WO2021013834A1

WO2021013834A1 - Method for producing a cutting tool from a blank, and grinding worm for producing a cutting tool

Info

Publication number: WO2021013834A1
Application number: PCT/EP2020/070556
Authority: WO
Inventors: Mirko THEUER; Berend Denkena
Original assignee: Gottfried Wilhelm Leibniz Universität Hannover
Priority date: 2019-07-25
Filing date: 2020-07-21
Publication date: 2021-01-28
Also published as: DE102019120155B4; DE102019120155A1

Abstract

The invention relates to a method for producing a cutting tool (20) from a blank (14) by means of generation grinding, wherein the generation grinding is performed using a grinding worm (12), which has a reference worm profile (16). According to the invention, the reference worm profile has no plane of mirror symmetry.

Description

Method for producing a cutting tool from a blank and grinding worm for producing a cutting tool

The invention relates to a method for producing a cutting tool from a blank. According to a second aspect, the invention relates to a grinding worm with a worm reference profile which has (a) a first reference profile section and (b) a second reference profile section.

Cutting tools, especially milling cutters, are often made by grinding. It is necessary to carry out two or more grinding operations one after the other.Although this makes it possible to always select a grinding process that optimizes the corresponding grinding task, the disadvantage is that either the blank has to be re-clamped several times or the tool has to be changed got to. Both are undesirable, albeit inevitable.

The invention is based on the object of reducing the disadvantages of the prior art.

The invention solves the problem by a method for producing a cutting tool on a blank by generating grinding, wherein generating grinding is preferably carried out by means of a grinding worm that has a worm reference profile, and wherein the worm reference profile has no mirror plane of symmetry.

According to a second aspect, the invention solves the problem by a generic grinding worm, in which a difference angle between the first reference profile section and the second reference profile section is at least 25 °, in particular to- is at least 30 ° and / or in which the screw reference profile has no plane of symmetry and / or at least one profile angle is at least 25 ° at most, in particular 20 ° at most.

The advantage of the invention is that an increase in productivity is possible.

In addition, it is often possible to increase the workpiece quality, in particular the concentricity and / or the dimensional accuracy. This is due in particular to the fact that the circumferential cutting of the milling tool can be machined within the scope of just one grinding treatment by means of precisely one grinding tool, which is a preferred embodiment of the invention. In particular, all cutting edges and cutting teeth of the cutting tool can be processed by means of only one grinding tool, namely the grinding worm.

It is also advantageous that regrinding of worn cutting tools can also be carried out particularly easily. The reason for this is that from the geometry of the grinding worm for the cutting position of the cutting tool, a geometry of a regrinding grinding worm can easily be derived, by means of which worn cutting tools can be reground.

It is also advantageous that, as a rule, a higher product quality can be achieved when the cutting tool is used. The reason for this is that due to the silicon generation of the cutting tool edges and the rotation of the same, a better concentricity of the cutting tool is produced. Through the use of shift strategies, wear effects on the grinding worm and the resulting deviations in shape of the cutting tool can also be compensated or reduced. Furthermore, the thermal load on the cutting tool that occurs during the grinding process decreases as the cutting speed increases, since there is a coupling of the speeds of the workpiece and the grinding tool. This improves the quality (residual stresses) of the cutting tool and can therefore increase its service life when it is used later.

Another advantage can be that the division accuracy of the ground workpieces is very high if the number of teeth on the workpiece is not a multiple of The number of flights of the worm is what constitutes a preferred embodiment of the invention.

In the context of the present description, the designations for the screw reference profile according to DIN ISO 21771 are used.

A grinding worm is understood to mean a grinding tool which has at least one helically extending grinding section.

Explanations of the terms used in the description can be found, for example, in Weck, M. and Neupert, B .: Exact calculation of the tooth form of helical toothed spur gears, VDI-Z 125 (1983), No. 17 (Sept. 1983), p. 653 -656.

According to the invention is also a method for producing a cutting tool from a blank by generating grinding, wherein generating grinding takes place by means of a grinding worm which has a worm reference profile, the worm reference profile having a first reference profile section and a second reference profile section and wherein a difference angle between the first reference profile section and the second reference profile section is at least 25 °, in particular at least 30 °. This screw reference profile preferably has no mirror plane of symmetry.

