DRILL UNIT WITH THREE CUTTING EDGES

Abstract: The present invention relates to a drill unit with a drill (1), having a cooling channel (2), and with a device for supplying cooling fluid to the cooling channel of the drill. According to the invention the drill (1) comprises three teeth (3, 4, 5), of which the first tooth (3) extends from the periphery of the drill to its centre, while the second and the third teeth (4, 5) extend inward from the periphery of the drill without reaching its centre thereof. Further the cooling channel axially extends in the centre through the drill and is deflected in the bit point of the drill so that it emerges in the space between the centre and the terminal points of the second and the third teeth (4, 5). The supply arrangement for the cooling fluid is applied to supply the fluid under high pressure.

Description: TITLE DRILL UNIT WI TH THREE' CUTTING EDGES DESCRIPTION TECHNICAL AREA The present invention relates to a drill unit with a drill having a cooling channel, and with a device for supplying cooling fluid to the cooling channel of the drill. BACKGROUND OF THE INVENTION The engineering industry has at all times aimed at productivity increases and quality improvements. For accomplishing this at hole cutting operations, which constitute one of the most difficult operations within the engineering industry, one usually aims at increasing the cutting data of the drill in order to in this way obtaining a higher productivity. A higher cutting speed also gives a more finished surface, since the burr formation decreases. A problem with increased cutting speed, in particular when drilling in metal, is however, that a strong wear of the corners of the drill are obtained, due to the high temperature coming up at the machining. For decreasing the wear cooling liquid is supplied, recently by means of cooling channels shaped in the drill. An example of such a drill is shown in US-A-5,173,014, which describes a drill with two complete teeth, two peripherally working teeth and two cooling channels. By using a number of teeth, a more advantageous power distribution of the drill is obtained, which increases the precision of the drill. US-A- 5,174,691 shows a long drill with a central cooling channel, which is completed with two openings. For enabling a good chip transport at long drilled holes, the cooling liquid is supplied under a pressure of about 5500 kPa. It has also been shown to be difficult achieving holes with required tight tolerances using conventional drilling, and the feeding of the drill must often be restricted due to the fact that high axial forces are required. An available method providing good tolerances and requiring low axial force is gun drilling. However, in this method a good control of the drill is required and small feedings, which gives a low manufacturing rate. These requirements lead to that it is often not possible to use this method, but traditional drilling is used with after-treatment with broach. Moreover, in many cases the holes must be reamed. The present invention relates to achieving a drill unit, which is not afflicted with the drawbacks mentioned above, and which admits a high productivity except renouncing the quality of the holes and with a long lifetime of the drill. SUMMARY OF THE INVENTION The purpose of the invention is obtained by means of a drill unit with a drill having a cooling channel, and with a device for supplying cooling fluid to the cooling channel of the drill, characterized in that the drill comprises three teeth, of which the first tooth extends from the periphery of the drill to its centre, while the second and the third teeth extend inward from the periphery of the drill without reaching its centre, that the cooling channel extends axially in the centre of the drill and is deflected in the bit point of the drill so that it emerges in the space between the centre and the terminal points of the second and the third teeth, as well as the supply arrangement for the cooling fluid is applied for supplying the fluid under high pressure. By shaping the drill with three teeth, a high productivity is enabled with tight tolerances of the drilled holes at the same time as only a small axial feeding power is required, as only one of the teeth works in the centre of the hole. By means of supplying the cooling medium under high pressure a more effective cooling is obtained, which leads to a small wear of the drill and a lesser risk for structural changes in the machined material. At the same time the chip transport is facilitated providing a decreased risk for chip stopping, tool breakdown and damages on the hole surfaces. As the cooling channel extends substantially in the centre of the drill, a maximum rigidity of the drill is