Method for rapidly removing ineffective area of hot forging die additive remanufacturing

Abstract

The invention discloses a hot forging die additive remanufacturing failure area rapid removal method, and relates to the technical field of hot forging die failure layer cleaning, and the method comprises the following steps: S1, heat balance state analysis; finite element simulation analysis is conducted on the hot forging die, a heat balance state temperature field is determined based on overall heat flux balance of the hot forging die, and temperature field characteristics when the hot forging die enters the heat balance state are determined; s2, identifying a failure area; a 540 DEG C isothermal curve is used for defining a hot forging die failure area, and it is ensured that a fatigue stress layer, exceeding 510 MPa, on the surface of the hot forging die is removed; s3, performing three-dimensional reverse modeling and path planning; a 3D digital model is reversely established by extracting point cloud data of a failure area, and meanwhile, an accurate robot path code is generated; s4, machining is conducted; the hot forging die is subjected to high-temperature spheroidizing annealing heat treatment, the hot forging die is machined according to the digital model obtained in the step S3, and a failure area of the hot forging die is removed; and the processing difficulty and complexity of subsequent additive remanufacturing repair are effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of hot forging die failure layer cleaning, and in particular to a method for quickly removing a failure area of ​​a hot forging die in additive remanufacturing. Background Art

[0002] During the production process, hot forging dies for automobile half-axles need to withstand special working conditions such as mechanical loads and hot and cold cycles. Their lifespan is usually low, and the lifespan of hot forging dies may even be only 1,000-1,200 pieces, far lower than the 4,000-6,000 pieces of general hot forging dies. Therefore, companies have an urgent need for batch remanufacturing and life extension of hot forging dies for automobile half-axles. At present, there is an urgent need for a theory that can quickly eliminate the failure area of ​​hot forging dies for automobile half-axles, and establish an arc additive remanufacturing model based on this.

[0003] Although existing research has conducted a lot of research on the process, mechanical properties, etc. of automobile half-axle forgings, there is less exploration in hot forging dies. Some scholars have proposed a method to divide the additive repair layer of the hot forging die by temperature field and stress field, and proposed a method for metal gradient additive repair of the die. However, these methods usually only focus on the temperature field after a single forging, and ignore the temperature field characteristics of the hot forging die when it enters a thermal equilibrium state during the continuous forging process, which may lead to inaccurate selection of the failure layer. In addition, the existing repair methods do not fully consider the heat flux of the hot forging die during the continuous forging process, that is, the thermal equilibrium temperature field, which may lead to inaccurate selection of the repair layer, thereby affecting the effect of hot forging die remanufacturing.

[0004] Traditional methods for determining the repair layer, such as non-destructive testing technology (including magnetic particle testing MT, penetrant testing PT, eddy current testing ET), visual inspection and thermal imaging testing, all have certain limitations. For example, these methods cannot effectively detect longitudinal cracks, and the test results are greatly affected by the operator's subjective judgment. Although ultrasonic testing (UT) can detect internal defects, its equipment cost is relatively high, and it requires professionally trained technicians to operate, and good coupling is required to achieve effective detection.

[0005] Since the repair layer cannot be confirmed quickly and in batches, and the selection of the repair layer is not accurate enough, it often leads to more waste of material and labor costs. Therefore, the present invention proposes a method for quickly removing the failure layer of hot forging die additive remanufacturing based on a thermal equilibrium temperature field. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for quickly removing the failure area of ​​hot forging die additive remanufacturing. The method combines theoretical basis with computer-aided manufacturing technology, improves the surface cleaning quality while ensuring batch cleaning efficiency, effectively reduces the processing difficulty and complexity of subsequent additive remanufacturing repairs, and simplifies the entire process.

[0007] The object of the present invention is achieved through the following technical solution: A method for quickly removing the failure area of ​​a hot forging die additive remanufacturing, comprising the following steps:

[0008] S1. Thermal equilibrium analysis: perform finite element simulation analysis on the hot forging die, determine the thermal equilibrium temperature field based on the overall heat flux balance of the hot forging die, and determine the temperature field characteristics when the hot forging die enters the thermal equilibrium state;

[0009] S2. Failure zone identification: Use the 540℃ isothermal curve to define the failure zone of the hot forging die, and ensure that the fatigue stress layer exceeding 510MPa on the surface of the hot forging die is removed;

[0010] S3, 3D reverse modeling and path planning: by extracting the point cloud data of the failure area, reversely establish a 3D digital model and generate accurate robot path code to achieve precise directional remanufacturing of the hot forging die surface cavity;

[0011] S4, mechanical processing; performing high-temperature spheroidizing annealing heat treatment on the hot forging die, and machining the hot forging die according to the digital model obtained in step S3, removing the failure area of ​​the hot forging die, and obtaining the hot forging model cavity to be added and remanufactured.

