Abstract:
A rotating cutting tool that is internally cooled by cryogenic fluid has a generally cylindrical outer shape. At least one flute is formed on the cutting tool and a cutting edge is formed on an outer edge of the flute for cutting a workpiece. An internal cold flow delivery path for cryogenic coolant is in proximity to the cutting edge. A coolant cavity is formed in the cutting tool for supplying cryogenic coolant to the internal cold flow delivery path and a return path for cryogenic coolant is downstream from the cold flow delivery path. An exhaust port is coupled to the return path for exhausting cryogenic coolant to atmosphere. The exhaust port is remote from the cutting edge so that the cryogenic coolant is exhausted away from the cutting edge and away from a workpiece so that the cryogenic coolant does not cool and toughen the workpiece.

Description:
[0001]    This application is a 371 national phase U.S. Non-Provisional patent application, which claims the benefit of priority from Patent Cooperation Treaty International Application No. PCT/US15/14100 filed on Feb. 2, 2015, and United States Provisional Patent Application 61/934,257 for a Rotary Cutting Tool With an Internal Cooling Cavity filed on Jan. 31, 2014, the entire disclosures of which are incorporated herein by reference and made a part hereof. 
     
    
     FIELD 
       [0002]    The invention relates to a cooling flow path design for cryogenically cooled tools in which the shape of the flow path follows the outer shape of the tool, and the coolant is exhausted from the tool at a location that is remote from the workpiece. 
       BACKGROUND 
       [0003]    Workpiece materials which have a hexagonal lattice structure such as inconel, titanium, cobalt, and the like toughen and become more difficult to machine when a cryogenic fluid is applied to the surface of the material. For this reason, it is advantageous to cool a cutting tool internally when using a cryogenic coolant rather than spray the cryogen coolant on the workpiece when machining such materials. 
         [0004]    The increase in cooling on the cutting edge will allow an increase in cutting speed. For example, a 100% increase in cutting speed in titanium material will result in a 30% increase in heat. This means that a 30% reduction in heat at the cutting edge will allow the cutting edge to operate at twice the cutting speed without exceeding the original operating temperature. A tool that is operated at a cutting speed that is twice the original cutting speed can cut the same amount of material in half the time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is an exploded side sectional view of a cutting tool. 
           [0006]      FIG. 2  is a perspective view of the core of the cutting tool and a bushing that mounts on the core. 
           [0007]      FIG. 3  is a side view showing the assembled cutting tool. 
           [0008]      FIG. 4  is a sectional view taken along lines  4 - 4  of  FIG. 3 . 
           [0009]      FIG. 5  is a sectional view taken along lines  5 - 5  of  FIG. 3 . 
           [0010]      FIG. 6  is a side view of a drill body and a bushing that mounts on the drill body. 
           [0011]      FIG. 7  is a side view of the assembled drill body and bushing of  FIG. 6 . 
           [0012]      FIG. 8  is an end view of the drill body and bushing of  FIG. 7 . 
           [0013]      FIG. 9  is a sectional view taken along line  9 - 9  of  FIG. 7 . 
           [0014]      FIG. 10  is a sectional view taken along line  10 - 10  of  FIG. 7 . 
           [0015]      FIG. 11  is a perspective view of an assembled drill body and bushing taken along line  11 - 11  of  FIG. 8 . 
           [0016]      FIG. 12  is a perspective view of a drill having twisted flutes. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]      FIG. 1  is an exploded side sectional view of a cutting tool  50 . The cutting tool  50  comprises a generally cylindrical body  54  having a central blind bore  55  that extends along the longitudinal axis of the cylindrical body  54  from the rear face  56  thereof to a position proximate the front face  58  thereof. Cold flow delivery paths are formed by radial bores  52  that may be formed proximate the front face  58  of the cylindrical body  54  and intersect the central bore  55 . The cold flow delivery paths are located so as to be proximate the cutting edges that may be located on the front face  58 . Longitudinal grooves  59  may be formed along a front portion  60  of the outer surface of the cylindrical body  54  from the radial bores  52  to a position toward the rear face  56 . The longitudinal grooves  59  are downstream from the cold flow delivery path formed by the radial bores  52  and form a return path for cryogenic coolant. The longitudinal grooves  59  may intersect an exhaust manifold groove  61  that is formed around the circumference of the front portion  60 . In the embodiment shown, the longitudinal grooves  59  may end at a shoulder portion  62  that is formed on the cylindrical body  54 . The shoulder portion  62  has a diameter that is greater than the diameter of the front portion  60  of the cylindrical body  54  on which the longitudinal grooves  59  are formed. A bushing  64  may be inserted over the front portion  60  of the cylindrical body  54  until the rear face  65  of the bushing  64  abuts against the shoulder portion  62 . The bushing  64  may have a bore  66  with an internal diameter that allows it to fit tightly over the front portion  60  of the cylindrical body  54 . Exhaust ports  68  may be formed on the interior of the bore  66  proximate the rear face  65  of the bushing  64 . The length of the bushing  64  may be approximately equal to the length of the front portion  60  of the cutting tool  50 . With the bushing  64  in place, the longitudinal grooves  59  form longitudinal passageways that lead from the radial bores  52  in the front portion  60  of the cylindrical body  54  to the exhaust ports  68  formed proximate the rear face  65  of the bushing  64 . The cylindrical body  54  and the bushing  64  may be formed from high speed steel, tool steel, carbide, or any other material normally used in the manufacture of cutting tool devices. 
