Milling head with constant profiles

Abstract

Proposed in a milling head, which has a plurality of machining milling teeth and tooth gaps arranged therebetween, whereby the milling teeth and the tooth gaps are arranged along a circumferential surface of the milling head, which milling head is to be provided with a number of milling teeth, which is greater than and/or substantially equal to the number of milling teeth ascertained using the equation y=a.Math.x.sup.5+b.Math.x.sup.4+c.Math.x.sup.3+d.Math.x.sup.2+e.Math.x+f, wherein x is the diameter of the milling head in millimeters and y is the tooth pitch, i.e. the distance between two adjacent milling teeth in millimeters, and it substantially applies that the value of a ranges between a=1.7.Math.10.sup.−9 and a=2.3.Math.10.sup.−9, the value of b between b=−5.Math.10.sup.−7 and b=−11.Math.10.sup.−7, the value of c between c=0.7.Math.10.sup.−4 and c=1.3.Math.10.sup.−4, the value of d between d=8.5.Math.10.sup.−3 and d=9.7.Math.10.sup.−3, the value of e between e=2.6.Math.10.sup.−1 and e=3.7.Math.10.sup.−1 and the value of f between f=−1.5.Math.10.sup.−1 and f=−2.6.Math.10.sup.−1.

Claims

1. A form cutter milling head with a plurality of machining milling teeth and tooth gaps arranged there-between, which are arranged along a circumferential surface of the form cutter milling head, wherein an actual number of said milling teeth is greater than or equal to a calculated number of milling teeth ascertained from the relationship n=C/y wherein n is the number of milling teeth, y is a tooth pitch of the form cutter milling head defined as a distance in millimeters between two said milling teeth situated adjacent to one another, and C is a circumference in millimeters of the form cutter milling head, wherein the tooth pitch relates to a diameter of the form cutter milling head via a fifth-order polynomial of the form y=a.Math.x.sup.5+b.Math.x.sup.4+c.Math.x.sup.3+d.Math.x.sup.2+e.Math.x+f, wherein x is the diameter of the milling head in millimeters, y is the aforesaid tooth pitch in millimeters, and a, b, c, d, e, and f are coefficients of the fifth-order polynomial.

2. The form cutter milling head according to claim 1, wherein a tooth face angle (γ) and/or a clearance angle (α) of the milling teeth remains constant with a resharpening and/or relief grinding of the milling teeth.

3. The form cutter milling head according to claim 1, said form cutter milling head having form constancy with a profile-constant or logarithmic relief-ground surface.

4. The form cutter milling head according to claim 1, wherein the milling teeth are arranged with constant spacing along the circumference of the milling head.

5. The form cutter milling head according to claim 1, wherein the milling teeth are disposed with a spacing varying with respect to one another along the circumference of the milling head.

6. The milling head according to claim 1, wherein the value of a ranges between a=1.8.Math.10.sup.−9 and a=2.2.Math.10.sup.−9.

7. The milling head according to claim 1, wherein the value of b ranges between b=−6.Math.10.sup.−7 and b=−10.Math.10.sup.−7.

8. The milling head according to claim 1, wherein the value of c ranges between c=0.8.Math.10.sup.−4 and c=1.2.Math.10.sup.−4.

9. The milling head according to claim 1, wherein the value of d ranges between d=8.7.Math.10.sup.−3 and d=9.5.Math.10.sup.−3.

10. The milling head according to claim 1, wherein the value of e ranges between e=2.8.Math.10.sup.−1 and e=3.5.Math.10.sup.−1.

11. The milling head according to claim 1, wherein the value of f ranges between f=−1.7.Math.10.sup.−1 and f=−2.4.Math.10.sup.−1.

12. The milling head according to claim 6, wherein the value of a ranges between a=1.9.Math.10.sup.−9 and a=2.1.Math.10.sup.−9.

13. The milling head according to claim 7, wherein the value of b ranges between b=−7.Math.10.sup.−7 and b=−9.Math.10.sup.−7.

14. The milling head according to claim 8, wherein the value of c ranges between c=0.9.Math.10.sup.−4 and c=1.1.Math.10.sup.−4.

