A forming process for reducing hot forging die wear

Abstract

The present invention discloses a forming process for reducing the wear of hot forging dies, the forming process includes the processes of blanking, blank heating, upsetting and die forging, wherein when the upsetting piece is transferred to the die forging process, the surface of the upsetting piece is subjected to rapid cooling treatment, so that the surface temperature of the upsetting piece is rapidly cooled and the surface temperature of the upsetting piece is higher than the final forging temperature, and then a lubricant is evenly sprayed on the surface of the upsetting piece, followed by die forging. The forming process of the present invention can effectively reduce the temperature rise of the die and the temperature gradient of the core surface, so that the stress of the die is reduced during the forging cycle, thereby increasing the life of the forging die.

Description

Technical Field

[0001] The invention belongs to the technical field of dies, and in particular relates to a forming process for reducing the wear of a hot forging die. Background Art

[0002] Forging is generally used for the forming of key parts in the automotive, aerospace, machinery, medical equipment and other industries. If hot forging is used, it generally includes upsetting, pre-forging, final forging and trimming. Because the temperature of the blank in contact with the pre-forging die is high, and the deformation and load are large during forming, severe thermal mechanical fatigue will occur under the action of cyclic thermal stress and mechanical stress, and wear will occur after a small number of forging times. It seriously affects product quality, die life and production continuity.

[0003] Under sliding contact conditions, temperature and load are important factors affecting the wear performance of the die. When a high-temperature metal billet contacts a low-temperature die, part of the die surface expands due to heat, and at the same time, compressive stress is formed on the surface due to the restraint from the inside of the die. When the compressive stress exceeds the high-temperature yield strength, plastic deformation occurs. After forming, the forging is ejected from the die, and the die surface is cooled and lubricated with a water-based or oil-based lubricant, which generates tensile stress on the die surface. With the increase in the number of forging cycles, the die surface is repeatedly heated and cooled, resulting in fatigue, which eventually leads to thermal cracking. The oxide scale on the surface of the billet enters the die and causes abrasive wear. Under the combined influence of these factors, the die will be severely worn, thereby reducing the service life of the die. Therefore, it is necessary to propose a new process technology solution to reduce die wear. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a forming process for reducing the wear of the hot forging die, which can significantly reduce the wear of the pre-forging die.

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

[0006] A forming process for reducing the wear of a hot forging die includes the processes of blanking, blank heating, upsetting and die forging, wherein when the upsetting piece is transferred to the die forging process, the surface of the upsetting piece is subjected to a rapid cooling treatment so that the surface temperature of the upsetting piece is rapidly cooled and the surface temperature of the upsetting piece is higher than the final forging temperature, and then a lubricant is evenly sprayed on the surface of the upsetting piece, followed by die forging.

[0007] Preferably, after the surface of the upsetting piece is subjected to rapid cooling treatment, the temperature difference between the core and the surface of the upsetting piece is controlled within 300°C-400°C.

[0008] Preferably, when the surface of the upsetting piece is subjected to rapid cooling, the average cooling rate of the upsetting piece is controlled at 200° C. / s-300° C. / s.

[0009] Preferably, after the blank is upset, the core temperature of the upset piece is maintained within ±50°C of the furnace temperature.

[0010] Preferably, the above process of the present invention is suitable for die forging of claw poles of automobile generators and any other products that can be processed by die forging.

[0011] Preferably, when the surface of the upsetting piece is subjected to the rapid cooling and cooling treatment, the surface of the upsetting piece is subjected to the rapid cooling and cooling treatment by spraying cooling water.

[0012] Preferably, the lubricant is water-based graphite, and after the water-based graphite is evenly sprayed on the surface of the upsetting part, a graphite lubricant layer is attached to the surface of the upsetting part.

[0013] Preferably, the method further includes preheating the die forging die at a temperature of 200°C-300°C.

[0014] The present invention has the following beneficial effects:

[0015] The forming process for reducing the wear of the hot forging die of the present invention adopts a rapid cooling and cooling treatment on the surface of the upsetting part to greatly reduce the surface temperature of the upsetting part. In this way, when the pre-forging is continued, the temperature gradient when the blank contacts the die is greatly reduced, so the temperature rise and thermal stress on the surface of the pre-forging die are also greatly reduced. After the stress level on the surface of the pre-forging die is greatly reduced, the generation of cracks is delayed, and the fatigue cycles that the die can withstand are greatly improved. Since only the surface of the upsetting part is subjected to a rapid rapid cooling and cooling treatment, the core temperature of the upsetting part is still maintained near the furnace temperature, which will not affect the fluidity of the blank, nor the filling performance of the blank. Subsequently, the lubricant is evenly sprayed on the surface of the upsetting part to increase the lubrication effect, prevent the forging forming load from increasing, and effectively prevent the problem of reduced die life caused by the increase in forging load. Rapid cooling of the surface of the upsetting part is also beneficial to remove the oxide scale remaining on the surface of the upsetting part. Later, lubricant can be evenly sprayed to prevent the surface of the upsetting part from being oxidized again during the transfer process, which is beneficial to improving the surface quality of the forging and preventing the oxide scale from entering the die cavity and causing abrasive wear. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a forming process flow chart of the present invention;