         [0018]      FIG. 2  is a perspective view of the front portion  60  of the cylindrical body  54  and the bushing  64 . Longitudinal grooves  59  may be formed along the front portion  60  from the radial bores  52  to the shoulder portion  62 . The radial bores  52  intersect the longitudinal grooves  59 , and the longitudinal grooves intersect the exhaust manifold groove  61 . 
         [0019]      FIG. 3  is a side view showing an assembled cutting tool  50 . A sleeve of insulating material  70  having a through passage  76  may be placed in the central longitudinal blind bore  55 . The sleeve of insulating material  70  is positioned in the longitudinal bore  55  to create a front coolant cavity  72  in the blind end of the bore  55 , and proximate to the front face  58  of the cutting tool  50 . The radial bores  52  couple the coolant cavity  72  to the longitudinal grooves  59 . The insulating sleeve  70  may comprise polytetrafluorethylene (PTFE) or other suitable insulating material. The insulating sleeve  70  helps to maintain the cryogenic temperature of the coolant by retarding heat gain by the coolant that is delivered through the sleeve  70  to the front coolant cavity  72 . The exhaust ports  68  in the end of the bushing  64  create exit vents at the end of the cutting portion of the tool  50  that lead from the exhaust manifold groove  61  to atmosphere, and direct the coolant away from the workpiece to prevent the coolant from cooling and toughening the workpiece. The cutting tool  50  may be mounted in a tool holder  75  so that the cutting tool  50  can be installed in a spindle in a conventional manner. At least one flute  57  may be formed on the front face  58  of the cutting tool, and as shown in  FIG. 4 , cutting edges  78  may be formed on the outer edge of the flutes  77 . 
         [0020]    In order to assemble the cutting tool  50  shown in  FIG. 3 , the front portion  60  may be machined to form the longitudinal grooves  59 , and radial bores  52  may be formed to connect the grooves  59  to the front coolant cavity  72 . For clarity, the longitudinal groves  59  are shown to be straight, but it will be understood that spiral grooves will be used if the final cutting tool is provided with spiral cutting edges formed on spiral flutes. The bushing  64  may then be fitted over the front portion  60  of the core. The assembled body  54  and bushing  64  may then be sintered to fuse them together. The front face  58  of the cylindrical body  54  and of the bushing  64  may be machined to form flutes  57 , and the outer surface of the bushing  64  may then be machined to form flutes  77 . The flutes  57  on the face of the tool may be sharpened and the flutes  77  on the outer cylindrical surface of the tool may be sharpened to provide the cutting edges  78 . Alternatively, cutting edges  78  may be brazed or otherwise affixed to the ends of the flutes  57  and  77 . The insulating sleeve  70  is then fitted into the blind bore  55  of the body  54 . Other methods of assembly may be used. 
         [0021]      FIG. 4  is a sectional view taken along lines  4 - 4  of  FIG. 3 . The radial bores  52  provide passages from the coolant cavity  72  formed in the end of the blind bore  55  to the longitudinal grooves  59  formed on the front portion  60  of the body. The radial bores  52  are positioned in alignment with and proximate to the flutes  57  that may be formed on the front face  58  of the cutting tool. The longitudinal grooves  59  are positioned in alignment with and proximate to the flutes  77  and the cutting edges  78  that are formed on the outer surface of the bushing  64 . The coolant in the radial bores  52  and the longitudinal grooves  59  is effective in removing heat from the cutting edges on the front face  58  of the tool and the cutting edges  78  on the outer circumference of the tool. For simplicity, the flutes  77  in  FIGS. 3 and 4  have been shown as being straight, but spiral flutes may also be employed. Because the flutes  77  are shown as being straight, the longitudinal grooves  59  are also shown as being straight, but it will be understood that in cutting tools having spiral flutes, spiral grooves may be employed so that the grooves follow the path of the flutes. 
