Edge-trimming and punching method for hot-formed part, and edge-trimming and punching die

Abstract

Disclosed in the present invention are an edge-trimming and punching method for a hot-formed part and an edge-trimming and punching die. The method comprises the following steps: S1, performing hot stamping, first quenching, and heat preservation on a workpiece in a hot stamping die; S2, when the temperature is cooled to a preset temperature, taking out the workpiece and moving same into an edge-trimming and punching die; S3, determining the positions to be edge-trimmed and punched, and heating said positions; S4, when a set condition is met, performing edge-trimming and punching on the workpiece; and S5, performing second quenching on the workpiece. In the present invention, a hot-stamped part can be quickly punched and edge-trimmed. Furthermore, by precisely controlling the cooling rate of the workpiece during machining, the temperature at each part of the workpiece can be cooled in a controllable manner, which is conducive to preventing deformation or cracking, and ensuring the performance of a critical position of the workpiece.

Description

Method and die for trimming and piercing of a hot formed part

[0001] The present application claims priority to the Chinese patent application No. 202411389562.X, filed on September 30, 2024, and entitled "Method and die for trimming and piercing of a hot formed part", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of mechanical processing manufacturing technology, in particular to a method and die for trimming and piercing of a hot formed part. BACKGROUND

[0003] With the increasing requirements of the automotive industry on vehicle performance, safety and lightweight, high-strength steel sheets have become one of the important ways to meet these requirements due to their light weight and high strength. However, high-strength steel sheets have a small plastic deformation range at room temperature and poor formability, which brings challenges to traditional cold stamping methods. Hot stamping forming technology allows the steel sheet to be stamped at high temperature, making the steel sheet material soft and easy to form in a heated state. This technology not only solves the problem of forming difficulty of high-strength steel sheets at room temperature, but also improves the dimensional accuracy and mechanical properties of the parts. With the wide application of hot stamping forming technology, the trimming and piercing technology of hot formed parts has gradually become an important link in the manufacturing of automobile stamping parts. Due to the high material strength and high hardness of hot stamped parts, traditional trimming and piercing methods cannot meet the processing requirements. Therefore, advanced trimming and piercing technologies such as laser cutting and water cutting need to be used to ensure the processing precision and surface quality of hot formed parts. Compared with traditional cutting technology, current laser cutting technology has significant advantages such as fast cutting speed, high precision and strong material adaptability, but also has some problems:

[0004] The technical threshold is high, and laser cutting technology requires professional technicians to operate and maintain, and the cost is higher. The trimming time is long, and the use of laser cutting technology requires longer time for parts.

[0005] How to quickly pierce and trim hot stamped parts is one of the important problems to be solved in the field. SUMMARY

[0006] The purpose of the present application is to provide a method and die for trimming and piercing of a hot formed part, which can quickly pierce and trim hot stamped parts.

[0007] The present application provides a method for trimming and piercing of a hot formed part, comprising the following steps:

[0008] S1, in the hot stamping die, hot stamping, first quenching and heat preservation are performed on the workpiece;

[0009] S2, when the temperature cools to a preset temperature, the workpiece is taken out and moved to a trimming and piercing die;

[0010] S3, determining the positions to be trimmed and pierced, and heating the positions to be trimmed and the positions to be pierced;

[0011] S4, trimming and piercing the workpiece when a set condition is reached, wherein the set condition is that the temperature of a region on the workpiece within a set distance from a notch corresponding to the positions to be trimmed and pierced is within a set temperature range;

[0012] S5, quenching the workpiece a second time.

[0013] The method for trimming and piercing a hot formed workpiece as described above, wherein, optionally, liquid cooling is performed on the workpiece during the first quenching or the second quenching; the cooling channels used for liquid cooling are multiple;

[0014] The method for liquid cooling a workpiece comprises:

[0015] S01, determining the cooling time and the initial cooling liquid flow rate at the inlet of each cooling channel according to the heat dissipation needs of the pre-selected key points on the workpiece and the initial cooling liquid temperature;

[0016] S02, determining the target flow rate at the inlet of each cooling channel as a function of time and the target temperature of each key point at different times within the cooling time according to the cooling time, and monitoring the actual temperature of each key point;

[0017] S03, controlling the flow rate at the inlet of each cooling channel according to the target flow rate at the inlet of each cooling channel as a function of time;

[0018] S04, comparing the actual temperature of each key point at the current time with the target temperature, and correcting the target flow rate at the inlet of each cooling channel as a function of time according to the comparison result during the cooling process;

[0019] S05, controlling the flow rate of the cooling liquid at the inlet of each cooling channel according to the corrected target flow rate at the inlet of each cooling channel as a function of time; repeating step S04 and step S05 until the cooling time ends.

