A Skiving Head And Process For Peeling Of Cylinders Cylinder Tubes And The Like"

Abstract

The invention relates to a skiving head (9) for skiving out cylinders, cylinder tubes and the like, said skiving head having skiving blades arranges therein so as to be radially oscillating, at least three skiving blades (10) are provided, that all of said skiving blades (10) are directly or indirectly supported by a common conical or pyramidal body (12) which is slidably disposed within the skiving head and by means of which said blades are slidable in the radial direction relative to the skiving head, that the conical or pyramidal body (12) is float - mounted within the skiving head (9) so as to be allowed to float with two degrees of freedom (12', 12"), and that second spring means (13) for biasing every skiving blade against the conical or pyramidal body (12) is provided.

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Specification

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a skiving head and process for skiving cylinders, cylinder
tubes and the like, using a skiving head. The skiving head has a number of
skiving blades arranged radially and floating in the skiving head.
2. The Prior Art
Such processes and skiving heads are known, for example, from German Patent
Nos. DE 22 23 969 and DE 27 23 622. They serve in the machining, and in
particular the fine machining, of cylindrical hole walls such as are found in
hydraulic cylinders and cylinder tubes. Such hole walls are fine-machined most
economically by skiving and roller burnishing. Initial materials are generally
drawn precision steel tubes or soft steel tubes with prepared by boring out, with
a small machining allowance of approx. 0.3 to 1 mm in diameter. These tubes
feature straightness errors incurred by manufacturing, which are not detrimental
to the purpose of the tubes and which therefore do not need to be corrected by
the skiving process.
However, the surface of the hole wall must be peeled and roller burnished over
the full surface even with cambered cylinders. Under the given conditions, the
skiving blade must follow the macroform of the tube at almost constant chip
depth. To achieve this, skiving blades arranged in floating fashion have proved
their worth, such as described in DE 27 23 622 or DE 25 18 170 already referred
to. The skiving head in this situation is capable of free radial movement in two
planes in relation to the tool, and the skiving blade(s) is/are in addition capable
of radial movement.
The known arrangement of the skiving blades guarantees the self-centering of
the blades due to the passive cutting forces of both cutting edges even when the
skiving head is not rotating centricaily due to the effect of outside forces. A
disadvantage with this arrangement, however, is that the skiving blades,
equipped with two mutually-opposed cutting edges, do not necessarily create a
circular hole. Rather, such skiving blades can carry out a radially floating
movement during the rotation of the skiving head, and in this situation create a
hole cross-section which deviates from the circular. This movement can be
incurred due to an error in roundness already present in the tube, or a slight
disturbance in the balance of force, possibly due to fluctuating passive cutting
force with regular intentional chip breakage, and may build up and propagate
over the entire machining length.
The hole, measured between two mutually-opposed points, may indeed feature a
constant diameter, but the interior enveloping circle may be smaller and the
outer enveloping circle larger than the skiving diameter measured in the two-
point process. In this situation "polygons" may be formed, with 3, 5, 7 or more
"corners". These errors in roundness may lead to problems with the assembly of
pistons and seals. The error in roundness frequently runs over the length of the
tube with an angle offset from one tool revolution to the next, resulting in a
helical contour of the cylinder, which as a rule is regarded as a quality deficiency.
Tools without floating blades are also known. These include the reamers such as
described in German Patent Nos. DE 19 62 181 B, DE 16 52 790 A, DE 73 21 746
U, and in U.S. Pat. No. 2,638,020. The reamer blades are all only capable of
adjustment jointly, by the same dimension in relation to the basic structure of
the tool, and are therefore not installed in a radially floating manner. Reamers
are conceptually designed to produce holes with the smallest possible errors in
straightness. Continuation of machining is therefore effected in continuation of
