KR100907225B1 - Hot forming apparatus and hot forming method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot forming manufacturing method for molding a product by heating above a predetermined temperature, and more particularly, to a hot forming apparatus and a hot forming manufacturing method for improving the strength of a product manufactured by a mold operation.

The hot forming apparatus according to the present invention includes a lower mold on which a work object is placed, an upper mold coupled to the lower mold to mold the work object, and interposed between the lower mold and the upper mold to form an internal space of the work object. It characterized in that it comprises a cam for shaping, and a cooling device for cooling the work object.

The hot forming method according to the present invention is the pressing step of performing the hot forming by mounting the work object on the lower mold and combining the upper mold, the lower mold, and the cam, and completion of molding to determine whether the set time has elapsed after the pressing step is started. If the time set in the determination step and the molding completion step has elapsed, characterized in that it comprises a cooling step of cooling the work object by supplying a cooling fluid around the work object.

Manufacturing equipment, beam, automobile, rear wheel, suspension

Description

Hot forming apparatus and hot forming method {HOT FORMING APPARATUS AND HOT FORMING METHOD}

1 is a perspective view showing an embodiment of a hot forming apparatus according to the present invention.

Figure 2 is a front sectional view showing a flow path of an embodiment of a hot forming apparatus according to the present invention.

3 is a side cross-sectional view showing a flow path of a hot forming apparatus according to another embodiment of the present invention.

Figure 4 is a side cross-sectional view showing a cam flow path of the hot forming apparatus according to another embodiment of the present invention.

5 is a flowchart illustrating a method for manufacturing hot forming according to an embodiment of the present invention.

6 is a perspective view illustrating a torsion beam manufactured by a hot forming apparatus and a hot forming method according to an embodiment of the present invention.

7 is a cross-sectional view taken along the line A-A shown in FIG.

FIG. 8 is a cross-sectional view taken along the line B-B shown in FIG. 6.

9 is a cross-sectional view taken along the line C-C shown in FIG.

<Explanation of symbols on main parts of the drawings>

10: base 12: lower base

14: upper base 16: base cylinder

20: upper mold 30: lower mold

32: guide 40: cam

42: cam cylinder 50: cooling device

52: cooling flow path 52a: mold flow path

52b: cam flow path 52c: suction flow path

52d: exhaust passage 54: cooling pipe

54a: mold pipe 54b: cam pipe

56: valve 70: torsion beam

72: center 74: end

76: connection

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot forming apparatus and a hot forming manufacturing method for molding a product by heating above a predetermined temperature, and more particularly, to a hot forming apparatus and a hot forming manufacturing method for improving the strength of a product manufactured by a mold operation.

Although the products manufactured by the hot forming apparatus and the hot forming method are various, the present invention will be described taking as an example a torsion beam of a rear wheel suspension of an automobile.

The torsion beam of the rear suspension of the automobile is composed of the beam and the trailing arms on both sides of the torsion beam, which is responsible for maintaining the posture by torsion of the beam against the centrifugal force applied during the turning of the vehicle. Is required.

Initially, the steel plate was bent in cross-section "U" type or "V" shape to construct the beam, and to reinforce it with torsion bar inside, and to have torsional rigidity and bending rigidity by welding through a reinforcement plate separate from the trailing arm. .

The torsion beam of the above structure can be sufficiently satisfied with torsional rigidity and bending stiffness as the strength is reinforced, but it causes a significant productivity decrease due to the increased number of parts such as torsion bar and reinforcement plate and the number of assembling and welding process, and tolerance during welding process. Problems have been pointed out, such as the failure rate is very high due to the difficulty of management, and provide a cause of lowering the fuel efficiency of the vehicle by weighting the product.

Recently, the cylindrical pipe is press-molded so that the center part has two layers of "U" or "V" shape for torsional rigidity, and both sides are "ㅁ" for securing a wide welding surface and bending strength with the trailing arm. A beam having a cross section is used, which is a beam of a torsion beam, which has sufficient rigidity against torsion and bending, and can reduce the number of parts, assembly and welding processes, resulting in improved productivity, reduced defect rate, and lighter weight. It is evaluated to improve the fuel efficiency of the vehicle.

However, in order to obtain a beam having a different cross-sectional shape for each part as described above, as the number of processes increases, the productivity decreases and the price competitiveness decreases due to an increase in manufacturing cost. To get.