[0020] The method for trimming and piercing a hot formed workpiece as described above, wherein, optionally, in step S02, the step of determining the target flow rate at the inlet of each cooling channel as a function of time comprises:

[0021] S021, determining the cooling capacity of each cooling channel for each key point;

[0022] S022, respectively determining the ratio of the influence of each cooling channel on each key point;

[0023] S023, determining cooling intensity requirements of each key point;

[0024] S024, determining total target flow rate at the entrance of each cooling channel over time according to the cooling intensity requirements of each key point, the cooling capacity of each cooling channel to each key point, and the ratio of the influence of each cooling channel on each key point;

[0025] S025, distributing the target flow rate at the entrance of each cooling channel according to the cooling intensity requirements of each key point and the ratio of the target flow rate at the entrance of each cooling channel.

[0026] The method for trimming and punching a thermoformed part as described above, wherein, optionally, in step S021, the target flow rate at the entrance of each cooling channel over time is determined according to the cooling capacity of each cooling channel to each key point.

[0027] The cooling capacity of each cooling channel to each key point is determined by the following formula:

[0028] wherein sa is the cooling capacity, a1 is a constant coefficient, c is the specific heat capacity of the cooling liquid, S is the cross-sectional area of the cooling channel, v is the flow rate of the cooling liquid, Tm is the temperature at the wall surface of the cooling channel, Ts is the temperature of the cooling liquid, t1 is the time for the cooling liquid to flow from the entrance of the cooling channel to the first end point of the cooling section, t2 is the time for the cooling liquid to flow from the entrance to the second end point of the cooling section, and l(t) is the distance between the point where the cooling liquid is located at time t and the corresponding key point.

[0029] The method for trimming and punching a thermoformed part as described above, wherein, optionally, the cooling section is selected by taking the key point as the center and a preset distance as the radius to form a sphere, and the part of the cooling channel located within the sphere is the cooling section.

[0030] The method for trimming and punching a thermoformed part as described above, wherein, optionally, the formula for correcting the target flow rate at the entrance of each cooling channel over time according to the comparison result is q(t) = S v = Q(t) + b△q.

[0031] wherein q(t) is the target flow rate at the entrance of the cooling channel over time after correction, Q(t) is the target flow rate at the entrance of the cooling channel over time before correction, b is the adjustment factor, and△q is the unit adjustment amount.

[0032] The calculation formula of the adjustment factor is:

[0033] a2 is a constant coefficient, T sj is the actual temperature of the corresponding key point, and T mb is the target temperature of the corresponding key point.

[0034] The method for trimming and punching a hot formed piece as described above, wherein, optionally, the middle part of at least one of the cooling channels has multiple branches.

[0035] The method for trimming and punching a hot formed piece as described above, wherein, optionally, step S1 comprises the following steps,

[0036] S11, placing the blank into a hot stamping die and heating the blank;

[0037] S12, stamping the blank to form a workpiece;

[0038] S13, performing the first quenching and holding for a set time;

[0039] Wherein, the heating process in step S11 and step S3 is controlled by PID.

[0040] The present application also provides a trimming and punching die for any of the above-mentioned methods, comprising a first die, a second die and a third die;

[0041] The first die and the second die are used to press the workpiece to be trimmed and punched from both sides;

[0042] The first die is provided with a plurality of first holes, and the side of the first die close to the workpiece is provided with a punching part, and the first holes penetrate through the punching part; a first heating element is embedded in the punching part; the first heating element is used to heat the temperature of the area to be punched to a set temperature range before punching;

[0043] The second die is provided with a plurality of second holes corresponding to the first holes;

[0044] The side wall of the first die is provided with a trimming area, and at least one second heating element is arranged in the trimming area;

[0045] The third die is located on the same side of the workpiece as the first die, and the third die is distributed along the circumferential side of the first die, and the third die is provided with a second heating element for heating the trimming position;

[0046] The first die is provided with a cooling channel for executing steps S01 to S05.

[0047] The trimming and punching die as described above, wherein, optionally, a groove is arranged in the trimming area, and the second heating element is arranged in the groove; the second heating element is used to heat the trimming area of the workpiece; a gap is arranged between the circumferential side of the second heating element and the wall of the groove.

[0048] Compared with the prior art, the workpiece is moved to the trimming and punching die after hot stamping, first quenching and heat preservation of the workpiece in the hot stamping die. The workpiece is heated in the trimming and punching die, and the tensile strength of the corresponding position of the workpiece is reduced to below 600 MPa when the corresponding region of the workpiece is heated to a set temperature range, so as to facilitate trimming and punching operation. By locally heating the workpiece, the tensile strength of the position to be trimmed and punched can be reduced, and rapid punching and trimming can be realized to ensure processing quality and efficiency. Since local heating can reduce the tensile strength of the position to be trimmed and punched, actual verification shows that the efficiency of trimming and punching can be improved by about 50% to 70%.

