Patent Publication Number: US-6662619-B1

Title: Mold clamping device for pressing machine

Description:
TECHNICAL FIELD 
     The present invention relates to a mold clamping device for a pressing machine in which a plate material is subjected to bending or other working between upper and lower mold sections clamped against each other. 
     BACKGROUND ART 
     Various forms of pressing machines for bending plate materials are known. Where a plate material is to be bent by a blade for upper and lower molds being clamped against each other, the blade tends to exert a large force to the plate material, leading to a deviation therein. If the upper mold is pressed against the lower mold by a linearly straight force from a hydraulic cylinder or from a simple conversion of the rotation of a motor, a very large power is required. The main body of the pressing machine supporting these power sources will be subjected to overload. 
     The inventors have found the technical problems inherent in the proposed mold clamping device, improved it to overcome the problems and came up with the present invention. 
     First of all, the technical problems raised by our previously proposed mold clamping device will be described in connection with FIG.  5 . 
     The mold clamping device shown in FIG. 5 has a main frame  50  which comprises a lower frame portion  51  having a lower mold  53  and an upper frame portion  52  having an upper mold  54 . The lower and upper frame portions  51 ,  52  are pivotally connected to each other at the rearward ends through a pivot shaft  55 . The lower and upper frame portions  51 ,  52  are also connected to each other at their forward ends through an arch-type thick spring  56 . Thus, the structure thereof necessarily becomes complicated. And yet, the arch-type thick spring  56  causes the whole height of the mold clamping device to increase since the arch-type thick spring  56  must be curved rearwardly to an increased extent such that it will not interfere the plate bending action in the pressing machine. In addition, the arch-type thick spring  56  is a bulky metal working matter, for example, having a thickness of 15 cm and a width of 20 cm in cross-section since it must provide a strong and instantaneous force. This not only increases the manufacturing cost, but also requires a huge driving energy for moving the upper frame portion together with the arch-type thick spring. This additionally raises a poor response in power transmission. 
     A crank mechanism  58  for driving the arch-type thick spring  56  is provided on the upper frame portion at the top thereof. The upper end of the arch-type thick spring  56  is connected with a crank pin  60  in the crank mechanism  58  while the bottom end thereof is supported by another pin  61 . 
     In such an arrangement, the crank mechanism will provide an opening force for elongating the arch-type thick spring. A closing spring force for depressing a holding ram  62  is created from a reactive force associated with the resilient opening deformation of the arch-type thick spring. However, the arch-type thick spring  56  highly restricts the amount of resilient deformation. It is thus difficult that the clamping force is regulated into the desired level. 
     For such a reason, the length of the arch-type thick spring needs to be increased. As a result, its point of action  60  will positioned upward from the upper frame portion, so that a forward thrusting force P will act on the holding ram  62  in association with the structure of opening/closing frame  1 . This may destabilize the engagement between the upper and lower molds. 
     Even in the regulation of clamping force, the mold clamping device hardly accommodates the change in the set height of the holding ram, for example, due to mold exchange or corrective grinding since the amount of resilient opening deformation in the arch-type thick spring is smaller, that is, the range of track using the clamping force in the crank pin  60  is smaller. 
     Moreover, the upper mold must be replaced by another mold when it is to change the plate bending process or the shape of the product. This is very troublesome in operation. To facilitate such an operation, a shaped mold such as a rounded mold  21  may be placed on the upper mold  54 . To accomplish this, the height of the holding ram  52  must greatly be changed. However, this operation is very difficult since the holding ram  62  must be moved up and down with the opening/closing motion of the upper frame portion  52 , rather than the independent movement of the holding ram  62  itself. In addition, when any shaped mold is mounted on the upper mold  54 , a deviation tends to create in the engagement between the upper and lower molds  54 ,  53  since the upper mold  54  mounted on the holding ram  62  will be moved up and down along a circular track R about the pivot pin  55 . To overcome such a deviation, the mold clamping device must be designed and regulated in an extremely delicate manner. 
     DISCLOSURE OF THE INVENTION 
     An object of the present invention is therefore to provide a mold clamping device for a plate bending pressing machine, which is of a simple structure with a low manufacturing cost, is superior in saving the energy, provides an accurate and stable clamping operation and has an improved operability. 
     To this end, the present invention provides a mold clamping device comprised in a plate bending pressing machine including a main frame having an integral structure, upper and lower molds between which a plate material is inserted and the upper mold being pressed against the lower mold to bend the plate material, comprising: 
     a vertically movable holding ram for holding the upper mold; 
     at least a pair of left and right arch-type thick springs vertically mounted on an upper half of the main frame; 
     a crank mechanism being connected with each of upper portions of the arch-type thick springs through a crank pin and creating a rotational force at a position near a dead center on each of the crank pins, 
     wherein the rotational force of the crank mechanism compresses the arch-type thick springs to produce a resilient force which presses the upper mold against the lower mold. 
     In such an arrangement, the crank mechanism is actuated to lift the holding ram together with the arch-type thick springs for opening the upper mold. When the upper mold is opened, a plate material is inserted into the machine. The crank mechanism is then re-actuated to lower the holding ram together with the arch-type thick springs for closing the upper mold. At this point, the arch-type thick springs are largely compressed near the dead centers of the crank pins. Therefore, the plate material may be clamped against the lower mold under an appropriate resilient force with flexibility but without being stiffened. Furthermore, since the holding ram is moved in the vertical direction, the upper mold may be accurately and stably engaged with the lower mold regardless of the height thereof. 
