy consumption, characterized in that, Includes the following steps: S1: Determine the effective deformation volume of the billet end that needs to participate in plastic flow based on the forming volume of the target upsetting head and the effective volume of the mold cavity, and determine the theoretical deformation length based on the effective deformation volume and the original cross-sectional area of ​​the billet. S2: Determine the total length of local heating at the end of the billet based on the theoretical deformation length. Within the total length of local heating, divide the section near the end of the billet into the main plastic deformation zone, divide the section behind the main plastic deformation zone into the gradient transition deformation zone, and form a low-temperature constraint zone behind the gradient transition deformation zone. S3: Local gradient heating is applied to the end of the billet, so that the main plastic deformation zone is heated to the first temperature, the gradient transition deformation zone is heated to the second temperature which is lower than the first temperature, and the heat is restricted from continuing to diffuse to the low temperature constraint zone. This allows the gradient transition deformation zone to have a higher deformation resistance than the main plastic deformation zone in the early stage of hydraulic upsetting, and to generate limited material replenishment in the direction of the diameter expansion forming section after the filling resistance of the mold cavity increases. S4: Place the billet after local gradient heating into the mold, so that the main plastic deformation zone corresponds to the expansion forming section of the mold cavity, so that the gradient transition deformation zone is at least located in the mold entrance constraint section of the mold cavity, and so that the low temperature constraint zone is supported or clamped by the clamping and positioning part. S5: Upsetting, filling, and shaping of the blank end within the mold cavity; S6: Collect pressure signals and displacement signals of the hydraulic upsetting head during the process, form a pressure-displacement curve, and correct the total length of local heating of the subsequent billet, the second temperature or the length of the gradient transition deformation zone based on the pressure-displacement curve.

2. The energy-saving hydraulic upsetting head local heating forging process according to claim 1, characterized in that: The effective deformation volume is determined based on the target upsetting head solid volume, transition fillet volume, allowable flash volume, and oxidation burn-off compensation volume; when the billet is a solid round bar, the theoretical deformation length is determined according to the ratio of the effective deformation volume to the original cross-sectional area of ​​the billet.

3. The energy-saving hydraulic upsetting head local heating forging process according to claim 1, characterized in that: The total length of the local heating is 1.05 to 1.30 times the theoretical deformation length.

4. The energy-saving hydraulic upsetting head local heating forging process according to claim 3, characterized in that: The total length of the local heating is 1.10 to 1.18 times the theoretical deformation length.

5. The energy-saving hydraulic upsetting head local heating forging process according to claim 1, characterized in that: The total length of local heating is composed of the length of the main plastic deformation zone and the length of the gradient transition deformation zone, and the low-temperature constraint zone is not included in the total length of local heating; wherein, the main plastic deformation zone accounts for 60% to 85% of the total length of local heating, and the gradient transition deformation zone accounts for 15% to 40% of the total length of local heating.

6. The energy-saving hydraulic upsetting head local heating forging process according to claim 5, characterized in that: The main plastic deformation zone accounts for 68% to 78% of the total length of local heating, and the gradient transition deformation zone accounts for 22% to 32% of the total length of local heating.

7. The energy-saving hydraulic upsetting head local heating forging process according to claim 1, characterized in that: The first temperature is 900°C to 1100°C, and the second temperature is 80°C to 250°C lower than the first temperature; the second temperature is the temperature representing the temperature measurement position within the gradient transition deformation zone.

8. The energy-saving hydraulic upsetting head local heating forging process according to claim 7, characterized in that: The first temperature is 960°C to 1030°C, and the second temperature is 120°C to 180°C lower than the first temperature; the temperature measurement position is located near the rear end of the gradient transition deformation zone, or is the detection position corresponding to the second heating unit.

9. The energy-saving hydraulic upsetting head local heating forging process according to claim 1, characterized in that: The hydraulic upsetting head includes a pre-upsetting stage, a die filling stage, and a pressure holding and shaping stage. In the pre-upsetting stage, the hydraulic head advances axially at a speed of 20 mm / s to 60 mm / s. In the die filling stage, the hydraulic head continues to press the billet at a speed of 3 mm / s to 15 mm / s. In the pressure holding and shaping stage, the hydraulic head holds pressure for 2 to 20 seconds after reaching the final forging position.

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