DIE CLAMPING APPARATUS

Abstract: The known die clamping apparatus including a fixed die plate, a movable die plate, means for moving the movable die plate relative to the fixed die plate, means for fixedly coupling the fixed die plate with the movable die plate and tie bars for carrying out clamping of dies, is improved. The tie bars (264) are fixedly secured to the fixed die plate (254) and a hydraulic cylinder (260) having a ram (262) is provided on the movable die plate (258), or vice versa. The fixedly coupling means consists of a half-nut (280) or the like provided on the surface of the fixed die plate so as to be movable in the axial direction of the tie bar insert hole (274), and threads (272) or the like provided on the outer circumference of the tip end of the tie bar and adapted to be meshed with the half-nut. Stopper means (290, 292, 293) is provided between the fixed die plate (258) and the half-nut (280). A part of the ram (262) is made to butt against the stopper means (290, 292, 293) to perform positioning of the ram in the axial direction of the tie bar insert hole (274). The end surface of the half-nut (280) opposed to the ram is brought into press contact with the ram. At that position, the half-nut can be positioned so as to mate with the threads (272) on the tie bar (264).

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a die clamping apparatus that is available in an injection molding machine, a press machine or the like. Description of the Prior Art: One example of the die clamping apparatus in the prior art is illustrated in Fig. 10. In this figure, reference numeral 50 designates a support frame 50, on one end of this support frame 50 is fixedly secured a fixed die plate 54 having a fixed die 52 mounted thereon, and on the other end of the support frame 50 is slidably placed a movable die plate 58 having a movable die 56 mounted thereon in an opposed relation­ ship to the fixed die plate 54. On the fixed die plate 54 are provided a plurality of hydraulic cylinders 60, and tie bars 64 are provided so as to extend from internal pistons 62 of these respective hydraulic cylinders 60 towards the movable die plate 58. In addition, at one portion of the fixed die plate 54 is fixedly secured a boost cylinder 66, and a tip end portion of a rod 70 con­ nected to an internal piston 68 of this boost cylinder 66 is appropriately fixed to one portion of the movable die plate 58. Furthermore, at the tip end portions of the tie bars 64 are respectively formed threads 72, and on the opposite side of the movable die plate 58 provided with insert holes 74 through which the tie bars 64 are pene­ trated, to the movable die 56, are disposed half-nuts 76 adapted to be meshed with the threads 72 of the tie bar 64, by any appropriate moving means 80 so as to be movable in the directions nearly at right angles to the axes of the above-mentioned insert holes 74. The tie bars 64 have such dimensions that their tip ends may be located at the positions somewhat separated from the insert holes 74 of the movable die plate 58, and at one portion of each tie bar 64 is provided a stop ring 78 so as to be adjustable in position. In this case, in order to allow the centering between the insert hole 74 in the movable die plate 58 and the tie bar 64 to be carried out smoothly, the edge of opening of the insert hole 74 is formed in a tapered shape. In addition, under a standby condition of the tie bars 64, positioning of stopper rings 78 provided on the tie bars 64 is effected in such manner that just before the movable plate 58 moves and the fixed die 52 and the movable die 56 complete closure of dies when the movable plate 58 is moved, the stop ring 78 provided on the tie bar 64 may be engaged with the end of the insert hole 74 in the movable die plate 58 on the side of the die mounting surface, and the threads 72 provided on the tie bar 64 may be meshed with the half-nut 76 provided on the movable die plate 58. It is to be noted that reference numeral 92 designates a seal member for the hydraulic cylinder 60. In the die clamping apparatus having the above-­ described construction, upon closing the dies, if the movable die plate 58 is moved towards the fixed die plate 54 by feeding pressurized oil into one oil chamber 84 of the boost cylinder 66, then just before the die closure of the fixed die 52 and the movable die 56 is completed, the stop ring 78 provided on the tie bar 64 is engaged with the edge of opening of the insert hole 74 in the movable die plate 58. At this moment, the half-nut 76 provided on the