U.S. patent application number 12/297093 was filed with the patent office on 2009-09-24 for method and smoothing tool for finishing surfaces.
This patent application is currently assigned to Mauser-Werke Oberndorf Maschinenbau GmbH. Invention is credited to Frieder Asser, Siegfried Gruhler, Franz Weidinger.
Application Number | 20090235503 12/297093 |
Document ID | / |
Family ID | 38461857 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090235503 |
Kind Code |
A1 |
Gruhler; Siegfried ; et
al. |
September 24, 2009 |
METHOD AND SMOOTHING TOOL FOR FINISHING SURFACES
Abstract
The invention relates to a method and a smoothing tool for
finishing surfaces as well as a workpiece that is machined by
smoothing. In accordance with the invention, the surface that is to
be machined is smoothed by a shaping process with the aid of a
convex smoothing tool.
Inventors: |
Gruhler; Siegfried;
(Voehringen Wittershausen, DE) ; Asser; Frieder;
(Villingen-Schwenningen, DE) ; Weidinger; Franz;
(Wien, AT) |
Correspondence
Address: |
BOYLE FREDRICKSON S.C.
840 North Plankinton Avenue
MILWAUKEE
WI
53203
US
|
Assignee: |
Mauser-Werke Oberndorf Maschinenbau
GmbH
Oberndorf a. N.
DE
|
Family ID: |
38461857 |
Appl. No.: |
12/297093 |
Filed: |
April 16, 2007 |
PCT Filed: |
April 16, 2007 |
PCT NO: |
PCT/DE2007/000666 |
371 Date: |
February 2, 2009 |
Current U.S.
Class: |
29/90.01 |
Current CPC
Class: |
Y10T 29/47 20150115;
B24B 39/02 20130101; B24B 41/002 20130101 |
Class at
Publication: |
29/90.01 |
International
Class: |
B24B 39/02 20060101
B24B039/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2006 |
DE |
10 2006 017 468.2 |
Aug 14, 2006 |
DE |
10 2006 038 117.3 |
Mar 16, 2007 |
DE |
10 2007 012 764.4 |
Claims
1. A method for finishing surfaces, especially bearing recesses,
comprising the steps of: pre-machining a surface, including
fine-boring the surface; and smoothing the machined surface by
partial re-shaping by means of a convex smoothing tool which is
pressed against the surface and moved along the same.
2. A method according to claim 1, wherein the smoothing tool is
guided approximately along the track of the tool for
pre-machining.
3. A method according to claim 1, wherein the smoothing tool is
pressed against the surface with a predetermined surface pressure
or a predetermined biasing force.
4. A method according to claim 1, wherein the roughness depth after
smoothing is less than 1/1000 mm.
5. A method according to claim 1, wherein groove-shaped or
slot-shaped recesses are formed in the surface.
6. A method according to claim 5, wherein a circumferential groove
having a depth within the micrometer range is formed in the
surface.
7. A method according to claim 1, wherein the smoothing tool is
operatively connected such that the surface pressure or the biasing
force is constantly within a predetermined tolerance range.
8. A method according to claim 1 comprising the steps of:
presetting a pre-machining tool used in the pre-machining step to a
theoretical setting; wherein the pre-machining step is performed
until approximately a middle of a tolerance range is reached;
picking up a dimension associated with the pre-machining step and
identifying the dimension as a zero dimension in the machine;
transferring the zero dimension to a measuring station and fixing
it; in the case of tool change, picking up the zero dimension from
the measuring station and transferring it to the tool in the
machine.
9. A method according to claim 1, wherein after the smoothing step
the smoothing tool is checked in a measuring station to determine
whether the smoothing tool is in position.
10. A method according to claim 1, wherein a deformation of the
smoothing tool during smoothing is compensated.
11. A smoothing tool comprising a convex smoothing member which
projects from a rigid tool shaft.
12. A smoothing tool according to claim 11, wherein the smoothing
member consists of diamond.
13. A smoothing tool according to claim 11, wherein the tool shaft
is clamped in a radially feedable infeed head.
14. A smoothing tool according to claim 13, wherein the infeed head
is a diaphragm tilting head.
15. A smoothing tool according to claim 11, comprising at least one
pre-machining cutting edge.
16. A smoothing tool according to claim 15, wherein the
pre-machining cutting edge is arranged approximately diametrically
with respect to the smoothing member.
17. A smoothing tool according to claim 11, wherein the radius of a
smoothing surface of the smoothing member is between 2 and 6
mm.
