Patent Publication Number: US-2019184474-A1

Title: Hole saw structure

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 106144261, filed Dec. 15, 2017, which is herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a hole saw structure. More particularly, the present disclosure relates to a hole saw structure which has a simple structure, a high strength and is easy to discharge chips. 
     Description of Related Art 
     Hole saw can be used to cut a workpiece and cause a circular incision correspondingly, and then a circular opening can be formed on the workpiece corresponding to the circular incision. Therefore, the hole saw plays an important role in the manufacturing industry. 
     The conventional hole saw can be classified into the bi-metal hole saw and the tungsten carbide steel tooth hole saw according to the structure and manufacturing method thereof. Please refer to  FIG. 1 , which is a schematic view of a conventional bi-metal hole saw  10 . As shown in  FIG. 1 , the bi-metal hole saw  10  includes a peripheral wall  11 , an end surface  12  and a sawtooth  13 . One end portion of the peripheral wall  11  is connected around a circumference of the end surface  12 , and the sawtooth  13  is disposed on the other end portion of the peripheral wall  11  along the circumference of the peripheral wall  11 . The peripheral wall  11  is made of a steel sheet by a rolling-up process and is further welded to the end surface  12 , and the other end portion of the end surface  12  is turned so as to form the sawtooth  13 . Therefore, the manufacturing process of the bi-metal hole saw  10  is relatively quick and simple, and the specification of the peripheral wall  11  can be adjusted according to actual needs of the size of the opening. However, because the bi-metal hole saw  10  is made of a steel sheet by the rolling-up process, the strength of the overall structure and the sawtooth  13  is insufficient. Furthermore, although the bi-metal hole saw  10  can be perfectly applied to the perforating operation of a softer workpiece such as wood or resin, the sawtooth  13  is prone to break during the perforating operation of a hard metal workpiece so as to cause the damage of the bi-metal hole saw  10 . Moreover, the structure of the sawtooth  13  is not favorable for discharging the cutting chips, so that it is necessary to perform cleaning operation for several times so as to avoid the blockage of the cutting chip and affecting the efficiency of the perforating operation. 
     Please refer to  FIG. 2 , which is a schematic view of a conventional tungsten carbide steel tooth hole saw  20 . As shown in  FIG. 2 , the tungsten carbide steel tooth hole saw  20  includes a mainbody  21 , a shank body  22  and a plurality of cutting teeth  23 , and a plurality of chip discharging notches  24  are disposed thereon corresponding to the cutting teeth  23 . In the tungsten carbide steel tooth hole saw  20 , the mainbody  21 , the shank body  22  and the chip discharging notches  24  are integrally made of a metal block by a turning process, wherein the cutting teeth  23  are disposed on one side of each of the chip discharging notches  24 , respectively. Therefore, the tungsten carbide steel tooth hole saw  20  made by a turning process has an overall structure with high strength, and the cutting teeth  23  are made of hard alloys such as tungsten steel or tungsten-chromium alloy, so that the tungsten carbide steel tooth hole saw  20  is favorable for applying to the perforating operation of the hard metal workpieces, such as iron sheets and steel sheets. However, the manufacturing process of the tungsten carbide steel tooth hole saw  20  made by the turning process integrally is complicated, the cost of the metal block used as the turning raw materials is high, and the size of the opening made by the tungsten carbide steel tooth hole saw  20  is also limited. Thus, the application of the tungsten carbide steel tooth hole saw  20  is not universal. 
     As shown above, both of the conventional bi-metal hole saw and the conventional tungsten carbide steel tooth hole saw cannot be satisfied with the demands of high strength, high chip removal efficiency and low manufacturing cost in the same time, so that the application thereof will be further limited. In order to solve the aforementioned problems, a bi-metal tungsten carbide steel tooth hole saw which combines the partial structures of the conventional bi-metal hole saw and the conventional tungsten carbide steel tooth hole saw appears in the market. Please refer to  FIG. 3 , which is a schematic view of a conventional bi-metal tungsten carbide steel tooth hole saw  30 . As shown in  FIG. 3 , the bi-metal tungsten carbide steel tooth hole saw  30  includes a peripheral wall  31 , an end surface  32 , a plurality of cutting teeth  33  and a plurality of chip discharging notches  34 , wherein the peripheral wall  31  is made of a steel sheet by a rolling-up process and further welded to the end surface  32 , and the cutting teeth  33  are welded on and the chip discharging notches  34  are disposed on a side portion different from the end surface  32  of the peripheral wall  31 , respectively. Therefore, the manufacturing cost of the bi-metal tungsten carbide steel tooth hole saw  30  is lower than the cost of the conventional tungsten carbide steel tooth hole saw, and the cutting ability and the chip discharging efficiency thereof can be further enhanced by the arrangement of the cutting teeth  33  and the chip discharging notches  34  compared to the conventional bi-metal hole saw. However, the structure strength of the bi-metal tungsten carbide steel tooth hole saw  30  is still far less than the structure strength of the conventional tungsten carbide steel tooth hole saw, and the damage rate thereof is quite high during the perforating operation of hard metal workpieces. Furthermore, a number of the cutting teeth  33  is also limited, so that the efficiency of the perforating operation for hard metal workpieces of the bi-metal tungsten carbide steel tooth hole saw  30  is not as well as expected. 
