Abstract:
An elastic member is disposed on a load supporting device such as cushion pins and wear plates, which are placed between at least a workpiece and a die cushion pad and transfer a load applied to the work to the die cushion pad, to support the load. The load supporting device is disposed in two or more on the die cushion pad to realize equalization of the load applied to a die cushion. Thus, use of a conventional large-scale hydraulic circuit is eliminated, and the device can be simplified. Also, the press machine can be produced at a low cost.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a cushion pin with an elastic member, a wear plate and a load supporting device; to a die cushion for equalizing a cushion pressure by using two or more of them; and further to a press machine having the die cushion. The invention also relates to a pressing method. 
   2. Description of the Related Art 
   When the die cushion is used to perform pressing (especially, deep drawing), it is necessary to keep constant a work&#39;s blank holding force (cushion pressure) by eliminating poor accuracy (inclination) of a blank holder, variations in length of cushion pins, parallelism error of a die cushion pad for holding the cushion pins, deflection or inclination of a slide of a press machine, and the like. Therefore, a cushion pin pressure-equalizing device is used conventionally. Such a cushion pin pressure-equalizing device is described in, for example, Patent Document 1 (Japanese Utility Model Publication No. 5-27215, pp. 1-2,  FIG. 4 ). 
     FIG. 15  is a sectional diagram of a press machine using a conventional cushion-equalizing device, showing an example of a cushion pin pressure-equalizing device described in the Patent Document 1. This prior art will be described with reference to  FIG. 15 . 
   In  FIG. 15 , an upper press die  51  is fixed to a slide  52  of the press machine, and a lower press die  53  is fixed to a bolster plate  54 . The bolster plate  54  is supported by a carrier (corresponding to a press carrier 55 of Patent Document 1). A blank holder (corresponding to a cushion pad of Patent Document 1)  56  is disposed within the lower press die  53 . The blank holder  56  is supported by the top ends of plural cushion pins  57 , and the bottom ends of the individual cushion pins  57  are supported by a cushion plate  69  of a die cushion  59  through hydraulic cylinders  58 . The die cushion  59  is provided with a cushion cylinder  61  for supporting the cushion plate  69 , and a prescribed air pressure, which is determined by an air regulator  63 , is supplied from an air pressure source  62  to the cushion cylinder  61  via an air tank  64 . The individual hydraulic cylinders  58  are connected to an oil feeding means  67  through a common pipe  65  and a flexible tube  66 . The oil feeding means  67  has a function to assure an amount of oil being supplied to the individual hydraulic cylinders  58 . 
   According to the above configuration, a work W is placed on the blank holder  56 , the slide  52  is lowered, its lowering force is transmitted to the die cushion  59  through the cushion pins  57 , and the die cushion  59  generates a cushion pressure, namely a blank holding force. At this time, an oil pressure generated within each of the hydraulic cylinders  58  disposed at the bottom ends of the cushion pins  57  becomes constant because the individual hydraulic cylinders  58  are mutually communicated. Thus, unbalanced cushion pressures of the individual cushion pins  57  are smoothed (namely, equalized) to improve blank holding accuracy. 
   But, the above-described conventional cushion pin pressure-equalizing device has the following drawbacks. Specifically, to smooth the unbalanced cushion pressures among the cushion pins  57 , it is necessary to provide an equalizing hydraulic circuit, which has the hydraulic cylinders  58  disposed for the individual cushion pins  57  connected to the oil feeding means  67  through the common pipe  65  or an oil passage. Thus, the cushion pin pressure-equalizing device has disadvantages that it becomes large in scale and its cost is high. Besides, a press production site generally has a press machine, which is used for trials to determine pressing conditions in advance before real production. This press machine is in addition to the press machine that is used for the real production. This tryout press machine is also provided with the above-described cushion pin pressure-equalizing device, so that the cost is doubled, and the high cost problem cannot be neglected. 
   Besides, for pressing with high accuracy, it may be necessary to vary the blank holding force for each portion depending on the shape even if the work is the same. For example, areas D 1  to D 4  are provided by dividing the portion around the center of the die into four areas as shown in  FIG. 16 , and four die cushions  59  with different cushion pressures for the individual areas D 1  to D 4  and the cushion pin pressure equalizing device corresponding to the individual die cushions  59  are provided. Therefore, the cost becomes higher. 
   The present invention has been made in view of the above circumstances and provides equalization of the cushions without using a large-scale hydraulic circuit and results in reduction of a press machine production cost. 
