Torsional molding apparatus for crank shaft
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a torsional molding apparatus for arranging each crank pin of a crank shaft at a predetermined angular position wherein a plurality of crank pins are arranged on the same plane passing through an axis of the crank shaft. 
     2. Description of the Prior Art 
     In conventional torsional molding apparatuses of the above type, a crank shaft is clamped between clamp arms or split molds for torsional molding. These apparatuses are, however, used only for torsion operation and have a large size. A torsional force is obtained by a cylinder or the like means provided separately from a driving source for clamping operation, and therefore, the structure inevitably becomes complicated. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed for overcoming the disadvantages noted above inherent to prior art devices and has as its object the provision of a torsional molding apparatus for crank shaft which can simplify and miniaturize the structure by enabling a single mechanism to serve both as a clamping mechanism and a twisting mechanism for crank shaft and which can utilize an existing universal press machine by adding a few parts thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings show one embodiment of the present invention. 
     FIG. 1 is a plan view of a crank shaft; 
     FIG. 2 is a view showing the arrangement of crank pins; 
     FIG. 3 is a longitudinal sectional front view of torsional molding apparatus; 
     FIG. 4 is a plan view taken on line IV--IV of FIG. 3; 
     FIG. 5 is a sectional view taken on line V--V of FIG. 3; 
     FIG. 6 is a sectional view taken on line VI--VI of FIG. 3; and 
     FIG. 7 is a partially cutaway side view as viewed from the left side of FIG. 3 when twisting operation is completed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     One embodiment of the present invention will now be described with reference to the drawings. 
     Turning now to FIG. 1, a crank shaft S to be torsional molded is, for example, for a 3-cylinder 2-cycle internal combustion engine and molded by a forging machine. Three crank pins P 1 , P 2  and P 3  and balance weights B 1 , B 2  and B 3  which are disposed in pairs on both sides of respective pins are arranged on the shaft through journal portions J 1  and J 2 . The crank pins P 1 , P 2  and P 3  of the crank shaft S after having been forged by the forging machine are arranged on the same plane passing through the axis of the crank shaft S, as shown in FIG. 2. A torsional apparatus in accordance with the present invention is used in order that these crank pins P 1 , P 2  and P 3  be arranged with an angular phase of 120° offset relative to one another around the axis of the crank shaft S, which arrangement corresponds to the 3-cylinder 2-cycle internal combustion engine. That is, the crank pin P 2  is twisted by 60 degrees clockwise in FIG. 2, and the crank pin P 3  is twisted by 60 degrees counterclockwise in FIG. 2. 
     In FIGS. 3, 4 and 5, a torsional molding apparatus 1 includes a pair of posts 3, 4 stood upright on a fixed support bed 2 and a vertically movable cushion bed 5 arranged through a resistance means 6 which resists to downward movement of the cushion bed 5. A vertically movable bed 7 which is driven to be moved up and down is arranged above the cushion bed 5. Secured to the cushion bed 5 and vertically movable bed 7 are respectively a fixed lower mold 8 and a fixed upper mold 9 which can cooperate to hold the crank pin P 1  part at the center of the crank shaft S. Two sets of rotatable lower molds 10, 12 and rotatable upper molds 11, 13 which can cooperate to hold the remaining crank pin P 2 , P 3  parts are carried on respective beds 5 and 7 rotatably about the axis of the crank shaft S. Arms 14, 15 in abutment with the upper ends of both the posts 3, 4 are integrally projected from both rotatable lower molds 10, 12 radially and outwardly. 
     The fixed support bed 2 is for example a bolster of a press machine, and a lower bed 16 is integrally provided on the fixed support bed 2. Two sets of mutually opposed and paired guide posts 17a, 17b; 17c, 17d are stood upright on the lower bed 16 in spaced relation, and the cushion bed 5 is guided up and down by these guide posts 17a, 17b; 17c, 17d. That is, vertically extending guide grooves 18a, 18b; 18c, 18d are respectively bored in opposed surfaces of the paired guide posts 17a, 17b; 17c, 17d, and four projections 19a-19d to be fitted into these guide grooves 18a-18d are projected on the side of the cushion bed 5. Vertically extending four guide cylinders 20a-20d are respectively stood upright on the lower bed 16 at positiones corresponding to four corners of the cushion bed 5, and guide posts 21a-21d  to be fitted into the guide cylinders 20a-20d are mounted on the lower surface of the cushion bed 5. Thus, the cushion bed 5 is guided up and down while keeping its horizontal posture upwardly of the lower bed 16. 
     A resistance means 6 is interposed between the fixed support bed 2 and the cushion bed 5. The resistance means comprises for example, a hydraulic cushion device, which is provided with four cushion rods 22a-22d which extend through the lower bed 16 and abut with the lower surface of the cushion bed 5 to apply a resistance, by oil pressure, to lower displacement of the cushion rods 22a-22d, that is, downward operation of the cushion bed 5. Thereby, the downward operation of the cushion bed 5 caused by pressing from the above becomes slow. 
