Cutting tool, a method for manufacturing a cutting tool and a method for machining of a workpiece

Abstract

A rotatable cutting tool for machining of a honeycomb core includes a front end; a rear end; a peripheral surface extending between the front and rear ends; a set of helical flutes formed in the peripheral surface at a first helix angle 4565, having a first depth; and a set of helical ridges. At least one helical groove formed in the peripheral surface at a second helix angle 90<100, has a second depth, which is smaller than the first depth. The at least one helical groove intersects the helical ridges so that a plurality of cutting teeth are formed on each helical ridge. Each cutting tooth includes a second ridge formed in a transition between two lands, a cutting edge and a clearance edge join in a tooth tip constituting the radially outermost point of the cutting tooth.

Claims

1. A rotatable cutting tool for machining of a workpiece having a honeycomb core, the cutting tool having a longitudinal axis around which the cutting tool is rotatable in a direction of rotation, the cutting tool comprising: a front end; a rear end opposite the front end, the cutting tool being arranged to be fastened to a tool holder or a machine spindle; a peripheral surface extending around the longitudinal axis between the front end and the rear end; a set of helical flutes arranged for chip evacuation formed in the peripheral surface, the helical flutes extending from the front end towards the rear end at a first helix angle with respect to the longitudinal axis, wherein 4565, the helical flutes having a first depth; a set of helical ridges, each helical ridge being associated with and formed between a pair of adjacent helical flutes comprising a first associated helical flute and a second associated helical flute, wherein the second associated helical flute is positioned behind the first associated helical flute in the direction of rotation; and at least one helical groove formed in the peripheral surface, the at least one helical groove having a second depth which is smaller than the first depth, so that the at least one helical groove is interrupted by the helical flutes, wherein the at least one helical groove intersects the helical ridges so that a plurality of lands are formed on each helical ridge, each land extending between the first associated helical flute and the second associated helical flute, and wherein a plurality of cutting teeth are formed on each helical ridge, each cutting tooth being delimited at least by a pair of associated adjacent lands of said plurality of lands, said pair of associated adjacent lands comprising a first associated land and a second associated land, wherein the second associated land is positioned at a larger axial distance from the front end than the first associated land, wherein the at least one helical groove extends at a second helix angle with respect to the longitudinal axis, wherein 90<<100, and wherein each cutting tooth of said plurality of cutting teeth comprises: a second ridge, the second ridge being formed in a transition between the first associated land and the second associated land, a cutting edge formed in a transition between the first associated land and the first associated helical flute, and a clearance edge formed in a transition between the second associated land and the first associated helical flute, wherein the second ridge, the cutting edge and the clearance edge join in a tooth tip constituting the radially outermost point of the cutting tooth and being located at a cutting radius of the cutting tool.

2. The cutting tool according to claim 1, wherein the cutting edge of each cutting tooth of the plurality of teeth, when seen in a plane perpendicular to the longitudinal axis, extends radially inwards from the tooth tip at an angle with respect to a radial line extending between the longitudinal axis and the tooth tip.

3. The cutting tool according to claim 2, wherein 20+30, when seen in a plane perpendicular to the longitudinal axis.

4. The cutting tool according to claim 1, wherein each second ridge has a first end that coincides with the tooth tip and a second end situated behind the first end in the direction of rotation.

5. The cutting tool according to claim 4, wherein a radial distance between the second end of each second ridge and the longitudinal axis is smaller than or equal to a radial distance between the first end of each second ridge and the longitudinal axis.

6. The cutting tool according to claim 1, wherein a largest land width of each of said plurality of lands, as measured along a direction of extension of the at least one helical groove, is less than 30% of a shortest distance between two of said lands situated on two neighboring helical ridges, as measured along a direction of extension of the at least one helical groove.

7. The cutting tool according to claim 1, wherein each land of said plurality of lands, as measured along a direction of extension of the at least one helical groove, has a land width that varies along a direction of extension of the helical ridge on which the land is located.

