Abstract:
An extrusion press includes a means which can prevent phenomena in which a billet is blown out during an extrusion process as well as prevent billet blowout with a simple and inexpensive constitution. The extrusion press drives a main cylinder device to extrude, by a stem , a billet filled into a container from a die and form a product. A gap measurement means that measures a gap arising at the container seal surface formed by pressing the die side end surface of the container against the container side end surface of the die is provided on an end platen on the outer edge part of the container side end surface of the die. When the gap arising during the extrusion process is measured and the measured value is within a predetermined range of allowable values, a set value for the extrusion rate is lowered and a warning is issued. When the measured value exceeds the predetermined allowable values, the extrusion process is stopped.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention claims priority from, and incorporates by reference the entire disclosure of, Japanese Patent Application No. 2011-192212, filed on Sep. 5, 2011. 
     TECHNICAL FIELD 
     The present invention relates to an extrusion press which is used for extrusion of aluminum alloy etc. and a control method for an extrusion press, more particularly relates to an extrusion press which prevents leak out of metal from a gap between a container and die in the extrusion process and thereby improve the product yield and to a control method for such an extrusion press. 
     BACKGROUND ART 
     In a conventional extrusion press, provision is made for an end platen and a main cylinder device which are coupled by tie rods. At the end platen side, a container in which a billet is loaded is arranged across a die, while at a main cylinder device side, a stem is attached to a cross head which is driven together with a ram which is inserted into and withdrawn from this cylinder. Further, the stem is pushed under pressure toward the billet which is loaded in the container by the extrusion force of the main cylinder device whereby a product of a predetermined shape is extruded from the die. 
     In such an extrusion press, in the extrusion process, the length of the billet inside the container gradually becomes shorter, so it is usual that the extrusion action force becomes larger at the time of start of the extrusion process than at the time of end of the extrusion process. That is, even if the extrusion resistance of the die (required extrusion force) is constant, the frictional force between the container and the billet becomes smaller along with the decrease in the length of the billet, so overall the extrusion action force gradually ends up falling. 
     The change in the extrusion action force is due to the decrease in the frictional force between the billet and the inside walls of the container along with the billet length, but such a decrease in the extrusion action force causes a decrease in the container seal force with respect to the die. When the force falls below the seal force which prevents breakout of the billet, the billet ends up breaking out from the seal surface of the container and die in a so-called “blooming phenomenon”. This blooming phenomenon causes the product yield to drop and lowers the operating efficiency of the extrusion press due to the work of removing the residue from the seal surface. 
     For this reason, when the extrusion action force falls and becomes less than the seal force which prevents break out of the billet, a means which compensates for the drop in the extrusion action force which imparts the container seal force between the container and the die may be provided at the cross head so as to avoid break out of the billet. (See PLT 1.) 
     In this regard, since, in the above conventional type of extrusion press, to prevent break out of the billet, a means for compensating for the drop in extrusion action force is provided at the cross head, this led to enlargement of the facility and complication of the control and further resulted in a rise in the cost of manufacture of the facility. 
     CITATION LIST 
     Patent Literature 
     PLT 1: Japanese Patent Publication No. 4-274821A 
     SUMMARY OF INVENTION 
     Technical Problem 
     The present invention is made in order to solve the above problem and has as its object the provision of an extrusion press which can prevent the phenomenon of the billet breaking out during the extrusion process and which is provided with a simple and inexpensive configuration of a means for preventing break out of the billet and a control method for such an extrusion press. 
     Solution to Problem 
     To achieve the above object, according to a first aspect of the present invention, there is provided an extrusion press which drives a main cylinder device to extrude a billet which is loaded in a container from a die by a stem so as to form a product, the extrusion press characterized in that a gap measuring means for measuring a gap in an extrusion process which is formed at a container seal surface which is formed by pushing a die side end face of the container against a container side end face of the die is provided at an end platen of the outer edge of the container side end face of the die through an attachment member. 
     To achieve the above object, according to a second aspect of the present invention, there is provided a control method for an extrusion press which drives a main cylinder device to extrude a billet which is loaded in a container from a die by a stem to form a product, the control method is characterized by measuring a gap which is formed during an extrusion process at a container seal surface which is formed by pushing a die side end face of the container against a container side end face of the die, when the measured value is in a predetermined range of an allowable value, lowering a setting of an extrusion speed and emitting an alarm, and, when the measured value is over a predetermined allowable value, making the extrusion process stop. 
