Method for repairing local defects of roller through electric arc additive manufacturing

Abstract

The invention relates to the technical field of roller local repairing, in particular to a method for repairing roller local defects through electric arc additive manufacturing. The method comprises the following steps: (1) cleaning defects of the roller, milling the roller into an inverted frustum shape, and cleaning the roller with acetone after polishing; (2) scanning the repair area by using a three-dimensional scanner, and generating a corresponding deposition path plan through slicing software; (3) analyzing stress field distribution of the roller by utilizing finite element software, and judging the rationality of the deposition path; (4) locally preheating the area around the gap of the roller by using an induction heating device; (5) a robot is adopted for conducting electric arc additive manufacturing on the defect area, and the defect area is gradually cooled to the room temperature from the periphery to the center; and (6) machining is conducted, and the flatness and smoothness of the roller repairing area are improved. The method is characterized in that the roller cracking risk under a specific deposition path is estimated in advance by adopting a finite element simulation method, a scientific basis is provided for optimizing an electric arc additive manufacturing repair process, the roller is fully utilized, and the steel rolling cost is remarkably reduced.

Description

Technical Field

[0001] The invention relates to the technical field of local repair of rolling mill rolls, and in particular to a method for repairing local defects of rolling mill rolls through arc additive manufacturing. Background Art

[0002] my country is a major steel producer and consumer in the world. Most steel products need to be rolled to a specific size and shape before they can be supplied to downstream industries to meet their requirements for product accuracy and performance. Rollers are responsible for plastic deformation of rolled pieces and are important consumables in steel rolling production lines. Not only is their performance directly related to product quality, but they also account for a large proportion of production costs. In the actual rolling process, the working conditions of the rolls are extremely complex. They not only bear high-load rolling forces, but also face cyclic alternating stresses caused by high-temperature rolled pieces and cooling water. This complex stress state makes the rolls prone to defects such as wear, chipping, and cracks, which significantly reduces the service life of the rolls. Generally speaking, the mass of the rolls ranges from a few tons to dozens of tons. If the entire roll is directly scrapped due to these local defects, it will cause huge economic losses.

[0003] At present, the repair methods of rollers mainly include machining, welding surfacing and laser cladding. Machining is to remove the defective parts on the surface of the roller by grinding, which will reduce the overall roller diameter of the roller, thereby shortening its service life and increasing production costs. The existing roller surfacing process mostly relies on manual experience to repair the defective parts, and does not quantitatively consider the impact of welding stress. Since the roller material is mostly medium and high carbon steel, it has a high hardening tendency and crack sensitivity. After surfacing, cracks are easily generated around the defects or at the welded joints, which buries serious production risks in the subsequent rolling process. The laser cladding process is to deposit metal powder on the surface of the roller by laser. The repair cost of this method is high, the process control requirements are high, and the repair efficiency is low when the defect size is large. Therefore, it is urgent to establish a standardized arc additive manufacturing roller repair method to achieve precise control of the temperature field and stress field, avoid roller cracking, extend the service life of the roller, and thus achieve the purpose of reducing the cost of steel rolling. Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for repairing local defects of a rolling mill roll by using arc additive manufacturing.

[0005] The technical solution adopted by the present invention is:

[0006] (1) Use a gantry machining center to clean the defective position of the roll. The milling area should be 2~3 mm extended outward from the actual defect contour, and the machining depth should exceed the deepest point of the defect by 0.5~1.0 mm to ensure that the defect is completely removed and the roll body material is exposed. According to the three-dimensional geometric shape of the actual defect, the defective area is milled into an inverted cone shape with a groove feature. The outer surface of the inverted cone is finely polished to improve the surface finish and adhesion, and then cleaned with acetone to ensure that oil and impurities are completely removed to prepare for the subsequent arc additive deposition process.

[0007] (2) Use a 3D scanner to accurately obtain the specific geometry and size of the repair area. Use slicing software to process the scanned data and generate the corresponding deposition path planning based on the selected arc additive manufacturing process parameters.

