Abstract:
A tool positioning device and a machining element have simple structures which can reduce running cost. In addition to a hole that engages with a shank of an end mill, a channel is provided so that it penetrates through the device such that one end thereof communicates with an upper face of the device and the other end communicates with a lower end of the device. In this case, it is more effective to provide a concave portion that is opened to the upper face and communicates with the hole. The same effect may be obtained by making a cylindrical hole, for example, instead of the channel.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a cylindrical and hollow tool positioning device having a hole that fits with a tool to position an edge of the tool when attached with the tool and to a machining element using the same. 
   BACKGROUND TECHNOLOGY 
     FIG. 4  is a front view of a main part of a conventional printed board machining apparatus,  FIGS. 5A and 5B  are drawings showing a collet chuck section of the printed board machining apparatus, wherein  FIG. 5A  is a front section view thereof and  FIG. 5B  is a view taken in the direction of an arrow A in  FIG. 5A .  FIG. 6  is a front section view of a tool holding unit. 
   In  FIG. 4 , an X table  1  is movable in an X direction perpendicular to the face of the sheet. A tool holding unit  20  and a printed board  15  are placed on the X table  1 . A Y table  2  is movable horizontally in a Y direction in the figure. The Y table  2  holds a Z table  3  so as to be movable vertically in the Z direction in the figure by a motor  4  having an encoder and a ball screw  5 . The Z table  3  holds a spindle  6  that rotatably holds a tool (here an end mill)  8  through the intermediary of a collet chuck  7 . An NC unit  9  controls rotation of the motor  4  to accurately position an edge  7   a  of the collet chuck  7 . 
   As shown in  FIGS. 5A and 5B , the collet chuck  7  has a hole  7   b  formed at the center thereof and slits  7   s  having a width of around 0.5 mm and provided at the edge portion thereof. The portion where the slits  7   s  are provided will be referred to as a claw portion  7   d  hereinafter (note that only the claw portion  7   d  is shown in  FIG. 5A ). The claw portion  7   d  is provided with a channel  7   m  in a middle part thereof. A pad  10  made of an elastic member is disposed in the channel  7   m . A thickness of the pad  10  itself is thicker than a width of the slit  7   s , so that the pad  10  urges the claw portion  7   d  in a direction of widening the slit  7   s.    
   An outer periphery of the claw portion  7   d  is formed so as to have a tapered plane  7   f  having the same angle as a tapered plane  6   f  of the spindle  6 . When the tapered plane  7   f  is separated from the tapered plane  6   f  by moving the collet chuck  7  downward in the figure by means not shown, the claw portion  7   d  is opened due to the resilience of the collet chuck  7  itself and the pad  10 , and a diameter of the hole  7   b  becomes larger than that of a shank  8   a  of the end mill  8 . When the collet chuck  7  is moved upward in the figure by the means not shown, and when it is urged further upward in a state when the tapered plane  7   f  abuts against the tapered plane  6   f , the claw portion  7   d  is urged in a direction of narrowing the slit  7   s , thus holding the shank  8   a  rigidly with frictional force. 
   The Z table  3  supports a pressure foot  11  by means of a pair of cylinders  12  that urges the pressure foot  11  downward in the figure. A ringed brush  13  is disposed at a bottom face of the pressure foot  11 . It is noted that the pressure foot  11  is located at its rising end in the figure. 
   As shown in  FIG. 6 , a base  21  of a tool holding unit  20  supports a holder  22  so as to be movable in the vertical direction. A spring  23  urges the holder  22  upward. The holder  22  is provided with, at the center part thereof, a hole  22   a  whose diameter is larger than an outer diameter of the shank  8   a  of the end mill  8 , i.e., the tool, or larger than a blade portion  8   t  when an outer diameter of the blade portion  8   t  is larger than the outer diameter of the shank  8   a . Still more, the holder  22  is configured so that its upper face  22   u  reaches a preset height from the surface of the X table  1 . 