movable die plate 58 is moved in the direc­ tions nearly at right angles to the axis of the insert hole 74 by the moving means 80 to mesh it with the threads 72 formed on the tie bar 64. As a result, fixed coupling between the tie bar 64 and the movable plate 58 can be easily achieved. Subsequently, if pressurized oil is fed into one oil chamber 86 of the hydraulic cylinder 60 provided on the fixed die plate 60, the movable die plate 58 is moved towards the fixed die plate 54 by directly moving the tie bar, and thereby die clamping for the fixed die 52 and the movable die 56 can be achieved. However, the die clamping apparatus in the prior art as described above, involves various problems as enumerated in the below: (1) The stop ring 78 provided on the tie bar 64 engages with the edge of opening of the insert hole 74 in the movable die plate 58 just before completion of the closure of dies as described above. Accordingly, the inner piston 62 of the hydraulic cylinder 60 is preliminarily positioned so as to attain such engaging relationship. This positioning would vary depending upon the thickness of the dies 52 and 58 when they are closed. To that end, the hydraulic cylinder 60 is neces­ sitated to have a stroke that is large enough to be adapted to the variable range of the thickness of the dies used in this die clamping apparatus, and con­ sequently, as the variable range of the thickness of the dies to be used becomes large, the cylinder stroke is compelled to be selected also large. (2) In addition, the tie bar 64 also serves as a rod of the hydraulic cylinder 60, and so, it tends to be­ come thicker and longer as the die clamping apparatus becomes large-sized. Since this rod is only supported in a cantilever-like state at the seal member 92 of the hydraulic cylinder 60, there are problems such that if no provision is made, the tie bar 64 would tilt due to its own weight, hence it becomes unable to be centered with the insert hole 74 in the movable die plate 58, and besides, oil leakage from the location of the seal member 92 would be increased. In order to make this arrangement practically available, various contrivances for preventing this tie bar from tilting are necessitated to be made. (3) As described previously, the tie bar also serves as a rod of the hydraulic cylinder 60, and the portion of this rod to come in and out of the hydraulic cylinder is placed at a location where an operator comes close frequently and where the rod portion is apt to be trod by operator's safety shoes, and moreover, the plate is a location where the rod is liable to be hurt by being struck against a die upon replacement of dies. If the rod should be hurt, then there would occur a serious problem that oil leakage is increased due to that cause. (4) The half-nut 76 and the threaded portions 72 of the tie bar 64 are necessitated to be preset in such positional relationship that when the stop ring 78 has engaged with the edge of opening of the insert hole 74, the phases of the respective threads of then are matched with each other, and they can be meshed with each other, and so, there occurs also the problem that in the event that the tie bar 64 should rotate within the hydraulic cylinder 60, the above-mentioned phases would become unmatched. (5) It is necessary to make the stop ring 78 engage with the edge of opening of the insert hole 74 just before closure of dies, and in the case where replace­ ment of dies has been effected, for instance, from a thin die to a thick die, there is a problem that even the work of preliminarily feeding pressurized oil to the head side of the hydraulic cylinder 60 to make the tie bar 34 advance, is a troublesome time-consum­ ing work. SUMMARY OF THE INVENTION: The present invention has been worked out in order to resolve the above-mentioned various problems due to the structure of the die clamping apparatus in the prior art, and it is one object of the present invention to provide a die clamping apparatus having a novel structure that is quite different from the mechanisms employed in the prior art. To that end, in a die clamping apparatus includ­ ing a fixed die plate for holding a fixed die, a movable die plate for holding a movable die, means for making the mov­ able die plate operatively advance and retire with respect to the fixed die plate, means for fixedly coupling the movable die plate to the fixed die plate after the movable die plate has come close to the fixed die plate and the fixed die plate and the movable die plate have closed, and tie bars for carrying out clamping of