The screw reference profile can have more than two reference profile sections. In this case there are preferably at least three or exactly three or at least four or exactly four reference profile sections for which the entered relationship applies. There can also be more than four reference profile sections. There are preferably fewer than eight reference profile sections. The reference profile sections are preferably linear, with deviations of ± 2 ° being possible. However, it is favorable if the deviation is less than ± 1 °. The first reference profile section and the second reference profile section are preferably designed in such a way that a convex cutting tool flank and a concave cutting tool flank are produced when the cutting tool is manufactured. It is favorable if the first reference profile surface section runs at a first profile angle to a normal to a head line of the screw reference profile and the second reference profile section runs at a second profile angle to the normal to the head line. The difference between the amounts of the profile angles is preferably at least 20 °, in particular at least 25 °, particularly preferably at least 30 °.

It applies to the profile angles that they lie in the interval between 0 ° and 90 °.

The second reference profile section is preferably arranged in such a way that it generates a rake face of the cutting tool when it is reached into the blank. It is favorable if the second profile angle is at most 25 °, in particular at most 20 °. An undercut then results on the rake face, which allows the chips to flow away when the cutting tool is used later.

According to a preferred embodiment, the worm reference profile has a head line and a profile reference line, the head height distance between the head line and the profile reference line being so small that a tool is created whose rake face has the shape of a rolling trochoid. During generating grinding, a surface is created in the base of the later cutting tool, the shape of which can be described by a generating trochoid. In the manufacture of gears, attempts are made to keep this area as small as possible, as it affects the mechanical strength of the gear. However, it has been found that this structure is very useful when not a gear is to be made but a cutting tool.

The profile reference line is the line in which the gap width is equal to the tooth gap. The head line is the line of maximum distance to the profile reference line that runs through the worm reference profile. The head height distance cannot be negative, but it can be zero, which is a preferred embodiment.

Preferably, the screw reference profile has a basic reference profile section whose distance from the head line is greater than the distance from all other reference profile sections. The basic reference profile section preferably has a profile angle to the normal to the head line which is at most 85 °. In other words it runs the basic reference profile section preferably in the technical sense essentially parallel to the profile reference line.

It is favorable if the screw reference profile has (a) a first profile flight and (b) a second profile flight, the second profile flight being arranged off-center to the first profile flight, so that an unevenly divided cutting tool is created. The feature that the second profile passage is arranged eccentrically to the first profile passage is understood - if exactly two profile passages exist - in particular that a distance from the first profile passage to the second profile passage differs from the distance from the second profile passage to the first profile passage. Whilst an unevenly divided cutting tool is advantageous, unevenly divided gears are highly undesirable, so that worm reference profiles with two profiles are not known from gear manufacturing. Although double-flight worms can also be used in gear production, all flights have the same reference profile and the same pitch. In addition, to avoid the unequal division, gear numbers are used that do not represent a multiple of the number of gear teeth.

A number of teeth Z of the cutting tool is always an integral multiple of the number of turns G. Preferably, the number of teeth Z of the resulting cutting tool is less than 13, in particular less than 10.

It is favorable if the screw reference profile also has (c) a third profile flight, with (d) the three profile flights being arranged unequally divided. This creates an unevenly divided cutting tool. The feature that the profile passages are arranged unevenly divided is understood in particular that of the distances (i) first profile passage to second profile passage, (ii) second profile passage to third profile passage and (iii) third profile passage to first profile passage at least two of the Distinguish distances from each other. The two distances preferably differ by at least 2%, in particular at least 5%.

It is particularly favorable if the screw reference profile also has (e) at least one fourth profile flight, with (d) the at least four profile flights being arranged unequally divided. This creates an unevenly divided cutting tool. Under The feature that the profile passages are arranged unevenly divided is understood in particular that from the distances (i) first profile passage to second profile passage, (ii) second profile passage to third profile passage, (iii) third profile passage to fourth profile passage and ( iv) fourth profile passage to first profile passage at least two of the distances, in particular at least three of the distances differ from one another in pairs. The distances preferably differ by at least 2%, in particular at least 5%.