[0049] In addition, in the process of cooling by liquid cooling, the cooling liquid flow at the inlet of each cooling channel is controlled respectively based on the cooling of the key points, so that the entire workpiece can be cooled in a controllable and proportional manner, thereby preventing deformation or cracks of the workpiece due to uneven changes in internal structure during cooling. BRIEF DESCRIPTION OF DRAWINGS

[0050] Fig. 1 is a step flow chart of the method for trimming and punching the hot formed workpiece according to the present application;

[0051] Fig. 2 is a step flow chart of the method for liquid cooling the workpiece according to the present application;

[0052] Fig. 3 is a specific step flow chart of step S02 according to the present application;

[0053] Fig. 4 is a specific step flow chart of step S1 according to the present application;

[0054] Fig. 5 is a perspective view of the trimming and punching die according to the present application;

[0055] Fig. 6 is an exploded view of Fig. 5;

[0056] Fig. 7 is a structural schematic view of the workpiece before trimming and punching according to the present application;

[0057] Fig. 8 is a structural schematic view of the workpiece after trimming and punching according to the present application;

[0058] Fig. 9 is a perspective view of the first die according to the present application.

[0059] Reference signs: 1-first die, 2-second die, 3-third die; 11-first hole, 12-punching part, 13-trimming area, 14-groove, 15-first heating member; 21-second hole, 22-second heating member. DETAILED DESCRIPTION

[0060] The embodiments described below with reference to the drawings are exemplary and are intended merely to explain the present application, and are not to be construed as limiting the present application.

[0061] Embodiment 1

[0062] In view of the problems in the background art, since the material strength of the hot stamped part is high, it is not convenient to trim and punch, the present application provides a hot forming part trimming and punching method, please refer to figure 1 to figure 4, which includes the following steps,

[0063] S1, in the hot stamping die, the workpiece is hot stamped, quenched for the first time and kept warm. Through this step, the hot stamping forming of the workpiece is realized.

[0064] Specifically, please refer to figure 2, this step includes the following steps,

[0065] S11, the blank is placed in the hot stamping die, and the blank is heated.

[0066] In specific implementation, the blank is placed in the hot stamping die for hot stamping forming. The high-temperature heating unit is used to preheat the hot stamping die to an appropriate forming temperature, and the specific value of the forming temperature can be obtained according to the empirical value or experimental value or table lookup. Through the cooperation of temperature sensor and heating / cooling pipeline control system, the temperature data of the mold fed back by the temperature sensor is collected in real time, and automatic adjustment is made according to the need, so as to ensure the consistency of the hot stamped workpiece. In specific implementation, the high-temperature heating unit, cooling channel and temperature sensor are embedded in the hot stamping die. In this step, the heating of the blank can be controlled by PID, and the error accumulation can be prevented by limiting the integral term or using integral anti-saturation technology.

[0067] S12, the blank is punched to form a workpiece. In specific implementation, by using high-performance servo motor and control system, the punching speed and time of the punching machine are accurately controlled to ensure that the parts are subjected to uniform force and pressure during the forming process. Through the punching of this step, the blank is formed.

[0068] S13, quenched for the first time and kept warm for a set time.

[0069] Through the quenching process, the microstructure of the workpiece can be changed, thereby improving the strength of the workpiece. In actual application, the first quenching process and keeping warm are carried out in the hot stamping die, which can ensure that the workpiece will not be deformed during the quenching process. In specific implementation, through this step, the blank can be formed by hot stamping.

[0070] S2, when the temperature cools to a preset temperature, the workpiece is taken out and moved to the trimming and piercing die; in specific implementation, the preset temperature is 360-400 DEG C, wherein the optional temperature values are 360 DEG C, 365 DEG C, 370 DEG C, 375 DEG C, 380 DEG C, 385 DEG C, 390 DEG C, 395 DEG C, 400 DEG C, etc., and preferably 380 DEG C. Since piercing and trimming are performed after hot stamping, the workpiece does not need to be completely lowered to room temperature during this process, thus avoiding the need to increase the workpiece from room temperature to the set temperature range in subsequent steps, which is beneficial to energy saving.

[0071] S3, the positions to be trimmed and pierced are determined, and the positions to be trimmed and pierced are heated. In specific implementation, the trimming and piercing positions can be heated by heating components prearranged in the trimming and piercing die. Since the first quenching after hot stamping has been completed, the strength of the workpiece can meet the requirements, and the purpose of this step is to reduce the strength of the trimming and piercing positions by heating.