     Advantageous Effects of Invention 
     Since the invention is configured to measure a gap between a container end face and a die end face during the extrusion process, it is possible to detect this as compression strain of the die and possible to obtain a grasp of the behavior of the container in a state where the container seal surface is in action as a forewarning of a break out phenomenon of the billet. Further, a configuration which provides a means for measuring a gap between a container and a die at an end platen of an outer edge part of the container seal surface side of the die never invites increased size of the facility or higher cost. 
     Since the invention is configured to measure a gap between a container end face and a die end face to compare it with an allowable value, lower the extrusion speed and emit an alarm when it is in a range of the allowable value, and stop the extrusion process when exceeds the allowable value, the break out phenomenon of the billet never occurs. 
     For this reason, fall of the product yield due to loss of the material which accompanies break out or fall of the operating rate due to the facility stopping along with disposal of the broken out residue never occurs. 
     The present invention will become more clearly understood from the attached drawings and the explanation of preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view which shows the overall configuration of an extrusion press according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view which shows the configuration of a gap measuring means according to an embodiment of the present invention. 
         FIG. 3  is a cross-sectional view which shows principal parts of the gap measuring means which is shown in  FIG. 2 . 
         FIG. 4  is a cross-sectional view which shows the configuration of a gap measuring means according to another embodiment. 
         FIG. 5  is a cross-sectional view which shows principal parts of the gap measuring means which is shown in  FIG. 4 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The extrusion press device and control method for an extrusion press according to the present invention will be explained in detail with reference to the drawings. 
     As shown in  FIG. 1 , the extrusion press has an end platen  10  and a main cylinder device  12  arranged facing each other. The two are coupled by a plurality of tie rods  14 . At the inner surface side of the end platen  10 , a container  18  is arranged across a die  16  in which an extrusion opening is formed. The container  18  is loaded with a billet  20 . By pushing this toward the die  16 , a product of a cross-section corresponding to the die opening  16 A is extruded. 
     The main cylinder device  12  which generates an extrusion force is comprised of a main cylinder  12 A in which a main ram  12 B is housed. This can be moved toward the container  18  for extrusion. At a front end part of this main ram  12 B, a main cross head  22  is attached. At the center of this front surface, an extrusion stem  24  is attached in a state sticking out toward the container  18  so as to be arranged coaxially with a billet loading opening  18 A of the container  18 . 
     Therefore, if driving the main cylinder device  12  to make the cross head  22  advance, the extrusion stem  24  is inserted in the loading opening  18 A of the container  18  and the back end face of the loaded billet  20  is pressed to extrude a product  20 A. 
     Note that, at the main cylinder  12 A, a side cylinder device  26  is attached in parallel to an axial center of the extrusion press. A rod  26 A is coupled with the main cross head  22 . Due to this, as a preparatory process of the extrusion process, an extrusion stern  24  is made to initially move to a position which approaches a container  18  band an extrusion pressure operation is configured to be performed by both the main cylinder device  12  and side cylinder device  26 . 
     Further, the extrusion press is provided with a variable discharge type of hydraulic pump  30 . Through a hydraulic circuit  32 , discharge oil pressure is supplied to the main cylinder device  12  and side cylinder device  26 . 
     In this regard, during the extrusion process, the main cylinder device  12  and the side cylinder device  26  are used to perform an extrusion action, and the extrusion action force Fs is expressed by the sum of the required extrusion force Fa which acts on the die  16  and the billet frictional force Fb between the billet  20  and the container  18 . The billet frictional force Fb changes in proportion to the length of the billet  18  and is maximum at the time of extrusion start. As the extrusion process proceeds and the billet length becomes shorter, it decreases along with the extrusion action force Fs. 
     The billet frictional force Fb acts as the seal force of the die  16  and the container  18 , so if the billet frictional force Fb decreases too much, the seal force which prevents the billet  18  from leaking out (so-called “blooming phenomenon”) from the seal surface of the die  16  and the container  18  ends up falling. 
     In the extrusion press according to the present embodiment, as shown in  FIG. 2  and  FIG. 3 , a gap measuring means  60  for measuring the gap which is formed in the extrusion process at the seal surface which is formed by the die side end face of the container  18  and the container side end face of the die  16  abutting against each other is attached to the end platen of an outer edge part of the die  16  of the container side end face through an attachment member. 
