Abstract:
A double action extrusion press has: a main crosshead provided freely movable with the application of pressure in an axial direction by a main cylinder and having a pressing system disposed on the tip thereof; and a piercer cylinder built into the main cylinder and provided within the main ram, allowing a mandrel to slide within the pressing system and the main crosshead. The double action extrusion press complements the extrusion force by force equivalent to a mandrel pull force acting on a mandrel stop rod by affixing the piercer cylinder in contact to a piercer crosshead that is joined with the mandrel stop rod and applying hydraulic force to the rod side of the piercer cylinder.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a double action extrusion press which applies hydraulic pressure to a rod side of a piercer cylinder which is attached inside a main ram to thereby supplement an extrusion force to counter a mandrel pull force which acts on a mandrel stop rod. 
       BACKGROUND ART 
       [0002]    In the past, for example, in a known configuration, an extrusion press which uses copper, aluminum, or their alloys etc. to extrude tubular shaped products by double action extrusion comprises a cylinder platen and end platen which are arranged facing each other. The cylinder platen is provided with a main cylinder, main ram, pressure stem, and mandrel. The end platen is provided with a die. A container is provided between the pressure stem and the die so as to be able to advance and retract by a container cylinder. 
         [0003]    The pressure stem, which has a dummy block arranged at its front end, has been attached through a main cross head to a main ram which is assembled in the main cylinder which is provided at the cylinder platen. At a center position of the pressure stem, a mandrel is arranged to be able to advance and retract accompanying the pressure stem together with the piercer cylinder rod. Further, the die has been attached to the end platen facing the pressure stem. 
         [0004]    Between the pressure stem and the die, the container has been arranged to be able to advance and retract. In the container, a billet has been held. The pressure stem moves the billet which is held in the container to the die side whereby the billet is pushed and upset is completed. After upset, the mandrel advances and the billet is pierced. The mandrel stops at a predetermined advancing position in the die and the pressure stem again advances, whereby the billet is extruded as a tubular shaped product by double action extrusion. 
         [0005]    In a double action of extrusion press, the front end part of the mandrel is made to stop at a predetermined position of the bearing part of the die to extrude the product. At that time, even if the relative positions of the mandrel and the bearing part of the die are pulled by the product, the mandrel position is held so that the stop position does not shift. 
         [0006]    PLT 1 discloses a double action type of extrusion press where a piercer cylinder which is provided inside the main cylinder and a stop fastener which detaches from the axial center of the extrusion press to forcibly couple with the mandrel are provided. The stop fastener acts on a hydraulic pilot valve to start the supply of a certain amount of the pressurized oil medium to the rod side chamber of the piercer cylinder so as to hold a predetermined axial direction position (stop position) of the bearing part of the die. The supply of the pressurized oil medium is made to match the increase in volume of the piercer cylinder rod side chamber when the mandrel stops and the main ram advances during control to hold the position. 
         [0007]    In this regard, the conventional type of double action extrusion press is designed to mechanically switch the hydraulic pilot valve through the stop fastener and connecting rod to supply a certain amount of pressurized oil medium to thereby hold the mandrel at a predetermined position of the bearing part of the die, so a delay occurs in control of exactly the stroke of movement corresponding to the land of the spool of the hydraulic pilot valve, and the front end part of the mandrel moves back and forth by several millimeters with respect to a predetermined stop position during extrusion. 
         [0008]    For this reason, variation occurred in the thickness of the extruder tubular shaped product and a stable quality of tubular shaped product could not be obtained. 
         [0009]    Furthermore, in a conventional double action extrusion press, there is the following problem: 
         [0010]    When pushing a billet into the container by the pressure stem, then upsetting the billet and piercing the inside of the billet by the mandrel, then extruding the billet by a fixed mandrel, frictional force occurs between the billet and the mandrel surface and a pull force acts on the mandrel during extrusion. Due to this, the extrusion force which acts on the die decreases by that amount and the extrusion force could not be effectively utilized at the start of extrusion when the required extrusion force is most necessary. 
       CITATIONS LIST 
     Patent Literature 
       [0011]    PLT 1: Japanese Patent Publication No. 49-26188B2 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0012]    The present invention is made in consideration of the above conventional problem and has as its object the provision of a double action extrusion press which supplements the extrusion force which falls due to the mandrel pull force which acts during extrusion due to the frictional force which occurs between the billet and mandrel surface by using a piercer cylinder which is fastened to a piercer cross head. 