[0072] S4, when the set condition is reached, the workpiece is trimmed and pierced; wherein the set condition is that the temperature of the region within a set distance from the corresponding cutout is within a set temperature range; in specific implementation, the set temperature range is 550-600 DEG C, and specifically, the temperature in the region should be ensured to be within 550-600 DEG C, that is, the maximum and minimum temperatures in the region are set to be 550-600 DEG C. When the workpiece is within this temperature range, its tensile strength is reduced to below 600 MPa, which is beneficial to trimming and piercing operations. In specific implementation, after the corresponding region of the workpiece reaches the set temperature range, the trimming and piercing process is started. The precise trimming and piercing die and control system are used to ensure the precision and consistency of trimming and piercing. During the entire process, the part is kept within the set temperature range to ensure the processing quality and efficiency. In specific implementation, the set distance can be 2-5 cm to ensure that the tensile strength of the workpiece in the region corresponding to the cutout position is below 600 MPa. Since local heating can reduce the tensile strength of the trimming and piercing positions, actual verification shows that the efficiency of trimming and piercing can be increased by about 50-70%.

[0073] S5, the workpiece is subjected to second quenching. The second quenching process is performed in the trimming and piercing die, which can prevent the workpiece from being deformed during the second quenching process. Since the second quenching is performed in the trimming and piercing die, that is, a cooling channel is arranged in the trimming and piercing die. After this step, the workpiece is cooled to room temperature. In actual application, the heating position is local heating before trimming and piercing, and for a workpiece with a specific shape, the piercing position and trimming position are fixed, thus the corresponding cooling channel can be directly arranged at the corresponding position according to the different heating regions.

[0074] In the actual implementation, the edge cutting and punching are performed through the above steps S1 to S5, and the first quenching and the second quenching are respectively performed in the hot stamping die and the edge cutting and punching die. In the process of the first quenching and the second quenching, the temperature drop speed of each part of the workpiece is difficult to accurately control, and when the temperature drop speed is uneven, the internal structure of the workpiece is prone to uneven change, thereby causing the workpiece to be deformed and cracked. In order to solve this problem, in the present implementation, the workpiece is liquid-cooled during the first quenching and the second quenching; the cooling channels used for liquid cooling are multiple. Taking the first quenching as an example, referring to FIG. 3, the method of liquid-cooling the workpiece includes:

[0075] S01, according to the heat dissipation needs of the key points on the workpiece and the initial cooling liquid temperature, determine the cooling time, the initial cooling liquid flow rate at the inlet of each cooling channel. In the actual implementation, the key points are selected according to the shape of the workpiece, heat dissipation needs, design strength and other factors. The key points can be the geometric center points or feature points of the key heat dissipation areas. In the actual implementation, the key heat dissipation areas are one or more areas on the workpiece that are difficult to dissipate heat after the workpiece is formed by the hot stamping die, such as the area close to the center of the entire hot stamping die, the area with large thickness of the hot stamping die, and the area with concentrated mass on the workpiece. One or more key points are selected in each difficult-to-dissipate heat area to form a set of key points, such as n key points K1, K2, K3, K4, K5, K6...Kn.

[0076] In the actual implementation, the initial cooling liquid temperature refers to the temperature of the cooling liquid entering the inlet of the cooling channel. In use, tap water or the like can be directly used for cooling, and only the temperature of the cooling liquid entering the inlet of the cooling channel needs to be ensured. In the entire cooling process, the cooling liquid is not recycled, so only the temperature of the cooling liquid at the inlet of the cooling channel needs to be ensured to be basically constant. Of course, in some implementations, the temperature at the inlet of the cooling channel can also be controlled as needed.

[0077] The initial cooling liquid flow rate at the inlet of each cooling channel is only used at the beginning of cooling, because in the cooling process, the target flow rate at the inlet of each cooling channel needs to be calculated by relying on the cooling capacity, and the cooling capacity of the cooling channel to the key point is related to the cooling liquid flow rate. Therefore, at the beginning of cooling, the cooling is performed through the initial cooling liquid flow rate at the inlet of each cooling channel. In the subsequent cooling process, the target flow rate at the inlet of each cooling channel is accurately controlled by continuously correcting. The selection of the initial cooling liquid flow rate at the inlet of each cooling channel directly affects the control accuracy, which can be selected according to experience.

[0078] S02, according to the cooling time, determine the target flow rate of each cooling channel at the inlet over time and the target temperature of each key point at different times during the cooling time, and monitor the actual temperature of the key point.

[0079] In the hot stamping die, a plurality of cooling channels are arranged, each cooling channel is respectively C1, C2, C3, C4, Cm. For each key point, a plurality of cooling channels can affect the key point, but due to the cooling capacity of the cooling channel itself and the distance from the key point, the cooling capacity of each cooling channel for the same key point is different.

