Small-batch hot stamping die based on surface direct air cooling

Abstract

The utility model discloses a small-batch hot stamping die based on surface direct air cooling, which comprises a convex die and a concave die, the concave die is provided with a concave part matched with a punch of the convex die, the surface of the convex die is provided with a first concave cavity which is concave towards the inside of the convex die, and the surface of the concave die is also provided with a second concave cavity which is concave towards the inside of the concave die. The first concave cavity and the second concave cavity are used for forming an airflow cooling channel communicated with an external pipeline, the air inlet end of the airflow cooling channel is connected with an air compressor through a compressed air pipeline, compressed air is blown into the mold through the pipeline, and circulation and heat exchange are carried out in the airflow cooling channel and on the surface of the mold. And the heated gas is discharged through the gas outlet end of the gas flow cooling channel. According to the stamping die, the concave cavity is formed in the surface of the die, the manufacturing cost and the maintenance cost of the die are lower than those of a mass production die, and the service life and the productivity of the die are higher than those of a trial-production die.

Description

Technical Field

[0001] The utility model relates to the technical field of hot stamping, and more specifically to a small batch hot stamping die and a cooling process based on direct surface air cooling. Background Art

[0002] High-strength steel structural parts are an effective means to improve the collision safety of automobiles. Hot stamping is one of the main processing methods for high-strength steel structural parts. It effectively solves the problems of poor formability and large springback of high-strength steel plates under room temperature stamping, and is widely used in the field of automobile manufacturing. There are two main types of steel plates suitable for hot stamping. The most widely used one is boron steel, which needs to be heated to 900-950℃ and kept warm for a few minutes to austenitize the metallographic structure, and then quickly stamped and formed and kept in the mold for pressure quenching. The cooling rate is required to be not less than 27℃ / s to achieve the transformation of austenitized structure into martensite structure and obtain high-strength stamping parts. The other is medium manganese steel. Due to the addition of an appropriate amount of manganese, the austenitization temperature only needs to be 800-850℃, and the cooling rate requirement is also greatly reduced (not less than 0.5℃ / s). For example, natural cooling in the air can achieve complete martensite and reach a high-strength state.

[0003] Since martensitic transformation can only occur at a higher cooling rate, hot stamping of boron steel requires mold cooling or direct water cooling, and single air cooling cannot achieve the required cooling rate; hot stamping of medium manganese steel can undergo martensitic transformation at a very low cooling rate, but if it is removed from the mold and air-cooled in a free state after forming, it will undergo large deformation and fail to meet the dimensional accuracy requirements, so it is also necessary to maintain pressure cooling in the mold, and from the perspective of production cycle, the cooling rate cannot be too low. The mass production molds and processes of hot stamping of medium manganese steel are basically the same as those of boron steel, and the molds of trial parts are also similar to those of boron steel. For both sample trial production and mass production, the mold structure and cooling method are also different.

[0004] Prototype trial production is generally a small number of trial production (within a few hundred pieces), and batch production is a large-scale mass production (more than 100,000 pieces). The corresponding molds are also called trial molds (or soft molds) and mass production molds (or hard molds). Trial molds are generally cast with cast iron, and there is no water channel inside. The manufacturing cycle is short and the cost is low. Due to the small number of stamping times and low cycle, the mold is usually cooled by manual watering or automatic spraying. A pool is placed on the press table and the mold is in the pool. For mass production molds, cooling water channels are arranged inside the mold. The coolant circulates in the water channel to take away the heat transferred from the sheet to the mold. The traditional cooling water channels include drilled straight water channel direct row cooling structure and drilled straight water channel mixed row cooling structure. The mold body is composed of several inserts, and each insert is processed separately. Whether it is a straight row structure or a mixed row structure, there are disadvantages such as difficulty in straight water channel processing and positioning, high requirements for insert assembly positioning accuracy and sealing, and straight water channels cannot guarantee the uniformity and sufficiency of cooling for parts with large fluctuations.

[0005] However, as users' demands for differentiated, personalized and customized cars become increasingly strong, there are more and more small-batch segmented models. On the other hand, the sales of many new energy models are difficult to predict. The planned production volume is often hundreds of thousands or even hundreds of thousands of units, but only 20,000 or 30,000 units are sold before the production is discontinued. Here, small-batch models are defined as those with a life cycle output of less than 100,000 units, an annual output of less than 20,000 units or even a few thousand units. Obviously, the traditional trial mold cannot meet the requirements of production capacity and mold life. The traditional mass production mold will have overcapacity, high mold cost and great waste. Therefore, a hot stamping forming technology for high-strength steel structural parts suitable for small-batch models is urgently needed. Utility Model Content

[0006] Technical problem to be solved by the utility model: The purpose of the utility model is to overcome the above-mentioned technical defects and provide a small-batch hot stamping die based on direct surface air cooling to reduce the mold manufacturing cost and the unit production cost, and provide technical support for the production of small-batch vehicles.