The profile shift factor is preferably at most as large as x * min. x * min is the profile shift factor at the undercut limit. The profile shift factor is the profile shift divided by the normal module. The normal module m _n is the quotient of the normal division p _n and the circle number p. The profile shift is the distance between the profile reference line and the pitch circle cylinder. The pitch cylinder is the cylinder whose axis coincides with the axis of rotation of the cutting tool and whose diameter d is given by d = (Z ^* m _n ) A ^. Z is the number of teeth on the cutter. m _n is the normal module l is the helix angle on the pitch circle.

The profile shift factor x * min at the undercut limit is the profile shift factor at which an undercut occurs at the base of the cutting tool.

A tool head height factor h _ap o ^* is preferably less than 0.7, in particular at most 0.5, particularly preferably at most 0.3. The tool head height factor is particularly favorable to zero. The tool head height factor is defined in DIN 3960 from March 1987.

The reference worm profile of the grinding worm according to the invention preferably has one of the properties mentioned above. In the following the invention is tert erläu with reference to the accompanying drawings. It shows

FIG. 1 shows a three-dimensional view of a generating grinding machine according to the invention with a grinding worm according to the invention for carrying out a method according to the invention,

FIG. 2a shows a screw reference profile which has a profile flight and also a

Cross section through a cutting tool that was made with a pitch worm that has this worm reference profile,

FIG. 2b shows a worm reference profile of a second embodiment of a grinding worm according to the invention and, in the right partial image, a cross section through a cutting tool produced therewith, and FIG

FIG. 3 shows a perspective side view of a grinding worm to explain multi-start grinding worms.

FIG. 1 shows a machine tool 10 according to the invention with a grinding worm 12 according to the invention for grinding a blank 14 from which a cutting tool, in the present case in the form of a milling cutter, is ground. The process of dividing the cutting tool from the blank 14 corresponds in terms of kinematics to the grinding process for gears, but differs fundamentally with regard to the generated geometry of the cutting tool.

FIG. 2a shows a worm reference profile 16 of the grinding worm 12 (see FIG. 1). It can be seen that the screw reference profile 16 has a first reference profile section 18.1 and a second reference profile section 18.2. The first reference profile section 18.1 extends at a first profile angle a1 to a normal N on a head line K of the screw reference profile 16. The second profile section 18.2 extends at a second profile angle a2 to the normal N. In the present case, a1 = 68 ° and a2 = 88 °. In the present case, the worm reference profile 16 has more than one thread G. In the present case, G = 4. In the right partial image, a cutting tool 20 in the form of a milling cutter can be seen. A number of teeth Z of the cutting tool 20 is always an integral multiple of the number of threads G. In the present case, the screw reference profile 16 can thus also be single-thread (G = 1) or two-thread (G = 2).

A difference Da the profile angle is in the present case Da = a2 - a1 = 20 °.

Between the head line K and the profile reference line P there is a head height distance d. This is so small that all rake faces 22.1, ..., 22. Z have the shape of a rolling trochoid. In particular, the head height distance d is chosen such that the rake faces 22. i (i = 1, ..., Z) are convex.

There are programs for the analytical or Sumerian simulation of the resulting shape of the machined object, depending on the worm profile. By varying the head height distance d that head height distance d is determined for which the specified requirement is met.

In the present case, the screw reference profile 16 has a basic reference profile section 18.3, the distance from which to the head line is greater than the distance from all of the reference profile sections. A profile angle a3 is preferably at most a = 88 °. In this case, the flank of the cutting tool can be completely produced during generating grinding.

According to an alternative embodiment of the invention, however, it is advantageous that the profile angle a3 is at least a = 88 °. In this case, very small clearance angles are generated, which is desirable, for example, with reamers.

In the case shown in FIG. 2a, the screw reference profile has four profile flights, each of which is equally divided. In other words, a length PGangi of the first gear is equal to a length pGang2 of the second gear and this in turn is equal to a length pGang3 of the third gear. If, as in the present case, there is a fourth gear, then it applies to the length pGang4 that this is as great as the lengths of the other gears. In other words, for each of the i gears (i = 1, ... g; g is the number of gears) the relation pGangj = PG / Q applies. In other words, all profile courses are divided equally, where PG is the total length of all courses. In other words, PG is the pitch of the worm, it does not mean the entire length of the worm, which is determined by the number of complete "revolutions" of the flights. With the given reference profile, grinding worms of any length can ultimately be created, since the first gear starts again after one revolution where the fourth gear ends. Of course, this applies to all length designations in this and the previous / following paragraphs.