     Therefore, how to develop a hole saw structure which has a simple structure, low manufacturing cost, high strength and is easy to discharge chip has become a major aim of the people in the related business. 
     SUMMARY 
     According to one aspect of the present disclosure, a hole saw structure, which is cooperated with a hole saw arbor for performing a perforating operation, includes a cylindrical body and a blade set. The cylindrical body has a central chamber and includes an end surface and a peripheral wall. The end surface has a central opening for connecting to the hole saw arbor. One end portion of the peripheral wall is connected around a circumference of the end surface, the other end portion of the peripheral wall is outwardly folded and overlapped around the peripheral wall so as to form a folded portion, the folded portion includes a folded end, and an inner diameter of the cylindrical body is smaller than an outer diameter of the folded portion. The blade set is disposed on the folded portion and includes at least two cutting teeth and at least two chip discharging notches. The at least two cutting teeth are separately disposed on the folded portion, wherein a blade tip of each of the at least two cutting teeth projects from the folded end, and there is an angle between a long axis of each of the at least two cutting teeth and a long axis of the cylindrical body. The at least two chip discharging notches are disposed around the folded portion, wherein each of the at least two chip discharging notches is correspondingly disposed on one side of each of the at least two cutting teeth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1  is a schematic view of a conventional bi-metal hole saw. 
         FIG. 2  is a schematic view of a conventional tungsten carbide steel tooth hole saw. 
         FIG. 3  is a schematic view of a conventional bi-metal tungsten carbide steel tooth hole saw. 
         FIG. 4  is a schematic view of a hole saw structure according to the 1st embodiment of the present disclosure. 
         FIG. 5  is a schematic view of a blade set of the hole saw structure of  FIG. 4 . 
         FIG. 6  is a cross-sectional view of one of the cutting teeth of the hole saw structure of  FIG. 4  during a perforating operation. 
         FIG. 7  is a schematic view of a hole saw structure according to the 2nd embodiment of the present disclosure. 
         FIG. 8  is a bottom schematic view of one of the cutting teeth of the hole saw structure of  FIG. 7 . 
         FIG. 9  is a partial schematic view of the hole saw structure of  FIG. 7  during the perforating operation. 
         FIG. 10  is a schematic view of a hole saw structure according to the 3rd embodiment of the present disclosure. 
         FIG. 11  is a schematic view of a hole saw structure according to the 4th embodiment of the present disclosure. 
         FIG. 12  is a schematic view of a blade set of the hole saw structure of  FIG. 11 . 
         FIG. 13  is a bottom schematic view of one of the cutting teeth of the hole saw structure of  FIG. 11 . 
         FIG. 14  is a bottom schematic view of the hole saw structure of  FIG. 11 . 
         FIG. 15  is a partial schematic view of the hole saw structure of  FIG. 11  during the perforating operation. 
         FIG. 16  is a schematic view of a hole saw structure according to the 5th embodiment of the present disclosure. 
         FIG. 17  is a bottom schematic view of the hole saw structure of  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 4 , which is a schematic view of a hole saw structure  100  according to the 1st embodiment of the present disclosure. The hole saw structure  100  is cooperated with a hole saw arbor (not shown) for performing a perforating operation, and the hole saw structure  100  includes a cylindrical body  110  and a blade set  130 . 
     The cylindrical body  110  has a central chamber  101  for accommodating the hole saw arbor, and the cylindrical body  110  includes an end surface  111  and a peripheral wall  112 . The end surface  111  has a central opening  113  for connecting to the hole saw arbor. One end portion of the peripheral wall  112  is connected around a circumference of the end surface  111 , the other end portion of the peripheral wall  112  is outwardly folded and overlapped around the peripheral wall  112  so as to form a folded portion  120 . The folded portion  120  includes a folded end  121 , and an inner diameter of the cylindrical body  110  is smaller than an outer diameter of the folded portion  120 . Preferably, the folded portion  120  can be fixedly connected to the peripheral wall  112  by a welding method, a bonding method or a combination thereof, but the present disclosure is not limited thereto. Therefore, the production difficulty and the manufacturing cost of the hole saw structure  100  can be significantly reduced by the arrangement that the end surface  111  and the peripheral wall  112  are connected to each other so as to form the cylindrical body  110 , so that the manufacturing efficiency of the hole saw structure  100  can be enhanced. Furthermore, the overall strength of the cylindrical body  110  can be stronger and further enhanced by the arrangement of the folded portion  120 . It is favorable for preventing the efficiency of the perforating operation from affecting by the distortion and the deformation of the cylindrical body  110  which is caused by the perforating operation of the hard metal workpieces by the hole saw structure  100  cooperated with the hole saw arbor. Therefore, the application breadth and the service life of the hole saw structure  100  of the present disclosure can be further expanded. 
