Process and device for machining bars, tubes or tube blanks

A process and device for machining bars, tubes or tube blanks, especially strand-cast copper blanks, in which the work piece to be machined--supported in the cross-plane of the metal-cutting device is cut on its periphery and along its length, while the die and the work piece are continually moved relative to one another in the longitudinal direction of the work piece. At least one die rotates concentrically around the work piece, which is held in a rotation-proof manner, on a plane inclined toward the longitudinal axis of the work piece and with its cutters simultaneously machines two areas of the work piece surface that are located opposite to one another.

SUMMARY OF THE INVENTION 
The object of the present invention is to provide a process for outwardly 
machining long round cross-sections, such as cast copper blanks, for 
example, at extremely high advance speeds while maintaining good surface 
qualities and in a manner which maintains tolerances. The process should 
also permit the use of units that can be automated. It should also be 
possible to cut long labile work pieces without deformation. 
Pursuant to this object, and others which will become apparent hereafter, 
one aspect of the present invention resides in a process which at least 
one die rotates concentrically around the work piece on a plane inclined 
to the longitudinal axis of the work piece and, with its cutters, 
simultaneously machines two areas of the work piece surface, which are 
located opposite to one another. The invention thus consists of 
simultaneously machining two opposite peripheral areas of the work piece 
with one die, whereby the metal-cutting forces introduced on the opposite 
sides, which act transversely to the work piece, neutralize one another. 
Special advantages result when, according to a further embodiment of the 
invention, two directly adjacent dies rotate concentrically around the 
work piece on two different planes and the two planes are inclined toward 
the common longitudinal axis of the work in directions which are offset 
from one another by approximately 90 degrees. 
The inventive process makes it possible to machine the entire outer 
periphery of the work piece using only two dies, whereby the slight 
inclination of the die planes and the offset of their inclination 
directions by 90 degrees creates a polygonal cross-section, consisting of 
four elliptical arcs which are located, in pairs, opposite to one another. 
The two dies also allow very high advance speeds to be achieved, while a 
work piece length is machined only once and four adjacent peripheral areas 
of the work piece are machined simultaneously. 
When, according to a further feature of the inventive process, the dies 
rotate around the longitudinal axis of the work piece in opposite 
directions, the metal-cutting forces acting in the peripheral direction as 
well as the forces acting transversely to the work piece are automatically 
neutralized. The remaining forward motion forces in the longitudinal 
direction of the work piece are low. 
A device to carry out the process, pursuant to the present invention, has 
dies designed as inner cutters, the inner diameter of which between the 
die blades is slightly larger than the outer diameter of the work piece to 
be cut. 
Given an inner diameter between the die blades which is only slightly 
larger than the outer diameter of the work piece to be cut, the result, 
when the die is inclined, is the polygonal cross-sectional form described 
above. The smaller the inclination of the die to the longitudinal axis of 
the work piece, the more closely this polygonal cross-section approaches a 
circle. Preferably, the inclination of the die is permanently set, while 
the inner diameter is adjustable. This makes it possible to combine stable 
machine construction with the possibility of varying the outer diameter to 
be machined by adjusting the blades of the inner cutter. When the die is 
precisely set to the longitudinal axis of the work piece and the cutter 
diameters on the die heads are precisely adjusted, high accuracy in wall 
thicknesses can be attained. 
According to a further embodiment of the invention, in order to guarantee 
accurate machining, the work piece resting on guidance rollers can be 
fixed on both sides of the dies in a rotation-proof fashion on the face 
and axially by means of clamping and holding rods. It should be noted that 
the guides extend as closely as possible to the dies and the dies rotate 
as closely as possible to one another. The clamping and holding rods are 
simultaneously responsible for guiding the work piece into the machine 
prior to machining. 
According to another embodiment of the invention, at least the entry side 
of the work piece into the dies is designed as a guidance bush for the 
work piece. The guidance bush includes guides which are adjustable 
automatically and in a play-free manner, and guide the work piece in a 
centered fashion. Such a guidance bush ensures the precisely centered 
entry of the bars, tubes or tube blanks and thus helps to maintain 
required tolerances. 