[0008] (3) Use finite element software to establish a three-dimensional solid model of the roller with a notch, and perform numerical simulation based on the deposition path generated by the slicing software to analyze the temperature field and stress field distribution of the roller under this path. Use the stress cloud map to determine whether the maximum stress is lower than the tensile strength of the roller body material to ensure that the roller will not crack. If the maximum stress on the roller exceeds the tensile strength, the deposition path needs to be readjusted until the force on the roller body meets the requirements during the arc additive manufacturing process, thereby effectively avoiding the risk of cracking.

[0009] Preferably, thermal effects and phase change mechanisms are introduced into the material model to comprehensively consider the coupling effects of thermal stress and tissue stress.

[0010] Furthermore, the total strain It can be expressed as elastic strain , plastic strain , thermal strain Phase transformation strain sum:

[0011]

[0012]

[0013]

[0014]

[0015]

[0016] In the formula, is Young's modulus; is Poisson's ratio; is the yield surface; is the plastic flow factor; is the volume fraction of the i-th phase; is the thermal expansion coefficient of the i-th phase; The volume difference.

[0017] Furthermore, the phase transition types include diffusion-type phase transition and non-diffusion-type phase transition.

[0018] The diffusion phase transition kinetics under isothermal conditions can be expressed as:

[0019]

[0020] In the formula, and It is the temperature-dependent coefficient obtained from the isothermal transformation curve.

[0021] The kinetics of non-diffusion phase transformation, such as martensitic phase transformation, can be expressed as:

[0022] f M = f γ * { 1 − exp [ − c ( M s − T ) ] }

[0023] Where: is the volume fraction of newly formed martensite; is the martensitic transformation starting temperature; To reflect the phase change evolution rate constant; is the current temperature; When the temperature reaches Austenite volume fraction.

[0024] Furthermore, heat exchange during arc additive manufacturing includes convection, radiation and heat conduction types.

[0025] Convective heat exchange It can be expressed as:

[0026]

[0027] In the formula, is the convective heat transfer coefficient; is the ambient temperature.

[0028] Radiant heat exchange It can be expressed as:

[0029] q rad = ε σ ′ [ ( T − T z ) 4 − ( T ∞ − T z ) 4 ]

[0030] In the formula, is the material emissivity; is the Stefan-Boltzmann constant, take ; is absolute zero, ; is the ambient temperature.

[0031] Heat conduction within the material It can be expressed as:

[0032]

[0033] In the formula, is the thermal conductivity, is the cross-sectional area, is the temperature gradient.

[0034] (4) Use an induction heating device to locally preheat the area around the notch of the roll. The preheating area is 8 to 10 times the maximum size of the notch to ensure uniform temperature distribution. The preheating temperature is set at 300 to 500 °C, and the heating rate is 10 to 20 °C / s. The induction heating device is mainly composed of an induction heating power supply and an induction coil, where the induction coil can be in the shape of a disk or a box.

[0035] (5) Multi-pass and multi-layer arc additive manufacturing can be carried out using arc forms such as tungsten inert gas welding (TIG) or metal inert gas welding (MIG).

[0036] Preferably, a cold metal transfer (CMT) process with a smaller heat input is used to reduce the accumulation of thermal stress and improve the repair quality.

[0037] According to the selected welding wire and specific process requirements, select appropriate shielding gas, such as a mixture of argon and helium, to prevent oxidation during the deposition process and ensure the quality of the weld.

[0038] The welding gun is installed on the robot arm. The robot posture is adjusted according to the optimized deposition path, and the robot moves along the axial, radial and vertical directions of the roller to complete the arc additive repair process. The thickness of the single layer deposition ranges from 1 to 3 mm, ensuring the forming quality and stability of each layer, thereby ensuring the repair effect and the performance of the roller.

[0039] An infrared imager is used to monitor the temperature distribution in the notch area and surrounding areas in real time, and the induction current is adjusted according to the detection results to ensure that the interlayer temperature during the arc additive manufacturing process is maintained in the range of 300~500 ℃ to avoid excessive residual stress caused by uneven temperature distribution.

[0040] After the deposition is completed, the roller repair area and its surroundings are insulated with insulation cotton for 1 to 3 hours. Then, the roller is gradually cooled from the outer ring to the center of the repair area to ensure that the temperature drops evenly and avoid the generation of new internal stress during the cooling process. When the temperature drops below 200 °C, the heating device and insulation cotton are removed to allow the roller to cool naturally to room temperature.

