Patent Publication Number: US-8528380-B2

Title: Bending apparatus

Description:
TECHNICAL FIELD 
     This invention relates to a bending apparatus. Specifically, the present invention relates to a bending apparatus for manufacturing a bent member by applying two-dimensional or three-dimensional bending to an elongated metal material having a closed cross section. 
     BACKGROUND ART 
     Strength members, reinforcing members, and structural members which are made of metal and have a bent shape are used in automobiles, various types of machines, and the like. These bent members need to have a high strength, a light weight, and a small size. In the past, this type of bent member has been manufactured by methods such as welding of press formed members, punching of thick plates, and forging. However, it is difficult to further reduce the weight and size of bent members manufactured by these methods. 
     Non-Patent Document 1, for example, discloses the manufacture of this type of bent member by so-called tube hydroforming Page 28 of Non-Patent Document 1 discloses that there are various challenges in the tube hydroforming technique, such as the development of materials for use in the method and increasing the degree of freedom of shapes which can be formed, and that further technological development is necessary. 
     In Patent Document 1, the present applicant disclosed a bending apparatus.  FIG. 13  is an explanatory view schematically showing that bending apparatus  0 . 
     As shown in  FIG. 13 , the bending apparatus performs the following operations on a steel tube  1  which is a material to be processed and which is supported by a support means  2  so as to be movable in its axial direction while being fed from an upstream side towards a downstream side by a feed device  3  such as a ball screw: 
     (a) rapidly heating a portion of the steel tube  1  with a high frequency heating coil  5  located downstream of the support means  2  to a temperature range in which quench-hardening is possible, 
     (b) rapidly cooling the steel tube  1  with a water cooling device  6  disposed downstream of the high frequency heating coil  5 , and 
     (c) imparting a bending moment to the heated portion of the steel tube  1  to perform bending two-dimensionally or three-dimensionally by varying the position of a movable roller die  4  having at least one set of roll pairs  4   a  which can support the steel tube  1  while feeding it. 
     As a result, a bent member  8  is manufactured with high operating efficiency while guaranteeing an adequate bending accuracy. 
     LIST OF PRIOR ART DOCUMENTS 
     Patent Document 1: WO 2006/093006 
     Non-Patent Document 1: Jidosha Gijustsu (Journal of Society of Automotive Engineers of Japan), Vol. 57, No. 6, 2003, pages 23-28 
     SUMMARY OF THE INVENTION 
     If the feed device  3  does not suitably support the front end or rear end of a steel tube  1 , the bending apparatus  0  has the following problems (a)-(e). 
     (a) The bent member  8  does not have a sufficient bending accuracy. 
     (b) A large force becomes necessary at the time of bending. The yield of the bent member  8  decreases. Furthermore, the interior of the steel tube  1  which is exposed to the atmosphere at a high temperature oxidizes, and the quality of the bent member  8  decreases. 
     (c) Cooling water which is sprayed at the steel tube  1  from the water cooling device  6  enters inside the steel tube  1  and interferes with heating of the steel tube  1  by the high frequency heating coil  5 , so the dimensional accuracy of the bent member  8  decreases. 
     (d) The steel tube  1  is impeded from successively passing through the support means  2 , the high frequency heating coil  5 , and the water cooling device  6 , and bending of the steel tube  1  can no longer take place. 
     (e) The portions which hold the steel tube  1  are heated by the high frequency coil  5  to a temperature at which deformation is possible, and as a result, the dimensional accuracy of the bent member  8  decreases. 
     The object of the present invention is to eliminate problems (a)-(e) of bending apparatus  0  and to provide a bending apparatus for manufacturing an elongated bent metal member having a closed cross section with higher productivity and superior dimensional accuracy compared to bending apparatus  0 . 
     The present invention is based on the finding that above-described problems (a)-(e) can be solved by (i) providing the feed device  3  of the bending apparatus  0  or a malformation preventing device or the like disposed downstream of the moveable roller die  4  in the feed direction of a steel tube  1  with a cylindrical chuck which is disposed on the interior or the exterior of the steel tube  1  to grip the steel tube  1 , and (ii) optimizing the shape, structure, and function of this chuck. 
     The present invention is a bending apparatus characterized by having the below-described first support mechanism, heating mechanism, cooling mechanism, second support mechanism, and malformation preventing mechanism, wherein at least one of the second support mechanism and the malformation preventing mechanism has the below-described chuck: 
     First Support Mechanism: It is disposed at a first position and supports a hollow metal material while feeding it. 