[0007] Technical solution: In order to achieve the above-mentioned purpose, the technical solution provided by the utility model is: a small-batch hot stamping mold based on direct surface air cooling, including a punch and a die, the die is provided with a recessed portion matching the punch of the punch, the surface of the punch is provided with a first cavity recessed toward its interior, and the surface of the die is also provided with a second cavity recessed toward its interior, the first cavity and the second cavity are used to form an airflow cooling channel connected to a compressed air pipeline, so that the air inlet end of the airflow cooling channel is connected to the air compressor through the compressed air pipeline, the compressed air is blown into the mold through the pipeline, circulated and heat exchanged in the airflow cooling channel and on the surface of the mold, and the heated gas is discharged through the air outlet end of the airflow cooling channel.

[0008] As a further improvement of the utility model, the first cavity starts from one side of the punch and passes through the punch punch uninterruptedly along the width direction of the punch until it extends to the other side, and the second cavity starts from one side of the die and passes through the recessed portion of the die uninterruptedly along the width direction of the die until it extends to the other side.

[0009] As a further improvement of the utility model, the first cavity and the second cavity are arranged alternately and spaced in sequence along the length direction of the punch and the die, respectively, so that air flow cooling channels connected to the compressed air pipeline are formed on the surfaces of the punch and the die.

[0010] As a further improvement of the utility model, the air inlet and outlet ends of the air flow cooling channel are respectively wedge-shaped air inlet and wedge-shaped air outlet located on both sides of the mold. The wedge-shaped air inlet is connected to the air compressor through multiple compressed air pipelines, and the wedge-shaped air outlet is used to discharge the heated gas.

[0011] As a further improvement of the utility model, the air outlet of the air compressor is connected to the water tank through a water pipe, and the pressure of the compressed air and the water inlet flow rate are adjusted to form a mixture of compressed air and water mist in different proportions. The mixture is blown in through the wedge-shaped air inlet and heat exchange occurs when it enters the air flow cooling channel formed by the first cavity and the second cavity and the mold surface.

[0012] As a further improvement of the utility model, the first concave cavity on the surface of the punch, the second concave cavity on the surface of the die, and the upper and lower surfaces of the stamping part all form a cavity. After the water mist mixture with a water-gas ratio in the range of 100-1000 enters the cavity, it contacts the surface of the stamping part and the inner wall of the concave cavity on the surface of the mold to exchange heat and take away the heat from the surface of the stamping part.

[0013] As a further improvement of the utility model, the gap between the male die and the female die is 50-100 mm, and a water mist mixture with a water-gas ratio in the range of 10-100 is blown into the gap, and heat exchange occurs in the airflow cooling channel and the mold surface to take away the heat from the mold surface.

[0014] As a further improvement of the utility model, the wedge-shaped air inlet and the wedge-shaped air outlet have the same wedge shape, and the included angle is 30-60°.

[0015] As a further improvement of the present invention, the cross-sectional shape of the first cavity and the second cavity is semicircular, cylindrical, ridge-shaped, wavy or triangular.

[0016] As a further improvement of the present invention, the shape of the airflow cooling channel is linear, spiral or cross-grid.

[0017] Beneficial effects:

[0018] 1. Compared with the traditional hot stamping mold with cooling pipelines, the stamping mold provided by the present invention has a concave cavity on the mold surface. The manufacturing cost and maintenance cost of the mold are lower than those of mass production molds, and the mold life and production capacity are higher than those of trial molds.

[0019] 2. Based on the surface air cooling of the mold provided by the utility model, since the production cycle is not high, mass production can be achieved on the trial mold line, which reduces the production cost of a single piece and meets the production needs of small batch models. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the structure of the hot stamping die punch and the concave die provided by the present invention;

[0021] Figure 2 for Figure 1 The structural perspective view of the punch and die;

[0022] Figure 3 Schematic diagram of the structure connecting the stamping die to the external pipeline and water tank;

[0023] Figure 4 for Figure 3 Schematic diagram of the structure of the punch and die opening;

[0024] Figure 5 It is a schematic diagram of the gas flow during pressure-maintaining cooling in the die after the stamping part is formed;

[0025] Figure 6 Schematic diagram of the structure of a wedge-shaped air inlet and a wedge-shaped air outlet;

[0026] Figure 7 Schematic diagram of the arrangement and cross-section of the cavities on the surfaces of the punch and die.

