Edge miller for machining the edges of sheet metal

An edge miller for machining the edges of sheets advanced in motion relative thereto includes a milling unit supported for rotation therein and in turn supporting circular cutters for rotation relative thereto. The milling unit has bearings for each of the circular cutters supporting such rotation thereof, the bearings disposing the longitudinal cutter axes such that the axial and radial positions thereof are alternatively above and below the thickness centerline of the sheet and that each circular cutter has a cutting edge range between first and second cutting edge points. Machining forces between such cutting edge and the workpiece druing engagement produce a torque for rotating said circular cutter.

FIELD OF THE INVENTION 
This invention concerns an edge miller for machining the edges of sheets 
that are fed forward or along the edges of sheets in motion relative to a 
milling unit, with the edge miller provided with circular cutters in 
motor-driven rotation and the longitudinal cutter axes of the circular 
cutters being placed radially relative to the milling head so that they 
lie alternately above and below the thickness centerline of the sheet at 
uniform radial and diagonal distances. 
BACKGROUND OF THE INVENTION 
The machining of the edges of sheets with edge millers is a generally 
well-known process. In such cases the loaded cutter length is constant as 
a function of the strip thickness and the advance position of the cutters. 
In machining with high power, this results in a concentrated cutting load, 
that has the effect of reducing the working life. One possibility for 
improving this situation consists of lengthening the active cutting 
length. 
Milling units with cylindrical cutter units that are mounted on their 
longitudinal axes are disclosed by European Patent No. 0 038 923 and 
elsewhere. The rotating cutting tool described in this publication is a 
face miller for sheet metal edges in which the machined surface is 
perpendicular to the axis of rotation of the milling unit. The axes of 
rotation of the cutters of this known face miller are arranged parallel to 
the working surface. Consequently, the fronts of the cylindrical cutters 
are used for the chip-removing tool surfaces. However, this known face 
miller cannot be used under conditions of practical application, and one 
of the main reasons for this is the excessively low achievable rate of 
milling, that results from small contact lengths corresponding to the 
geometric conditions. Thus, the machining conditions prevailing with this 
known cutting tool and thus the chipping efficiency are unfavorable. 
An edge miller of the type mentioned initially is disclosed essentially in 
German patent application Disclosure No. 2 735 283. In this case there is 
a solid, nonrotating screw connection between the milling unit and the 
circular cutters, so that it is impossible for the cutters to rotate 
during the contact. For this reason, because of the concentrated load on 
the cutter edges, only very short lifetimes are possible in high-output 
applications. Another substantial drawback of this known edge miller is 
the fact that the machining of the V-shaped diagonal cut running on the 
centerline of the plate has to be done either with two sloping millers or 
with a two-part miller consisting of upper and lower cutters. In both 
cases the chipping conditions in the area of the centerline of the plate 
are extremely unfavorable, since in this case the value of the rake angle 
is equal to zero in each case with the contact points of the cutting 
wheels in the area of the cutting lines. Consequently, this known edge 
miller is practically unusable for machining metallic workpiece. 
SUMMARY OF THE INVENTION 
Therefore, the basic purpose of this invention is to describe an edge 
miller for machining the edges of sheet metal that meets the requirements 
for high-performance machining processes with very good durability. 
Proceeding from an edge miller of the type defined at the outset, this 
problem is solved pursuant to the invention by providing that the circular 
cutters are placed to rotate on the milling unit by means of bearings, and 
the axial and radial positions of the axes of cutter rotation above and 
below the thickness centerline of the sheet, respectively, are determined 
by these bearings in such a way that each circular cutter has a cutting 
edge region effective for the milling process between two cutting edge 
points P1 and P2. When a circular cutter is in engagement with the 
workpiece, P1 is the point obtained by projecting the axis rotation of the 
cutter perpendicular to the direction of rotation of the milling unit 
until it intersects the circumference of the cutter. When a circular 
cutter is in engagement with the workpiece, P2 is the point obtained by 
projecting the axis of rotation of the cutter parallel to the direction of 
rotation of the milling unit until it intersects the circumference of the 
cutter. P1 and P2 thus comprise points bounding the effective cutting 
range of the circular cutter. Machining forces during engagement produce a 
torque acting on the shell of the circular cutter for rotating the cutter. 
Because of the design of the edge miller pursuant to the invention, a more 
favorable oblique cut is provided in connection with the load on the 
cutting edge, and complete utilization of the cutter length corresponding 
to the circumference of the cutting edge is provided for. Because of the 
circular cutters rotating around their own axes as a result of the 
machining forces, the cutting power acting on a tooth during the machining 
is distributed corresponding to the length of the cutting edge 
circumference, because of which substantially lower specific cutting edge 
loads are reached than with a conventional edge miller. 
However, it is also particularly beneficial that the effective cutting edge 
area of a circular cutter is given in each case by the range between the 
two cutter edge points P1 and P2 in such a way that these cutter edge 
points are not reached, so that on the one hand the cutter edge point P1 
with a rake angle approaching zero is avoided, but on the other hand the 
cutter edge point P2 at which the machining forces produce no torque is 
also excluded. 
The relative motion between the miller and the sheet metal can be brought 
about in a known way, by advancing either the sheet or the miller. The 
design pursuant to the invention has special significance in the machining 
of sheet metal strips, since in practice higher milling outputs are used 
in this field than in machining with advancing miller. 
For this reason, the characteristics of the edge miller pursuant to the 
invention are illustrated with the example of the machining of advancing 
sheet metal strips. 
The circular cutters of the milling unit can preferably be designed with 
cylindrical or similar shape, with concave or conical envelope contour 
line. The cutters can suitably be designed so that both limiting edges of 
the rotary cutter being used can be used as cutting edges. Carbide cutters 
are used in particular. 
In accordance with a beneficial refinement of the invention, it is 
desirable to choose the slope of the axis of rotation of the cutter 
relative to a desired machining plane with a rake angle in such a way that 
the desired machining plane in the area of the top and bottom edge angles 
conforms to an elliptical cut arc of a circular cutter. PG,6 
The circular cutters with their circular cutting edges, corresponding to 
the attitude of their radial longitudinal axial positions parallel to the 
milling unit, produce a machining contour that can be described as 
elliptical arcs. This produces a possible correction of the cut face 
surface in comparison with the top and bottom planes of the sheet. 
In order to be able to utilize the machining forces as a torque acting on 
the cutters, it is necessary for the resultant cutting forces to be 
effective above or below the particular axis of rotation of the cutters. 
This results in the mentioned elliptical arcs lying mostly or completely 
between the two elliptical axes, which produces arched surfaces differing 
slightly from the desired position if the horizontal cutter axial position 
is on the desired cutting plane. The smallest deviation from the position 
of the desired machining plane can be reached when the curved surface 
determined by the elliptical arcs conforms to the desired plane of 
machining in the area of the two edge angles of the sheet. In order to be 
able to adhere to this condition, it is necessary for the axes of rotation 
of the circular cutters, observed in the machining position, to be 
appropriately slanted from the direction of the desired plane of 
machining. 
Further details and benefits of the invention will be described in detail 
with reference to the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS AND PRACTICES 
FIG. 1 shows an edge miller corresponding to an example of embodiment of 
the invention, in sectional side elevation, with a cylindrical milling 
unit 1 being set in rotation around its longitudinal axis O in a direction 
of rotation D, and machining the edge of an advancing sheet 2 in the 
direction V. The machining position of the sheet edge is determined by 
guide rolls 3 acting with pressure on the two faces of the sheet. 