     Heating Mechanism: It is disposed at a second position downstream of the first position in the feed direction of the metal material and heats all or a portion of the metal material being fed. 
     Cooling Mechanism: It is disposed at a third position downstream of the second position in the feed direction of the metal material, and it cools the portion of the metal material being fed which was heated by the heating mechanism to form a high temperature portion in part of the metal material. 
     Second Support Mechanism: It is disposed at a fourth position downstream of the third position in the feed direction of the metal material and it moves two-dimensionally or three-dimensionally while supporting at least one location of the metal material being fed, thereby imparting a bending moment to the high temperature portion of the metal material so as to bend the metal material into a desired shape. 
     Malformation Preventing Mechanism: It is disposed at a fifth position downstream of the fourth position in the feed direction of the metal material, and it prevents malformation of the metal material being fed. 
     Chuck: It comprises a tubular member having a circular, polygonal, or shaped transverse cross-sectional shape and grips the metal material. 
     In the present invention, it is preferable that (I) there be a feed mechanism which feeds the metal material in its lengthwise direction and which preferably has the above-described chuck, or (II) the first support mechanism feed the metal material in its lengthwise direction. 
     In the present invention, the chuck is preferably inserted inside the metal material and contacts the inner surface of the metal material, and the outer dimensions of this tubular member can preferably be enlarged. 
     In the present invention, the chuck is preferably installed on the exterior of the metal material and contacts the outer surface of the metal material, and the inner dimensions of the tubular member can preferably be contracted. 
     In the present invention, the chuck can preferably prevent cooling water from entering inside the metal material by sealing the interior of the metal material or applying a positive pressure to the interior of the metal material. In the present invention, it is still more preferable that oxidation of the interior of the metal material can be prevented by sealing an inert gas or the like inside the metal material. 
     In the present invention, the tubular member of the chuck is preferably installed so that its longitudinal axis roughly coincides with the longitudinal axis of the metal material, and it preferably has outer dimensions which roughly correspond to the outer dimensions of the metal material. 
     In the present invention, the tubular member preferably has chuck claws and an operating bar which are made of a high hardness material. 
     In the present invention, the tubular member is preferably constituted by a plurality of components which are divided in the circumferential direction and by an insulating member disposed between adjoining components. 
     In the present invention, the tubular member is preferably non-magnetic. Specifically, the tubular member is preferably made of a ceramic, an austenitic stainless steel such as SUS 304, or a nickel alloy, for example. 
     In the present invention, the tubular member preferably has a laminated structure. A laminated structure means a structure formed by stacking thin metal sheets on one another. Due to the laminated structure, it becomes difficult for induced currents caused by high frequencies to flow inside the tubular member, and as a result, it becomes difficult for the chuck to undergo induction heating. 
     The present invention eliminates above-described problems (a)-(e). Therefore, according to the present invention, it is possible to reliably manufacture a strength member, a reinforcing member, or a structural member which is made of metal and which has a shape which is bent two-dimensionally or three-dimensionally with high operating efficiency while guaranteeing sufficient dimensional accuracy. 
    
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an example of the structure of a bending apparatus according to the present invention. 
         FIG. 2  is an explanatory view showing an example of the structure of a first industrial robot, a second industrial robot, a heating coil support robot, or a third industrial robot. 
         FIG. 3(   a ) is an explanatory view schematically showing an elongated chuck which is used as an end effector when a steel tube is directly gripped by a second industrial robot used as a second support means,  FIG. 3(   b ) is an explanatory view schematically showing a short chuck which is used as an end effector when a steel tube is directly gripped by a second industrial robot used as a second support means, and  FIG. 3(   c ) is an explanatory view schematically showing an elongated chuck which is used as an end effector when a steel tube is directly gripped by a second industrial robot used as a second support means. 
         FIG. 4  is an explanatory view showing that an elongated chuck can decrease a bending load. 
         FIG. 5(   a ) is an explanatory view showing a chuck of a type which is disposed on the exterior of a steel tube and which grips the end of the steel tube by contacting the outer surface of the steel tube, and  FIG. 5(   b ) is an explanatory view of a chuck of a type which is inserted into the interior of the steel tube and which grips the end of the steel tube by contacting the inner surface of the steel tube.  FIG. 5(   c ) is an explanatory view showing various chucks  35 - 43 . 
