The present invention relates to a mold for a press brake and a hemming method using the mold, and more particularly relates to a mold for a press brake that can reduce residual stress near a cut edge of a plate-like (sheet-like) workpiece which has been cut for example by laser cutting, and a hemming method using the mold.
When a plate-like workpiece is to be cut into a rectangular shape for example, laser cutting may be performed. A workpiece that has been cut into a rectangular shape as described above by laser cutting may be subjected to bending along a long bending line in a longitudinal direction of the workpiece. When laser cutting is performed on the plate-like workpiece, residual stress occurs near a cut edge of the workpiece. As exemplified in Japanese Patent Application Laid-open No. 2012-157902 (Patent Literature 1), when the shape of the workpiece cut into a rectangular shape as described above has a strip shape, it has been known that residual stress at the cut edge in the longitudinal direction of the workpiece affects warpage of the workpiece after bending. Further, as exemplified in Japanese Patent Application Laid-open No. 2013-116502 (Patent Literature 2), a mold for reducing residual stress has been proposed.
Patent Literature 1 describes that, when laser cutting is performed on a workpiece SPCC with a thickness of 1.2 millimeters, residual stress at a position close to a cut surface is in a positive (+) direction (tensile stress) and there is a region in which the residual stress changes to a negative direction (a compression direction). In
Furthermore, in
In Patent Literature 2, it is described that before performing bending of a workpiece by using a mold for a press brake, an end surface of the workpiece is pressurized by the mold.
Bending of a plate-like workpiece is generally performed by a press brake. Therefore, as described in Patent Literature 1, the configuration in which laser beams are irradiated, the configuration in which a workpiece is punched and pressed by a punch and a die, and the configuration in which a workpiece is pressurized by a pair of pressing rollers require relevant devices other than the press brake, which is not desirable.
The configuration described in Patent Literature 2 is such that a workpiece is pressed in a small pressing width adjusted by a pressing width adjustment mechanism between a flat surface of an end-face pressing upper mold and a flat surface of an end-face pressing lower mold provided in a mold for a press brake, over the entire surface from an end face of the workpiece.
In the configuration of the mold described in Patent Literature 2, when a workpiece is positioned between the end-face pressing lower mold and the end-face pressing upper mold to pressurize the vicinity of the cut surface of the workpiece, if the workpiece is inserted deeply and positioned between the end-face pressing lower mold and the end-face pressing upper mold, a pressure receiving area of the workpiece increases. If the workpiece is inserted shallowly and positioned between the end-face pressing lower mold and the end-face pressing upper mold, a thrust load acts on the end-face pressing upper mold that moves vertically, thereby readily causing a galling (scuffing) phenomenon or the like.
In order to reduce the residual stress by pressurizing the vicinity of the cut surface of the workpiece that has been cut by laser cutting, it is desired to cause plastic deformation by pressurizing the workpiece up to an upper yield point stress or higher, which is the maximum stress in an elastic region. However, in a case of reducing several tens of percent of residual stress, pressurization can be performed under the upper yield point stress or close to the upper yield point stress. That is, in order to reduce the residual stress, it is not always necessary to pressurize the workpiece to the upper yield point stress or higher. However, when a press brake having a small pressurizing force is used, a pressurizing force thereof is insufficient to reduce the residual stress.
In order to solve the above problems and to achieve the above object, a mold for a press brake according to a first aspect of the present invention comprises: an ascending and descending member that is relatively pressed and lowered by an upper table in a press brake, the ascending and descending member provided vertically movably with respect to a mold base mountable on a lower table in the press brake; a workpiece supporting member provided in the mold base, the workpiece supporting member having an upper surface; and, a workpiece pressing member provided in the ascending and descending member, the workpiece pressing member having a lower surface, wherein the upper surface and the lower surface vertically face each other, and, the upper surface of the workpiece supporting member is inclined so that a front side of the upper surface becomes relatively lower than the lower surface of the workpiece pressing member.
