DRILL BIT

Abstract: A drill bit (1) for working of metal, which drill bit has a centre tip (2) that passes into cutting edges (3) extending towards the periphery, and a centre line (A). The drill bit (1) has a cutting angle ( alpha ) of 1-20 DEG between the normal direction of the drill axis and a cutting edge (3) which thus is included towards the centre line (A). The centre tip (2) forms a point finning angle of 90 +/- 2 DEG and a base that takes up 23-45 %, or preferably 30-40 %, and preferably one third of the total diameter of the drill bit (1). The drill bit has a tip angle ( beta ) of 90 +/- 10 DEG .

Description: DRILL BIT Technical Field The present invention relates to a drill for working metal . Technical Background When drilling in metal, the drill bit is subjected to great strain. The drill often gets heavily worn, which quickly affects the accuracy in the making of holes. One way of trying to solve the problem has been to use hard materials for manufacturing the drill bits. This type of drills is often strong but brittle at the same time and often causes the drill to be coated with chips from the tougher material in which the drill operates. This coating with chips means that the difference between the de- sired and the achieved accuracy in bore diameter often deviates significantly. Moreover, great demands are placed on the service life of the drill and the quality of the result when using the drill, in particular as regards industrial use. EP 0,761,352 discloses a drill which is designed with a certain reduction of the consumption of material and involves easier working of metal . This document concerns drills of roll-forged steel which is not really usable for industrial or other professional use, but is devel- oped to meet the need from the lower part of the market. However, EP 0,761,352 indicates that a certain design of the cutting edges of the drill, from the centre tip towards the external edge of the drill, in which direction the cutting edges of the drill are given an inclination upwards, produces a better drill hole. Also DE 3123048 discloses a drill with drill bits which are inclined towards the centre axis of the drill. Due to this design of the drill bits, the chips find their way towards the centre instead of towards the pe- riphery of the hole and a better accuracy as regards the diameter of the hole is achieved. Yet another patent specification DE 911 799 discloses a drill that uses the principle described above to remove the chips in a better way during the actual drilling and, thus, reduce the risk of the drill being coated with chips. The documentation of the two latter drills clearly shows that they are intended for materials such as wood, plastic, concrete and plaster. For metal and especially industrial working of various metals, completely different material properties of the drills are required since, on the one hand, they must often satisfy stricter standards of quality and demands and, on the other, they are subjected to heavier wear and greater forces than other types of drills. When drilling in metal, also the drilling spindle and its bearings are subjected to great strain as a result of great radial forces, which makes it necessary for the drilling spindle to be serviced or even changed on frequent occasions. The problem of achieving high quality of the worked material without simultaneously obtaining excessive radial forces, which shortens the service life of both drills and spindles, thus remains to be solved when drilling metal. Summary of the Invention An object of the present invention is thus to provide a drill that offers an improved solution, in relation to prior-art technique, to the problem with drill chips and their negative effect on the making of holes, without simultaneously obtaining excessive radial forces when drilling in metal. According to the invention, this object is achieved by a drill of the type stated by way of introduction being given the features that will be evident from claim 1. Preferred embodiments of the drill will be evident from the subclaims. Thus, the invention relates to a drill bit for working of metal, which drill bit has a centre tip that passes into cutting edges extending towards the periphery, and a centre line (A) , and which drill bit has a cutting angle ( ) of 1-20° between the normal direction of the drill axis and a cutting edge which thus is inclined towards the centre line (A) , and the centre tip forming a point finning angle (η) of 90 ± 2° and a base that takes up 23-45 %, or preferably 30-40 %, and pref- erably about one third of the total diameter of the drill bit. The above-described relationship between the extension of the base of the drill bit and the diameter of the drill bit as well as the inclination of the cutting edges towards the centre of the drill means that the radial forces are decreased at the same time as coating of the drill with chips is avoided. With a point finning angle of 90°, a sharply marked point finning that comprises the centre tip and a chip face is obtained. The point finning angle is defined as the angle between a line in the normal direction of the drill axis and the point finning, comprising the side of the centre