         FIG. 6  is an explanatory view schematically showing one example of a chuck which is used in the third industrial robot in  FIG. 1 . 
         FIG. 7  is an explanatory view schematically showing an example of a chuck which is used in the feed device of  FIG. 1 . 
         FIG. 8(   a )- FIG. 8(   c ) are explanatory views schematically showing mechanisms for enlarging the outer dimensions of a chuck which grips an end of a steel tube by being inserted inside the steel tube and contacting the inner surface of the steel tube. 
         FIG. 9(   a ) is an explanatory view schematically showing an example of the structure of a chuck which is suitable for use in a bending apparatus according to the present invention,  FIG. 9(   b ) shows a comparative example of a chuck, and  FIG. 9(   c ) shows an example of a chuck according to the present invention. 
         FIG. 10  is an explanatory view showing an example of the structure of a chuck of a type having a sleeve with slits which is suitable for use in a bending apparatus according to the present invention. 
         FIG. 11(   a ) is an explanatory view showing an example of the structure of a chuck of a type having a hydraulic sleeve which is suitable for use in a bending apparatus according to the present invention, and  FIG. 11(   b ) is an explanatory view showing a modification thereof. 
         FIG. 12  is an explanatory view showing a mechanism for applying a positive pressure to the interior of a steel tube. 
         FIG. 13  is an explanatory view schematically showing the structure of a bending apparatus disclosed in Patent Document 1. 
     
    
    
     EXPLANATION OF SYMBOLS 
       0 : bending apparatus disclosed in Patent Document 1, 
       1 : steel tube,  2 : support means,  3 : feed device,  4 : movable roller die, 
       4   a : roll pair,  5 : high-frequency heating coil,  6 : water cooling device, 
       8 : bent member, 
       10 : bending apparatus according to the present invention, 
       11 : feed means,  12 : first support means,  12   a ,  12   a : roll pairs, 
       13 : heating means,  13   a : heating coil,  14 : cooling means, 
       14   a ,  14   b : nozzles for spraying cooling water, 
       15 : second support means,  16 : malformation preventing means, 
       17 : steel tube,  17   a : end portion,  18 : first industrial robot, 
       19 : upper arm,  20 : front arm,  20   a : wrist,  21 : controller, 
       22 : input unit,  23 : pallet,  24 : end effector,  25 : movable roller die, 
       25   a ,  25   b : roll pairs,  26 : second industrial robot,  26   a : gripper, 
       27 : high frequency coil support robot:  28 : third industrial robot, 
       29 : end effector,  30 - 44 ,  46 ,  48 ,  49 ,  57 ,  58 : chucks, 
       45 : cylinder,  47 : support guide,  50 : body,  51 : shaft,  52 : operating bar, 
       53 : chuck claws,  54 : conical bar,  55 : segments,  56 : elastic claws, 
       57   a ,  57   b : components,  59 : insulating member,  60 : chuck,  61 : sleeve, 
       62 : slit,  63 : sealing ring,  70 ,  70 - 1 : chucks,  71 : high pressure liquid, 
       72 : flow passage,  73 : sleeve,  74 : cylinder 
     MODES FOR CARRYING OUT THE INVENTION 
     The present invention will be explained while referring to the attached drawings. In the following explanation, an example will be given of the case in which a hollow metal material having a closed cross section in the present invention is a steel tube  17 , but the present invention is not limited to a steel tube, and it can be applied in the same manner to any hollow metal material having a closed cross section (such as a rectangular tube or a tube with a shaped cross section). 
       FIG. 1  is a perspective view showing in simplified and abbreviated form a portion of an example of the structure of a bending apparatus  10  according to the present invention. In  FIG. 1 , a first industrial robot  18 , a heating coil support robot  27 , a second industrial robot  26 , and a third industrial robot  28  are shown with manipulators and the like illustrated conceptually and in simplified form. 
     The bending apparatus  10  has a feed mechanism  11 , a first support mechanism  12 , a heating mechanism  13 , a cooling mechanism  14 , a second support mechanism  15 , and a malformation preventing mechanism  16 . 
     [Feed Mechanism  11 ] 
     The feed mechanism  11  feeds a steel tube  17  in its lengthwise direction. The feed mechanism  11  is constituted by a first industrial robot  18 . 
     The first industrial robot  18 , the heating coil support robot  27 , and the third industrial robot  28  are all the same type of robot as the second industrial robot  26 . 
