Method for trimming and punching thermoformed part, and trimming and punching die

Abstract

Provided is a method for trimming and punching a thermoformed part and a trimming and punching die. The method includes the following steps: S1: in a hot stamping die, subjecting a workpiece to hot stamping, initial quenching, and temperature preservation; S2: when a temperature of the workpiece is cooled to a preset temperature, taking out the workpiece and moving the workpiece into a trimming and punching die; S3: determining a to-be-trimmed position and a to-be-punched position, and heating the to-be-trimmed position and the to-be-punched position; S4: after a set condition is reached, trimming and punching the workpiece; and S5: subjecting the workpiece to secondary quenching, so that a hot stamped part can be rapidly punched and trimmed. By accurately controlling cooling rate of the workpiece during machining, temperatures of the workpiece at various positions can be cooled, which helps prevent deformation or cracks and ensures performance of the workpiece.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of International Application No. PCT / CN2025 / 076677, filed on Feb. 10, 2025, which claims priority to Chinese Patent Application No. 202411389562.X, filed on Sep. 30, 2024, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] The present disclosure relates to the field of mechanical machining and manufacturing technologies, and in particular, to a method for trimming and punching a thermoformed part and a trimming and punching die.BACKGROUND

[0003] With the increasing requirements of the automobile industry on vehicle performance, safety, and light weight, high-strength steel plates have become one of the important ways to meet these requirements due to their light weight and high strength. However, the high-strength steel plates have a small plastic deformation range at ambient temperature and poor formability, which poses challenges to conventional cold stamping methods. The hot stamping technology makes steel plate materials soft and easy to form in a heated state by stamping the steel plates at a high temperature. Such technology can solve the problem of difficulty in forming the high-strength steel plates at ambient temperature, and can also improve dimensional accuracy and mechanical properties of parts. With the widespread application of the hot stamping technology, a trimming and punching technology of thermoformed parts has gradually become key point in manufacture of automobile stamped parts. Due to high material strength and hardness of a hot stamped part, conventional trimming and punching methods are difficult to meet machining requirements. Therefore, there is a need to adopt advanced trimming and punching technologies, such as laser cutting and water cutting, to ensure machining accuracy and surface quality of the thermoformed part. Although the current laser cutting technology has significant advantages compared with the conventional cutting technology such as a fast cutting speed, high precision, and strong material adaptability, there are also some problems to be solved:

[0004] High technical threshold: higher costs since the laser cutting technology requires professional technicians to operate and maintain, and a long trimming time because it takes a longer time for the parts to be manufactured by the laser cutting technology.

[0005] As a result, how to rapidly punch and trim hot stamped parts is one of the important issues in the art that is to be solved urgently.SUMMARY

[0006] An objective of the present disclosure is to provide a method for trimming and punching a thermoformed part, and a trimming and punching die, which can rapidly punch and trim hot stamped parts.

[0007] The present disclosure provides a method for trimming and punching a thermoformed part, including the following steps: S1: in a hot stamping die, subjecting a workpiece to hot stamping, initial quenching, and temperature preservation; S2: when a temperature of the workpiece is cooled to a preset temperature, taking out the workpiece and moving the workpiece into a trimming and punching die; S3: determining a to-be-trimmed position and a to-be-punched position, and heating the to-be-trimmed position and the to-be-punched position; S4: after a set condition is reached, trimming and punching the workpiece, the set condition includes a temperature of a region on the workpiece within a set distance from notches corresponding to the to-be-trimmed position and the to-be-punched position is within a set temperature range; and S5: subjecting the workpiece to secondary quenching.

[0008] In one or more embodiments, during the initial quenching or the secondary quenching, the workpiece is subjected to liquid cooling, and a plurality of cooling channels are used for liquid cooling. The subjecting the workpiece to liquid cooling includes: S01: determining cooling time and initial coolant flow rates at inlets of the cooling channels according to heat dissipation requirements of pre-selected key points on the workpiece and initial coolant temperatures; S02: determining, according to the cooling time, a relationship between target flow rates at the inlets of the cooling channels and time, target temperatures at the key points at different moments within the cooling time, and monitoring actual temperatures at the key points; S03: controlling flow rates at the inlets of the cooling channels according to the relationship between the target flow rates at the inlets of the cooling channels and the time; S04: during the cooling, comparing actual temperatures of the key point at a current moment with the target temperature, and correcting the relationship between the target flow rates at the inlets of the cooling channels and the time according to comparison results; and S05: controlling coolant flow rates at the inlets of the cooling channels according to a relationship between the target flow rates at the inlets of the cooling channels and the time after correction; and repeating step S04 and step S05 until the cooling time ends.

[0009] In one or more embodiments, in step S02, the determining a relationship between target flow rates at the inlets of the cooling channels and time includes: S021: determining cooling capacities of the cooling channels for the key points; S022: determining a ratio of degrees of influence of the cooling channels on the key points; S023: determining cooling intensity requirements of the key points; S024: determining a relationship between a total target flow rate at the inlets of the cooling channels and time according to the cooling intensity requirements of the key points, the cooling capacities of the cooling channels for the key points, and the ratio of degrees of influence of the cooling channels on the key points; and S025: allocating the target flow rates at the inlets of the cooling channels according to the cooling intensity requirements of the key points and a ratio of the target flow rates at the inlets of the cooling channels.