[0017] Figure 2 It is the sn curve diagram of the pre-forging die material;

[0018] FIG3 (a) is a schematic diagram of the temperature field of an upsetting piece in a conventional forging process; FIG3 (b) is a schematic diagram of the temperature field of an upsetting piece in an embodiment of the present invention;

[0019] FIG. 4 (a) is a schematic diagram of the temperature field of a pre-forged part in a conventional forging process; FIG. 4 (b) is a schematic diagram of the temperature field of a pre-forged part in an embodiment of the present invention;

[0020] FIG5(a) is a schematic diagram of the temperature field of the pre-forging upper die in the existing forging process; FIG5(b) is a schematic diagram of the temperature field of the pre-forging upper die in the embodiment of the present invention;

[0021] FIG. 6 ( a ) is a schematic diagram of the temperature field of the pre-forging lower die in the existing forging process; FIG. 6 ( b ) is a schematic diagram of the temperature field of the pre-forging lower die in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] The forming process flow chart of the present invention for reducing the wear of hot forging dies is as follows: Figure 1 As shown in FIG. 1 , the specific implementation process of the process is as follows: (1) blanking: the long bar is cut into a cylindrical billet of a certain diameter and length by a shearing device; (2) billet heating: the cylindrical bar is heated to a specified temperature; (3) upsetting: the heated billet is quickly transferred to a flat anvil for upsetting to remove the surface oxide scale; (4) the upset piece is quickly transferred to the top of the pre-forging die. In this process, an automatic spray system is used to firstly perform a short-term, high-flow, high-speed and high-pressure spray quenching and cooling treatment on the surface of the upset piece to quickly cool the surface of the upset piece; then, water-based graphite is sprayed on the upset piece to make a layer of graphite lubricant adhere to the surface of the upset piece; (5) forging: the upset piece with quenching and cooling treatment and graphite adhered on the surface is placed in a forging die for forging to complete the forging.

[0024] In the forging process, the wear, thermal cracking and plastic deformation of hot forging dies are all related to the surface temperature of the die, so it is important to understand the changes in the surface temperature of the die. During the hot forging process, the high-temperature billet contacts the surface of the die cavity, causing the temperature of the die surface to rise rapidly. If the temperature rise exceeds the tempering temperature, it will lead to deterioration of the structure and performance. If the temperature rise exceeds the yield strength of the die material at this temperature, the die will be plastically deformed at this location under the action of the forging load. As the forging is ejected from the die cavity, the die will be sprayed to cool and lubricate, and the die surface will be rapidly cooled. This reciprocating temperature cycle causes the surface of the die cavity to be subjected to periodic tensile and compressive stresses. Thermal cracking is a thermal fatigue phenomenon caused by repeated heating and cooling of the hot forging die surface. The stress in a cycle can be expressed as:

[0025] (1)

[0026] Where: Stress; E—elastic modulus; α—thermal expansion coefficient; Temperature gradient; μ—Poisson’s ratio.

[0027] Since the three parameters of elastic modulus, thermal expansion coefficient and Poisson's ratio change little with temperature, generally not exceeding 5%, they can be approximately considered as constants. Therefore, in order to prevent mold wear, the general method is to reduce the temperature gradient △T, or increase the yield strength of the material. After the mold material is selected, the temperature gradient can only be reduced to reduce thermal stress.

[0028] The forming process of the present invention can effectively reduce the temperature rise of the die and the temperature gradient of the core surface, so that the stress of the die during the forging cycle is reduced, thereby increasing the life of the forging die.

[0029] Example

[0030] The forming process of this embodiment, taking the claw pole of the automobile generator as an example, adopts a method of rapid cooling and cooling the surface of the upset part by spraying with high-flow, high-pressure and high-speed for a short time, and rapidly reducing the surface temperature of the blank from the original 1200℃~1250℃ to 800℃~900℃, and the average cooling rate is controlled at 200℃~300℃ / s, and the core surface temperature difference is 300℃~400℃, as shown in Figure 3 (b). This can effectively reduce the temperature gradient between the blank and the die, and reduce the stress level in the forging die cycle. The temperature distribution of the conventional blank that has not been treated with high-flow, high-pressure and high-speed spraying is shown in Figure 3 (a).

[0031] The claw pole pre-forging process was simulated by finite element software, and the temperature field of the forgings of the new process and the original process were compared, as shown in Figure 3 (a) and Figure 3 (b). The surface temperature of the pre-forging was reduced from the original 779℃ (Figure 4 (a)) to 656℃ (Figure 4 (b)).