In the production of cross-section "U" type or "V" type products by pressure-molding cylindrical pipes, two sets of molds having different shapes of lower molds are used, or a set of molds composed of upper molds and several lower molds moving toward each other. Methods and tools are known for obtaining the finished product.

In the above process using two sets of molds, the first preform molding process and the second precision molding process are performed using a mandrel and the initial pipe is firmly fixed. The process is divided into a shelf-shaped upper die, one intermediate tank and two side bars, and is performed through the lower dies moving toward each other by guides of the inclined surfaces between the upper dies and each other, and each of the cross-sections "U" or "V". It is expected that a product made of a mold can be sufficiently obtained, and further, even if the cross-sectional shape of each part is different, such as a beam constituting the torsion beam of the rear suspension of an automobile, it is expected that a finished product can be obtained with a minimum process.

However, products having cross-sectional shapes of various shapes, such as beams of torsion beams, which are different from each other, may be deformed at both ends or cross-sectional shapes when manufactured by the conventional manufacturing apparatus and the manufacturing method as described above. Since the strength of the part is difficult to improve more than a predetermined value, there is a problem that it is easily deformed or broken.

The present invention has been made to improve the above problems of the prior art, and an object thereof is to provide a hot forming apparatus and a hot forming manufacturing method for manufacturing a product having a symmetrical symmetry.

It is also an object of the present invention to provide a hot forming apparatus and a hot forming method for improving the strength of a product manufactured by a mold operation.

In addition, an object of the present invention is to provide a hot forming apparatus and a hot forming manufacturing method that can reduce the occurrence of defective products caused by shape deformation during molding.

The hot forming apparatus according to the present invention comprises: a lower mold on which a workpiece is placed; An upper mold coupled to the lower mold to mold the workpiece; A cam interposed between the lower mold and the upper mold to form an internal space of the workpiece; And it characterized in that it comprises a cooling device for cooling the work object.

The cooling device is preferably installed in any one of the lower mold, the upper mold, or the cam. In addition, the cooling device is preferably formed in the lower mold, the upper mold or the cam.

The cooling device may include: a cooling passage through which a cooling fluid is supplied so as to transform the austenite structure of the workpiece into martensite structure; A pump for supplying the cooling fluid to the cooling flow path; And a cooling pipe connecting the cooling passage and the pump. Here, the cooling flow path, a mold flow path formed in the lower mold and the upper mold; And a cam flow path formed inside the cam. In addition, the cam flow path, the suction flow path; And an exhaust passage formed to maintain a predetermined interval outside the suction passage.

It is preferable that a guide is further installed between the lower mold and the upper mold.

Preferably, a space portion is formed between the cam, the lower mold, and the upper mold.

It is preferred that the cooling unit further includes a direct cooling passage for supplying a cooling fluid.

The direct cooling flow path is preferably formed in any one of the lower mold, the upper mold, and the cam.

In addition, the hot forming manufacturing method according to the present invention comprises: a pressing step of performing a hot forming by mounting the workpiece to the lower mold, and combining the upper mold, the lower mold, and the cam; A molding completion determination step of determining whether a set time has elapsed after the pressing step is started; And a cooling step of cooling the work object by supplying a cooling fluid around the work object when the time set in the molding completion determination step has elapsed.

The cooling step is characterized in that to change the tissue of the workpiece from austenite tissue to martensite tissue by quenching the temperature of the workpiece within a predetermined time or less than a predetermined temperature.

In the cooling step, the cooling fluid is circulated into one of the upper mold, the lower mold, and the cam. At this time, the cooling step is to circulate the cooling fluid into the inside of the lower mold, circulate into the inside of the upper mold, or circulate inside the cam. That is, various modifications can be made, such as circulating the cooling fluid only in the member of any one of the upper mold, the lower mold, or the cam, or cooling them sequentially.

In the cooling step, the cooling fluid may be supplied between the cam, the upper mold, and the lower mold to contact the cooling fluid with the work object.

The hot forming manufacturing method according to the present invention comprises: a temperature judging step of determining whether a temperature of the workpiece is below a set temperature after the cooling step is started; And a separating step of separating the work object by separating the upper mold, the lower mold and the cam when the work object is below the set temperature in the temperature determining step.