[0010] In one or more embodiments, in step S021, the relationship between the target flow rates at the inlets of the cooling channels and the time is determined by the cooling capacities of the cooling channels for the key points; and the cooling capacities of the cooling channels for the key points are determined by the following formula:

[0011] sa=∫t<sub2>1< / sub2>t<sub2>2< / sub2>a1cSv(Tm−Ts) / l(t)2 dt, where sa denotes a cooling capacity, a1 denotes a constant coefficient, c denotes a specific heat capacity of coolant, S denotes a cross-sectional area of a cooling channel, v denotes a flow rate of the coolant, Tm denotes a temperature at a wall surface of the cooling channel, and Ts denotes a temperature of the coolant; t1 denotes a time for the coolant to flow from an inlet of the cooling channel to a first endpoint of a cooling section; t2 denotes a time for the coolant to flow from the inlet to a second endpoint of the cooling section; and l(t) denotes a distance between a position of the coolant at a certain point at time t and the corresponding key point starting from the inlet.

[0012] In one or more embodiments, the cooling section is selected by using the key point as a center of a circle and using a preset distance as a radius to form a sphere, and a portion of the cooling channel located in a spherical surface is the cooling section.

[0013] In one or more embodiments, a formula for correcting the relationship between the target flow rates at the inlets of the cooling channels and the time according to comparison results is:

[0014] q(t)=Sv=Q(t)+bΔq, where q(t) denotes the relationship between the target flow rates at the inlets of the cooling channels and the time after the correction, Q(t) denotes the relationship between the target flow rates at the inlets of the cooling channels and the time before the correction, b denotes an adjustment factor, and Δq denotes a unit adjustment amount of a target flow rate; and a calculation formula for the adjustment factor is:b=a2⁢Tsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[LeftBracketingBar]"< / annotation>< / semantics>Tsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[RightBracketingBar]"< / annotation>< / semantics>,where a2 denotes a constant coefficient, Tsj denotes an actual temperature at the corresponding key point, and Tmb denotes a target temperature of the corresponding key point.

[0016] In one or more embodiments, a middle portion of at least one of the cooling channels is provided with a plurality of branches.

[0017] In one or more embodiments, step S1 includes the following steps: S11: placing a blank material into the hot stamping die, and heating the blank material; S12: stamping the blank material to form the workpiece; and S13: carrying out the initial quenching and the temperature preservation for a set time, the heating processes in step S11 and step S3 are both controlled by proportional-integral-derivative (PID)

[0018] The present disclosure further provides a trimming and punching die for the method according to any one of the above embodiments, including a first die, a second die, and a third die, the first die and the second die are configured to be pressed on a to-be-trimmed-and-punched workpiece from two sides. The first die is provided with a plurality of first holes, a side of the first die close to the workpiece is provided with a punching portion, and the first holes pass through the punching portion; a first heating element is embedded into the punching portion; and the first heating element is configured to heat a temperature of a to-be-punched region to a set temperature range prior to punching; the second die is provided with a plurality of second holes corresponding to the first holes; a side wall of the first die is provided with a trimming region, the trimming region is provided with at least one second heating element; the third die and the first die are located on a same side of the workpiece, the third die is arranged along a circumferential side of the first die, and the third die is provided with the second heating element configured to heat a trimming position; and the first die is provided with cooling channels configured to carry out the liquid cooling in step S01 to step S05.

[0019] In one or more embodiments, the trimming region is provided with a groove, and the second heating element is arranged in the groove; the second heating element is configured to heat the trimming region of the workpiece. A gap is provided between a circumferential side of the second heating element and a wall of the groove.

[0020] Compared with the prior art, in the present disclosure, after hot stamping, initial quenching, and temperature preservation of the workpiece in the hot stamping die, the formed workpiece is moved into the trimming and punching die. When the workpiece is heated in the trimming and punching die and the corresponding region of the workpiece is heated to the set temperature range, tensile strength of the corresponding position of the workpiece is reduced to less than 600 M Pa to facilitate trimming and punching operations. Local heating of the workpiece can help reduce tensile strength of the to-be-trimmed position and the to-be-punched position and achieve rapid punching and trimming to ensure quality and efficiency of machining. Since local heating can reduce the tensile strength of the to-be-trimmed position and the to-be-punched position, actual verification has shown that efficiency of trimming and punching can be increased by about 50% to 70%.