[0032] The temperature fields of the pre-forging dies of the process of the present invention and the original process are compared, as shown in Figures 5 (a), 5 (b) and 6 (a), 6 (b). During forging, the die is preheated at 250°C. After the pre-forging is completed, the temperature of the easily worn area of ​​the pre-forging upper die without surface quenching treatment rises to 759°C, as shown in Figure 5 (a), while the temperature of the easily worn area of ​​the pre-forging upper die after the surface high-flow high-speed high-pressure spraying treatment of the process of the present invention rises to 687°C, as shown in Figure 5 (b). Correspondingly, the temperature of the easily worn area of ​​the pre-forging lower die of the original process rises to 745°C, as shown in Figure 6 (a), and the temperature of the easily worn area of ​​the pre-forging upper die after the surface high-flow high-speed high-pressure spraying treatment of the process of the present invention rises to 679°C, as shown in Figure 6 (b).

[0033] The simulation results show that after the surface rapid cooling treatment, the surface temperature of the upsetting part is reduced from 1120℃ to 824℃ for the forging, which in turn affects the temperature change of the pre-forging part, and the surface temperature of the pre-forging part is reduced from 779℃ to 656℃. For the pre-forging die, the surface contact temperature range of the pre-forging upper die is reduced from 248℃~759℃ to 165℃~687℃, and the surface contact temperature range of the pre-forging lower die is reduced from 249℃~745℃ to 184℃~679℃.

[0034] The simulation results show that in the forming process of the present invention, after the upsetting process, a high-flow, high-speed, and high-pressure spray treatment is performed, and the surface temperature of the blank is significantly reduced, which in turn affects the temperature change of the pre-forging die, reduces the temperature influence area of ​​the pre-forging upper die, and significantly reduces the surface contact temperature. This effectively reduces the temperature gradient between the blank and the die, and also reduces the force in the forging die cycle, thereby delaying the generation of cracks.

[0035] From the above, it can be seen that the molding process of the present invention has the following advantages:

[0036] 1) This process can significantly reduce the surface temperature of the upsetting part by using a short-term, high-flow, high-speed, high-pressure spray to rapidly cool the surface of the upsetting part. In this way, when the new process is used for pre-forging, the contact temperature gradient between the billet and the die is greatly reduced.

[0037] Since the elastic modulus, thermal expansion coefficient and Poisson's ratio change little with temperature, generally not exceeding 5%, they can be approximately considered constants. When the temperature gradient △T between the billet and the die surface drops significantly, the stress on the pre-forging die surface also drops significantly. When the stress level drops significantly, the generation of cracks is delayed, and the number of fatigue cycles that the die can withstand is greatly increased. Figure 2 shown.

[0038] 2) Since only the surface of the upsetting part is subjected to short-term rapid strong cooling, the core of the upsetting part is still maintained at the original furnace temperature, which will not affect the fluidity of the billet or the filling performance of the billet. Subsequently, the upsetting part is sprayed with water-based graphite to increase the lubrication effect and prevent the increase of the forging forming load, thereby effectively preventing the problem of reduced die life caused by the increase of the forging load. Short-term high-flow, high-speed and high-pressure spraying treatment is also conducive to removing the oxide scale remaining on the surface of the upsetting part. Later, water-based graphite is sprayed to prevent the surface of the upsetting part from being oxidized again during the transfer process, which is conducive to improving the surface quality of the forging.

Claims

1. A forming process for reducing hot forging die wear, characterized in that: The process includes blanking, blank heating, upsetting and die forging. When the upsetting piece is transferred to the die forging process, the surface of the upsetting piece is subjected to rapid cooling to rapidly cool the surface of the upsetting piece and to make the surface temperature of the upsetting piece higher than the final forging temperature. Then, a lubricant is evenly sprayed on the surface of the upsetting piece, and then die forging is performed. After the surface of the upsetting part is rapidly cooled, the temperature difference between the core and the surface of the upsetting part is controlled within 300℃-400℃; When the surface of the upsetting part is subjected to rapid cooling treatment, the average cooling rate of the upsetting part is controlled at 200°C / s-300°C / s.

2. A forming process for reducing hot forging die wear according to claim 1, characterized in that: After the billet is upset, the core temperature of the upset piece is maintained within ±50°C of the furnace temperature.

3. A forming process for reducing hot forging die wear according to claim 2, characterized in that: The forged piece after die forging is a claw pole of an automobile generator.

4. A forming process for reducing hot forging die wear according to claim 2, characterized in that: When the surface of the upsetting part is subjected to rapid cooling and cooling treatment, the surface of the upsetting part is subjected to rapid cooling and cooling treatment by spraying cooling water with high pressure.

5. A forming process for reducing hot forging die wear according to claim 1, characterized in that: The lubricant is water-based graphite. After the water-based graphite is evenly sprayed on the surface of the upsetting part, a graphite lubricant layer is attached to the surface of the upsetting part.

6. A forming process for reducing hot forging die wear according to claim 1, characterized in that: It also includes preheating treatment of the die forging die, with the preheating temperature being 200°C-300°C.

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