Patent Publication Number: US-2022234112-A1

Title: Machine tool and machining method

Description:
TECHNICAL FIELD 
     This disclosure relates to machine tool and machining method. 
     BACKGROUND 
     A machine tool for joining two workpieces is known in the art (see, for example, JP 2010-269364 A1 (PTL 1)). 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2010-269364 A1 
     SUMMARY 
     Technical Problem 
     There is known a machine tool that is provided with a support portion for guiding a workpiece that projects from the spindle. In such machine tool, when machining a joined workpiece in which two workpieces are joined to each other, if the two workpieces are eccentrically joined, there may be a situation where the joint portion cannot be passed through the support section and, thus, the machining cannot be carried out smoothly. 
     The present disclosure has been made in view of the abovementioned problem, and it is an object of the present disclosure to provide a machine tool and a machining method that are capable of smoothly carrying out machining even when the joined workpiece is eccentrically joined with each other. 
     Solution to Problem 
     According to a first aspect of the present disclosure, there is provided a machine tool comprising a grip section for gripping a joined workpiece having a joint portion between two workpieces, and a support section for supporting the joined workpiece gripped by the grip portion, wherein the joined workpiece is supported by the support section at an inner peripheral surface having a predetermined width, and rotated by the grip section for machining. The machine tool is characterized in that it further comprises: a joint portion processing control means for controlling the processing of the joint portion in the joined workpiece such that a first workpiece, as one of the workpieces forming the joined workpiece, is gripped by the grip section with the joint portion of the joined workpiece projecting from the support section, and a predetermined region extending from the joint portion of the joined workpiece toward a second workpiece, as the other of the workpieces forming the joined workpiece, is processed over a range of not less than the predetermined width, to have an outer diameter of not more than an outer diameter of the first workpiece; and a movement control means for controlling the movement of the joined workpiece so as to slidingly move the joined workpiece relative to the support section, from a state in which the first workpiece is supported by the support section, up to a state in which the second workpiece is supported by the support section. 
     Preferably, the machine tool according to the first aspect of the present disclosure with the abovementioned constitution further comprises a guide bush provided with the support portion in the above configuration. 
     Preferably, the machine tool according to the first aspect of the present disclosure with the abovementioned constitution further comprises two spindles facing each other, including a spindle having the grip section and a further spindle different from said spindle; and a joining control means for controlling joining of the two workpieces such that the two workpieces are gripped by the two spindles one by one to form the joined workpiece. 
     According to a second aspect of the present disclosure, there is provided a machine tool comprising an openable and closable grip section for gripping a joined workpiece having a joint portion between two workpieces, and a workpiece supply unit for gripping a first workpiece as one of workpieces forming the joined workpiece, with the joint portion projecting from the grip section joined workpiece, and moving the joined workpiece so as to be drawn into the grip section in its open state, wherein the joined workpiece drawn by the workpiece supply unit is gripped and processed at an inner peripheral surface of the grip section having a predetermined width. The machine tool is characterized in that it further comprises: a joint portion processing control means for controlling the processing of the joint portion in the joined workpiece by gripping the first workpiece by the grip section with the joint portion projecting from the grip section, and machining a predetermined region extending from the joint portion of the joined workpiece toward a second workpiece, as the other of workpieces forming the joined workpiece, over a range of not less than said predetermined width, to have an outer diameter of not more than an outer diameter of the first workpiece; and a movement control means for controlling the movement of the joint portion workpiece so as to be gripped by a portion and slidingly moved relative to the grip portion, by gripping the joined workpiece by means of the workpiece supply unit, of which the joint portion has been processed by means of the joint portion processing control means, and slidingly move the joined workpiece relative to the grip section, until the second workpiece projecting from the grip section in the open state is received in the grip section. 