dies, the present invention is characterized in that the tie bars are fixedly secured to either one of the fixed die plate and the movable die plate, and more particularly, the die clamping apparatus according to the present invention is character­ ized by the following features: (1) One ends of the tie bars are fixedly secured to either one of the fixed die plate and the movable die plate. (2) A ram having an insert hole for the tie bar of a hydraulic cylinder for clamping dies, is made to be contained in the other of the fixed die plate and the movable die plate. This ram is not in a directly coupled relation to the tie bar. (3) At the outlet of the insert hole is provided a half-nut or a locking block. (4) At the tip end portion of the tie bar are formed threads or circumferential grooves to be engaged with the half-nut or locking block over a length correspond­ ing to the variation range of the thickness of the dies to be used. (5) Between the aforementioned the other die plate and the half-nut or locking block is provided stopper means, which can adjust the movement and positioning in parallel to the axis of the tie bar insert hole, a part of the ram is made to butt against the stopper means to perform the positioning of the ram, and the half-nut or locking block is brought into press con­ tact with the ram to allow it to move back and forth for adjustment, for the purpose of setting the half-­ nut or locking block to a poisition where it can be meshed with the threads or circumferential grooves on the tie bar. The above-featured tie clamping apparatus ac­ cording to the present invention can operate in the following manner and affords the following advantages: (1) Owing to the fact that the length of the threads on the tie bar is chosen to be the length corresponding to the variable range of the thickness of the dies to be used, and the half-nut is allowed to move for adjustment, the threads on the tie bar and the half-­ nut can be surely meshed with each other. (2) Since the tie bar does not serve also as a rod of a hydraulic cylinder as is the case with the apparatus in the prior art, the unfavorable result of oil leakage caused by such reason would not occur at all. (3) Accordingly, even if the tie bar should be hurt, there is no need to mind it as is the case with the prior art apparatus. (4) As the tie bar is fixedly secured to either one of the fixed die plate and the movable die plate, it would never rotate about its axis during operation, and so, upon matching the phases of the threads, the adjustment can be performed according to preset phase values. (5) Phase matching for the threads or circumferential grooves on the tie bar can be achieved by moving the half-nut or locking block by a minute amount in the lengthwise direction, by means of a movement adjusting device, and hence, even in the event that the thickness of the dies has changes as a result of replacement of dies, the phase matching can be achieved in a short period of time. (6) When the tie bar is mounted to the movable die plate, since the driving means such as the hydraulic cylinder for opening or closing the half-nut or locking block is mounted to the fixed die plate, there is no need to provide a hydraulic hose or like acces­ sory parts on the movable die plate, hence the periph­ eral structure of the movable die plate can be simplified, the movable die plate can be moved with the minimum necessary power, and also troubles caused by damage of the hose or the like can be reduced. The above-described and other objects, features and advantages of the present invention will become more apparent by reference to the following description of preferred embodiments of the invention taken in conjunc­ tion with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 is a front view of a first preferred embodiment of the present invention showing an opened state of dies; Fig. 2 is an enlarged view of an encircled part A in Fig. 1; Fig. 3 is a side view partly in cross-section of the portion of a half-nut in Fig. 2 as viewed in the direc­ tion of arrow B; Fig. 4 is a front view of the same preferred embodiment but showing a closed state of dies; Fig. 5 is a side view partly in cross-section of the portion of the half-nut in Fig. 4 as viewed in the direction of arrow C; Fig. 6 is a front view of a second preferred embodiment of the present invention showing an opened state of dies; Fig. 7 is an enlarged view of an encircled part A′ in Fig. 6: Fig. 8 is a front view of the same preferred embodiment but showing a closed state of dies; Fig. 9 is a