GB1591771A - Face milling head with bar-shaped milling tools - Google Patents

Abstract

Each rod-shaped milling cutter (3) projecting beyond the front end face (4) of the basic body (1) of the milling head has a plane flank clearance face (5) and a plane head clearance face (6). These two faces, together with the plane rake face (7), form the cutting edges (8, 9). The flank clearance face (5) and the head clearance face (6) of each milling cutter (3) are allocated to one another in such a way that their intersection line (10) forms a plane (12) with the longitudinal axis (11) of the milling-cutter shank. This plane (12) is parallel to the milling-cutter shank surface (13) bearing against the base of the milling-cutter locating groove (2) and in the assembled state is parallel to the milling-head axis (14). The re-grinding of these two clearance faces and of the rake face (7) can thus be carried out without adhering to the proportionality between the amounts of stock removal at the clearance faces (5, 6) and the amount of stock removal at the rake face. <IMAGE>

Description

(54) FACE MILLING HEAD WITH BAR-SHAPED MILLING TOOLS (71) We, VEB WERKZEUGKOMBI NAT SCHMALKALDEN of Asbacher Strasse 17, DDR-608 Schmalkalden, German Democratic Republic, a Corporation organised under the laws of the German Democratic Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a face milling head with bar-shaped milling tools for machining trapezoidal grooves, more particularly for producing tooth systems, e.g., on bevel gears with arcuate tooth flanks.

In order to produce trapezoidal grooves, more particularly to produce tooth systems it is known to use milling heads the cutting tools of which project out beyond the front end face of the milling head, each tool having a planar end surface and two side rake surfaces, one or both of the side rake surfaces being arcuate. A planar surface of the cutting tool intersects the end surface and the side surfaces, cutting edges of the tool being formed by the lines of intersection of said planar surface with the side surfaces and by the line of intersection of said planar surface with said end surface.

In order to avoid high maintenance costs and expensive maintenance apparatus, such milling heads are reground only on the planar surfaces of the cutting tools, whilst the edge geometry, the original edge profile and its radial position with respect to the milling head axis are maintained. Circularity errors which may arise after grinding are corrected by means of adjusting elements, e.g., by wedge plates. Cutting tools with arcuate rake surfaces have the disadvantage that a comparatively large amount of precious material must be ground off on the planar surfaces in order to repair them, because the entire width of the wear mark must be eliminated. The number of regrindings possible with these milling heads is small and results in relatively high tool costs when milling, and relatively high consumption of high grade cutting tool material.

These disadvantages have led to the development of milling heads, the cutting tools of which are of bar-shaped construction and have planar rake surfaces.

The repair of a milling head with barshaped cutting tools is effected by regrinding the cutting tools outside the milling head in a special device.

It is also already known, for the purpose of repairing milling heads with bar-shaped cutting tools, to use a method in which the planar rake surfaces are ground by so much that the cutting edge is displaced along the shank axis whilst maintaining its edge geometry (German specification No.

1577451).

The bar-shaped cutting tools repaired by this grinding method are reinserted, after being sharpened, into the milling head, the edges being brought into their original position. This is done by sliding the cutting tools along their bar axis in the housing groove of the milling head up to a fixed stop and then clamping them. These milling head constructions only partly overcome the disadvantages of the known milling heads which are equipped with cutting tools with arcuate side rake surfaces. In fact the necessity of maintaining the original edge geometry makes it necessary for a considerable amount of material to be ground away, without this being necessary due to the amount of wear on the surfaces to be ground.

Another disadvantage of the known barshaped cutting tools is that a complicated grinding device is necessary to repair them.

The reason for this is that the side rake surfaces occupy an inconvenient position on the bar-shaped cutting tool with reference to the end surface and the cutting tool shank, with the result that a special support surface is necessary for each different type of bar-shaped cutting tool to be ground.