[0012] Furthermore, after the hot forging die continuously works for 20 cycles in step S1, the heat flux tends to be stable, and the temperature of the reference surface of the hot forging die approaches a stable value of 788°C.

[0013] Furthermore, in step S3, digital reverse modeling of the failure layer of the hot forging die is performed, including: for the failure area of ​​the hot forging die, a reverse digital model is established using MATLAB and three-dimensional software, and the failure area of ​​the hot forging die is removed by CNC machining using computer-aided manufacturing software (CAM), ensuring that there are no defects such as cracks on the surface of the hot forging die after machining, thereby obtaining the H13 steel hot forging die substrate to be manufactured by arc additive manufacturing.

[0014] Furthermore, in step S3, MATLAB is used to extract the point cloud portion above the 540°C isothermal surface, and then three-dimensional software is used for reverse modeling.

[0015] Further, in step S4, the hot forging die to be welded is subjected to pre-welding pretreatment, including: a high-temperature spheroidizing annealing process before hot forging die machining, the temperature being higher than the heating critical point temperature Ac1 of H13 steel, keeping warm at about 860±10°C for 2 hours, then slowly cooling to 740±10°C, and keeping warm for another 4 hours, and then continuing to slowly cool to below 550°C, and finally taking out of the furnace and air cooling, and welding the two lower dies into one body for convenient machining.

[0016] Furthermore, reverse digital modeling combined with CNC machining is used to accurately remove the failed area to obtain the cavity to be remanufactured.

[0017] Furthermore, finite element analysis technology was used to determine the arc additive remanufacturing area based on the overall heat flux balance of the hot forging die, and a digital model was reversely established to remove the fatigue stress layer of the lower die and plan the arc additive remanufacturing path for the digital model.

[0018] The beneficial effects of the present invention are:

[0019] 1. Simplify the process flow: By using the steady state of heat flux to study the steady-state temperature field and stress field of the hot forging die, the remanufacturing process is simplified and the process complexity is reduced.

[0020] 2. Efficient removal of failure areas: The remanufacturing area is divided through precise thermal balance analysis, which effectively removes cracks in the longitudinal depth of the hot forging die and improves the cleaning efficiency.

[0021] 3. Improve surface quality: The surface quality of the hot forging die is high after machining, which reduces the difficulty of subsequent robot path planning and improves the reliability of the remanufacturing forming trajectory.

[0022] 4. Improve forming quality: The flat cavity surface is conducive to improving the forming morphology of each layer of deposited metal in the arc additive manufacturing process, avoiding the change of arc length caused by the rugged surface grooves, thereby reducing the occurrence of arc extinction and other phenomena, and significantly improving the forming quality.

[0023] 5. Save materials and costs: This technical method effectively saves the consumption of original hot forging die materials, reduces the batch remanufacturing cost of hot forging dies, and improves economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The hot swing mill production conditions and numerical model diagram of the present invention;

[0025] Figure 2 The hot forging die wear and the lower die wear condition diagram after a single simulated forging of the present invention;

[0026] Figure 3 It is a heat flux diagram of the whole lower die in a method for quickly removing the failure area of ​​a hot forging die additive remanufacturing of the present invention;

[0027] Figure 4 The isothermal curves of the hot forging die of the present invention at 540°C for different times after the hot forging die has been continuously operated for 30 times;

[0028] Figure 5 This is the relative thickness Z diagram of the hot forging die 510MPa equivalent effect field of the present invention;

[0029] Figure 6 This is a digital model diagram of the 540°C isothermal surface and failure area after the 20th working cycle of the present invention;

[0030] Figure 7 A diagram showing the removal of a hot forging die failure layer after machining in a method for quickly removing a failure area of ​​a hot forging die in additive remanufacturing of the present invention;

[0031] In the figure, 1-upper die, 2-workpiece, 3-lower die, 4-actual wear and theoretical wear verification, 5-reference area with the most serious failure, 6-digital model of failure area, 7-H13 steel hot forging die model matrix. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0033] The invention discloses a lower die ( Figure 1 The originality of the method for rapid removal of failure areas in additive remanufacturing (labeled 2) lies in the stable determination of the thermal equilibrium temperature field by heat flux, and the determination of the failure area of ​​the hot forging die by studying the thermal equilibrium temperature field and stress field. This innovation is not limited to the geometric configuration or application scope of a specific hot forging die. Therefore, although the following description takes a hot forging die of a certain structure as an example, it is intended to elaborate on the essence of this method, but it should be understood that the steps are generally applicable to hot forging dies of various shapes and functional requirements, demonstrating the wide applicability and flexibility of this method.