[0021] In addition, during the cooling by liquid cooling, the coolant flow rates at the inlets of the cooling channels are controlled respectively by taking cooling of the key points as a reference, so that the entire workpiece can be cooled down in an equal proportion in a controllable manner, thereby preventing deformation or cracks caused by uneven changes in an internal organizational structure of the workpiece during the cooling.BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a flowchart showing steps of a method for trimming and punching a thermoformed part according to the present disclosure;

[0023] FIG. 2 is a flowchart showing steps of a liquid cooling method for a workpiece according to the present disclosure;

[0024] FIG. 3 is a flowchart showing specific processes of step S02 according to the present disclosure;

[0025] FIG. 4 is a flowchart showing specific processes of step S1 according to the present disclosure;

[0026] FIG. 5 is a perspective view of a trimming and punching die according to the present disclosure;

[0027] FIG. 6 is a schematic diagram of disassembly of FIG. 5;

[0028] FIG. 7 is a schematic structural diagram of a workpiece prior to trimming and punching according to the present disclosure;

[0029] FIG. 8 is a schematic structural diagram of a workpiece subsequent to trimming and punching according to the present disclosure; and

[0030] FIG. 9 is a perspective view of a first die according to the present disclosure.REFERENCE SIGNS1: first die, 2: second die, 3: third die;

[0032] 11: first hole, 12: punching portion, 13: trimming region, 14: groove, 15: first heating element;

[0033] 21: second hole, 22: second heating element.DESCRIPTION OF EMBODIMENTS

[0034] Embodiments described below with reference to the accompanying drawings are exemplary and are only intended to explain the present disclosure, and shall not be construed as limiting the present disclosure.Embodiment 1

[0035] With respect to the problems in the art, since the hot stamped part has high material strength and is not easy to trim and punch, the present disclosure proposes a method for trimming and punching a thermoformed part, which, as shown in FIG. 1 to FIG. 4, includes the following steps.

[0036] In S1, in a hot stamping die, a workpiece is subjected to hot stamping, initial quenching, and temperature preservation. Through this step, hot stamping of the workpiece is achieved.

[0037] Specifically, referring to FIG. 2, step S1 includes the following steps.

[0038] In S11, a blank material is put into the hot stamping die, and the blank material is heated.

[0039] In specific implementation, the blank material is placed in the hot stamping die and then hot stamped. The hot stamping die is pre-heated to an appropriate molding temperature by using a high-temperature heating unit. A specific value of the molding temperature may be obtained according to an empirical value or an experimental value or a look-up table. Through mutual cooperation of a temperature sensor and a heating / cooling pipeline control system, temperature data of the die fed back by the temperature sensor is collected in real time and automatically adjusted as required to ensure consistency of the hot stamped workpiece. In specific implementation, a high-temperature heating unit, a cooling channel, and a temperature sensor are embedded into the hot stamping die. In this step, the heating of the blank material may be controlled by the proportional-integral-derivative (PID) algorithm, and error accumulation may be prevented by limiting an integral term or using an integral anti-saturation technology.

[0040] In S12, the blank material is stamped to form the workpiece. In specific implementation, by use of high performance servo motor and control system, a stamping speed and time of a stamping machine are precisely controlled to ensure that parts are subjected to uniform force and pressure during the molding. The blank material is molded by the stamping in this step.

[0041] In S13, the initial quenching is carried out and the temperature preservation is preserved for a set duration.

[0042] Through the quenching process, an organizational structure within the workpiece can be changed, thereby improving strength of the workpiece. In practical applications, the initial quenching process and temperature preservation are carried out in the hot stamping die, which can ensure that the workpiece may not deform during the quenching. In specific implementation, through this step, the blank material can be molded by hot stamping.

[0043] In S2, when a temperature is cooled to a preset temperature, the workpiece is taken out and moved into a trimming and punching die. In specific implementation, the preset temperature is 360° C. to 400° C. For example, the temperature value is 360° C., 365° C., 370° C., 375° C., 380° C., 385° C., 390° C., 395° C., 400° C., or the like, in which 380° C. is preferred. Since punching and trimming are carried out after hot stamping, there is no need to completely lower the workpiece to an ambient temperature in this process, which can avoid the need of increasing the workpiece from the ambient temperature to the set temperature range in subsequent steps and thus help to save energy.

[0044] In S3, a to-be-trimmed position and a to-be-punched position are determined, and the to-be-trimmed position and the to-be-punched position are heated. In specific implementation, a trimming position and a punching position may be heated in a targeted manner through a heating component preset in the trimming and punching die. Since the initial quenching of hot stamping has been completed, strength of the workpiece has reached certain requirement. This step is intended to reduce the strength of the to-be-trimmed position and the to-be-punched position by heating.

[0045] In S4, after a set condition is reached, the workpiece is trimmed and punched; the set condition refers to a temperature of a region within a set distance from corresponding notches is within a set temperature range. In specific implementation, the set temperature range is 550° C. to 600° C. For example, it should be ensured that the temperature in this region ranges from 550° C. to 600° C. That is, in this region, a maximum temperature and a minimum temperature are set within the range of 550° C. to 600° C. When the workpiece is in the temperature range, tensile strength thereof is reduced to less than 600 MPa, making it easier for trimming and punching operations. In specific implementation, after the corresponding region of the workpiece reaches the set temperature range, a trimming and punching procedure is started. Accuracy and consistency of trimming and punching are ensured by using a high-precision trimming and punching die and control system. During the entire procedure, the parts are kept within the set temperature range to ensure quality and efficiency of machining. In specific implementation, a setting distance may be 2 cm to 5 cm to ensure that tensile strength of the workpiece in a region corresponding to a notch position is less than 600 MPa. Since local heating can reduce the tensile strength of the to-be-trimmed position and the to-be-punched position, actual verification has shown that efficiency of trimming and punching can be increased by about 50% to 70%.