A mold for a press brake according to a second aspect of the present invention comprises an upper mold that is mountable on an upper table and a lower mold mountable on a lower table in a press brake, wherein the upper mold and the lower mold are vertically face each other, and have respective pressurizing surfaces, and, one of the pressurizing surfaces is formed as a level surface and the other is formed as an inclined surface.
With reference to
A die holder 11 as an ascending and descending member that can detach and replace a die 9 is vertically movably provided on the upward protruding portion 7. More specifically, the die holder (ascending and descending member) 11 is provided with a lower surface 13 that can abut on an upper surface of the upward protruding portion 7, and a suspending portion 15 that vertically movably comes in surface contact with a vertical rear surface 7A of the upward protruding portion 7 is integrally provided with the die holder 11. Further, a workpiece pressing member 17 that vertically movably comes in surface contact with a vertical front surface 7B of the upward protruding portion 7 and is long in the horizontal direction is provided on the die holder 11 detachably and replaceably via an attachment tool 19 such as a screw.
A workpiece supporting member 21 that vertically faces the workpiece pressing member 17 and is long in the horizontal direction is provided on the mold base 5 detachably and replaceably. In order to provide the die holder 11 vertically movably with respect to the mold base 5, an actuator 23 for vertical movement such as a fluid pressure cylinder is installed in the mold base 5. As the configuration in which the die holder 11 is provided vertically movably with respect to the mold base 5, such a configuration is also possible that a biasing (an energizing) unit such as a coil spring is provided instead of the actuator 23 for vertical movement to press and bias (energize) the die holder 11 in an upward direction at all times.
The die holder 11 is detachably and replaceably provided with the die 9 that works with a punch 27 detachably and replaceably provided on an upper table 25 in the press brake to perform bending of a plate-like workpiece W.
In the configuration described above, after the workpiece W is positioned on the die 9, while holding the lower surface 13 of the die holder 11 in a state of abutting on the upper surface of the upward protruding portion 7 in the mold base 5, by relatively lowering and engaging the punch 27 with the die 9, bending of the workpiece W in a V shape can be performed. As described above, when the workpiece W is formed in a rectangular shape by laser cutting, residual stress at opposite end edges of the workpiece W in the longitudinal direction may affect warpage of the workpiece W after the bending.
Therefore, the mold 1 according to the present embodiment has a function of pressurizing an end edge of the plate-like workpiece W to reduce residual stress at the end edge. More specifically, the configuration is such that the end edge of the workpiece W is pressurized between the lower surface of the workpiece pressing member 17 and the upper surface of the workpiece supporting member 21. That is, when the lower surface 13 of the die holder 11 abuts on the upper surface of the upward protruding portion 7 in the mold base 5, the lower surface of the workpiece pressing member 17 and the upper surface of the workpiece supporting member 21 come into contact with each other, or are slightly away from each other.
An upper surface 21F of the workpiece supporting member 21 is formed as an inclined surface with the front side (the right side in
As described above, when the workpiece W is inserted between the workpiece pressing member 17 and the workpiece supporting member 21, the end edge of the workpiece W abuts on the front surface 7B of the upward protruding portion 7 and is positioned. Accordingly, the front surface 7B of the upward protruding portion 7 constitutes a guide surface along which the workpiece pressing member 17 slides vertically, and constitutes a workpiece positioning surface with which the workpiece W is brought into contact to perform positioning.
As described above, when the workpiece W is inserted between the workpiece pressing member 17 and the workpiece supporting member 21 and abuts on the front surface 7B of the upward protruding portion 7, the end edge of the workpiece W corresponds to a topmost portion of the inclined upper surface 21F of the workpiece supporting member 21. Accordingly, when the upper table 25 in the press brake is relatively lowered to press the die 9, the workpiece pressing member 17 is lowered, and the lower surface 17F comes into contact with the workpiece W to press the workpiece W. In this stage, the contact between the end edge of the workpiece W and the upper surface 21F of the workpiece supporting member 21 becomes line contact.