15. The milling head according to claim 9, wherein the value of d ranges between d=8.9.Math.10.sup.−3 and d=9.3.Math.10.sup.−3.

16. The milling head according to claim 10, wherein the value of e ranges between e=3.0.Math.10.sup.−1 and e=3.3.Math.10.sup.−1.

17. The milling head according to claim 11, wherein the value of f ranges between f=−1.9.Math.10.sup.−1 and f=−2.2.Math.10.sup.−1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details of the invention and in particular example embodiments of the proposed device and of the proposed method will be explained in the following with reference to the attached drawings:

(2) FIG. 1 shows a form cutter milling head 1 in a schematic, perspective view;

(3) FIG. 2 shows, in a schematic, perspective view, an enlarged detail of the form cutter milling head shown in FIG. 1;

(4) FIG. 3 shows a schematic cross section through the tooth region of a form cutter milling head perpendicular to the material machining direction of the form cutter milling head;

(5) FIG. 4 shows a schematic lateral view of the tooth region of a form cutter milling head during a relief grinding operation;

(6) FIG. 5 shows an enlarged detail of the tooth region of a logarithmic form cutter milling head in a schematic side view from above for explanation of various terms.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(7) To be seen in FIG. 1, in a schematic perspective view, is a form cutter milling head 1. The form cutter milling head 1 serves the purpose of material-removing machining of a workpiece (not shown) to be machined by milling. The surface regions of the workpiece are thereby chipped in a way known per se. For this purpose the form cutter milling head 1 is rotated in direction of arrow A (milling direction or respectively material machining direction).

(8) The form cutter milling head 1 has a greater number of in the present case asymmetrically shaped milling teeth 2. These are shaped in such a way that a so-called logarithmic milling head is formed, which will be gone into more closely later.

(9) Provided between each two milling teeth 2 situated adjacent to one another is a tooth gap 3.

(10) The reason for the term form cutter milling head 1 (or respectively form milling tooth 2) is that the surface 4 of the milling teeth 2 turned toward the workpiece has a structuring. It is thereby possible for the workpiece to be machined to be shaped with a certain surface structuring as a result of the milling. The relationships are also to be seen in FIG. 2, which shows a detail of the form cutter milling head 1 shown in FIG. 1, likewise in a schematic, perspective view.

(11) Represented in FIG. 5 are in addition the relationships of a detail of a form cutter milling head 1 in a side view from above. The line 5 thereby represents a circumference line about the central point of the form cutter milling head 1. It can thereby be seen very well in FIG. 4 that the milling teeth 2 are not symmetrically designed. Instead these teeth have a face with a cutting edge region 6, whereby the cutting edge 6 forms the transition between surface 4 of the milling tooth 2 and its leading edge 7 (face) during rotation of the form cutter milling head 1 in direction of arrow A (machining direction). During a machining operation, the tangent line to the circumference line 5 (at the cutting edge 6) would correspond to the surface of the workpiece to be machined. Accordingly the angle between tooth leading edge 7 and circumference line 5 at the cutting edge 6 constitutes the tooth face angle γ during the workpiece machining.

(12) In the rear in machining direction (towards the left as seen in FIG. 5) the milling tooth 2 tapers so that an increasing spacing arises between surface 4 of the milling tooth 2 and circumference line 5. The angle between the tangent line to the circumference line 5 and the tangent line to the surface 4 at the cutting edge 6 forms the so-called clearance angle α. In the present case, the surface 4 of the milling teeth 2 is designed to be planar; the surface 4 of the milling teeth 2 thus forms a kind of “oblique plane”. However it is also conceivable that the surface 4 of the milling teeth 2 is not designed to be planar and for instance is designed as a slightly convex surface disposed in a sloping way (“bump-like”).