[0034] Embodiment 1

[0035] like Figures 1 to 7 As shown, a method for quickly removing a failure area of ​​a hot forging die additive remanufacturing comprises the following steps:

[0036] S1. Thermal equilibrium analysis: Conduct finite element simulation analysis on the hot forging die, determine the thermal equilibrium temperature field based on the overall heat flux balance of the hot forging die, and determine the temperature field characteristics when the hot forging die enters the thermal equilibrium state; thereby dividing the arc additive remanufacturing area of ​​the hot forging die to ensure effective identification and location of the parts that are subjected to excessive heat load and produce fatigue failure

[0037] S2. Failure zone identification: Use the 540℃ isothermal curve to define the failure zone of the hot forging die, and ensure that the fatigue stress layer exceeding 510MPa on the surface of the hot forging die is removed;

[0038] S3, 3D reverse modeling and path planning; use reverse digital modeling combined with CNC machining to accurately remove the failure area, extract the point cloud data of the failure area to reversely establish a 3D digital model, and generate accurate robot path code to achieve precise directional remanufacturing of the hot forging die surface cavity; use MATLAB to extract the point cloud area above the 540℃ isothermal surface, use MATLAB to extract the 540℃ isothermal surface after the 20th forging in the simulation results, import the grid node data above 540℃ into the 3D software for reverse engineering, and establish a 3D digital model for mechanical processing. This model not only provides an accurate basis for CNC machining, but also uses a precise path planning algorithm to design the optimal manufacturing path for the subsequent arc additive remanufacturing process to ensure repair accuracy and efficiency, that is, using finite element analysis technology, based on the overall heat flux balance of the hot forging die, determine the arc additive remanufacturing area, reversely establish a digital model to remove the fatigue stress layer of the lower die, and plan the arc additive remanufacturing path for the digital model;

[0039] S4, mechanical processing; perform high-temperature spheroidizing annealing heat treatment on the hot forging die, and perform mechanical processing on the hot forging die according to the digital model obtained in step S3 to remove the failure area of ​​the hot forging die, so as to obtain high-precision surface quality and cavity, which is beneficial to the subsequent additive remanufacturing of the hot forging die. At the same time, the digital model can be used to directly simplify the subsequent three-dimensional scanning process, and the digital model can be used to directly plan and design the additive manufacturing path.

[0040] Before performing thermal equilibrium analysis on the hot forging die, pretreatment is required, including the following steps:

[0041] S11. Basic information of hot forging die: The blank is heated to 1100℃ by medium frequency induction furnace, pre-forged, and then forged by pendulum die. Finally, the forging is polished to obtain parts with qualified size. The hot forging die material is AISIH13 steel. The life of pendulum die forging depends on the lower die. The main failure form is thermal wear (the lower die is the research object), which is manifested as an increase in die bore size and forging size exceeding the tolerance range. The life of the forging die is about 1200 pieces.

[0042] S12. Preprocessing of simulation model for hot forging process: Establish a thermal-mechanical coupling numerical analysis model for pendulum rolling forming, use finite element software to divide the hot forging die into hexahedron meshes, and divide the pre-forged parts into regular tetrahedron meshes, and import the mesh model into DEFORM finite element analysis software. Use DEFORM adaptive mesh technology to reconstruct the mesh of the severely distorted area of ​​the billet;

[0043] S13, hot forging process simulation: the upper die works at an offset angle of 2°, a single hot forging time is about 9 seconds, the upper die swings 3 times per second, the lower die feeds along the Z axis at a speed of 14.5 mm / s, and the stroke is 132 mm;

[0044] S14, Wear verification: The simulation results are roughly consistent with the actual hot forging die wear position. In the swing and rolling stage, due to the long working time and contact heat transfer time of the middle cone, this is the most serious failure site. During the swing and rolling process, the blank metal flows rapidly at a specific position, resulting in more serious wear and failure in this area. At the same time, the surface of the hot forging die is locally worn and cracked under the action of alternating mechanical loads and surface hot and cold stresses. In actual production, the upper die works at an offset angle of 2°, from 2° offset mold closing to 2° offset mold parting, the frequency is consistent, and the phase angle position of each working cycle at the moment of mold parting and closing is the same. Since the initial phase contacts first, the wear of the starting part corresponding to the lower die is relatively serious;

