JP5768663B2 - Hot shearing method - Google Patents

Description

The present invention relates to a hot shearing method in which a heated metal plate material is sheared in a mold and quenched in the mold at the same time as the shearing process, and in particular, the hardness of the sheared surface is made uniform, The present invention relates to a hot shearing method that can reduce the tensile residual stress of a sheared surface.
In the hot shearing method according to the present invention, a heated metal plate material is press-molded in the mold, and sheared in the mold at the same time as or immediately after the press-molding. Including a hot shearing method through a hot press forming step of quenching in the mold.

  As described above, the hot shearing method according to the present invention includes a hot shearing method that undergoes a hot press molding process immediately before or simultaneously with the hot shearing process, and a hot shearing process that does not undergo the hot press molding process. Including both methods. Therefore, in order to avoid duplication of description, the prior art and its problems relating to the hot shearing method that undergoes the hot press forming step will be described sequentially.

The press forming of a metal plate material is a forming method with high productivity, excellent dimensional accuracy, little variation in strength between pressed products, and stable quality. For this reason, press molding of metal plate materials is widely used in the manufacture of automobiles, home appliances, building structures, ships, bridges, construction machines, various plants, penstocks and the like.
However, press products in recent years, particularly automobile parts, have been required to have high strength from the viewpoint of weight reduction and thinning, and this has led to a decrease in formability. For example, a springback that is elastically deformed by releasing the residual stress generated in the metal plate during molding occurs at the time of mold release, which reduces shape freezeability and makes it difficult to manufacture complex shaped press products. It has become.

  For this reason, in the metal plate press industry, the material strength or deformation resistance of the metal plate material is reduced by heating the metal plate material to be molded to a high temperature using a predetermined heating means. The metal plate material with reduced strength is press-molded using a predetermined die, and the molded product is rapidly cooled using a predetermined cooling means at the same time or immediately after the press molding, thereby increasing the strength of the molded product. Hot press molding methods are attracting attention.

The hot press molding method press-molds a metal plate heated to a high temperature as described above, so that the metal plate with reduced material strength is deformed straight along the molding surface of the mold and has a complicated shape. Even so, it can be molded with excellent dimensional accuracy.
In addition, since the metal plate material deforms straightly along the molding surface of the mold, there is little residual stress generated in the metal plate material during molding, and since it is cooled rapidly at the same time as or immediately after press molding, no springback occurs. Excellent shape freezing property.
And when the metal plate material is steel, it is heated to the austenite region, and after press molding, it is held in a mold and rapidly cooled by the mold contact heat removal effect, for example, by martensite. High strength can be achieved by transformation.

  Thus, although it is a hot press molding method that can achieve high strength by going through the steps of heating → press molding → quenching of the metal plate material, the shear resistance increases as the quenching hardness increases, There is a problem that it is difficult to perform shearing such as drilling (piercing) or cutting (trim) after quenching.

For this reason, the molded product whose shear resistance has increased by quenching is often sheared using a laser. However, since shearing using a laser is costly and troublesome, it is an urgent task to improve it.
As another method, there is a method in which a metal plate material before press forming, in other words, a metal plate material whose material strength has been reduced by high-temperature heating is sheared and then press-formed. That is, it is a hot press forming method through a process of heating, shearing, press forming, and quenching of a metal plate material. However, the metal plate material during press forming is elongated or thinned by the flow of metal accompanying the forming. For this reason, in this method, distortion or misalignment of the shape occurs in a portion subjected to shearing in advance, and dimensional accuracy, which is one of the excellent features of the hot press molding method, is lost.

  As another method for solving the above-mentioned problem of hot pressing, a predetermined shearing means installed in the mold is used at the same time or immediately after the press forming and before the metal plate (molded product) is cooled and hardened. In addition, a method has been proposed in which a metal plate material is subjected to a shearing process such as drilling (piercing) or cutting (trim). In other words, this is a hot press forming method through a process of heating metal plate material → press forming → shearing → quenching (see, for example, the fourth embodiment of Patent Document 1 and claim 1 of Patent Document 2).

In the hot press forming method described in Patent Document 2, a heated metal plate material is press formed using a press forming punch having a hole at the tip. The hole is formed in the punch tip because of the contact heat removal caused by contact with the punch tip at the part of the metal plate material facing the punch tip part, specifically, the part to be punched, and this. This is to avoid a temperature drop. As a result, it is for maintaining the state where the material strength of the site | part which carries out a punching process is falling.
In the hot press forming method described in Patent Document 2, a portion that avoids contact heat removal with the press forming punch is punched using a predetermined shearing means at the same time or immediately after the press forming. This solves the problem that shearing after quenching becomes difficult.

As described above, the method described in Patent Document 2 takes into consideration the contact heat removal of the metal plate material during press forming, that is, the temperature decrease of the metal plate material caused by contact with the mold. And in order to avoid the temperature fall of the metal plate material by contact heat removal, the punch for press molding which formed the hole in the front-end | tip is used (paragraph [0015] of patent document 2).
On the other hand, in the method described in Patent Document 1, contact heat removal during press molding does not significantly affect the shear workability, and the temperature of the metal plate is still high even after contact heat removal. The position is that resistance is low (paragraph [0068] of Patent Document 1).

According to the method described in Patent Documents 1 and 2, that is, a method of performing shearing before or after quenching and hardening at the same time or immediately after press molding, and thereafter quenching to increase strength as a molded member. The above-mentioned problem that shearing after quenching becomes difficult can be solved.
Further, since the shearing process is performed while the material strength is reduced, the shear resistance can be kept low, which can contribute to the extension of the die life and the prevention of the die breakage. In addition, wrinkles generated on the sheared surface can be suppressed.
Furthermore, since the high strength by press molding, shearing, and quenching is consistently performed in the same mold, productivity is also improved.
As described above, the hot press forming method proposed by Patent Documents 1 and 2 through the steps of heating, press forming, shearing, and quenching of a metal plate material has an extremely excellent technical effect.