       FIG. 2  is an explanatory view showing an example of the structure of the first industrial robot  18 , the second industrial robot  26 , the heating coil support robot  27 , or the third industrial robot  28 . 
     The first industrial robot  18 , the second industrial robot  26 , the heating coil support robot  27 , and the third industrial robot  28  (referred to below as the robots) are each so-called vertical articulated robots having first through sixth axes. 
     The first axis allows an upper arm  19  to pivot in a horizontal plane. The second axis allows the upper arm  19  to swing forwards and backwards. The third axis allows a front arm  20  to swing up and down. A fourth axis allows the forearm  20  to rotate. The fifth axis allows a wrist  20   a  to swing up and down. The sixth axis allows the wrist  20   a  to rotate. 
     In addition to the first through sixth axes, the robots may if necessary have a seventh axis which allows the upper arm  19  to pivot. The first through seventh axes are driven by AC servomotors. 
     In the same manner as other general purpose industrial robots, each of the robots has a controller  21  which performs overall control of the operation of the first through sixth axes and an input unit  22  for providing instructions for the operation of the first through sixth axes. 
     An end effector  24  is provided on the end of the wrist  20   a  of the first industrial robot  18 . The end effector  24  is used for gripping a steel tube  17  housed in a pallet  23  disposed in the vicinity of the side of the first industrial robot  18  and for passing the gripped steel tube  17  through holes provided in the first support means  12  and the heating means  13 . 
     The end effector  24  is used not only when the feed mechanism  11  is feeding a steel tube  17  but also when a steel tube  17  is directly gripped by the second industrial robot  26  without using the movable roller die  25  as a below-described second support mechanism  15  and when the steel tube  17  is supported by the malformation preventing mechanism  16 . 
     The end effector  24  greatly affects the dimensional accuracy and productivity of a bent member which is manufactured by this bending apparatus  10 . The end effector  24  will be explained below in detail. 
     In the following explanation, an example of an end effector will be given for the case in which a movable roller die  25  is not used as a second support mechanism  15  and a steel tube  17  is directly gripped by the second industrial robot  26 . This description applies to the end effector  24  of the feed mechanism  11  and an end effector  29  of the malformation preventing mechanism  16 . 
       FIG. 3(   a ) is an explanatory view schematically showing an end effector in the form of an elongated chuck  30  for the case in which a steel tube  17  is directly gripped by the second industrial robot  26  without using a movable roller die  25  as a second support mechanism  15 ,  FIG. 3(   b ) is an explanatory view schematically showing an end effector in the form of a short chuck  31  for the case in which a steel tube  17  is directly gripped by the second industrial robot  26  without using a movable roller die  25  as a second support mechanism  15 , and  FIG. 3(   c ) is an explanatory view schematically showing an end effector in the form of an elongated chuck  32  for the case in which a steel tube  17  is directly gripped by the second industrial robot  26  without using a movable roller die  25  as a second support mechanism  15 . 
     The chucks  30 - 32  each comprise a tubular member for gripping an end of a steel tube  17 . 
     Chuck  30  is disposed on the exterior of a steel tube  17 . Chuck  30  grips an end of a steel tube  17  by contacting the outer surface  17   b  of the steel tube  17 . Chuck  30  has a structure such that its inner diameter can be contracted by a below-described suitable mechanism. 
     Each of chucks  31  and  32  is inserted inside a steel tube  17 . Chucks  31  and  32  grip an end of a steel tube  17  by contacting the inner surface of the steel tube  17 . Each of chucks  31  and  32  has a structure such that its outer diameter can be expanded by a below-described suitable mechanism. 
     Each of these chucks  30 - 32  properly holds an end of a steel tube being fed in its axial direction. Therefore, the bending apparatus  10  can bend a steel tube  17  with a sufficient working accuracy. 
     Each of chucks  30 - 32  has a tube end sealing mechanism which contacts a sealing surface formed on the end of a steel tube or an inner surface sealing mechanism which contacts a sealing surface formed on the inner surface of a steel tube. As a result, the chucks  30 - 32  seal a steel tube  17  by directly contacting the end or the inner surface of the steel tube  17 . The chucks  30 - 32  prevent water from entering inside the steel tube  17 , so heating of the steel tube  17  by the high frequency heating coil  13   a  can be properly carried out. Therefore, the bending apparatus  10  can bend a steel tube  17  with sufficient accuracy. 