   SUMMARY OF THE INVENTION 
   To achieve the above-described object, a first aspect of the invention relates to cushion pins which are extended through a bolster plate of a press machine, and have their bottom ends disposed on a die cushion through a die cushion pad and hold a work by their top ends directly or through a blank holder. An elastic member for producing a pushing force in an axial direction is provided to enable the work to be held through the elastic member. 
   According to the first aspect of the invention, the cushion pins are provided with the elastic member for generation of the pushing force in the axial direction and hold the work through the elastic member. If there are variations in cushion pressures because of an inclination of the blank holder, variations in the length of the cushion pins and an error of parallelism of the die cushion pad, the contracted length of the elastic member is varied accordingly, and the length of the cushion pins are reduced. At this time, the contraction in length of the cushion pins smoothes variations in the axial position such as an inclination of the blank holder, variations in the length of the cushion pins and an error of parallelism of the die cushion pad. Also, a difference in pushing force by the elastic member of each of the cushion pins involved in the variations in the axial direction is generated, but the axially transmitted pressures of the individual cushion pins can be equalized by determining an elastic modulus of the elastic member so that a difference in pushing force of the elastic member for each of the cushion pins becomes small with respect to the cushion pressure level. As a result, the equalization can be performed by a simple structure having the elastic member for each of the cushion pins. Thus, the device does not become large in scale, and the production cost can be reduced. Besides, when a different cushion pressure is set for each of the plural areas of the die, only one die cushion is mounted, and a different elastic modulus of the elastic member can be set for each area. Therefore, the cost can be reduced. 
   A second aspect of the invention relates to a die cushion which equalizes axially transmitted pressures of the individual cushion pins by the cushion pins according to the first aspect of the invention. 
   A third aspect of the invention relates to a press machine provided with the die cushion according to the second aspect of the invention. 
   According to the second and third aspects of the invention, the cushion pins having the elastic member can be used to equalize the axially transmitted pressures of the individual cushion pins, and processing accuracy of deep drawing or the like using the die cushion can be improved. Thus, the die cushion and the press machine can be configured at a low cost. 
   A fourth aspect of the invention relates to a pressing method which performs press work by equalizing axially transmitted pressures of plural cushion pins by smoothing variations in the positions of the ends of the cushion pins by contraction of an elastic member provided for each of the cushion pins disposed on a die cushion through a die cushion pad. 
   According to the fourth aspect of the invention, the variations in a cushion pin&#39;s axial position involved in the variations in working accuracy or rigidity of individual components are smoothed by the contraction of the elastic member provided for each of the cushion pins without using a conventional cushion pin pressure-equalizing device based on a hydraulic circuit including individual hydraulic cylinders which are communicated by a common pipe or oil passage, and the axially transmitted pressures of the individual cushion pins are equalized. Thus, the equalization can be achieved by a simple structure, and the cost can be reduced. 
   A fifth aspect of the invention relates to a wear plate which is provided with a supporting section having an elastic member and supports a load applied from one direction by the supporting section. 
   A sixth aspect of the invention relates to a load supporting device which is disposed on one surface of a die cushion pad and supports a load applied from a direction opposite to the surface, wherein a supporting section having an elastic member is provided to support the load. 
   The fifth and sixth aspects of the invention will be described with reference to  FIG. 9 . 
   A sliding section  13 , which slides along a bolt member  15  used as a guide, is disposed on one surface of a wear plate (a load supporting device)  11 , and an elastic member  16 , which produces a pushing force in a direction of the load received from the cushion pin  57  and its opposite direction, is disposed within the sliding section  13 . A lid section  14  is disposed on one end of the sliding section  13  so to come into contact with the cushion pin  57 . Thus, the load of the slide transmitted through the cushion pin  57  is supported by the sliding section  13 , the lid section  14  and the elastic member  16 . The other surface of the wear plate  11  is attached to one surface of a die cushion pad  21  and disposed so as to correspond to each cushion pin  57 . 
   The each elastic member  16  contracts depending on variations in length of the individual cushion pins  57 , an error in parallelism of the die cushion pad  21 , and the like to keep the die cushion pad  21  horizontal. At this time, the individual elastic members  16  have different pushing forces, but the transferred pressures of the individual wear plates  11  can be equalized by setting the elastic modulus of the elastic member  16  so as to reduce the difference in pushing force with respect to the cushion pressure level. 