side view partly in cross-section of the portion of a half-nut in Fig. 8 as viewed in the direc­ tion of arrow B′; and Fig. 10 is a plan view partly in cross-section of a die clamping apparatus in the prior art showing an opened state of dies. DESCRIPTION OF THE PREFERRED EMBODIMENTS: In the following, first and second preferred embodiments of the present invention will be described in more detail with reference to Figs. 1 to 9. Figs. 1 to 5 illustrate a first preferred em­ bodiment of the present invention, in which reference numeral 150 designates a base for fixedly mounting the die clamping apparatus thereon. At one end of the base 150 is fixedly secured a fixed die plate 154 for mounting a fixed die 152 thereto. Reference numeral 158 designates a mov­ able die plate, on the side faced to the fixed die plate 154 of the movable die plate 158 is mounted a movable die 156, and at the foot of the movable die plate 158 are integrally mounted slide shoes 159, which are placed on guide rails 151 disposed on the base 150 so as to be slidable in the back and forth directions along the guide rails 151. It is to be noted that the guide portions of the above-mentioned movable die plate 158 could be either a sliding type guide or a rolling type guide, or else it could be of the type of floating the die plate 158 by means of air or magnetic force. At the four corners of the above-described fixed die plate 154 are formed hydraulic cylinders 160 for generating a die clamping force after closure of dies, and each of these hydraulic cylinders 160 has oil chambers 161A and 161B therein with a ram 162 placed therebetween, as will be described later. As shown in Fig. 2 in an enlarged scale, the ram 162 has its outer circumference formed in a multi-step form having large, middle and small diameters, respectively, and has an insert hole 174 for a tie bar 164 formed therein so as to penetrate therethrough along its axis. Upon clamping dies by raising a pressure, the ram 162 is moved rightwards as viewed in Fig. 1 by feeding pressurized oil into one oil chamber 161A to make its tip end butt against a half-nut 180, and under the condition where the half-nut 180 has been meshed with the tie bar 164, the half-nut 180 is further pushed rightwards to generate a die clamping force. On the side of the ram 162 faced to the half-nut 180, a stopper pin 193 is fixed to the ram 162, the same stopper pin 193 penetrates through a center bore 191 of a sprocket 190, double nuts 192 are mounted to the tip end portion of the stopper pin 193, and a dimension ℓ between the surface of the ram 162 having the stopper pin 193 mounted thereon and the double nuts 192 is made finely adjustable. In other words, by presetting the above-­ mentioned dimension ℓ , a width of movement (cylinder stroke) of the ram 162 can be determined. Reference numeral 164 designates a tie bar having its one end fixedly secured to the movable die plate 158 by means of a nut 165. At the tip end portion of the tie bar 164 are formed threads 172 over a predetermined length, and these threads 172 can be meshed with the half-nut 180 provided on the back side of the fixed die plate 154, upon clamping dies. Reference numeral 166 designates a die opening/­ closing cylinder mounted to either the fixed die plate 154 or the movable die plate 158, and this cylinder causes the movable die plate 158 to advance or retire. According­ ly, the tip end of a rod 170 of the die opening/closing cylinder 166 is fixedly secured to the movable die plate 158 or to the fixed die plate 154. Reference numerals 175 and 176, respectively, designate packing glands fixedly provided at the front and rear ends of the portion forming the above-described die clamping cylinder in the fixed die plate 154, to the packing gland 176 on the back side of the fixed die plate 154 is fixedly secured a guide bar 177 for supporting the half-nut 180 so as to be movable in the back and forth directions, and a threaded hole 182 is provided in the proximity of the inner circumferential portion of the packing gland 176. From the guide bar 177 fixedly secured to the packing gland 176 is slidably supported via a bracket 178 the half-nut 180, in which a nut is divided into two pieces and they are opposed as shown in Fig. 3, and this half-nut 180 is biased by a spring 179 so as to be always held in press contact with the tip end portion 163 of the ram 162. The half-nut 180 can be opened and closed in the lateral directions along a guide bar 181 fixed to the bracket 178 by an opening/closing mechanism not shown, and upon closing dies, the