Patent Publication Number: US-2002013178-A1

Title: Reciprocating type thread rolling apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention relates to an apparatus for rolling a thread (hereinafter referred to as thread rolling) mounting thereon a flat die composed of a stationary die and a reciprocating moving die.  
       [0002] Conventionally, a flat die type thread rolling apparatus for performing thread rolling by means of a moving die mounted on a reciprocating ram and a stationary die mounted on a base causes a problem that productivity is low since the moving die is reciprocated to subject one bolt stock to thread rolling. Hereupon, the inventors of the present application have devised a thread rolling apparatus, in which flat dies composed of a stationary die and a moving die are arranged in a zigzag manner with a ram therebetween, as disclosed in Japanese Provisional Patent Publication No. 11-151545. More specifically, with the apparatus, one of the flat dies can perform thread rolling when the ram advances, and the other of the flat dies can perform thread rolling when the ram retreats, and thus thread rolling can be applied on two bolt stocks in one reciprocation of the ram to considerably enhance productivity.  
       [0003] However, it has proved that the thread rolling apparatus, in which the flat dies are arranged in a zigzag manner with the ram therebetween, involves the following defects.  
       [0004] Thread rolling load is acted on the ram at the time of thread rolling. Since the thread rolling pressure bearing block is divided into two halves, which are small in pressure receiving area to be insufficient in rigidity to be liable to cause backward bending deformation on the ram, thus resulting in a degraded accuracy of threads as formed.  
       [0005] Commonly, the set-up work is performed on the stationary die at the time of thread rolling. Since the flat dies are arranged in a zigzag manner, it is necessary to move to the opposite side, which makes workability worse.  
       [0006] Since there is a need of setting-up spaces on the opposite side at the time of bolt thread rolling, there must be a large work space.  
       SUMMARY OF THE INVENTION  
       [0007] The invention has been devised to solve the above-mentioned problems of the prior art and to provide a reciprocating type thread rolling apparatus, which involves high accuracy for threads and favorable workability at the time of setting-up and which does not require any large setting-up adjusting space.  
       [0008] That is, a reciprocating type thread rolling apparatus according to the invention comprises a ram reciprocated by a crank shaft and fixing to one side thereof at least two moving dies, the other side of the ram being disposed along a single thread rolling pressure bearing block, and stationary dies adapted to pair with the moving dies for thread rolling, the stationary dies being the same in number as that of the moving dies and disposed to be opposite to the moving dies. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 is a plan view showing an embodiment of the invention.  
     [0010]FIG. 2 is a plan view showing another embodiment of the invention.  
     [0011]FIG. 3 is a plan view showing a still further embodiment of the invention.  
                               Explanation of characters                                                 1   drive mechanism            2   base            3   pulley            4   small gear            5   large gear            6   connecting rod            7, 7a, 7b   ram            8   connecting member            9, 10   flat die            9a, 9b   stationary die           10a, 10b   moving die           11   thread rolling pressure bearing block           12, 13   part feeder           14, 15   guide rail           16, 17   projection plate           18a, 18b   upper cover           19a, 19b   die block bearing frame                      
 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0012] The invention will be described below in detail with reference to the drawings, in which typical embodiments of the invention are shown.  
     [0013]FIG. 1 shows an embodiment of the invention, the reference numeral  1  denoting a drive mechanism provided on a base  2 , the drive mechanism comprising a pulley  3  driven through a belt by a motor (not shown) or the like, a small gear  4  mounted on a shaft of the pulley, and a large gear  5  for meshing with the small gear.  
     [0014] A connecting rod  6  for converting torque of the large gear into reciprocation of a ram  7  is pivoted at one end thereof in an eccentric position on a side of the large gear, and at the other end thereof on the ram.  
     [0015] The reference numeral  9  denotes a flat die composed of stationary dies  9   a,    9   b,  which are detachably mounted on the base  2  on the same side of the ram  7  through die block bearing frames  19   a,    19   b.  The reference numeral  10  denotes a flat die composed of moving dies  10   a,    10   b,  which are detachably mounted on one side of the ram  7  to face the stationary dies (the moving die  10   a  pairs with the stationary die  9   a  while the moving die  10   b  pairs with the stationary die  9   b.  In addition, while two sets of the stationary die and the moving die are shown in the figure, they may be suitably set taking account of freedom in arrangement of the apparatus, manufacturing cost of the ram, weight of the apparatus, and the like. The same may be said of the rest.).  