     Chuck  30  comprises an elongated tubular member. Therefore, the bending load W is restrained to a small value, and interference between the second industrial robot  26  and equipment in its periphery is prevented even when bending begins from the vicinity of the front end of a steel tube  17 . 
     Chuck  31  comprises a short tubular member. Quench hardening of a steel tube  17  is carried out from the end of the steel tube  17 , so the product yield is increased. 
     Chuck  32  comprises an elongated tubular member, so bending loads W are suppressed to a low value. Interference between the second industrial robot  26  and equipment in its periphery is prevented even when bending starts from the vicinity of the end of a steel tube  17 , and quench hardening is carried out from the end of the steel tube  17 , thereby increasing the product yield. 
       FIG. 4  is an explanatory view showing that chucks  30  and  32  can reduce the bending load W. 
     In  FIG. 4 , symbol W indicates the bending load, symbol M indicates the moments necessary for bending of a steel tube  17 , symbol l 1  indicates the length of the chuck, symbol l 2  indicates the chucking contact length, and symbol l 3  indicates the distance from the end of the steel tube  17  to the point where bending begins. 
     The bending load is defined as W=M/L=M/(l 1 +l 3 ). The longer L is, the smaller W can be. In order to improve the product yield, it is preferable to start bending in the vicinity of an end of a steel tube  17 , namely, it is preferable to make l 3  small. When there are limits on the allowable load of bending equipment, l 3  can be shortened by lengthening l 1 . 
     For example, when carrying out bending of a steel tube having an outer diameter of 25 mm and a wall thickness of 1.0 mm with a bending radius of 200 mm, the moment necessary for bending is approximately 36 Nm. 
     If the allowable bending load is 500 N, then when L=d, W=1440 N&gt;500 N, and when L= 2   d , W=720 N&gt;500 N, so bending cannot be carried out in either case. In contrast, when L= 3   d , W=480 N≦500 N, when L= 4   d , W=360 N≦500 N, and when L= 5   d , W=288 N≦500 N, so bending can be carried out in each case. 
     For this reason, under the above-described conditions, the relationship is preferably satisfied. 
       FIG. 5(   a ) is an explanatory view showing a chuck  33  of a type which is disposed on the exterior of a steel tube and which grips an end of the steel tube by contacting the outer surface of the steel tube, and  FIG. 5(   b ) is an explanatory view of a chuck  34  of a type which is inserted inside a steel tube and which grips an end of the steel tube by contacting the inner surface of the steel tube. 
     Chuck  34  is preferable to chuck  33  since it can be more easily centered with respect to a steel tube and can more easily obtain a gripping force by a tensile force in the circumferential direction of a steel tube. 
       FIG. 5(   c ) is an explanatory view showing various chucks  35 - 43 . 
     Chucks  35  and  36  are disposed on the exterior of a steel tube and contact the outer surface of the steel tube. 
     Chucks  37  and  38  are inserted inside a steel tube and contact the inner surface of the steel tube. 
     Chucks  39  and  40  are disposed on the exterior of a steel tube and contact the outer surface of the steel tube, and they are also inserted inside the steel tube and contact the inner surface of the steel tube. 
     Chucks  41 - 43  are each chucks for rectangular tubes. In order to obtain a sufficient holding force even with a rectangular tube and to grip a rectangular tube with certainty, chucks  41 - 43  are preferably inserted into a steel tube and contact the inner surface of the steel tube and also contact the inner corners of the rectangular tube. 
     Each of the above chucks is preferably disposed such that its central axis approximately coincides with the central axis of a steel tube so that the chuck can pass through the first support device  12 , the heating device  13 , the cooling device  14 , and the second support device  15  with certainty. 
       FIG. 6  is an explanatory view schematically showing an example of a chuck  44  used by the third industrial robot  28  in  FIG. 1 . Symbol  45  in  FIG. 6  indicates a cylinder. 
     As shown in  FIG. 6 , when a steel tube  17  undergoes bending while being quench-hardened from the vicinity of its front end, the chuck  44  is preferably an elongated chuck having an outer diameter with dimensions roughly corresponding to the outer diameter of the steel tube  17 . 
       FIG. 7  is an explanatory view schematically showing an example of a chuck  46  used in the feed mechanism in  FIG. 1 . Symbol  47  in  FIG. 7  indicates a support guide. 
