Crankshaft blank forming process

Abstract

The invention discloses a crankshaft blank forming process, and relates to the technical field of crankshaft blank forming, medium carbon alloy steel is selected as a raw material, a rare earth mixture is added, after vacuum degassing smelting, low-pressure vacuum pouring is combined with electromagnetic rotary stirring, and molten steel stable mold filling and component homogenization are achieved; a conformal cooling structure of a casting mold is combined with a gradient cooling technology, a static magnetic field is synchronously applied in the cooling process, the casting solidification process is cooperatively controlled, and thermal stress concentration and structure defects are reduced; after the primary forging step, local pressure supplementation is applied to a forging blank, micro-pores are closed, and structure streamline distribution is optimized; after finish forging, the surface layer structure of the crankshaft forging is strengthened through laser shock to form a nanocrystalline strengthened layer, and the completeness of the interior and the surface layer structure of the forging is ensured through post-treatment and multi-stage flaw detection; the advantages of the casting process and the forging process are combined, air holes and surface cracks of the crankshaft blank are reduced, the material utilization rate in the forming process is increased, and meanwhile the mechanical property of the crankshaft blank is improved.

Description

Technical Field

[0001] The invention relates to the technical field of crankshaft blank forming, and in particular to a crankshaft blank forming process. Background Art

[0002] The crankshaft is a key power conversion or transmission component in mechanical equipment such as forging machines or punching machines. It is widely used in the fields of automobiles, ships, aviation, power generation equipment, etc. Its working environment is complex and it usually needs to withstand high-intensity torque, bending force and fatigue load; therefore, the mechanical properties, surface quality and overall reliability of the crankshaft have a decisive influence on the operating stability, life and energy efficiency of the mechanical equipment.

[0003] At present, the forming process of crankshaft blanks mainly includes casting, forging and powder metallurgy. Among them, forging is widely used in the manufacturing process of high-performance crankshafts because it can improve the density and mechanical properties of the internal structure of the material; although the traditional crankshaft forging process can meet the needs of mass production, with the continuous increase in market demand for high-performance crankshafts, the existing process has also exposed many limitations.

[0004] (1) Surface crack problem

[0005] In the existing crankshaft blank forming process, surface cracks are one of the most common quality defects; these cracks usually occur during forging, heat treatment or cooling, and the main reasons include uneven material force, unreasonable mold design, uneven temperature control during heating or cooling, etc. Surface cracks will not only reduce the fatigue resistance of the crankshaft, but may also expand during subsequent processing or use, causing the crankshaft to fail prematurely, thereby affecting the reliability and safety of mechanical equipment.

[0006] (2) Porosity and internal defects

[0007] In addition to surface cracks, pores and internal defects are also important factors affecting the quality of crankshafts; pores are mostly caused by the failure to completely discharge gas during the forging process, high impurity content in raw materials or improper heating temperature control; pores can lead to discontinuous structural lines of the metal organization, reducing the mechanical strength, wear resistance and fatigue resistance of the crankshaft. After high-intensity use, large cracks often occur at the location where the pores are formed, thereby affecting the overall stability of the mechanical equipment.

[0008] (3) Low material utilization

[0009] In the traditional forging process, a large machining allowance needs to be reserved on the forging blank, resulting in material waste and increasing the subsequent processing steps and costs. At the same time, the limitations of mold design and uneven metal flow during the forging process will also lead to excessive waste, further reducing the utilization rate of materials and increasing production costs.

[0010] (4) Limitations of heat treatment and cooling processes

[0011] After forging, crankshaft forgings need to undergo heat treatment to improve their mechanical properties. However, in the existing process, the temperature control in the heating and cooling links is uneven, which can easily lead to problems such as internal residual stress and uneven surface hardness, thereby affecting the wear resistance and crack resistance of the crankshaft; especially in the manufacturing process of large-size crankshafts, the temperature difference problem in the heat treatment process is more prominent, which can easily generate large internal stress, which will directly lead to cracking or deformation of the blank.