   Thus, according to the fifth and sixth aspects of the invention, the equalization can be made by a simple structure having the elastic member on the side of the die cushion pad. Therefore, the hydraulic circuit for equalization can be eliminated, and the equalizing device has a very simple structure. Accordingly, the production cost of the press machine can be reduced. 
   When a different cushion pressure is determined for each of the plural areas of the die, the difference in cushion pressure produced among the plural areas may be set with the elastic modulus of the individual elastic members differentiated. Therefore, it is advisable to dispose a single die cushion for the press machine, and the production cost of the press machine can be reduced. 
   Besides, the hydraulic circuit for equalization becomes unnecessary. Thus, oil stains, noise of hydraulic equipment, and the like are reduced, and the work environment at the work site can be improved. 
   A seventh aspect of the invention relates to a die cushion which receives a load applied through plural cushion pins  57  by a die cushion pad  21 , wherein the load supporting device according to the sixth aspect of the invention is provided in two or more on one surface of the die cushion pad, and each cushion pin and each load supporting device are mutually contacted to support the load. 
   An eighth aspect of the invention relates to a press machine using the die cushion according to the seventh aspect of the invention. 
   According to the seventh and eighth aspects of the invention, the pressures applied by the cushion pins can be equalized by means of the load supporting device having the elastic member, so that the pressing accuracy of the deep drawing, or the like using the die cushion can be enhanced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional diagram of a press machine having cushion pins according to the present invention; 
       FIG. 2  is a partially sectional side view of the cushion pin according to a first embodiment; 
       FIG. 3  is a sectional diagram taken along line A-A of  FIG. 2 ; 
       FIG. 4  is a sectional diagram of a press machine of an embodiment different from  FIG. 1 ; 
       FIG. 5  is a partially sectional side view of a cushion pin according to a second embodiment; 
       FIG. 6  is a partially sectional side view of a cushion pin according to a third embodiment; 
       FIG. 7  is a sectional diagram of a press machine using a load supporting device according to the invention; 
       FIG. 8  is a sectional diagram of the press machine using the load supporting device according to the invention; 
       FIG. 9  is a partially sectional side view of a load supporting device according to a fourth embodiment; 
       FIG. 10  is a sectional diagram taken along line A-A of  FIG. 9 ; 
       FIG. 11  is a partially sectional side view of a load supporting device according to a fifth embodiment; 
       FIG. 12  is a partially sectional side view of a load supporting device according to a sixth embodiment; 
       FIG. 13  is a partially sectional side view of a load supporting device according to a seventh embodiment; 
       FIG. 14  is a partially sectional side view of a load supporting device according to an eighth embodiment; 
       FIG. 15  is a sectional diagram of a press machine using a conventional cushion equalizing device; and 
       FIG. 16  is an example arrangement of hydraulic cylinders of a conventional cushion equalizing device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
   The first to third embodiments will cover cushion pins, a die cushion using the cushion pins and a press machine according to the present invention, and the fourth to eighth embodiments will cover a load supporting device (wear plate), a die cushion using the load supporting device and a press machine. 
     FIG. 1  is a sectional diagram of a press machine using the cushion pins according to the invention. Like reference numerals are used to indicate like components such as those shown in  FIG. 15  and their descriptions will be omitted. 
   In  FIG. 1 , cushion pins  1  are disposed so as to extend through the bolster plate  54 , their top ends support the blank holder  56 , their bottom ends are supported by a die cushion pad  60 , which is attached to the cushion cylinder  61  of the die cushion  59 , via a pad  68 . 