JP 2003-328031 A JP 2005-138111 A Japanese Patent Laid-Open No. 2000-210731

  By the way, in the production site of press products such as automobile parts, it is natural that the excellent press formability, shape freezing property, shearing workability, and productivity as described above are required. In addition, in order to eliminate variations in mechanical strength, it is required to make the hardness of the sheared surface uniform, and it is not allowed that a significant difference in hardness occurs between a specific part and other parts.

  In addition, it is required to reduce the tensile residual stress on the sheared surface from the viewpoint of suppressing the occurrence of cracks on the sheared surface and the progress thereof. The tensile residual stress generated on the sheared surface may promote the occurrence and development of cracks on the sheared surface and reduce the fatigue life of the sheared surface.

Patent Documents 1 and 2 do not have any description or suggestion regarding these. For example, the method described in Patent Document 1 is intended to make the strength of each part different, rather than making the strength of each part of the press product uniform. That is, it is intended to cause a difference in strength between a specific part and other parts.
In addition, according to a predetermined experiment, the present inventor has found that in a hot shearing method using a punch having a normal shape that does not form a taper, there is a significant hardness difference between a specific part on the shearing surface and other parts. Since it was confirmed that this occurs and a high tensile residual stress is generated on the sheared surface, it will be described in detail later.

As described above, the hot shearing method according to the present invention includes both a hot shearing method that undergoes a hot press molding step and a hot shearing method that does not undergo a hot press molding step. In order to avoid the duplication of description, the hot shearing method and the problems thereof that have undergone the hot press forming process were described in detail with reference to Patent Documents 1 and 2 according to the prior art.
However, the hot metal plate material is subjected to a shearing process in a mold and quenched in the mold simultaneously with the shearing process (for example, refer to claim 3 of Patent Document 3), that is, heat Even in the hot shearing method that does not go through the hot press forming step, the hardness of the sheared surface becomes uniform and the tensile residual on the sheared surface, as in the hot shearing method that goes through the hot press forming step. It is desirable to reduce the stress.

  The method described in Patent Document 3 is to solve the problem of obtaining a punched product with less sagging (paragraphs [0003] to [0004] of Patent Document 3). As with the method, it is not a problem to make the hardness of the sheared surface uniform and to reduce the tensile residual stress of the sheared surface.

  A problem to be solved by the present invention is a hot shearing method that does not go through a hot press molding process, wherein a heated metal plate material is sheared in a mold and simultaneously quenched in the mold. In addition, the hot metal plate material is press-molded in the mold, sheared in the mold simultaneously with or immediately after the press molding, and quenched in the mold simultaneously with the shearing. An object of the present invention is to provide a hot shearing method that can make the hardness of the sheared surface uniform and reduce the tensile residual stress of the sheared surface with respect to the hot shearing method that undergoes the forming step.

  The present inventor has obtained the following technical knowledge as a result of various theoretical and experimental studies to solve the above problems. In particular, as described above, in the hot shearing method using a punch having a normal shape that does not have a taper, a significant difference in hardness occurs between a specific part on the sheared surface and other parts, and shearing Since it confirmed that a high tensile residual stress arises in a processed surface, this is demonstrated.

(A) The inventor shears a steel plate heated to 950 ° C. using a punch 2 having a normal shape that does not have a taper shown in FIG. 1, and measures the tensile residual stress generated on the sheared surface. Experimented. As a result, a high tensile residual stress of about 1 GPa was confirmed on the sheared surface. As described above, the tensile residual stress promotes the generation and propagation of cracks on the sheared surface and may reduce the fatigue life of the sheared surface.

(B) In order to investigate the cause of such a result, the hardness was measured at a predetermined hardness measurement position in the cross section of the sheared surface shown in FIG.
FIG. 2B is a graph in which the vertical axis represents the distance [mm] from the lower surface of the plate and the horizontal axis represents the hardness [Hv] for each hardness measurement position. In FIG. 2B, ◇ indicates the hardness measurement position in the first column from the right in FIG. 2A, □ indicates the hardness measurement position in the second column from the right, and Δ indicates the hardness measurement position in the third column from the right. Represents the position.
As a result, as shown in FIG. 2 (b), the hardness of the portion corresponding to the fracture surface, that is, the distance from the lower surface of the plate at the hardness measurement position in the first row from the right in FIG. It was confirmed that the hardness of the part over 1.5 mm was lower by about 200 Hv than the other parts. That is, it was confirmed that a significant difference in hardness was produced between a specific part and other parts on the sheared surface.

(C) As shown in FIG. 1, when a punch 2 having a normal shape without a taper is used, the non-contact surface 9 where the side surface of the punch 2 does not contact the metal plate 1 is It is presumed that the non-contact surface 9 is harder than the other surfaces.
That is, on the non-contact surface 9, the side surface of the punch 2 does not contact the metal plate 1 except for the cutting edge, and even if it contacts, the contact heat removal capability is small because the contact time is short. On the other hand, the contact heat removal capability is large at the surface where the side surface of the punch 2 and the metal plate 1 are in contact. For this reason, it is presumed that heat unevenness occurs on the shearing surface of the metal plate 1 and a significant hardness difference is generated between the non-contact surface 9 and other surfaces. Further, it is presumed that a high tensile residual stress was generated on the sheared surface due to the thermal stress due to such thermal unevenness.

(D) Therefore, if there is no thermal unevenness or thermal stress generated on the non-contact surface 9 or the sheared surface, the hardness difference or tensile residual stress generated on the sheared surface can be eliminated.
However, it is practically impossible to bring the entire side of the shearing surface into contact with the entire side of the shearing surface and to remove the entire surface of the shearing surface equally in consideration of the shape of the shearing surface and the shape of the punch. .