tip, and is here designated (η) . Since the drill bit is preferably made double- cutting, there will be enough space to remove the chips. In a preferred embodiment of the invention, the drill bit has a tip angle (β) of 90 ± 10°. The tip angle is here defined as the angle between two lines that each constitute an imaginary extension of the centre tip sides and this tip angle is here designated (β) . In this range of angles for the tip angle, the drill has optimal performance for metal working. Metals that the drill bit is preferably intended to work are brass, copper and light metals, such as aluminium. According to a preferred embodiment of the inven- tion, the drill bit has a cutting angle (α) of 10 ± 3° between the normal direction of the drill axis and a cutting edge which thus is inclined towards the centre line (A) and maintains this angle all the way to the periphery of the drill bit. The cutting angle is here designated ( ) . This design of the cutting edges and the above- defined form and extension of the tip angle means that the centre tip hits the material first. Thus, vibrations and movements of the spindle are stabilised before the cutting edges start working the material. The distance between centre tip and edge ends should thus not be too long, especially if the drill bit is to be used for thinner metal sheets. The centre tip then presses down and deforms the metal sheet before the cutting edges engage with the metal sheet and can even cause the metal sheet to be split open. The angle of the cutting edges is not allowed to be too steep, because this would shorten the service life of the cutting edges. In accordance with the inventive idea, the cutting edges of the drill bit have a chip face with a point finning which at the external periphery of the drill bit is at least 0.7 mm. Since the edge is straight instead of pointed, the accuracy of the drilling will be maintained for a longer period of time, whereby the service life of the drill increases. The extension of the point finning may, of course, be varied with regard to the dimension of the drill. The extension of the point finning is also determined by the previously mentioned point finning angle. In a preferred embodiment of the invention, the drill bit has a cutting edge with a primary angle of clearance of 10 ± 3° in relation to the normal direction of the drill axis. This primary angle of clearance is here designated (φ) . If the primary angle of clearance is greater than the upper limit indicated above, the generation of heat becomes very high during the working. A smaller angle than the indicated lower limit is unsuit- able as regards working of precisely the metals mentioned above. Most preferably, the primary angle of clearance should be 10-12°. According to another preferred embodiment of the drill bit, the cutting edge has a secondary angle of clearance of 25 + 5° in relation to the normal direction of the drill axis. This secondary angle of clearance is here designated (θ) . Owing to the two-part clearance described above, the drill obtains a more continuous transition from the cutting edges down towards the helical guiding edges. This design provides space for removing chips and other residual products. By enabling a quick and efficient removal of the chips, the risk of local imperfections and high frictional heat is reduced. Both the angles of clearance mentioned above have a decreasing inclination in a direction opposite to the direction of rotation of the drill . The clearance can be provided by, for example, cutting in facets or frinding the envelope surface of the cone. In a preferred embodiment of the drill bit, it is made of hard metal . The drill bit comprises in another preferred embodiment a diamond portion. Also other mate- rials with material properties that are good enough may be used for making drill bits of the above-mentioned design. A drill bit which has one or more of the above- mentioned features is preferably included in a twist drill. The helix angle is preferably 0-30°, but the in- vention is not limited to a specific helix angle. Within the scope of the invention as regards a drill or a drill bit of the type indicated above, the features described above can, of course, be combined freely or be present as separate embodiments. Today there are a plurality of types of drills which have means for internal cooling. The drill described above is in this respect no exception, but can without difficulties be provided with means for internal cooling. There are, for instance, solutions where a coolant is passed into a duct that is internally located in the drill. This solution can also be used for said drill if such demands are made on the production. Brief Description of the Drawing In the following, the invention will be described in more detail by way of an example and with reference to the accompanying drawing, in which Fig. 1 is a side view of the drill bit, Fig. 2 is a side view of the drill bit rotated through 90°, and Fig. 3 is a front view of the drill bit. Description of an Embodiment Fig. 1 is a side view of a drill bit 1 according to a preferred embodiment of the invention. The drill bit 1 is mainly intended for working of brass, copper