obtained. In a preferred embodiment the pressure of the cooling fluid supplied is larger than 3000 kPa and the teeth are unequally distributed around the circumference of the drill, whereby the angle, seen a circumferential way between the first tooth and the second and the third teeth, respectively, are 110° and 200°, respectively. Further, partially conical slots are shaped in the drill core between the three teeth, which slots extend toward the centre of the drill. The partially conical slots are preferably shaped using the same tool consisting of a conical grinding tool, the generatrix of which at the machining of the drill core forms an angle of at least 30°to the drill axle. A most significant difference having only one tooth extending to the centre of rotation relative the situation when two teeth are allowed to extend therein is that one is (100%) completely bespared an annoying chisel edge and its negative cutting geometry which rather ploughs than cuts. Due to the fact that no chisel edge exists, the power picture is changed so that more cranky details resilience less in the longitudinal direction of the hole, which leads to better tolerances. For drills having a large chisel edge 20% of the hole diameter in the centre of the hole corresponds to 80% of the axial force. A small part of the axial force reduction can be recovered at high cutting fluid pressures. When the angle of clearance from a geometrical point of view can not be done sufficiently large on drills having two or several teeth extending to the centre, it is evident from the geometry that this problem is considerably better solved having only one tooth extending to the centre. This is done for eliminating the negative impact the angle of clearance has in the centre. According to our judgement the invention according to US-A-5, 173,014 has not solved the problem with a high feeding power in the axial way, which is the consequence with teeth extending to the centre than having one tooth. Only one tooth extending to the centre, makes it possible to obtain positive cutting angles at the centre. An additional aspect is that it is considerably more difficult to achieve four points to coincide on a circle than three points resulting in a better cylindricity of the complete hole due to a disadvantageous power picture, with differentiated angles and in the present case there is a possibility to reduce the risk for self-generated torsional oscillations. Further a drill with four teeth has a lesser chip space leading to increased chip problems. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the enclosed figures, in which; Fig. 1 shows a view of a gun drill from below in a preferred embodiment of a drill unit according to the invention, Fig. 2 shows a side-view of the bit point of the gun drill in figure 1, and Fig. 3 and 4 show the same views as figure 1 and 2, respectively, of a half twist bit according to a second embodiment of the invention. DESCRIPTION OF EMBODIMENTS In figures 1 and 2 in a first preferred embodiment of the invention the lowermost part of a drill 1 is shown, which drill is connected to a drill unit not shown, which contains a device for supplying cooling liquid under high pressure to an axial substantially centrally running cooling channel 2 in the drill 1. The drill 1 has three teeth 3, 4, 5 of which only the first tooth 3 extends from the periphery of the drill all the way to the centre of the drill. The teeth 4 and 5 end at a distance in front of the centre, and their inner ends are located at the same distance from the centre. The edges 6, 7 and 8, respectively of the teeth 3, 4, 5 all extend radially from the periphery towards the centre and the angle between the edges 6 and 7, 7 and 8, 8 and 6, respectively, are 140, 110 and 110°, respectively. The edges 6, 7, 8, all have one internal and one external part, whereby the internal part closest to the centre of the drill forms a large angle to the axis of the drill, while the external parts form a more acute angle. As previously mentioned only the tooth 3 has an edge 6 with an internal part extending all the way to the centre of the drill. The teeth 4 and 5 will by means of this shaping work substantially peripherally. As the teeth 4 and 5 do not extend to the centre of the drill, these will less be effected by force than the tooth 3, implying that the teeth must be unequally distributed around the circumference of the drill, to obtain the desired power distribution at the drilling. Further the internal part of the tooth 3, which extends towards the centre of the drill, provides different contributions to the total power depending on the material in the work piece. The angles between the tooth 3 extending towards the centre, and the other two teeth may therefore differ between 135-145, 105-115 and 215-225°, respectively. The teeth 3, 4 and 5 convert into spars 9, 10 and 11, respectively, which extend axially along the drill 1. The spars 9, 10, 11 are provided with margin strips 12, 13 and 14, respectively. Further the drill core at the bit point of the drill is provided with slots 15, 16, 17, which extend between the respective adjacent tooth from the periphery of the core to the centre of the drill. These slots are achieved with assistance of a conical body, whereby the same conical body is preferably used for achieving all slots. Thus the slots have the same form as a section of the envelope surface of said conical body. In the present description, this form is denoted " partial conical form". The cone angle of said conical body is preferably larger than 60° and the conical body is preferably directed in such a way, at the working of the drill core, that its generatrix forms an angle of at least 30° to the drill axis. The conical body is also preferably used for attending to that the interior edge parts of the teeth 4, 5 are completed at the intended distance from the centre of the drill. The cooling channel 2 emerges in the space between the internal parts of the teeth 3 and 4, and thus, run inclined to the drill axis in the bit point of the drill. As the cooling channel substantially extends along the axis of the drill a maximum rigidity of the drill 1 is obtained. As the tooth 3 extends to the centre of the drill, the drill 1 has no chisel edge, whereby the so-called plough effect appearing at the chisel edge of conventional double cutting drills are eliminated, which to a high degree decreases the plastical deformation of the material machined at the end of the hole. Thereby if is obtained that only a slight burring occurs at the end of the hole and a small protrusion of the machined material occurs at a drilling through. Compared to drills with two teeth, which work in the centre of the drill, a lesser feeding power of a drill according to the invention is required at the same feed per revolution. The peripherally working teeth 4, 5 contribute to that a higher volume cutting may take place than if only one tooth has been used and enable to achieve a power balance between the three teeth so that the drill has a steady centre of rotation during the complete operation. Further the teeth 4, 5 contribute to provide a good quality of the hole surfaces implying that no after-treatment of these is required in several cases after finished drilling. As the drill 1 works with a power balance and a good steering by means of the three margin strips less vibrations of the drill occur while operating, and the risk for eccentricity of the hole drilled is small. The risk for eccentricity by means of deflection of long drills decreases as well due to the fact that only a small axial feeding power is required when operating a drill according to the invention. A pre-condition to be able to run the drill described in an effective way, i.e. with high velocity and feeding speed, is that the cooling medium is supplied under high pressure. For this purpose the drilling machine, the drilling tool or the like, in which the drill 1 is supported, is provided with a device for supplying cooling medium under high pressure to the cooling channel 2. The device may for instance be constituted of a pump, e.g. a gear-driven pump from PARKER, USA, which pumps cooling medium, e.g. a cutting fluid emulsion KFL 360 BIO from QUAKER, USA, from a tank. The pump should have a displacement of at least K*D 2 , where K=0,15 1/min and D=drill diameter, and the pressure of the cooling medium should be at least 3000 kPa. The transition between the stationary line from the pump to the rotating cooling channel in the drill is provided by means of a swivel, preferably a swivel from WTO, Germany. Other components of a drilling machine, a drilling tool or the similar, comprising a drill unit according to the invention, are of a conventional type and do no need to be closer described more in detail. It is pointed out that the drill 1 may be used at all types of drilling tools or the like provided with a high pressure equipment according to the invention. The shaping itself of the drilling tool in other respects, do not constitute a part of the invention and therefore do not need to be illustrated in the drawing. At the supplying of a cooling liquid a steam film is formed having the largest extension at the outer corners of the edges, which constitute the parts of the teeth running with the highest speed. This film insulates the edges from the surrounding cooling liquid and makes it more difficult to dispose the heat from there. By supplying the cooling liquid under high pressure, the thickness as well as the extension