In the framework of the invention, it is equally conceivable for the 
milling unit, consisting of the dies and the guides for the work piece, to 
be moved relative to the work piece in the longitudinal direction or for 
the work piece to be moved relative to the dies. 
The advantages of the present invention are that an unusual increase in 
forward motion performance can be achieved, compared to the prior art, in 
a machine of compact construction and with only two cutters. Short support 
lengths between the guidance rollers and the force-neutral process permit 
the surfaces of the work piece to be machined in a manner especially 
conducive to maintaining tolerances, so that all in all a compact, stable 
and economical solution has been created.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The drawings are simplified depictions of a device according to the 
invention and are meant to illustrate its principle. FIG. 1 shows a 
milling machine 1 arranged on a foundation 2. The milling machine 1 
accommodates a work piece 5 to be machined between two lateral posts 3, 4. 
The work piece 5 is clamped and held between two clamping and holding rods 
6, 7, which will be described in greater detail below. The work piece 5 
rests, like the clamping and holding rod 6, on guidance rollers 33, which 
prevent bending between the clamps. 
The machining of the work piece 5 is carried out by dies 8, 9, which are 
arranged on a die carrier 10, which is provided to be continuously movable 
on a guide path 11 in the longitudinal direction of the work piece. 
According to the invention, the dies 8, 9 are arranged in an inclined 
fashion and are rotary-driven via respective drives 12, which are not 
described in more detail and are within the knowledge of those skilled in 
the art. 
FIG. 2 shows--again, very schematically--a top view of the dies 8, 9. It 
can be seen that both dies are inclined toward the longitudinal axis 13 of 
the tube; specifically, both dies are inclined at an angle .gamma., as can 
be seen in the case of die 8, shown on the left of FIG. 2. The die 9 is 
inclined at the same angle, concentric to the longitudinal axis 13 of the 
tube and vertical to the plane of the drawing. The dies 8, 9 mounted at 
bearings 14, 15 are designed as inner cutters and have, distributed on 
their inner periphery, cutting disks 16 which cut the peripheral surface 
of the work piece 5. The inner radius between the cutting disks 16 as well 
as the angle .gamma. of the dies 8, 9 are chosen so that when the dies 8, 
9 rotate around the work piece 5, the respective work piece areas located 
across from the cutting disks 16 are machined. Because the angles of the 
die planes of both dies are set in directions which are offset to one 
another by 90 degrees, four peripheral areas of the work piece 5 are 
machined at the same time. When, as foreseen, the inner diameter between 
the cutting disks 16 is only slightly larger than the outer diameter of 
the work piece 5 and the selected angle .gamma. is suitably small, a 
slightly polygonal cross-section is achieved in the work: piece 5, with 
gentle transitions between the four polygon sides. A cross-section of this 
type, which has been cut into a slightly polygonal profile, is suitable 
for further processing, i.e., the fact that the cross-section of the 
milled work piece 5 is not circular does no harm. 
As described above, the dies 8, 9 rotate in opposite directions, so that 
the forces striving to turn the work piece neutralize one another. Because 
of this, guiding and holding the work piece is relatively simple. The dies 
8, 9 are driven via a gearing (not shown) by spur gears 17, 18, which 
engage into serrations 19, 20 on the dies 8, 9. The bearings 14, 15 rest 
against die carriers 21, 22, which are connected to the die carrier 10. 