[0080] In this step, in order to make each key point be able to uniformly or proportionally synchronized cooling, please refer to Figure 4, this step includes the following specific steps, S021, determine the cooling capacity of each cooling channel to each key point. In this step, the cooling capacity of any cooling channel to any key point is characterized by the following formula:

[0081] Wherein, a1 is a constant, the specific value can be obtained according to the experience value or experimental value or table lookup, c is the specific heat capacity of the cooling liquid, S is the cross-sectional area of the cooling channel, v is the flow rate of the cooling liquid, Tm is the temperature of the cooling channel wall, Ts is the temperature of the cooling liquid; t1 is the time of the cooling liquid from the inlet to the first end point of the cooling section; t2 is the time of the cooling liquid from the inlet to the second end point of the cooling section; l(t) is the distance between the cooling liquid at the point and the corresponding key point from the inlet at t time. In order to facilitate the description, sa(i,j) represents the cooling capacity of the jth cooling channel to the ith key point. In specific implementation, the cooling section is the part of the corresponding cooling channel that has a greater influence on the key point. Specifically, the cooling section is selected by taking the key point as the center and a predetermined distance as the radius to make a sphere, and the part of the cooling channel located in the sphere is the cooling section, that is, the part of the cooling channel that has the greatest cooling effect on the key point. The first end point and the second end point of the cooling section are respectively the intersection of the cooling section and the sphere.

[0082] In some implementations, the cross-sectional area of the cooling channel can also be set as a variable cross-section for a single cooling channel, i.e., the cross-sectional area S is set as a variable, which in a specific implementation can be transformed into a relationship between the cross-sectional area S and the distance from the inlet of the cooling channel, and further transformed into a relationship between the cross-sectional area S and the time and flow rate, substituted into the above formula to obtain the cooling capacity of the cooling channel with a variable cross-section for the key points. In a specific implementation, the inlet of the cooling channel is not always located on the same side of the mold, and for the upper mold, the inlet of the cooling channel can be set in the middle of the top surface of the upper mold, and for the lower mold, the inlet of the cooling channel can also be set in the middle of the bottom surface of the upper mold, and the outlet is set on the side surface of the mold. Of course, the inlet and outlet can also be set on opposite sides of the mold. By setting the inlet of the cooling channel in the middle of the top surface or the bottom surface, the cooling liquid can directly reach the position close to the corresponding key point, thereby improving the cooling capacity for the key point.

[0083] For the ith key point, the influence of each cooling channel is

[0084] S022, respectively determine the ratio of the influence of each cooling channel on each key point; for the ith key point, the ratio of the influence of each cooling channel is: sa(i,1):sa(i,2):...:sa(i,j):...:sa(i,m).

[0085] By determining the ratio of the influence of each cooling channel on each key point, it is convenient to select the cooling channel with greater influence on a certain key point according to the ratio, which is beneficial to quickly determine the target flow rate at the inlet of each cooling channel.

[0086] S023, determine the cooling intensity requirement of each key point; in a specific implementation, the cooling intensity requirement can be determined according to the position and temperature change requirement of each key point. Specifically, when it is required to simultaneously cool each key point, and the initial temperatures of each key point are different, the cooling intensity requirement can be determined according to the actual temperature of each key point, the required quenching condition, etc. For example, the cooling intensity requirement is related to the difference between the actual temperature of the key point at the beginning of quenching and the temperature required to be reached by the key point at the end of quenching, the quenching time, and the specific heat capacity of the material of the workpiece; more specifically, the cooling intensity requirement is directly proportional to the difference between the actual temperature of the key point at the beginning of quenching and the temperature required to be reached by the key point at the end of quenching, the cooling intensity requirement is inversely proportional to the quenching time, and the cooling intensity requirement is directly proportional to the specific heat capacity of the material of the workpiece. In other aspects, the cooling intensity requirement of the key point is also related to its position, and the closer to the middle position, the greater the cooling intensity requirement.

[0087] S024, determining the total target flow rate at the inlet of each cooling channel as a function of time according to the cooling intensity requirement of each key point, the cooling capacity of each cooling channel to each key point, and the ratio of the influence of each cooling channel on each key point.

[0088] Specifically, the role of this step is to determine the total target flow rate at the inlet of each cooling channel as a function of time, because as the cooling progresses, the difference between the temperature of the workpiece and the temperature of the cooling liquid gradually decreases at different times, and to allow the workpiece to have the same cooling rate at different times, the total cooling liquid flow rate needs to be changed, that is, the total target flow rate at the inlet of each cooling channel is a function of time.

[0089] S025, distributing the target flow rate at the inlet of each cooling channel according to the cooling intensity requirement of each key point and the ratio of the flow rate at the inlet of each cooling channel, and controlling the flow rate at the inlet of the corresponding cooling channel according to the target flow rate.

[0090] In this step, the purpose is to control the flow rate at the inlet of each cooling channel differently at the same time to make the temperature of each key point decrease synchronously.

