Abstract:
The invention relates to a single-lip drill ( 10 ) having at least one cutting edge ( 160 ) for solid drilling, comprising a drill head ( 13 ) arranged on a shaft ( 12 ), a chip removal channel ( 151 ) extending substantially along the axis of the drill head ( 13 ) and of the shaft ( 12 ) and arranged in both the drill head ( 13 ) and the shaft ( 12 ), and a plurality of guiding elements ( 170, 171, 172, 173 ) arranged on the circumference of the drill head ( 13 ), wherein the single-lip drill is characterized in that at least one guiding element ( 170 ) is arranged at least partially in an angle range of greater than or equal to 245°, measured from the cutting edge ( 160 ) arranged at 0° in a direction opposite the rotational direction of the single-lip drill.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of PCT/DE2011/001927 filed on Nov. 3, 2011, which claims priority under 35 U.S.C. §119 of German Application No. 10 2010 050 351.7 filed on Nov. 5, 2010, the disclosure of which is incorporated by reference. The international application under PCT article 21(2) was not published in English. 
     The invention relates to a single-lip drill. 
     DESCRIPTION OF THE PRIOR ART 
     Such a single-lip drill is disclosed for example in DE 79 22 246 U1. 
     Single-lip drills are used for introducing boreholes into workpieces. Various types of single-lip drills are shown in the VDI guidelines VDI 3210 and VDI 3208. Single-lip drills are mainly used for producing boreholes of comparatively small diameters which are predominantly in the range of 0.5 mm to 50 mm, wherein the drilling depth can be a multiple of the drilling diameter. Usual values for the drilling depth lie in the range of 10 times to 100 times the drilling diameter, but can also be in excess of or less than this value. 
     Single-lip drills are used as solid drilling tools or boring tools. Solid drilling tools are used for introducing boreholes into solid material. The entire circular cross-section of the borehole will be machined by the drilling tool during drilling from the solid. Boring tools are used for enlarging the diameter of a borehole already present in a workpiece. The already existing “borehole” or opening can be produced by drilling, casting or in any other manner and is smaller in its diameter than the borehole to be produced by the drilling tool. An annular cross-section will be machined during the enlargement of the borehole. 
     Single-lip drills generally consist of a drill head and a drill shaft (also often referred to as shaft) and comprise a chucking end. At least one cutting edge is arranged on the drill head, which in the case of a solid drilling tool extends from the central axis of the drill to the circumference of the drill. 
     Furthermore, guide elements are usually arranged on the circumference of the drill head. Moreover, at least one channel is provided which extends in the drill shaft and in the drilling head and which comprises openings on the drill head and on the chucking end. Coolant will be supplied under pressure through this channel starting from the chucking end, which coolant will exit at the drill head and is provided with the task, in addition to cooling the cutting edge and the guide elements, to flush the chips produced during the drilling through a chip removal channel which is provided in the drill head and in the drill shaft and is mostly arranged in a substantially V-shaped way. The groove is also known as the chip space and usually encloses an angle of approx. 90° to 120°. 
     A single-lip drill is known from JP 63-102813A, in which an arc-shaped groove is arranged in the region of the drill head in a wall of a V-shaped groove for discharging the chips and which extends in the direction of the drill axis. 
     Such single-lip drills are usually accommodated on the machine side at their chucking end in a receiver in a spindle provided for this purpose, and are made to rotate by the spindle about the central axis of the drill. At the same time, the tool will be moved towards the workpiece along a central axis with a defined feed per rotation. The single-lip drill will penetrate the workpiece, with the material of the workpiece being cut on the cutting edge arranged on the drill head and will be severed from the workpiece in form of chips. The chips produced in this process will be flushed out of the borehole along the chip removal groove by the coolant which is supplied through the at least one interior channel via the spindle. 
     It is further also possible to allow the workpiece to perform the rotation and/or the feeding movement, or to perform the rotation and/or the feeding movement partly by the tool and partly by the workpiece. 