     This gap measuring means  60  is basically comprised of a guide box  61  which is attached to a container side bottom surface of an upper gib  27  which is fastened to the end platen  10  so that its axial line becomes parallel to the extrusion direction, a gap measurement rod  62  which has a tip which abuts against a die side end face of the container  18 , which has another end which is provided to be able to slide inside the guide box  61 , and which has a stepped shaft shape, a coil spring  63  which is arranged inside the guide box  61  and which pushes the gap measurement rod  62  in the axial direction, and a displacement sensor  64  and fastening nut  65  for the displacement sensor. 
     The displacement sensor  64  which is used for the gap measuring means  60  is preferably an eddy current type or optical type or ultrasonic type or other noncontact type. In this embodiment, the gap measuring means  60  which is comprised by a single displacement sensor  64  is provided above the die  16  avoiding the shear blade which shears off the discharge, but it is also possible to provide a plurality of gap measuring means  60  and output their measured values as an average value. When providing a plurality of gap measuring means  60 , for example, one of the gap measuring means  60  is provided below the die  16 , a through hole is formed at the container seal surface side of the lower gib  28  which is shown in  FIG. 2 , and the means is attached buried in this. 
     As shown in  FIG. 3 , if the container  18  moves in the counter extrusion direction (right direction in figure) from the state where the end faces of the die  16  and container  18  abut, the gap measurement rod  62  is pushed by the coil spring  63  and moves in the counter extrusion direction linked with movement of the container. 
     l 0  is the gap between the displacement sensor  64  and the gap measurement rod  62 . It is the reference value of the measured gap which has as the minimum value the value after upset is completed and the die side end face of the container  18  and container side end face of the die  16  abut to form a container seal surface and which changes to expand in accordance with the decrease of the billet frictional force Fb which accompanies progress in the extrusion process. 
     l 1  is the allowable value of the gap with the die  16  which is formed when the seal force which prevents the billet  18  from leaking out from the seal surface between the die  16  and the container  18  during the extrusion process (so-called “blooming phenomenon”) falls and the container  18  retracts in the counter extrusion direction (separates from the die  16 ). 
     l 2  is the gap between the displacement sensor  64  and the gap measurement rod  62  when the container  18  retracts during the extrusion process and is the upper limit value of the measured gap comprised of the reference value of the measured gap l 0  and the allowable value l 1  added together at the time of start of extrusion by the die  16  and the container  18 . 
     Further, the gap measuring means  60  is used to measure the value of the reference value of the measured gap l 0  during the extrusion process and output it to the extrusion press device. When the measured value is in the range of the allowable value, the extrusion speed is controlled to a low speed to slow the flow of the material in the container and prevent leak out of the billet. 
     Next, the control method for the extrusion press which is configured in this way will be explained. The reference value of the measured gap l 0  is found by making the container  18  move forward to abut against the die  16 , making the extrusion stem  24  push against the billet  20 , detecting the gap at the advanced position of the container when the upset is completed, and storing this rewritten for each extrusion operation in the controller  36  of the extrusion press. Further, when replacing the die  16  or the container  18 , the reference value of measured gap l 0  is detected each time and is rewritten as new data. 
     The allowable value l 1  is set in the controller  36  in advance as a predetermined value. For example, the range of this value is set to an optimum value from 0.1 to 1.0 mm or multiplied by a ratio of 0.7 to 0.8 in range. 
     In the control method for an extrusion press of the present invention, when the gap between the container  18  and the die  16  is in the set range of the allowable value l 1 , the gap is kept from becoming larger by having the controller  36  perform control so as to output a signal through an amplifier  46  to the hydraulic pump  30  to lower the extrusion speed and emit an alarm. Further, when, even if controlling the extrusion speed, the gap between the container  18  and the die  16  exceeds the set range of the allowable value l 1 , the extrusion process is made to stop. 
     The gap measuring means  60  measures the gap between the container  18  and the die  16  in the extrusion process, calculates the rate of change, and controls the discharge of the hydraulic pump  30  in accordance with the calculated rate of change of the measured gap. 
     Further, in the control of the hydraulic pump, the gap between the die  16  and the container  18  may be set as a parameter and a means for controlling the extrusion speed to become slower in steps based on this parameter or means for increasing the extrusion speed in steps if the gap between the die  16  and the container  18  is reduced may be used. 
     In this way, in the control method for the present invention, it is possible to accurately measure the position of the container with respect to the container side end face of the die  16  so as to obtain a grasp of a forewarning of break out of the billet from the gap between the container  18  and the die  16  and lower the extrusion speed so as to prevent break out of the billet. 