     As shown in  FIG. 7 , when a steel tube  17  is being bent while being quench-hardened up to the vicinity of its rear end, it is preferable to use an elongated chuck  46  having an outer diameter with dimensions roughly corresponding to the outer diameter of the steel tube  17 .  FIGS. 8(   a )- 8 ( c ) are explanatory views schematically showing mechanisms for enlarging the outer dimensions of chucks  48 ,  49 , and  48 - 1  which grip an end of a steel tube  17  by being inserted into the steel tube  17  and contacting the inner surface of the steel tube  17 . 
     Inside a cylindrical body  50 , chuck  48  has a shaft  51  which can be advanced and retracted by an unillustrated cylinder or the like and an operating bar  52 , for example, which is disposed at the front end of the shaft  51 . Four chuck claws  53  are disposed at predetermined positions in the axial direction of the body  50  on the sloping surface of the operating bar  52 . The chuck claws  53  are moved in the radial direction by movement of the shaft  51  in the axial direction of the body  50 , thereby increasing or decreasing the outer dimensions of the chuck  48 . 
     Inside a cylindrical body  50 , chuck  49  has a shaft  51  which can be advanced and retracted by an unillustrated cylinder or the like and a conical bar  54 , for example, which is disposed at the front end of the shaft  51 . A large number of segments  55  and an elastic claw  56  are disposed on the sloping surface of the conical bar  54 . When the shaft  51  is moved in the axial direction of the body  50 , the segments  55  are moved in the radial direction, and as a result, the outer dimensions of the chuck  49  are increased or decreased. 
     Chuck  48 - 1  is a modification of chuck  48 . The operating bar  52  has a tapered shape. The tapered operating bar  52  can increase the cross-sectional area of the joint with the shaft  51  and thereby increase the strength of the operating bar  52 . 
     The chuck claws  53  preferably have dovetail grooves which extend in the axial direction of the body  50  to enable unclamping to be carried out with certainty. 
     Examples of the materials used for the chuck claws  53  and the operating bar  52  are austenitic stainless steel and tool steel. Austenitic stainless steel is suitable because it is non-magnetic and does not readily undergo inductive heating, but it is somewhat inferior with respect to wear resistance (resistance to damage) and antiseizure properties. On the other hand, tool steel has superior durability in a cold state. Tool steel is magnetic and is easily affected by inductive heating, but there are no problems in actual use unless the vicinity of the chuck claws  53  undergoes inductive heating. The body  50  is preferably a non-magnetic member made of austenitic stainless steel or the like. 
       FIG. 9(   a ) is an explanatory view schematically showing an example of the structure of a chuck  57  suitable for use in a bending apparatus  10  according to the present invention,  FIG. 9(   b ) shows a chuck  58  as a comparative example, and  FIG. 9(   c ) shows a chuck  57  as an example according to the present invention. 
     As shown in  FIG. 9(   a ) and  FIG. 9(   c ), chuck  57  has components  57   a  and  57   b  and insulating members  59 . Components  57   a  and  57   b  are divided into a plurality of members (two in the illustrated example) in the circumferential direction. The insulating members  59  are disposed between two adjoining components  57   a  and  57   b . The insulating members  59  are made of polytetrafluoroethylene or the like, for example. 
     As shown in  FIG. 9(   c ), by disposing insulating members  59  between a plurality of components  57   a  and  57   b  of the chuck  57 , currents flowing in the components  57   a  and  57   b  cancel each other. As a result, current induced by the high frequency heating coil  13   a  is prevented from flowing around the components  57   a  and  57   b  and heating the chuck  58 . 
       FIG. 10  is an explanatory view showing the structure of a chuck  60  of a sleeve type with slits which is suitable for use in a bending apparatus according to the present invention. 
     Chuck  60  has a shaft  51  which can be advanced and retracted by an unillustrated cylinder or the like and an operating bar  52 , for example, disposed at the front end of the shaft  51 , both of which are inside a cylindrical body  50  of the chuck  60 . A sleeve  61  having slits  62  and a sealing ring  63  are disposed on the sloping surface of the operating bar  52  in predetermined positions in the axial direction of the body  50 . The sleeve  61  with slits elastically deforms and increases or decreases in diameter when the shaft  51  moves in the axial direction of the body  50 . As a result, the outer dimensions of the chuck  60  are increased or decreased. 
     Because the sleeve  61  has a plurality of slits  62 , it can elastically deform under a small force and it is not readily heated by induction heating even when it is made of metal. 