[0091] Specifically, when it is required to synchronously lower the temperature of each key point, and the initial temperatures of each key point are the same, the inlet flow rate of each cooling channel is determined according to the ratio of the influence of each cooling channel on each key point, so that the influence of each cooling channel on each key point is basically the same, thereby achieving the purpose of synchronously lowering the temperature of each key point to avoid deformation and cracks caused by different changes in temperature change rate and internal structure.

[0092] When it is required to synchronously lower the temperature of each key point, and the initial temperatures of each key point are the same, as long as the influence of each cooling channel on each key point is the same, synchronous cooling can be guaranteed, that is, it is required to guarantee that sa1=sa2=...sa i ...=sa n ;

[0093] The flow rate of each cooling channel is adjusted to satisfy the above equation. That is, the flow rate at the inlet of each cooling channel that satisfies the above equation can be used as the target flow rate at the inlet of each cooling channel. When the number of cooling channels is small and the number of key points is large, it may lead to no solution, at this time, the target flow rate at the inlet of each cooling channel at different times can be changed to achieve the purpose of basically synchronously lowering the temperature of each key point.

[0094] When it is required to lower the temperature of each key point at the same rate, the cooling capacity of each cooling channel can also be adjusted to achieve the purpose of lowering the temperature at the same rate. In this way, the different key points of the workpiece can have corresponding properties.

[0095] In practical application, the number of cooling channels can be less than the number of key points, which results in that it can be difficult to achieve the synchronous control of the temperature of each key point by fixed flow control of the cooling channel inlet flow. Therefore, the cooling channel inlet flow is set to change with time, so as to achieve the purpose of cooling the multiple key points basically as needed.

[0096] S03, controlling the flow of each cooling channel inlet according to the target flow of each cooling channel inlet changing with time. In specific implementation, the target flow of each cooling channel inlet changing with time is a function relationship obtained by theoretical calculation, in which many factors are ignored, such as cooling channel resistance, natural heat dissipation, cooling liquid evaporation, etc. In practical application, the target flow changing with time needs to be adjusted.

[0097] S04, comparing the actual temperature of each key point at the current time with the target temperature, and correcting the target flow of each cooling channel inlet changing with time according to the comparison result; in specific implementation, due to errors and other factors, the actual temperature will deviate from the target flow changing with time, so in actual control process, the target flow changing with time is corrected in real time, and specifically, the formula is as follows: q(t) = S v = Q(t) + b△q;

[0098] Wherein, q(t) is the corrected target flow changing with time, Q(t) is the target flow changing with time, b is the adjustment factor, and△q is the unit adjustment amount of the target flow.

[0099] Wherein, the adjustment factor is related to the actual temperature and the target temperature, and specifically, the calculation formula of the adjustment factor is:

[0100] Wherein, a2 is a constant, and the specific value can be obtained according to the empirical value or experimental value or table lookup, T sj is the actual temperature of the corresponding key point, T mb is the target temperature of the corresponding key point. The adjustment factor b is used to correct the target flow changing with time, so that the corrected target flow changing with time is more accurate. Wherein, the role of a2 is to determine the size of the adjustment factor, The sign of the adjustment factor is determined. b is a dimensionless parameter; the size of a2 is related to the thermal conductivity coefficient and other factors. In practical applications, the size of the value can be determined according to the test combined with theoretical calculation. More specifically, in practical applications, the relationship between the target flow rate and the actual flow rate over time is recorded in the coordinate system with time as the horizontal coordinate and flow rate as the vertical coordinate, and the sum of the areas enclosed by the target flow rate-time curve and the actual flow rate-time curve is minimized to solve a2 to obtain a better a2 value.

[0101] S05, controlling the flow rate at the inlet of each cooling channel according to the target flow rate-time relationship of each modified cooling channel; and repeating steps S04 and S05 until the cooling time ends.

[0102] In specific implementation, the cooling intensity of each key point is represented by the sum of the cooling capacity of each cooling channel to the corresponding key point; the cooling capacity of the same cooling channel to different key points is different. Only when the cooling capacity of the cooling channel to different key points is different, can the purpose of synchronously cooling each key point in a specific proportion be achieved by adjusting the inlet flow rate of each cooling channel.

[0103] The middle part of at least one of the cooling channels has multiple branches. When the cooling channel has branches, the cooling liquid flowing into the branches can be beneficial to heat dissipation in a larger area. When there are branches, especially when the cooling section contains branches, the cooling capacity of all branches corresponding to the key points on the cooling channel can be calculated in a superimposed manner for each branch.