[0012] In order to meet the future demand for high-performance crankshafts, the existing process must be improved and optimized to improve the overall quality of crankshaft blank forming, increase the yield rate, extend the service life, and reduce production costs. This is not only of great significance for improving the power performance of mechanical equipment, but also lays a solid foundation for the sustainable development of the crankshaft manufacturing industry.

[0013] In summary, it is found that the prior art has at least the following technical problems:

[0014] The existing crankshaft blank forming process has process and technical problems such as surface cracks, pore defects and material waste. Summary of the invention

[0015] The purpose of the present invention is to provide a crankshaft blank forming process to solve the process and technical problems of surface cracks, pore defects and material waste in the existing crankshaft blank forming process.

[0016] The various technical effects that can be produced by the preferred technical solutions among the various technical solutions provided by the present invention are described in detail below.

[0017] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0018] The present invention provides a crankshaft blank forming process, comprising the following steps: S1, raw material pretreatment: alloy steel is selected as the raw material, rare earth mixture is added, and vacuum degassing and smelting is performed;

[0019] S2, smelting: the smelting temperature is controlled at 1500-1550°C, and the smelting time is controlled at 25-30 minutes;

[0020] S3. Pouring: The casting mold is preheated in advance, and the molten steel is poured in a low-pressure vacuum. While pouring, the molten steel in the mold is stirred by electromagnetic rotation;

[0021] S4. Solidification control: In conjunction with the mold-conforming cooling structure of the casting mold, the cooling temperature and cooling speed are controlled by gradient, the connecting rod journal and crank parts are cooled first, and the main journal area is kept warm and cooled slowly; a static magnetic field of 0.8-1T is applied to the entire mold during the entire cooling process;

[0022] S5, take out the crankshaft casting, heat it to the initial die forging temperature, and keep it warm for standby use;

[0023] S6, initial forging: preheat the forging die in advance, put the crankshaft casting in for initial die forging;

[0024] S7, local pressure replenishment: local pressure replenishment is performed on the connecting rod journal and main journal area, the temperature is controlled in the austenite formation area, the pressure is controlled at 125-135MPa, and the pressure is maintained for at least 30s;

[0025] S8. After final forging, the crankshaft forging is formed and placed in the room for air cooling;

[0026] S9, laser shock strengthening: laser shock strengthening is performed on the entire peripheral wall of the forging;

[0027] S10, post-processing the forging as a whole to form a crankshaft blank;

[0028] S11. After local milling of the main journal area of ​​the crankshaft blank, medium frequency quenching is performed to control the hardness to HRC52-56, and then magnetic particle inspection is performed;

[0029] S12. Perform ultrasonic flaw detection on the crankshaft blank and then accept it.

[0030] In one of the embodiments, in step S1, the raw material is medium carbon alloy steel; the added rare earth mixture is a rare earth mixture containing La and Ce, and 0.12Wt%-0.15Wt% of the rare earth mixture is added in mass percentage during the raw material smelting to refine the grains.

[0031] In one embodiment, in step S3, the casting mold preheating temperature is 900-1000°C, the molten steel pouring temperature is controlled at 1620-1680°C; the filling pressure is controlled at 0.6-0.8MPa, and the filling speed is controlled at 3-5m / s.

[0032] In one embodiment, the vacuum degree of the pouring environment of vacuum pouring is controlled at ≤10 -3 Pa is used to eliminate the pores generated when molten steel is filling the mold.

[0033] In one of the embodiments, the stirring frequency of the electromagnetic rotary stirring is controlled at 35-50 Hz, and the stirring time is ≥10 min, so as to uniformly distribute the composition of the molten steel in the mold and discharge the internal gas.

[0034] In one embodiment, in step S4, the connecting rod journal and crank portion of the crankshaft casting are preferentially water-cooled and the cooling rate is controlled at 10-12°C / s, the cooling rate of the main journal area is controlled at ≤2°C / s, and the cooling rate of the front and rear ends is controlled at 3-5°C / s.