     The blade set  130  is disposed on the folded portion  120 , and the blade set  130  includes at least two cutting teeth  140  and at least two chip discharging notches  150 . More preferably, a number of the at least two cutting teeth  140  can be two or a multiple of two, and a number of the at least two chip discharging notches  150  can be two or a multiple of two. In detail, in the 1st embodiment of  FIG. 4 , the blade set  130  includes eight cutting teeth  140 , and the number of the chip discharging notches  150  is eight corresponding to the number of the cutting teeth  140 . The cutting teeth  140  are separately disposed on the folded portion  120 , and a blade tip  141  of each of the cutting teeth  140  projects from the folded end  121 . More preferably, the material of the cutting teeth  140  can be tungsten steels, tungsten-chromium alloys or other hard alloys. Therefore, the cutting teeth  140  which are separately disposed on the folded portion  120  can perform a cutting process to the workpiece evenly, and the cutting ability of the hole saw structure  100  of the present disclosure to hard metal pieces can be further enhanced by the cutting teeth  140  made of tungsten steels or other hard alloys. The chip discharging notches  150  are disposed around the folded portion  120 , wherein each of the chip discharging notches  150  is correspondingly disposed on one side of each of the cutting teeth  140 . Therefore, the cutting chips can be discharged outward from the central chamber  101  through the chip discharging notches  150  and removed away from the peripheral region of the blade set  130  so as to prevent the efficiency of the perforating operation of hole saw structure  100  from affecting by the accumulation of the cutting chips. 
     However, it must be noted that the numbers of the cutting teeth  140  and the chip discharging notches  150  can be adjusted according to actual needs, and the numbers of the cutting teeth  140  and the chip discharging notches  150  can be two, four, six, ten, or set in pairs, but the present disclosure is not limited thereto. 
     Please refer to  FIG. 5  and  FIG. 6 , wherein  FIG. 5  is a schematic view of the blade set  130  of the hole saw structure  100  of  FIG. 4 , and  FIG. 6  is a cross-sectional view of one of the cutting teeth  140  of the hole saw structure  100  of  FIG. 4  during the perforating operation. As shown in  FIG. 5 , a shape of the blade tip  141  of each of the cutting teeth  140  is a flat-convex shape, the cutting teeth  140  are separated from each other and equidistantly disposed on the folded portion  120 , and the chip discharging notches  150  are also equidistantly disposed on one side of each of the cutting teeth  140 , respectively. There is an angle θ 1  between a long axis of each of the cutting teeth  140  and a long axis of the cylindrical body  110 , wherein the angle θ 1  can be 1° to 5°. More preferably, in the 1st embodiment of  FIG. 5 , the angle θ 1  is 5°, but the present disclosure is not limited thereto. Therefore, it is favorable for performing the perforating operation to a workpiece by the cutting teeth  140  under a proper range of the angle θ 1 , and the wear on the cutting teeth  140  caused by the perforating operation can be reduced. Thus, the service time of the hole saw structure  100  can be further extended. Furthermore, in the 1st embodiment, a shape of each of the chip discharging notches  150  is upside-down U-shaped. However, although the figure is not shown, the shape of each of the chip discharging notches  150  can also be V-shaped, and the present disclosure is not limited thereto. Therefore, each of the cutting teeth  140  can provides the same cutting power to the workpiece by being disposed separately and equidistantly. It is favorable for preventing the cylindrical body  110  from being distorted or deformed or preventing the cutting teeth  140  from falling off caused by the uneven force to the hole saw structure  100  during the perforating operation, so that the cutting efficiency of the hole saw structure  100  can be further enhanced. Furthermore, by the chip discharging notches  150  which are disposed separately and equidistantly and corresponding to the arrangement of the cutting teeth  140 , the cutting chips can be discharged outward from each of the chip discharging notches  150  evenly. Therefore, it is favorable for preventing the cutting chips from being accumulated in the specific one of the chip discharging notches  150  and then affecting the work of the hole saw structure  100 . Moreover, the cutting teeth  140  has the blade tip  141  being flat-convex can increase the area of contact between the cutting tooth  140  and the workpiece so as to enhance the cutting power of the hole saw structure  100 . 