   A ring  30  is made of hard synthetic resin, for example, and has a hole  30   a  which is provided at the center thereof and whose diameter is slightly smaller than the outer diameter of the shank  8   a . As a result, when the shank  8   a  is inserted into the hole  30   a , the ring  30  is combined in a body with the end mill  8  due to its resilience. That is, the ring  30  is a tool positioning device of the end mill  8 . The holder  22  supports the end mill (machining tool)  8  attached with the ring  30 . It is noted that the ring  30  has an outer diameter of around 7 to 8 mm and a height h of around 4 to 8 mm, and the shank  8   a  has the outer diameter of around 3 mm. 
   Next, an operation of the conventional printed board machining apparatus will be explained. 
   At first, a procedure for holding the end mill  8  with the spindle  6  will be explained. It is noted that the holder  22  supports the end mill  8  in a state in which it is inserted into the ring  30 . Still more, the ring  30  is fixed with the end mill  8  so that a distance from a bottom face  30   d  thereof to a point  8   p  of the end mill  8  becomes a distance k. Accordingly, because a height h of the ring  30  in the vertical direction is preset, a distance from an upper face  30   u  of the ring  30  to the point  8   p  of the end mill  8  is determined. 
   The X and Y tables  1  and  2  are moved so that the axial center of the collet chuck  7 , i.e., the spindle  6 , coincides with an axial line of the hole  22   a . Then, the Z table  3  is moved downward while opening the collet chuck  7  to position the edge  7   a  of the collet chuck  7  at position N indicated by a two-dot-chain line in  FIG. 6 . When the collet chuck  7  is closed in this state, the end mill  8  is held in a state in which the edge  7   a  of the chuck  7  contacts with the upper face  30   u  of the ring  30 . 
   Next, a procedure for machining a channel on the printed board  15  will be explained. 
   After positioning the axial center of the end mill  8  to the center of the channel to be machined, the Z table  3  is moved downward while supplying air to the center part of the spindle  6  so that the point  8   p  of the end mill  8  cuts to a predetermined depth of the printed board  15 . Then, the X and Y tables  1  and  2  are moved in accordance to a machining program. The air supplied to the center of the spindle flows out of the slits  7   s  of the collet chuck  7  and prevents chips from entering the slits  7   s.    
   Because the use of the ring  30  enables one to accurately control the position of the point  8   p  of the end mill as described above, the cutting depth can be set at a required minimum value in machining the printed board, thus improving the machining efficiency. It also causes no insufficient cutting of the end mill  8 . Still more, it becomes unnecessary to confirm the position of the point  8   p  during machining. 
   By the way, the life of the tool may be prolonged by suppressing an increase of temperature of the tool during machining. The prolongation of life of the tool not only improves the machining efficiency but also reduces running cost. 
   A linear and concave coolant supplying section in parallel with an axial line, from the rear end of the shank portion to a cutting face of the blade portion, to directly apply the coolant to the cutting face of the blade portion of the end mill is disclosed in Japanese Publication Patent No. 2894924. A plurality of independent cutting blades disposed in spiral in the axial direction on a rectangle whose width can be defined in the axial direction, so that an interval in the axial direction is wider than the cutting blade, is disclosed in Japanese Patent Laid-Open No. 2002-337016. A blow outlet of compressed air is disposed in the vicinity of the tool as disclosed in Japanese Patent Laid-Open No. 1997-117815. 
   However, because the channel is provided on the shank portion in both the conventional technologies disclosed in Japanese Publication Patent No. 2894924 and Japanese Patent Laid-Open No. 2002-337016, the unit cost of their tools becomes expensive as compared to a standard tool. Still more, because the structure of the tool disclosed in Japanese Patent Laid-Open No. 1997-117815 is complicated, its maintenance and inspection are cumbersome. 
   Accordingly, it is an object of the invention to provide a tool positioning device and a machining element which are capable of solving the above-mentioned problem, whose structures are simple, and which allow a running cost to be reduced. 