18. A smoothing tool according to claim 11, wherein the smoothing
member is fixed to the tool shaft.
19. A workpiece comprising at least one bearing recess the
circumferential wall of which is finished by smoothing.
20. A workpiece according to claim 19, wherein a circumferential
groove is formed in a center portion of the circumferential
wall.
21. A workpiece according to claim 20, wherein the groove has a
depth of less than 20 .mu.m.
22. A workpiece according to claim 21, wherein the depth is between
about 1 .mu.m and 5 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a method for finishing surfaces, a
smoothing tool suited for the method and a workpiece.
[0003] 2. Description of the Related Arts
[0004] Methods and smoothing tools of this type are used, for
instance, in finishing surfaces of a connecting rod. In internal
combustion engines a piston is supported via a piston pin at a
small connecting rod eye of the connecting rod, whose large
connecting rod eye is connected to a crankshaft. So far a bearing
bush has been inserted in the small connecting rod eye. In the
course of efforts made for light-weight manufacture and for cost
minimization, this bearing bush is to be dispensed with so that the
small connecting rod eye directly encompasses the piston pin. It is
necessary in this context to manufacture the bearing surface of the
small connecting rod eye with high precision. So far the small
connecting rod eye has been formed to be round, elliptical and/or
trumpet-like in the longitudinal axis of the piston pin by
precision lathing. It has turned out that the surface quality to be
achieved by precision lathing is not good enough to ensure the
durability of the bearing connection.
[0005] Another problem consists in the fact that increased wear has
been observed especially with bush-less forged connecting rods.
Applicant stated that this increased wear has to be traced back to
segregations in the cast blank. Such segregations (black cores) are
decompositions of the melt during the casting operation. These
areas have a higher hardness than the regular structure of the
workpiece. If from such a casting blank a connecting rod is
manufactured by forging, the segregations will occur especially in
the central circumferential areas of the large and the small
connecting rod eyes so that the bearing combination is subjected to
wear in this area.
[0006] Compared to that, the object underlying the invention is to
provide a method and a tool by which the surface quality of such
surfaces is improved with simple efforts in terms of devices.
Moreover, a workpiece having an improved surface quality and wear
resistance is to be provided.
SUMMARY OF THE INVENTION
[0007] The method by the combination of features of a method for
finishing surfaces, a smoothing tool as well as a workpiece.
[0008] According to the invention, the finishing of the surface is
performed by partial reshaping, wherein a smoothing tool is used
which is pressed with a convex surface against the surface to be
machined and is moved along the same. Thus the invention does not
make use of conventional finishing methods in which the surface is
smoothed by chip removal. The peculiarity of the method according
to the invention consists in the fact that a convex smoothing
member is merely pressed against the surface and itself performs no
rotation or the like--as for instance during a spinning
operation.
[0009] The method according to the invention and the smoothing tool
according to the invention can be used with particularly great
success in finishing a connecting rod eye.
[0010] The shaft of the smoothing tool is preferably clamped in a
radially feedable infeed head. For instance, the infeed head is a
diaphragm tilting head. By such infeed head bearing recesses which
are oval in cross-section or trumpet-like in axial direction,
surfaces provided with recesses or structured in any other way can
be provided or machined.
[0011] In a preferred embodiment the convex smoothing member is
supported at a substantially rigid tool shaft and thus is not
pre-stressed in engaging direction by spring bias or the like.
However, in particular cases of application it may be necessary to
elastically pre-stress the convex smoothing member in the engaging
position. In this case the area receiving the smoothing member can
be elastic. In accordance with an especially preferred embodiment
of the invention, the tool shaft is in the form of a parallel link
which is cut clear from the tool shaft by eroding, for instance. In
an alternative variant of the invention, the tool shaft is in the
form of a spring link by means of at least one spring, especially a
leaf spring. By process control with a micro measuring stylus which
detects the deflection of the parallel link it is confirmed that
the diameter generation has taken place rotation-symmetrically for
instance with a share of smoothing of 5 .mu.m.
[0012] As smoothing member preferably a natural diamond or a
correspondingly hard material is formed. For instance, use is made
of a diamond ball or a diamond ball segment. The radius of a
smoothing surface of the smoothing member in a preferred embodiment
of the invention is within the range of from approx. 2 to 6 mm.
[0013] In an especially preferred variant of the method the
smoothing tool is guided approximately along the same track of
motion as that of the previously used machining tool.