     Furthermore, an oscillating lifting movement of the tool and/or the workpiece can be provided, which movement is possible by means of a drilling apparatus known from DE 10 2005 025 364 A1. 
     Single-lip drills are preferably used for the purpose of introducing boreholes into workpieces which cannot be produced with other production methods or cannot be produced economically. These workpieces are often produced in large series. Improvements which lead to an increase in the production speed are therefore generally desirable and even small improvements lead to significant savings in the production costs. 
     The production speed is defined in drilling tools by the product of feed per rotation of the tool and the number of the rotations per minute and is generally known as the feeding speed. 
     It is now the object of deep drilling technology to produce deep drilling tools which enable precise boreholes with a low deviation of hole straightness in the most cost-effective manner. 
     The hole straightness deviation is a measuring quantity that characterizes the quality of boreholes. The hole straightness deviation is the deviation of the borehole outlet in relation to the borehole inlet transversely to the ideal axis of the borehole. Such boreholes can usually not be produced with known single-lip drills in one work step. For this reason, it was necessary up until now to pre-drill the workpieces at first with a solid drilling tool. In this first step, the desired hole straightness is not yet achieved. In a second work step, the workpieces will be re-bored with a boring tool. In this second boring work step, it is possible to achieve the desired hole straightness. It is problematic in this respect that two work steps are necessary, i.e. pre-drilling with the help of a solid drilling tool and subsequent re-boring with the help of a boring tool. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the object of further developing a single-lip drill in such a way that a borehole of high-quality with an especially low hole straightness deviation is possible in a single work step. 
     This object is achieved by the features described herein. 
     With the help of the single-lip drill in accordance with the invention, in which at least one part of the at least one guide element is arranged in such a way that predeterminable angular ranges of greater than 245°—as measured from the cutting edge against the direction of rotation of the drill—are covered by the guide element, it is possible to produce boreholes in a single work step by drilling from the solid whose hole straightness deviation is substantially smaller than the hole straightness deviation of the single-lip drills as known from the state of the art. As a result, a second work step for achieving the desired hole straightness can be omitted. It was determined in extensive tests that the hole straightness deviation of boreholes which were produced with the tool in accordance with the invention is under equal test conditions on average only 50% of the hole straightness deviation of boreholes which were produced with conventional single-lip drills as known from the state of the art. 
     An important feature of the single-lip drill in accordance with the invention is the substantially improved guidance of the single-lip drill in the borehole. It is achieved in such a way that at least one (additional) guide element is arranged in an angular range of greater than 245°, measured from the cutting edge arranged at 0° in a direction opposite the rotational direction of the single-lip drill. When reference is made below to an angle or angular range, it shall apply generally that this angle shall be measured from the cutting edge against the direction of rotation of the drill. 
     As a result of this configuration, the single-lip drill in accordance with the invention offers support on both sides over a large angular range and therefore especially good guidance in the borehole. 
     Further advantages and features of the invention are the subject matter of the dependent claims. It can be provided for example that the at least one guide element is arranged in a range of 270°, measured from the cutting edge in a direction opposite the rotational direction of the drill. “In an angular range of 270°” shall mean that the guide element is configured and arranged in such a way that an angle which starts for example at 260° and reaches beyond 270° (e.g. up to 275° or 280°) will be covered. Furthermore, it can be provided for example that the angular range greater than 270° extends from 270° to 280°, especially 270° to 275°, and that the angular range of less than 270° extends from 260° to 270°, especially from 265° to 270°. 
     It is a further, very relevant feature of the single-lip drill in accordance with the invention that the outer surface of the at least one guide element which faces the borehole has a slightly smaller radial distance from the central axis of the tool in an angular range of greater than 245° than the outer surface of the guide element in an angular range of less than 245° or the outer surfaces of further guide elements which face the borehole. One or several guide elements can be provided in the range of greater than 245°, which guide elements have a radial distance from the central tool axis which is smaller than the radial distance from the central tool axis of the guide elements) which is/are arranged in an angular range of less than 245°. This achieves optimal guidance of the deep-hole drill in the borehole without giving rise to the likelihood that the drill will get stuck in the borehole. These guide elements have a radial distance from the central tool axis which is smaller by up to 50 μm, especially up to 20 μm, than the distance of the outer surface of the guide elements in an angular range of less than 245°. 