8. The cutting tool according to claim 7, wherein, between each pair of adjacent second ridges located on the same helical ridge, said pair of adjacent second ridges comprising a first associated second ridge and a second associated second ridge, the first associated second ridge being positioned closer to the front end than the second associated second ridge, the land width increases from the first associated second ridge towards the second associated second ridge.

9. The cutting tool according to claim 1, wherein the first depth is such that a shortest radial distance between a surface of each of said helical flutes and the longitudinal axis is 55-70% of the cutting radius.

10. The cutting tool according to claim 1, wherein the second depth is such that a shortest radial distance between a surface of each land of said plurality of lands and the longitudinal axis is 85-99.9% of the cutting radius (r.sub.1).

11. The cutting tool according to claim 1, wherein each land of said plurality of lands is in the form of a curved surface.

12. The cutting tool according to claim 1, wherein, as measured in the axial direction of the cutting tool, a smallest axial distance (y) between two tooth tips of the cutting tool is 0<y0.3 mm.

13. The cutting tool according to claim 12, wherein said smallest axial distance is measured between a first tooth tip located on a first one of said helical ridges and a second tooth tip located on a second one of said helical ridges located directly behind the first helical ridge in the direction of rotation, wherein the second tooth tip is located closer to the front end than the first tooth tip.

14. A method for manufacturing a cutting tool according to claim 1, the method comprising: providing a cylindrical tool blank with a circular base; forming the set of helical flutes using a first grinding wheel having a first grinding surface and a second grinding surface, the second grinding surface being formed at an angle .sub.1 of 35-55 with respect to the first grinding surface; and forming the at least one helical groove using a second grinding wheel having a first grinding surface and a second grinding surface, the second grinding surface preferably being formed at an angle .sub.2 of 10-20 with respect to the first grinding surface.

15. A method for machining of a workpiece having a honeycomb core, the method comprising: providing a cutting tool according to claim 1; and simultaneously rotating the cutting tool in the direction of rotation and moving the cutting tool with respect to the workpiece in a feeding direction, or moving the workpiece with respect to the cutting tool, such that at least some of the cutting edges of the cutting teeth are brought into engagement with the honeycomb core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended drawings, wherein:

(2) FIG. 1 is a side view of a cutting tool according to an embodiment of the invention,

(3) FIG. 2 is a perspective view of the cutting tool in FIG. 1,

(4) FIG. 3 is a side view of a portion of the cutting tool in FIG. 1,

(5) FIG. 4 is a perspective view of a portion of the cutting tool in FIG. 1,

(6) FIG. 5 is a detail view showing a portion of the cutting tool in FIG. 1,

(7) FIG. 6 is a section along the line VI-VI in FIG. 1,

(8) FIG. 7 is a section along the line VII-VII in FIG. 1,

(9) FIG. 8 is a detail view showing a portion of the section in FIG. 6,

(10) FIG. 9 is a flow chart illustrating a method of manufacturing a cutting tool according to an embodiment of the invention, and

(11) FIG. 10 is a flow chart illustrating a method for machining of a honeycomb structure according to an embodiment of the invention.

(12) It should be noted that the appended drawings are schematic and that individual components are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(13) FIGS. 1-2 show a rotatable cutting tool 1 for machining of a workpiece comprising or consisting of a honeycomb core according to an embodiment of the invention. The cutting tool 1 has a longitudinal axis A around which the cutting tool 1 is rotatable in a direction of rotation R, the longitudinal axis A extending between a front end 2 and an opposite rear end 3 of the cutting tool 1. Extending from the rear end 3, a mounting portion is provided, which mounting portion is adapted to be fastened to a tool holder (not shown). When mounted, the rear end 3 of the cutting tool 1 thus faces the tool holder. Reference is also made to FIGS. 3-4, showing a portion of the cutting tool 1 including the front end 2 in more detail, and to FIGS. 6-7, showing sectional views of the cutting tool 1.