the previous direction of the hole bore, If the previous bore was cambered, it is
expected of the reamers that they will eliminate this cambering as much as
possible.
Cylinder tubes are manufactured from drawn precision steel tubes with a length
of up to 10 meters. Due to the chipless manufacturing process employed
hitherto, these tubes feature errors in straightness of up to 2 mm/m. At the
same time, however, to save material and money, work is carried out with
machining allowances of less than 1 mm in the diameter. This means that
insufficient machining allowance is provided to make a straight hole out of the
cambered hole. To achieve this with the camber indicated heretofore, a
machining allowance of at least 4 mm in the diameter would be required. Tools
which, like the reamers described earlier, are designed for the manufacture of
the straightest possible holes, would remove a great deal of material to chips,
and in return would leave other places unmachined. Accordingly, the
requirement is imposed on a skiving head for the skiving of cylinders, cylinder
tubes, and the like, for the skiving tool to follow the macroform of the hole
during machining, and accordingly repeats the existing errors in straightness.
The reamers do not meet this requirement.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a skiving head and process
for skiving which will allow for errors in roundness to be eliminated as far as
possible, and to prevent the occurrence of helical waves.
This object is accomplished by a skiving head with skiving blades arranged
radially floating in the skiving head, in which at least three skiving blades are
provided for. With such an arrangement, both the requirement for self-centering
of the skiving blade set as well as circular skiving geometry with constant cutting
depth will be fulfilled.
In addition to this, the invention has the great advantage that due to the three
skiving blades, the skiving capacity can be increased in relation to known skiving
heads with only two skiving blades.
In a preferred embodiment of the invention, in which the skiving head features a
central axis, adjacent skiving blades seen in the direction of the central axis of
the skiving head are arranged at similar angular distances to one another. This
guarantees the greatest possible centering probability in every rotation position
of the skiving head. The angular distance would accordingly be 120 degrees with
three skiving blades, 90 degrees with four skiving blades, 72 degrees with five
skiving blades, and 60 degrees with six skiving blades. These angles may vary
slightly from sector to sector if appropriate in order to avoid shatter marks.
In another preferred embodiment of the invention, in which the skiving head has
a central axis and each skiving blade featured at least one cutting edge, there
are at least three cutting edges of different skiving blades arranged rotationally
symmetrically to the central axis of the skiving head. For each one cutting edge
of a skiving blade, corresponding cutting edges of up to at least two other
skiving blades are provided for, so that corresponding points of corresponding
cutting edges define a plane which runs perpendicular to the central axis of the
skiving head, Because the centra! axis of the skiving head is the main axis of
rotation during the operation of the head, this arrangement likewise has a
positive effect on the centering of the skiving head in the hole which is to be
peeled out.
The skiving capacity can be further increased by each skiving blade featuring at
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In a particularly advantageous embodiment of the invention, all skiving blades
are supported directly or indirectly by a common conical or pyramidal body
arranged in a displaceable manner in the skiving head, and can be displaced via
this body radially to the skiving head. In this situation, depending on the design
of the skiving head, the body may also take the form of a cone or truncated cone
as well as of a pyramid or truncated pyramid. The term pyramid is not restricted
here in the conventional sense to such regular polyhedra as have a square base
and four congruent isosceles triangles as side surfaces, but is to be understood
in the meaning of the geometric definition, and in particular may have a base
with as many sides as skiving blades are provided.
Both a conical and pyramidal body allow, by simple displacement of the body
alone the central axis of the skiving head, for the skiving blades to be pressed
radially outwards. In this way, the corresponding skiving diameter can be