(E) Therefore, in order to prevent the side surface of the punch 2 from coming into contact with the metal plate 1, the present inventor, as shown in FIG. 3, in order to eliminate the influence of contact heat removal that occurs during the shearing process. The metal plate 1 was sheared using a reverse-tapered punch 10. Specifically, the metal plate 1 is sheared using a punch 10 having a base shaft portion 20 having a constant diameter in the axial direction and a reverse taper portion 21 that tapers toward the punch tip continuous with the base shaft portion 20. did.
This prevents thermal unevenness and thermal stress from occurring on the sheared surface. As a result, the hardness of the sheared surface was made uniform and the tensile residual stress on the sheared surface was reduced.

The present invention has been completed mainly based on the above technical knowledge, and the gist thereof is as follows.
(1) In a hot shearing method in which a heated metal plate material is sheared in a mold and quenched in the mold simultaneously with the shearing process, a base shaft portion having a constant diameter in the axial direction is continuous with the base shaft portion. A hot shearing method comprising: shearing the metal plate material using a punch having a reverse taper portion having a taper angle of 4 to 7 ° that tapers toward a tip of the punch.

(2) The hot shearing method according to (1), wherein the metal plate material is press-molded in the mold immediately before or simultaneously with the shearing process.

(3) The hot shearing method according to (1) or (2), wherein the quenching is performed by heat removal from contact with the mold.
(4) The hot shearing method according to any one of (1) to (3), wherein the quenching is performed by ejecting a refrigerant from the mold.
(5) The metal plate material is sheared by providing a gap of 5 to 100% of the thickness of the metal plate material between the base shaft portion of the punch and the plate presser, and the quenching is performed by flowing a coolant through the gap. The hot shearing method according to any one of (1) to (4), wherein the hot shearing method is performed.

(6) The hot metal according to any one of (1) to (5), wherein the metal plate material is sheared by using a punch having a chamfered or rounded edge on the blade edge of the punch. Shearing method.

All the hot shearing methods according to the present invention use a punch 10 having a base shaft portion 20 having a constant diameter in the axial direction and a reverse taper portion 21 that tapers toward a punch tip continuous with the base shaft portion 20. The plate material 1 is sheared.
(A) For this reason, it is possible to prevent the side surface of the punch 10 excluding the blade edge from coming into contact with the metal plate 1, and no heat unevenness occurs on the sheared surface. Thereby, a remarkable hardness difference does not arise in the specific site | part and other site | part in a shearing surface. Accordingly, the hardness of the sheared surface can be made uniform, and variations in mechanical properties can be eliminated.

(B) In addition, since the side surface of the punch 10 excluding the blade edge is not brought into contact with the metal plate material 1, thermal stress due to heat unevenness does not occur on the sheared surface. For this reason, the tensile residual stress caused by thermal stress can be reduced. Therefore, generation | occurrence | production of the crack of a shearing surface and its progress can be suppressed.

(C) In addition, since the side surface of the punch 10 excluding the cutting edge is not brought into contact with the metal plate 1, adhesion of the metal plate 1 to the punch 10 can be reduced. Therefore, wrinkles generated on the sheared surface can be suppressed.

(D) Moreover, since all the hot shearing methods according to the present invention shear a metal plate material whose material strength has been reduced by heating, the shear resistance can be kept low. Therefore, it is possible to contribute to the extension of the mold life and the prevention of mold breakage. It is also possible to suppress wrinkles generated on the sheared surface.

(E) Furthermore, since quenching is performed simultaneously with the shearing process, the quenching start temperature of the metal plate material is high. For this reason, the strength can be increased.

(F) Since quenching is performed simultaneously with the shearing process in the same mold, it is possible to contribute to the improvement of productivity. In particular, according to the hot shearing method according to the present invention in which the metal plate 1 is press-molded immediately before or simultaneously with the shearing process, that is, the hot shearing method according to the present invention that undergoes a hot press-molding step, the same Since press molding, shearing, and quenching are performed continuously and consistently in the mold, there is a great contribution to improving productivity.

It is a figure which shows typically the non-contact surface 9 where the side surface of the punch 2 and the metal plate material 1 do not contact. It is a figure which shows that local quenching shortage arises when using a punch of a normal shape, (a) is a figure which shows the measurement position of hardness, (b) is a graph which shows the hardness in the measurement position. is there. It is a figure which shows typically an example of the punch 10 of the reverse taper shape used by this invention. It is a figure which shows typically an example of the punch 10 of the reverse taper shape used by this invention. It is a figure which shows typically an example of the lower surface of the board presser. It is a figure which shows typically an example of this invention which quenches by ejecting the refrigerant | coolant 16 from the board presser 8 which formed the refrigerant | coolant ejection hole and the refrigerant | coolant introduction groove | channel in the lower surface. It is a figure which shows typically an example of this invention which quenches by ejecting the refrigerant | coolant 16 from the plate holder 8 and the punch 10 which formed the refrigerant | coolant injection hole and the refrigerant | coolant introduction groove | channel. FIG. 2 is a diagram schematically showing an example of the present invention in which a gap 17 is provided between a punch base shaft portion 20 and a plate presser 8 so that the metal plate 1 is sheared and quenched by flowing a refrigerant 16 through the gap 17. is there. It is a figure which shows typically an example of the punch 10 of the reverse taper shape used by this invention. It is a figure which shows typically the conditions of the verification experiment 1 which confirms the effect of this invention which quenches by contact heat removal with a metal mold | die, (a) is just before a shearing process, (b) is the state immediately after a shearing process. It is a figure shown typically. It is a graph which shows the measurement result of the tensile residual stress in the verification experiment 1. FIG. It is a figure which shows typically the conditions of the verification experiment 2 which confirms the effect of this invention which quenches by ejecting a refrigerant | coolant from a metal mold | die, (a) is just before a shearing process, (b) is the state immediately after a shearing process FIG. It is a graph which shows the measurement result of the tensile residual stress in the verification experiment 2. It is a figure which shows typically the conditions of the verification experiment 3 which confirms the effect of this invention which passes through a hot press molding process, (a) is immediately before hot press molding, (b) is a hot press molding process, (c ) Is a diagram schematically showing a hot shearing process. It is a graph which shows the measurement result of the tensile residual stress in the verification experiment 3.