[0027] Explanation of the symbols in the schematic diagram:

[0028] 10. Stamping part; 20. Punch; 21. First cavity; 30. Die; 31. Second cavity; 40. Air compressor; 41. Compressed air pipeline; 50. Water tank; 51. Water pipe; 61. Wedge-shaped air inlet; 62. Wedge-shaped air outlet; 230. Gap between punch and die; 101. Edge of stamping part; 102. Starting point; 600. Angle. DETAILED DESCRIPTION

[0029] In order to further understand the content of the utility model, the utility model is described in detail in conjunction with the accompanying drawings and specific implementation methods.

[0030] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0031] In the description of the present utility model, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0032] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0033] like Figure 1-7 A small batch hot stamping die based on surface direct air cooling includes a punch 20 and a die 30. The main bodies of the punch 20 and the die 30 are integrally cast from alloy cast iron or assembled from hot working die steel inserts. Compared with traditional hot stamping dies, the die manufacturing and maintenance costs are low.

[0034] In this embodiment, the upper die is a male die 20, the lower die is a female die 30, the male die punch is a roughly trapezoidal protrusion, the female die 30 is provided with a recessed portion matching the male die punch, and after the stamping is completed, the stamped part 10 is left in the die for pressure quenching. The surface of the male die 20 is provided with a first concave cavity 21 that is concave toward the inside thereof, and the surface of the female die 30 is also provided with a second concave cavity 31 that is concave toward the inside thereof, and the first concave cavity 21 and the second concave cavity 31 are cut by a CNC machine tool and serve as airflow cooling channels during cooling.

[0035] The first cavity 21 starts from one side of the punch 20 and passes through the punch punch uninterruptedly along the width direction of the punch 20 until it extends to the other side. The second cavity 31 starts from one side of the die 30 and passes through the die recessed part uninterruptedly along the width direction of the die 30 until it extends to the other side. A plurality of first concave cavities 21 are sequentially spaced along the length direction of the punch 20, and a plurality of second concave cavities 31 are sequentially spaced along the length direction of the die 30, and may not be arranged at equal intervals, thereby constructing a plurality of parallel airflow cooling channels on the surfaces of the punch 20 and the die 30. The air inlet end of the airflow cooling channel (i.e., the starting end of the air inlet of the first and second concave cavities 21 and 31) is a wedge-shaped air inlet 61 located on one side of the mold, and the air outlet end of the airflow cooling channel (i.e., the end of the air outlet of the first and second concave cavities 21 and 31) is a wedge-shaped air outlet 62 located on the other side of the mold. The wedge-shaped air inlet 61 is connected to the air compressor 40 through a plurality of compressed air pipelines 41. The compressed air provided by the air compressor 40 flows through the airflow cooling channel formed by the first and second concave cavities 21 and 31, thereby taking away the heat of the stamping part 10 and the mold surface to achieve the purpose of cooling. The wedge-shaped air outlet 62 is used to discharge the heated gas. The wedge-shaped air inlet 61 and the wedge-shaped air outlet 62 both adopt the same wedge-shaped opening, and the angle 600 thereof is between 30-60°. The distance between the starting point 102 of the wedge-shaped air inlet 61 and the wedge-shaped air outlet 62 in the mold and the edge 101 of the stamping part is about 10 mm.

[0036] The transition portion where the compressed air pipeline 41 contacts the wedge-shaped air inlet 61 is defined as an air nozzle (not shown in the figure). The air nozzle can cover the entrances of multiple cavities, or an air nozzle can be provided at the entrance of each cavity. The specific design is carried out according to the arrangement of the cavities. The shape of the air nozzle can be a straight circular shape or a flat nozzle, which is not limited here.

[0037] The arrangement and cross-sectional shape of the first cavity 21 and the second cavity 31 refer to Figure 7As shown, the cross-section 210 of the first cavity 21 and the cross-section 310 of the second cavity 31 are both semicircular, and the diameter is preferably between 8-20 mm. The first cavity 21 and the second cavity 31 are staggered in sequence, and the spacing is preferably between 20-100 mm. As mentioned above, the adjacent cavities are not necessarily equidistant. In this embodiment, from the top view of the male mold 20 and the female mold 30, the wheel frame line of the first cavity 21 and the second cavity 31 is a straight line. In fact, it may not be a straight line, that is, the shape of the airflow cooling channel formed by the first cavity 21 and the second cavity 31 can be various, and it can be a spiral cavity distributed in a spiral shape on the mold surface. The spiral structure helps the cooling gas or water mist to form a continuous rotating flow on the mold surface, so as to evenly and effectively take away the heat; a cross-grid cavity can also be used, so that the cavities intersect with each other to form a grid or checkerboard pattern, the purpose of which is to increase the total length and surface area of ​​the cavity, which can greatly improve the cooling efficiency. At the same time, the cross structure helps to form turbulence, which can further enhance the cooling effect. It can also be an inclined cavity, which is inclined toward a specific direction of the mold. Other shapes of cavities can also be used. In practical applications, the design is based on the specific shape of the mold and the cooling effect. In addition, the cross-section of the first cavity and the second cavity can be cylindrical, ridge-shaped, wavy, triangular, etc. in addition to the semicircular shape. Considering the manufacturing convenience and cooling effect, a semicircular shape with a diameter of 8-20 mm is preferred.