[0041] (6) Machining the arc additive deposition area, and improving the flatness and finish of the roll repair area by grinding to ensure that the surface is smooth and meets the use requirements of the roll.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The use of robots to precisely control the arc additive deposition path makes it possible to repair complex defect shapes, greatly improving repair accuracy and efficiency;

[0044] The coupling effect of temperature effect and phase change mechanism on stress is considered in the material model, so as to achieve accurate prediction of roller stress field;

[0045] The finite element simulation method is used to predict the cracking risk index under a specific deposition path in advance, providing a scientific basis for optimizing the arc additive manufacturing repair process;

[0046] Realize the effective utilization of the rolls, avoid the scrapping of the entire rolls due to local defects, extend the service life of the rolls, significantly reduce the cost of steel rolling, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a flow chart of the method for repairing local defects of a rolling mill roll by arc additive manufacturing according to the present invention;

[0048] Figure 2 It is a schematic diagram of a roller with defects in the present invention.

[0049] Figure 3 A schematic diagram of a roller after the defects are milled in the present invention;

[0050] Figure 4 It is the inverted frustum-shaped area that needs to be repaired in the present invention. DETAILED DESCRIPTION

[0051] This embodiment provides a method for repairing local defects of a rolling mill roll by arc additive manufacturing, such as Figure 1 As shown. Specifically including the following steps:

[0052] (1) Use the gantry machining center to clean the defective positions of the steel rolls, such as Figure 2 The milling area should be 2 mm outward from the actual defect contour, and the processing depth should exceed the deepest point of the defect by 0.5 mm to ensure that the defect is completely removed and the roll body material is exposed. According to the three-dimensional geometric shape of the actual defect, the defect area is milled into an inverted cone shape with a groove feature, such as Figure 3 The outer surface of the inverted cone is finely ground to improve surface cleanliness and material adhesion, and then cleaned with acetone to ensure that oil and impurities are completely removed to prepare for the subsequent arc additive deposition process.

[0053] (2) Use a 3D scanner to accurately obtain the specific geometry and size of the repair area. Use slicing software to process the scanned data and generate the corresponding path planning based on the selected arc additive manufacturing process parameters.

[0054] (3) Abaqus finite element software is used to establish a three-dimensional solid model of a roll with a notch, and numerical simulation is performed based on the deposition path generated by the slicing software to analyze the temperature field and stress field distribution of the roll under this path. The stress cloud diagram is used to determine whether the maximum stress is lower than the tensile strength of the roll body material to ensure that the roll will not crack. If the maximum stress on the roll exceeds the tensile strength, the deposition path needs to be readjusted until the force on the roll body meets the requirements during the arc additive manufacturing process, thereby effectively avoiding the risk of cracking.

[0055] Preferably, thermal effects and phase change mechanisms are introduced into the material model to comprehensively consider the coupling effects of thermal stress and tissue stress.

[0056] Furthermore, the total strain Can be expressed as elastic strain , plastic strain , thermal strain Phase transformation strain sum:

[0057]

[0058]

[0059]

[0060]

[0061]

[0062] In the formula, is Young's modulus; is Poisson's ratio; is the yield surface; is the plastic flow factor; is the volume fraction of the i-th phase; is the thermal expansion coefficient of the i-th phase; The volume difference.

[0063] Furthermore, the phase transition types include diffusion-type phase transition and non-diffusion-type phase transition.

[0064] The diffusion phase transition kinetics under isothermal conditions can be expressed as:

[0065]

[0066] In the formula, and It is the temperature-dependent coefficient obtained from the isothermal transformation curve.

[0067] The kinetics of non-diffusion phase transformation, such as martensitic phase transformation, can be expressed as:

[0068] f M = f γ * { 1 − exp [ − c ( M s − T ) ] }

[0069] Where: is the volume fraction of newly formed martensite; is the martensitic transformation starting temperature; To reflect the phase change evolution rate constant; is the current temperature; When the temperature reaches Austenite volume fraction.