[0035] In one embodiment, the crankshaft casting is heated to 1250°C in step S5; and the temperature of the forging blank is maintained between 1150-1220°C in the initial forging step S6; the temperature is controlled between 920-1000°C in the local pressurizing step S7; and after the final forging in step S8, the crankshaft forging is placed in the air cooling temperature zone in the room and cooled to 300°C.

[0036] In one embodiment, in step S9, the surface temperature of the crankshaft forging is raised to 320-330°C, and the surface of the crankshaft forging is laser-shock-hardened; the laser energy density is controlled at 5-8 GW / cm 2 The pulse width is 20ns, which is used to make the average surface residual stress of the entire peripheral wall of the crankshaft forging reach at least -400MPa.

[0037] In one of the embodiments, in step S10, after the crankshaft forging has passed step S9, it is placed in an air cooling temperature zone and air-cooled to a surface temperature of 300°C, and then the crankshaft forging is placed in a furnace for normalizing treatment; after normalizing treatment, the crankshaft forging is placed in an air cooling temperature zone and air-cooled to 300°C, and then placed in a furnace for tempering treatment; after tempering treatment, the crankshaft forging is placed in a furnace for insulation at 650°C for 2 hours, and after the insulation is completed, the crankshaft forging is placed in a furnace for furnace cooling to 300°C, and then the crankshaft forging is air-cooled to room temperature.

[0038] In one embodiment, after the local magnetic particle inspection of the journal area of ​​the crankshaft blank is passed in step S11, the process proceeds to step S12 for the overall ultrasonic inspection and acceptance of the crankshaft blank; in step S12, the ultrasonic inspection quality of the crankshaft blank must reach level three before it can be accepted.

[0039] The present invention aims at the problems of surface cracks, pore defects and material waste in the existing crankshaft blank forming process, and proposes a set of composite process solutions, the beneficial effects of which are mainly reflected in the following aspects:

[0040] First, the defects of crankshaft forming metal are suppressed by optimizing the materials; adding 0.12-0.15wt% of a rare earth mixture containing La and Ce can significantly refine the grain size inside the casting metal by adsorbing grain boundary impurities (such as sulfur and oxygen) and forming high-melting point compounds, thereby suppressing the generation of internal or surface cracks in the casting from the root of the overall metal structure.

[0041] Combined with vacuum degassing smelting, vacuum environment pouring and electromagnetic rotary stirring filling, the hydrogen and oxygen contents in the molten steel are reduced, and the porosity is reduced by more than 70% compared with the traditional crankshaft forming process. The size of the subcutaneous pores on the casting surface is controlled within a diameter of 0.2mm.

[0042] Thirdly, the processes during pouring work together to improve the density. During pouring, low-pressure vacuum pouring and electromagnetic stirring are superimposed, and low-pressure filling is used during pouring, combined with electromagnetic stirring, to increase the Reynolds number of the molten metal flow in the casting mold, thereby avoiding the generation of air turbulence during filling, and at the same time eliminating the interdendritic component segregation of the metal structure, reducing the shrinkage defect rate to below 0.3%, further optimizing the grain distribution, uniformizing the stress field, and reducing the occurrence of internal and surface defects of the casting.

[0043] During cooling, gradient cooling and static magnetic field are applied by controlling the temperature, and a conformal cooling structure is used to give priority to water cooling of the high stress bend area in the crankshaft casting. The main journal area is heat-insulated and slowly cooled to stagger the cooling rate ranges of the two areas, forming a cooling and forming sequence. Combined with the 0.8-1T static magnetic field applied during the entire cooling process, the dendrite coarsening phenomenon of the metal structure is jointly suppressed, the thermal stress peak of the casting is reduced by 40%, and the surface crack incidence is controlled below 5%. Among them, the heat-insulating and slow cooling of the main journal area combined with the static magnetic field treatment significantly improves the fatigue resistance of the main journal area of ​​the casting.