[0038] After stamping, the stamped part 10 remains in the mold for pressure-holding quenching. Each first concave cavity 21 on the surface of the punch 20 forms a cavity with the upper surface of the stamped part, and each second concave cavity 31 on the surface of the die 30 forms a cavity with the lower surface of the stamped part. The air compressor 40 is turned on to control the pressure of the gas in the compressed air pipeline 41. The compressed gas enters these cavities from the wedge-shaped air inlet 61, contacts the surface of the stamped part 10 and the inner wall of the concave cavity on the mold surface to transfer heat. The heated gas flows out from the wedge-shaped air outlet 62, taking away part of the heat of the stamped part and the mold.

[0039] The air outlet of the air compressor 40 is connected to the water tank 50 through the water pipe 51, so as to mix the compressed air in the compressed air pipeline 41 with the water in the water pipe 51 to produce a certain concentration of water mist, thereby accelerating the cooling effect. By controlling the pressure of the compressed air and the water inlet flow rate, a mixture of compressed air and water mist is formed, which is blown into the mold through the wedge-shaped air inlet 61, passes through the air flow cooling channel formed by the first cavity 21 and the second cavity 31, exchanges heat with the mold surface, takes away the mold temperature, and is finally discharged from the wedge-shaped air outlet 62.

[0040] The opening and closing of the water channel is selected according to different situations. For example, when cooling bare plate stampings, the water channel is in a closed state to prevent water mist from causing rust on the stampings and aggravating the formation of oxide scale. When cooling coated plate stampings, the water channel can be opened for cooling.

[0041] In this embodiment, the water tank 50 is open, and the pressure of the compressed air generated by the air compressor 40 is between 3-7 Bar (atmospheric pressure). The water therein is sucked into the nozzle by the force of the compressed air under natural atmospheric pressure, that is, a siphon-type liquid supply method. With this supply method, when cooling the stamping part 10 and the mold respectively, it is necessary to use water mist mixtures of different proportions. When the stamping part 10 is cooled, the pressure of the compressed air is increased to produce a lower water mist concentration, and the air-water ratio is between 100-1000; when the mold is cooled, the pressure of the compressed air is reduced to produce a higher water mist concentration, and the air-water ratio is between 10-100. The air-water ratio refers to the volume flow ratio. The unit of water flow is liters / hour, and the unit of air flow is liters / minute.

[0042] When the stamping part 10 is cooled, the air-water ratio is first adjusted to between 100 and 1000, so that the air flow is much greater than the water flow, thereby producing a lower concentration of water mist; then the compressed air generated by the air compressor 40 is used to siphon the water in the water tank 50 and mix it to form a water mist mixture; then the water mist mixture is blown into the gap between the mold and the stamping part 10 through the wedge-shaped air inlet 61, that is, the cavity formed by the first cavity 21 and the upper surface of the stamping part, and the cavity formed by the second cavity 31 and the lower surface of the stamping part; finally, the water mist mixture undergoes heat transfer with the surface of the stamping part and the inner wall of the cavity, effectively taking away the heat from the surface of the stamping part 10. The heated airflow is then discharged from the wedge-shaped air outlet 62. Figure 6 , showing the gas flow during pressure holding and cooling in the mold after the stamping part is formed.

[0043] During the pressure-holding cooling process, part of the heat of the stamping part 10 is directly taken away by the airflow in the cavity. When the mold structure is relatively complex or the cooling rate requirement is high, the airflow cannot take away all the heat. Then part of the heat of the stamping part will be conducted to the mold, causing the temperature of the mold to gradually increase from the room temperature at the beginning of production. When the mold temperature is higher than 200°C after quenching, continuing production will lead to defects such as insufficient cooling rate, insufficient martensite transformation, and unqualified mechanical properties. At this time, production should be suspended, the mold should be cooled to about 50°C, and then production should be resumed.