     FIG. 2  is a partially sectional side view of the cushion pin according to the first embodiment, and  FIG. 3  is a sectional diagram taken along line A-A of  FIG. 2 . The cushion pin  1  will be described with reference to  FIGS. 2 and 3 . The cushion pin  1  has a first member  2 , a sliding member  3  and a second member  4 . The first member  2  is a solid pillar (a cylindrical shape in this embodiment), and a screw hole  2   a  is formed in the axial direction at substantially the center of one end. Also, the sliding member  3  is a hollow pillar (a cylindrical shape in this embodiment) and has a screw hole section, which has a female thread  3   a  at substantially the center, formed at one end, and a through hole  3   d  having a diameter smaller than the inside diameter of the female thread  3   a  formed in a bottom  3   b  of the screw hole section substantially perpendicular to the screw axis. Besides, a cylindrical hole  3   c  which is larger than the through hole  3   d  and communicated with the through hole  3   d  is formed at substantially the center of the other end of the sliding member  3 . Within the hole  3   c  are housed a ring-shaped elastic member  6  and a ring-shaped spacer  7  in this order from the inner part of the hole. The elastic member  6  is formed of an elastic material such as a coned disc spring, a spring or a rigid urethane material which produces a pushing force when it is contracted in its axial direction to have a short length, and it is comprised of the coned disc spring in this embodiment. The bolt member  5  is slidably inserted from the second member  4  of the sliding member  3  to extend through the through hole  3   d , the ring-shaped elastic member  6  and the ring-shaped spacer  7  in this order, and a threaded portion  5   a  of the leading end of the bolt member  5  is screwed into the screw hole  2   a  of the first member  2 . The bolt member  5  has a small-diameter head  5   b  on its end opposite to the threaded portion  5   a  and a large-diameter head  5   c  on the side of the axial center from the small-diameter head  5   b , and also has a small-diameter intermediate portion, which is smaller than the large-diameter head  5   c , between the large-diameter head  5   c  and the threaded portion  5   a . And, when the bolt member  5  is screwed into the first member  2 , a stepped end face  5   d  formed on the small-diameter intermediate portion of the large-diameter head  5   c  comes into contact with a bottom face  3   b  of the screw hole section of the sliding member  3  to push the elastic member  6  through the sliding member  3  so to produce a prescribed pushing force in the axial direction. 
   Here, the bolt member  5  is screwed into the first member  2  so that a stepped end face  5   f  between the small-diameter intermediate portion of the bolt member  5  and the threaded portion  5   a  comes into contact with the stepped end face  2   b  of the screw hole  2   a  of the first member  2 , and the sliding member  3  is pushed by the pushing force of the elastic member  6  against the stepped end face  5   d  of the large-diameter head  5   c  of the bolt member  5 . At this time, it is configured in such a way that a gap with a prescribed distance L 1  is formed between the end face of the sliding member  3  and the end face of the first member  2 . This distance L 1  may be determined to be a distance having an allowance for the displacement of the elastic member  6 , so that when a prescribed cushion pressure is added to the cushion pin  1 , the pushing force corresponding to the contracted length (displaced amount) of the elastic member  6  and the cushion pressure can be balanced considering an elastic modulus of the elastic member  6 . And, it may be set to a distance to provide an allowance for the displacement of the elastic member  6 , and to, for example, approximately 0.1 to 0.2 mm according to the analysis made by the applicant. 
   Meanwhile, the second member  4  has a substantially pillar shape (a cylindrical shape in this embodiment), its one end has an external thread  4   a  having the same diameter as that of the female thread  3   a  of the sliding member  3  formed on the outer peripheral surface, and its substantially center section has a hole  4   b  having a diameter slightly larger than that of the large-diameter head  5   c  of the bolt member  5 . When the external thread  4   a  of the second member  4  is screwed into the female thread  3   a  of the sliding member  3 , the hole  4   b  of the second member  4  is slidably inserted on the outer peripheral surface of the large-diameter head  5   c  of the bolt member  5 , and a grease chamber  8  is formed between the inner peripheral surface of the hole  4   b  of the second member  4  and the outer peripheral surface of the small-diameter head  5   b  of the bolt member  5 . Grease is filled into the grease chamber  8  through an unshown injection port. 
   Two mutually parallel cut end faces  5   e ,  5   e  are formed on the outer peripheral surface of the small-diameter head  5   b  of the bolt member  5 , and two mutually parallel cut end faces  4   c ,  4   c  are also formed on the outer peripheral surface of the second member  4 . These cut end faces  5   e ,  5   e  and  4   c ,  4   c  are used to fit a tool such as a spanner at the time of removal or attachment. 
   As to the vertical direction of attaching the cushion pin  1 , either the first member  2  or the second member  4  may be positioned on the upper side. 
   The operation of the above structure will be described with reference to  FIG. 1  and  FIG. 2 . 
   When the slide  52  of the press machine is lowered, the upper press die  51  comes into contact with the work W which is positioned on the blank holders  56 , and the outer edge of the work W is held between the upper press die  51  and the blank holders  56 . Then, the upper press die  51  pushes the cushion pins  1  and the die cushion  59  through the blank holders  56  to lower together with the cushion pins  1  and the die cushion  59  and presses the work W between the upper press die  51  and the lower press die  53 . At this time, the load applied when the slide lowers is transmitted to the individual cushion pins  1  through the blank holders  56  and integrally pushes the second member  4  and the sliding member  3  of the each cushion pin  1  to slide with the bolt member  5  used as a guide, thereby contracting the elastic member  6 . 