Hereinafter, an embodiment of a hot forming apparatus and a hot forming method according to the present invention will be described in detail with reference to the accompanying drawings. For convenience of description, the method of manufacturing hot forming of the rear suspension of an automobile will be described as an example. In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of description. In addition, terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to the intention or convention of a user or an operator. Therefore, the definitions of these terms should be made based on the contents throughout the specification.

1 is a perspective view showing an embodiment of a hot forming apparatus according to the present invention, Figure 2 is a front sectional view showing a flow path of an embodiment of the hot forming apparatus according to the present invention.

1 and 2, the hot forming apparatus according to an embodiment of the present invention includes a base 10, a lower mold 30 installed on the base 10, on which a work object is placed, and a base 10. When installed in a fluidly coupled to the lower mold 30, the upper mold 20 for hot forming the workpiece and the base 10 is installed to be flowable between the upper mold 20 and the lower mold 30 A cam device 40 interposed to form the internal space of the work object, and a cooling device 50 installed in the lower mold 30, the upper mold 20, and the cam 40 to cool the work object after the hot forming is finished. ).

Here, the base 10 is installed on the bottom surface of the lower base 12, the lower mold 30 is installed, and the lower base 12 by the base cylinder 16 on the upper surface so as to be movable in the vertical direction and the top It includes the upper base 14, the mold 20 is installed.

After the workpiece is placed on the lower mold 30, the base cylinder 16 is driven to lower the upper base 14 and the upper mold 20, and the upper mold 20 and the lower mold 30 are coupled to the mold. Press work is performed.

At this time, the upper mold 20 and the lower mold 30 is heated above a predetermined temperature to hot-form the workpiece. The heating apparatus (not shown) for heating the mold to perform the hot forming operation is well known to those skilled in the art to which the present invention belongs, so detailed drawings and description thereof will be omitted. Since the base cylinder 16 is also a hydraulic cylinder that is well known to those skilled in the art, detailed drawings, descriptions, and a description of the driving method will be omitted.

In addition, since the base cylinder 16 is also a conventional hydraulic cylinder, detailed drawings and explanations and driving methods will be omitted.

The guide 32 is installed between the lower mold 30 and the upper mold 20, which is a device for allowing the upper mold 20 and the lower mold 30 to be coupled in the correct position.

In addition, the guide 32 allows the workpiece to be accurately centered when it is placed on the lower mold 30, so that the finished product can be precisely symmetrical.

The guide 32 is made of a piece of a predetermined size that is installed on the groove rim of the lower mold 30 on which the work object is seated, the side forming the guide 32 is lower by a conventional fastening member such as bolts, rivets, etc. It is coupled to the upper surface of the mold (30).

The cam 40 is installed on a pair of cam cylinders 42 installed in the horizontal direction on the upper surface of the lower base 12.

When the arm of the cam cylinder 42 protrudes, the cam 40 installed at the end of the arm is interposed between the lower mold 30 and the upper mold 20, and when the arm is inserted into the cam cylinder 42, the cam 40 is inserted. ) Is discharged from the space between the lower mold 30 and the upper mold 20.

In this configuration, when the pipe-shaped torsion beam 70 is placed on the lower mold 30 and the cam cylinder 42 is driven, the cam 40 is inserted into both ends of the torsion beam 70.

After the base cylinder 16 is driven and the upper mold 20 is lowered and coupled to the lower mold 30, the hot forming is made.

As described above, the mold apparatus for manufacturing the pipe-shaped beam by the upper mold 20, the lower mold 30, and the cam 40 can be easily carried out by a person having ordinary knowledge in the art. The exploded perspective view showing the upper mold 20, the lower mold 30, and the cam 40 in detail because of the device will be omitted.

The cooling device 50 is formed inside any one of the lower mold 30, the upper mold 20, and the cam 40. The cooling device 50 includes a cooling flow path 52 through which a cooling fluid is supplied, a pump (not shown) for supplying cooling fluid to the cooling flow path 52, and a cooling pipe 54 connecting the pump and the cooling flow path 52. And a tank (not shown) that is filled with a cooling fluid and connected to the cooling pipe 54. Here, the cooling flow path 52 is arranged so that the structure of the torsion beam, which is a workpiece having austenite structure, is directly transformed into martensite structure by hot forming. Cooling flow path 52 is preferably disposed in the lower mold 30, the upper mold 20 or the cam 40 so as to quench the workpiece. More preferably, a plurality of cooling passages 52 are disposed in the lower mold 30, the upper mold 20, or the cam 40.