Hereinafter, the form for implementing this invention is demonstrated with reference to FIGS.
The present invention presupposes a hot shearing method in which a heated metal sheet 1 is sheared in a mold and quenched in the mold at the same time as the shearing process and does not go through a hot press forming step. It is. Furthermore, the heated metal plate 1 is press-molded in the mold, sheared in the mold simultaneously with or immediately after the press molding, and quenched in the mold simultaneously with the shearing. It is based on a hot shearing method that undergoes an intermediate press forming process.
In addition, as will be described later, quenching simultaneously with shearing is performed by (a) quenching and quenching a metal plate by cooling ability by contact heat removal with a mold used for shearing during shearing; and (b) In addition to this, it includes both cases where the metal plate material is quenched and quenched by the cooling ability of the refrigerant ejected from the mold.

The metal plate 1 can be applied to any steel plate such as an Al-plated steel plate, a Zn-plated steel plate, a high-strength steel plate, and ordinary steel.
Further, a steel sheet that undergoes martensitic transformation or bainite transformation can be increased in strength by quenching by rapid cooling, and therefore, a steel plate that undergoes martensitic transformation or bainite transformation is desirable.
In addition, in addition to non-ferrous metals such as aluminum, magnesium, titanium, and copper, these alloy plate materials can also be applied.

The method for heating the metal plate 1 is not particularly limited as long as the metal plate 1 can be heated to the Ac3 transformation point or higher. For example, furnace heating in a heating furnace, an electric furnace, or a gas furnace may be used. Alternatively, flame heating, electric heating, high frequency heating, induction heating may be used. Alternatively, a heating method using an infrared heat beam, a laser beam, or an electric heater may be used.
The metal plate 1 may be heated in the above-mentioned heating furnace or the like and conveyed to a mold using a predetermined conveying means. Alternatively, after the metal plate is set in the mold, The metal plate 1 may be heated in the mold.

FIG. 3 is a diagram schematically showing an example of a reverse-tapered punch 10 used in the present invention. As shown in the figure, in the present invention, the metal plate 1 is sheared using a punch 10 having a base shaft portion 20 and a reverse taper portion 21.
The base shaft portion 20 continuing to the reverse taper portion 21 is a portion having a constant diameter in the axial direction. Here, the constant diameter in the axial direction is different from the reverse tapered portion 21 that tapers toward the tip of the punch, and the diameter is constant without tapering or tapering toward the tip of the punch. This means that the cross-sectional shape or cross-sectional area in the vertical cross section is the same at any position in the axial direction and does not change.

The shape of the reverse taper portion 21 is tapered toward the tip of the punch, and may be any shape as long as the side surface of the punch 10 does not contact the metal plate 1 except for the cutting edge. It is sufficient that the plate material 1 has a reverse taper shape corresponding to the plate thickness.
If the side surface of the punch 10 excluding the cutting edge does not contact the metal plate 1, that is, if only the cutting edge contacts the metal plate 1, the unevenness of heat does not occur on the sheared surface. For this reason, a remarkable hardness difference does not arise between the specific site | part in a shearing process surface, and another site | part. Therefore, the hardness of the sheared surface can be made uniform, thereby eliminating the variation in mechanical properties.
Moreover, if the side surface of the punch 10 excluding the cutting edge does not contact the metal plate 1, thermal stress due to heat unevenness does not occur on the sheared surface. For this reason, the tensile residual stress of the shearing surface caused by thermal stress can be reduced. Therefore, generation | occurrence | production of the crack of a shearing surface and its progress can be suppressed.
Furthermore, if the side surface of the punch 10 excluding the cutting edge does not contact the metal plate 1, adhesion of the metal plate 1 to the punch 10 can be reduced. Therefore, wrinkles generated on the sheared surface can be suppressed.
Here, in order to make the hardness of the shearing surface uniform as described above and to suppress the occurrence of cracks and the progress of the cracking of the shearing surface, the taper angle (reference numeral 18 in FIG. 10), that is, the punch The angle formed between the central axis and the flared portion of the punch is preferably 3 to 10 ° on a plane parallel to the central axis. Further, in order to achieve both higher durability of the punch and uniformity of the hardness of the sheared surface, 4 to 7 ° is desirable.

The base shaft portion 20 and the reverse taper portion 21 are continuous portions, and the base shaft portion 20 and the reverse taper portion 21 integrated from one base material may be formed, or each may be formed from separate base materials. These may be joined in the axial direction by welding or brazing. In addition, these forming methods can be performed by cutting or electric discharge machining using industrial diamond or the like, but are not limited thereto.
As the material of the base shaft portion 20 and the reverse tapered portion 21, hot working die steel, high-speed steel, carbide, or the like can be used.

FIG. 4 is a diagram schematically showing an example of a reverse tapered punch 10 used in the present invention. The punch 10 illustrated in FIG. 3 includes a reverse taper portion 21 at the punch tip and a base shaft portion 20 at the rear thereof, but may be a punch including the smooth portion 12 at the punch tip illustrated in FIG. That is, the base shaft portion 20, the reverse taper portion 21, and the smooth portion 12 that is a portion having a constant diameter in the axial direction may be used as a punch that continues in this order. Even if it is such a shape, since the side surface of the punch 10 and the metal plate 1 do not contact at the bottom dead center of the punch, the same effect as the punch 10 illustrated in FIG. 3 can be obtained. It is also effective from the viewpoint of extending the punch life and preventing chipping of the blade edge.
Also in this case, the base shaft portion 20, the reverse taper portion 21, and the smooth portion 12 that are integrated from one base material may be formed, or each may be formed from a separate base material, You may join to an axial direction by brazing. In addition, these forming methods can be performed by cutting or electric discharge machining using industrial diamond or the like, but are not limited thereto. Further, as the material of the smooth portion 12, die steel for hot working, high-speed steel, carbide or the like can be used.