   The contraction of the elastic member  6  smoothes variations in the position in the axial direction of the cushion pins including an inclination of the blank holders  56 , variations in the length of the cushion pins  1  and an error of parallelism of the die cushion pad  60 , and the contracted length of the elastic member  6  is determined according to the variations in the axial positions of the cushion pins. And, a pushing force corresponding to the contracted length of each elastic member  6  is generated for each cushion pin  1 , and the variations in the pushing force of the elastic member  6  of each cushion pin  1  correspond to the variations in the cushion pressure of each cushion pin  1 . Here, the axially transmitted pressures of the individual cushion pins  1  are equalized by setting an elastic modulus of the elastic member  6  so that the variation in the pushing force of the elastic member  6  becomes so small that it can be neglected in view of the predetermined cushion pressure of the die cushion  59 . Thus, the blank holding forces of the individual cushion pins  1  can be made substantially constant, and pressing accuracy can be improved. 
   As shown in  FIG. 4 , the top ends of the cushion pins  1  may directly contact the work W, and their bottom ends may directly contact the die cushion pad  60 . 
   The entire shape of the cushion pin  1  is not required to be cylindrical but may be formed to have, for example, a partly large diameter at the top end as shown in  FIG. 4 . 
   By configuring as described above, the die cushion equalizes the pin cushion pressure by using the cushion pins  1  having the elastic member  6  which produces a pushing force in the axial direction. Therefore, a hydraulic circuit for equalization is unnecessary, the equalizing device has a very simple structure, and the production cost becomes low. When a different cushion pressure is set for each of the plural areas (D 1  to D 4 ) of the die as described above, only one die cushion is mounted to determine the main cushion pressure level, and a difference in cushion pressure among the plural areas is dealt with by appropriately setting the elastic modulus of the elastic member  6  which varies for each of the areas. Thus, the cost can be lowered. Besides, a hydraulic circuit for equalization is unnecessary, oil stains, noise of hydraulic equipment, and the like are reduced, and the work environment of the work site can be improved. 
   The cushion pin according to the present invention is not limited to the structure of the first embodiment but may have a structure of, for example, the second embodiment or the third embodiment as shown in  FIG. 5  or  FIG. 6 . In  FIG. 5 , the elastic member  6  is disposed between the first member  2  and the second member  4 , and the elastic member  6  is fitted into the holes of the first member  2  and the second member  4  for fixation. The cushion pin shown in  FIG. 6  has the elastic member  6  fixed to one end of the first member  2 . In either case, variations in the axial position of the each cushion pin can be smoothed by the contraction of the elastic member  6  to equalize the axially transmitted pressures of the individual cushion pins. Thus, the same effects as in the above-described embodiment can be obtained. 
   As described above, the following effects can be obtained by the first to third embodiments. 
   The cushion pins having the elastic member for producing the pushing force in the axial direction are used to configure the die cushion for equalization of the axially transmitted pressures of the individual cushion pins. Thus, the equalizing device has a very simple structure and can be produced at a low cost. And, a different cushion pressure can be set for each of the plural areas of the die by appropriately determining a different elastic modulus of the elastic member for the individual areas, so that the cost can be reduced. 
   And, a hydraulic circuit for equalization is unnecessary, oil stains, noise of hydraulic equipment, and the like are reduced, and the work environment at the work site can be improved. 
     FIG. 7  is a sectional view of a press machine using the load supporting device according to the present invention. 
   The press machine shown in  FIG. 7  has a wear plate as the load supporting device. Like reference numerals are used for like components as those shown in  FIG. 15 , and their descriptions will be omitted. 
   As shown in  FIG. 7 , the press machine has the work W to be pressed placed between the upper press die  51  on the slide  52  side and the lower press die  53  on the bolster plate  54  side. The bottom of the work W is supported by the plural cushion pins  57 . The individual cushion pins  57  are extended through the lower press die  53  and the bolster plate  54  so as to have one end in contact with the work W through the blank holder  56 , and the other end in contact with the wear plate  11  on the die cushion pad  21 . The bolster plate  54  is supported by the frame  30  through the carrier  55 . 
   The die cushion  20  is disposed on the frame  30  side. The die cushion  20  is roughly comprised of a die cushion pad  21 , a cushion cylinder section  22  and a stopper section  23 . The plural wear plates  11  corresponding to the individual cushion pins  57  are disposed on the surface of the die cushion pad  21  opposed to the bolster plate  54 . The individual cushion pins  57  are supported by the corresponding wear plates  11 . And, the other surface of the die cushion pad  21  is supported by the cushion cylinder section  22 . 