     The vertically movable bed 7 is moved up and down by hydraulic apparatus not shown, and an upper bed 23 is secured to the lower surface of the vertically movable bed 7. A part of an existing press machine can be employed as this movable bed 7. Four control rods 24a-24d which extend downwardly at positions corresponding to four guide posts 18a-18d on the lower bed 16 are secured to the upper bed 23, these control rods 24a-24d being provided at their lower ends with fitting recesses 26 into which are fitted fitting projections 25 respectively projected on the upper ends of the guide posts 18a-18d. The control rods 24a-24d can be at their lower ends placed in abutment with the upper ends of the guide posts 18a-18d to thereby restrain further downward movement of the vertically movable bed 7. That is, the lower-limit position of the vertically movable bed 7 and cushion bed 5 are controlled by the control rods 24a-24d. As a consequence, a torsional angle of the crank shaft S is determined, for example, to 60 degrees. 
     The fixed lower mold 8 is provided on a mold adjusting surface with a recess 27 as corresponding to the crank pin P 1  at the axially central portion of the crank shaft S and one side of balance weights B 1  on both sides thereof, and the fixed upper mold 9 is provided on its mold adjusting surface opposed to the adjusting surface of the fixed lower mold 8 with a recess 28 corresponding to the crank pin P 1  and the other side of the balance weights B 1 . Thus, the central portion of the crank shaft S, that is, the portion of the crank pin P 1  is positively held by the fixed lower mold 8 and fixed upper mold 9 by pressing their mold adjusting surfaces toward each other. 
     A pair of lower rotatable support beds 29, 30 are secured to the cushion bed 5 on both sides of the fixed lower mold 8, and a pair of upper rotatable support beds 31, 32 are secured to the lower surface of the upper bed 23 on both sides of the fixed upper mold 9. One lower rotatable support bed 29 is located correspondingly to the crank pin P 2  of the crank shaft S, and the other lower rotatable support bed 30 is located correspondingly to the crank pin P 3  of the crank shaft S. One upper rotatable support bed 31 is arranged above the one lower rotatable support bed 29, and the other upper rotatable support bed 32 is arranged above the other lower rotatable support bed 30. 
     In FIG. 6, the lower rotatable support bed 29 is provided with a circular guide rail 33 opened obliquely and upwardly, and the upper rotatable support bed 31 is provided with a circular guide rail 34 opened obliquely and downwardly opposing to the guide rail 33. The other lower rotatable support bed 30 is provided with a guide rail 35 opened obliquely and upwardly in a direction perpendicular to the opening direction of the guide rail 33, and the upper rotatable support bed 32 is provided with a guide rail 36 opened obliquely and downwardly opposing to the guide rail 35. 
     The rotatable lower mold 10 and rotatable upper mold 11, and the rotatable lower mold 12 and rotatable upper mold 13 are respectively formed into a semi-circular cylinder so that they basically form a circular cylinder when their mold adjusting surfaces are brought into contact with each other. Circular guide projections 10a-13a are respectively projected on the outer peripheries of these rotatable molds 10, 11, 12 and 13, which projections 10a -13a are fitted into guide rails 33-36 with slide bearings 37-40 interposed between its bottom and the mold. Accordingly, each of the rotatable molds 10-13 is rotatably supported by each of the support beds 29-32. 
     The upper surfaces of both the rotatable lower molds 10, 12, that is, their mold adjusting surfaces relative to both the rotatable upper molds 11, 13 are respectively formed with recesses 42, 43 which correspond to the crank pin P 2  and one side of balance weights B 2  on both sides, and the crank pin P 3  and one side of balance weights B 3  on both sides, respectively. The mold adjusting surfaces of both rotatable upper molds 11, 13 are respectively formed with recesses 44, 45 corresponding to the crank pin P 2  and the other side of balance weights B 2  on both sides and the crank pin P 3  and the other side of balance weights B 3  on both sides, respectively. These recesses 42-45 are formed so as not to provide an obstacle to pulling-out operation of the crank shaft S in a vertical direction after completion of torsional operation. That is, notched surfaces 42a, 43a, 44a and 45a are formed on respective recesses 42-45 in a manner that they extend vertically from portions of the recesses at which the horizontal distance from the axis is greatest at the time of completion of torsional operation. At the time of starting torsional operation as shown in FIG. 6, these notched surfaces 42a-45a do not lie on a vertical plane but are formed by estimating the positions of the recesses when the torsional operation has been completed. 
     Bored in the ends of both the rotatable lower molds 10, 12 on the side of the fixed lower mold 8 are grooves 47, 48 corresponding to two journal portions J 1  and J 2 . Both grooves 47, 48 are formed so as to be perpendicular at the completion of torsional operation, and the upper ends of the grooves 47, 48 are positioned below the journal portions J 1 , J 2 . A pair of through-holes 49, 50 in communication with these grooves 47, 48 are bored in the cushion bed 5, and a pair of knock-out cylinders 51, 52 which extend vertically and correspondingly to both the through-holes 49, 50 are supported on the lower bed 16. Piston rods 53, 54 of the knock-out cylinders 51, 52 extend upwardly, and have their ends secured with flat knock-out pins 55, 56 which can come into contact with the lower portions of the journal portions J 1 , J 2  by passing through the through-holes 49, 50 and grooves 47, 48. 