     As shown in  FIG. 6 , the inner diameter of the cylindrical body  110  is smaller than the outer diameter of the folded portion  120 , and the cutting teeth  140  are disposed centrally on the folded portion  120  and project from the folded end  121 . When the hole saw structure  100  is used to perform the perforating operation to a workpiece A, a diameter of an opening (not shown) formed on the workpiece A can be larger than the inner diameter of the cylindrical body  110 , so that a chip discharging space S will exist between an inner wall of the opening and the peripheral wall  112 . Thus, the cutting chip B can be discharged outward from the chip discharging space S. Therefore, it is favorable for preventing the perforating operation of the hole saw structure  100  from affecting by the accumulation of the cutting chip B, so that the efficiency of the perforating operation of the hole saw structure  100  can be enhanced. 
     Please refer to  FIG. 7  and  FIG. 8 , wherein  FIG. 7  is a schematic view of a hole saw structure  200  according to the 2nd embodiment of the present disclosure, and  FIG. 8  is a bottom schematic view of one of the cutting teeth  240  of the hole saw structure  200  of  FIG. 7 . The structure of the hole saw structure  200  of the 2nd embodiment is similar with the hole saw structure  100  of  FIG. 4 , and the detail of the same structure and elements will not be described again. The hole saw structure  200  includes a cylindrical body  210  and a blade set  230 . 
     The cylindrical body  210  has a central chamber  201  and includes an end surface (reference number is omitted) and a peripheral wall  212 . As shown in  FIG. 7 , the blade set  230  includes eight cutting teeth  240 , and the number of the chip discharging notches  250  is eight corresponding to the number of the cutting teeth  240 , but the present disclosure is not limited thereto. In the 2nd embodiment, a blade tip  241  of each of the cutting teeth  240  projects from the folded end  221 , a shape of the blade tip  241  of each of the cutting teeth  240  is a sharp-convex shape, the cutting teeth  240  are separated from each other and equidistantly disposed on the folded portion  220 , and each of the chip discharging notches  250  is correspondingly disposed on one side of each of the cutting teeth  240 . Therefore, the hole saw structure  200  can be positioned on the workpiece first by the blade tip  241  being sharp-convex before the perforating operation so as to prevent the hole saw structure  200  from displacing in the primary period of the perforating operation and then affecting the efficiency thereof. 
     As shown in  FIG. 7  and  FIG. 8 , each of the cutting teeth  140  of the hole saw structure  200  includes a front blade surface  242 , an inner annular surface  243  and an outer annular surface  244 . A width of the inner annular surface  243  is larger than a width of the outer annular surface  244 , so that the front blade surface  242  is tilting from the central chamber  201  toward the outer annular surface  244 . Therefore, the cutting chips generated from the perforating operation of the hole saw structure  200  can be discharged outward from the chip discharging notches  150  along the front blade surfaces  242  which is tilting disposed so as to prevent the efficiency of the perforating operation of hole saw structure  200  from affecting by the accumulation of the cutting chips. 
     Please refer to  FIG. 9 , which is a partial schematic view of the hole saw structure  200  of  FIG. 7  during the perforating operation. As shown in  FIG. 9 , when the hole saw structure  200  is used to perform the perforating operation to a workpiece A, the blade tip  241  of each of the cutting teeth  240  will contact with the surface of the workpiece A directly, and the blade tip  241  being sharp-convex will be positioned on the workpiece A and then performed the cutting process, and a cutting chip B will be produced correspondingly. Then, the cutting chip B will flip toward the outer annular surface  244  due to the front blade surface  242  which is tilting disposed and will be further discharged outward from the chip discharging notches  250 . Therefore, by the front blade surface  242  which is tilting disposed, it is favorable for discharging the cutting chip B outward from the hole saw structure  200  along the tilting direction of the front blade surface  242 , and the cutting resistance caused by the accumulation of a plurality of the cutting chip B can also be reduced. Thus, the times of the cleaning operation of the cutting chip can be reduced, so that the efficiency and the speed of the perforating operation of the hole saw structure  200  can be further enhanced. 
     Please refer to  FIG. 10 , which is a schematic view of a hole saw structure  300  according to the 3rd embodiment of the present disclosure. The structure of the hole saw structure  300  of the 3rd embodiment is similar with the hole saw structure  200  of  FIG. 7 , and the detail of the same structure and elements will not be described again. The hole saw structure  300  includes a cylindrical body  310  and a blade set  330 . 