   The cushion cylinder section  22  is comprised of the cylinder  22   a  formed on the die cushion pad  21  and the piston  22   b  formed on the frame  30 . The piston  22   b  is slidably inserted into the cylinder  22   a , and a pressure chamber  22   c  is formed by the inner surface of the cylinder  22   a  and the end face of the piston  22   b . A prescribed air pressure determined by an air regulator  63  is supplied from the air pressure source  62  to the pressure chamber  22   c  through the air tank  64 . 
   The stopper section  23  is comprised of a cylinder  23   a  and a nut  23   b . The nut  23   b  and the die cushion pad  21  are mutually connected by a rod  23   c . The nut  23   b  is slidably inserted into the cylinder  23   a . Operating oil is filled into the cylinder  23   a , and when the nut  23   b  slides within the cylinder  23   a  with the operation of the die cushion pad  21 , the operating oil is reduced by the cylinder  23   a  and the nut  23   b . Therefore, the die cushion pad  21   a  is gently stopped at the top dead center. 
     FIG. 8  is a sectional view of a press machine having the load supporting device according to the present invention. 
     FIG. 7  shows a state of the work W set in position, while  FIG. 8  shows a state of die carry-in-and-out. At the time of the die carry-in-and-out, the air in the pressure chamber  22   c  of the cushion cylinder section  22  is discharged, and the die cushion pad  21  is positioned at the bottom end. In this state, the cushion pins  57  and the wear plates  11  are separated from one another. At the time of die carry-out, the carrier  55  is removed from the frame  30 , and the upper press die  51 , the lower press die  53 , the bolster plate  54 , the carrier  55 , the blank holder  56  and the cushion pins  57  are integrally removed. At the time of die carry-in, the upper press die  51 , the lower press die  53 , the bolster plate  54 , the carrier  55 , the blank holder  56  and the cushion pins  57  are integrally carried in, and the carrier  55  is attached to the frame. 
     FIG. 9  is a partially sectional side view of the load supporting device according to the fourth embodiment, and  FIG. 10  is a sectional view taken along line A-A of  FIG. 9 . 
   The wear plate  11  will be described with reference to  FIG. 9  and  FIG. 10 . The wear plate  11  has a plate section  12 , a slide section  13  and a lid section  14 . 
   The plate section  12  is made of a plate member, and its material has hardness of a level adequate to prevent a hole from being formed when it is contacted by the slide section  13 . The plate section  12  is formed with a screw hole  12   a  having a ring-shaped stepped end face  12   b  in it and two or more bolt holes  12   c , which are formed in the same direction as that of the center axis of the screw hole  12   a . The screw hole  12   a  has a large diameter portion on the opening side from the stepped end face  12   b . A threaded portion  19   a  is formed on one end of the bolt  19 , and a head section  19   b  is formed on the other end. Screw holes  21   a  are formed on the surface of the die cushion pad  21 . The threaded portion  19   a  of the bolt  19  is extended through a washer  10  and the bolt hole  12   c  of the plate section  12  and screwed into the screw hole  21   a  of the die cushion pad  21 . Then, the plate section  12  is attached to the die cushion pad  21  by the pressure of the bolt head  19   b  transmitted via the washer  10 . 
   The slide section  13  is formed of a pillar (a cylindrical shape in this embodiment) member. A screw hole section  13   e , which has a bottom  13   b  and a female thread  13   a  formed on the inner peripheral surface, is formed in one end of the slide section  13 . A cylindrical hole  13   c  is formed in the other end, and a through hole  13   d  which connects the screw hole section  13   e  and the hole  13   c  is also formed. The screw hole section  13   e , the hole  13   c  and the through hole  13   d  have the same center axis, and the screw hole section  13   e  and the hole  13   c  have a diameter that is larger than that of the through hole  13   d . In the hole  13   c , the ring-shaped elastic member  16  and the ring-shaped spacer  17  are housed in this order from its inner part. The elastic member  16  is formed of an elastic material such as a coned disc spring, a spring or a rigid urethane material which produces a pushing force when it is contracted in the axial direction. The elastic member  16  of this embodiment is a coned disc spring. 