     According to the present disclosure, there is also provided a machining method using a machine tool that comprises a grip section for gripping a joined workpiece having a joint portion between two workpieces, and a support section for supporting the joined workpiece gripped by the grip portion, wherein the joined workpiece is supported by the support section at an inner peripheral surface having a predetermined width, and rotated by the grip section for machining. The machining method according to the present disclosure comprises a joint portion processing control step for controlling the processing of the joint portion in the joined workpiece such that a first workpiece, as one of the workpieces forming the joined workpiece, is gripped by the grip section with the joint portion of the joined workpiece projecting from the support section, and a predetermined region extending from the joint portion of the joined workpiece toward a second workpiece, as the other of the workpieces forming the joined workpiece, is processed over a range of not less than said predetermined width, to have an outer diameter of not more than an outer diameter of the first workpiece; and a movement control step for controlling the movement of the joined workpiece so as to slidingly move the joined workpiece relative to the support section, from a state in which the first workpiece is supported by the support section, up to a state in which the second workpiece is supported by the support section. 
     Advantageous Effect 
     According to the present disclosure, it is possible to provide a machine tool and a machining method that are capable of smoothly carrying out the machining even when the joined workpiece is eccentric. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating the constitution of the machine tool according to one embodiment of the present disclosure. 
         FIG. 2  is a schematic view illustrating the state in which a predetermined machining is being performed on a workpiece. 
         FIG. 3  is a schematic view illustrating the state in which the product has been processed from the workpiece. 
         FIG. 4  is a schematic view illustrating the state in which the machining of the workpiece has been completed and the workpiece becomes an old material. 
         FIG. 5  is a schematic view illustrating the state in which the second workpiece as an old material is passed from the front spindle to the rear spindle, and a first workpiece as a new material is supplied to the front spindle. 
         FIG. 6  is a schematic view illustrating the state which the end faces of the second workpiece and the first workpiece are joined by friction welding to form a joined workpiece. 
         FIG. 7  is a schematic view illustrating the state in which the joint portion has been processed. 
         FIG. 8  is a schematic view illustrating the state which the joined workpiece is gripped by the front spindle and slidingly moved relative to the support section of a guide bush, with the joint portion passed through the support section. 
         FIG. 9  is a schematic view illustrating the state which the joined workpiece is further slidingly moved and the second workpiece is supported by the support section. 
     
    
    
     DETAILED DESCRIPTION 
     The machine tool and machining method according to one embodiment of the present disclosure will now be described below in detail, with reference to the drawings. 
     The machine tool  1  illustrated in  FIG. 1  is an automatic lathe (CNC lathe) for machining workpieces W, and includes two spindles facing each other, i.e., a front spindle  10  and a rear spindle  20 . 
     The two workpieces W are rods each having a center axis O and extending in an elongated manner along the center axis O, and are of the same outer diameters with each other. The two workpieces W are each of a cylindrical shape, though the present disclosure is not limited to this; for example, a regular prism shape may be used. While each of the two workpieces W is a solid rod, the present disclosure is not limited to this; for example, a hollow rod may be used. The two workpieces W are each made of a metal material, though the present disclosure is not limited to this. 
     The front spindle  10  and the rear spindle  20  are arranged to face each other, with the center axis of the front spindle  10  and the center axis of the rear spindle  20  in parallel to each other. Hereinafter, the direction parallel to the center axes of the front spindle  10  and the rear spindle  20  is defined as the Z-axis direction, the direction perpendicular to the Z-axis direction is defined as the X-axis direction, and the direction perpendicular to the Z-axis direction and the X-axis direction is defined as the Y-axis directions. 
     On the base  2  of the machine tool, there is installed a front headstock  11  that is movable in the Z-axis direction by means of a front side moving mechanism  3 , such as a ball screw mechanism, for example. The front spindle  10  is rotatably supported by gripping the workpiece W on the front headstock  11 , and is rotationally driven by a spindle motor. As the spindle motor, for example, there may be used a built-in motor configured between the front headstock  11  and the front spindle  10  inside the front headstock  11 . 
     On the base  2 , there is further installed a rear headstock  21  that is movable in the Z-axis direction by means of a rear side moving mechanism  4 , such as a ball screw mechanism, for example. The rear spindle  20  is rotatably supported by gripping the workpiece W on the rear headstock, and is rotationally driven by the spindle motor. As the spindle motor, for example, there may be used a built-in motor inside the rear headstock  21 , which is configured between the rear headstock  21  and the rear spindle  20 . 
     Also, a Y-axis moving mechanism may be provided between the rear-side moving mechanism  4  and the rear spindle  21 , so that the rear spindle  20  can be moved in the Y-axis direction. 