[0044] Furthermore, composite plastic strengthening and laser shock surface modification are combined with die forging to improve the tensile strength and fatigue life of forgings. After the initial die forging, the temperature of the forging is controlled in the temperature zone where austenite is formed. A local pressure-compensation process is used to apply a high pressure of 125-135MPa to key locations such as the connecting rod journal and the main journal to promote the closure of microscopic pores in the metal's internal structure, form a continuous streamline structure, optimize the streamline distribution of the metal structure, and improve the tensile strength. The local pressure-compensation process can also ensure higher dimensional accuracy at key locations.

[0045] Then through laser shock peening (LSP), 5-8GW / cm 2 High-energy laser pulses impact the surface of the forging, inducing a nanocrystalline layer with a depth of at least 0.3 mm, making the surface residual compressive stress at least -400 MPa, and increasing the fatigue life of the forging by more than 50%.

[0046] Furthermore, for the main journal area, through the combination of laser shock strengthening and medium frequency quenching, a gradient strengthening layer is formed on the outer periphery of the main journal perpendicular to the axis, thereby improving the fatigue limit of the main journal area.

[0047] Green manufacturing and cost optimization are achieved by saving the metal materials used in forming crankshaft blanks. A near-net-shape process design is adopted to cast crankshaft castings with a shape close to the finished product through a casting mold, and then the castings are precision forged to form crankshaft forgings with enhanced performance. Finally, local milling is combined to form the finished crankshaft blank, thereby increasing the metal material utilization rate of the entire crankshaft blank forming process to more than 85%, reducing machining allowance by at least 30% compared with traditional forging processes.

[0048] Magnetic particle testing is used to detect the key main journal area of ​​the crankshaft forging, and ultrasonic testing is used to detect the entire forging. Through double-stage testing, online control of crankshaft blank defects is achieved, the defect detection rate is improved to ensure the quality grade of the finished crankshaft blank, and the scrap rate in subsequent crankshaft blank processing is reduced to below 0.2%, saving overall costs.

[0049] In summary, the comprehensive performance of the crankshaft blank is improved. After the crankshaft blank is treated by this process, the hardness of the main journal area reaches HRC52-56, the core impact toughness of the entire crankshaft blank is maintained at AKV≥40J, and the dynamic stiffness is increased by 25%, which can meet the extreme transmission working conditions of high-power density mechanical equipment and greatly improve the comprehensive mechanical properties and operating conditions of the crankshaft blank. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the implementation mode will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0051] Figure 1 It is a structural schematic diagram of a crankshaft blank of the present invention;

[0052] Figure 2 It is a schematic diagram of the internal fiber structure of the crankshaft blank of the present invention;

[0053] Figure 3 It is a flow chart of the crankshaft blank forming process of the present invention.

[0054] The reference numerals are as follows:

[0055] 1. Crankshaft blank; 11. Front end; 12. Rear end; 13. Main journal; 14. Connecting rod journal; 15. Crank. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0057] A specific embodiment provides a crankshaft blank forming process, in which medium-carbon alloy steel is selected as raw material, a rare earth mixture is added, and after vacuum degassing and smelting, low-pressure vacuum pouring combined with electromagnetic rotary stirring is used to achieve smooth filling of molten steel and uniform composition; the conformal cooling structure of the casting mold is combined with gradient cooling technology, and a static magnetic field is simultaneously applied during the cooling process to coordinately control the solidification process of the casting to reduce thermal stress concentration and tissue defects; after the initial forging step, local compensating pressure is applied to the forging blank to close microscopic pores and optimize the streamline distribution of the metal structure; after the final forging, the surface structure of the crankshaft forging is strengthened by laser shock to form a nanocrystalline strengthening layer, and the integrity of the internal and surface structures of the forging is ensured by combining post-processing and multi-stage flaw detection; the present invention combines the advantages of casting and forging processes, reduces the pores and surface cracks of the crankshaft blank, and improves the material utilization rate in the forming process, while improving the mechanical properties of the crankshaft blank; effectively solves the process and technical problems of surface cracks, pore defects and material waste in the existing crankshaft blank forming process.