[0045] S15. Temperature field analysis: The temperature field after a single working cycle is very different from the temperature field in thermal equilibrium. When the hot forging die is forged 20 times in a row, the heat flux and the maximum surface temperature of the hot forging die tend to a state of equilibrium, indicating that the hot forging die enters a state of thermal equilibrium. At 540°C, the allowable fatigue strength of the H13 steel hot forging die is 510MPa. The relative depth of the 540°C isothermal curve and the reference surface under the thermal equilibrium temperature field state is 28mm. The relative thickness of the hot forging die area with a stress exceeding 510MPa is about 26.3mm. Therefore, the 540°C isothermal curve is used as a reference for dividing the hot forging die additive remanufacturing area, which can remove the fatigue stress layer with a stress higher than 510MPa.

[0046] In summary, this method determines the temperature field characteristics when the hot forging die enters the thermal equilibrium state through finite element simulation analysis, and uses the 540℃ isothermal curve to define the hot forging die failure layer. This method can more accurately determine the location of the failure layer, thereby improving the pertinence and effectiveness of the repair. The point cloud data of the failure layer is extracted by MATLAB, a digital model is established, and CAM manufacturing technology is used to achieve rapid removal of the failure layer. This method improves the repair efficiency, reduces manual intervention, and reduces the repair cost. Using reverse modeling technology and offline path programming technology, multi-layer and multi-path planning of the remanufacturing layer can be achieved, which improves the accuracy level of the remanufacturing process. Through accurate failure layer division, the good combination of the remanufacturing layer and the original hot forging die material can be ensured, extending the service life of the hot forging die.

[0047] Embodiment 2

[0048] Based on the first embodiment, in step S1, first, Figure 1 As shown in the figure, the working process of the hot forging die is simulated by using finite element analysis software. After the hot forging die has worked continuously for 20 times, Figure 3 As shown in Figure 2, the heat flux tends to be stable, and the temperature of the reference surface of the hot forging die is close to the stable value of 788℃, as shown in Figure 2. Figure 4 and Figure 5 As shown, the thermal equilibrium temperature field and the corresponding stress distribution state inside the hot forging die can be accurately identified;

[0049] Secondly, Figure 2 The actual wear and theoretical wear area consistency in area 4 (actual wear and theoretical wear verification) and area 5 (the most serious failure reference area) verifies the accuracy of the thermal-mechanical coupling model. According to the data in the material manual, the fatigue strength of H13 steel at 540°C is 510MPa. Figure 4 It can be seen that the 540℃ isothermal curve of the hot forging die no longer expands after 20 working cycles, and the hot forging die enters a thermal equilibrium state. By comparing the reference 5 area, the vertical height of the temperature field area above the 540℃ isothermal line is about 28mm ( Figure 4 ) and the vertical height of the stress field area above 510MPa is about 26.3mm ( Figure 5 ), and found that the area above the 540℃ isotherm can remove the fatigue stress layer failure area of ​​the hot forging die of 510MPa. The 540℃ isotherm was established as the scientific basis for defining the arc additive remanufacturing area, ensuring the effective identification and isolation of the high stress fatigue layer that needs to be removed.

[0050] Embodiment 3

[0051] Based on the second embodiment, Figure 6 The H13 steel hot forging die model substrate 7 in step S3 is digitally reverse modeled for the hot forging die failure layer, including: for the failure area of ​​the hot forging die, a reverse digital model is established using MATLAB and three-dimensional software, and the failure area of ​​the hot forging die is removed by numerical control machining using computer-aided manufacturing software (CAM), ensuring that there are no defects such as cracks on the surface of the hot forging die after machining, thereby obtaining the H13 steel hot forging die model substrate 7 to be manufactured by arc additive manufacturing.

[0052] Embodiment 4

[0053] Based on the third embodiment, Figure 7 As shown, in step S4, the hot forging die to be welded is subjected to pre-welding pretreatment, including: a high-temperature spheroidizing annealing process before machining the hot forging die, the temperature is higher than the heating critical point temperature Ac1 of H13 steel, and it is kept at about 860±10°C for 2 hours, and then slowly cooled to 740±10°C, and then kept for 4 hours, and then continued to slowly cool to below 550°C, and finally taken out of the furnace and air-cooled, and the two lower dies are welded as one to facilitate machining, and then the hot forging die is machined through a reverse digital model to remove the failed part of the hot forging die to obtain the cavity to be remanufactured.