(14) A peripheral surface 4 of the cutting tool 1 extends around the longitudinal axis A between the front end 2 and the rear end 3. In the peripheral surface 4, a set of helical flutes 5 for chip evacuation, in the shown embodiment eight helical flutes 5, are formed. The helical flutes 5 extend from the front end 2 towards the rear end 3 at a first helix angle with respect to the longitudinal axis A, wherein 4565.

(15) As shown in FIGS. 6 and 8, the helical flutes 5 have a first depth d.sub.1 as measured radially towards the longitudinal axis A from a point on an imaginary cylinder centered on the longitudinal axis A and having a radius corresponding to a cutting radius r.sub.1 of the cutting tool 1. The first depth d.sub.1 is such that a radial distance r.sub.2 between a bottom of each of the helical flutes and the longitudinal axis is 55-70% of the cutting radius r.sub.1 of the cutting tool 1, preferably 60-65% of the cutting radius r.sub.1. Thus, d.sub.1+r.sub.2=r.sub.1.

(16) Between each pair of adjacent helical flutes 5, 5, a helical ridge 6 is formed. Thus, a set of eight helical ridges 6 are formed in the shown embodiment. Each helical ridge 6 is associated with the pair of adjacent helical flutes 5, 5 comprising a first associated helical flute 5 and a second associated helical flute 5, wherein the second associated helical flute 5 is positioned behind the first associated helical flute 5 in the direction of rotation R.

(17) A helical groove 7 is formed in the peripheral envelope surface at a second helix angle with respect to the longitudinal axis A, wherein 90<100, as shown in FIG. 3. For clarity, the extension of the helical groove 7 is marked by dashed lines.

(18) In the shown embodiment, =91. As shown in FIGS. 3, 6 and 8, the helical groove 7 has a second depth d.sub.2 as measured radially towards the longitudinal axis A from a point on the above defined imaginary cylinder. The second depth d.sub.2 is smaller than the first depth d.sub.1, so that the helical groove 7 is interrupted by the helical flutes 5. For clarity, the extension of the helical groove 7 is marked by dashed lines in FIG. 3.

(19) The second depth d.sub.2 is such that a radial distance r.sub.3 between a radially innermost point of each land 8 and the longitudinal axis A is 85-99.9% of a cutting radius r.sub.1 of the cutting tool 1, preferably 92-99% of the cutting radius r.sub.1, more preferably 95-97% of the cutting radius r.sub.1. Thus, d.sub.2+r.sub.3=r.sub.1.

(20) The helical groove 7 intersects the helical ridges 6 so that a plurality of lands 8 are formed on each helical ridge 6, each land 8 extending between the first associated helical flute 5 and the second associated helical flute 5. The intersection of the helical groove 7 and the helical ridges 6 also results in the formation of a plurality of identical cutting teeth 11 on each helical ridge 6.

(21) Each cutting tooth 11 is associated with and delimited by a pair of associated adjacent lands 8, 8 of the plurality of lands 8, namely a first associated land 8 and a second associated land 8. Each cutting tooth 11 is further delimited by the helical flutes 5, 5. The second associated land 8 is positioned at a larger axial distance from the front end 2 than the first associated land 8 and consequently also behind the first associated land 8 in the direction of rotation R.

(22) Each cutting tooth 11 on the helical ridges 6 comprises a second ridge 10 formed in a transition between the first associated land 8 and the second associated land 8. Thus, a plurality of sharp second ridges 10 are formed on each helical ridge 6. The second ridges 10 may have a short extension along the helical groove 7, as in the shown embodiment. Furthermore, each cutting tooth 11 comprises a cutting edge 9 formed in a transition between the first associated land 8 and the first associated helical flute 5, and a clearance edge 16 formed in a transition between the second associated land 8 and the first associated helical flute 5. The second ridge 10, the cutting edge 9 and the clearance edge 16 join in a tooth tip 12 constituting the radially outermost point of the cutting tooth 11 and being located at the cutting radius r.sub.1 of the cutting tool 1.