     The pressing machine of the present invention may comprise a C-shaped main frame having an opening, upper and lower molds located within the opening, a blade drive located in the lower half of the main frame and a blade for bending the plate material clamped between the upper and lower molds when driven. In such an arrangement, when the blade is to bend the plate material, the upper mold is clamped by the resilient force from the arch-type thick springs. Thus, a little deviation is created in the plate material. This provides stable bending with improved dimensional precision. The holding ram may include a bracket extending therefrom. If a displacement crank mechanism using the pins connecting the arch-type thick springs to the holding ram as crank pins is mounted on the bracket, the upper mold can be mounted and used when the holding ram is lifted by the displacement crank mechanism. The holding ram is slidably and vertically held on guide rails on the main frame through guide blocks. 
     According to the present invention, the upper portion of the integral main frame structure can include relatively small arch-type thick springs. Thus, the present invention may provide a simple and inexpensive structure with less energy. Since the crank mechanism vertically drives the upper mold holding ram through the arch-type thick springs to compress them, the compressed arch-type thick springs creating the resilient force for clamping the molds, the clamping process can be quickly carried out with accuracy and stability. In addition, the displacement crank mechanism using the pins connecting the arch-type thick springs to the holding ram as crank pins can provide advantages in that the machine can properly accommodate changes and modifications of the mold and improve the operability. In the aforementioned structure of the crank mechanism, the displacement crank mechanism located on the bottom of the arch-type thick springs may be used for clamping the upper mold while the crank mechanism on the top end thereof may be used to displace the upper mold for mounting a shaped mold thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a plate bending pressing machine according one preferred embodiment of the present invention; 
     FIG. 2 is an enlarged side view of the main parts in the mold clamping device of the plate bending pressing machine; 
     FIG. 3 is a front view of the plate bending pressing machine; 
     FIG. 4 is an enlarged side view of the primary parts of the pressing machine when a shaped mold is mounted therein; and 
     FIG. 5 is a side view of a pressing machine according to the prior art. 
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     The present invention will be described in connection with the work of plate material as shown in the accompanying drawings. 
     Referring to FIG. 1, a plate bending pressing machine comprises a main frame  1  having an integral structure including side plates  3 . The main frame  1  also includes an intermediate opening  5  into which a plate material W is to be inserted. The upper half of the main frame  1  above the opening  5  includes a mold clamping device A including a pair of left and right arch-type thick springs  6 . The lower half of the main frame  1  below the opening  5  includes a drive B for a blade  7 . When an upper mold  8  clamps the plate material W against a lower mold  9  through the mold clamping device A, the plate material W is bent into a predetermined shape by the blade  7 . The blade  7  has vertically bifurcated configuration so that the plate material W can be bent easily in both forward and backward directions. 
     The mold clamping device A includes a crank mechanism  10  which includes a crank shaft  11  rotatably mounted on the upper end of the main frame  1  at an upper position of the opening  5 . The mold clamping device A also includes a bracket  15  located below the crank shaft  11  and laterally extending from a holding ram  13  and a pair of left and right arch-type thick springs  6  each of which connects between a crank pin  17  and each of the brackets  15 . The lower end of each of the arch-type thick springs  6  is connected with the corresponding bracket  15  through a pin  18 . The holding ram  13  is supported for vertical movement, by so-called LM guide rails  20  on the main frame  1  through guide blocks  22  on the holding ram  13 . 
     The trajectory of movement in the crank pins  17  is as shown by one-dot-chain line. A servomotor  19  having a reduction gear rotatably drives the crank pins  17  to move the arch-type thick springs  6  in the vertical direction. Thus, the holding ram  13  is vertically moved to open or close the upper mold  8 . When the upper mold  8  is opened, the plate material W is inserted into the opening  5 . The crank pins  17  are then rotated in the downward direction to close the upper mold  8 . At a position near the bottom dead center, an additional pressure is created to compress the arch-type thick springs  6  so as to produce a resilient, stable and strong force by which the upper mold  8  clamps the plate material W against the lower mold  9 . 
     At this point, it is assumed that the holding ram  13  has height L. In this embodiment, furthermore, a displacement crank mechanism  23  is mounted on each of the brackets  15  and moves the holding ram  13  to an upward position M for mounting a shaped mold  21  on the underside of the upper mold  8 . Each of the displacement crank mechanisms  23  includes a servomotor  25  with a reduction gear for driving it. Each of the displacement crank mechanisms  23  also includes a crank shaft  27  rotatably driven by the servomotor  25 . The connection pin  18  in each of the arch-type thick springs  6  functions as a crank pin in the corresponding displacement crank mechanism  23 . As the crank pins  18  are at or near its top dead center, the shaped mold  21  is used. 
     Automatic mounting devices  29  are used to mount the shaped mold  21 . Each of the automatic mounting device  29  comprises a vertically movable slider  31 , an arm  33  for mounting the shaped mold  21  and an air cylinder  35  for driving the arm  33  invertedly. The shaped mold  21  has a rounded working face which cooperates with the blade  7  to bend the plate material W into the desired rounded form. Since the shaped mold  21  is moved in the vertical direction without outwardly deforming the holding ram  13 , the shaped mold  21  can uniformly and accurately be pressurized against the lower mold  9  by simply parallel working the top and bottom faces of the shaped mold  21 . 
     The drive B for the blade  7  is in the form of a linkage comprising a drive link  37  extending substantially in X-axis direction and another drive link  39  extending in Y-axis direction and coupled with the drive link  37 . Each of the links  37  and  39  is driven by any suitable crank mechanism. Reference numeral  40  denotes an automatic control box. 
     INDUSTRIAL APPLICABILITY 
     As described, the mold clamping device in the pressing machine according to the present invention is particularly effective for various bending fields such as forward bending and backward bending. Nevertheless, the mold clamping device can similarly be used to perform highly accurate bending directly using the upper and lower molds as for example when a V-shaped bending is to be carried out by using a lower mold having a V-shaped groove and an upper mold of V-shaped wedge configuration.