Accordingly, when the workpiece pressing member 17 is relatively pressed and lowered by the upper table 25, stress concentration occurs at the end edge of the workpiece W, the end edge of the workpiece W has upper yield point stress, and residual stress at the end edge of the workpiece W is reduced. When the end edge of the workpiece W plastically deforms and the contact between the upper surface 21F of the workpiece supporting member 21 and the end edge of the workpiece W becomes a slight surface contact, residual stress at this portion is also reduced. Because there is a limit in the pressurizing force of the press brake, when the range of the plastic deformation near the end edge of the workpiece W gradually increases, and surface contact between the upper surface 21F of the workpiece supporting member 21 and the vicinity of the end edge of the workpiece W gradually increases, it becomes difficult to pressurize the vicinity of the end edge of the workpiece W up to the upper yield point stress.
As is understood from the above descriptions, because the contact between the end edge of the workpiece W and the inclined upper surface 21F of the workpiece supporting member 21 changes from the initial line contact to the surface contact by pressurization, the vicinity of the end edge of the workpiece W can be pressurized up to the upper yield point stress in the range where the surface contact is small, and the residual stress can be reduced. It is relative as to whether to form the upper surface 21F of the workpiece supporting member 21 as an inclined surface or to form the lower surface 17F of the workpiece pressing member 17 as an inclined surface. Therefore, it suffices to form at least one of the lower surface 17F of the workpiece pressing member 17 and the upper surface 21F of the workpiece supporting member 21 as an inclined surface.
Meanwhile, a case where the upper surface 21F of the workpiece supporting member 21 is formed as an inclined surface has been described. However, as shown in
The upper mold 53 includes a workpiece pressing portion 61 formed in a V shape at a lower part thereof to press the workpiece W into the bending groove 57. A pressurizing surface 63 that can pressurize the workpiece W by putting the workpiece W between the upper surface 59 of the lower mold 55 and the pressurizing surface 63 is provided at an upper position of the workpiece pressing portion 61. The pressurizing surface 63 is formed by forming a step portion on the both front and rear sides of a base end portion of the workpiece pressing portion 61 in the upper mold 53.
The pressurizing surface 63 is formed at the step portion positioned inside of extending portions 61A on the V-shaped inclined surfaces of the workpiece pressing portion 61. Accordingly, when bending of the workpiece W in a V shape is performed by the workpiece pressing portion 61, the pressurizing surface 63 does not interfere with the workpiece W. The pressurizing surfaces 63 are slightly inclined so that the both front and rear sides become higher than a middle portion, respectively. The pressurizing surface 63 can be formed as a curved surface or the like as in the configuration of the lower surface 17F shown in
In the above configuration, the workpiece pressing portion 61 of the upper mold 53 is engaged with the bending groove 57 in the lower mold 55 and is held in a state where the upper surface 59 of the lower mold 55 and the pressurizing surface 63 of the upper mold 53 are slightly away from each other. The end edge of the workpiece W is then inserted between the upper surface 59 and the pressurizing surface 63 and is brought into contact with a vertical front surface 61F or a vertical rear surface 61R in the workpiece pressing portion 61, to perform positioning of the end edge of the workpiece W. Accordingly, the front surface 61F and the rear surface 61R of the workpiece pressing portion 61 in the upper mold 53 constitute a workpiece positioning surface with which the end edge of the workpiece W is brought into contact to perform positioning.
As described above, after the end edge of the workpiece W is inserted between the upper surface 59 of the lower mold 55 and the pressurizing surface 63 of the upper mold 53 and is positioned so that the end edge of the workpiece W abuts on the front surface 61F of the upper mold 53, when the upper mold 53 is relatively lowered to pressurize the workpiece W, stress concentration occurs at the end edge of the workpiece W because the pressurizing surface 63 is inclined. Therefore, distortion (plastic deformation) equal to or larger than distortion at the upper yield point occurs at the end edge of the workpiece W. The contact surface between the end edge portion of the workpiece W and the pressurizing surface 63 gradually increases. Accordingly, the residual stress near the end edge portion of the workpiece W can be reduced.