     The drill head of the single-lip drill advantageously tapers towards its chucking end. Jamming of the drill in the borehole is also prevented by this configuration. 
     It can be provided according to an advantageous embodiment that a first part of the drill head is arranged conically and a second part of the drill head adjacent thereto is arranged cylindrically. 
     In order to enable the best possible removal of chips, at least one wall of the chip removal channel is preferably curved. A larger opening cross-section than in the case of a non-curved flat wall is achieved especially in the region of the drill head as a result of the curved configuration of the at least one wall of the chip removal channel in order to achieve optimal chip removal despite the smaller opening angle. The term curved shall not only mean a continuous curvature in the present case, but a facet-like curvature for example, i.e. a series of flat areas which are arranged at an angle with respect to each other or a series of curved areas which are arranged at an angle with respect to each other. The curvature of the at least one wall is arranged in such a way that the largest possible cross-section of the chip removal is produced in order to ensure the best possible chip removal. 
     The walls delimiting the chip removal channel enclose an opening angle in the region of the drill head which is less than 115°. The opening angle is less than 90° according to an advantageous embodiment. 
     In the region of the shaft, the walls which delimit the chip removal channel have an opening angle which can be larger than 90° in order to enable the use of known conventional shafts. 
     However, it can also be provided that both the drill head and also the shaft enclose an opening angle which is smaller than 90°. In order to enable the removal of the chips in an operationally reliable manner through this chip space which is smaller in comparison with known solid drilling tools, a cutting edge geometry can further be used which is provided for the use of a drilling apparatus with oscillation. As a result of this cutting edge geometry in conjunction with the drilling apparatus with oscillation, the chip volume will be reduced substantially and the chips can be removed in an operationally reliable manner even through a chip space with an opening angle of less than 90°. The cutting edge geometry is advantageously arranged in such a way as described in DE 20 2009 012 569 U1, to which reference is made in full in this respect. The cutting edge therefore comprises a chip divider which divides the cutting edge into an inner cutting edge region and at least one outer cutting edge region, with the at least one outer cutting edge region having an outwardly curved contour. 
     In accordance with an advantageous embodiment, the drilling head is materially connected to the shaft. The drilling head and the shaft can also be provided with an integral arrangement. Furthermore, an exchangeable drilling head can be provided. 
     In accordance with one embodiment, the shaft is made of a profile tube. The shaft can be made of steel and/or hard metal. 
     Further embodiments relate to the drilling head, which can be made of hard metal and/or can be provided with a coating, e.g. a hard-material coating. The operational lifespan of the single-lip drill can be extended substantially by these measures. 
     It can further be provided that the drilling head consists of a carrier on which cutting edges and/or guide elements made of a wear-proof material, especially hard metal, are arranged. It can be provided that the cutting edges and/or the guide elements are exchangeable. 
     As already mentioned above, the cutting edge preferably comprises a chip divider which subdivides the cutting edge into an inner and at least one outer cutting edge area, with the at least one outer cutting edge area having an outwardly curved contour. 