FIG. 3 shows a state immediately after the shearing process. In other words, the plate presser 8 constituting the mold and the punch 10 constituting the mold reach the bottom dead center and the metal plate 1 is quenched.
When the punch 10 is lowered and the cutting edge of the reverse taper portion 21 of the punch 10 enters the metal plate 1, the plate retainer 8 descending toward the bottom dead center is the upper surface of the metal plate 1 (surface on the plate retainer 8 side). ), Whereby the upper surface of the metal plate 1 is quenched and quenched by contact heat removal with the plate retainer 8.
Further, the lower surface (surface on the die 3 side) of the metal plate material 1 comes into contact with the die 3 constituting the die when the metal plate material 1 heated to a high temperature is set in the die. Heat quenching has already started.
Then, the shearing surface (the surface on the punch 10 side) of the metal plate 1 is rapidly cooled and quenched by contact heat removal from the moment when the blade 10 of the punch 10 enters the metal plate 1 to the moment of removal. As described above, in the present invention, since the side surface of the punch 10 excluding the cutting edge is not brought into contact with the metal plate material 1, the entire sheared surface of the metal plate material 1 is uniformly quenched.

FIG. 5 is a diagram schematically illustrating an example of the lower surface of the plate presser 8.
As described above, the shearing surface of the metal plate 1 is rapidly cooled by contact heat removal from the moment when the blade tip of the punch 10 enters the metal plate 1 to the moment when it is removed. Moreover, the upper surface of the metal plate 1 is rapidly cooled by contact heat removal with the plate presser 8 from the moment when the blade tip enters. The lower surface of the metal plate 1 is rapidly cooled by contact heat removal from the die 3 immediately after the metal plate 1 is set.
For this reason, the quenching time of the sheared surface and the upper surface of the metal plate 1 is shorter than the quenching time of the lower surface of the metal plate 1.
Accordingly, the hardness of the sheared surface and the upper surface of the metal plate 1 may be lower than the hardness of the lower surface of the metal plate 1.
In addition, if the stroke speed (push-in speed) of the punch 10 is lowered, the quenching time of the sheared surface of the metal plate 1 is increased. Further, if the holding time at the bottom dead center of the plate presser 8 is lengthened, the quenching time of the upper surface of the metal plate material 1 is lengthened. However, productivity is lowered in either method.
In order to solve this, as shown in the figure, it is desirable to form a refrigerant ejection hole 13 for ejecting the refrigerant 16 from the lower surface of the plate retainer 8 on the lower surface of the plate retainer 8. And it is desirable to form the refrigerant | coolant supply pipe | tube 15 which communicates with the refrigerant | coolant injection hole 13 and supplies the refrigerant | coolant 16 to the refrigerant | coolant injection hole 13 in the inside of the board holder 8. FIG. Further, it is desirable to form a refrigerant introduction groove 14 that allows the jetted refrigerant 16 to flow along the lower surface of the plate retainer 8 on the lower surface of the plate retainer 8. The formation of the coolant introduction groove 14 is not essential, and whether or not the coolant introduction groove 14 is formed is arbitrary.

FIG. 6 is a diagram schematically showing an example of the present invention in which quenching is performed by ejecting the refrigerant 16 from the plate presser 8 in which the refrigerant ejection holes 13 and the refrigerant introduction grooves 14 are formed on the lower surface. The refrigerant introduction groove 14 is not shown.
As shown in the figure, the cooling rate of the shearing surface and the upper surface of the metal plate 1 is increased by ejecting the coolant 16 from the lower surface of the plate retainer 8. For this reason, insufficient hardness of the sheared surface and the upper surface of the metal plate 1 due to a shorter quenching time than the lower surface of the metal plate 1 is eliminated. Further, since the cooling rate increases, it is not necessary to decrease the stroke speed of the punch 10 or lengthen the holding time at the bottom dead center of the plate presser 8, and the productivity does not decrease.

It is desirable that the coolant 16 be ejected at the same time as or immediately after the moment when the cutting edge of the punch 10 enters the metal plate 1. Thereby, the cooling ability of the shearing surface of the metal plate 1 is a cooling ability obtained by adding the cooling ability by contact heat removal with the blade edge of the punch 10 and the cooling ability by jetting the refrigerant. And the cooling capacity of the upper surface of the metal plate 1 is a cooling capacity obtained by adding the cooling capacity by contact heat removal with the plate presser 8 and the cooling capacity by refrigerant ejection.
In addition, it is not preferable to eject the coolant 16 before the cutting edge of the punch 10 enters the metal plate 1. The present invention shears a metal sheet whose material strength has been reduced by heating to keep the shear resistance low, thereby preventing an increase in mold life, damage to the mold, and occurrence of damage on the sheared surface. When the refrigerant is ejected before the cutting edge enters, the shear resistance of the metal plate 1 increases, and these effects are lost.

The refrigerant jet 13 and the refrigerant supply pipe 15 communicating therewith can be formed by mechanical drilling with a drill or drilling by electric discharge machining. The coolant introduction groove 14 can also be formed by mechanical cutting with a drill or dissolution or evaporation of a groove forming portion by electric discharge machining.
In addition, as a material of the plate retainer 8, it is desirable to use hot working die steel, high-speed steel, carbide or the like. The material of the die 3 is the same.

It is desirable to connect the refrigerant supply pipe 15 with a flow rate adjusting pump 22 that supplies the refrigerant 16 from the refrigerant tank 23 to the refrigerant supply pipe 15.
The pump 22 with the flow rate adjusting function is not particularly limited, and for example, a precision gear pump, a trochoid pump, an oscillating pump, a plunger pump, or the like can be used.
Moreover, about the flow volume adjustment of the pump 22 with a flow volume adjustment function, you may use the control means which consists of a computer (electronic computer), and may set manually.