(23) Reference is made to FIG. 5, showing identical first, second and third cutting teeth 11, 11 and 11 in larger detail, the first cutting tooth 11 being located closest to the front end 2 of the cutting tool 1. The second cutting tooth 11 is associated with and delimited by the pair of associated adjacent lands 8, 8. The first, second and third cutting teeth 11, 11 and 11 are respectively associated with the second ridges 10, 10 and 10, cutting edges 9, 9 and 9, and clearance edges 16, 16 and 16.

(24) The land 8 is delimited by the pair of adjacent second ridges 10, 10, of which the first associated second ridge 10 is positioned closer to the front end 2 than the second associated second ridge 10. The land 8 is in the form of a concavely curved surface as seen from a position on the land 8, with a flat or substantially flat foremost portion 8a and a bent rearmost portion 8b.

(25) The land width w of the land 8 varies along a direction of extension of the helical ridge 6. Moving between from the first associated second ridge 10 towards the second associated second ridge 10, the land width w of the flat foremost portion 8a increases towards the rearmost portion 8b. The land width w thereafter decreases when moving along the bent rearmost portion 8b. For each land 8, a largest land width w of the land 8, as measured along a direction of extension of the helical groove 7, is less than 30%, preferably less than 20%, more preferably less than 15% and most preferably less than 10%, of a shortest distance w between two of said lands 8, 8 situated on neighboring helical ridges 6, 6, as measured along the direction of extension of the helical groove 7.

(26) The cutting edge 9 of the second cutting tooth 11 and the clearance edge 16 of the first cutting tooth 11 together form a curved line extending between the pair of associated second ridges 10, 10. During machining of a workpiece, the foremost portions 8a of the lands 8 as well as the clearance edges 16 form clearance surfaces, which are not in contact with the machined honeycomb structure. For cutting edges 9 located on the helical ridge 6, the first associated helical flute 5 constitutes a rake surface.

(27) The cutting edge 9 of each cutting tooth 11, when seen in a plane perpendicular to the longitudinal axis, extends radially inwards from the tooth tip 12, at an angle with respect to a radial line extending between the longitudinal axis A and the tooth tip 12. In the shown embodiment, the angle is a small positive angle as shown in FIG. 8. The angle is measured at a first end of the cutting edge 9 adjacent to the tooth tip 12. If the cutting edge 9 at its first end has a direction of extension such that the cutting edge 9 extends in front of the radial line between the longitudinal axis A and the tooth tip 12, seen in the direction of rotation R, the angle has a negative value. If the cutting edge 9 at its first end has a direction of extension such that the cutting edge 9 extends behind the radial line between the longitudinal axis A and the tooth tip 12, seen in the direction of rotation R, the angle has a positive value. In FIG. 8, the angle has a positive value. The angle may be such that 20+30, more preferably 5+20, most preferably =0, when seen in a plane perpendicular to the longitudinal axis.

(28) The clearance edge 16 of each cutting tooth 11 also extends inwards from the tooth tip 12, but at an angle with respect to a radial line extending between the longitudinal axis A and the tooth tip 12, as shown in FIG. 6. The angle is in the shown embodiment about 70. In general, and in independence of the other features of the cutting tool, the angle should be such that 50<90. If the angle is 90 or more, the clearance edge 16 does not have a function of a clearance which results in unnecessary heat generation and lower tool life. If the angle is less than 50, the thermal conductivity of the tooth is lower, and the heat generated in the cutting zone of the tooth is not conducted away from the tooth tip fast enough, which may result in reduced tool life.

(29) Referring again to FIG. 5, each second ridge 10 (illustrated by the second ridge 10) has a first end 13 that coincides with the tooth tip 12 and a second end 14 situated behind the first end 13 in the direction of rotation R. A radial distance between the second end 14 of the second ridge 10 and the longitudinal axis A is smaller than or equal to a radial distance between the first end 13 of the second ridge 10 and the longitudinal axis A. In other words, the second end 14 is located closer to the longitudinal axis A than the first end 13. Thus, behind the cutting edge 9, the second ridge 10 is not in contact with the workpiece during machining.