   SUMMARY OF THE INVENTION 
   In order to solve the above-mentioned problem, according to a first aspect of the invention, there is provided a hollow and cylindrical tool positioning device for positioning an edge of a tool. A hole penetrates through a center part of the device in an axial direction to attach the tool. An upper face is a plane orthogonal to the axial direction, a lower face is a plane orthogonal to the axial direction, and an outside face connects an outer edge of the upper face with an outer edge of the lower face. A hollow portion in the axial direction communicates with the upper and lower faces. 
   In this case, there may be provided a concave portion that communicates with the hole and is opened to the upper face and one end of the hollow portion may communicate with the upper face via the concave portion. 
   The hollow portion may communicate with the hole across the whole range thereof in the axial direction. 
   The hollow portion may be a channel provided on an outside face of the device or may be a cylindrical hole. 
   According to another aspect of the invention, there is provided a machining element wherein the tool positioning device described above is removably attached with a shank portion of the tool having the shank portion and a blade portion. 
   The invention described above allows a standard tool to be used and the life of the tool to be prolonged, so that the running cost may be reduced. Still more, the invention requires no change in the structure of a printed board machining apparatus, so that it is applicable to the conventional printed board machining apparatus. 
   Still more, because the inventive device is provided with the concave portion, it requires no positioning of a channel in the collet chuck with the hollow portion, thus facilitating the work of attaching the tool to the collet chuck and holding the tool in the tool holding unit. 
   Further, because air flows along the surface of the tool in using the apparatus, the tool cooling effect may be enhanced. 
   According to the invention, the hollow portion may be readily formed, so that the tool positioning device and the machining element may be formed at low cost. 
   It is noted that the summary of the invention described above does not necessarily describe all necessary features of the invention. The invention may also be a sub-combination of the features described above. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIGS. 1A and 1B  show an inventive ring, wherein  FIG. 1A  is a plan view thereof and  FIG. 1B  is a front section view. 
       FIG. 2  is a graph showing machining results when the invention is applied. 
       FIGS. 3A and 3B  show a ring according to a modified example of the invention, wherein  FIG. 3A  is a plan view thereof and  FIG. 3B  is a front section view. 
       FIG. 4  is a front view of a main part of a printed board machining apparatus to which the invention is applicable. 
       FIGS. 5A and 5B  show a collet chuck portion, wherein  FIG. 5A  is a front section view thereof and  FIG. 5B  is a view taken in the direction of an arrow A in  FIG. 5A . 
       FIG. 6  is a front section view of a tool holding unit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention will now be described based on preferred embodiments, which are not intended to limit the scope of the invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiments are not necessarily essential to the invention. 
     FIGS. 1A and 1B  show an inventive ring, wherein  FIG. 1A  is a plan view thereof and  FIG. 1B  is a front section view. It is noted that parts therein which are the same or have the same function with those shown in  FIGS. 4 through 6  will be denoted by the same reference numerals and overlapping explanation thereof will be omitted here. 
   The inventive ring (tool positioning device)  30  has a hole  30   a  that penetrates through a center part of the device in an axial direction (O-O) to attach the tool. An upper face  30   u  is a plane orthogonal to the axial direction. A lower face  30   d  is a plane orthogonal to the axial direction. An outside face  30   p  connects an outer edge of the upper face with an outer edge of the lower face. It is then provided with a concave portion  31  that opens to the upper face  30   u  of the ring  30  and communicates with the hole  30   a  and four channels (hollow portions)  32  that communicate with the hole  30   a  across the whole length of the hole  30   a  in the axial direction and are formed in parallel with the axial line of the hole  30   a . The upper end of the channel  32  communicates with the upper face  30   u  through the concave portion  31  and the lower end thereof communicates with a lower end  30   d , penetrating through the ring in the axial direction. Then, in using the inventive ring  30 , it is attached to an end mill (tool)  8  so that the concave portion  31  faces to the side of a collet chuck  7 . 