[0054] In summary, this method simplifies the process flow and adopts the steady state of heat flux to study the steady-state temperature field and stress field of the hot forging die, and proposes a theory to effectively remove the failure area of ​​the hot forging die. This method can not only remove cracks in the longitudinal depth of the hot forging die, but also improve the surface quality of the hot forging die through mechanical processing, reduce the complexity of subsequent robot path planning, and improve the reliability of the remanufacturing forming trajectory. In addition, the flat cavity surface helps to improve the forming morphology of each layer of deposited metal during the arc additive manufacturing process, avoid arc extinction caused by changes in arc length due to surface unevenness, and thus improve the forming quality. This technical method significantly saves the consumption of original hot forging die materials and reduces the batch remanufacturing cost of hot forging dies.

Claims

1. A method for quickly removing failure areas of hot forging die additive remanufacturing, characterized in that: The following steps are involved: S1. Thermal equilibrium analysis: perform finite element simulation analysis on the hot forging die, determine the thermal equilibrium temperature field based on the overall heat flux balance of the hot forging die, and determine the temperature field characteristics when the hot forging die enters the thermal equilibrium state; S2. Failure zone identification: Use the 540℃ isothermal curve to define the failure zone of the hot forging die to ensure that the fatigue stress layer exceeding 510MPa on the surface of the hot forging die is removed; S3, 3D reverse modeling and path planning: by extracting the point cloud data of the failure area, reversely establish a 3D digital model and generate accurate robot path code to achieve precise directional remanufacturing of the hot forging die surface cavity; S4, mechanical processing; performing high-temperature spheroidizing annealing heat treatment on the hot forging die, and machining the hot forging die according to the digital model obtained in step S3, removing the failure area of ​​the hot forging die, and obtaining the hot forging model cavity to be added and remanufactured.

2. A method for rapidly removing failure areas of hot forging die additive remanufacturing according to claim 1, characterized in that: After the hot forging die has been continuously operated for 20 cycles in step S1, the heat flux tends to be stable, and the temperature of the reference surface of the hot forging die approaches a stable value of 788°C.

3. A method for rapidly removing failure areas of hot forging die additive remanufacturing according to claim 1, characterized in that: In step S3, the failure layer of the hot forging die is digitally reverse modeled, including: using MATLAB and three-dimensional software to establish a reverse digital model for the failure area of ​​the hot forging die, using computer-aided manufacturing software (CAM), and numerically controlling the removal of the failure area of ​​the hot forging die by CNC machining, ensuring that there are no defects such as cracks on the surface of the hot forging die after machining, and obtaining the H13 steel hot forging die substrate to be manufactured by arc additive manufacturing.

4. A method for rapidly removing failure areas of hot forging die additive remanufacturing according to claim 3, characterized in that: In step S3, MATLAB is used to extract the point cloud portion above the 540°C isothermal surface, and then three-dimensional software is used for reverse modeling.

5. The method for rapidly removing the failure area of ​​hot forging die additive remanufacturing according to claim 1 is characterized in that: In step S4, the hot forging die to be welded is subjected to pre-welding pretreatment, including: a high-temperature spheroidizing annealing process before machining the hot forging die, the temperature being higher than the heating critical point temperature Ac1 of H13 steel, keeping warm at about 860±10°C for 2 hours, then slowly cooling to 740±10°C, and keeping warm for another 4 hours, and then continuing to slowly cool to below 550°C, finally taking out of the furnace and air cooling, welding the two lower dies into one body for easy machining, and then machining the hot forging die through a reverse digital model to remove the failed part of the hot forging die to obtain the cavity to be remanufactured.

6. A method for rapidly removing failure areas of hot forging die additive remanufacturing according to claim 5, characterized in that: Use reverse digital modeling combined with CNC machining to accurately remove the failed area.

7. A method for rapidly removing failure areas of hot forging die additive remanufacturing according to claim 1, characterized in that: Finite element analysis technology is used to determine the arc additive remanufacturing area based on the overall heat flux balance of the hot forging die. A digital model is reversely established to remove the fatigue stress layer of the lower die and the arc additive remanufacturing path is planned for the digital model.

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