     [0016] A single thread rolling pressure bearing block  11  for preventing backward bending deformation of the ram  7  at the time of thread rolling is mounting to the base  2  on an opposite surface of the ram  7  to a surface, on which the moving dies  10   a,    10   b  are mounted, whereby the block bears thread rolling pressure acting on the ram.  
     [0017] The respective sets ( 9   a,    10   a ), ( 9   b,    10   b ) of the stationary die and the moving die are arranged to be shifted in phase in such a manner that thread rolling is alternately carried out with reciprocation of the ram  7 . That is, the respective sets of the flat die do not perform thread rolling at the same time but one of the sets terminates thread rolling and performs returning action when the other of the sets performs thread rolling. In other words, one of the sets is located in the thread rolling terminating position when the other of the sets is located in the thread rolling beginning position. This suppresses deformation of the ram  7  caused by the thread rolling pressure at the time of thread rolling and prevents degradation in thread rolling accuracy and an increase in load on the motor.  
     [0018] The reference numerals  12 ,  13  denote part feeders, which impart vibrations to bolt stocks being later on subjected to thread rolling to successively align the bolt stocks having been regulated in position to feed the same one by one to guide rails  14 ,  15  and which are arranged on one side of the ram in the same manner as the stationary die. The reference numerals  16 ,  17  denote projection plates having tip ends thereof facing outlets of the guide rails  14 ,  15  and serving to feed the bolt stocks, having reached to the outlets of the guide rails, between a set of the moving die  10   a  and the stationary die  9   a  and a set of the moving die  10   b  and the stationary die  9   b,  which are in a state prior to thread rolling.  
     [0019] In addition, the reference numerals  18   a,    18   b  denote upper covers for preventing floating of the ram in a motion (advancing motion), in which the connecting rod  6  pushes the ram  7  and for adjusting sliding accuracy of the ram (the ram  7  moves while the upper surface thereof is sliding on the inner surfaces of the upper covers).  
     [0020]FIG. 2 shows another embodiment of the invention, in which the part feeders  12 ,  13  disposed adjacent to each other in the previous embodiment are disposed in somewhat spaced positions (the other arrangement is the same as that shown in FIG. 1).  
     [0021] In the embodiments shown in FIGS. 1 and 2, the ram  7  is single and lengthy. Thus the ram  7  is made single and lengthy, and the single thread rolling pressure bearing block  11  is arranged on the opposite surface of the ram  7  to a surface, on which the moving dies  10   a,    10   b  are mounted, whereby backward bending deformation of the ram  7  at the time of thread rolling is prevented and accuracy of threads manufactured in thread rolling can be kept high. Meanwhile, since the ram is great in weight (in addition, the weight increases as the number of sets of the dies increases), the drive mechanism must have a larger capacity. Since the ram is large in length (the relationship with the number of sets of the dies is the same as the weight), it is necessary to pay attention to maintaining machining accuracy of the ram. Also, since the ram is small in specific surface area, it is necessary to pay attention to favorable radiation of frictional heat.  
     [0022] The matters, to which attention is paid, in the embodiments shown in FIGS. 1 and 2 are taken into account in an embodiment shown in FIG. 3, in which the ram  7  is divided into two rams  7   a,    7   b  and the moving dies  10   a,    10   b,  respectively, are arranged on the respective rams (the respective rams are connected to each other by a connecting member  8 . The remaining construction is the same as that shown in FIG. 1). However, it is necessary in this embodiment to take measure of suppressing an increased backward bending deformation of the rams, in particular, the ram  7   a  (for example, strengthening of the upper cover  18   a  and strict adjustment of a clearance between the ram and the upper cover).  
     [0023] In addition, as a measure to positively avoid influences caused by floating of the ram at the time of advancement of the ram (leftward motion in the figure), it is proposed that the ram  7   a  in the embodiment shown in FIG. 3 be made a idle ram (on one side of which the moving die  10   a  is not arranged and which is used as a simple drive force transmitting member. Accordingly, the ram in this embodiment is not required to have a length as long as that of the ram  7   a  shown therein), and the remaining ram  7   b  be constructed in the same manner as the ram  7  shown in FIG. 1 or FIG. 2 is, or further divided like the rams  7   a,    7   b  in the embodiment shown in FIG. 3.  