   Because the ring  30  is constructed as described above, a part of the air supplied to the axial center part of a spindle  6 , which flows out of the collet chuck  7 , enters the concave portion  31  and flows out of the lower face  30   d  of the ring  30  after passing through the channels  32 . At this time, the air flows along the shank  8   a , so that the end mill  8  is cooled due to heat transmission. The part of the air flowing out of the ring  30  also cools down a blade portion  8   t.    
   As a result, even if the flow amount of air fed to the axial center part of the spindle, i.e., air flowing to the collet chuck  7 , is equalized with that of the conventional device, the end mill  8  is cooled down effectively. 
     FIG. 2  is a graph showing machining results of the tool when the inventive ring is applied. The abscissa represents cutting speeds and the ordinate represents cutting lengths. Results of using the conventional ring are also shown for the purpose of comparison. 
   The test has been carried out under the following conditions:
         (1) Outer diameter of the blade portion of the end mill  8 : 1 mm;   (2) Rotational speed of the spindle: 50,000 rpm, 60,000 rpm and 80,000 rpm;   (3) A flow amount of air supplied to the center part of the spindle: 50 l/min.; and   (4) Work: A pile of three glass epoxy resin boards (glass content: 20 wt. %) having a thickness of 1 mm.
 
It is noted that the number of channels  32  has been four, their width w has been 1.5 mm and a length l across the both ends of the channels  32  located on a diameter has been 5 mm. Still more, the diameter of the hole  30   a  has been 3.0 mm and the diameter of the shank  8   a  has been 3.175 mm.
       

   As is apparent from the graph, the inventive ring can increase the cutting length by eight to ten times as compared to that of the conventional ring. 
   That is, because the invention allows the cutting speed to be increased, the machining efficiency may be improved. Still more, because the invention allows the cutting length to be prolonged, the number of times of replacement of the tool may be reduced when the cutting length is the same. Accordingly, the invention allows the machining efficiency to be improved further. 
   Still more, because the invention allows a standard tool to be used, the running cost may be reduced. 
   Further, because the invention allows the ring  30  to be used repeatedly, the running cost may be reduced. 
   The concave portion  31  is provided in the embodiment described above, so that it becomes unnecessary to adjust the position of the slit  7   s  of the collet chuck  7  with the channel  32 , thus facilitating the work of attaching the end mill  8  with the collet chuck  7  and holding the end mill  8  with the holder  22 . 
   It is noted that although four channels have been provided in the embodiment, the number is not limited to be four and even one channel will do. Still more, the channel  32  may be formed into a spiral shape instead of a linear shape. 
   Further, it is not always necessary to provide the concave portion  31 . 
     FIGS. 3A and 3B  show a structure of a ring  30 ′ according to a modification of the invention, wherein  FIG. 3A  is a plan view thereof and  FIG. 3B  is a front section view. 
   The cutting length may be prolonged and the machining efficiency may be improved in the same manner as described above by providing holes (hollow portions)  33 , instead of the channels  32 , as shown in the figures. 
   It is noted that although the linear or spiral channel  32  may be provided on the outside face  30   p  of the ring  30 , the cooling effect is apt to drop when the channel  32  is provided on the side face of the ring  30  as compared to the case described above. 
   Still more, in the invention, a large amount of air is supplied to the outer periphery of the blade portion as compared to the conventional case, so that chips caused by the machining are blown upward. As a result, dust collecting efficiency improves when the inside of the pressure foot is connected with a dust collector, reducing the chips remaining on the surface of the printed board and within the machined channels. 
   Although the case when the tool is an end mill has been explained above, the invention is also applicable to a case when the tool is a drill and to other tools as well. 
   Although the invention has been described by way of the exemplary embodiments, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and scope of the invention. It is obvious from the definition of the appended claims that the embodiments with such modifications also belong to the scope of the invention.