         [0022]      FIG. 5  is a sectional view taken along lines  5 - 5  of  FIG. 3 . The longitudinal grooves  59  are positioned near the outermost extremity of the flutes  77 , next to the cutting edges  78  formed in the front portion of the tool body. The longitudinal grooves  59  vent back toward the tool holder and spindle and are vented to atmosphere through the exhaust ports  68 . The exhaust ports  68  direct the coolant away from the front of the tool and prevent cooling and toughening the workpiece. 
         [0023]    In use, a source of coolant is coupled to the rear face  56  of the cutting tool  50  and to the passage  76  that is formed in the sleeve of insulating material  70 . The coolant flows from the rear face  56  of the tool  50  to a coolant cavity  72  formed at the end of a blind bore, and from the end of the coolant cavity  72  through the radial bores  52  into the ends of the longitudinal grooves  59  formed on the front part  60  of the tool. The coolant flows along the longitudinal grooves  59  from the front face  58  of the tool toward the rear face  56  until the coolant reaches the exhaust ports  68 . The exhaust ports  68  form exit vents to atmosphere for the coolant, and direct the coolant away from the workpiece. The coolant that is used may be a cryogenic coolant such as liquid nitrogen having a temperature of −196° C., or other cryogenic coolants may be used. Non-cryogenic coolants may also be used. The coolant in the radial bores  52  and the longitudinal grooves  59  are much closer to the flutes and the cutting edges  57  on the face  58  of the tool and to the cutting edges  78  along the length of the tool than the coolant in the coolant cavity  72 , allowing the cutting edges to operate at a lower temperature. 
         [0024]    The flutes  77  in the outer surface of the tool  50  may be right handed, left handed, variable, staggered or straight without departing from the design described herein. In order to maximize the cooling effect of the coolant in the coolant cavity, the internal shape of the coolant cavity and the passageways for the coolant should closely follow the outer shape of the tool. In this way, the distance is minimized between the cutting edges of the tool, which is the heat source, and the coolant in the flutes  77 , resulting in maximum heat absorption by the coolant in the cavity. 
         [0025]    The device as shown may be applied to boring tools, drills, reamers, endmills, thread mills, taps, and pressed carbide inserts. 
         [0026]    The centrifugal force developed by the rotating tool will force the coolant from the coolant cavity  72  to the outermost ends of the radial bores  52 , and through the longitudinal grooves  59  to the exhaust ports  68 . 
         [0027]      FIGS. 6-11  are directed to an embodiment of the device in which the cooling is applied to a cutting tool such as a drill.  FIG. 6  is a side view of a drill body  80  and a bushing  82  that fits on the forward end  84  of the drill body  80  in order to produce a drill as explained more fully below. The forward end  84  of the drill body  80  has a reduced diameter portion  85  in order to fit into a blind bore  86  formed in the bushing  82 . The blind bore  86  in the bushing  82  is dimensioned to be a tight fit over the reduced diameter portion  85  of the drill body  80 . The drill body  80  has an axial blind bore  88  in the shank end  90  which extends from the end  91  of the drill body  80  as shown in  FIG. 7  to the reduced diameter portion  85  at the forward end  84  of the body. Cross-drilled holes  92  are formed in the reduced diameter portion  85  from the outer surface of the reduced diameter portion  85  to a coolant cavity  89  formed at the end of the blind bore  88  in the drill body as explained more fully below. Grooves  94  may be formed along a portion of the length of the reduced diameter portion  85  to provide a path for coolant in the finished drill as explained more fully below. The grooves  94  may extend along a U-shaped path  93  from the cross-drilled holes  92  at the beginning of the cutting portion of the tool  80  to the tip  95  of the reduced diameter portion  85  and back toward end of the cutting portion of the tool. Each U-shaped path  93  may comprise a cold flow delivery path  96 , a cross-over portion  97 , and a return path  98 . Each cold flow delivery path  96  may communicate with a cross-drilled hole  92 , and each return path  98  may communicate with an exhaust gap  101  formed between the end  99  of the bushing  82  and the shoulder  100  formed on the shank end  90  of the drill body  80 . 