After reduction of the residual stress at the end edge portion of the workpiece W, as described above, the workpiece W is placed and positioned on the upper surface 59 of the lower mold 55, and the workpiece W is pressed into the bending groove 57 in the lower mold 55 by the workpiece pressing portion 61 of the upper mold 53, thereby enabling to perform bending on the workpiece W in the V shape.
As is understood from the above descriptions, residual stress at a rear edge of the workpiece W can be reduced by the molds 1 and 51 mounted on the press brake, and bending of the workpiece W in a V shape can be performed by the molds 1 and 51.
As described above, in the mold 1, hemming of the workpiece can be performed between the lower surface 17F of the workpiece pressing member 17 and the upper surface of the workpiece supporting member 21. Results as shown in
That is, the workpiece W bent in an acute angle beforehand is placed on the upper surface 21F of the workpiece supporting member 21, and a bent portion WB of the workpiece W is positioned so as to abut on the front surface 7B of the upward protruding portion 7. When the workpiece pressing member 17 is lowered to press a flange portion WF of the workpiece W, a front end edge 17E of the lower surface 17F in the workpiece pressing member 17 presses the flange portion WF (see
Thereafter, the flange portion WF is further pressed and bent to gradually decrease a bending angle of the workpiece W, and the pressing direction with respect to the flange portion WF by the front end edge 17E of the workpiece pressing member 17 is gradually changed to the vertical direction (see
At this time, the pressing force of the workpiece pressing member 17 to press the flange portion WF increases more on the side of the bent portion WB than on the end side of the flange portion WF (see
Subsequently, when the flange portion WF is further bent by the workpiece pressing member 17, the end side of the flange portion WF is gradually lowered. The contact area between the lower surface 17F of the workpiece pressing member 17 and the flange portion WF gradually decreases, and the position where the workpiece pressing member 17 presses the flange portion WF shifts toward the bent portion WB even further. The position where the workpiece W strongly presses the upper surface 21F of the workpiece supporting member 21 also further shifts toward the bent portion WB corresponding to the pressing position on the side of the flange portion WF (see
When the flange portion WF is further bent by the workpiece pressing member 17, as is understood from
Accordingly, a reaction force when the workpiece W presses the upper surface 21F acts on the workpiece W. The workpiece W becomes the free state detached from the end edge of the upper surface 21F of the workpiece supporting member 21 due to the moment caused by the reaction force (see
As described above, in the state where the end side of the flange portion WF of the workpiece W abuts on the upper surface of the workpiece W, hemming is performed by strongly pressing and squashing the bent portion WB of the workpiece W. At this time, the lower surface 17F of the workpiece pressing member 17 does not come into contact with the flange portion WF over the entire surface, and presses the vicinity of the bent portion WB from above. The upper surface 21F of the workpiece supporting member 21 also supports the vicinity of the bent portion of the workpiece W from below (see
That is, an area where the lower surface 17F of the workpiece pressing member 17 pressurizes the workpiece W and an area where the upper surface 21F of the workpiece supporting member 21 pressurizes the workpiece W are areas of pressing upper and lower curved surfaces in the bent portion WB of the workpiece W which are small. Accordingly, even if stress concentration occurs and a pressing force (a pressurizing force) of the workpiece pressing member 17 is relatively small, hemming can be performed.