[0044] When the mold is cooling, first stop the stamping operation, open the punch 20, and take out the stamped part 10; then adjust the mold gap and the water-gas ratio, keep the gap 230 between the punch and the die between 50-100mm, so that the water mist mixture can fully enter and cover the mold surface, and adjust the air-water ratio to between 10-100 to form a mixture of compressed air and water mist, producing a higher concentration of water mist; then these higher concentrations of water mist are blown into the mold gap through the wedge-shaped air inlet 61; the water mist mixture exchanges heat with the first cavity 21, the second cavity 31 and the mold surface to take away the mold temperature; the heated air flow after heat exchange is discharged from the wedge-shaped air outlet 62 to complete the cooling process of the mold.

Claims

1. A small batch hot stamping die based on direct surface air cooling comprises a punch (20) and a die (30), wherein the die (30) is provided with a recessed portion matching the punch of the punch, and is characterized in that: The surface of the male mold (20) is provided with a first cavity (21) which is recessed toward the inside thereof, and the surface of the female mold (30) is also provided with a second cavity (31) which is recessed toward the inside thereof. The first cavity (21) and the second cavity (31) are used to form an airflow cooling channel which is connected to a compressed air pipeline (41). The air inlet end of the airflow cooling channel is connected to an air compressor (40) through the compressed air pipeline (41). Compressed air is blown into the mold through the pipeline, circulated and heat exchanged in the airflow cooling channel and on the surface of the mold, and the heated gas is discharged through the air outlet end of the airflow cooling channel.

2. The small batch hot stamping die based on surface direct air cooling according to claim 1 is characterized in that: The first cavity (21) starts from one side of the punch (20) and passes through the punch punch uninterruptedly along the width direction of the punch (20) until it extends to the other side. The second cavity (31) starts from one side of the die (30) and passes through the die recessed portion uninterruptedly along the width direction of the die (30) until it extends to the other side.

3. The small batch hot stamping die based on surface direct air cooling according to claim 2 is characterized in that: The first concave cavity (21) and the second concave cavity (31) are arranged in a staggered manner along the length direction of the male mold (20) and the female mold (30), respectively, so that air flow cooling channels communicating with the compressed air pipeline (41) are formed on the surfaces of the male mold (20) and the female mold (30).

4. The small batch hot stamping die based on surface direct air cooling according to claim 1 is characterized in that: The air inlet and outlet ends of the air flow cooling channel are respectively a wedge-shaped air inlet (61) and a wedge-shaped air outlet (62) located on both sides of the mold; the wedge-shaped air inlet (61) is connected to the air compressor (40) through a plurality of compressed air pipelines (41); and the wedge-shaped air outlet (62) is used to discharge the heated gas.

5. The small batch hot stamping die based on surface direct air cooling according to claim 4 is characterized in that: The air outlet of the air compressor (40) is connected to the water tank (50) through a water pipe (51), and the pressure of the compressed air and the water inlet flow rate are adjusted to form a mixture of compressed air and water mist in different proportions. The mixture is blown in through the wedge-shaped air inlet (61) and enters the air flow cooling channel formed by the first cavity (21) and the second cavity (31) as well as the mold surface, where heat exchange occurs.

6. The small batch hot stamping die based on surface direct air cooling according to claim 5, characterized in that: The first concave cavity (21) on the surface of the male mold (20), the second concave cavity (31) on the surface of the female mold (30) and the upper surface and the lower surface of the stamping part (10) all form a cavity. After the water mist mixture with a water-gas ratio in the range of 100-1000 enters the cavity, it contacts the surface of the stamping part and the inner wall of the concave cavity on the mold surface to exchange heat and remove the heat from the surface of the stamping part.

7. The small batch hot stamping die based on surface direct air cooling according to claim 5, characterized in that: The gap (230) between the male mold (20) and the female mold (30) is 50-100 mm, and a water mist mixture with a water-gas ratio in the range of 10-100 is blown into the gap, and heat exchange occurs in the air flow cooling channel and the mold surface to remove the heat from the mold surface.

8. The small batch hot stamping die based on surface direct air cooling according to claim 4, characterized in that: The wedge-shaped air inlet (61) and the wedge-shaped air outlet (62) have the same wedge shape, and the included angle (600) is 30-60 degrees.

9. The small batch hot stamping die based on surface direct air cooling according to claim 1, characterized in that: The cross-sectional shapes of the first cavity (21) and the second cavity (31) are semicircular, cylindrical, ridge-shaped, wavy or triangular.

10. The small batch hot stamping die based on surface direct air cooling according to claim 1, characterized in that: The shape of the airflow cooling channel is linear, spiral or cross-grid.

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