[0104] In the method, the heating process, the holding process and the second quenching process of the foregoing steps are all controlled by PID (proportional-integral-derivative), and the error accumulation is prevented by limiting the integral term or using integral anti-windup technology. The temperature of the mold, the temperature of the part in the mold during quenching, the holding temperature, the quenching and holding time, the cooling liquid flow rate, the flow rate, the pipe diameter, the distance between the pipe and the mold surface, the energy loss rate and other parameters are automatically and dynamically adjusted by the PID algorithm. The input is the set temperature for the mold temperature control. For the temperature control, the output can be the power of the heating / cooling device; of course, for the cooling device, it can also be the flow rate or flow speed of the cooling liquid at the inlet of each cooling channel.

[0105] The control of the punching speed and the punching time can also be PID control, and the speed or position of the servo motor is adjusted according to the output of the PID controller.

[0106] Example 2

[0107] Please refer to FIG. 5 to FIG. 9, the embodiment proposes a trimming and punching die for the method described in embodiment 1, which includes a first die 1, a second die 2 and a third die 3. Specifically, the first die 1 and the second die 2 are used to press from both sides on the workpiece to be trimmed and punched. In the implementation, the first die 1 and the second die 2 are both adapted to the workpiece.

[0108] The first die 1 is provided with a plurality of first holes 11, and the first die 1 is provided with a punching part 12 on the side close to the workpiece, and the first holes 11 penetrate through the punching part 12; the punching part 12 is embedded with a first heating element 15; the first heating element 15 is used to heat the temperature of the area to be punched to a set temperature range before punching. In the specific implementation, the position needing to be punched is heated to 550-600℃ by the first heating element 15, so that the tensile strength of the position is lower than 600MPa, so as to facilitate the completion of punching. In this way, the punching cost can be reduced to realize the punching of hot stamping parts at low cost.

[0109] The second die 2 is provided with a plurality of second holes 21 corresponding to the first holes 11; in the specific implementation, the center line of the second hole 21 and the corresponding first hole 11 are located on the same line, and preferably, the cross-sectional shape and size of the second hole 21 and the corresponding first hole 11 are equal.

[0110] The periphery of the first die 1 is provided with a trimming area 13, and at least one second heating element 22 is arranged in the trimming area 13; the second heating element 22 is used to heat the part of the workpiece located in the trimming area 13, so that the tensile strength of the part is lower than 600MPa.

[0111] The third die 3 is located on the same side of the workpiece as the first die 1 and is distributed along the periphery of the first die 1, and the third die 3 is provided with a second heating element 22 for heating the trimming position. In the specific implementation, when heated to 550-600℃, the punching position is punched by a punching device. Remove the third die 3 and cut the trimming position.

[0112] In the specific implementation, the trimming area 13 is provided with a groove 14, and the second heating element 22 is arranged in the groove 14; the second heating element 22 is used to heat the position to be cut of the workpiece; a gap is provided between the periphery of the second heating element 22 and the wall of the groove 14. Specifically, the shape of the groove 14 is U-shaped, and by providing a gap between the periphery of the second heating element 22 and the wall of the groove 14, it is beneficial to reduce the heat diffusion to the second die 2 and more to the workpiece.

[0113] In the specific implementation, the first mold 1 is provided with a cooling channel. By passing the cooling liquid into the cooling channel, the cooling of the workpiece is realized. In cooperation with the first heating member 15 and the second heating member 22, the accurate control of the local temperature of the workpiece is realized. The specific control method can refer to the embodiment 1.

[0114] The above describes the structure, features and effects of the present application according to the embodiments shown in the drawings. The above description is only the preferred embodiments of the present application, but the present application is not limited to the embodiments shown in the drawings. Any change or modification made according to the concept of the present application, or the equivalent embodiments with equivalent changes, shall be within the protection scope of the present application.

Claims

1. A method of trimming and piercing a thermoformed piece, characterized in that: The method comprises the following steps, S1, hot stamping, first quenching and holding of the workpiece in a hot stamping die; S2, when the temperature cools to a preset temperature, the workpiece is taken out and moved to a trimming and piercing die; S3, the position to be trimmed and the position to be pierced are determined, and the position to be trimmed and the position to be pierced are heated; S4, when the set condition is reached, the workpiece is trimmed and pierced; wherein the set condition is that the temperature of the region on the workpiece within the set distance from the cutout corresponding to the position to be trimmed and the position to be pierced is within the set temperature range; S5, second quenching of the workpiece.

2. The method of trimming and piercing a hot formed part according to claim 1, characterized in that: During the first quenching or the second quenching, the workpiece is liquid-cooled; the cooling channels used for liquid cooling are multiple; The method for liquid cooling the workpiece comprises: S01, determining the cooling time and the initial cooling liquid flow rate at the inlet of each cooling channel according to the heat dissipation needs of the pre-selected key points on the workpiece and the initial cooling liquid temperature; S02, determining the target flow rate at the inlet of each cooling channel with respect to time and the target temperature of each key point at different time points within the cooling time according to the cooling time, and monitoring the actual temperature of each key point; S03, controlling the flow rate at the inlet of each cooling channel according to the target flow rate at the inlet of each cooling channel with respect to time; S04, comparing the actual temperature of each key point at the current time point with the target temperature, and correcting the target flow rate at the inlet of each cooling channel with respect to time according to the comparison result during the cooling process; S05, controlling the cooling liquid flow rate at the inlet of each cooling channel according to the corrected target flow rate at the inlet of each cooling channel with respect to time; repeating step S04 and step S05 until the cooling time ends.