(30) As measured in the axial direction of the cutting tool 1, i.e. along the longitudinal axis A, a smallest axial distance y between two tooth tips of the cutting tool 1 is 0<y0.3 mm. This distance y is measured between a first tooth tip 12 located on a first one of said helical ridges 6 and a second tooth tip 12 located on a second one of said helical ridges 6 located directly behind the first helical ridge 6 in the direction of rotation R as shown in FIG. 3. The second tooth tip 12 is located closer to the front end 2 than the first tooth tip 12. For a cutting tool 1 comprising a single helical groove 7, the smallest axial distance y between two tooth tips 12 can be approximated by a pitch of the helical groove 7 divided by the number of helical ridges 6. For a cutting tool 1 having eight helical ridges 6, a cutting radius r.sub.1 of 8 mm, and a second helix angle of 91, the axial distance y is approximately 0.13 mm.

(31) The cutting tool 1 in the shown embodiment further comprises two front cutting edges 15 formed at the front end 2 of the cutting tool 1. It is also possible to provide the cutting tool without front cutting edges if the tool is to be used merely for contouring or edge milling. Also, only a portion of the cutting tool may be provided with the at least one helical groove, i.e. the at least one helical groove may not necessarily extend over the same length along the longitudinal axis as the helical flutes. For example, the helical flutes may extend from front cutting edges of the cutting tool, while as the helical groove(s) extend(s) from a position closer to the rear end of the cutting tool.

(32) In the shown embodiment, only one helical groove 7 is formed in the peripheral surface 4. However, more than one helical groove may be provided, as long as two adjacent lands 8 formed on one of the helical ridges 6 intersect to form the second ridge 10.

(33) A method for manufacturing a cutting tool as described above according to an embodiment of the invention is illustrated in the flow chart in FIG. 9.

(34) In a first step 101, a cylindrical tool blank with a circular base is provided. The tool blank may e.g. be a cemented carbide tool blank.

(35) In a second step 102, the set of helical flutes 5 for chip evacuation are formed using a first grinding wheel having a first grinding surface and a second grinding surface, the second grinding surface preferably being formed at an angle .sub.1 of 35-55 with respect to the first grinding surface. The first grinding surface thus forms a first sidewall of the helical flutes 5 and the second grinding surface forms a second sidewall of the helical flutes 5. The grinding wheel may e.g. have a V-shaped or a rounded profile, depending on a desired bottom profile of the helical flutes 5.

(36) In a third step 103, the helical groove 7 or grooves are formed using a second grinding wheel having a first grinding surface and a second grinding surface, the second grinding surface preferably being formed at an angle .sub.2 of 10-20 with respect to the first grinding surface. The second grinding wheel preferably has a rounded profile to create curved lands 8 on the helical ridges 6. The land width w of the lands 8 depends on the grinding depth used when creating the helical groove 7. The first grinding wheel and the second grinding wheel may be the same wheel, but preferably the second grinding wheel is different from the first grinding wheel.

(37) The step 103 may be performed before or after the step 102. Grinding of the helical flutes 5 and the helical grooves 7 together create the helical ridges 6, the second ridges 10, the cutting edges 9 and the lands 8.

(38) A method for machining of a workpiece comprising a honeycomb core according to an embodiment of the invention is illustrated in the flow chart in FIG. 10.

(39) In a first step 201, a cutting tool 1 as described above is provided and fastened to a tool holder.

(40) In a second step 202, the cutting tool 1 is simultaneously rotated in the direction of rotation R and moved with respect to the honeycomb workpiece in a feeding direction, such that at least some of the cutting edges 9 of the cutting tool 1 are brought into engagement with the honeycomb core. The multiple cutting edges 9 thereby remove material from the honeycomb core. In the second step 202 it is also possible to move the honeycomb workpiece toward the tool. It is also possible to move both the cutting tool and the honeycomb workpiece.

(41) The embodiments herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the embodiments, which is defined by the appended claims.