     The arms 14, 15 are integrally provided on the rotationally front side ends of respective rotatable lower molds 10, 12, and rollers 57, 58 in abutment with the upper ends of the posts 3, 4 are supported on the fore ends of the arms 14, 15. 
     Next, the operation of the above-described embodiment will be described. In twisting the crank shaft S, the heated crank shaft S is placed on the fixed lower mold 8 and on the rotatable lower molds 10, 12 with their mold adjusting surfaces being set on a horizontal plane in a state where the vertically movable bed 7 is at raised position. The vertically movable bed 7 is then driven to be moved down. Thereby, the crank shaft S is clamped at respective three crank pin P 1 , P 2  and P 3  parts thereof between the fixed lower mold 8 and fixed upper mold 9; rotatable lower mold 10 and rotatable upper mold 11; and rotatable lower mold 12 and rotatable upper mold 13. 
     When the vertically movable bed 7 is further driven to be moved down, the cushion bed 5 is gradually moved down along with the vertically movable bed 7 due to the resistance of the resistance means 6. At this time, since rollers 57, 58 at the ends of the arms 14, 15 are in abutment with the upper ends of the posts 3, 4, as the cushion bed 5 moves down, one rotatable lower mold 10 rotates clockwise in FIGS. 5 and 6, and the other rotatable lower mold 12 rotates counterclockwise in FIGS. 5 and 6 (though not shown). Thus, the crank shaft S is twisted at the journal portions J 1 , J 2 . That is, when the vertically movable bed 7 moves down until the lower ends of the control rods 24a-24d come to abutment with the upper ends of the guide posts 17a-17d in a manner as described, the rotatable lower mold 10 is rotated through 60 degrees clockwise and the rotatable lower mold 12 is rotated through 60 degrees counterclockwise, as shown in FIG. 7. As a result, as shown in FIG. 2, the crank pin P 2  is twisted through 60 degrees clockwise from its original position, and the crank pin P 3  is twisted through 60 degrees counterclockwise from its original position. Thereby, a crank shaft is molded with the crank pins P 1 , P 2  and P 3  spaced through 120 degrees from each other in the circumferential direction around the axis of the crank shaft. 
     Upon completion of torsional operation, the cushion bed 5 and vertically movable bed 8 are moved up to the original position, and the vertically movable bed 7 is further moved up. At this time, since the notched surfaces 44a, 45a are formed in the recesses 44, 45 of the rotatable upper molds 11, 13, the fitting between the rotatable upper molds 11, 13 and crank shaft S is easily released in line with upward movement of the vertically movable bed 7. Next, the knock-out cylinders 51, 52 are driven to be extended to displace the knock-out pins 55, 56 upwardly into abutment with the lower portions of the journal portions J 1 , J 2 , which journal portions are then pushed up to enable the crank shaft S to be pulled out of the fixed lower mold 8 and both rotatable lower molds 10, 12. At this time, owing to the notched surfaces 42a, 43a on the recesses 42, 43 as extending vertically, there exists no obstacle to pulling out operation of the crank shaft S. 
     After removal of the crank shaft S, the rotatable upper molds 11, 13 are rotated to return to their original positions by drive means such as a cylinder or motor not shown, while the rotatable lower molds 10, 12 are rotated to go back to their original positions with use of no specific drive means since the rollers 57, 58 at the tip ends of the arms 14, 15 integrally formed on the molds 10, 12 can serve as weight therefor. Thus, torsional operation of the crank shaft S is completed. 
     While in the above-described embodiment, a description has been made of a torsional apparatus for crank shaft for use with a 3-cylinder 2-cycle internal combustion engine, it should be noted that the present invention can be practicised irrespective of the number of engine cylinders. While the rotatable axes of the rotatable molds 10-13 have been one and the same, those axes can be located selectively in correspondence to the torsional portion, that is, to the journal portion, if necessary. 
     As described above, according to the present invention, the posts are stood upright on the fixed support bed, the vertically movable cushion bed is arranged on the fixed support bed through a resistance means which resists to downward operation of the cushion bed, the vertically movable bed adapted to be driven for vertical displacement is arranged upwardly of the cushion bed, the fixed lower mold and fixed upper mold adapted to cooperate together to hold a certain crank pin part are secured to the cushion bed and vertically movable bed, respectively, the rotatable lower mold and rotatable upper mold adapted to cooperate together to hold the other crank pin part are carried on respective cushion bed and vertically movable bed rotatably about the axis of the crank shaft, and the arms in abutment with the upper ends of the posts are integrally projected radially and outwardly from the rotatable lower mold. Therefore, the rotatable upper mold and rotatable lower mold are rotated in accordance with the downward operation of the vertically movable bed. Accordingly, the aforesaid other crank pin part is twisted with respect to the certain crank pin part. As a result, the clamp mechanism and torsional mechanism need not be provided separately, and thus the structure can be simplified and miniaturized. Moreover, a conventional universal press machine can be utilized merely by adding molds, arms, posts and the like.