     Further advantageous developments and embodiments of the single-lip drill in accordance with the invention are the subject matter of the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are shown in the drawings and will be explained in the description below in closer detail, wherein: 
         FIG. 1 a    shows an isometric view of a single-lip drill for drilling from the solid as known from the state of the art; 
         FIG. 1 b    shows a side view of the single-lip drill as shown in  FIG. 1   a;    
         FIG. 2 a    shows an isometric view of a single-lip drill in accordance with the invention for drilling from the solid; 
         FIG. 2 b    shows a side view of the single-lip drill as shown in  FIG. 2   a;    
         FIG. 3 a    shows an isometric view of another embodiment of a single-lip drill in accordance with the invention for drilling from the solid; 
         FIG. 3 b    shows a side view of the single-lip drill as shown in  FIG. 3   a;    
         FIG. 4 a    shows a cross-section through the drilling head of the single-lip drill as shown in  FIG. 1 b    along the line A-A; 
         FIG. 4 b    shows a cross-section through the single-lip drills shown in  FIGS. 1 b , 2 b  and 3 b    along the line B-B; 
         FIG. 4 c    shows a cross-section through the single-lip drills shown in  FIGS. 2 b  and 3 b    along the line C-C; 
         FIG. 4 d    shows a cross-section through the single-lip drill shown in  FIG. 3 b    along the line D-D; 
         FIG. 5 a    schematically shows the hole straightness of a borehole produced with a single-lip drill known from the state of the art, and 
         FIG. 5 b    shows the hole straightness of a borehole produced with a single-lip drill in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 a  and 1 b    show a single-lip drill  10  with a cutting edge  14 , as known from the state of the art. The single-lip drill  10  comprises a chucking end  11  for accommodation in a drill chuck (not shown in  FIGS. 1 a  and 1 b    in closer detail) and a drill shaft  12  with a drill head  13 . The drill shaft  12  and the drill head  13  are realized in an integral configuration for example or are materially joined from two parts. At least one coolant channel  14  is provided in the drill shaft  12 , which channel opens into the front end of the drill head  13 . The coolant which is pumped through the coolant channel  14  is used not only for cooling the drill head  13 , but also for removing the chips produced during drilling through a chip removal groove  15  which starts at the cutting edge  16  of the single-lip drill  10  and extends virtually over the entire length of the drill shaft  12 . At least one guide element  17 , but preferably several thereof, can be provided on the circumference of the drill head  13 , which guide elements are used for guiding the tool. 
       FIG. 4 a    shows a sectional view along the line A-A shown in  FIG. 1 b    through the drill head  13  and  FIG. 4 b    shows a sectional view along the line B-B shown in  FIG. 1 b    through the drill shaft, which is also referred to herein as shaft  12 . These sectional views show a cross-section of the chip removal groove. The chip removal groove  15  has a substantially V-shaped contour and its flat walls enclose an opening angle w 1  of approximately 115°. The opening angle w 2  in the region of the shaft  12  can deviate from the opening angle w 1  in the region of the drill head  13 . The shaft can be provided with a hollow configuration, with the hollow space  141  being flow-connected with the coolant channels  14 . Such a single-lip drill leads to a hole straightness deviation during drilling from the solid as schematically shown in  FIG. 5 a   . The hole straightness deviation is designated as a measuring quantity which characterizes the quality of boreholes. The hole straightness deviation is the deviation of the borehole outlet in relation to the borehole inlet transversely to the ideal axis of the borehole. As is shown in  FIG. 5 a   , the hole straightness fluctuates to a relatively high extent in the borehole as shown there, which has a diameter of 7.5 mm and a length of 510 mm and which was produced with a single-lip drill as known from the state of the art and as shown in  FIGS. 1 a , 1 b   . Its average lies at values of approximately 0.4 to 0.5 mm. 
     Precise deep drill boreholes of substantially cylindrical shape are desired in industrial production, wherein the borehole is to extend along the cylinder axis and the wall thickness is to be especially uniform after completion of the drilling. The borehole should further be realized in a cost-effective way. In order to achieve a wall thickness that is as uniform as possible, boreholes with an especially low hole straightness deviation are required. Such boreholes cannot be achieved in one work step with the single-lip drills which are shown in  FIG. 1 a    and  FIG. 1 b    and which are known from the state of the art, because the hole straightness deviation could become too large, as shown in  FIG. 5 a   . For this reason, boreholes must be produced in two work steps. The workpiece will be predrilled with a solid drilling tool at first. The desired hole straightness will not be achieved in this process (cf.  FIG. 5 a   ). The workpieces will then be re-bored with a boring tool in a second work step. The desired hole straightness can then be achieved with this work step. Two such work steps for the production of a borehole are time-consuming and costly, and therefore undesirable in industrial production. 