     A front chuck  12  is provided at the tip end of the front spindle  10  so as to be openable and closable. The front chuck  12  is accommodated inside a chuck sleeve  13 . The front chuck  12  is closed when the chuck sleeve  13  moves slidingly toward the tip end side of the front spindle  10 , and opened when the chuck sleeve  13  moves slidingly toward the proximal end side of the front spindle  10 . The front spindle  10  is adapted to grip the workpiece W by inserting the workpiece W into the front chuck  12  in its open state and closing the front chuck  12  into the closed state. 
     A rear chuck  22  is provided at the tip end of a rear spindle  20  so as to be openable and closable. The rear chuck  22  is accommodated inside a chuck sleeve  23 . The rear chuck  22  is closed when the chuck sleeve  23  moves slidingly toward the tip end side of the rear spindle  20 , and opened when the chuck sleeve  23  moves slidingly toward the proximal end side of the rear spindle  20 . The rear spindle  20  is adapted to grip the workpiece W by inserting the workpiece W into the rear chuck  22  in its open state and closing the rear chuck  22  into the closed state. 
     A guide bush  30  is provided between the front spindle  10  and the rear spindle  20 . The guide bush  30  is mounted on the guide bush support base  31  on the base  2 , and is arranged coaxially with the front spindle  10 . In the present embodiment, the guide bush  30  has a support section  80  formed on an inner peripheral surface to have a predetermined width Sw. The support section  80  is adjusted to have an inner diameter corresponding to the outer diameter of the workpiece W so that, by adjusting the position of the guide bush  30  relative to the guide bush support base  31  in the Z-axis direction, the workpiece W can be supported rotatably and slidably in the Z-axis direction. The size of the guide bush  30  differs depending on the diameter of the workpiece W that can be supported, and the predetermined width Sw is appropriately set according to the size of the guide bush and the outer diameter of the workpiece W, for example, about 5 to 100 mm. 
     The machine tool  1  has a machining unit  40  that includes a tool  41  for machining the workpiece W. The tool  41  is adapted to cut into the workpiece W gripped and rotated by the front spindle  10  by moving in the X-axis direction, and is fed by moving the front spindle  10  (front headstock  11 ) in the Z-axis direction. That is to say, the X-axis direction is the cutting direction, and the Z-axis direction is the feeding direction. The tool  41  is held by a tool post  42 . In the tool post  42 , the tool  41  is arranged in front of the guide bush  30  and supported by the guide bush support  31  so as to be movable in the X-axis direction and the Y-axis direction. The position of the tool post  42  in the Z-axis direction is constant. The tool post  42  is equipped, for example, with an outer diameter cutting tool or a parting tool as the tool  41 , wherein each tool  41  is appropriately switched according to the contents of machining by moving the tool post  42  in the Y-axis direction, for example. 
     A workpiece supply unit  50  composed of a bar feeder is arranged behind the front spindle  10  of the machine tool  1 . The workpiece supply unit  50  has a finger  51  for gripping the rear end of the workpiece W, and a drive rod  52  for driving the finger  51  in the Z-axis direction. The workpiece supply unit  50  is adapted to sequentially supply the workpiece W to the front spindle  10 , as a new material. The workpiece supply unit  50  is also adapted to feed the workpiece W each time predetermined machining and parting are carried out. 
     The machine tool  1  includes a control unit  60 . The control unit  60  may be composed of a computer having a processor, such as a CPU (Central Processor Unit) and a memory. The control unit  60  is adapted to carry out an integrated control of the operation of each of the front headstock  11 , the front spindle  10  (including the front chuck  12 ), the rear headstock  21 , the rear spindle  20  (including the rear chuck  22 ), the guide bush  30 , the machining unit  40 , and the workpiece supply unit  50 . 
     Next, explanation will be made of a machining method according to an embodiment of the present disclosure, as an exemplary machining method of the workpiece W using the machine tool  1  constituted as described above. This method is carried out by an integrated control of each part of the machine tool  1  by means of the control unit  60 . 