       Solution to Problem 
       [0013]    The double action extrusion press according to a first aspect of the present invention is a double action extrusion press comprising a main cross head adapted to be able to be pushed in an axial direction by a main cylinder and having a pressure stem at its front end, and a piercer cylinder adapted to slide a mandrel in the pressure stem and the main cross head and being provided in a main ram which is built into the main cylinder, wherein the piercer cylinder is fixedly connected to a piercer cross head which is connected with mandrel stop rods, and wherein an extrusion force is supplemented by applying hydraulic pressure to a rod side of the piercer cylinder so as to counter the mandrel pull force which acts on the mandrel stop rods. 
         [0014]    In the present invention, the double action extrusion press further comprises a means for detecting the mandrel pull force which acts on the mandrel stop rods and controls the hydraulic pressure at the rod side of the piercer cylinder to become a hydraulic pressure of a predetermined force corresponding to the mandrel pull force which is detected by the means to thereby supplement the part of the extrusion force which is lost as the mandrel pull force. 
         [0015]    In the double action extrusion press of the present invention, mandrel cylinders which drive a mandrel which is fastened with a piercer cross head may be used to position the front end part of the mandrel at the bearing part of the die which determines the size of the tubular shape by making an advancing limit of the mandrel cylinder the positioning of the mandrel. 
         [0016]    In the double action extrusion press of the present invention, the mandrel cylinders may be fastened to the outer circumference of the main cylinder. 
         [0017]    In the double action extrusion press system of the present invention, the piercer cross head which is fastened to the mandrel stop rod can move inside the main cross head. 
         [0018]    In the double action extrusion press system of the present invention, the piercer cylinder and the mandrel cylinder rods may be fastened to the piercer cross head. 
         [0019]    In the double action extrusion press system of the present invention, a variable discharge type hydraulic pump is preferably used to enable adjustment of the amount of oil of the piercer cylinder. 
       Advantageous Effects of Invention 
       [0020]    The mandrel cylinder rods are connected to the piercer cross head which operates to be able to freely slide inside the main cross head. Furthermore, the mandrel cylinders are fastened to the main cross head, so if making hydraulic pressure act on each rod side of the mandrel cylinders, a force acts making the piercer cylinder retract. A counter force acts on the main cross head and the load is propagated to the front end of the pressure stem to extrude the billet. 
         [0021]    For this reason, a larger extrusion force than the past acts on the pressure stem during extrusion and therefore a thin tubular shaped product or long billet which could not be extruded in the past can be extruded. Further, even if extruding extruded products of the same tube diameter, it becomes possible to extrude them by a small sized double action extrusion press. For this reason, it is possible to improve the productivity and save energy or save labor. 
         [0022]    A means is provided for detecting the mandrel pull force which acts on the mandrel stop rods when the pressure stem pushes the billet to move in the extrusion direction. The hydraulic pressure at the rod side of the piercer cylinder is controlled to a hydraulic pressure of a predetermined force corresponding to the mandrel pull force which is detected by this means so as to make up for the part of the extrusion force which is lost as mandrel pull force, so even if the extrusion force fluctuates during the extrusion operation, there is no need to adjust the pressure or amount of feed of the working oil which is supplied to the piercer cylinder each time and the operability can be improved. Below, the present invention will be able to be better understood from the attached drawings and description of a preferred embodiment of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS  
         [0023]      FIG. 1  is a cross-sectional view of an elevation which shows an outline of a double action extrusion press of the present invention. 
           [0024]      FIG. 2  is a cross-sectional view of a front view which shows an outline of a double action extrusion press of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Below, a double action extrusion press  10  according to the present invention will be explained with reference to  FIG. 1 . 
         [0026]    As shown in  FIG. 1 , the extrusion press  10  comprises an end platen  11  and a cylinder platen  15  arranged facing each other. The end platen  11  is provided with a die  12 , while the cylinder platen  15  is provided with a main cylinder  25 , main ram  24 , main cross head  23 , and pressure stem  22 . Between the end platen  11  and the cylinder platen  15 , there is a container  13  which can advance and retract by a not shown container cylinder which is arranged at the end platen  11 . 