In order to machine the surface of the work piece 5 accurately and with the 
minimum amount of metal being removed, the work piece must be held exactly 
in the center of the rotating dies 8, 9. To this end, the entry side of 
the device is equipped with a guide bush 24, which consists of eight 
segments lying on the surface of the work piece and distributed on its 
periphery. In the front (right-hand) area of the bush 24, the bush is 
provided on its outer periphery with a cone-shaped segment 24a, which 
rests against a cone-shaped member 26 of similar design on the die carrier 
21. By moving the bush 24 in the longitudinal direction of the work piece 
5 with the help of, for example, a piston-cylinder unit (not described 
further), at 25, the cone-shaped segments of the bush 24 can be pushed 
against the cone-shaped member 26 and thus clamped against the surface of 
the work piece 5. In this way, the work piece 5 can be set and guided in 
the exact center, whereby the clamping strengths are chosen in such a way 
that forward movement by the work piece 5 or by the die carrier 10 
relative to the surface of the work piece 5 is possible. 
On the exit side of the device according to the invention, there are 
withdrawal rollers 27, which guide the clamping and holding rod 7 and/or 
the work piece 5 and draw the work piece in and out at the beginning and 
the end of the work sequence. The housings that carry the withdrawal 
rollers 27 are equipped with strips 42 which are arranged to prevent cut 
metal chips from getting between the surface of the work piece 5 and the 
withdrawal rollers 27 and being pressed into the soft material there. 
FIG. 3a illustrates, in schematic fashion, the principle of the clamping 
and holding rods 6, 7. The work piece 5 is placed onto the clamping and 
holding rod 6 (left, in FIG. 1 ) and is clamped on its own inner surface 
by means of clamping segments 28 via conically surfaced elements 29, 30, 
which are activated with the help of a drawing bar 31. In this way, the 
work piece 5 can be held by the clamping and holding rod 6 so that it 
cannot rotate in the peripheral direction and can also be axially clamped 
by an annular intermediate part 32, which clamps against the faces of the 
work piece 5, without it being necessary for clamping and holding means to 
act upon the outer periphery of the work piece 5. It is thus possible to 
machine the work piece 5 all the way to its end. 
The clamping and holding rod 7, which is partially shown in FIG. 3b, acts 
upon the other side of the work piece 5. The work piece is clamped between 
the clamping and holding rods 6, 7, while the die carrier 10 with the dies 
8, 9 travels continually across the length of the work piece. As the die 
carrier 10 advances, the respective guidance rollers 33 are swung away, 
and after passing of the work piece they are swung back, in order to 
achieve the most secure support possible. 
With only two cutting dies 8, 9, the invention provides a compact unit 
across the length of the work piece, with short support lengths between 
the guidance rollers 33. Apart from the forward motion forces on the work 
piece 5, the process is force-neutral, because the dies 8, 9, which rotate 
in opposite directions, neutralize their respective turning moments. This 
simplifies the drive and works to the benefit of the accuracy of the 
cutting process, so that excellent tolerances can be expected. The work 
piece 5 is machined simultaneously with two dies on four peripheral areas, 
thereby increasing the efficiency of the milling procedure, so that 
complete external machining can be carried out in the shortest possible 
time with only one process route across the length of the work piece 5. To 
set the metal removal for the outer peripheral surface of the work piece 
5, the dies 8, 9 and/or the cutting disks 16 can be adjusted, whereby 
automated adjustment is conceivable. Because the dies 8, 9 rotate in 
opposite directions, arresting the work piece against rotation can largely 
be dispensed with. It is necessary for turning moments to be held briefly 
only at the beginning of the machining sequence, when only one die 8 or 9 
is engaged. This purpose is served by the clamping and holding rods 6, 7, 
which are supported by the bush 24. The bush 24 serves to accurately guide 
the work piece 5 in the area of the dies 8, 9, whereby it is especially 
advantageous that the bush 24 extends close to the cutting plane of the 
dies. The slight positioning angle of the dies 8, 9 relative to the work 
piece axis leads to no noticeable bending forces in the work piece, 
especially since machining is carried out simultaneously on two opposite 
sides of the work piece. It is necessary to absorb only the forward motion 
forces acting in the work piece center, which can easily be transmitted 
with sufficient rigidity. 
The invention is not limited by the embodiments described above which are 
presented as examples only but can be modified in various ways within the 
scope of protection defined by the appended patent claims.