[0046] In S5, the workpiece is subjected to secondary quenching. The secondary quenching process is carried out in the trimming and punching die. By carrying out the secondary quenching in the trimming and punching die, deformation of the workpiece during the secondary quenching can be prevented. Since the secondary quenching is carried out in the trimming and punching die, the trimming and punching die is provided with a cooling channel. After this step, the workpiece is cooled to ambient temperature. In practical applications, prior to trimming and punching, the heating position is local heating. For a workpiece in a specific shape, a punching position and a trimming position thereof are fixed. Therefore, according to different heating regions, corresponding cooling channels may be directly arranged at corresponding positions.

[0047] In specific implementation, through the trimming and punching carried out in step S1 to step S5 above, there is a need to carry out initial quenching and secondary quenching in the hot stamping die and the trimming and punching die, respectively. During the initial quenching and the secondary quenching, since it is difficult to accurately control a temperature drop rate of each part of the workpiece, when the temperature drop rate is uneven, it is easy to cause uneven changes in the internal organizational structure of the workpiece, resulting in deformation and cracks in the workpiece. To solve this problem, in this embodiment, during the initial quenching and the secondary quenching, the workpiece is subjected to liquid cooling, and a plurality of cooling channels are used for liquid cooling. Taking the initial quenching as an example, referring to FIG. 3, a method for subjecting the workpiece to liquid cooling includes the following steps.

[0048] In S01, cooling time and initial coolant flow rates at inlets of the cooling channels are determined according to heat dissipation requirements of pre-selected key points on the workpiece and initial coolant temperatures. In specific implementation, the key points are selected first according to factors such as a shape of the workpiece, a heat dissipation requirement, and a design strength. The key points may be geometric center points or characteristic points in a key heat dissipation region. In specific implementation, the key heat dissipation region is one or more regions on the workpiece that are difficult to dissipate heat after the hot stamping die stamps the workpiece, for example, in a die closing state, a region near a center of the entire hot stamping die, a thicker region of the hot stamping die, and a region on the workpiece where the mass is more concentrated. One or more key points are selected in each region that is difficult to dissipate heat, to jointly form a set of key points. For example, n key points are denoted as K1, K2, K3, K4, K5, K6, . . . , and Kn, respectively.

[0049] In specific implementation, the initial coolant temperature refers to a coolant temperature when the coolant enters the inlet of the cooling channel. During use, tap water may be directly used for cooling, and there is a need to only ensure the temperature when the coolant enters the cooling channel. In the entire cooling process, the coolant is not recycled, so there is a need to only ensure that the temperature of the coolant at the inlet of the cooling channel is basically constant. In some embodiments, the temperature at the inlet of the cooling channel may alternatively be controlled according to certain requirements.

[0050] The initial coolant flow rates at the inlets of the cooling channels are used only when cooling starts. This is because during the cooling, the target flow rates at the inlets of the cooling channels are required to be calculated based on cooling capacities. Moreover, the cooling capacities of the cooling channels for the key points are related to the coolant flow rates. Therefore, when cooling starts, cooling is carried out by the initial coolant flow rates at the inlets of the cooling channels. During subsequent cooling, precise control is achieved by continuously correcting the target flow rates at the inlets of the cooling channels. The selection of the initial coolant flow rates at the inlets of the cooling channels directly affects control accuracy, which may be selected according to experience.

[0051] In S02, a relationship between target flow rates at the inlets of the cooling channels and time and target temperatures at the key points at different moments within the cooling time are determined according to the cooling time, and actual temperatures at the key points are monitored.

[0052] The hot stamping die is provided with a plurality of cooling channels. The cooling channels are denoted as C1, C2, C3, C4, . . . , and Cm, respectively. For each key point, the plurality of cooling channels can affect the key point. However, due to different cooling capacities of the cooling channels and distances from the key point, each cooling channel has different cooling capabilities for the same key point.

[0053] In this step, in order to ensure that each key point can be cooled down uniformly or at a certain ratio, please refer to FIG. 4. This step includes the following specific steps. In S021, cooling capacities of the cooling channels for the key points are determined. In this step, the cooling capacity of any cooling channel for any key point is characterized by the following formula:sa=∫t1 t2a1⁢cSv⁡(Tm-Ts)l⁡(t)2⁢dt.