Known milling heads with bar-shaped cutting tools also have the disadvantage that sensitivity of adjustment for the cutting tools is lacking. This has disadvantageous infuences on the degree of circularity of the tool edges which can be achieved. In order to reduce such disadvantages in the repair of milling heads with bar-shaped cutting tools, it has therefore also been attempted previously to use a shank surface of the bar-shaped cutting tool simultaneously as a rake surface and to regrind the cutting tools only on planar surfaces intersecting the said shank surface (German Democratic Republic specifications Nos. 112923 and 121731, and U.S. specification No. 3881889).But these milling heads have the disadvantage that they can be used economically only when little or no wear occurs on the said shank surface, because otherwise too much has to be ground away from the intersecting planar surfaces and the repair thus becomes more onerous than for the cutting tools provided with arcuate rake surfaces.

The invention aims at obviating the disadvantages existing in the known milling head constructions and endeavours to enable simplified repair of the cutting tools, improved use of the tool material and better adjustability.

It is an underlying object of the invention to develop for milling heads for machining trapezoidal grooves, more particularly for producing tooth systems, e.g., on bevel gears with arcuate tooth flank lines, a structurally novel bar-shaped cutting tool construction which whilst retaining the advantage of simplified production makes it possible to regrind the cutting tools on all rake surfaces for the purpose of repair, without the need to respect any direct proportionality between the amounts of grinding on the respective surfaces.

At the same time it should be possible to perform the regrinding of the cutting tool edge with simple means without recourse to complicated holding or clamping devices.

The novel cutting tool construction is also intended to enable a simple adjustment of the cutting tool edges into their correct positions in the milling head.

To this end, the present invention consists in a face milling head with bar-shaped cutting tools, for machining trapezoidal grooves, more particularly for machining tooth systems, e.g. on bevel gears with arcuate tooth flanks, each cutting tool having a planar end surface functioning as a front rake surface and a planar flank surface functioning as a side rake surface and a further planar top rake surface which meets the end surface and the said flank surface to define therewith two cutting edges of the tool, the intersection line between the said flank surface and the end surface of the tool lying in a plane to which the longitudinal axis of the cutting tool shank and the axis of the milling head are parallel, a shank surface of the cutting tool also being parallel to said plane.

Advantageously, an intersection line between the further rake surface and a shank surface of the cutting tool adjacent to the further rake surface and extending parallel to the longitudinal axis of the cutting tool shank is perpendicular to said longitudinal axis.

Face milling heads with bar-shaped cutting tools constructed according to the invention provide the possibility to regrind the said further rake surface independently of the amounts ground off on th planar end surface and the said planar flank surface, while the required position of the cutting tools in the milling head with reference to the edge geometry and to the profile is achieved in that the cutting tools are slid out more or less, as a function of the relevant position of the said further rake surface, beyond the front end face of the milling head, so that the edges once again come to lie in the original milling head axial planes and change their position solely in the milling head axial direction.

The construction of the cutting tools in the milling head according to the invention also has the advantage that for sharpening, all the cutting tools to be ground can simultaneously be laid upon a common plane surface of the grinding device, both for grinding the end surface and said flank surface and for grinding the said further rake surface, and thus makes a considerable contribution to simplifying the work of repair.

In addition to the clamping screws which serve to fix the cutting tools, a pretensioning element may be provided for each cutting tool. The pre-tension generated in the pre-tensioning element ensures a stable position of the cutting tools even in the unclamped state and permits a sensitive sliding of the cutting tools, such as is necessary in order to adjust an accurate position of the milling head for the required circularity of the flank edges.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example one embodiment thereof, and in which: Figure 1 shows a detail in plan view of a milling head: Figure 2 is a detail in side elevation of the milling head of Figure 1; Figure 3 is an axial section through the milling head of Figure 1; Figure 4 shows a cutting tool for the milling head of Figure 1, for external cutting; Figure 5 shows the shank cross-section of the cutting tool of Figure 3; Figure 6 shows the fixing and clamping of the cutting tools in the milling head; Figure 7 shows a modified fixing and clamping of the cutting tools; and Figure 8 is a perspective view illustrating in greater detail the geometry of a cutting tool of the milling head of Figures 1 to 3.