of the steam film are considerably decreased and the disposal of the heat is considerably facilitated. Thereby the temperature of the edges may be kept low leading to a decreased wear, which is especially noticeable at the outer corners, as well as a lesser risk for structural transformations in the machined material. The risk for building-ups by weldings, for instance at margin strips, is considerably decreased. Besides for cooling the drill, the cooling medium provides a good lubrication of the margin strips so that the friction between these and the hole surface becomes small. Another important advantage having a high pressure of the cooling medium is that the disposal of the chips from the bit point of the drill to the spaces between the spars 9, 10, 11 and along these spaces is clearly improved. Thereby the risks for chip stopping, tool breakdown and damages on the hole surfaces are substantially decreased. The figures 3 and 4 show the same views, as the figures 1 and 2, respectively, of a half twist bit 18 according to a second embodiment of the invention. Likewise, this drill has three teeth 19, 20, 21 with edges 22, 23, 24. Only the edge 22 of the tooth 19 works in the centre of the drill and reaches up to this. The edges 23, 24 of the teeth 20, 21 stop before the centre of the drill, and the slots 25, 26 extend between the internal ends of these edges and the centre of the drill. A cooling channel, which is not shown in figure 4, extends centrally in the centre of the drill core, and is as in the same way as in the drill of the first embodiment deflected in the bit point of the drill, so that it emerges at the side of the centre of the drill. The orifice of the cooling channel 27 is shown in figure 3. The teeth 19, 20, 21 convert in helical spars, of which the spar 28 of the tooth 19 is shown with its margin strip 29. The edges of the drill 18 are, as in the same way as at the drill 1, formed in such a way that a power balance occurs at drilling. The drill 18 shows the same advantages and good characteristics as the drill 1. The material of the drills is preferably hard metal, but other materials as high speed steel (HSS) may also be used. It is also possible that the shaft may be formed in another material than the bit point of the drill. The described drill unit may of course be modified within the scope of the invention, especially with respect to the geometrical shape of the edges. The invention should therefore only be limited by the content in the enclosed claims.

Claims: CLAIMS 1. Drill unit with a drill (1), having a cooling channel (2), and with a device for supplying cooling fluid to the cooling channel of the drill, characterized in that the drill (1) comprises three teeth (3, 4, 5), of which the first tooth (3) extends from the periphery of the drill to its centre, while the second and the third teeth (4, 5) extend inward from the periphery of the drill without reaching its centre, that the cooling channel extends axially in the centre of the drill and is deflected in the bit point of the drill so that it emerges in the space between the centre and the terminal points of the second and the third teeth (4, 5), and that the supply arrangement for the cooling fluid is arranged to supply the fluid under high pressure. 2. Drill unit as claimed in claim 1, characterized in that the pressure of the cooling fluid supplied exceeds 3000 kPa. 3. Drill unit as claimed in claim 2, characterized in that the teeth (3,4,5) are unequally distributed around the circumference of the drill. 4. Drill unit as claimed in claim 3, characterized in that the angle in relation to the circumference between the first tooth (3) and the second (4) and the third teeth (5), respectively vary between 135- 145, 105-115 and 215-225°, respectively. 5. Drill unit as claimed in claim 4, characterized in that the angle in relation to the circumference between the first tooth (3) and the second (4) and the third teeth (5), respectively, are 110° and 200°, respectively. 6. Drill unit as claimed in claim 1-3, characterized in that the partial conical slots (15, 16, 17) are shaped in the drill core between the three teeth (3, 4, 5), which slots extend toward the centre of the drill. 7. Drill unit as claimed in claim 6, characterized in that the partial conical slots (15, 16, 17) are preferably shaped with the same tool constituting of a conical grinding tool, the generatrix of which at the machining of the drill core forms an angle of at least 30°to the drill axis.

Inventors: BENO TOMAS, MUHREN CURT, BENO, TOMAS, MUHREN, CURT
Applicants: BENO TOMAS, FORSKARPATENT I VAESTSVERIGE A, MUHREN CURT, BENO, TOMAS, FORSKARPATENT I VAESTSVERIGE AB, MUHREN, CURT
Application year: 2000
Main classification: B23B51
IPC codes: B23B51