     As illustrated in  FIGS. 2 to 3 , the control unit  60  serves to control the machining of the workpiece W by means of a continuous processing control step as the function of the continuous processing control means, wherein the workpiece W gripped by the front spindle  10  is rotated and predetermined machining (removal process) and parting are alternately and continuously carried out by the tool  41  of the machining unit  40 , in order to continuously obtain, from the workpiece W, a predetermined number of products P of a predetermined length. The workpiece W is inserted through the guide bush  30 , supported by the support section  80  over a predetermined width Sw to project from the guide bush  30 , and processed at the portion projecting from the guide bush  30 . In  FIGS. 2 to 9 , the entirety of the front spindle  10  and the rear spindle  20  are not illustrated, i.e., only the front chuck  12  and the rear chuck  22  are illustrated. 
     As illustrated in  FIGS. 4 to 6 , the control unit  60  serves to carry out the joining control step, as the function of the joining control means, wherein an old material, which consists of the workpiece W remaining after machining of the predetermined number of products P (residual material), is gripped by the rear spindle  20 , as the second workpiece W 2 , and a new material supplied to the front spindle  10  is gripped by the front spindle  10 , as the first workpiece W 1 , such that, with the two works W gripped one by one by the front spindle  10  and the rear spindle  20 , respectively, the two workpieces W are joined as a single joined workpiece W 3  by means of the friction welding. As used herein, the term “friction welding” refers to a conventional technology known in the art, wherein frictional heat is generated between the end faces of two workpieces W by relative rotation of the front spindle  10  and the rear spindle  20 , and the end faces of the two workpieces W are pressed against each other with a predetermined friction pressure, and then, the relative rotation of the two workpieces W is stopped and a predetermined upset pressure is applied to press them against each other for joining the end faces, for which detailed description is omitted. 
     In the present embodiment, the friction welding is carried out by means of the joining control means, wherein the end portion of the first workpiece W 1  is projected from the guide bush  30 , and the end of the first workpiece W 1  and the end of the second workpiece W is arranged between the guide bush  30  and the rear chuck  22 , with the first workpiece W 1  supported by the support portion  80 . By joining the two workpieces W, i.e., the first workpiece W 1  and the second workpiece W 2 , by means of the friction welding, there is formed a joint portion  70  at the contact portion between the first workpiece W 1  and the second workpiece W 2 , with burrs  71  projecting from the outer periphery of both workpieces W. 
     As illustrated in  FIGS. 6 to 7 , after the joining control step has been completed, the control unit  60  serves to carry out the joint portion processing step as the function of the joint portion processing means, wherein the joined workpiece W 3  is rotated about a first center axis O 1  and, with the first workpiece W 1  gripped the grip portion  81 , the predetermined region on the outer peripheral surface of the joined workpiece W 3  extending from the joint portion  70  toward the second workpiece, inclusive of burrs  71 , is removed by the tool  41  of the machining unit  40 , as the machining of the joint portion  70  of the joined workpiece W 3  between the two workpieces W. In the present embodiment, the grip portion  81  is composed of the front chuck  12  of the front spindle  10 . The removal process by means of the tool  41 , inclusive removal of burrs  71 , is carried out over a range R of not less than a predetermined width Sw in the Z-axis direction, from a state where the tool  41  is applied to the outer peripheral surface of the first workpiece W 1 , by forming a tapered surface  72  at the end of that range R. 
     As illustrated in  FIGS. 7 to 9 , after the joint portion processing control step has been completed, the control unit  60  serves to carry out the movement control step as the function of the movement control means, wherein the joined workpiece W 3  is supported by the support section  80  such that it is gripped by the grip section  81  and slidingly moved relative to the support section  81  from a first state (see  FIG. 7 ) in which the first workpiece W 1  is gripped by the support section  80 , to a second state (see  FIG. 9 ) in which the second workpiece W 2  is supported by the support section  80 . The front spindle  10  gripping the first workpiece W 1  of the joined workpiece W 3  is moved away from the rear spindle  20 , with the rear spindle  20  releasing gripping of the joined workpiece W 3 , so as to slidingly move the joined workpiece W 3  from the first state to the second state. 