The cutting tools 3 arranged in housing grooves 2 of the milling head body 1 project outwards beyond the front end face 4 of the milling head body 1 and have a planar side rake surface 5 and a planar front rake surface 6, which intersect a planar top rake surface 7 so as to define the cutting edges 8, 9. The planar side rake surface 5 and the front rake surface 6 of each cutting tool 3 are mutually associated in such a way that the prolongation of their intersection line 10 forms, with the assumed cutting tool shank longitudinal axis 11, a plane 12 which is parallel to the shank surface 13 of the cutting tool 3 and, in the assembled state, parallel to the milling head axis 14. The geometry of the rake surfaces 5, 6, 7 and the shank surfaces 13 in relation to the axis 11 and the plane 12 can be seen from Figure 8.

For the purpose of repair, the cutting tools 3 are reground outside the milling head in a set on the planar rake surfaces 5, 6 and 7, and upon reassembly they are brought out more or less beyond the front end face 4 as a function of the instantaneous position of the rake surfaces 7, so that the cuting edges 8 and 9 again come to lie in the original milling head axial plane. As compared with previous or subsequent edge positions, the individual edge points 15 are displaced along straight lines 16 which are parallel to the axis 14 of the milling head.In order to regrind on the rake surfaces 5, 6, all the cutting tools 3 to be reground simultaneously are placed with one of the shank surfaces 13, 17 or 18 (see Figure 5) but preferably with the mutually parallel shank surfaces 13 or 17, upon a plane surface of a grinding machine or grinding device, and inclined in that plane correspondingly to the required grinding direction, which must coincide with the direction of the intersection lines 10. For regrinding on the rake surfaces 7, all the cutting tools 3 to be ground simultaneously are placed with their particular shank surface 19 which forms, with the rake surface 7, an intersection line 20 which is preferably perpendicular to a line 21 parallel to the assumed cutting tool shank axis 11, upon a plane face of a grinding machine or grinding device.

In addition to clamping screws 22, which are accommodated in a clamp ring 23 in order to fix the cutting tools 3, pretensioning elements 24, 25, (Figure 6) or 25, 26 (Figure 7) are provided to ensure that the cutting tools 3 are held in a stable position in the milling head in the unclamped state and so make it possible to perform a sensitive adjustment.

In the embodiments illustrated, the pretensioning elements comprise a screwthreaded pin with a spring bolt 24 and pressure piece 25 (Figure 6) or a shaped spring 26 and a pressure piece 25.

WHAT WE CLAIM IS: 1. A face milling head with bar-shaped cutting tools, for machining trapezoidal grooves, more particularly for machining tooth systems, e.g. on bevel gears with arcuate tooth flanks, each cutting tool having a planar end surface functioning as a front rake surface and a planar flank surface functioning as a side rake surface and a further planar top rake surface which meets the end surface and the said flank surface to define therewith two cutting edges of the tool, the intersection line between the said flank surface and the end surface of the tool lying in a plane to which the longitudinal axis of the cutting tool shank and the axis of the milling head are parallel, a shank surface of the cutting tool also being parallel to said plane.

2. A face milling head as claimed in claim 1, wherein an intersection line between the further rake surface and a shank surface of the cutting tool adjacent to the rather rake surface and extending parallel to the longitudinal axis of the cutting tool shank is perpendicular to said longitudinal axis.

3. A face milling head as claimed in claim 1 or 2, wherein a pre-tensioning element is provided for each cutting tool to hold the latter in the milling head during adjustment.