     The cylindrical body  310  has a central chamber  301  and includes an end surface  311  and a peripheral wall  312 . As shown in  FIG. 10 , the blade set  330  includes eight cutting teeth  340 , and the number of the chip discharging notches  350  is eight corresponding to the number of the cutting teeth  340 , but the present disclosure is not limited thereto. The cutting teeth  340  are separated from each other and equidistantly disposed on the folded portion  320 , and a blade tip  341  of each of the cutting teeth  340  projects from the folded end  320 . In the 3rd embodiment, a shape of the blade tip  341  of each of the cutting teeth  340  is a flat-convex shape, and a front blade surface (reference number is omitted) of each of the cutting teeth  340  is tilting disposed. Therefore, an area of contact between each of the cutting teeth  340  and the workpiece (not shown) can be increase by the blade tips  341  of the cutting teeth  340  being flat-convex, so that the cutting power of the cutting teeth  340  can be increased. Furthermore, by the front blade surface which is it is tilting disposed, the discharging efficiency of the cutting chips can be enhanced, so that the cutting power of the hole saw structure  300  to a hard workpiece can be significantly increased. 
     Please refer to  FIG. 11 , which is a schematic view of a hole saw structure  400  according to the 4th embodiment of the present disclosure. The hole saw structure  400  is cooperated with a hole saw arbor (not shown) for performing a perforating operation, and the hole saw structure  400  includes a cylindrical body  410  and a blade set  430 . 
     The cylindrical body  410  has a central chamber  401  for accommodating the hole saw arbor, and the cylindrical body  410  includes an end surface  411  and a peripheral wall  412 . The end surface  411  has a central opening  413  and at least two limiting holes  414  for connecting to the hole saw arbor correspondingly. One end portion of the peripheral wall  412  is connected around a circumference of the end surface  411 , the peripheral wall  412  includes at least two chip discharging holes  415 , and the at least two chip discharging holes  415  are corresponding to each other. The chips of the workpiece can be removed quickly outward from the central chamber  401  by the arrangement of the chip discharging holes  415  after finishing the perforating operation of the hole saw structure  400 . Therefore, it is favorable for simplifying the preparation procedure between different perforating operations of the hole saw structure  400 . The other end portion of the peripheral wall is  412  is outwardly folded and overlapped around the peripheral wall  412  so as to form a folded portion  420 . The folded portion  420  includes a folded end  421 , and an inner diameter of the cylindrical body  410  is smaller than an outer diameter of the folded portion  420 . Preferably, the folded portion  420  can be fixedly connected to the peripheral wall  412  by a welding method, a bonding method or a combination thereof, but the present disclosure is not limited thereto. Therefore, the production difficulty and the manufacturing cost of the hole saw structure  400  can be significantly reduced by the arrangement that the end surface  411  and the peripheral wall  412  which are connected to each other so as to form the cylindrical body  410 , so that the manufacturing efficiency of the hole saw structure  400  can be enhanced. Furthermore, the overall strength of the cylindrical body  410  can be stronger and further enhanced by the arrangement of the folded portion  420 , so that it is favorable for preventing the efficiency of the perforating operation from affecting by the distortion and the deformation of the cylindrical body  410  which is caused by the perforating operation of the hard metal workpieces by the hole saw structure  400  cooperated with the hole saw arbor. Therefore, the application breadth and the service life of the hole saw structure  400  of the present disclosure can be further expanded. 
     The blade set  430  is disposed on the folded portion  420 , and the blade set  430  includes at least two cutting teeth  440  and at least two chip discharging notches  450 . More preferably, a number of the at least two cutting teeth  440  can be two or a multiple of two, and a number of the at least two chip discharging notches  450  can be two or a multiple of two. In detail, in the 4th embodiment of  FIG. 11 , the blade set  430  includes eight cutting teeth  440 , and the number of the chip discharging notches  450  is eight corresponding to the number of the cutting teeth  440 . The cutting teeth  440  are separately disposed on the folded portion  420 , and a blade tip  441  of each of the cutting teeth  440  projects from the folded end  421 . More preferably, the material of the cutting teeth  440  can be tungsten steels, tungsten-chromium alloys or other hard alloys. Therefore, the cutting teeth  440  which are separately disposed on the folded portion  420  can perform a cutting process to the workpiece evenly, and the cutting ability of the hole saw structure  400  of the present disclosure to hard metal pieces can be further enhanced by the cutting teeth  440  made of tungsten steels or other hard alloys. The chip discharging notches  450  are disposed around the folded portion  420 , wherein each of the chip discharging notches  450  is correspondingly disposed on one side of each of the cutting teeth  440 . Therefore, the cutting chips can be discharged outward from the central chamber  401  through the chip discharging notches  450  and removed away from the peripheral region of the blade set  430  so as to prevent the efficiency of the perforating operation of hole saw structure  400  from affecting by the accumulation of the cutting chips. 