         [0027]    The pressure stem  22  is attached to the main ram  24  which is assembled in the main cylinder  25  which is provided at the cylinder platen  15  through the main cross head  23 . At a center position of the pressure stem  22 , a mandrel  31  is attached through a sub mandrel  32  and mandrel holder  39  to a piercer cross head  33  and is arranged to be able to advance and retract freely accompanying the pressure stem. The die  12  is provided at the end platen  11  facing the pressure stem  22 . 
         [0028]    Further, a billet  14  is supplied between the die  12  and the container  13  which moves to the cylinder platen  15  side together with a dummy block  21  by a not shown billet loader. Alternatively, in order to enable smooth supply of the billet  14 , after only the billet  14  is inserted into the container  13  and the pressure stem  22  is retracted, the dummy block  21  may be moved to the center of the extrusion press by a not shown dummy block supply device and inserted into the container  13 . 
         [0029]    At the main cylinder  25 , mandrel cylinders  38  are fastened. At mandrel stop rods  37  of the mandrel cylinders  38 , the piercer cross head  33  is attached and is arranged to be able to freely advance and retract inside of the main cross head  23 . 
         [0030]    Furthermore, at the piercer cross head  33 , a piercer cylinder rod  35  is attached via a connecting part  34 . Further, a piercer cylinder  36  is attached inside of the main ram  24  by bolting or other fastening to the main cross head  23 . 
         [0031]    Next, the operation of the double action extrusion press  10  will be explained. A billet which is carried on a not shown billet loader is positioned at the center of the container, then the main ram  24  is made to advance to insert the billet in the container  13  in the state where front end of the pressure stem  22  is made to contact the end face of the dummy block  21 . Next, the pressure stem  22  is made to retract once, then pressurized oil is introduced to each head side of the mandrel cylinders  38  and the billet is pierced while making the mandrel  31  advance. The front end of the mandrel  31  is made to stop and be held at a predetermined position of the bearing part of the die  12 . 
         [0032]    At this time, pressurized oil is applied to the head side so that the mandrel stop rods  37  of the mandrel cylinders  38  become the advancing limit whereby the mandrel  31  is prevented from shifting in position even in the later extrusion process. 
         [0033]    Further, the length of the mandrel stopper rod  37  can be freely adjusted by a mandrel stopper device  42 . Accordingly, even if the die  12  changes in size and the bearing part changes in position, the front end of the mandrel  31  can be fixed in position. 
         [0034]    After the above operation is performed, the pressure stem  22  is made to advance to start the extrusion. 
         [0035]    After the extrusion ends, the pressure of the pressurized oil which pushes the main ram  24  to the advancing side is lowered, pressurized oil is made to act on the piercer cylinder  36  and mandrel cylinders  38  at the rod side port to make the mandrel  31  retract, and pressurized oil is supplied to the rod side of the side cylinder  27  and the ram cylinder body  25  to make the main cross head  23  and pressure stem  22  retract. Further, the container is made to separate from the die  12 , and a not shown shear device is used to cut off a discard. Then, the dummy block  21  is unloaded from the press by a not shown dummy block recovery device and the press is newly supplied with a not shown dummy block at the press center by a loading device to prepare for the next extrusion operation. 
         [0036]    After this, the container  13  is again made to advance to make it abut against the die  12 , a billet is supplied to an intermediate position of the container  13  and the pressure stem  22  to insert the billet in the container  13 , then the above operation is repeated. 
         [0037]    The function of the piercer cylinder  36  which supplements the extrusion force to counter the mandrel pull force in the above such double action extrusion press will be explained with reference to  FIG. 1 . 
         [0038]    If starting extrusion, the frictional force between the inside walls of the billet  14  and the mandrel  31  will cause a pull force to act on the mandrel  31  in the extrusion direction. There is a loss of extrusion force of exactly the amount of this force. If applying pressurized oil to the rod side  40  of the piercer cylinder  36  which is fastened at the inside of the main ram  24  against this pull force, a force F will act on the piercer cylinder rod  35  in the counter-extrusion direction and, simultaneously, a force F will act on the main cross head  23  as reaction force in the extrusion direction. 
         [0039]    This force F acts on the main cross head  23  in the extrusion direction, so the load is propagated to the pressure stem  22  at its front end and the force F is added to this extrusion force whereby the extrusion force is increased. 