       FIG. 4  and  FIG. 5  will be used to explain a gap measuring means according to another embodiment. As shown in  FIG. 4  and  FIG. 5 , a gap measuring means  60  for measuring the gap which is formed in the extrusion process at a seal surface which is formed by a die side end face of the container  18  and a container side face of the die  16  is provided at the outer edge part seal surface side of the die  16 . 
     This gap measuring means  60  is basically configured by a displacement sensor  64  which is attached to the container side end face of an upper gib  27  which is fastened to the end platen  10  so that its axial line becomes parallel with the extrusion direction and a fastening nut  65  for the displacement sensor, a fixed shaft  67  which is screwed into a die side end face of the container holder  19 , is attached so that its axial line becomes parallel with the extrusion direction, and is made a stepped shaft shape, a gap measurement plate  66  which has a bottom end which abuts against a seal surface side end face of the container  18  and which has another end which is provided able to be guided by the fixed shaft  67 , and a coil spring  63  which is arranged inside of the gap measurement plate  66 , is clamped by another end of the fixed shaft  67 , and moves pushing in the axial direction. 
     The displacement sensor  64  which is used for the gap measuring means  60  is preferably an eddy current type or optical type or ultrasonic type or other noncontact type. In this embodiment, a gap measuring means  60  which is configured by a single displacement sensor  64  is provided away from the shear blade which shears off the discard above the die  16 , but it is also possible to provide a plurality of gap measuring means  60  and output their detection values as an average value. 
     The relationship among the reference value of measured gap l 0 , allowable value l 1 , and upper limit value of measured gap l 2  and the control method for an extrusion press in accordance with the data of the measured gap are based on the explanation of the above  FIG. 2  and  FIG. 3 . 
     In the gap measuring means  60  of the present invention, rather than directly attaching the gap measurement rod  62  and the gap measurement plate  66  to the container  18 , the gap from the displacement sensor  64  is measured. Being configured in this way, when replacing the container  18 , it is possible to do so without detaching the gap measurement rod  62  and the gap measurement plate  66 , so it is possible to perform the work of replacing the container  18  efficiently. 
     The gap measurement rod  62  and the gap measurement plate  66  are pushed at one end by the coil spring  63  against the die  16  side end face of the container  18 , so even if the container  18  moves to the counter extrusion direction to separate from the die  16 , that gap can be reliably measured. 
     The reference value of measured gap l 0  is found in advance by for example using Siebel&#39;s formula to calculate the required extrusion force Fa which acts on the die  16 , which fluctuates during the extrusion process for each product, and the billet frictional force Fb between the billet  20  and the container  18  and storing them in the controller  36 . Further, it is possible to use the data which is set during extrusion as the basis to find l 0  and l 2  in real time and compare them with actually measured data to thereby prevent break out of the billet in a control routine. 
     Further, the gap measuring means  60  may be configured to detect a reference value of the measured gap l 0  (minimum value) for each extrusion process, compare it with the measured gap at the immediately preceding extrusion process (minimum value), and judge that there is an inclusion at the abutting surfaces of the container  18  and the die  16 , for example, discard, when the compared value is larger than a predetermined value. With this configuration, residue at the abutting faces of the container  18  and the die  16  can be detected before the start of extrusion and break out of the billet due to residue can be prevented during the extrusion process, so it is possible to improve the operating rate of the extrusion press. 
     As explained above, in the extrusion press device and control method for extrusion press device of the present invention, it is possible to prevent break out by a simple, inexpensive means without compensating for the extrusion force to prevent break out of the billet and thereby increasing the container seal force. 
     Further, it is possible to eliminate interruptions in the extrusion process due to breakout of the billet and to improve the product yield and operating rate. 
     The present invention is explained by reference to specific embodiments selected for the purpose of explanation, but it will be clear to a person skilled in the art that a large number of modifications are possible without departing from the basic idea and scope of the present invention. 
     Reference Signs List 
       10  end platen 
       12  main cylinder device 
       16  die 
       18  container 
       20  billet 
       20 A product 
       24  stem 
       60  gap measuring means 
       61  guide box 
       62  gap measurement rod 
       63  coil spring 
       64  displacement sensor 
       65  fastening nut 
       66  gap measuring plate 
       67  fixed shaft 
     l 0  reference value of measured gap 
     l 1  allowable value 
     l 2  upper limit value of measured gap