half nut 180 is closed to be meshed with the threads 172 on the tie bar 164. Reference numeral 190 designates a sprocket having the outer circumference of its boss portion threaded, and screwed into the above-described threaded hole 182 provided in the proximity of the inner circumference of the packing gland 176. This sprocket 190 is moved back and forth in the direction of arrows indicated in Fig. 1 via a chain 195 by means of a chain driving device such as a stepping motor or the like not shown. It is to be noted that while the threads at the tip end portion of the tie bar and the half-nut on the side of the fixed die plate are employed as means for fixedly coupling a movable die plate (tie bar) and a fixed die plate with each other in the illustrated embodiment, as a matter of course, the present invention should not be limited to this type of embodiment, but instead the fixed coupling means can be constructed, for instance, by forming one or more circumferential grooves, not shown, on the tip end portion of the tie bar and employing a locking block provided with one or more projections corresponding to the circumferential grooves and engageable therewith, in place of the above-described half-nut. In essence, the fixedly coupling means employed according to the present invention is not limited to the above-described embodiment, so long as it comprises a gripping member which can be surely engaged with and disengaged from the tip end of the tie bar at a preset position and which is movable jointly with the ram with its one end butting against the ram. Now the operation of the die clamping apparatus having the above-mentioned construction will be explained in the following. If pressurized oil is fed into one oil chamber 168A of the die opening/closing cylinder 166, then the movable die plate 158 advances towards the fixed die plate 154 as guided by the guide rails 151, the tip end portion of the tie bar 164 passes through the tie bar insert 174 in the fixed die plate 154, and at the place where the fixed die 152 and the movable die 156 join together, the movable die plate 158 stops as shown in Fig. 4. The sprocket 190 threadedly coupled to the pack­ ing gland 176 is preliminarily positioned by driving the chain 195, and then by applying a hydraulic pressure to the right-hand oil chamber 161B as viewed in Fig. 1, the ram 162 is moved leftwards in Fig. 4 until the right end surface of the sprocket 190 comes into contact with the double nut 192, when the ram 162 is stopped. At this time, the half-nut 180 is also moved by the distance of movement of the ram 162 as pushed by the spring 179, and it is held stopped under the condition that the tip end portion 163 of the ram 162 is kept in press contact with the left end surface of the half-nut 180. This half-nut stop position is determined by preliminarily calculating the position by means of a control device so that at the time point when the tie bar 164 has passed through the fixed die plate 154 and stopped as described above, the phase of the threads in the half nut 180 may nearly match with that of the threads 172 on the tie bar 164. These hydraulic cylinders 160 are provided so as to respectively correspond to the four tie bars 164. Since the threads 172 of the four tie bars 164 are not always coincident in phase with one another, the phase deviation of the threads 172 at the time of finishment of closure of the dies is, if necessary, finely adjusted by means of the double nut 192. At the moment when the closure of the dies has finished, the half-nut 180 is closed by means of a half-­ nut opening/closing device (not shown), and subsequently an oil pressure is applied to the left-hand oil chamber 161A of the hydraulic cylinder. Since the threads 172 of the tie bar 164 and the threads in the half-nut 180 are already held in a meshed condition at this time, the half-­ nut 180 is pushed rightwards by the ram tip end portion 163, thereby the tie bar 164 is drawn, and a die clamping force is generated. When the shaping has been finished and the dies are to be opened, at first the oil pressure in the oil chamber 161A of the hydraulic cylinder 160 is lowered, subsequently the half-nut 180 is opened by means of a half-nut opening/closing device (not shown) to release the meshing with the tie bar 164, and thereafter, when pressurized oil is fed to the right-hand oil chamber 168B of the dies opening/closing cylinder 166, the movable die plate 158 is moved leftwards and the dies are opened. Next, a second preferred embodiment of the present invention will be