In this situation, the conical or pyramidal body is preferably arranged floating in
the skiving head. There is a means for the changeable determination of a first
relative position of the conical or pyramidal body relative to the skiving blades,
so that the conical or pyramidal body can be subjected to preliminary tension by
appropriate spring media into the first relative position. This first relative position
is as a rule the operating position of the skiving head, in which the skiving blades
are therefore adjusted to the desired skiving diameter.
In order to be able to withdraw the skiving head from the peeled-out body easily
and without the occurrence of markings, the conical or pyramidal body can be
designed so that it is capable of being moved against the preliminary tension by
the use of an outer force, and a hydraulic force in particular, into a second
relative position relative to the skiving blades. This second relative position
corresponds to the withdrawn position of the skiving blades, so that this is
accordingly no longer located close to the surface to be peeled out and the
skiving head is capable of being moved and positioned in the body which is to be
peeled out.
In order to guarantee that the skiving blades are always in contact, directly or
indirectly, in the conical or pyramidal body, and therefore, by changing the
relative position of conical or pyramidal body and skiving blades, follow the
desired setting of the skiving diameter, there are spring media which subject the
skiving blades to preliminary tension against the conical or pyramidal body.
These second spring media are arranged so that their direction of effect does not
run through the center of the tool.
To prevent the tilting of the skiving blades, they are guided in guides, of which
the length to breadth ratio is greater than 1.5, and preferably greater than 2.
The ratio of length to breadth may even reach 4 or 5 in order to achieve good
guidance effect. In this context, the term length means the extension of the
guide in the radial direction, while the term breadth means the extension of the
guide in the axial direction.
The invention also comprises a process for skiving out a cylinder, cylinder tube,
or the like by means of a skiving head introduced into the body which is to be
peeled out with a central axis and a number of skiving blades. The skiving head
has at least three skiving blades radially movable relative to the central axis of
the skiving head.
In a preferred embodiment of the process, whereby each skiving blade features
at least one cutting edge, the radial distance between the cutting edges and the
central axis of the skiving head, and therefore the skiving diameter, is adjusted
via a conical or pyramidal body arranged so as to be capable of movement in the
skiving head.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Other objects and features of the present invention will become apparent from
the following detailed description considered in connection with the
accompanying drawings. It is to be understood, however, that the drawings are
designed as an illustration only and not as a definition of the limits of the
invention.
In the drawings, wherein similar reference characters denote similar elements
throughout the several views:
FIG. 1 shows a skiving head according to the invention in a partially sectional
side view along the central axis;
FIG. la is a detailed view of the skiving head shown in FIG. 1, in the area of the
blades;
FIG. 2 is a partially sectional view of the skiving head according to FIG. 1, seen
in the direction of the central axis;
FIG. 3 illustrates the effect of the centering forces during the operation of the
skiving head; and
FIG. 4 shows an alternative embodiment of a skiving head in a partial sectional
side view along the central axis.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now in detail to the drawings, FIGS. 1 to 3 show a skiving head
designated in its entirety by 9, in which a total of three skiving blades 10 are
arranged in a radially displaceable manner in a cylindrical housing 11.
Each skiving blade 10 has two cutting edges 3 and 3*. Skiving blades 10 are
guided in guides 10' with large length-to-breadth ratios, which prevent the tilting
of the skiving blades. In the embodiment shown, this guide is more than three
times longer than wide, and to be precise even more than five times. There are
guides 25 that are always arranged between the skiving blades.
As indicated in FIG. 2 with only one blade, each skiving blade 10 is pressed by
spring media, in this case in the form of pressure spring elements 13, radially
inwards against a conical body which adjusts the skiving diameter. The conical
body is in the form of a truncated cone 12. For this purpose each skiving blade
10 features a mounting i3: for one pressure spring element 13 in each case.
Each skiving blade 10 is subjected to preliminary tension by a pressure spring
element 13 in the direction onto the cone, as indicated by the arrows 13" in
FIGS. 2 and 3, of which only a few have been provided with reference indicators
for the sake of easier overview. Truncated cone 12 is thereby stored swimmingly
in the skiving head with the degrees of freedom 12* and 12"
Pressure spring elements 13, during the skiving process and in the introduced
state, in which the skiving blades are located in a withdrawn position seen in a
radial direction towards the central axis, provide for sustained contact of the
blades 10 with the truncated cone 12.
To determine a first relative position of the truncated cone 12 and skiving blades
10, a screw-spacer element combination 15 is provided for. Spring media, in this
case in the form of a coil spring 14, tension the truncated cone into this relative
position, which corresponds to the operating position in which the tool is ready
to carry out skiving.
By the application of a force in the direction of arrow 16, for example by means
of an inherently known hydraulic system, not shown here in any greater detail,
the truncated cone 12 can be displaced along the common central axis 16' of
skiving head 9 and truncated cone 12 against the preliminary tension of the
spring 14, as a result of which the skiving blades 10 move radially inwards into a
withdrawn position.
Truncated cone 12 is arranged floating in skiving head 9. As shown in FIG. 3, an
error in straightness of a cylinder tube which is to be peeled out by the
dimension 19 means a change in the hole contour 17 and the hole axis 17a by