     Since the range R, inclusive of burrs  71 , has already been processed to have an outer diameter not more than that of the first workpiece W 1 , by means of the removal process in the joint portion processing control step, so as not to project from the outer peripheral surface of the first workpiece W 1 , it is possible to advance the range R through a gap larger than the gap between the support section  80  and the first workpiece W 1 . Further, when the first center axis O 1  as the center axis of the first workpiece W 1  and the second center axis O 2  as the center axis of the second workpiece W 2  are offset from each other, and the first workpiece W 1  and the second workpiece W 2  are thereby eccentric at the joint portion  70 , a larger gap is formed between the outer peripheral surface of the second workpiece W 2  and the support portion  80  over the range R. Thus, the terminal region of the range R can be guided by the tapered surface  72  and passed through the support section  80 , with the second workpiece W 2  deflected by the amount of the gap, whereby the second workpiece W 2  is supported by the support section  80 . Therefore, according to the present embodiment, it is possible to allow the joint portion  70  to pass through the support section  80  even when the joined workpiece W 3  is eccentric and, thus, it is possible to change from the first state to the second state. However, in the second state, the joined workpiece W 3  is supported by the support section  80  in a slightly deflected state due to the eccentricity. 
     Incidentally, since the product P cannot be processed in the predetermined range R, it is preferred for the range R to be the minimum necessary range allowing passage of the joint portion  70  and the second workpiece W 2  through the support section  80  and, preferably, to be of generally the same amount as the predetermined width Sw of the support section  80 . 
     When the movement control step has been completed, the control unit  60  returns to the continuous processing control step and repeats the movement control step from the continuous processing control step. 
     As described above, according to the machine tool and machining method of the present embodiment, the predetermined region extending from the joint portion  70  toward the second workpiece W 2  is subjected to removal process over a range R having a predetermined width Sw or more to have an outer diameter of not more than the outer diameter of the first workpiece W 1 , thereby allowing a smooth passage of the joint portion  70  through the support section  80  even when the joint portion workpiece W 3  is eccentric, and realizing a smooth machining of the joined workpiece W 3 . 
     It goes without saying that the present disclosure is not limited to the above-described embodiment, and may be variously modified without departing from the scope thereof. 
     For example, in the above-described embodiment, the joined workpiece W 3  is gripped by the front chuck  12  of the front spindle  10  and slidingly moved relative to the support portion  80  in the movement control step. However, the present disclosure is not limited to this. Thus, for example, the joined workpiece W 3  may be gripped in the movement control step by the workpiece supply unit  50  and slidingly moved relative to the support portion  80 . 
     Further, when the front chuck  12  of the front spindle  10  is configured to grip the workpiece W on the inner peripheral surface having a predetermined width Sw, the joined workpiece W 3  with the joint portion  70  processed by the joint portion processing control means may be gripped by the workpiece supply portion  50  and slidingly moved in the movement control step relative to the front chuck  12 , until the second workpiece W 2  projecting from the front chuck  12  in the open state is accommodated in the front chuck  12 . In this case, the guide bush  30  may be omitted. 
     In the above embodiment, the joined workpiece W 3  is formed by friction welding. However, the joined workpiece W 3  may be formed by a method other than friction welding. Further, in the above embodiment, the front spindle  10  and the rear spindle  20  are used to form the joined workpiece W 3 , but the present disclosure is not limited to this; for example, the joined workpiece W 3  may be joined by means other than the front spindle  10  and the rear spindle  20 , or a pre-formed joint portion workpiece W 3  may be machined by the machine tool  1 . 
     REFERENCE SIGNS LIST 
     
         
           1  Machine tool 
           2  Base 
           3  Front side moving mechanism 
           4  Rear side moving mechanism 
           10  Front spindle 
           11  Front headstock 
           12  Front chuck 
           13  Chuck sleeve 
           20  Rear spindle 
           21  Rear headstock 
           22  Rear chuck 
           23  Chuck sleeve 
           30  Guide bush 
           31  Guide bush support 
           40  Machining unit 
           41  Tool 
           42  Tool post 
           50  Workpiece supply unit 
           51  Finger 
           52  Drive rod 
           60  Control unit (continuous processing control means/joining control means/joint portion processing control means/movement control means) 
           70  Joint portion 
           71  Burr 
           72  Tapered surface 
           80  Support section 
           81  Grip section 
         W Workpiece 
         W 1  First workpiece 
         W 2  Second workpiece 
         W 3  Joined workpiece 
         O Center axis 
         O 1  First center axis 
         O 2  Second center axis 
         P Product 
         Sw Predetermined width 
         R Range