The cooling passage 52 includes a mold passage 52a formed inside the lower mold 30 and the upper mold 20, and a cam passage 52b formed inside the cam 40.

Here, the cooling pipe 54 includes a mold pipe 54a connected to the upper mold 20 and the lower mold 30 from the tank, and a cam pipe 54b connected to the cam 40 from the tank.

The cooling pipe 54 is provided with a valve 56 in a pipe extending from the tank, from which the mold pipe 54a and the cam pipe 54b branch off.

Thus, when the pump is driven after the hot forming is completed, the cooling fluid is supplied along the cooling flow path 54 formed in the lower mold 30, the upper mold 20, and the cam 40, so that the lower mold 30 and the upper portion are The temperature of the workpiece | work interposed between the metal mold | die 20 and the cam 40 is rapidly cooled below predetermined temperature.

Here, the cam flow path 52b includes a suction flow path 52c extending from the suction port of the cap 40 and an exhaust flow path 52d formed to maintain a predetermined interval outside the suction flow path 52c.

By this configuration, the cooling fluid introduced into the cam 40 is moved along the suction flow path 52c to the end of the cam 40, and the cooling fluid discharged to the end of the suction flow path 52c is the suction flow path 52c. It is moved along the space between the outer wall and the inner wall of the exhaust passage 52d and is discharged again to the outside of the cam 40.

In addition, the cam 40 has a square cross section of an outer end portion corresponding to the cam cylinder 42, and its cross sectional shape decreases toward the inner end portion.

In addition, since the cam 40 has a 'V' shaped groove toward the inner end, the cam 40 can process the shape of the torsion beam 70.

3 is a side cross-sectional view showing a flow path of the hot forming apparatus according to another embodiment of the present invention, Figure 4 is a side cross-sectional view showing a cam flow path of the hot forming apparatus according to another embodiment of the present invention.

3 and 4, the hot forming apparatus according to another embodiment of the present invention as compared to the lower mold 130, the upper mold 120, the cam 140, the cooling device 150 Although the same thing is done, the cooling device 150 has the characteristics.

Unlike the embodiment, the cooling device 150 is characterized in that the space portion 100 is formed between the cam 140, the lower mold 130, the upper mold 120.

In addition, a direct cooling path 110 for supplying a cooling fluid to the space part 100 is provided.

Thus, when the torsion beam 70 is cooled, the cooling fluid supplied along the direct cooling path 110 flows into the space 100 and is in direct contact with the torsion beam 70 to accelerate the cooling of the torsion beam 70. Let's do it.

By such a configuration and operation, the torsion beam 70 can be more easily converted to martensite structure, so that the strength reinforcement of the torsion beam 70 can be made more effectively.

The direct cooling flow path 110 is formed on any one of the lower mold 130, the upper mold 120, and the cam 140, where the direct cooling flow path 110 is formed on the cam 140. As shown.

However, the direct cooling passage 110 may be formed in the upper mold 120 or the lower mold 130, and the grooves formed in the respective components may be combined to each other to be formed to form the direct cooling passage 110. Do.

When the direct cooling flow path 110 is formed in the cam 140, it extends from the upper surface of the cam 140 into the cam 140 and is bent between the cam flow paths 152b so as to communicate with the space part 100. It is preferred to extend.

Looking at the operation of the hot forming method according to an embodiment of the present invention configured as described above are as follows.

5 is a flow chart showing a hot forming method according to an embodiment of the present invention, Figure 6 is a perspective view showing a torsion beam produced by the hot forming apparatus and the hot forming method according to an embodiment of the present invention 7 is a cross-sectional view taken along line AA of FIG. 6, FIG. 8 is a cross-sectional view taken along line BB shown in FIG. 6, and FIG. 9 is a cross-sectional view taken along line CC shown in FIG. 6.