described with reference to Figs. 6 to 9. Fig. 6 shows the entire assembly of the die clamping apparatus according to the second preferred em­ bodiment of the invention. In this figure, reference numeral 250 designates a base for fixedly mounting the die clamping apparatus thereon, and at one end of the base 250 is fixedly secured a fixed die plate 254 for mounting a fixed die 252 thereon. Reference numeral 258 designates a movable die plate, on the side faced to the fixed die plate 254 of the movable die plate 258 is mounted a movable die 256, and at the foot of the movable die plate 258 are integrally mounted slide shoes 259, which are placed on guide rails 251 disposed on the base 250 so as to be slidable in the back and forth directions along the guide rails 251. It is to be noted that the guide portions of the above-mentioned movable die plate 258 could be either a sliding type guide or a rolling type guide, or else it could be of the type of floating the die plate 258 by means of air or a magnetic force. At the four corners of the above-mentioned movable die plate 258 are formed hydraulic cylinders 260 for generating a die clamping force after closure of dies, and each of these hydraulic cylinders 260 has oil chambers 261A and 261B therein with a ram 262 placed therebetween as will be described later. As shown in Fig. 7 in an enlarged scale, the ram 262 has its outer circumference formed in a multi-step form having large, middle and small diameters, respectively, and has an insert hole 274 for a tie bar 264 formed therein so as to penetrate therethrough along its axis. Upon clamping dies by raising a pressure, the ram 262 is moved leftwards as viewed in Fig. 6 by feeding pressurized oil into one oil chamber 261A to make its tip end butt against a half-nut 280, and under the condition where the half-nut 280 has been meshed with the tie bar 264, the half-nut 280 is further pushed leftwards to generate a die clamping force. On the side of the ram 262 faced to the half-­ nut 280, a stopper pin 293 is fixed to the ram 262, the same stopper pin 193 penetrates through a center bore 291 of a sprocket 290, double nuts 292 are mounted to the tip end portion of the stopper pin 293, and a dimension ℓ between the surface of the ram 262 having the stopper pin 293 mounted thereon and the double nuts 292 is made finely adjustable. In other words, by presetting the above-­ mentioned dimension ℓ , a width of movement (cylinder stroke) of the ram 262 can be determined. Reference numeral 264 designates a tie bar hav­ ing its one end fixedly secured to the movable die plate 258 by means of a nut 265. At the tip end portion of the tie bar 264 are formed threads 272 over a predeter­ mined length, and these threads 272 can be meshed with the half-nut 280 provided on the back side of the movable die plate 258, upon clamping dies. Reference numeral 266 designates a die opening/­ closing cylinder mounted to either the fixed die plate 254 or the movable die plate 258, and this cylinder causes the movable die plate 258 to advance or retire. Accord­ ingly, the tip end of a rod 270 of the die opening/closing cylinder 266 is fixedly secured to the movable die plate 258 or to the fixed die plate 254. Reference numerals 275 and 276, respectively, designate packing glands fixedly provided at the front and rear ends of the portion forming the above-described die clamping cylinder in the movable die plate 258, to the packing gland 275 on the back side of the movable die plate 258 is fixedly secured a guide bar 277 for support­ ing the half-nut 280 so as to be movable in the back and forth directions, and a threaded hole 282 is provided in the proximity of the inner circumferential portion of the packing gland 276. From the guide bar 277 fixedly secured to the packing gland 275 is slidably supported via a bracket 278 the half-nut 280, in which a nut is divided into two pieces 280a and 280b as shown in Fig. 9, and this half-nut 280 is biased by a spring 279 so as to be always held in press contact with the tip end portion 263 of the ram 262. The half-nut 280 can be opened and closed in the lateral directions along a guide bar 281 fixed to the bracket 278 by an opening/closing mechanism not shown, and upon closing dies, the half-nut 280 is closed to be meshed with the threads 272 on the tie bar 264. Reference numeral 290 designates a sprocket having the outer circumference of its boss portion threaded, and screwed into the above-described threaded hole 282 provided in the proximity of the inner circum­ ference of the packing gland 276. The