[0054] In the above formula, a1 denotes a constant coefficient, whose specific value may be determined according to an empirical value or an experimental value or a look-up table, c denotes a specific heat capacity of coolant, S denotes a cross-sectional area of a cooling channel, v denotes a flow rate of the coolant, Tm denotes a temperature at a wall surface of a cooling channel, Ts denotes a temperature of the coolant, t1 denotes a time for the coolant to flow from an inlet of the cooling channel to a first endpoint of a cooling section, t2 denotes a time for the coolant to flow from the inlet to a second endpoint of the cooling section, and l(t) denotes a distance between a position of the coolant at a certain point at time t and the corresponding key point starting from the inlet. For ease of expression, a cooling capacity of a jth cooling channel for an ith key point is represented with sa(i,j). In specific implementation, the cooling section is a portion of the corresponding cooling channel that has a greater influence on a certain key point. For example, a method for selecting the cooling section is to use the key point as a center of a circle and a preset distance as a radius to make a sphere, and a portion of the cooling channel located within a spherical surface is the cooling section, that is, a section of the cooling channel that has the greatest cooling effect on the key point. Intersections of the cooling section and the spherical surface are a first endpoint and a second endpoint, respectively.

[0055] In some embodiments, for a single cooling channel, a cross-sectional area of the cooling channel may alternatively be set to a variable cross-section structure. That is, a cross section S is set to a variable. In specific implementation, the cross section S may be transformed into a relationship between distances from the inlet of the cooling channel, and further transformed into a relationship between the cross section S and time as well as flow velocities, which is substituted into the above formula, to obtain the cooling capacity of the variable cross-section cooling channel for the key point. In specific implementation, the inlet of the cooling channel is not always located on a same side of the die. For an upper die, the inlet of the cooling channel may be located in the middle of a top surface of the upper die. For a lower die, the inlet of the cooling channel may be located in the middle of a bottom surface of the upper die, and an outlet is arranged on a side surface of the die. It is understandable that, the inlet and the outlet may alternatively be arranged on opposite side surfaces of the die, respectively. By arranging the inlet of the cooling channel in the middle of the top surface or the bottom surface, the coolant can directly reach a position close to the corresponding key point, to improve the cooling capacity for the key point.

[0056] For the ith key point, an influence of each cooling channel is sai=∑ j=1j=m⁢sa⁡(i,j).

[0057] In S022, a ratio of degrees of influence of the cooling channels on the key points is determined. For the ith key point, the ratio of degrees of influence of the cooling channels is:sa⁡(i,1): sa⁡(i,2): …⁢ sa⁡(i,j): … : sa⁡(i,m).

[0058] By determining the ratio of degrees of influence of the cooling channels on the key points, it is convenient to select, according to the ratio, the cooling channel that has a greater influence on a certain key point, which helps rapidly determine the target flow rates at the inlets of the cooling channels.

[0059] In S023, cooling intensity requirements of the key points are determined. In specific implementation, the cooling intensity requirements may be determined according to positions of the key points and temperature change requirements. For example, when the key points are required to be cooled synchronously and the initial temperatures at the key points are different, the cooling intensity requirements may be determined according to the actual temperatures at the key points, required quenching conditions, and the like. For example, the cooling intensity requirement may be related to a difference between an actual temperature at the key point at the beginning of quenching and a temperature that the key point is required to reach at the end of quenching, quenching time, and a specific heat capacity of a material used in the workpiece. For example, the cooling intensity requirement is directly proportional to the difference between the actual temperature at the key point at the beginning of quenching and the temperature that the key point is required to reach 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 used in the workpiece. In other aspects, the cooling intensity requirements of the key points are further related to positions thereof. The key point closer to the middle position indicates a greater cooling intensity requirement.

[0060] In S024, a relationship between a total target flow rate at the inlets of the cooling channels and time is determined according to the cooling intensity requirements of the key points, the cooling capacities of the cooling channels for the key points, and the ratio of degrees of influence of the cooling channels on the key points.

[0061] For example, this step is intended to determine the relationship between the total target flow rate at the inlets of the cooling channels and the time. As cooling proceeds, the difference between the temperature of the workpiece and the temperature of the coolant gradually becomes smaller at different moments. To make the workpiece have a same cooling rate at different moments, the total coolant flow rate is required to be changed. The total target flow rate at the inlets of the cooling channels changes over time.

[0062] In S025, the target flow rates at the inlets of the cooling channels are allocated according to the cooling intensity requirements of the key points and a ratio of flow rates at the inlets of the cooling channels. Moreover, flow rates at the inlets of the corresponding cooling channels are controlled according to the target flow rates.

[0063] This step is intended to differentially control the flow rates at the inlets of the cooling channels at a same moment so that the temperatures at the key points decrease synchronously.

[0064] For example, when the key points are required to be cooled synchronously and initial temperatures at the key points are the same, the flow rates at the inlets of the cooling channels are determined according to the ratio of the degrees of influence of the cooling channels on the key points, so that the degrees of influence of all the cooling channels on the key points are basically the same, thereby achieving the purpose of synchronously reducing the temperatures at the key points, to prevent deformation and cracks caused by different temperature change speeds and different changes in the internal organizational structure.