From the viewpoint of ensuring the accuracy of the timing at which the refrigerant 16 is ejected, it is desirable to provide the on-off valve 24 in series with the pump 22 with a flow rate adjusting function. As described above, it is desirable that the refrigerant 16 be ejected at the same time as or immediately after the cutting edge of the punch 10 enters the metal plate 1. By providing the on-off valve 24, the refrigerant 16 is ejected. Timing accuracy can be improved.
The on-off valve 24 is not particularly limited as long as it can turn on (off) / off (not flow) the flow of the refrigerant 16 in the refrigerant supply pipe 15, but is on (open) / off (closed). From the viewpoint of the response speed, it is desirable to use a three-way valve.

The control means 25 for controlling on / off (closed) of the on-off valve 24 or the control means 25 for switching the flow path when using a three-way valve is not particularly limited, Mechanical means, electronic means, or a combination of these may be used. For example, a relay switch may be employed for the valve mechanism, and opening / closing (ON / OFF) of the relay switch may be controlled using a computer (computer).
Furthermore, as described above, it is desirable that the refrigerant 16 be ejected at the same time as or immediately after the moment when the cutting edge of the punch 10 enters the metal plate 1. From the viewpoint of ensuring the accuracy, It is desirable to synchronize the timing at which the refrigerant is ejected from the ejection holes 13 with the amount of pressing of the punch 10 or the stroke position of the punch 10. That is, it is desirable that the refrigerant be ejected when a predetermined punch push-in amount is reached, or that the refrigerant be ejected when the punch reaches a predetermined stroke position.
For this purpose, the control means 25 of the on-off valve is supplied with data indicating the push-in amount and stroke position of the punch 10 or a trigger signal indicating that a predetermined push-in amount or stroke position has been reached. desirable. Thereby, ON / OFF (closed) of the on-off valve 24 can be controlled in synchronization with the pushing amount and stroke position of the punch 10, and the timing accuracy at which the refrigerant 16 is ejected from the refrigerant outlet 13 is improved. be able to.

As the refrigerant 16, water, polyhydric alcohols, polyhydric alcohol aqueous solutions, polyglycol, mineral oil having a flash point of 120 ° C. or higher, synthetic ester, silicon oil, fluorine oil, dropping point 120 are used because of flame retardancy and corrosiveness. It may be any of a water emulsion in which a surfactant is blended with grease, mineral oil, or synthetic ester at a temperature of ℃ or higher, or a mixture thereof.
The refrigerant 16 may be gas, and it is desirable to use nitrogen, carbon dioxide, or an inert gas with low activity from the viewpoint of avoiding oxidation of the metal plate 1 and the mold.

Up to now, the coolant injection hole 13 and the coolant introduction groove 14 are formed on the lower surface of the plate presser 8 constituting the mold, and the coolant 16 is jetted from the lower surface of the plate presser 8, thereby comparing with the lower surface of the metal plate 1. An example in which the insufficient hardness of the sheared surface and the upper surface of the metal plate 1 due to the short quenching time is eliminated has been described with reference to FIG.
However, the present invention is not limited to this. As described above, the sheared surface of the metal plate 1 is quenched by contact heat removal with the blade edge of the punch 10, and the upper surface of the metal plate 1 is quenched by contact heat removal with the plate retainer 8. The contact area with the metal plate 1 is significantly different from that of the plate retainer 8. That is, the cutting ability of the punch 10 and the plate presser 8 are greatly different in cooling ability due to contact heat removal. For this reason, the hardness of the shearing surface of the metal plate 1 may be lower than the hardness of the upper surface of the metal plate 1.

In order to solve this problem, a refrigerant ejection hole 13 and a refrigerant introduction groove 14 are formed on the side surface of the plate retainer 8 that faces the punch 10 so that the refrigerant 16 is ejected from the side surface of the plate retainer 8. Also good. Thereby, since the shearing surface of the metal plate 1 is rapidly cooled by the refrigerant 16, the cooling ability of the shearing surface of the metal plate 1 is increased, and the contact area is narrower than that of the plate holder 8. Insufficient hardness of the sheared surface of the metal plate 1 can be resolved.
Alternatively, as shown in FIG. 7, the coolant injection hole 13 and the coolant introduction groove 14 are formed on the side surface of the base shaft portion 20 of the punch 10 that faces the plate presser 8, and the side surface of the base shaft portion 20 of the punch 10 is formed. The refrigerant 16 may be ejected from the refrigerant. Also in this case, since the shearing surface of the metal plate 1 is rapidly cooled by the refrigerant 16, the cooling ability of the shearing surface of the metal plate 1 is increased, and the contact area is narrower than that of the plate holder 8. The lack of hardness of the sheared surface of the metal plate 1 can be resolved. In this case, the refrigerant supply pipe 15 is formed inside the punch 10.
In these cases, the formation of the refrigerant introduction groove 14 is not essential, and whether or not the refrigerant introduction groove 14 is formed is arbitrary.

Up to now, (a) the lower surface of the plate presser 8, (b) the side surface of the plate presser 8 that faces the punch 10, or (c) the side surface of the base shaft portion 20 of the punch 10 and the plate presser 8 By ejecting the refrigerant 16 from the opposite side surfaces, the cooling ability of the sheared surface of the metal plate 1 is combined with the cooling ability by contact heat removal with the blade edge of the punch 10 and the cooling ability by refrigerant ejection. The present invention example has been described. And the example of this invention which made the cooling capability of the upper surface of the metal plate material 1 the cooling capability which added the cooling capability by the contact heat removal with the plate holder 8 and the cooling capability by the refrigerant jet was explained. That is, the example of the present invention was described in which the cooling ability by contact heat removal with the mold was fixed, and the cooling ability by refrigerant ejection was added to this.
However, the present invention is not limited to this. FIG. 8 schematically illustrates an example of the present invention in which a gap 17 is provided between the punch base 20 and the plate presser 8 to shear the metal plate 1 and quench by flowing a refrigerant 16 through the gap 17. Unlike the examples so far, instead of actively reducing the cooling ability due to heat removal from the mold, instead of actively reducing the cooling ability due to refrigerant jet, an example of the present invention is schematically shown. It is.