[0058] The first embodiment of the crankshaft blank forming process is as follows Figures 1 to 3 As shown, the method comprises the following steps: S1, raw material pretreatment: alloy steel is selected as raw material, rare earth mixture is added, and vacuum degassing and smelting is performed;

[0059] S2, smelting: the smelting temperature is controlled at 1500-1550°C, and the smelting time is controlled at 25-30 minutes;

[0060] S3. Pouring: The casting mold is preheated in advance, and the molten steel is poured in a low-pressure vacuum. While pouring, the molten steel in the mold is stirred by electromagnetic rotation;

[0061] S4. Solidification control: In conjunction with the mold-conforming cooling structure of the casting mold, the cooling temperature and cooling speed are controlled by gradient, the connecting rod journal and crank parts are cooled first, and the main journal area is kept warm and cooled slowly; a static magnetic field of 0.8-1T is applied to the entire mold during the entire cooling process;

[0062] S5, take out the crankshaft casting, heat it to the initial die forging temperature, and keep it warm for standby use;

[0063] S6, initial forging: preheat the forging die in advance, put the crankshaft casting in for initial die forging;

[0064] S7, local pressure replenishment: local pressure replenishment is performed on the connecting rod journal and main journal area, the temperature is controlled in the austenite formation area, the pressure is controlled at 125-135MPa, and the pressure is maintained for at least 30s;

[0065] S8. After final forging, the crankshaft forging is formed and placed in the room for air cooling;

[0066] S9, laser shock strengthening: laser shock strengthening is performed on the entire peripheral wall of the forging;

[0067] S10, post-processing the forging as a whole to form a crankshaft blank;

[0068] S11. After local milling of the main journal area of ​​the crankshaft blank, medium frequency quenching is performed to control the hardness to HRC52-56, and then magnetic particle inspection is performed;

[0069] S12. Perform ultrasonic flaw detection on the crankshaft blank and then accept it.

[0070] The crankshaft blank forming process provided by the present invention can effectively solve the common problems of surface cracks, pore defects and material waste in the existing process through multiple process steps, and significantly improve the overall quality grade of the crankshaft blank. The specific beneficial effects are analyzed as follows: (1) First, the defects of the crankshaft forming metal are suppressed by optimizing the material; 0.12-0.15wt% of a rare earth mixture containing La and Ce is added, which can significantly refine the grain size inside the casting metal by adsorbing grain boundary impurities (such as sulfur and oxygen) and forming high-melting point compounds, thereby suppressing the generation of internal or surface cracks in the casting from the root of the overall metal structure.

[0071] Combined with vacuum degassing smelting, vacuum environment pouring and electromagnetic rotary stirring filling, the hydrogen and oxygen contents in the molten steel are reduced, and the porosity is reduced by more than 70% compared with the traditional crankshaft forming process. The size of the subcutaneous pores on the casting surface is controlled within a diameter of 0.2mm.

[0072] (2) Secondly, the processes in the casting process work together to improve the density; during the casting, low-pressure vacuum casting and electromagnetic stirring are superimposed, and low-pressure filling is adopted during the casting, combined with electromagnetic stirring, so that the Reynolds number of the molten metal flow in the casting mold is increased, thereby avoiding the generation of air turbulence during filling, and at the same time eliminating the interdendritic component segregation of the metal structure, reducing the shrinkage defect rate to below 0.3%, further optimizing the grain distribution, uniformizing the stress field, and reducing the occurrence of internal and surface defects of the casting.

[0073] During cooling, gradient cooling and static magnetic field are applied by controlling the temperature, and a conformal cooling structure is used to give priority to water cooling of the high stress bend area in the crankshaft casting. The main journal area is heat-insulated and slowly cooled to stagger the cooling rate ranges of the two areas, forming a cooling and forming sequence. Combined with the 0.8-1T static magnetic field applied during the entire cooling process, the dendrite coarsening phenomenon of the metal structure is jointly suppressed, the thermal stress peak of the casting is reduced by 40%, and the surface crack incidence is controlled below 5%. Among them, the heat-insulating and slow cooling of the main journal area combined with the static magnetic field treatment significantly improves the fatigue resistance of the main journal area of ​​the casting.