[0065] When the key points are required to be cooled synchronously and the initial temperatures at the key points are the same, synchronous cooling can be guaranteed as long as the key points are affected by each cooling channel to the same extent. That is, there is a need to ensures⁢a1=s⁢a2=…⁢ sai⁢ …=s⁢an.

[0066] The above equation is satisfied by adjusting the flow rates at the cooling channels. That is, all flow rates at the inlets of the cooling channels that satisfy the above formula may be regarded as the target flow rates at the inlets of the cooling channels. When there are a small number of cooling channels and a large number of key points, it may lead to no solution. In this case, basically synchronous cooling of the key points can be achieved by changing the target flow rates at the inlets of the cooling channels at different moments.

[0067] When the key points are required to be cooled at the same proportional rate, the cooling capacities of the cooling channels may be adjusted similarly to achieve the purpose of reducing the temperatures in an equal proportion. In this way, different key points of the workpiece may have corresponding performance.

[0068] In practical applications, since the number of the cooling channels may be less than the number of the key points, it may be difficult to achieve synchronous control over the temperatures at the key points by controlling the flow rates at the inlets of the cooling channels at a fixed flow rate. Therefore, the flow rates at the inlets of the cooling channels are set to change over time, thereby achieving the purpose of cooling the plurality of key points basically as required.

[0069] In S03, flow rates at the inlets of the cooling channels are controlled according to the relationship between the target flow rates at the inlets of the cooling channels and the time. In specific implementation, the relationship between the target flow rates at the inlets of the cooling channels and the time is a functional relationship obtained by theoretical calculation, in which many factors are ignored, such as resistance of the cooling channels, natural heat dissipation, and evaporation of the coolant. In practical applications, there is a need to further adjust the relationship between the target flow rates and time.

[0070] In S04, during the cooling, actual temperatures of the key point at a current moment are compared with the target temperatures, and the relationship between the target flow rates at the inlets of the cooling channels and the time is corrected according to comparison result. In specific implementation, due to factors such as errors, the actual temperatures may deviate from the relationship between the target flow rates and the time. Therefore, during actual control, the relationship between the target flow rates and the time is corrected in real time. For example, a formula thereof is as follows:q⁡(t)= Sv=Q⁡(t)+b⁢Δ⁢q.

[0071] In the above formula, q(t) denotes the relationship between the target flow rates and the time after the correction, Q(t) denotes the relationship between the target flow rates and the time before the correction, b denotes an adjustment factor, and Δq denotes a unit adjustment amount of a target flow rate.

[0072] The adjustment factor is related to the actual temperature and the target temperature. For example, a calculation formula for the adjustment factor is:b=a2⁢Tsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[LeftBracketingBar]"< / annotation>< / semantics>Tsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[RightBracketingBar]"< / annotation>< / semantics>.

[0073] In the above formula, a2 denotes a constant coefficient, whose specific value may be determined according to an empirical value or an experimental value or a look-up table, Tsj denotes an actual temperature at the corresponding key point, and Tmb denotes a target temperature of the corresponding key point. The adjustment factor b is intended to correct the relationship between the target flow rates and the time, so that the relationship of the target flow rates and the time after the correction is more accurate. a2 is intended to determine a size of the adjustment factor, andTsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[LeftBracketingBar]"< / annotation>< / semantics>Tsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[RightBracketingBar]"< / annotation>< / semantics>is intended to determine a sign of the adjustment factor. b is dimensionless parameter. A size of a2 is related to factors such as a thermal conductivity coefficient. In practical applications, the value may be determined based on experiments combined with theoretical calculation. For example, in practical applications, the relationship between the target flow rates and the time and a relationship between actual flow rates and the time are recorded in a coordinate system in which the abscissa is time and the ordinate is flow rates. A solution a2 may be solved with a goal of minimizing a sum of areas enclosed by a change curve of the target flow rates over the time and a change curve of the actual flow rates over the time, to obtain an optimal a2.In S05, the flow rates at the inlets of the cooling channels are controlled according to a corrected relationship between the target flow rates at the cooling channels and the time, and step S04 and step S05 are repeated until the cooling time ends.

[0075] In specific implementation, degrees of cooling of the key points are represented by a sum of the cooling capabilities of the cooling channels for the corresponding key points. A same cooling channel has different cooling capabilities for different key points. The purpose of synchronous cooling of the key points according to a specific ratio is achieved by adjusting the inlet flow rates at the cooling channels only when the cooling capabilities of the cooling channels for different key points are different.

[0076] A middle portion of at least one of the cooling channels is provided with a plurality of branches. When the cooling channel is provided with the branches, the coolant flowing into the branches can help dissipate heat over a larger region. When branches exist, especially when the cooling section includes branches, cooling capacities of the key points corresponding to all the branches on the cooling channel may be calculated by superimposing the branches.