Rotating circular cutters 4 are mounted with bearings 7 at uniform 
distances from one another in uniform radial positions on the milling unit 
1. Each of the circular cutters 4 is connected solidly with screws 5 to 
the shafts 6 placed approximately radially to the milling unit 1 on the 
same longitudinal axis. It is beneficial for the axes of rotation of the 
shafts 6 to be arranged alternately at uniform distances above and below 
the sheet thickness centerline. The bearings 7 are connected to the 
milling unit 1 by fasteners 8. The positions of the shafts 6 and the 
circular cutters 4 connected to them above or below the thickness 
centerline of the sheet 2 are determined by the bearings 7 in both the 
axial and radial directions in such a way that each of the circular 
cutters 4 has a cutting edge range effective for the milling process 
between two cutting edge points P1 and P2, as described below in detail 
with reference to FIG. 2, in which the shell of an edge miller pursuant to 
the invention is ilustrated in development schematically in a partial 
illustration. 
The position of the sheet 2 is indicated in broken lines. The directions of 
rotation R1 and R2 of the circular cutters 4 cutting in succession, whose 
axes of rotation 9 are alternately above and below the sheet thickness 
centerline at uniform distances, are opposite. Consequently, the reaction 
force components occurring on the sheet faces have compensating effects on 
one another with the circular cutters 4 cutting in succession. 
When circular cutter 4 is in engagement with the workpiece, P1 is the point 
obtained by projecting the axis rotation of the cutter perpendicular to 
direction D until it intersects the circumference of the cutter. When 
circular cutter 4 is in engagement with the workpiece, P2 is the point 
obtained by projecting the axis of rotation of the cutter parallel to 
direction D until it intersects the circumference of the cutter. P1 and P2 
thus comprise points bounding the effective cutting range of the circular 
cutter. Machining forces during engagement produce a torque acting on the 
shell of the circular cutter for rotating the cutter. 
Since on the one hand the rake angle approaches zero at the cutting edge 
point P1 and the machining forces can produce no torque on the other hand 
at the cutting edge point P2, the cutting range must always lie inside of 
these two cutting edge points P1 and P2. These conditions can be met very 
satisfactorily if the cutting range is designed approximately in the 
center between the two cutting edge points P1 and P2, and it is also very 
beneficial for the sheet thickness used to be less than half of the radius 
of the cutting edge. 
Because of these features, the machining forces occurring during the 
cutting can each exert a torque on the circular cutters 4 and set them in 
rotation in this way. This produces two important effects, namely an 
oblique cut with low chipping resistance and a low cutting edge load by 
utilizing the cutting edge length corresponding to the circumference. In 
the last analysis, the two effects increase the lifetime and the load 
capacity of the milling unit. 
Another advantage of the cutter system illustrated is that a substantially 
higher number of teeth can be reached than in a milling head design 
without diagonal cutter offset. 
FIG. 3 shows the position of an offset axis of rotation of a cutter 9 
projected relative to the plane of rotation of the milling unit, in 
schematic representation. 
A sheet 2, a milling unit 1, and a circular cutter 4 mounted on it whose 
axis of rotation 9 is shifted by a shown offset E in the direction of 
rotation D of the milling unit 1 parallel to its radial direction, are 
shown schematically in plan view. This makes the excursion circle of the 
face of the circular cutting edge placed in the direction of rotation 
greater than that of the other face in the plane of the sheet. With the 
cutter axial position placed radially to the milling unit 1, the face of 
the cutting edge against the direction of rotation D would slide on the 
cut surface, which would cause unnecessary wear. 
FIG. 4 shows the cut edge contour of a circular cutter 4 of the milling 
unit 1 driven in the direction of rotation D rotating around its own axis 
of rotation O, in schematic illustration, with the axial line of the 
circular cutter 4 being positioned parallel to the plane of rotation of 
the milling unit 1. The position for achieving the desired cut surface is 
indicated by the intended machining surface A. The actual machining 
contour lies on an elliptical arc diagonal to the intended surface. 
FIG. 5 shows the edge miller illustrated schematically in FIG. 4 with 
inclined axis of cutter rotation 9, whose angle of inclination phi 
relative to the intended machining plane A is chosen so that in the area 
of the two (top and bottom) edges of the sheet the curved surface 
determined by the elliptical arc conforms to the desired machining plane 
A. With such an arrangement very good accuracy of the position of the 
surface to be machined can be produced.