sprocket 290 is moved back and forth in the direction of arrows indicated in Fig. 6 via a chain 295 by means of a chain driving device such as a stepping motor or the like not shown. It is to be noted that while the threads at the tip end portion of the tie bar and the half-nut on the side of the movable die plate are employed as means for fixedly coupling a movable die plate and a fixed die plate (tie bar) with each other in the illustrated embodiment, as a matter of course, the present invention should not be limited to this type of embodiment, but instead the fixed coupling means can be constructed, for instance, by forming one or more circumferential grooves, not shown, on the tip end portion of the tie bar and employing a locking block provided with one or more projections corresponding to the circumferential grooves and engage­ able therewith, in place of the above-described half-nut. In essence, the fixedly coupling means employed according to the present invention is not limited to the above-­ described embodiment, so long as it comprises a gripping member which can be surely engaged with and disengaged from the tip end of the tie bar at a preset position and which is movable jointly with the ram with its one end butting against the ram. Now the operation of the die clamping apparatus having the above-mentioned construction will be explained in the following. If pressurized oil is fed into one oil chamber 268A of the die opening/closing cylinder 266, then the movable die plate 258 advances towards the fixed die plate 254 as guided by the guide rails 151, the tip end of the tie bar 264 passes through the tie bar insert hole 274 in the movable die plate 258, and at the place where the fixed die 252 and the movable die 256 join together, the movable die plate 258 stops as shown in Fig. 8. The sprocket 290 threadedly coupled to the packing gland 275 is preliminarily positioned by driving the chain 295, and then by applying a hydraulic pressure to the left-hand oil chamber 261B as viewed in Fig. 6, the ram 262 is moved rightwards in Fig. 8 until the left end surface of the sprocket 290 comes into contact with the double nut 292, when the ram 262 is stopped. At this time, the half-nut 280 is also moved by the distance of movement of the ram 262 as pushed by the spring 279, and it is held stopped under the condition that the tip end portion 263 of the ram 262 is kept in press contact with the right end surface of the half-nut 280. This half-nut stop position is determined by preliminarily calculating the position by means of a control device so that at the time point when the tie bar 264 has passed through the movable die plate 258 and the movable die plate 258 has stopped as described above, the phase of the threads in the half-nut 280 may nearly match with that of the threads 272 on the tie bar 264. These hydraulic cylinders 260 are provided so as to respectively correspond to the four tie bars 264. Since the threads 272 of the four tie bars 264 are not always coincident in phase with one another, the phase deviation of the threads 272 at the time of finishment of closure of the die is, if necessary, finely adjusted by means of the double nut 292. At the moment when the closure of the dies has finished, the half-nut 280 is closed by means of a half-­ nut opening/closing device (not shown), and subsequently an oil pressure is applied to the right-hand oil chamber 261A of the hydraulic cylinder 260. Since the threads 272 of the tie bar 264 and the threads in the half-nut 280 are already held in a meshed condition at this time, the half-nut 280 is pushed leftwards by the ram tip end por­ tion 263, thereby the tie bar 264 is tensioned, and a die clamping force is generated. When the shaping has been finished and the dies are to be opened, at first the oil pressure in the oil chamber 261A of the hydraulic cylinder 260 is lowered, subsequently the half-nut 280 is opened by means of a half-­ nut opening/closing device (not shown) to release the meshing with the tie bar 264, and thereafter, when pres­ surized oil is fed to the right-hand oil chamber 268B of the dies opening/closing cylinder 266, the movable die plate 258 is moved leftwards and the dies are opened. As described in detail above, according to the present invention, the following various advantages can be attained: (1) Owing to the fact that the threads on the tie bar are made to have a length corresponding to the variable range of thickness of the dies to be used and a fixedly coupling member for the tie bar such as a half-nut or the like is made