[0070] Furthermore, heat exchange during arc additive manufacturing includes convection, radiation and heat conduction types.

[0071] Convective heat exchange It can be expressed as:

[0072]

[0073] In the formula, is the convective heat transfer coefficient; is the ambient temperature.

[0074] Radiant heat exchange It can be expressed as:

[0075] q rad = ε σ ′ [ ( T − T z ) 4 − ( T ∞ − T z ) 4 ]

[0076] In the formula, is the material radiation coefficient, which is taken as 0.8; is the Stefan-Boltzmann constant, take ; is absolute zero, ; is the ambient temperature.

[0077] Heat conduction within the material It can be expressed as:

[0078]

[0079] In the formula, is the thermal conductivity, is the cross-sectional area, is the temperature gradient.

[0080] (4) Use an induction heating device to locally preheat the area around the notch of the roll. The preheating area is 10 times the maximum size of the notch to ensure uniform temperature distribution. The preheating temperature is set to 300 °C and the heating rate is 10 °C / s. The induction heating device is mainly composed of an induction heating power supply and an induction coil, where the induction coil can be in the shape of a disk or a box.

[0081] (5) Use low-carbon high-strength steel welding wire ER120S-G for multi-pass and multi-layer arc additive manufacturing, which can adopt arc forms such as tungsten inert gas welding (TIG) or metal inert gas welding (MIG).

[0082] Preferably, a cold metal transfer (CMT) process with a smaller heat input is used to reduce the accumulation of thermal stress and improve the repair quality.

[0083] A mixture of argon and helium is used as the shielding gas to prevent oxidation during the deposition process and ensure the quality of the weld.

[0084] The welding gun is installed on the robot arm. The robot posture is adjusted according to the optimized deposition path, and the robot moves along the axial, radial and vertical directions of the roller to complete the arc additive repair process. The thickness range of single-layer deposition is 1.5 mm, ensuring the forming quality and stability of each layer, thereby ensuring the repair effect and the performance of the roller.

[0085] The temperature distribution in the notch area and surrounding areas is monitored in real time using an infrared imager, and the induction current is adjusted based on the detection results to ensure that the interlayer temperature during arc additive manufacturing is kept within 300 °C. This helps avoid excessive residual stress caused by uneven temperature distribution.

[0086] After the deposition is completed, the repair area and its surroundings are insulated with heat insulation cotton for 2 hours. Then, the repair area is gradually cooled from the outer ring to the center to ensure that the temperature drops evenly and avoid the generation of new internal stress during the cooling process. When the temperature drops below 200 ° C, the heating device and heat insulation cotton are removed to allow the roller to cool naturally to room temperature.

[0087] (6) Machining the arc additive deposition area to improve the flatness and finish of the roller by grinding to ensure that the surface is smooth and meets the requirements for the use of the roller.

[0088] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for repairing local defects of a rolling mill roll by arc additive manufacturing, characterized in that The following steps are involved: (1) Use a gantry machining center to clean the defective position of the roll. The milling area should be 2 to 3 mm outside the actual defect contour, and the machining depth should exceed the deepest point of the defect by 0.5 to 1.0 mm to ensure that the defect is completely removed and the roll body material is exposed. According to the actual three-dimensional geometric shape of the defect, the defect area is milled into an inverted frustum with a bevel feature. The outer surface of the inverted frustum is finely polished to improve the surface finish and adhesion, and then cleaned with acetone to ensure that oil and impurities are completely removed to prepare for the subsequent arc additive deposition process; (2) Use a 3D scanner to accurately obtain the specific geometry and size of the repair area. Use slicing software to process the scanned data and generate the corresponding deposition path planning based on the selected arc additive manufacturing process parameters; (3) Use finite element software to establish a three-dimensional solid model of the roller with a notch, and perform numerical simulation based on the deposition path generated by the slicing software to analyze the temperature field and stress field distribution of the roller under this path. Use the stress cloud map to determine whether the maximum stress is lower than the tensile strength of the roller body material to ensure that the roller will not crack. If the maximum stress on the roller exceeds the tensile strength, the deposition path needs to be readjusted until the force on the roller body meets the requirements during the arc additive manufacturing process, thereby effectively avoiding the risk of cracking; (4) Use an induction heating device to locally preheat the area around the notch of the roll. The preheating area is 8 to 10 times the maximum size of the notch to ensure uniform temperature distribution. The preheating temperature is set at 300 to 500 °C, and the heating rate is 10 to 20 °C / s. The induction heating device is mainly composed of an induction heating power supply and an induction coil, where the induction coil can be disc-shaped or box-shaped; (5) Multi-pass and multi-layer arc additive manufacturing can be carried out using arc forms such as tungsten inert gas welding (TIG) or metal inert gas welding (MIG); (6) Machining the arc additive deposition area to improve the flatness and finish of the roller by grinding to ensure that the surface is smooth and meets the use requirements of the roller.