5 to 9, the hot forming method according to an embodiment of the present invention seats the workpiece, that is, the beam beam 70 to the lower mold 30, the upper mold 20 and the lower mold ( 30), the pressing step (S10) for performing hot forming by combining the cam 40, the molding completion determination step (S20) and the completion of the determination step for determining whether the set time has elapsed after the pressing step (S10) is started When the time set in S20 has elapsed, it is determined whether the cooling step S30 for supplying a cooling fluid around the torsion beam 70 and the temperature of the torsion beam 70 after the start of the cooling step S30 are below the set temperature. In the temperature judging step (S40) and the temperature judging step (S40), if the workpiece is less than the set temperature to separate the upper mold 20, the lower mold 30, the cam 40 to separate the torsion beam 70 It includes a separation step (S50).

The hot forming method will be described in detail below.

First, when the cam cylinder 42 is driven after the torsion beam 70 of a pipe shape metal is seated on the lower mold 30, the cam 40 is inserted into both ends of the torsion beam 70.

Thereafter, while the base cylinder 16 is driven, the upper mold 20 is coupled to the lower mold 30 so that the pressing step S10 is performed.

At this time, the upper mold 20, the lower mold 30, and the cam 40 forming the hot forming is heated to 600 ° C ~ 900 ° C to perform the hot forming.

Molding determination step (S20) is a step of measuring the time that the hot forming is in progress, it is made by a conventional time measuring device such as a timer.

When it is detected that the time set by the molding completion determination step (S20) has elapsed, the pump is driven so that the lower mold 30, the upper mold 20, and the cam 40 along the cooling pipe 54 and the cooling passage 52. Cooling step (S30) for quenching the torsion beam 70 while the cooling fluid is supplied to the inside of the.

In addition, the cooling fluid flowing into the cam 40 through the cam pipe 54b flows to the inner end of the cam 40 along the suction flow path 52c and discharged to the end of the suction flow path 52c. The gas flows into the space between the suction passage 52c and the exhaust passage 52d and is discharged again to the outside of the cam 40.

The torsion beam 70 that is quenched in this way is quenched for about 1 second to about 100 ℃ ~ 350 ℃.

The cooling step (S30) is to lower the temperature of the torsion beam 70 to less than a predetermined temperature within a set time to the tissue of the torsion beam 70 made of a metallic material from austenite tissue to martensite tissue The strength of the torsion beam 70, which is a work object, is improved.

At this time, the cooling fluid is circulated into the lower mold 30, the upper mold 20, and the cam 40 to cool the torsion beam 70.

In addition, in another embodiment, the cooling fluid may be circulated only inside the lower mold 30 and the upper mold 20 to perform the cooling step S30, and the cooling fluid may be circulated only inside the lower mold 30 to cool the cooling step. (S30) can also be performed.

In addition, when the cooling method for directly supplying the cooling fluid to the work object to accelerate the cooling rate is further included in the cooling step (S30), the work object is more easily converted into martensite tissue.

In order to achieve such a method, as shown in FIGS. 3 and 4, it may be made by a hot forming apparatus according to another embodiment of the present invention.

When the cooling step S30 is started, the cooling fluid is supplied to the cooling passage 152 and the cooling fluid is supplied to the space 100 along the direct cooling passage 110.

As a result, the upper mold 120, the lower mold 130, and the cam 140 are cooled while rapidly cooling the torsion beam 70 in contact with the upper mold 120, the lower mold 130, and the cam 140. As the cooling fluid filled in the part 100 and the torsion beam 70 are in contact with each other, the cooling speed is increased, thereby making the quenching work more effective.

Temperature determination step (S40) detects the time the cooling fluid is supplied by a conventional time measuring device as in the molding completion determination step (S20), and when the set time elapses, the cooling step (S30) is terminated by the torsion beam ( 70) to complete the production.

Thereafter, the base cylinder 16 is driven in the reverse direction, the cam cylinder 42 is driven in the reverse direction, and the upper mold 20 and the lower mold 30 are separated, and the cams 40 are formed from both ends of the torsion beam 70. The separation step S50 is performed.

By the above-described configuration and operation, both ends 74 of the torsion beam 70 form a square shape, and the central portion 72 forms a 'V' shape in which the upper and lower surfaces are in close contact with each other, and the central portion 72 is formed. The connecting portion 76 between the end portion 74 and the end portion 74 has a torsion beam 70 formed with a 'V' shaped groove in the center of the top surface.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and various modifications and equivalent other embodiments are possible to those skilled in the art. Will understand.