     Furthermore, please refer to  FIG. 11  as well as  FIG. 6 . The inner diameter of the cylindrical body  410  is smaller than the outer diameter of the folded portion  420 , and the cutting teeth  440  are disposed centrally on the folded portion  420  and project from the folded end  421 . Thus, a diameter of an opening (not shown) formed on the workpiece can be larger than the inner diameter of the cylindrical body  410 , so that a chip discharging space will exist between an inner wall of the opening and the peripheral wall  412 . Thus, the cutting chips can be discharged outward from the chip discharging space. Therefore, it is favorable for preventing the perforating operation of the hole saw structure  400  from affecting by the accumulation of the cutting chips, so that the efficiency of the perforating operation of the hole saw structure  400  can be enhanced. 
     However, it must be noted that the numbers of the cutting teeth  440  and the chip discharging notches  450  can be adjusted according to actual needs, and the numbers of the cutting teeth  440  and the chip discharging notches  450  can be two, four, six, ten, or set in pairs, but the present disclosure is not limited thereto. 
     Please refer to  FIG. 12  and  FIG. 13 , wherein  FIG. 12  is a schematic view of a blade set  430  of the hole saw structure  400  of  FIG. 11 , and  FIG. 13  is a bottom schematic view of one of the cutting teeth  440  of the hole saw structure  400  of  FIG. 11 . As shown in  FIG. 11  to  FIG. 13 , the cutting teeth  440  are separated from each other and equidistantly disposed on the folded portion  420 , each of the cutting teeth  440  projects from the folded end  421 , and the chip discharging notches  450  are equidistantly disposed on one side of each of the cutting teeth  440 , respectively. There is an angle θ 2  between a long axis of each of the cutting teeth  440  a long axis of the cylindrical body  410 , wherein the angle θ 2  can be 1° to 5°. More preferably, in the 4th embodiment of  FIG. 12 , the angle θ 2  is 5°, but the present disclosure is not limited thereto. Therefore, it is favorable for performing the perforating operation to a workpiece by the cutting teeth  440  under a proper range of the angle θ 2 , and the wear on the cutting teeth  440  caused by the perforating operation can be reduced. Thus, the service time of the hole saw structure  400  can be further extended. Furthermore, in the 4th embodiment of  FIG. 12 , a shape of each of the chip discharging notches  450  is upside-down U-shaped. However, although the figure is not shown, the shape of each of the chip discharging notches  450  can also be V-shaped, and the present disclosure is not limited thereto. Therefore, each of the cutting teeth  440  can provides the same cutting power to the workpiece by being disposed separately and equidistantly. It is favorable for preventing the cylindrical body  410  from being distorted or deformed or preventing the cutting teeth  440  from falling off caused by the uneven force to the hole saw structure  400  during the perforating operation, so that the cutting efficiency of the hole saw structure  400  can be further enhanced. Furthermore, by the chip discharging notches  450  which are disposed separately and equidistantly and corresponding to the arrangement of the cutting teeth  440 , the cutting chips can be discharged outward from each of the chip discharging notches  450  evenly. Thus, it is favorable for preventing the cutting chips from being accumulated in the specific one of the chip discharging notches  450  and then affecting the work of the hole saw structure  400 . 
     As shown in  FIG. 11  and  FIG. 13 , each of the cutting teeth  440  includes a front blade surface  442 , an inner annular surface  443  and an outer annular surface  444 . A width of the inner annular surface  443  is larger than a width of the outer annular surface  444 , so that the front blade surface  442  is tilting from the central chamber  401  toward the outer annular surface  444 . When the hole saw structure  400  is used to perform the perforating operation to workpiece, the blade tip  441  of each of the cutting teeth  440  will contact with the surface of the workpiece directly, and a plurality of the cutting chips will be generated correspondingly. Then, the cutting chips will be guided to the chip discharging notches  450  and then be further discharged outward thereon due to the front blade surface  442  which is tilting disposed. Therefore, by the front blade surface  442  which is tilting disposed, it is favorable for discharging the cutting chips outward from the hole saw structure  400  along the tilting direction of the front blade surface  442 , and the cutting resistance caused by the accumulation of the cutting chips can also be reduced. Thus, the times of the cleaning operation of the cutting chip can be reduced, so that the efficiency and the speed of the perforating operation of the hole saw structure  400  can be further enhanced. 