[0014] The smoothing tool is preferably pressed against the surface
at a predetermined surface pressure or a defined bias. This is
achieved by the fact that the surface pressure of the smoothing
tool or the biasing force of the smoothing tool to the surface is
kept within a predetermined tolerance range. By such a method
substantially lower roughness depths than by conventional methods
can be achieved. The roughness depth obtained in preliminary tests
was less than 1/1000 mm. It is confirmed by an appropriate process
control of the pressing force that the diameter generation has
taken place rotation-symmetrically for instance at a share of
smoothing of 5 .mu.m. The desired constant pressing force can be
obtained, for instance, due to the centrifugal force acting upon
the smoothing member and is adjustable by the speed of the
smoothing tool.
[0015] In the case of particular applications it is advantageous
when recesses are formed in the surface to be treated; they can be
in the form of a circumferential groove, circumferentially
spiral-shaped or a cross-shaped or else can be slots formed in
sections. By appropriately controlling the smoothing tool it is
advantageous in some cases when the smoothing tool is disengaged in
the area of said recesses in order to avoid stress concentrations
and thus damage of the workpiece and/or the smoothing tool.
Moreover, it is possible to introduce recesses, for instance
lubricating troughs, into the surface of the component by the
smoothing tool. Such tool can be a multi-purpose tool having a
small ball for introducing the trough and a large ball for
smoothing the diameter.
[0016] The dimensional stability of the surface to be machined can
be further improved, when the pre-machining tool is first adjusted
to the theoretical adjusting dimension and subsequently the
pre-machining, for instance fine boring, is performed by means of
controlling or adjusting the tool cutting edge, until the center of
any other value within the tolerance range is reached.
[0017] In a subsequent step this value is picked up as zero
dimension in the machine and is transferred to a measuring
station--a so-called master--and is fixed.
[0018] In the case of tool change zero measure can be picked up
from the master and transferred to the tool in the machine. This
transfer can be performed by the machine control or directly by
adjustment in the tool cutting edge (infeed tool).
[0019] In a preferred variant of the invention it is checked after
smoothing whether the smoothing tool is in position. In this way it
can be determined, for instance, whether the smoothing member is
damaged or is still existing at all.
[0020] The bias mentioned in the beginning is adjusted so that also
the deformation (flattening) of the smoothing tool during smoothing
can be compensated.
[0021] It has turned out to be especially advantageous in terms of
manufacture when the smoothing tool is a multi-purpose tool having
at least one pre-machining cutting edge.
[0022] The pre-machining cutting edge is preferably arranged
approximately diametrically with respect to the smoothing member so
that optionally the smoothing tool or the pre-machining cutting
edge can be engaged by a swivel movement.
[0023] The present application suggests for improving the wear
behavior to form a circumferential groove especially in forged
parts in the central portion of the circumferential walls of
bearing bores/recesses--for instance the large and small connecting
rod eyes. Said circumferential groove is designed such that the
segregations are partly abraded and thus are no longer located in
the main supporting area of the bearing bore so that surprisingly
the wear resistance can be substantially improved vis-a-vis
conventional solutions.
[0024] Under certain circumstances it can also be sufficient,
however, to machine the circumferential wall of the bearing recess
and the circumferential groove only by precision-turning, wherein
it is essential that the segregations are no longer located in the
main supporting area of the bearing. The applicant reserves the
right to direct a separate independent claim to the formation of a
groove--independently of the machining method.
[0025] Other advantageous further developments of the invention are
the subject matter of further subclaims.
[0026] These, and other aspects and objects of the present
invention will be better appreciated and understood when considered
in conjunction with the following description and the accompanying
drawings. It should be understood, however, that the following
description, while indicating preferred embodiments of the present
invention, is given by way of illustration and not of limitation.
Many changes and modifications may be made within the scope of the
present invention without departing from the spirit thereof, and
the invention includes all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Preferred embodiments of the invention shall be explained in
detail hereinafter by way of schematic representations, in
which:
[0028] FIG. 1 shows a connecting rod to be machined;
[0029] FIG. 2 shows a schematic representation of a smoothing tool
according to a first embodiment according to the invention;
[0030] FIG. 3 shows a front view of the smoothing tool from FIG. 2
inserted in a hollow shaft cone;
[0031] FIG. 4 is a spatial representation of the smoothing tool
from FIG. 3 inserted in a spindle of a machine tool;
[0032] FIG. 5 is a side view of the diaphragm tilting head
comprising the smoothing tool from FIG. 4;
[0033] FIG. 6 is a side view of the diaphragm tilting head
comprising the smoothing tool from FIG. 5 in the deflected
state;
[0034] FIG. 7 shows a top view of the diaphragm tilting head
comprising the smoothing tool from FIG. 6;
[0035] FIG. 8 is a side view of an elastic tool shaft;
[0036] FIG. 9 is an enlarged representation of the smoothing tool
from FIG. 8;
[0037] FIG. 10 is a side view of a smoothing tool in the form of a
multi-purpose tool;
[0038] FIG. 11 is a side view of the multi-purpose tool from FIG.