As shown in FIG. 8, when a clearance 17 is provided between the punch base shaft 20 and the plate presser 8 and shearing is performed, the cooling ability of the upper surface of the metal plate 1 is reduced by providing the clearance 17. Since the contact area between the upper surface of the metal plate and the plate presser 8 is reduced, the cooling ability by contact heat removal with the plate presser 8 is reduced. Further, regarding the cooling ability of the sheared surface of the metal plate 1, the cooling ability that is thermally conducted from the upper surface of the metal plate 1 is reduced by the amount that the cooling ability of the upper surface of the metal plate 1 is reduced. Therefore, the cooling capacity by contact heat removal between the upper surface of the metal plate 1 and the mold on the sheared surface is reduced.
However, since a large amount of the refrigerant 16 can be supplied to the gap 17, the cooling ability due to the refrigerant jet can be maximized. That is, in the examples so far, the coolant is ejected from the mold for the purpose of supplementing the cooling ability due to contact heat removal from the mold, but in the example shown in the figure, the cooling ability due to contact heat removal from the mold is reduced. By aggressively reducing, quenching can be performed with an emphasis on cooling ability by refrigerant jet.
In addition, since a large amount of the refrigerant 16 can be supplied to the gap 17, heat storage of the mold due to contact with the metal plate material 1 can be suppressed. In other words, hot shearing of metal plates using a mold is performed by continuously shearing hundreds to thousands, or thousands to tens of thousands of metal plates, and heat storage in the mold is inevitable. For this reason, the cooling ability by contact heat removal with the mold inevitably decreases. However, in the example shown in the figure, since a large amount of the refrigerant 16 is supplied to the gap 17 every time the metal plate 1 is sheared, the heat storage of the mold can be suppressed, and the cooling ability by the refrigerant injection is improved. Since quenching with emphasis is performed, stable quenching can be performed.

  The gap 17 provided between the punch base shaft 20 and the plate presser 8 is desirably 5 to 100% of the plate thickness of the metal plate 1 to be sheared. If it is less than 5%, the purpose of maximizing the cooling capacity by ejecting the refrigerant cannot be achieved instead of actively reducing the cooling capacity by heat removal from the mold. In addition, the object of suppressing heat storage of the mold due to contact with the metal plate 1 cannot be achieved. On the other hand, if it exceeds 100%, the shearability may be affected. In addition, the cooling ability due to the refrigerant jet is saturated.

  FIG. 9 is a diagram schematically showing an example of a reverse tapered punch 10 used in the present invention. From the viewpoint of preventing chipping of the cutting edge (chipping), it is desirable to chamfer or round the cutting edge of the punch 10 as shown in the drawing. If the chamfering or rounding 19 is too large, the punch 10 will not be pulled out from the metal plate material 1, so-called biting occurs. Therefore, the upper limit is preferably C1.0 mm or R1.0 mm.

In order to confirm the effect of the hot shearing method according to the present invention in which quenching is performed by heat removal with contact with a mold, as a comparative example, a punch with a normal shape (a punch without a taper), an example of the present invention As shown in FIG. 10 (a), the heated aluminum-coated steel sheet is subjected to hot shearing (round hole removal) using a reverse-tapered punch 10, and the tensile residual stress in the hole circumferential direction of the sheared surface is measured. Verification experiment 1 was performed.
The punch tip diameter 11 is 20 mm, the punch taper angle 18 is 5 °, and the clearance 5 between the punch 10 and the plate presser 8 is 1 mm.
The aluminum-coated steel sheet was heated to 950 ° C. in a heating furnace and held in the furnace for 30 seconds or more. Then, it conveyed to the metal mold | die using the predetermined conveyance means, and when the temperature of the aluminum coat steel plate set to the metal mold | die fell to 750 degreeC, it sheared as shown in FIG.10 (b). Note that the plate pressing force of the aluminum-coated steel plate by the plate pressing 8 during the shearing process is 50 tons.

FIG. 11 shows the measurement results of the tensile residual stress in the verification experiment 1. As shown in the figure, in the comparative example, the tensile residual stress up to 1000 MPa was measured. On the other hand, in the present invention example, it was confirmed that the tensile residual stress was reduced to 400 MPa or less.
Moreover, when the hardness in the vicinity of the sheared surface was measured in the entire plate thickness direction, it was 300 to 500 Hv in the comparative example, and it was confirmed that a significant hardness difference was generated between a specific portion and other portions on the sheared surface. . On the other hand, in the example of the present invention, it was confirmed that any part of the sheared surface was about 300 Hv, and the hardness of the sheared surface was uniform over the entire processed surface. The hardness other than the vicinity of the sheared surface was about 500 Hv in both the comparative example and the example of the present invention.
As described above, according to the hot shearing method according to the present invention in which quenching is performed by heat removal from the mold, the hardness of the sheared surface can be made uniform and the tensile residual stress on the sheared surface can be reduced. Was confirmed.

In order to verify the effect of the hot shearing method according to the present invention in which quenching is performed by ejecting a refrigerant from a mold, as a comparative example, a punch with a normal shape (a punch without a taper), the present invention As an example, using a reverse taper-shaped punch 10 shown in FIG. 12 (a), a heated aluminum coated steel sheet is subjected to hot shearing (round hole removal), and the tensile residual stress in the circumferential direction of the sheared surface is measured. Verification experiment 2 was conducted.
The punch tip diameter 11 is 20 mm, the punch taper angle 18 is 5 °, and the clearance 5 between the punch 10 and the plate presser 8 is 1 mm.
The aluminum-coated steel sheet was heated to 950 ° C. in a heating furnace and held in the furnace for 30 seconds or more. Then, it conveyed to the metal mold | die using the predetermined conveyance means, and when the temperature of the aluminum coat steel plate set to the metal mold | die fell to 750 degreeC, it sheared as shown in FIG.12 (b). In addition, simultaneously with the moment when the cutting edge of the punch 10 enters the metal plate 1, the refrigerant 16 was ejected from the refrigerant ejection holes 13 formed on the side surface of the plate retainer 8 and facing the punch 10. In addition, the plate pressing force of the aluminum coated steel plate by the plate pressing 8 at the time of shearing is 50 ton, and the refrigerant 16 is water.