[0074] (3) Furthermore, composite plastic strengthening and laser shock surface modification are combined with die forging to improve the tensile strength and fatigue life of forgings. After the initial die forging, the temperature of the forging is controlled in the temperature zone where austenite is formed. A local pressure-compensation process is used to apply a high pressure of 125-135 MPa to key locations such as the connecting rod journal and the main journal to promote the closure of microscopic pores in the metal internal structure, form a continuous streamline structure, optimize the streamline distribution of the metal structure, and improve the tensile strength. The local pressure-compensation process can also ensure higher dimensional accuracy of key locations.

[0075] Then through laser shock peening (LSP), 5-8GW / cm 2 High-energy laser pulses impact the surface of the forging, inducing a nanocrystalline layer with a depth of at least 0.3 mm, making the surface residual compressive stress at least -400 MPa, and increasing the fatigue life of the forging by more than 50%.

[0076] Furthermore, for the main journal area, through the combination of laser shock strengthening and medium frequency quenching, a gradient strengthening layer is formed on the outer periphery of the main journal perpendicular to the axis, thereby improving the fatigue limit of the main journal area.

[0077] (4) Save metal materials used in forming crankshaft blanks, achieve green manufacturing and cost optimization; by adopting a near-net-shape process design, a crankshaft casting with a shape close to the finished product is cast through a casting mold, and then the casting is precision forged to form a crankshaft forging with enhanced performance. Finally, combined with local milling, a finished crankshaft blank is formed, thereby increasing the metal material utilization rate of the entire crankshaft blank forming process to more than 85%, and reducing the machining allowance by at least 30% compared with the traditional forging process.

[0078] Magnetic particle testing is used to detect the key main journal area of ​​the crankshaft forging, and ultrasonic testing is used to detect the entire forging. Through double-stage testing, online control of crankshaft blank defects is achieved, the defect detection rate is improved to ensure the quality grade of the finished crankshaft blank, and the scrap rate in subsequent crankshaft blank processing is reduced to below 0.2%, saving overall costs.

[0079] (5) Improve the comprehensive performance of the crankshaft blank. After the crankshaft blank is treated by this process, the hardness of the main journal area reaches HRC52-56, the core toughness of the crankshaft blank as a whole remains AKV≥40J, and the dynamic stiffness is increased by 25%, which can meet the extreme transmission conditions of high-power density mechanical equipment and greatly improve the comprehensive mechanical properties and operating conditions of the crankshaft blank.

[0080] As one optional implementation,

[0081] In step S1, the raw material is medium carbon alloy steel; the added rare earth mixture is a rare earth mixture containing La and Ce, and 0.12Wt%-0.15Wt% of the rare earth mixture is added in mass percentage during the raw material smelting to refine the grains.

[0082] Specifically, the medium carbon alloy steel is 42CrMo.

[0083] Regarding step S3: in step S3, the preheating temperature of the casting mold is 900-1000°C, the molten steel pouring temperature is controlled at 1620-1680°C; the filling pressure is controlled at 0.6-0.8MPa, and the filling speed is controlled at 3-5m / s.

[0084] In addition, the vacuum degree of the pouring environment of vacuum pouring is controlled at ≤10 -3 Pa is used to eliminate the pores generated when molten steel is filling the mold.

[0085] While pouring, the entire casting mold is stirred by electromagnetic rotation, and the stirring frequency is controlled at 35-50 Hz, and the stirring time is ≥10 min.

[0086] During application, preheating the casting mold can reduce the temperature difference between the molten steel and the casting mold, improve the fluidity of the molten steel poured on the mold, and at the same time, vacuum pouring can effectively reduce the pores caused by pouring; electromagnetic rotary stirring is used to even out the composition of the molten steel in the mold and expel internal gas.