FIG. 2b shows a further screw reference profile 16 with four flights which are arranged unequally divided. It can be seen that the length pGangi does not correspond to the Gth fraction of the total length p _{n of} the screw reference profile. Rather, pGangi = 0.95 p _n. This results in an unevenly divided cutting tool 20, as shown in the right partial image. An angle β between two cutting edges of the cutting tool 20 is then not equal to the Z-th part of 360 °. In other words, β is not equal to 360 ° / Z. FIG. 3a shows a grinding worm 12 with g = 4 turns. FIG. 3b shows a further embodiment of a grinding worm 12 with g = 1 gear.

List of reference symbols

10 machine tool

12 grinding worm

14 blank

16 Reference screw profile

20 cutting tool

22 rake face G gear

hapo ^* tool head height factor

K head line

m _n normal module

N normal

P profile reference line

a profile angle

l Helix angle on the pitch circle

D difference in profile angle amounts

d Head height distance p _n Total length of the screw reference profile x * min Profile shift factor

Z number of teeth

Claims

Patent claims:

1. A method for producing a cutting tool (20) from a blank (14) by generating grinding, the generating grinding being carried out by means of a grinding worm (12) which has a worm reference profile (16), and wherein the worm reference profile does not have a mirror symmetry plane Has.

2. The method according to claim 1, characterized in that

(a) the screw reference profile (16)

(i) a first reference profile section (18.1) and

(ii) has a second reference profile section (18.2) and that (b) a difference angle (aD) between the first reference profile section (18.1) and the second reference profile section (18.2) is at least 20 °, in particular at least 25 °.

3. The method according to any one of the preceding claims, characterized in that

(a) the screw reference profile (16) of the first reference profile section (18.1) runs at a first profile angle (a) to a normal (N) to a head line (K) of the screw reference profile (16), and

(b) the second reference profile section (18.2) runs at a second profile angle to the normal (N) on the head line (K) and that

(c) the difference in the amounts of the profile angles is at least 20 °, in particular at least 25 °.

4. The method according to any one of the preceding claims, characterized in that

(a) the second reference profile section (18.2) generates a rake face (22) of the cutting tool (20) when it engages in the blank (14) and

(b) the second profile angle (0C2) is at most 25 °, in particular at most 20 °.

5. The method according to any one of the preceding claims, characterized in that

(A) the screw reference profile (16) has a head line (K) and a profile reference line (P) and

(b) a head height distance (d) between head line (K) and profile reference line is so small that a cutting tool (20) is created, the rake face (22) of which has the shape of a rolling trochoid and / or is concave.

6. The method according to any one of the preceding claims, characterized in that

(a) the screw reference profile (16) has a basic reference profile section (18) whose distance from the head line (K) is greater than the distance from all of the reference profile sections and that

(b) the basic reference profile section (18) has a profile angle (a) to the normal (N) to the head line (K) which is at most 88 °, in particular at most 85 °.

7. The method according to any one of the preceding claims, characterized in that the screw reference profile (16)

(a) a first profile walk (gear 1) and

(b) has a second profile gear (p gear 2),

(c) wherein the second profile passage is arranged eccentrically to the first profile passage, so that an unevenly divided cutting tool (20) is created.

8. The method according to any one of the preceding claims, characterized in that the screw reference profile (16)

(a) a first profile walk (gear 1) and

(b) has a second profile gear (p gear 2),

(c) has at least one third profile gear (p gear 3), at least two

Profile gears are arranged unequally divided.

9. The method according to any one of the preceding claims, characterized in that a profile shift factor is at most as large as a profile shift factor (x * min) at the undercut limit.

10. The method according to any one of the preceding claims, characterized in that the tool head height factor (h _ap o ^* ) is at most 0.7.

11. Grinding worm (12) with a worm reference profile (16), the

(a) a first reference profile section (18.1) and

(b) has a second reference profile section (18.2),

characterized in that

(c) a difference angle (a) between the first reference profile section and the second reference profile section is at least 25 °, in particular at least 30 °.

Pl / be-bro