     Inductive heating of the sleeve  61  can be adequately prevented simply by making the sleeve  61  from a non-magnetic member. The slits  62  are preferably provided when the strength of the sleeve  61  is adequately guaranteed. 
       FIG. 11(   a ) is an explanatory view showing the structure of a chuck  70  with a hydraulic sleeve which is suitable for use in a bending apparatus according to the present invention, and  FIG. 11(   b ) is an explanatory view of a modification  70 - 1  thereof. 
     A passage  72  for high pressure fluid  71  which was generated using an unillustrated high pressure pump is formed inside the chuck  70 . A sleeve  73  which is formed from an elastic member is provided on the outer periphery of the tip of the body of the chuck  70 . The sleeve  73  is deformed so as to expand by passing the high pressure fluid  71  through the passage  72 . Chuck  70  can decrease the outer diameter of the tip of the body, so it can be used as a chuck having a small inner diameter. The sleeve  73  is preferably made of a heat-resistant metal. Chuck  70 - 1  has a cylinder  74  which produces a high pressure fluid  71 . By making the cross-sectional area A 1  of the operating portion of the cylinder  74  larger than the cross-sectional area A 2  of a passage  72 , the pressure P 2  in the passage  72  can be made high even when the operating pressure P 1  of the cylinder  74  is low. 
       FIG. 12  is an explanatory view of a mechanism for producing a positive pressure inside a steel tube  17 . 
     If a sealing member at the end of the steel tube  17  is made of a soft material such as rubber, the durability of the sealing member is sometimes inadequate. If the sealing member is made of metal, it is sometimes not possible to prevent entry of water into the steel tube  17 . 
     Therefore, a feed side chuck  76  which has a passage  75  inside an operating bar for supplying compressed air or a compressed inert gas is used as a mechanism for producing a positive pressure inside a steel tube  17 . The mechanism is preferably designed such that the compressed air or a compressed inert gas supplied to the interior of the steel tube  17  is discharged from an exit side chuck  77 . As a result, a positive pressure is maintained inside the steel tube  17 , and cooling water from the cooling device  14  can be completely prevented from entering inside the steel tube  17 . 
     An inert gas such as nitrogen gas is preferably supplied to the interior of the steel tube  17  in order to suppress oxidation of the inside of the steel tube  17 . 
     When the above-described chucks grip the inner surface of a material being working having a polygonal transverse cross section such as a rectangular cross section or when gripping of a material being processed having a shaped transverse cross-sectional shape with corners, the gripping force can be increased and the material being processed can be centered with certainty if gripping is performed such that the chuck contacts each of the corners of the inner peripheral surface of the material being processed. 
     The first industrial robot  18  moves steel tubes  17  from a pallet  23  to the bending apparatus  10  and sets them in the bending apparatus  10 . As a result, a decrease in the cycle time and an increase in the productivity of the bending apparatus  10  can be achieved. 
     [First Support Mechanism  12 ] 
     The first support mechanism  12  is fixed at a first position A. The first support mechanism  12  supports a steel tube  17  while feeding it. In the same manner as in bending apparatus  0 , the first support mechanism  12  comprises a die. The die has at least one pair of roll pairs  12   a ,  12   a  (in the illustrated example, it also has one more set of roll pairs  12   b ,  12   b  for a total of two sets) which can support a steel tube  17  while feeding it. Such a die is well known by those skilled in the art, so an explanation of the first support mechanism  12  will be omitted 
     The first support mechanism  12  is constituted as described above. 
     [Heating Mechanism  13 ] 
     The heating mechanism  13  is disposed at a second position B downstream of the first position A in the feed direction of a steel tube  17  and is supported by a heating coil support robot  27 . The heating mechanism  13  heats all or a portion of a steel tube  17  being fed. 
     An induction heating device having a heating coil  13   a  which is disposed around and separated from a steel tube  17  is used as the heating mechanism  13 . A heating coil  13   a  is well known by those skilled in the art, so an explanation of the heating mechanism  13  will be omitted. 
     [Cooling Mechanism  14 ] 
     The cooling mechanism  14  is fixed at a third position C downstream of the second position B in the feed direction of a steel tube  17 . The cooling mechanism  14  forms a high temperature portion in a portion of the steel tube  17  by cooling the portion of the steel tube  17  being fed which was heated by the heating mechanism  13 . 