   A threaded portion  15   a  is formed on one end of the bolt member  15 , a small-diameter head  15   b  is formed on the other end, and a large-diameter head  15   c  is formed on the center side in the axial direction from the small-diameter head  15 . A ring-shaped stepped end face  15   d  is formed on the middle in the axial direction of the surface of the large-diameter head  15   c . An intermediate portion  15   g , which has a diameter smaller than that of the large-diameter head  15   c  and slightly larger than that of the threaded portion  15   a , is formed between the large-diameter head  15   c  and the threaded portion  5   a . A ring-shaped stepped end face  15   f  is formed on the joint between the intermediate portion  15   g  and the threaded portion  15   a.    
   The bolt member  15  is slidably inserted into the through hole  13   d , the ring-shaped elastic member  16  and the ring-shaped spacer  17  in this order from the screw hole section  13   e  of the slide section  13 . The threaded portion  15   a  on its leading end is screwed into the screw hole  12   a  of the plate section  12 . Thus, the stepped end face  15   d  of the bolt member  15  comes into contact with the bottom face  13   b  of the slide section  13 . From this state, the threaded portion  15   a  is further screwed so to contact the stepped end face  15   f  of the bolt member  15  with the stepped end face  12   b  of the plate section  12 . In this state, the stepped end face  15   d  of the bolt member  15  pushes the elastic member  16  through the slide section  13 , so that a pushing force is produced in the axial direction of the bolt member  15 . In other words, the slide section  13  is pushed against the stepped end face  15   d  of the bolt member  15  by the pushing force of the elastic member  16 . 
   The plate section  12 , the slide section  13 , the bolt member  15 , the elastic member  16  and the spacer  17  are designed to have their individual dimensions, so that a gap of a prescribed distance L 1  is formed between the end face of the slide section  13  and the end face of the plate section  12  by the produced pushing force. The distance L 1  may be determined to be a distance that provides an allowance for displacement of the elastic member  16 , so that when a prescribed cushion pressure is applied to the cushion pin  57 , a pushing force corresponding to a contracted length (displaced amount) of the elastic member  16  and a cushion pressure can be balanced in view of an elastic modulus of the elastic member  16 . According to the analysis performed by the applicant, the distance L 1  is desired to be, for example, about 0.1 to 0.2 mm. 
   The lid section  14  is formed of a pillar (a cylindrical shape in this embodiment) member. The external thread  14   a  having the same diameter as the diameter of the female thread  13   a  of the slide section  13  is formed on the outer peripheral surface of one end of the lid section  14 . A hole  14   b  having a diameter slightly larger than that of the large-diameter head  15   c  of the bolt member  15  is formed at substantially the center. When the external thread  14   a  of the lid section  14  is screwed in the female thread  13   a  of the slide section  13 , the hole  14   b  of the lid section  14  is slidably inserted on the outer peripheral surface of the large-diameter head  15   c  of the bolt member  15 , and the grease chamber  18  is formed between the inner peripheral surface of the hole  14   b  of the lid section  14  and the outer peripheral surface of the small-diameter head  15   b  of the bolt member  15 . Grease is supplied into the grease chamber  18  through an unshown injection port. The end of the cushion pin  57  comes into contact with the other end of the lid section  14 . 
   As shown in  FIG. 10 , two mutually parallel cut end faces  15   e ,  15   e  are formed on the outer peripheral surface of the small-diameter head  15   b  of the bolt member  15 , and two mutually parallel cut end faces  14   c ,  14   c  are similarly formed on the outer peripheral surface of the lid section  14 . These cut end faces  15   e ,  15   e  and  14   c ,  14   c  are used to fit a tool such as a spanner at the time of removal or attachment. 
   The operation of the above structure will be described with reference to  FIG. 7  and  FIG. 9 . 
   When the slide  52  of the press machine is lowered, the upper press die  51  comes into contact with the work W. The upper press die  51  pushes the work W, the blank holder  56 , the cushion pin  57 , the wear plate  11  and the die cushion pad  21  and lowers together with the work W, the blank holder  56 , the cushion pin  57 , the wear plate  11  and the die cushion pad  21  to form the work W between the upper press die  51  and the lower press die  53 . The load applied when the slide  52  lowers is transmitted to the individual wear plates  11  which support the cushion pins  57 . The load pushes the lid section  14  and the slide section  13  of the wear plate  11  against the plate section  12  to slide with the bolt member  15  functioning as a guide. At this time, the elastic member  16  is contracted. 