         [0028]      FIGS. 7 and 11  are side views of an assembled drill body  80  and bushing  82 . A sleeve  87  of insulating material such as PTFE may be inserted into the blind bore  88  in order to insulate the cryogenic coolant from heat gain from the drill body  80 . A coolant cavity  89  may be formed between the end of the sleeve  87  and the end of a blind bore  88  in the middle of the cutting tool, and the cross drilled holes  92  may intersect the coolant cavity  89 . The outer surface of the bushing  82  may be machined to form drill flutes  102  as best seen in  FIGS. 8 and 9 , and the flutes  102  may be sharpened to form cutting edges  104 . The cold flow delivery paths  96  extend along the axis  103  of the tool from the coolant cavity  89  to the tip  106  of the tool. The cross-over flow paths  97  are located at the tip  106  of the tool, and the return path  98  extends from the tip  106  of the tool to the shank end  90  of the tool. 
         [0029]      FIG. 8  is an end view of the drill body  80  and bushing  82  of  FIG. 7 . The bushing  82  may be machined to form two flutes  102  along the length of the bushing, but other numbers of flutes may be formed on the bushing  82  as desired. A pointed tip  106  having cutting edges  108  is formed by the merger of the two flutes  102 , and in operation, the cutting edges  108  surrounding the pointed tip  106  remove the greatest amount of material in a hole drilling operation. As a result, the cutting edges  108  and the pointed tip  106  become hotter during a cutting operation than the other portions of the drill, and consequently this portion of the drill benefits the most from cooling. The cold flow delivery path  96  is positioned to be in proximity to the cutting edge  104  of the flute  102  on the outer circumference of the cutting tool, and the return path  98  is adjacent to the trailing lip  110  of the flute. The cross-over portion  97  of each U-shaped path  93  connects the cold flow delivery path  96  to the return path  98 , and is proximate to a cutting edge  108  of the pointed tip  106 . The bushing  82  may be machined to form more than two flutes as well known in the art. 
         [0030]    In order to produce the assembled drill of  FIGS. 7-11 , the bushing  82  is first fit onto the reduced diameter portion  85  of the body portion  80  of the drill. The bushing  82  and the reduced body portion  85  are then sintered to fuse them together. The flutes  102  are then formed on the bushing  82  and the flutes are finish ground in order to form the sharpened edges  104  of the flutes. The flutes  102  are formed on the outer surface of the bushing  82  so that the sharpened edges  104  of the flutes are adjacent to the cold flow delivery paths  96  formed on the reduced diameter portion  85  of the drill body  80 , and the cutting edges  108  of the pointed tip  106 . The sleeve  87  of insulating material is then inserted into the blind bore in the body portion  80 . 
         [0031]    In use, coolant enters the drill body  80  through the insulating sleeve  87  and collects in the coolant cavity  89  formed between the end of the insulating sleeve  87  and the end of the blind bore  88 . The coolant in the coolant cavity  89  flows through the cross-drilled holes  92  to the cold flow delivery path  96 , and from the cold flow delivery path  96  through the cross-over portion  97  to the return path  98 , and from the return path  98  to the exhaust manifold groove  101  and to the exhaust ports  99  and to atmosphere. The cold flow delivery path  96  positions the coolant as close as possible to the sharpened flutes  104  of the drill and the cross-over portion  97  positions the coolant as close as possible to the cutting edges  108  at the tip of the drill to maximize the heat removed by the coolant from these areas of the drill. The return path  98  directs the coolant to the exhaust gap  101  that is located at the end of the cutting portion of the tool remote from the tip  106  of the drill so that the coolant can be exhausted to atmosphere and directed away from the workpiece. This prevents the cryogenic coolant from impinging on and toughening the workpiece. The coolant that is used may be a cryogenic coolant such as liquid nitrogen having a temperature of −196° C., or other cryogenic coolants may be used. Non-cryogenic coolants may also be used. 
         [0032]      FIG. 12  is a perspective view of a drill  112  having flutes that are twisted. The drill  112  that is shown has two flutes  114  that are twisted to form a spiral. The flutes  114  terminate in a pointed tip  116 . The construction shown and described in connection with  FIGS. 6-11  may be applied to the drill having two twisted flutes as shown in  FIG. 12 . A drill having flutes that are twisted may also be made with more than two flutes as will be understood by those skilled in the art. 
         [0033]    Having thus described the device, various modifications and alterations will occur to those skilled in the art, which modifications and alterations will be within the scope of the device as defined by the appended claims.