[0077] In this method, the heating process, the temperature preservation process, and the secondary quenching process of the foregoing steps are all controlled by PID (proportional-integral-derivative), and error accumulation is prevented by limiting an integral term or using an integral anti-saturation technology. Parameters such as the temperature of the die, quenching temperatures and holding temperatures of parts in the die, quenching and holding time, the coolant flow velocity, the flow rate, the pipeline diameter, the distance from a pipeline to a profile surface, and an energy loss rate are automatically and dynamically adjusted by using a PID algorithm. Input confirmation: for die temperature control, a set temperature is inputted. For temperature control, power of a heating / cooling device may be outputted. It is understandable that, for the cooling device, flow rates or flow velocities of the coolant at the inlets of the cooling channels may be controlled.

[0078] Control over a stamping speed and stamping time may be PID control. A speed or a position of a servo motor is adjusted according to output of a PID controller.Embodiment 2

[0079] Referring to FIG. 5 to FIG. 9, this embodiment proposes a trimming and punching die configured to implement the method in Embodiment 1, including a first die 1, a second die 2, and a third die 3. For example, the first die 1 and the second die 2 are configured to be pressed on a to-be-trimmed-and-punched workpiece from two sides. During implementation, both the first die 1 and the second die 2 are adapted to the workpiece.

[0080] The first die 1 is provided with a plurality of first holes 11, a side of the first die 1 close to the workpiece is provided with a punching portion 12, and the first holes 11 pass through the punching portion 12. A first heating element 15 is embedded into the punching portion 12. The first heating element 15 is configured to heat a temperature of a to-be-punched region to a set temperature range prior to punching. In specific implementation, the to-be-punched position is heated to 550° C. to 600° C. by the first heating element 15, so that tensile strength here is lower than 600 MPa, so as to facilitate completion of punching. In this way, punching costs can be reduced to achieve low-cost stamping of the hot stamped part.

[0081] The second die 2 is provided with a plurality of second holes 21 corresponding to the first holes 11. In specific implementation, center lines of the second hole 21 and the corresponding first hole 11 are located on a same line. Preferably, the second hole 21 has the same cross-sectional shape and size as the corresponding first hole 11.

[0082] A periphery of the first die 1 is provided with a trimming region 13, and at least one second heating element 22 is arranged in the trimming region 13. A portion of the workpiece located at the trimming region 13 is heated by the second heating element 22 so that the tensile strength of the portion is lower than 600 MPa.

[0083] The third die 3 is located on the same side of the workpiece as the first die 1 and is distributed along a circumferential side of the first die 1, and the third die 3 is provided with the second heating element 22 configured to heat the trimming position. In specific implementation, when heated to 550° C. to 600° C., the punching position is punched by a punching device. The third die 3 is removed, and the trimming position is cut.

[0084] In specific implementation, the trimming region 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 configured to heat a to-be-cut position of the workpiece. A gap is provided between a circumferential side of the second heating element 22 and a wall of the groove 14. For example, the groove 14 is U-shaped. The gap between the circumferential side of the second heating element 22 and the wall of the groove 14 can help reduce diffusion of heat to the second die 2 and transfer more heat to the workpiece.

[0085] In specific implementation, the first die 1 is provided with cooling channels. The workpiece is cooled by passing the coolant into the cooling channels. Accurate control of the local temperature of the workpiece is achieved through cooperation between the first heating element 15 and the second heating element 22. For a specific control method, refer to Embodiment 1.

[0086] The configurations, features, and effects of the present disclosure have been described in detail with reference to the embodiments as shown in the drawings. The above embodiments are only the preferred embodiments of the present disclosure, but the present disclosure is not limited to the scope as shown in the drawings. Any changes made according to the conception of the present disclosure, or equivalent embodiments that are modified to equivalent variations, which do not exceed the spirit covered by the specification and the drawings, should fall within the protection scope of the present disclosure.

Claims

1. A method for trimming and punching a thermoformed part, comprising following steps:S1: in a hot stamping die, subjecting a workpiece to hot stamping, initial quenching, and temperature preservation;S2: when a temperature of the workpiece is cooled to a preset temperature, taking out the workpiece and moving the workpiece into a trimming and punching die;S3: determining a to-be-trimmed position and a to-be-punched position, and heating the to-be-trimmed position and the to-be-punched position;S4: after a set condition is reached, trimming and punching the workpiece, wherein the set condition includes a temperature of a region on the workpiece within a set distance from notches corresponding to the to-be-trimmed position and the to-be-punched position is within a set temperature range; andS5: subjecting the workpiece to secondary quenching.

2. The method for trimming and punching a thermoformed part according to claim 1, wherein during the initial quenching or the secondary quenching, the workpiece is subjected to liquid cooling, and a plurality of cooling channels are used for liquid cooling; andthe subjecting the workpiece to liquid cooling comprises:S01: determining cooling time and initial coolant flow rates at inlets of the cooling channels according to heat dissipation requirements of pre-selected key points on the workpiece and initial coolant temperatures;S02: determining, according to the cooling time, a relationship between target flow rates at the inlets of the cooling channels and time, target temperatures at the key points at different moments within the cooling time, and monitoring actual temperatures at the key points;S03: controlling flow rates at the inlets of the cooling channels according to the relationship between the target flow rates at the inlets of the cooling channels and the time;S04: during the cooling, comparing actual temperatures of the key point at a current moment with the target temperature, and correcting the relationship between the target flow rates at the inlets of the cooling channels and the time according to comparison results; andS05: controlling coolant flow rates at the inlets of the cooling channels according to a relationship between the target flow rates at the inlets of the cooling channels and the time after correction; and repeating step S04 and step S05 until the cooling time ends.