2. The method for repairing local defects of a rolling mill roll by arc additive manufacturing according to claim 1, characterized in that: Thermal effects and phase change mechanisms are introduced into the material model, and the coupling effects of thermal stress and tissue stress are comprehensively considered.

3. The method for repairing local defects of a rolling mill roll by arc additive manufacturing according to claim 2, characterized in that: Furthermore, the total strain It can be expressed as elastic strain , plastic strain , thermal strain Phase transformation strain sum: ； ； ； ； ； In the formula, is Young's modulus; is Poisson’s ratio; is the yield surface; is the plastic flow factor; is the volume fraction of the i-th phase; is the thermal expansion coefficient of the i-th phase; is the volume difference; Furthermore, the phase transition types include diffusion phase transition and non-diffusion phase transition; The diffusion phase transition kinetics under isothermal conditions can be expressed as: ； In the formula, and is the temperature-dependent coefficient obtained from the isothermal transformation curve; The kinetics of non-diffusion phase transformation, such as martensitic phase transformation, can be expressed as: ； Where: is the volume fraction of newly formed martensite; is the martensitic transformation starting temperature; To reflect the phase change evolution rate constant; is the current temperature; When the temperature reaches Austenite volume fraction at ; Furthermore, heat exchange during arc additive manufacturing includes convection, radiation and heat conduction types; Convective heat exchange It can be expressed as: ； In the formula, is the convective heat transfer coefficient; is the ambient temperature; Radiant heat exchange It can be expressed as: ； In the formula, is the material emissivity; is the Stefan-Boltzmann constant, take ; is absolute zero, ; is the ambient temperature; Heat conduction within the material It can be expressed as: ； In the formula, is the thermal conductivity, is the cross-sectional area, is the temperature gradient.

4. The method for repairing local defects of a rolling mill roll by arc additive manufacturing according to claim 1, characterized in that: The cold metal transfer (CMT) process with less heat input is used to reduce the accumulation of thermal stress and improve the quality of repair.

5. The method for repairing local defects of a rolling mill roll by arc additive manufacturing according to claim 1, characterized in that: According to the selected welding wire and specific process requirements, select appropriate shielding gas, such as a mixture of argon and helium, to prevent oxidation during the deposition process and ensure the quality of the weld; The welding gun is installed on the robot arm. The robot posture is adjusted according to the optimized deposition path, and the robot moves along the axial, radial and vertical directions of the roller to complete the arc additive repair process. The thickness of the single layer deposition ranges from 1 to 3 mm, ensuring the forming quality and stability of each layer, thereby ensuring the repair effect and the performance of the roller.

6. The method for repairing local defects of a rolling mill roll by arc additive manufacturing according to claim 1, characterized in that: Use an infrared imager to monitor the temperature distribution in the notch area and surrounding areas in real time, and adjust the induction current according to the detection results to ensure that the interlayer temperature during arc additive manufacturing is maintained in the range of 300~500℃ to avoid excessive residual stress caused by uneven temperature distribution; After the deposition is completed, the roller repair area and its surroundings are insulated with insulation cotton for 1 to 3 hours. Then, the roller is gradually cooled from the outer ring to the center of the repair area to ensure that the temperature drops evenly and avoid the generation of new internal stress during the cooling process. When the temperature drops below 200 °C, the heating device and insulation cotton are removed to allow the roller to cool naturally to room temperature.

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