(13) If the form cutter milling head 1 is used for material machining, it is exposed of course to a certain wear and tear, which is concentrated in the region of the cutting edge 6. Accordingly here too a material removal on the milling head 1, i.e. in particular on the milling tooth 2, will occur to a certain extent. The cutting edge 6 thereby deforms over time, changing from a sharp edge (with a defined “true edge”) to a “rounded” (and thereby dull or blunt) edge. Consequently the form cutter milling head 1 becomes dull or blunt over time. Its cutting capability thereby decreases. Above and beyond this, the surface machined by the form cutter milling head 1 has a deteriorated quality.

(14) To restore the quality of the milling operation, it is therefore necessary to resharpen the form cutter milling head 1 so that there is once again a sharp cutting edge 6 (with a “true edge”) of the milling teeth 2. This takes place through a so-called resharpening operation, i.e. a grinding operation in the region of the face of the milling tooth 2 (seen in milling direction A). A portion of the leading edge 7 (a kind of “slice”) is thereby removed. Used for this purpose, as a rule, is a grinding wheel, in particular a pointed profile grinding wheel 8. Indicated schematically in FIG. 2 is how the form cutter milling head 1 can be ground down in the region of the tooth leading edge 7 multiple times in a stepwise (“slice-wise”) fashion in the course of its lifetime cycle.

(15) Depending upon the amount of attrition of the form cutter milling head 1, it can also prove necessary to carry out a combined resharpening operation and relief grinding operation. Typically such a combined resharpening and relief grinding operation is needed after several “purely resharpening operations”. The combined resharpening operation/relief grinding operation typically takes place in two steps. Thereby, on one hand, (typically as first step) the above-described resharpening operation is carried out, i.e. the face of the milling tooth 2 (seen in milling direction A) is ground.

(16) This stepwise (slice-wise) material removal in the region of the tooth leading edge 7 “alone” can however prove to be no longer sufficient, especially with form cutter milling heads, after longer use. In such a case it is additionally necessary that the surface structuring of the surface 4 of the milling teeth 2 be “renewed” by means of a grinding operation. For this purpose it has proven to be reliable, especially with form cutter milling heads 1, when in a second grinding step (the relief grinding step) a so-called pointed profile grinding wheel 8 is used for relief grinding of the surfaces 4 of the milling teeth 2. This is shown schematically in FIG. 3. A milling tooth 2 in cross section is to be discerned here (cross section is normal to the direction of movement of the milling tooth 2 during milling operation of the form cutter milling head 1; i.e. the material machining direction). On the surface 4 of the milling tooth 2 (turned toward the workpiece to be machined), the surface structuring of the same is to be discerned in the form of a number of differently formed ridges 9 and depressions 10. The relief grinding operation takes place with a pointed profile grinding wheel 8, whose protruding edge has a sufficiently small width so that the surface structuring of the surface 4 of the milling tooth 2 can be formed. For carrying out the relief grinding operation, the pointed profile grinding wheel 8 must be moved with a suitable movement pattern laterally back and forth as well as up and down in height. Above and beyond this, it also makes sense, as a rule, when the rotational axis 11 of the pointed profile grinding wheel 8 is inclined in relation to the rotational axis of the form cutter milling head 1. In particular the edge regions of the grooves or depressions 10 are to be formed better, as a rule, through such a tilting/inclining of the pointed profile grinding wheel 8 relative to the form cutter milling head 1.

(17) In additional to FIG. 3, the relief grinding operation is also represented in FIG. 4, here seen in a schematic lateral view from above. To make the operation clear, furthermore two different profile lines/profile points of the form cutter milling head 1 are represented, namely a ridge 9 as well as a depression 10. The radially outer line represents a ridge 9 along the shaped profile of the form cutter milling head 1, while the radially inner line shows a depression or groove 10 along the shaped profile of the form cutter milling head 1. To indicate that the relief grinding operation “works” both in the region of a ridge 9 as well as in a region of a groove or depression 10 of the form cutter milling head 1; the pointed profile grinding wheel 8 has been drawn in double (i.e. in different positions).

(18) The individual resharpening and/or relief grinding cycles are of course spaced apart from one another in time. Between two resharpening and/or relief grinding operations, the form cutter milling head 1 is usually used for milling workpieces to be machined.

(19) For the sake of completeness, it is pointed out that, in the case of the form cutter milling head shown in FIG. 3, the milling direction A diverges from that of the other figures.