In addition, the torsion beam for automobile rear suspension has been described as an example, but this is merely exemplary, and the hot forming manufacturing method of the present invention may also be used for torsion beams used in products other than torsion beams used in automobiles.

Therefore, the true technical protection scope of the present invention will be defined by the claims below.

The molding apparatus according to the present invention configured as described above is provided with a guide, so that the work object seated on the lower mold is disposed in the center, and the work object is prevented from being separated from the center when the upper mold and the lower mold are combined. There is an advantage in that to produce a symmetrical torsion beam.

In addition, in the hot forming apparatus and the hot forming method according to the present invention, a cooling apparatus is installed, and the hot formed workpiece is quenched, so that the martensite which is stable at room temperature and the metal beam of the austenitic structure is stable at room temperature improves its strength. Since it is converted into the metal beam of the tissue, there is an advantage that the deformation and breakage of the torsion beam more effectively prevented.

In addition, the present invention can simplify the work process by performing hot forming and quenching in one process, and quenching the work object after a set time elapses, and there is an advantage of reducing defects during molding.

Claims (18)

A lower mold on which the work object is placed; An upper mold coupled to the lower mold to mold the workpiece; A cam interposed between the lower mold and the upper mold to form an internal space of the workpiece; And It includes a cooling device for cooling the work object, The cooling device, A cooling passage for supplying a cooling fluid to the work object; A pump for supplying the cooling fluid to the cooling flow path; And A cooling pipe connecting the cooling flow path and the pump, The cooling passage, A mold flow path formed in the lower mold and the upper mold; And Hot forming apparatus comprising a cam flow path formed in the cam. The method of claim 1, wherein the cooling device, Hot forming apparatus, characterized in that installed in any one of the lower mold, the upper mold or the cam. The method of claim 2, The cooling apparatus is hot forming apparatus, characterized in that formed in the lower mold, the upper mold or the cam. delete delete The method of claim 1, wherein the cam flow path, The suction passage; And And an exhaust flow path formed to maintain a predetermined interval outside the suction flow path. The method of claim 1, Hot forming apparatus, characterized in that the guide is further installed between the lower mold and the upper mold. The method of claim 1, Hot forming apparatus, characterized in that the space portion is formed between the cam and the lower mold, the upper mold. The method of claim 8, And a direct cooling passage for supplying a cooling fluid to the space portion. The method of claim 9, The direct cooling flow path is hot forming apparatus, characterized in that formed in any one of the lower mold, the upper mold, and the cam. A pressing step of placing a work object on the lower mold and performing hot forming by combining the upper mold, the lower mold and the cam; A molding completion determination step of determining whether a set time has elapsed after the pressing step is started; And And a cooling step of cooling the work object by supplying a cooling fluid around the work object when the time set in the molding completion determination step has elapsed. The cooling step, Circulating the cooling fluid into any one of the upper mold, the lower mold, or the cam, The cooling step is hot forming manufacturing method, characterized in that for circulating the cooling fluid into the cam. The method of claim 11, wherein the cooling step, The method of manufacturing a hot forming according to claim 1, wherein the temperature of the workpiece is quenched to a temperature below a predetermined temperature to change the structure of the workpiece. delete The method of claim 11, The cooling step is hot forming manufacturing method, characterized in that for circulating the cooling fluid into the lower mold. The method of claim 11, The cooling step is hot forming manufacturing method, characterized in that for circulating the cooling fluid into the upper mold. delete A pressing step of placing a work object on the lower mold and performing hot forming by combining the upper mold, the lower mold and the cam; A molding completion determination step of determining whether a set time has elapsed after the pressing step is started; And And a cooling step of cooling the work object by supplying a cooling fluid around the work object when the time set in the molding completion determination step has elapsed. The cooling step is a hot forming manufacturing method characterized in that for supplying the cooling fluid between the cam and the upper mold and the lower mold to contact the cooling fluid to the workpiece. The method according to any one of claims 11, 12, 14, 15 and 17, A temperature judging step of judging whether the temperature of the workpiece is less than or equal to a preset temperature after the cooling step is started; And And a separating step of separating the work object by separating the upper mold, the lower mold, and the cam when the work object is below the set temperature in the temperature judging step.

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