   When the elastic member  16  is contracted, variations in axial position of the cushion pins including variations in the length of the cushion pins  57  and parallelism error of the die cushion pad  21  are smoothed. The contracted length of the elastic member  16  is determined depending on the variations in the axial position of the cushion pins. And, a pushing force is produced according to the contracted length of the each elastic member  16  for each of the wear plates  11 , and the variations in the pushing forces of the elastic members  16  of the individual wear plates  11  correspond to the variations in the cushion pressures of the individual wear plates  11 . Here, when the elastic modulus of the elastic member  16  is set so that the variations in the pushing forces of the elastic members  16  become small to a level negligible with respect to the prescribed cushion pressure level of the die cushion  20 , the transferred pressures of the individual wear plates  11  are equalized. Thus, the blank holding forces of the individual cushion pins  57  can be made substantially constant, and pressing accuracy can be improved. 
   The top ends of the cushion pins  57  may directly contact the work W. 
   And, the slide section  13  and the lid section  14  of the wear plate  11  are not required to have a cylindrical shape, and the lid section  14  may have a diameter that is larger than that of the slide section  13 . 
   According to the fourth embodiment, the die cushion is configured to equalize the cushion pressure through the wear plate  11  having the elastic member  16  for producing the pushing force in the direction of the load receiving from the cushion pin  57  and its opposite direction, so that the hydraulic circuit for equalization is unnecessary, and the equalizing device has a very simple structure. Thus, the press machine production cost can be reduced. 
   As shown in  FIG. 16 , when a different cushion pressure is determined for the plural areas (D 1  to D 4 ) of the die, the main cushion pressure is determined by the cushion cylinder section  22  of the die cushion  20 , and a cushion pressure difference produced among the plural areas may be determined with an elastic modulus of the elastic members  6  of the individual wear plates  11  differentiated. Therefore, the press machine is desirably provided with a single die cushion, and the press machine production cost can be reduced. 
   Besides, the hydraulic circuit for equalization is unnecessary, so that oil stains, noise of hydraulic equipment, and the like are reduced, and the work environment at the work site can be improved. 
     FIG. 11  is a partially sectional side view of the load supporting device according to the fifth embodiment. 
   The fifth embodiment has plural slide sections  13  and lid sections  14  on a single plate section  12 . The slide section  13  and the lid section  14  are configured in the same way as in the fourth embodiment. 
     FIG. 12  is a partially sectional side view of the load supporting device according to the sixth embodiment. 
   The sixth embodiment uses a cylindrical rigid urethane  16 ′ as the elastic member. One end of the rigid urethane  16 ′ is fitted into a hole  12 ′ a  formed in a plate section  12 ′, and one end face of the rigid urethane  16 ′ comes into contact with the bottom of the hole  12 ′. Meanwhile, the other end of the rigid urethane  16 ′ is fitted into a hole  14 ′ a  formed in a lid section  14 ′, and the other end face of the rigid urethane  16 ′ comes into contact with the bottom of the hole  14 ′ a . In this state, a gap with a prescribed distance L 1  is formed between one end face of the lid section  14 ′ and one end face of the plate section  12 ′. The other end face of the lid section  14 ′ comes into contact with the cushion pin  57 . 
     FIG. 13  is a partially sectional side view of the load supporting device according to the seventh embodiment. 
   The seventh embodiment also uses a cylindrical rigid urethane  16 ′ as the elastic member in the same way as in the sixth embodiment, but an end face of the rigid urethane  16 ′ is in direct contact with the cushion pin  57  without mounting a lid section in the seventh embodiment. In this state, a gap with a prescribed distance L 1  is formed between the end face of the cushion pin  57  and one end face of the plate section  12 ′. The rigid urethane  16 ′ has a diameter that is smaller than that of the cushion pin  57 . But, the rigid urethane  16 ′ may have a diameter that is larger than that of the cushion pin  57 . In this case, it is not necessary to have a gap between the end of the cushion pin  57  and one end face of the plate section  12 ′. 
     FIG. 14  is a partially sectional side view of the load supporting device according to the eighth embodiment. 
   The eighth embodiment does not have the plate section  12  of the fourth embodiment, and the bolt member  15  is directly screwed in the die cushion pad  21 . The threaded portion  15   a  of the bolt member  15  is screwed in the screw hole  21   b  formed in the surface of the die cushion pad  21 . In this state, a gap with a prescribed distance L 1  is formed between an end face of the slide section  13  and a surface of the die cushion pad  21 . In this case, it is necessary to make the surface of the die cushion pad  21  rigid to a level adequate to prevent a hole from being formed by the contact with the slide section  13 . 
   The same effects as in the fourth embodiment can also be obtained by the fifth to eighth embodiments.