     The cooling mechanism  14  uses a water cooling device, for example. The water cooling device has cooling water spraying nozzles  14   a  and  14   b  spaced from the outer surface of the steel tube  17 . Such cooling water spraying nozzles  14   a  and  14   b  are well known by those skilled in the art, so an explanation of the cooling mechanism  14  will be omitted. 
     [Second Support Mechanism  15 ] 
     The second support mechanism  15  is disposed at a fourth position D downstream of the third position C in the feed direction of a steel tube  17 . The second support mechanism  15  imparts a bending moment to the high temperature portion of the steel tube  17  between positions B and C (a portion which was heated and greatly decreased in resistance to deformation) and bends the steel tube  17  into a desired shape by moving two or three-dimensionally while supporting at least one location on the steel tube  17  being fed. 
     In the same manner as in bending apparatus  0 , the second support mechanism  15  is constituted by a movable roller die  25 . The movable roller die  25  has at least one set of roll pairs  25   a  and  25   b  which can support a steel tube  17  while feeding it. However, as a different arrangement, an end effector such as a gripper which is held by the second industrial robot  26  may be used as the second support mechanism  15 , and the steel tube  17  may be directly gripped by the end effector. 
     The movable roller die  25  is supported by the second industrial robot  26 . Like the above-described first industrial robot  18 , the second industrial robot  26  is a so-called vertical articulated robot. It has first through sixth axes and if necessary a seventh axis. The first through seventh axes are driven by AC servomotors. 
     The gripper  26   a  is provided at the end of the wrist  20   a  of the second industrial robot  26  as an end effector which holds the movable roller die  25 . However, the end effector need not be a gripper  26   a.    
     [Malformation n Preventing Mechanism  16 ] 
     The malformation n preventing mechanism  16  is disposed at a fifth position E downstream of the fourth position D in the feed direction of a steel tube  17 . The malformation preventing mechanism  16  prevents malformation of a steel tube  17  being fed. 
     A third industrial robot  28  is used as the malformation preventing mechanism  16 . 
     Like the above-described first industrial robot  18  and second industrial robot  27 , the third industrial robot  28  is a so-called vertical articulated robot. It has first through sixth axes and if necessary a seventh axis. The first through seventh axes are driven by AC servomotors. 
     Any of the chucks explained while referring to  FIGS. 3-11  is provided on the end of the wrist  20   a  of the third industrial robot  28  and is used as an end effector for holding an end  17   a  of a steel tube  17 . 
     The bending apparatus  10  preferably carries out bending in a warm or hot state. A warm state means a heating temperature range in which the resistance to deformation of a metal material is lower than at room temperature. For example, with some metal materials, it is a temperature range of around 500-800° C. A hot state means a heating temperature range at which the resistance to deformation of a metal material is lower than at room temperature and which is necessary for the metal material to be quench hardened. For example, for some steel materials, it is a temperature range of 870° C. or higher. In particular, when bending is carried out in a hot state, after a predetermined temperature for quench hardening is reached, quenching can be carried out by cooling at a predetermined cooling speed. When bending is carried out in a warm state, the occurrence of strains during working such as thermal strains can be prevented by cooling the bent portion. 
     The bending apparatus  10  has the structure described above. 
     Because at least one of the feed mechanism  11  and the deformation preventing mechanism  16  has a tubular chuck which can grip a steel tube  17 , the below-described effects are obtained. 
     (a) The feed mechanism  11  can properly hold the front end or the rear end of a steel tube  17 , and bending can be carried out with sufficient accuracy. 
     (b) The feed mechanism  11  can prevent oxidation of the interior of a steel tube  17  which is exposed to the atmosphere at a high temperature. 
     (c) The force required for bending does not become too large, and the yield of a steel tube  17  which has been bent is high. 
     (d) Water is prevented from entering inside a steel tube  17 , and heating of the steel tube by the high frequency heating coil  13   a  can be carried out as desired, so the bending accuracy is adequately increased. 
     (e) A steel tube  17  which is being bent can successively pass through the support mechanism  12 , the high frequency heating coil  13   a , and the water cooling mechanism  14 , and bending can be carried out with certainty. 
     (f) The chuck which grips a steel tube  17  is prevented from undergoing inductive heating by the high frequency heating coil  13   a , and it can hold the steel tube  17  continuously with certainty from the start to the finish of bending. As a result, the bending accuracy can be sufficiently increased.