3. The method for trimming and punching a thermoformed part according to claim 2, wherein in step S02, the determining a relationship between target flow rates at the inlets of the cooling channels and time comprises:S021: determining cooling capacities of the cooling channels for the key points;S022: determining a ratio of degrees of influence of the cooling channels on the key points;S023: determining cooling intensity requirements of the key points;S024: determining a relationship between a total target flow rate at the inlets of the cooling channels and time according to the cooling intensity requirements of the key points, the cooling capacities of the cooling channels for the key points, and the ratio of degrees of influence of the cooling channels on the key points; andS025: allocating the target flow rates at the inlets of the cooling channels according to the cooling intensity requirements of the key points and a ratio of the target flow rates at the inlets of the cooling channels.

4. The method for trimming and punching a thermoformed part according to claim 3, wherein in step S021, the relationship between the target flow rates at the inlets of the cooling channels and the time is determined by the cooling capacities of the cooling channels for the key points; andthe cooling capacities of the cooling channels for the key points are determined by following formula:sa=∫t1 t2a1⁢cSv⁡(Tm-Ts)l⁡(t)2⁢dt,where sa denotes a cooling capacity, a1 denotes a constant coefficient, c denotes a specific heat capacity of coolant, S denotes a cross-sectional area of a cooling channel, v denotes a flow rate of the coolant, Tm denotes a temperature at a wall surface of the cooling channel, and Ts denotes a temperature of the coolant; t1 denotes a time for the coolant to flow from an inlet of the cooling channel to a first endpoint of a cooling section; t2 denotes a time for the coolant to flow from the inlet to a second endpoint of the cooling section; and l(t) denotes a distance between a position of the coolant at a certain point at time t and the corresponding key point starting from the inlet.

5. The method for trimming and punching a thermoformed part according to claim 4, wherein the cooling section is selected by using the key point as a center of a circle and using a preset distance as a radius to form a sphere, and a portion of the cooling channel located in a spherical surface is the cooling section.

6. The method for trimming and punching a thermoformed part according to claim 3, wherein a formula for correcting the relationship between the target flow rates at the inlets of the cooling channels and the time according to comparison results is:q⁡(t)= Sv=Q⁡(t)+b⁢Δ⁢q,where q(t) denotes the relationship between the target flow rates at the inlets of the cooling channels and the time after the correction, Q(t) denotes the relationship between the target flow rates at the inlets of the cooling channels and the time before the correction, b denotes an adjustment factor, and Δq denotes a unit adjustment amount of a target flow rate; anda calculation formula for the adjustment factor is:b=a2⁢Tsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[LeftBracketingBar]"< / annotation>< / semantics>Tsj-Tmb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[RightBracketingBar]"< / annotation>< / semantics>,where a2 denotes a constant coefficient, Tsj denotes an actual temperature at the corresponding key point, and Tmb denotes a target temperature of the corresponding key point.

7. The method for trimming and punching a thermoformed part according to claim 3, wherein a middle portion of at least one of the cooling channels is provided with a plurality of branches.

8. The method for trimming and punching a thermoformed part according to claim 1, wherein step S1 comprises following steps:S11: placing a blank material into the hot stamping die, and heating the blank material;S12: stamping the blank material to form the workpiece; andS13: carrying out the initial quenching and the temperature preservation for a set time;wherein the heating processes in step S11 and step S3 are both controlled by proportional-integral-derivative (PID).

9. A trimming and punching die, applied for the method according to claim 2, comprising: a first die (1), a second die (2), and a third die (3);wherein the first die (1) and the second die (2) are configured to be pressed on a to-be-trimmed-and-punched workpiece from two sides;the first die (1) is provided with a plurality of first holes (11), a side of the first die (1) close to the workpiece is provided with a punching portion (12), and the first holes (11) pass through the punching portion (12); a first heating element (15) is embedded into the punching portion (12); and the first heating element (15) is configured to heat a temperature of a to-be-punched region to a set temperature range prior to punching;the second die (2) is provided with a plurality of second holes (21) corresponding to the first holes (11);a side wall of the first die (1) is provided with a trimming region (13), the trimming region (13) is provided with at least one second heating element (22);the third die (3) and the first die (1) are located on a same side of the workpiece, the third die (3) is arranged along a circumferential side of the first die (1), and the third die (3) is provided with the second heating element (22) configured to heat a trimming position; andthe first die (1) is provided with cooling channels configured to carry out the liquid cooling in step S01 to step S05.

10. The trimming and punching die according to claim 9, wherein the trimming region (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 configured to heat the trimming region of the workpiece; and a gap is provided between a circumferential side of the second heating element (22) and a wall of the groove (14).

Images