     Please refer to  FIG. 14  and  FIG. 15 , wherein  FIG. 14  is a bottom schematic view of the hole saw structure  400  of  FIG. 11 , and  FIG. 15  is a partial schematic view of the hole saw structure  400  of  FIG. 11  during the perforating operation. As shown in  FIG. 14 , the at least two cutting teeth  440  includes a cutting teeth  440  having the blade tip  441  being sharp-convex and a cutting teeth  440  having the blade tip  441  being flat-convex, and the cutting teeth  440  having the blade tip  441  being sharp-convex and the cutting teeth  440  having the blade tip  441  being flat-convex are separated from each other and equidistantly disposed around the folded portion  420 . In detail, in the 4th embodiment, the cutting teeth  440  of the hole saw structure  400  can include the cutting teeth  440   a  having the blade tips  441   a  being sharp-convex and the cutting teeth  440   b  having the blade tips  441   b  being flat-convex. The cutting teeth  440   a  having the blade tips  441   a  being sharp-convex and the cutting teeth  440   b  having the blade tips  441   b  being flat-convex are separated from each other and equidistantly disposed around the folded portion  420  and project from the folded end  421 . Furthermore, as shown in  FIG. 15 , when the hole saw structure  400  is used to perform the perforating operation to a workpiece A, the blade tip  441   a  of each of the cutting teeth  440   a  will contact with the surface of the workpiece A directly, and the blade tip  441   a  being sharp-convex can position the hole saw structure  400  on the workpiece A first before performing the cutting process so as to prevent the hole saw structure  400  from displacing in the primary period of the perforating operation and then affecting the efficiency thereof. Next, the cutting teeth  440   a  having the blade tips  441   a  being sharp-convex will cut the workpiece A along a center of the cutting trace caused by the hole saw structure  400  and a cutting chip B will be generated correspondingly. The cutting chip B will flip toward the outer annular surface  444  due to the front blade surface  442  which is tilting disposed and will be further discharged outward from the chip discharging notches  450 . Then, the cutting teeth  440   b  having the blade tip  441   b  being flat-convex will contact with the workpiece A and then cut the workpiece A continuously along two sides of the center of the cutting trace, wherein the cutting trace has cut by the cutting teeth  440   a  having the blade tips  441   a  being sharp-convex, and two cutting chips C will be generated correspondingly. The cutting chips C will also flip toward the outer annular surface  444  due to the front blade surface  442  which is tilting disposed and will be further discharged outward from the chip discharging notches  450 . By the separately arrangement of the cutting teeth  440   a  having the blade tips  441   a  being sharp-convex and the cutting teeth  440   b  having the blade tips  441   b  being flat-convex, the hole saw structure  400  can cut the workpiece by strips along the cutting trace thereon. Therefore, a width of each of the cutting chips can be reduced, and it is favorable for discharging the cutting chips. Moreover, all of the cutting teeth  440   a  and the cutting teeth  440   b  of the hole saw structure  400  include the front blade surfaces  442  which are tilting disposed, so that not only the cutting efficiency of the hole saw structure  400  can be enhanced, but also the demand for fast chip removing can be achieved. 
     Please refer to  FIG. 16  and  FIG. 17 , wherein  FIG. 16  is a schematic view of a hole saw structure  500  according to the 5th embodiment of the present disclosure, and  FIG. 17  is a bottom schematic view of the hole saw structure  500  of  FIG. 16 . The hole saw structure  500  is cooperated with a hole saw arbor (not shown) for performing a perforating operation, and the hole saw structure  500  includes a cylindrical body  510  and a blade set  530 . The structure of the hole saw structure  500  of the 5th embodiment is similar with the hole saw structure  400  of  FIG. 11 , and the detail of the same structure and elements will not be described again. 
     The cylindrical body  510  has a central chamber  501  for accommodating the hole saw arbor, and the cylindrical body  510  includes an end surface  511  and a peripheral wall  512 . The end surface  511  has a central opening  513  and two limiting holes  514  for connecting to the hole saw arbor correspondingly. One end portion of the peripheral wall  512  is connected around a circumference of the end surface  511 . The peripheral wall  512  includes two chip discharging holes  515 , and the two chip discharging holes  515  are corresponding to each other. The other end portion of the peripheral wall  512  is outwardly folded and overlapped around the peripheral wall  512  so as to form a folded portion  520 . The folded portion  520  includes a folded end  521 , and an inner diameter of the cylindrical body  510  is smaller than an outer diameter of the folded portion  520 . Preferably, the folded portion  520  can be fixedly connected to the peripheral wall  512  by a welding method, a bonding method or a combination thereof, but the present disclosure is not limited thereto. 
     The blade set  530  is disposed on the folded portion  520 , and the blade set  530  includes at least two cutting teeth  540  and at least two chip discharging notches  550 . More preferably, in the 5th embodiment of  FIG. 16 , the blade set  530  includes eight cutting teeth  540 , and a number of the chip discharging notches  550  is eight corresponding to the number of the cutting teeth  540 . The cutting teeth  540  are separately disposed on the folded portion  520 , and a blade tip  541  of each of the cutting teeth  540  projects from the folded end  521 . The chip discharging notches  550  are disposed around the folded portion  520 , wherein each of the chip discharging notches  550  is correspondingly disposed on one side of each of the cutting teeth  540 . 