     For this reason, the invention provides to arrange in a single-lip drill at least one guide element at least partly in a region in such a way that predeterminable angular ranges of less than and greater than 270°, as measured against the rotational direction from the cutting edge, will be covered. Preferably, more than one guide element will be arranged, wherein at least one of these guide elements will be arranged in the aforementioned angular ranges of less than and greater than 270°, so that guidance in the angular range of 270° will be realized. If reference is made below to angles or angular ranges with respect to the arrangement of the guide elements, then this shall always mean an angle against the direction of rotation of the single-lip drill as measured from the cutting edge. 
     A first embodiment of such a drill in accordance with the invention is shown in  FIGS. 2 a  and 2 b   . In  FIGS. 2 a  and 2 b   , the same elements are provided with the same reference numerals as in  FIGS. 1 a  and 1 b   , so that reference is made to the statements made above concerning their description. In contrast to the single-lip drill as shown in  FIGS. 1 a  and 1 b   , a guide element  170  is arranged in the single-lip drill in the region of the drill head as shown in  FIGS. 2 a  and 2 b    in an angular range as measured from the cutting edge of approximately 260° to 280°, preferably 265° to 275°, and especially 270°. The opening angle w 1  consequently decreases to less than 90°. The chip removal groove  151  therefore has an opening angle of less than 90°. In order to nevertheless ensure optimal removal of chips it is provided to arrange at least one wall of the chip removal groove  151 , e.g. wall  159 , in an arc-shaped curved way, as schematically shown in the sectional view of  FIG. 4 c   . Curved shall mean within the terms of the present invention that the wall is either continuously curved as shown in  FIGS. 4 c  and 4 d   , or that the wall is arranged in a facetted manner, which is not shown in the drawings. Arranged in a facetted manner shall mean that planar wall segments are provided which are arranged at angle with respect to each other and which form a curved surface. The segments need not comprise flat surfaces but can be arranged in a curved manner themselves. In any case, the curvature is intended to achieve an enlargement of the cross-section of the chip removal groove. As is also shown in  FIG. 4 c   , further guide elements  171 ,  172  are arranged in the region of the drill head adjacent to the guide element  170 . 
     Another embodiment of the single-lip drill in accordance with the invention is shown in  FIGS. 3 a  and 3 b   . The same reference numerals refer in these drawings to the same elements as in  FIGS. 2 a  and 2 b   , so that reference is made to the statements above concerning their description. In contrast to the embodiment as shown in  FIGS. 2 a  and 2 b   , two guide elements  172 ,  173  are respectively arranged on the drill head along the drill axis, which are separated from one another by a groove  178  in the longitudinal direction of the single-lip drill, said groove extending in the circumferential direction. The groove  178  divides the drill head into two regions, a first conical part and an adjacent cylindrical part which is situated further in the direction of the chucking end  11 . This arrangement leads to an especially good guidance in the borehole and simultaneously tight jamming in the borehole is prevented. A guide element is arranged in a range in this embodiment too which extends approximately from 260° to 280°, as measured from the cutting edge arranged at 0°, so that in this case too the opening angle w 1  of the chip removal channel  151  is less than 90°. At least one wall of the chip removal channel (e.g. wall  159 ) is arranged with a curved configuration in this case too in order to ensure the best possible removal of the chips. A sectional view through the portion of the drill head situated further in the direction of the chucking end  11  is the subject matter of  FIG. 4 d   . In addition to the guide element  171 , the guide elements  173 ,  174  are respectively arranged in the range of approximately 90° and 180°, as measured from the cutting edge arranged at 0°. This configuration allows a further improvement in the guidance of the single-lip drill in the borehole. 