[0087] Regarding step S4: In step S4, the connecting rod journal and crank part of the crankshaft casting are preferentially water-cooled and the cooling rate is controlled at 10-12°C / s, the cooling rate of the main journal area is controlled at ≤2°C / s, and the cooling rate of the front and rear ends is controlled at 3-5°C / s.

[0088] During application, the cooling structure of the casting mold adopts a conformal cooling structure, so that the temperature distribution of each structural area of ​​the casting is uniform during cooling, thereby improving the effect of temperature gradient control.

[0089] Regarding the control of the die forging steps: in step S5, the crankshaft casting is heated to 1250°C; and in the initial forging step of step S6, the temperature of the forging blank is maintained between 1150-1220°C; in the local pressurization step of step S7, the temperature is controlled between 920-1000°C; after the final forging in step S8, the crankshaft forging is placed in the air cooling temperature zone in the room and the crankshaft forging is cooled to 300°C.

[0090] During application, the temperature of the crankshaft forging must be controlled at 800 degrees in step S8 final forging.

[0091] Regarding step S9: In step S9, the surface temperature of the crankshaft forging is raised to 320-330°C, and the surface of the crankshaft forging is laser impact strengthened; the laser energy density is controlled at 5-8GW / cm 2 , the pulse width is 20ns.

[0092] During application, the crankshaft forging is subjected to surface laser shock peening (LSP) to cause plastic deformation of the entire circumferential wall, i.e., the surface layer, of the crankshaft forging, thereby generating residual stress of compressive residual stress in the impact area, so that the average residual stress on the surface of the crankshaft forging reaches at least -400MPa, which can effectively offset the tensile stress generated by the crankshaft during use, thereby improving the fatigue strength and fatigue life of the material, and at the same time, it can also refine the surface grains of the crankshaft and increase the surface hardness, thereby improving the wear resistance of the crankshaft.

[0093] Regarding the post-processing steps: in step S10, after the crankshaft forging has passed step S9, it is placed in the air cooling temperature zone until it is air-cooled to a surface temperature of 300°C, and then the crankshaft forging is put into a furnace for normalizing treatment; after normalizing treatment, the crankshaft forging is placed in the air cooling temperature zone and air-cooled to 300°C, and then put into the furnace for tempering treatment; after tempering treatment, the crankshaft forging is placed in the furnace for insulation at 650°C for 2h, and after the insulation is completed, the crankshaft forging is placed in the furnace for furnace cooling to 300°C, and then the crankshaft forging is air-cooled to room temperature.

[0094] Regarding the quality inspection steps: after the local magnetic particle inspection of the journal area of ​​the crankshaft blank is passed in step S11, the process proceeds to step S12 for the overall ultrasonic inspection and acceptance of the crankshaft blank; in step S12, the ultrasonic inspection quality of the crankshaft blank must reach level three before it can be accepted.

[0095] During application, the crankshaft blank meets the third-level quality acceptance according to the ultrasonic flaw detection GB / T6402-08 regulations.

[0096] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A crankshaft blank forming process, characterized in that: The following steps are involved: S1. Raw material pretreatment: alloy steel is selected as raw material, rare earth mixture is added, and vacuum degassing and smelting is performed; S2, smelting: the smelting temperature is controlled at 1500-1550°C, and the smelting time is controlled at 25-30 minutes; S3. Pouring: The casting mold is preheated in advance, and the molten steel is poured in a low-pressure vacuum. While pouring, the molten steel in the mold is stirred by electromagnetic rotation; S4. Solidification control: In conjunction with the mold-conforming cooling structure of the casting mold, the cooling temperature and cooling speed are controlled by gradient, the connecting rod journal and crank parts are cooled first, and the main journal area is kept warm and cooled slowly; a static magnetic field of 0.8-1T is applied to the entire mold during the entire cooling process; S5, take out the crankshaft casting, heat it to the initial die forging temperature, and keep it warm for standby use; S6, initial forging: preheat the forging die in advance, put the crankshaft casting in for initial die forging; S7, local pressure replenishment: local pressure replenishment is performed on the connecting rod journal and main journal area, the temperature is controlled in the austenite formation area, the pressure is controlled at 125-135MPa, and the pressure is maintained for at least 30s; S8. After final forging, the crankshaft forging is formed and placed in the room for air cooling; S9, laser shock strengthening: laser shock strengthening is performed on the entire peripheral wall of the forging; S10, post-processing the forging as a whole to form a crankshaft blank; S11. After local milling of the main journal area of ​​the crankshaft blank, medium frequency quenching is performed to control the hardness to HRC52-56, and then magnetic particle inspection is performed; S12. Perform ultrasonic testing on the crankshaft blank and then accept it.