     As shown in  FIG. 16  and  FIG. 17 , the cutting teeth  540  of the hole saw structure  500  includes the cutting teeth  540   a  having the blade tips  541   a  being sharp-convex and the cutting teeth  540   b  having the blade tips  541   b  being flat-convex. The cutting teeth  440   a  having the blade tips  541   a  being sharp-convex and the cutting teeth  540   b  having the blade tips  541   b  being flat-convex are separated from each other and equidistantly disposed on the folded portion  520  and project from the folded end  521 . Therefore, the cutting efficiency of the hole saw structure  500  can be further enhanced. 
     In the 5th embodiment of  FIG. 16 , the cylindrical body  510  can further include an inner peripheral surface  516  and at least two grooves  560 . The inner peripheral surface  516  is disposed on the peripheral wall  512  and surrounds the central chamber  501 . The at least two grooves  560  are disposed on the inner peripheral surface  516 , wherein each of the grooves  560  is disposed between one of the at least two cutting teeth  540  and one of the at least two chip discharging notches  550 . More preferably, in the 5th embodiment of  FIG. 16 , a number of the at least two grooves  560  is eight, a length of each of the grooves  560  is equal to or larger than one half of a length of the peripheral wall  512  perpendicular to the end surface  511 , each of the grooves  560  is equidistantly disposed between one of the at least two cutting teeth  540  and one of the at least two chip discharging notches  550 , and a shape of each of the grooves  560  can be triangular groove-shaped or circular groove-shaped, but the present disclosure is not limited thereto. 
     More preferably, in the 5th embodiment of  FIG. 16 , each of the grooves  560  is formed by a debossing method. In detail, when the grooves  560  are made by the debossing method, parts of the inner peripheral surface  516  of the peripheral wall  512  will become concave and embed into the folded portion  520 , so that the folded portion  520  can be further positioned and engaged by the grooves  560 . Therefore, it is favorable for enhancing the strength of the folded portion  520  fixedly disposed on the peripheral wall  512 . Furthermore, because the grooves  560  are made by the debossing method, bending structures perpendicular to the end surface  511  will be formed on the peripheral wall  512  corresponding to the arrangement of the grooves  560 . Thus, the rigidity of the cylindrical body  510  can be effectively increased, and the overall strength of the hole saw structure  500  can be greatly improved. Moreover, because the overall strength of the hole saw structure  500  can be improved after the arrangement of the grooves  560 , a sheet thickness of the peripheral wall  512  can be selectively reduced under the premise that the cylindrical body  510  has high degrees of rigidity and strength. In the case that the sheet thickness of the peripheral wall  512  is reduced, a thickness of each of the cutting teeth  540  perpendicular to the peripheral wall  512  (that is, a distance between the inner annular surface  443  and the outer annular surface  444  as shown in  FIG. 13 ) can be reduced correspondingly. Therefore, the cutting resistance of the hole saw structure  500  can be reduced, and the cutting speed can be further improved. 
     Therefore, by the arrangement of the folded portion  520  and the grooves  560 , the overall structure of the cylindrical body  510  can be stronger, and the rigidity of the hole saw structure  500  can be increased. It is favorable for preventing the efficiency of the perforating operation of the hole saw structure  500  from affecting by the distortion and the deformation thereof, and the application breadth and the service life of the hole saw structure  500  of the present disclosure can be further expanded. 
     According to the aforementioned embodiments, the present disclosure has the following advantages. First, the hole saw structure of the present disclosure has a simple structure by the arrangement of the folded portion, and the overall structure thereof can be further enhanced. Therefore, the hole saw structure of the present disclosure is suitable for applying to the perforating operation of hard metal workpieces, and the manufacturing cost of the hole saw structure can be significantly reduced and the cutting efficiency thereof can be further enhanced. Second, by the cutting teeth which are separated from each other and equidistantly disposed on the folded portion, each of the cutting teeth can provides the same cutting power to the workpiece. Therefore, it is favorable for preventing the cylindrical body from being distorted or deformed or preventing the cutting teeth from falling off caused by the uneven force to the hole saw structure during the perforating operation. Thus, the cutting efficiency of the hole saw structure can be further enhanced, and the service time thereof can be further increased. Third, by the arrangement of the chip discharging notches and the front blade surface being tilting, the cutting chips can be discharged outward from the hole saw structure along the tilting direction of the front blade surface. Therefore, the times of the cleaning operation of the cutting chip can be reduced, so that the efficiency and the speed of the perforating operation of the hole saw structure can be further enhanced. Fourth, by the arrangement of the cutting teeth with different types of blade tips, the hole saw structure can cut the workpiece by strips. Therefore, a width of each of the cutting chips can be reduced, so that not only the cutting efficiency of the hole saw structure can be enhanced, but also the demand for fast chip removing can be achieved. Fifth, by the grooves disposed on the inner peripheral surface, the rigidity of the cylindrical body can be significantly increased, and the overall strength of the hole saw structure can be significantly enhanced. 
     Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.