     [0024] With the reciprocating type thread rolling apparatus thus constructed, when bolt stocks are fed to the part feeders  12 ,  13  and the drive mechanism arranged on the base  2  is driven, the large gear  5  is caused to start rotation through rotation of the pulley  3  and hence rotation of the small gear  4  mounted on the shaft of the pulley. With rotation of the large gear  5 , the connecting rod  6 , one end of which is pivoted in the eccentric position on the side of the large gear, performs crank motion to reciprocate (rightward and leftward movements in the figure) the ram  7 , to which the other end of the connecting rod is pivoted. Reciprocation of the ram causes the moving dies  10   a,    10   b  mounted on one side of the ram to pair ( 10   a  and  9   a;    10   b  and  9   b ) with the mating stationary dies  9   a,    9   b,  so that the respective sets of the dies can alternately perform thread rolling.  
     [0025] With the embodiments shown in FIGS. 1 and 3, the ram  7  is in a most retreated position, the set of the stationary die  9   a  and the moving die  10   a  on the right side being in a state, in which thread rolling has been completed, and the set of the stationary die  9   b  and the moving die  10   b  on the left side being in a thread rolling start state, in which thread rolling can be performed when the ram  7  advances subsequently. Also, with the embodiment shown in FIG. 2, the ram  7  is in a most advanced position, the set of the stationary die  9   a  and the moving die  10   a  on the right side being in a state, in which thread rolling has been completed, and the set of the stationary die  9   b  and the moving die  10   b  on the left side being in a thread rolling start state, in which thread rolling can be performed when the ram  7  retreats subsequently. In this manner, thread rolling can be performed at either of advancing and retreating of the ram  7  by varying the relative positional relationship between the stationary dies  9   a,    9   b  and the moving dies  10   a,    10   b,  and positions of the part feeders  12 ,  13 , and thread rolling of two bolt stocks can be simultaneously performed in one stroke.  
     [0026] Also, thread rolling can preferably be performed at high speed (productivity is two times a conventional one) when anti-slipping serrations (not shown) are provided on that side of thread formation surfaces of the stationary dies  9   a,    9   b  and the moving dies  10   a,    10   b,  at which thread rolling is started, to improve seizure of bolt stocks being subjected to thread rolling. On the other hand, when speed of thread rolling is reduced to about a half of a conventional one, bolt stocks can surely bite the dies even without any serrations on the thread rolling starting side of the thread formation surfaces, thus making it possible to manufacture bolts with high accuracy and pretty threaded surfaces as formed (in this case, the volume of production is approximately the same as that in the prior art).  
     [0027] In addition, while the reciprocating type thread rolling apparatus according to the invention has been described by way of a bolt stock, it goes without saying that the reciprocating type thread rolling apparatus according to the invention can apply thread rolling on screws such as wood screws, tapping screws and the like.  
     [0028] Also, in the case where a longitudinally oriented flat die is used and a length of thread rolling is smaller than a half of a width of the flat dies  9 ,  10 , thread rolling can be again performed at non-used portions by turning the worn dies  9 ,  10  upside down for mounting, which doubles the life of the dies to enable achieving cutting-down of cost for dies by half.  
     [0029] As described above, with the reciprocating type thread rolling apparatus according to the invention, the ram adapted to be reciprocated by the crank shaft is arranged along the single thread rolling pressure bearing block and caused to slide on the side surface of the thread rolling pressure bearing block, whereby adequate rigidity can be ensured and thread rolling can be performed at high accuracy. Also, the moving dies adapted to pair with the stationary dies for thread rolling are arranged on the same side of the ram, whereby the need of moving to an opposite side at the time of setting-up is eliminated to make workability favorable, and the need of providing a setting-up regulating space on the opposite side is eliminated to enable making a work space smaller than that in the prior art. Further, in the case where a longitudinally oriented flat die is used and a length of thread rolling is smaller than a half of a width of the flat die, thread rolling can be again performed at non-used portions of the die by turning the worn die upside down for mounting, which doubles the life of the die to enable achieving cutting-down of cost for the die by half.