FIG. 13 shows the measurement results of the tensile residual stress in the verification experiment 2. As shown in the figure, in the comparative example, a tensile residual stress exceeding 1000 MPa was measured. On the other hand, in the present invention example, it was confirmed that the tensile residual stress was reduced to about 400 MPa.
Moreover, when the hardness in the vicinity of the sheared surface was measured in the entire plate thickness direction, it was 300 to 500 Hv in the comparative example, and it was confirmed that a significant hardness difference was generated between a specific portion and other portions on the sheared surface. . On the other hand, in the example of the present invention, it was confirmed that any part of the sheared surface was about 500 Hv, and the hardness of the sheared surface was uniform over the entire processed surface. The hardness other than the vicinity of the sheared surface was about 500 Hv in both the comparative example and the example of the present invention.
As described above, according to the hot shearing method according to the present invention in which quenching is performed by ejecting a coolant from the mold, the hardness of the sheared surface is made uniform and the tensile residual stress on the sheared surface is reduced. It was confirmed that it was possible.

In order to verify the effect of the hot shearing method according to the present invention through the hot press forming process, the heated aluminum coated steel sheet is hat-formed (bent-shaped bend-shaped cross section), and immediately after that, hot shearing (circle) A verification experiment 3 was conducted to measure the residual tensile stress in the circumferential direction of the sheared surface.
The aluminum-coated steel sheet was heated to 950 ° C. in a heating furnace and held in the furnace for 30 seconds or more. Thereafter, the sheet is conveyed to the mold using a predetermined conveying means, and immediately after the aluminum-coated steel plate is set in the mold, as shown in FIG. Hat molding was started using the die 7 and the press molding plate retainer 29.
Immediately after the press forming punch 6 reaches the bottom dead center, as shown in FIG. 14C, punching is performed using the punching punch 10 and the plate presser 8 incorporated in the press forming punch 6. After completion of punching, the punching punch 10 was held at the bottom dead center for 30 seconds.
In addition, the case where the punch of the normal shape (the punch of the shape which does not form a taper) was used as the punching punch 10 was made into the comparative example. Then, as shown in FIGS. 14A to 14C, the case of using a reverse taper-shaped punch as the hole punching punch 10 was set as an example of the present invention.
Moreover, the punch tip diameter of the punch 10 according to the present invention is 10 mm, the taper angle of the punch is 5 °, the clearance between the punch 10 and the plate presser 8 is 1 mm, and the punch 10 and the plate presser 8 are incorporated. The diameter 26 of the press molding punch 6 is 30 mm, and the clearance 27 between the press molding punch 6 and the punching die 7 is 2.3 mm. And the plate pressing force of the aluminum coated steel plate by the plate pressing 8 at the time of punching is 50 tons. Further, the press forming punch 6 and the punching die 7 are rounded 28 of R5.0 mm.

FIG. 15 shows the measurement results of the tensile residual stress in the verification experiment 3. As shown in the figure, in the comparative example, a tensile residual stress exceeding 1000 MPa was measured. On the other hand, in the present invention example, it was confirmed that the tensile residual stress was reduced to about 600 MPa.
Moreover, when the hardness in the vicinity of the sheared surface was measured in the entire plate thickness direction, it was 300 to 500 Hv in the comparative example, and it was confirmed that a significant hardness difference was generated between a specific portion and other portions on the sheared surface. . On the other hand, in the example of the present invention, it was confirmed that any part of the sheared surface was about 500 Hv, and the hardness of the sheared surface was uniform over the entire processed surface. The hardness other than the vicinity of the sheared surface was about 500 Hv in both the comparative example and the example of the present invention.
As described above, according to the hot shearing method according to the present invention that undergoes the hot press forming step, it was confirmed that the hardness of the sheared surface can be made uniform and the tensile residual stress of the sheared surface can be reduced. .

1 Metal plate material 2 Punch 3 Die 4 Shear piece 5 Clearance
6 Press forming punch 7 Hole die 8 Plate holding 9 Non-contact surface 10 Punch 11 Diameter of punch tip 12 Smooth portion 13 Refrigerant injection hole 14 Refrigerant introduction groove 15 Refrigerant supply pipe 16 Refrigerant 17 Gap 18 Taper angle 19 Round 20 Base portion 21 Reverse Taper 22 Pump with Flow Control Function 23 Refrigerant Tank 24 On / Off Valve 25 On / Off Valve Control Unit 26 Press Molding Punch Diameter 27 Clearance 28 Round 29 Press Forming Plate Presser

Claims (6)

In a hot shearing method in which a heated metal plate material is sheared in a mold and quenched in the mold simultaneously with the shearing process,
The metal plate material is sheared using a punch having a base shaft portion having a constant diameter in the axial direction and a reverse taper portion having a taper angle of 4 to 7 ° that tapers toward a punch tip continuous with the base shaft portion. A hot shearing method characterized by the above.   The hot shearing method according to claim 1, wherein the metal plate material is press-molded in the mold immediately before or simultaneously with the shearing process.   The hot shearing method according to claim 1 or 2, wherein the quenching is performed by heat removal from contact with the mold.   The hot shearing method according to any one of claims 1 to 3, wherein the quenching is performed by ejecting a coolant from the mold.   The metal plate material is sheared by providing a gap of 5 to 100% of the plate thickness of the metal plate material between the base portion of the punch and the plate holder, and the quenching is performed by flowing a coolant through the gap. The hot shearing method according to any one of claims 1 to 4, wherein the hot shearing method is performed.   The hot shearing method according to any one of claims 1 to 5, wherein the metal plate material is sheared by using a punch that has been chamfered or rounded at a cutting edge of the punch.

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