2. The crankshaft blank forming process according to claim 1, characterized in that: In step S1, the raw material is medium carbon alloy steel; the added rare earth mixture is a rare earth mixture containing La and Ce, and 0.12Wt%-0.15Wt% of the rare earth mixture is added in mass percentage during the raw material smelting to refine the grains.

3. The crankshaft blank forming process according to claim 1, characterized in that: In step S3, the casting mold preheating temperature is 900-1000°C, the molten steel pouring temperature is controlled at 1620-1680°C; the filling pressure is controlled at 0.6-0.8MPa, and the filling speed is controlled at 3-5m / s.

4. The crankshaft blank forming process according to claim 3, characterized in that: The vacuum degree of the pouring environment of vacuum pouring is controlled at ≤10 -3 Pa is used to eliminate the pores generated when the molten steel is filling the mold.

5. The crankshaft blank forming process according to claim 3, characterized in that: The stirring frequency of electromagnetic rotary stirring is controlled at 35-50Hz, and the stirring time is ≥10min, which is used to even out the composition of molten steel in the mold and expel internal gas.

6. The crankshaft blank forming process according to claim 1, characterized in that: In step S4, the connecting rod journal and crank part of the crankshaft casting are preferentially water-cooled and the cooling rate is controlled at 10-12°C / s, the cooling rate of the main journal area is controlled at ≤2°C / s, and the cooling rate of the front and rear ends is controlled at 3-5°C / s.

7. The crankshaft blank forming process according to claim 1, characterized in that: In step S5, the crankshaft casting is heated to 1250° C.; and in step S6, the temperature of the forging blank is maintained between 1150° C. and 1220° C.; In step S7, the temperature is controlled between 920-1000° C. during local pressure replenishment; After the final forging in step S8, the crankshaft forging is placed in an air cooling temperature zone in the room and cooled to 300°C.

8. The crankshaft blank forming process according to claim 1, characterized in that: In step S9, the surface temperature of the crankshaft forging is raised to 320-330°C, and the surface of the crankshaft forging is laser impact strengthened; the laser energy density is controlled at 5-8GW / cm 2 The pulse width is 20ns, which is used to make the average surface residual stress of the entire peripheral wall of the crankshaft forging reach at least -400MPa.

9. The crankshaft blank forming process according to claim 1, characterized in that: In step S10, after the crankshaft forging has passed step S9, it is placed in an air cooling temperature zone until the surface temperature reaches 300° C., and then the crankshaft forging is put into a furnace for normalizing treatment; After normalizing, the crankshaft forgings are placed in an air-cooling zone to be cooled to 300°C, and then put into a furnace for tempering. After tempering, the crankshaft forgings are placed in a furnace and kept at 650°C for 2 hours. After the insulation is completed, the crankshaft forgings are placed in a furnace and cooled to 300°C, and then air-cooled to room temperature.

10. The crankshaft blank forming process according to claim 1, characterized in that: After the crankshaft blank is subjected to partial magnetic particle inspection in the journal area and passes the inspection in step S11, the whole crankshaft blank is subjected to ultrasonic inspection and acceptance in step S12; In step S12, the ultrasonic flaw detection quality of the crankshaft blank must reach level three before it can be accepted.

Images