movable and adjustable, the fixed coupling can be done at any arbitrary posi­ tion, hence the stroke of the hydraulic cylinder is shortened, and reduction in size of the apparatus can be realized. In addition, the phase adjustment for the above-mentioned fixedly coupling member can be done by minute movement within a short period of time. (2) Since the tie bar is fixedly secured to either one of the fixed die plate and the movable die plate and does not serve also as a rod of a hydraulic cy­ linder, the anxiety of oil leakage caused by damage of the tie bar is perfectly eliminated, and there is no need to fear hurt of the rod as is the case with the prior art. (3) As the tie bar is fixedly secured to the movable die plate or the fixed die plate and does not rotate, there is no fear that deviation of the phase of the threads may arise. (4) In the case where the tie bar is mounted to the movable die plate, surplus devices and parts can be omitted from the environment of the movable die plate and the structure can be simplified. Moreover, generation of troubles caused by unexpected damages of these devices and parts is reduced, and surplus power is also not necessitated, resulting in energy saving. While a principle of the present invention has been described above in connection to preferred embodiments of the invention, it is intended that all matter contained in the above description and illustrated in the accompany­ ing drawings shall be interpreted to be illustrative and not in a limiting sense.

Claims: 1. A die clamping apparatus including a fixed die plate for holding a fixed die, a movable die plate for holding a movable die, means for making said movable die plate operatively advance or retire with respect to said fixed die plate, means for fixedly coupling said movable die plate to said fixed die plate after the mov­ able die plate has come close to the fixed die plate and the fixed die and the movable die have closed, and tie bars for carrying out clamping of dies; characterized in that said tie bars are fixedly secured to either one of the fixed die plate and the movable die plate, a hydraulic cylinder having a ram for clamping of dies is provided on the other die plate not provided with the tie bars, and said fixedly coupling means consists of a half-nut or a locking block which is provided on the surface of said the other die plate on the opposite side to the die mount­ ing surface, which is movable in the directions nearly at right angles to an axis of a tie bar insert hole and which can be moved and positioned in the axial direction of said tie bar insert hole, and threads or circumferential grooves provided on the outer circumference of the tip end portion of the tie bar and adapted to be meshed with said half-nut or locking block; and that between said the other die plate and said half-nut or locking block is provided stopper means, which can adjust the movement and position­ ing in parallel to the axis of the tie bar insert hole, a part of said ram is made to butt against said stopper means to perform positioning of said ram in the axial direction of the tie bar insert hole, the end surface of the half-nut or locking block opposed to said ram is brought into press contact with said ram, and at that position said half-nut or locking block can be positioned so as to mate with the threads or circumferential grooves on said tie bar. 2. A die clamping apparatus as claimed in Claim 1, wherein said stopper means is a sprocket having a bore penetrating therethrough along its axis, which is threaded on an outer circumference of its boss portion and mounted on a plate fixedly secured to said the other die plate and having inner screw threads, a stopper pin projected from an end surface of the ram is made to pass through the penetrating bore of said sprocket, a stepped portion having a larger diameter than that of the pene­ trating bore is formed at the tip end of the stopper pin projecting from said penetrating bore so that said stepped portion can be engaged with an end surface of said sprock­ et, and said half-nut or locking block is biased towards said ram. 3. A die clamping apparatus as claimed in Claim 2, wherein said stepped portion is composed of a threaded portion at the tip end of the stopper pin and a nut, and thereby fine adjustment of the position of the stepped portion is made possible.

Inventors: KUSHIBE, YUKI NAGOYA MACHINERY WORKS OF MITSUBISHI, SATO, HIROSHI NAGOYA MACHINERY WORKS OF MITSUBISHI
Applicants: MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: B29C45
IPC codes: B29C45