         [0040]    The method of control of the piercer cylinder which supplements the extrusion force to counter the mandrel pull force explained above will be explained with reference to  FIG. 1 . 
         [0041]    The pull force which acts on the mandrel  31  is propagated as load to the sub mandrel  32 , sub mandrel holder  39 , and piercer cross head  33 , so a tension force acts in the extrusion direction of the mandrel cylinder stop rods  37 . This tension force is detected by a load sensor  50 , then the obtained signal is amplified by an amplifier  51 , then a controller  52  converts the force to pressure and controls the pressure of a proportional solenoid relief  55 . The pressurized oil which is sent from a variable discharge type hydraulic pump  56  is sent to the rod side  40  of the piercer cylinder  36  by a pressure value of the pressure setting of the proportional solenoid relief  55  after a solenoid valve  53  is turned ON (in  FIG. 1 , the ON state shown). For example, the pressure value of the oil is 31 MPa etc. at the time of start of extrusion. Due to this pressurized oil, it is possible to increase the extrusion force. 
         [0042]    In summary, the pressure setting valve is changed in setting in accordance with a predetermined hydraulic pressure to set the initial pressure right after extrusion. During extrusion, the mandrel pull force is constantly detected while the pressure is controlled so that the above value becomes close to zero to thereby prevent a drop in the extrusion force acting on the die due to the mandrel pull force and enable a predetermined extrusion force to act on the die at all times. 
         [0043]    Next, the position of the front end of the mandrel  31  will be explained. 
         [0044]    The front end of the mandrel  31  is positioned through the sub mandrel  32 , sub mandrel holder  39 , piercer cross head  33 , and mandrel stop rods  37  by the mandrel cylinders  38 . The mandrel cylinders  38  are fastened to the cylinder platen  15 , while the cylinder platen  15  is fastened by not shown tierods to the end platen  11 . The die  12  is placed at the end platen  11 , so the position of the front end of the mandrel  31  is determined by the mandrel cylinders  38 . Furthermore, when the mandrel stop rods  37  are positioned at the advancing limit in the extrusion direction, it matches in position with the bearing part of the die  12 . 
         [0045]    Furthermore, by adjusting a screw of the mandrel stopper device  42 , it is possible to finely adjust the position of the front end of the mandrel  31  to match with the lengths of various mandrels  31 . 
         [0046]    In the above-mentioned embodiment of the present invention, the configuration of a conventional press of a direct double action extrusion press is explained, but the invention is not limited to this configuration. It may also be configured as a front loading pressure of a direct double action extrusion press or an indirect double action extrusion press. 
         [0047]    As explained above, the double action extrusion press of the present invention detects the pull force which acts on the mandrel and supplies pressurized oil, set in pressure so that the extrusion force which has been reduced by that pull force becomes a hydraulic pressure of a predetermined corresponding force, to the rod side of the piercer cylinder by a variable discharge type hydraulic pump to thereby supplement the extrusion force, so it becomes possible to extrude thin tubular shaped products or long size billets which could not be extruded in the past, it becomes possible to reduce the size of a double action extrusion press, and it becomes possible to improve the productivity and achieve energy savings and labor savings. Further, even if the extrusion force fluctuates during the extrusion operation, there is no need to adjust the pressure or amount of feed of the working oil which is supplied to the piercer cylinder each time and therefore the operability can be improved. 
         [0048]    Furthermore, there are the effects that it becomes possible to accurately position the front end of the mandrel, there is no longer a need to adjust the working oil or amount of oil each time, and the operability is improved. 
         [0049]    Note that, the present invention was explained in detail based on a specific embodiment, but a person skilled in the art could make various changes, corrections, etc. without departing from the claims and concept of the present invention. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           11  end platen 
           12  die 
           14  billet 
           15  cylinder platen 
           22  pressure stem 
           23  main cross head 
           24  main ram 
           26  side cylinder rod 
           27  side cylinder 
           31  mandrel 
           32  sub mandrel 
           33  piercer cross head 
           35  piercer cylinder rod 
           36  piercer cylinder 
           37  mandrel stop rod 
           38  mandrel cylinder 
           50  load sensor 
           51  amplifier 
           52  controller 
           55  proportional solenoid relief 
           56  variable discharge type hydraulic pump