the dimension 19 into the position 18 or 18a respectively. This leads to an
increase in the passive cutting forces of all the cutting edges operating in the
drawing above the center, and at the same time to a decrease in the lower
positions in the drawing. The truncated cone 12 reacts to this with a radial
downwards movement 20 by the dimension 19. In this way, the entire blade set
centers itself, white maintaining the envelope geometry onto the new tube
center. Accordingly, the requirements for the self centering of the skiving blade
set, circular skiving geometry, and consistent cutting depth are fulfilled. The
compensation movement is effected under the rotation of the skiving tool or
continuously with the tooi at a standstill and with the tooi rotating, and can be
carried out in any desired direction depending on the tube camber.
FIG. 4 shows an embodiment in which the force 16" engages on the broad side
of the truncated cone 12" and the coil spring 14* engages via the screw-spacer
combination 15' on the smaller diameter of the truncated cone 12'". This
arrangement also incurs a displacement of the cutting edges 3" and the skiving
blade 10" relative to the housing 11*.
Numerous divergences and further embodiments are possible within the
framework of the concept of me invention, which relate, for example, to the
numoer ana arrangement of ihe skiving blades and cutting edges. It is possible,
for example, for skiving out large diameters, to use skiving heads which feature
more than the three skiving blades described above. Central to the invention in
any event is the fact that there are more man two skiving blades, which clearly
reduces the probability of occurrence of unintentional radial oscillation.
Accordingly, while only a few embodiments of the present invention have been
shown and described, it is obvious that many changes and modifications may be
made thereunto without departing from the spirit and scope of the invention.
We Claim
1. A skiving head (9) for skiving out cylinders, cylinder tubes and the like,
said skiving head having skiving blades arranges therein so as to be
radially oscillating, characterized in that at least three skiving blades (10)
are provided, that all of said skiving blades (10) are directly or indirectly
supported by a common conical or pyramidal body (12) which is slidably
disposed within the skiving head and by means of which said blades are
slidable in the radial direction relative to the skiving head, that the conical
or pyramidal body (12) is float - mounted within the skiving head (9) so
as to be allowed to float with two degrees of freedom (12', 12*), and that
second spring means (13) for biasing every skiving blade against the
conical or pyramidal body (12) is provided.
2. The skiving head as claimed in claim 1, wherein when said skiving head
having a central axis (161) neighbouring skiving blades (10) are spaced a
similar angular distance apart from one another as viewed in the direction
of the central axis (160 of ^e skiving head (9).
3. The skiving head as claimed in claim 1 or 2, wherein when said skiving
head (9) having a central axis (161) and each skiving blade (10) having at
least one cutting edge (3, 3*) at least three cutting edges of different
skiving blades are arranged so as to be rotationally symmetrical about the
central axis of the skiving head.
4. The skiving head (9) as claimed in claim 1, wherein means (15, 15*) for
variably establishing a first relative position of the conical or pyramidal
body (12) to the skiving blades (10) is provided.
5. The skiving head as claimed in claim 4, wherein first spring means (14)
for biasing the conical or pyramidal body (12) to the first relative position
is provided.
6. The skiving head as claimed in claim 5, wherein the conical or pyramidal
body is movable by an external, more specifically hydraulic, force (16)
against the bias to a second relative position.
7. The skiving head as claim in claim 6, wherein the second spring means
(13) is arranged so as to act in a direction that will not pass through the
center of the tool.
8. The skiving head as claimed in one of the afore mentioned claims,
wherein the skiving blades (10) are guided in guide members (10') the
length / width ratio of which is greater than 1.5, preferably greater than
2.
9. A method of skiving out a cylinder, a cylinder tube or the like by means of
a skiving head that is provided with a central axis and a number of skiving
blades and is introduced into the body to be skived out, characterized in
that a skiving head as claimed in claim 1 being adapted, said skiving head
having at least three skiving blades that are movable in the radial
direction relative to the central axis of the skiving head.
10.The method as claimed in claim 9, wherein when each skiving blade
having at least one cutting edge, characterized in that the radial distance
of the blades from the central axis of the skiving head is adjusted by
means of a conical or pyramidal body which is movably arranged within
the skiving head.
11.The method as claimed in claim 10, wherein the skiving blades are biased
against the conical or pyramidal body.
12.The method as claimed in claim 10 or 11, wherein the conical or
pyramidal body is biased to a first relative position (work position) to the
skiving blades.
13.The method as claimed in claim 12, wherein, to move the skiving head
within the skived out body without machining said body, the conical or
pyramidal body is urged by an external, more specifically hydraulic, force
against the bias to a second relative position in which the cutting edges
are spaced a smaller radial distance from the central axis of the skiving
head than in the work position.

The invention relates to a skiving head (9) for skiving out cylinders, cylinder
tubes and the like, said skiving head having skiving blades arranges therein so as
to be radially oscillating, at least three skiving blades (10) are provided, that all
of said skiving blades (10) are directly or indirectly supported by a common
conical or pyramidal body (12) which is slidably disposed within the skiving head
and by means of which said blades are slidable in the radial direction relative to
the skiving head, that the conical or pyramidal body (12) is float - mounted
within the skiving head (9) so as to be allowed to float with two degrees of
freedom (12', 12"), and that second spring means (13) for biasing every skiving
blade against the conical or pyramidal body (12) is provided.

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