(20) Based on the logarithmic outer profile of the form cutter milling head 1, a resharpening operation or respectively relief grinding operation can be carried out substantially over the entire service life (and thereby with different amounts of attrition of the form cutter milling head 1), whereby the same pointed profile grinding wheel 8 can always be used. Typically over the entire service life of the form cutter milling head 1, the number of “exclusively resharpening steps” (material removal in the region of the tooth leading edge) will be greater than the number of “combined resharpening and relief grinding operations” (both on the tooth leading edge 7 as well as also on the surface 4 of the milling teeth 2).

(21) Of course the described resharpening and relief grinding steps are to be carried out in a similar way during production of the form cutter milling head 1.

(22) So that with the finished form cutter milling head 1 as high a machining speed as possible can be achieved (relative feed speed between form cutter milling head 1 and workpiece), as great as possible a number of milling teeth is to be provided, or respectively, seen in circumferential direction of the form cutter milling head 1, as minimal as possible spacing between two milling teeth 2 situated adjacent one another (minimal tooth pitch) because in this case, with a single rotation of the form cutter milling head 1, a greater number of material removal operations occur (a greater number of cutting edges 6 run past the workpiece to be machined).

(23) However, the number of teeth in practice is also limited upwardly (at least for reasons of practicality) (even if usually without sharp limits), since the dimensions of the tooth gaps 3 would be so small that the grinding operation in the region of the tooth leading edge 7 of the respective milling teeth 2 would have to be carried out with too delicate a workpiece (pointed profile grinding wheel 8) (cf. FIG. 2). Also the number of grinding steps to be carried out would increase much too greatly, which would take correspondingly long.

(24) For this reason, it makes sense to find a compromise as advantageous as possible. This results when the tooth pitch of the form cutter milling head 1 (spacing of two milling teeth 2 situated adjacent one another along the circumference of the form cutter milling head 1) as a function of the diameter of the form cutter milling head 1 complies substantially with the equation y=a.Math.x.sup.5+b.Math.x.sup.4+c.Math.x.sup.3+d.Math.x.sup.2+e.Math.x+f and/or the tooth pitch of the milling head 1 is selected to be lesser than the tooth pitch determined in such a way. In an advantageous way the coefficients a, b, c, d, e and f of the fifth-degree polynomial are thereby selected with the values a=2.Math.10.sup.−9, b=−8.Math.10.sup.−7, c=1.Math.10.sup.−4, d=9.1.Math.10.sup.−3, e=3.145.Math.10.sup.−1 and f=−2.062.Math.10.sup.−1. The number of teeth of the form cutter milling head 1 results (with units selected in a way suitable to one another) through division of the circumference of the form cutter milling head 1 by the value of the tooth pitch (spacing of two milling teeth situated adjacent to one another). Thus it applies that N=U/A with N as the number of milling teeth 2, U as the circumference of the form cutter milling head 1 and y as the tooth pitch, whereby, as is known, the circumference can be calculated from the radius r (or respectively the diameter d) by means of the equation U=2πr=πd.

(25) For the case where there results, with predefined diameter d of the milling head 1, a non-integer value N for milling teeth 2, it is possible to round up, round down, or round according to commercial practice the number of teeth (“limit tooth number”).

(26) It is however advantageous when, after the rounding of the tooth number of the form cutter milling head 1, the rounded, determined number of teeth 2 for the form cutter milling head 1 (after its conversion to the tooth pitch y) is put into the said formula as input parameter, and, based on the rounded number of teeth, the optimal diameter of the form cutter milling head 1 is calculated (which is possible without any problem especially using numerical solution methods). The instances of divergence of the diameter with respect to the “desired diameter” typically lie in the range of a few millimeters. Thereby accompanying disadvantageous effects are, as a rule, negligible. It is to be pointed out moreover that the diameter of a form cutter milling head 1 (or another such milling head) changes anyway in the course of its life cycle as a result of attrition and/or resharpening operations and/or relief grinding operations, and thus a certain divergence from the “desired diameter” will occur in any case.