As described above, when hemming of the workpiece W is to be performed, because the end side of the flange portion WF of the workpiece W is pressed to the upper surface of the workpiece W, the bent portion WB of the workpiece W undergoes deformation in the left direction in
Therefore, verification as to whether a pressing force (a pressurizing force) actually decreases when hemming is performed by the mold 1 having the configuration in which the upper surface 21F of the workpiece supporting member 21 is inclined to be low on the front side, was performed. That is, in molds 1 having the same configuration, hemming is performed by using a mold in which the lower surface 17B of the workpiece pressing member 17 is formed as a level surface and the upper surface 21F of the workpiece supporting member 21 is level (a lightweight hemming die) and by using a mold in which the upper surface 21F is inclined to be low on the front side (a new hemming method). The results are as shown in
As is clear from
In the mold in which the upper surface 21F of the workpiece supporting member 21 is formed low on the front side, the plate thickness after hemming can be made thinner even if the pressurization load is small (for example, in the case of 40 tons and 42 tons) (see
In order to prevent that the bent portion WB of the workpiece W is pressed to the front surface 7B and is slightly deformed, molds 1A and 1B as shown in
The mold 1A shown in
According to the molds 1A and 1B having the configuration described above, when hemming of the workpiece W is to be performed, as shown in
According to the present invention, when a workpiece is arranged between a workpiece supporting member and a workpiece pressing member and pressurized, an initial contact state between an end edge of the workpiece and the workpiece pressing member is line contact, because an upper surface of the workpiece supporting member is inclined relatively to a lower surface of the workpiece pressing member.
Therefore, even if an initial pressurizing force is small, stress concentration occurs at the end edge of the workpiece, thereby enabling to reduce residual stress at the end edge of the workpiece.
(United States Designation)
In case this international patent application designates the United States, this application claims the benefit of priority based upon Japanese Patent Application No. 2014-75088 filed on Apr. 1, 2014 and Japanese Patent Application No. 2014-264686 filed on Dec. 26, 2014, and the contents of which are incorporated herein by reference.
Number | Date | Country | Kind |
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2014-075088 | Apr 2014 | JP | national |
2014-264686 | Dec 2014 | JP | national |
This is a continuation application of pending U.S. application Ser. No. 15/124,918, filed Sep. 9, 2016, which is a National Stage Entry of PCT/JP2015/059883, filed on Mar. 30, 2015, which claims priority of Japanese Patent Application No. 2014-264686, filed Dec. 26, 2014, and Japanese Patent Application No. 2014-075088, filed Apr. 1, 2014, the contents of each are incorporated herein by reference in their entirety.
Number | Name | Date | Kind |
---|---|---|---|
4918971 | Makino | Apr 1990 | A |
5966976 | Haraga | Oct 1999 | A |
6257043 | Wiens | Jul 2001 | B1 |
9868144 | Artmayr et al. | Jan 2018 | B2 |
20100257914 | Makino | Oct 2010 | A1 |
20130283875 | Jin et al. | Oct 2013 | A1 |
20140283576 | Jin et al. | Sep 2014 | A1 |
20160096213 | Artmayr | Apr 2016 | A1 |
Number | Date | Country |
---|---|---|
51-17231 | May 1976 | JP |
54-118439 | Aug 1979 | JP |
56-80327 | Jul 1981 | JP |
60-56123 | Apr 1985 | JP |
60-66622 | May 1985 | JP |
03-230821 | Oct 1991 | JP |
6-87028 | Mar 1994 | JP |
06-238353 | Aug 1994 | JP |
3043386 | Nov 1997 | JP |
10-137852 | May 1998 | JP |
11-197763 | Jul 1999 | JP |
2003-181546 | Jul 2003 | JP |
2004-42061 | Feb 2004 | JP |
2005-349457 | Dec 2005 | JP |
2005349457 | Dec 2005 | JP |
2012-157902 | Aug 2012 | JP |
2013-116502 | Jun 2013 | JP |
2010099559 | Sep 2010 | WO |
Entry |
---|
Search Report issued in International Bureau of WIPO Patent Application No. PCT/JP2015/059883, dated Jun. 23, 2015. |
Extended European Search Report issued in Patent Application No. 15773240.5, dated Dec. 13, 2017. |
Office Action issued in Japan Counterpart Patent Appl. No 2014-264686, dated May 8, 2019, along with an English translation thereof. |
EPO Machine Translation of JP 06087028 A (Year: 2019). |
EPO Machine Translation of JP 10137852 A (Year: 2019). |
Number | Date | Country | |
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20200156135 A1 | May 2020 | US |
Number | Date | Country | |
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Parent | 15124918 | US | |
Child | 16747924 | US |