     Other arrangements of guide elements are generally also possible in the single-lip drills as shown in  FIGS. 2 a , 2 b , 3 a  and 3 b   . The invention focuses on the guide element which is arranged in the range of approximately 260° to 280°. 
     The outer surface of the guide element  170 , which is arranged in a range of approximately 260° to 280° and especially at 270°, is situated in a smaller radius r 2  as measured from the axis of symmetry (central axis) of the drill than the outer surface of the guide elements  171 ,  172 ,  173  and  174 , which describe a radius r 1  as measured from the axis of symmetry of the drill. As a result of this configuration of r 2  smaller than r 1 , tight jamming of the single-lip deep drill in the borehole is prevented in a very effective manner, wherein r 2  may only be slightly less than r 1  in order to further ensure guidance in the borehole. The radius r 2  will be chosen in such a way that it is smaller by up to 50 μm, especially up to 20 μm, than the radius r 1 . 
     The single-lip drills which are shown in  FIGS. 2 a , 2 b    and also in  FIGS. 3 a  and 3 b    are preferably arranged in such a way that the drill head  13  tapers towards its chucking end. It can also be provided that a first part of the drill head  13  is arranged in a conical manner and is followed by a second part of the drill head which is arranged in a cylindrical manner. In the drill head as shown in  FIGS. 3 a , 3 b   , a first part situated adjacent to the drill tip (shown in  FIG. 3 a    and  FIG. 3 b    on the left) is provided with a conical arrangement and a second region which is divided by the groove  178  and is situated in the direction of the chucking end  11  is provided with a cylindrical arrangement. 
     The drill head  13  is materially connected to the shaft  12  for example. The drill head  13  and the shaft  12  can also be arranged in an integral manner. It can also be provided that the drill head  13  is detachably fastened to the shaft  12  and is therefore exchangeable. The drill head preferably consists of hard metal. It can be coated at least partly with a hard material layer. 
     It can also be provided that the drill head consists of a carrier on which the cutting edge  160  or further cutting edges and/or guide elements made of a wear-proof material, especially hard metal, are arranged. The cutting edges and/or the guide elements can be exchangeable. 
     The shaft  12  preferably consists of a profile tube, by means of which a large opening cross-section for the fluidic channel  141  is provided. The shaft may be made of steel for example, but that is not mandatory. The drill head  13  and the shaft  12  may also consist of one single piece made of hard metal. 
     The drill shown in  FIGS. 2 a , 2 b  and 3 a , 3 b    allows substantially better drilling from the solid with a hole straightness deviation shown in  FIG. 5 b   . The hole straightness deviation shows substantially lower values (cf.  FIG. 5 a   ) in comparison with a drill as known from the state of the art and shown in  FIGS. 1 a , 1 b   . For this reason, the single-lip drills in accordance with the invention (as shown in  FIGS. 2 a , 2 b  and 3 a , 3 b   ) allow producing boreholes of low hole straightness deviation in one single work step. This will substantially be achieved in such a way that a support of the drill of a large angular range and therefore especially good guidance in the borehole will be achieved by the further guide element  170  which is arranged in the range of 270°. 
     It needs to be especially mentioned and stressed at this point that the drill in accordance with the invention may comprise a cutting edge  160  which differs from the cutting edge  16  known from the state of the art in such a way that it has a cutting edge geometry which is optimized for use in a drilling apparatus with oscillation as disclosed for example from DE 10 2005 025 364 A1 A cutting edge which is suitable for such a single-lip drill has been disclosed for example in DE 20 2009 012 569 U1, to which reference is made in full in this respect. At least one chip divider is provided in the cutting edge which divides the cutting edge into an inner cutting edge region and at least one outer cutting edge region. The at least one outer cutting edge region has an outwardly curved contour. This upwardly curved contour can be formed for example by planar straight lines but also by an arc of a circle or by a respectively convex curvature. 
     The single-lip drill in accordance with the invention as described above is preferably arranged as a solid drilling tool. It allows the production of boreholes in one single work step and therefore cost-optimized production of a highly precise borehole.