4. A face milling head described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. milling head of Figure 1; Figure 4 shows a cutting tool for the milling head of Figure 1, for external cutting; Figure 5 shows the shank cross-section of the cutting tool of Figure 3; Figure 6 shows the fixing and clamping of the cutting tools in the milling head; Figure 7 shows a modified fixing and clamping of the cutting tools; and Figure 8 is a perspective view illustrating in greater detail the geometry of a cutting tool of the milling head of Figures 1 to 3. The cutting tools 3 arranged in housing grooves 2 of the milling head body 1 project outwards beyond the front end face 4 of the milling head body 1 and have a planar side rake surface 5 and a planar front rake surface 6, which intersect a planar top rake surface 7 so as to define the cutting edges 8, 9. The planar side rake surface 5 and the front rake surface 6 of each cutting tool 3 are mutually associated in such a way that the prolongation of their intersection line 10 forms, with the assumed cutting tool shank longitudinal axis 11, a plane 12 which is parallel to the shank surface 13 of the cutting tool 3 and, in the assembled state, parallel to the milling head axis 14. The geometry of the rake surfaces 5, 6, 7 and the shank surfaces 13 in relation to the axis 11 and the plane 12 can be seen from Figure 8. For the purpose of repair, the cutting tools 3 are reground outside the milling head in a set on the planar rake surfaces 5, 6 and 7, and upon reassembly they are brought out more or less beyond the front end face 4 as a function of the instantaneous position of the rake surfaces 7, so that the cuting edges 8 and 9 again come to lie in the original milling head axial plane. As compared with previous or subsequent edge positions, the individual edge points 15 are displaced along straight lines 16 which are parallel to the axis 14 of the milling head.In order to regrind on the rake surfaces 5, 6, all the cutting tools 3 to be reground simultaneously are placed with one of the shank surfaces 13, 17 or 18 (see Figure 5) but preferably with the mutually parallel shank surfaces 13 or 17, upon a plane surface of a grinding machine or grinding device, and inclined in that plane correspondingly to the required grinding direction, which must coincide with the direction of the intersection lines 10. For regrinding on the rake surfaces 7, all the cutting tools 3 to be ground simultaneously are placed with their particular shank surface 19 which forms, with the rake surface 7, an intersection line 20 which is preferably perpendicular to a line 21 parallel to the assumed cutting tool shank axis 11, upon a plane face of a grinding machine or grinding device. In addition to clamping screws 22, which are accommodated in a clamp ring 23 in order to fix the cutting tools 3, pretensioning elements 24, 25, (Figure 6) or 25, 26 (Figure 7) are provided to ensure that the cutting tools 3 are held in a stable position in the milling head in the unclamped state and so make it possible to perform a sensitive adjustment. In the embodiments illustrated, the pretensioning elements comprise a screwthreaded pin with a spring bolt 24 and pressure piece 25 (Figure 6) or a shaped spring 26 and a pressure piece 25. WHAT WE CLAIM IS:

1. A face milling head with bar-shaped cutting tools, for machining trapezoidal grooves, more particularly for machining tooth systems, e.g. on bevel gears with arcuate tooth flanks, each cutting tool having a planar end surface functioning as a front rake surface and a planar flank surface functioning as a side rake surface and a further planar top rake surface which meets the end surface and the said flank surface to define therewith two cutting edges of the tool, the intersection line between the said flank surface and the end surface of the tool lying in a plane to which the longitudinal axis of the cutting tool shank and the axis of the milling head are parallel, a shank surface of the cutting tool also being parallel to said plane.

2. A face milling head as claimed in claim 1, wherein an intersection line between the further rake surface and a shank surface of the cutting tool adjacent to the rather rake surface and extending parallel to the longitudinal axis of the cutting tool shank is perpendicular to said longitudinal axis.

3. A face milling head as claimed in claim 1 or 2, wherein a pre-tensioning element is provided for each cutting tool to hold the latter in the milling head during adjustment.

4. A face milling head described with reference to and as shown in the accompanying drawings.