and light metals, such as aluminium. Also alloys with light metal are regarded as light metals. The drill bit is advantageously included in a drill made of a piece of hard metal or similar material. The drill is suitably ground in order to achieve its proper form. In the Figure, the centre tip 2 is shown from the side having a point finning angle (η) of essentially 90°. The point finning angle (η) is defined as the angle between a line in the normal direction B of the drill axis and the sharpening 7, comprising the centre tip 2 and the chip face 6. Furthermore, the inclination of the primary (φ) and the secondary (θ) angle of clearance will be evident from this Figure. The primary angle of clearance that extends in a sloping manner downwards in a direction opposite to the direction of rotation of the drill at an angle of preferably 10-12°. The secondary angle of clearance which here directly follows the primary one has a greater angle of clearance and is preferably about 25°. These angles are given only as examples of the preferred embodiment and should not be considered to restrict the invention. In order to obtain the angle of clearance described above, either the envelope surface of the cone of the drill bit can be frinded or the drill bit can be cut in facets. Both these angles are defined from a normal line B to the centre axis and in the opposite direction relative to the direction of propulsion of the drill. The definition will be evident from Fig. 1. Fig. 2 shows the drill bit 1 from the side rotated through 90° about its axis (A) . The centre tip 2 here has its tapering side with a tip angle (β) of essentially 90°. The cutting edges 3 which thus also have a point finning angle of 90° exhibit in the Figure an extension which is inclined towards the centre line. This angle which defines the angle of the cutting edges and also is designated cutting angle (α) is in a preferred embodiment essentially 10°. The chip face 6 extends essentially plane along the cutting edge 3. The essentially plane chip face has an extension in the direction of propulsion of the drill of about 1 mm all the way out to the periphery of the drill, but, of course, the extension also de- pends on the dimension of the drill. In this embodiment, the drill bit constitutes a part of a twist drill. The helix angle of the guiding edges 8 forms in a preferred embodiment an angle of 25-30° relative to the direction of extension of the drill axis. Fig. 3 shows the front side of the drill bit, the relationship between the base of the centre tip 2 and the total diameter of the drill bit being evident. In a preferred embodiment, this ratio of the extension of the base of the centre tip to the total diameter of the drill bit is about one third.

Claims: CLAIMS 1. A drill bit (1) for working of metal, which drill bit has a centre tip (2) that passes into cutting edges (3) extending towards the periphery, and a centre line (A) c h a r a c t e r i s e d in that the drill bit (1) has a cutting angle (α) of 1-20° between the normal direction of the drill axis and a cutting edge (3) which thus is inclined towards the centre line (A) , and that the centre tip (2) forms a point finning angle (η) of 90 ± 2° and a base that takes up 23-45 %, or preferably 30-40 %, and most preferably about one third of the total diameter of the drill bit (1) and which centre tip has a tip angle (β) of 90 ± 10°. 2. A drill bit (1) as claimed in the preceding claim, wherein the point finning angle (η), based on the normal direction (B) of the drill axis, defines a point finning (7) which comprises centre tip (2) and chip face (6) . 3. A drill bit (1) as claimed in any one of the preceding claims, having a cutting angle (α) of 10 ± 3° between the normal direction (B) of the drill axis and a cutting edge (3) which thus is inclined towards the centre line (A) and maintains this angle all the way to the periphery of the drill bit (1) . 4. A drill bit (1) as claimed in any one of the preceding claims, wherein the cutting edge (3) has a point finning (7) which at the external periphery of the drill bit is at least 0.7 mm. 5. A drill bit (1) as claimed in any one of the preceding claims, having a cutting edge (3) with a primary angle of clearance (φ) of 10 + 3°. 6. A drill bit (1) as claimed in any one of the preceding claims, having a cutting edge (3) with a secondary angle of clearance (θ) of 25 ± 5°. 7. A drill bit (1) as claimed in any one of the preceding claims, being made of hard metal. 8. A drill bit (1) as claimed in any one of the preceding claims, comprising a diamond portion. 9. A drill bit (1) as claimed in any one of the preceding claims, being included in a twist drill. 10. A drill bit (1) as claimed in any one of the preceding claims, comprising means for internal cooling. 11. A drill bit (1) as claimed in any one of the preceding claims, having a helix angle for the guiding edges (8) which, relative to the direction of extension of the centre line (A), is 0-30°. 12. A drill comprising a drill bit (1) as claimed in any one of the preceding claims.

Inventors: NYGAARD EERO, NYGAARD, EERO
Applicants: NYGAARD EERO, NYGAARD, EERO
Application year: 2001
Main classification: B23B51
IPC codes: B23B51