3. The method of trimming and piercing a hot formed part according to claim 2, characterized in that: In step S02, the step of determining the target flow rate at the inlet of each cooling channel with respect to time comprises: S021, determining the cooling capacity of each cooling channel to each key point; S022, respectively determining the ratio of the influence degree of each cooling channel on each key point; S023, determining the cooling intensity requirement of each key point; S024, determining the total target flow rate at the inlet of each cooling channel with respect to time according to the cooling intensity requirement of each key point, the cooling capacity of each cooling channel to each key point, and the ratio of the influence degree of each cooling channel on each key point; S025, distributing the target flow rate at the inlet of each cooling channel according to the cooling intensity requirement of each key point and the ratio of the target flow rate at the inlet of each cooling channel.

4. The method of trimming and piercing a thermoformed piece according to claim 3, characterized in that: In step S021, the target flow rate at the inlet of each cooling channel with respect to time is determined by the cooling capacity of each cooling channel to each key point; The cooling capacity of each cooling channel to each critical point is determined by the following equation: Wherein, sa is the cooling capacity, a1 is a constant coefficient, c is the specific heat capacity of the cooling liquid, S is the cross-sectional area of the cooling channel, v is the flow rate of the cooling liquid, Tm is the temperature of the cooling channel wall surface, Ts is the temperature of the cooling liquid; t1 is the time for the cooling liquid to flow from the inlet of the cooling channel to the first endpoint of the cooling section; t2 is the time for the cooling liquid to flow from the inlet to the second endpoint of the cooling section; l(t) is the distance between the position of the cooling liquid at t time point and the corresponding key point from the inlet of the cooling channel.

5. The method of trimming and piercing a thermoformed piece according to claim 4, characterized in that: The selection method of the cooling section is that a sphere is made with the key point as the center and a preset distance as the radius, and the part of the cooling path located in the sphere is the cooling section.

6. The method of trimming and piercing a hot formed part of claim 3, wherein: The formula for correcting the target flow rate at the inlet of each cooling path with respect to time according to the comparison result is q(t)=Sv=Q(t)+b△q; Wherein, q(t) is the target flow rate at the inlet of the cooling path with respect to time after correction, Q(t) is the target flow rate at the inlet of the cooling path with respect to time before correction, b is an adjustment factor, and △q is a unit adjustment amount of the target flow rate. The formula for the adjustment factor is: a2 is a constant, T sj is the actual temperature of the corresponding key point, T mb is the target temperature of the corresponding key point.

7. The method of trimming and piercing a hot formed part according to claim 3, characterized in that: The middle part of at least one of the cooling paths has a plurality of branch streams.

8. The method of trimming and piercing a hot formed part of claim 1, wherein: Step S1 includes the following steps, S11, placing the blank into the hot stamping die and heating the blank; S12, stamping the blank to form a workpiece; S13, performing first quenching and keeping for a set time; Wherein, the heating process in step S11 and step S3 is controlled by PID.

9. A trimming and piercing die for use in the method of any one of claims 2 to 8, characterized in that: The first mold (1), the second mold (2) and the third mold (3) are included. The first mold (1) and the second mold (2) are used to press the workpiece to be trimmed and punched from both sides; The first mold (1) is provided with a plurality of first holes (11), and the side of the first mold (1) close to the workpiece is provided with a punching part (12), and the first hole (11) penetrates through the punching part (12); The first heating element (15) is embedded in the punching part (12); The first heating element (15) is used to heat the temperature of the area to be punched to a set temperature range before punching; The second mold (2) is provided with a plurality of second holes (21) corresponding to the first holes (11); The side wall of the first mold (1) is provided with a trimming area (13), and at least one second heating element (22) is arranged in the trimming area (13); The third mold (3) is located on the same side of the workpiece as the first mold (1), and the third mold (3) is distributed along the circumferential side of the first mold (1), and the third mold (3) is provided with a second heating element (22) for heating the trimming position; The first mold (1) is provided with a cooling channel for executing steps S01 to S05.

10. The trim-piercing die of claim 9, wherein: The trimming area (13) is provided with a groove (14), and the second heating element (22) is arranged in the groove (14); The second heating element (22) is used for heating the trimming area of the workpiece; A gap is provided between the circumferential side of the second heating element (22) and the wall of the groove (14).

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