10;
[0039] FIG. 12 is a side view of the multi-purpose tool with the
smoothing tool being engaged;
[0040] FIG. 13 is a side view of the multi-purpose tool with the
pre-machining cutting edge being engaged;
[0041] FIG. 14 is a penetration curve of the smoothing member in
response to the biasing force;
[0042] FIG. 15 shows a surface smoothed in accordance with the
method according to the invention; and
[0043] FIG. 16 shows the roughness depths of a fine-bored and a
smoothed bearing recess of a connecting rod.
DETAILED DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 shows a connecting rod 1 subject to machining the
small bearing eye 2 of which is to be high-quality surface-finished
so that a piston pin of a piston (not shown) can be inserted
without utilizing a bearing bush. For finishing a smoothing tool 4
schematically shown in FIG. 2 is used in which a convex smoothing
member 8 is utilized at a tool shaft 6. The Figure shows an
embodiment in which the smoothing tool 4 is rigid without
elasticity. The smoothing tool 8 preferably consists of a natural
diamond or a comparable material and is mounted in the tool shaft 6
by means of a clamping screw 12 inserted in a receiving bore 10 of
the tool shaft 6 such that a convex or spherical smoothing surface
14 projects in radial direction from the tool shaft 6. In the shown
embodiment this smoothing surface 14 is designed to have a radius
of approx. 2.75 mm, of course also other radii, for instance a
radius of 5 mm can be used.
[0045] FIG. 3 shows the smoothing tool 4 from FIG. 2 including the
rigid tool shaft 6 inserted in a conventional hollow shaft cone
(HSK) 16 which in turn--as shown in FIG. 4--can be inserted in a
radially feedable tool so that the smoothing member 8 can be
pre-stressed and fed against the surface to be machined.
[0046] This tool arrangement can then be inserted, according to
FIG. 4, in a spindle 18 of a machine tool 20 so that the smoothing
member 8 is movable along a predetermined track of motion in the
connecting rod eye 2 (cf. FIG. 1). It is preferred in this context
when the track of motion approximately corresponds to the one
adjusted during fine-boring. In the shown embodiment the smoothing
tool 4 is inserted in a diaphragm tilting head 22.
[0047] In accordance with FIG. 5, such diaphragm tilting head 22
has a fork 24 adjustable in axial direction including a fork groove
26 extending obliquely with respect to the longitudinal axis into
which a pinion 28 of a tool head 30 immerses. Said tool head 30 is
operatively connected to a diaphragm 32 such that, when the fork
groove 26 is displaced, the tool head 30 is tilted and thus the
smoothing tool 4 is deflected--as represented in FIG. 6--in radial
direction and performs a radial infeed or reset motion. For this
purpose the tool head 30 is arranged, according to FIG. 7,
centrally between two webs 34, 36 forming a swivel axis. By
appropriately controlling the diaphragm tilting head 22 the
smoothing surface 14 of the smoothing member 8 can be brought into
a predetermined position relative to the surface to be machined. It
is preferred in the method according to the invention when the
smoothing surface 14 is pre-stressed by 10 .mu.m vis-a-vis the
surface to be machined. That is to say, the smoothing surface 14 is
pre-stressed in radial direction by 10 .mu.m into the workpiece
vis-a-vis the surface to be machined and thus defines the smoothing
plane.
[0048] In the case of special requirements it might be necessary to
design the tool shaft 6 to exhibit certain elasticity. In this case
the portion receiving the smoothing member 8 can be elastic. In the
embodiment shown in FIG. 8 this is done by a parallel link 38 which
is cut clear out of the tool shaft 6 by eroding, for instance. This
shall be illustrated hereinafter by way of FIG. 9 showing an
enlarged representation of the smoothing tool 4 from FIG. 8.
[0049] As one can take especially from FIG. 9, the parallel link 38
includes two legs 40, 42 which are connected via a web 44 receiving
the smoothing member 8. The smoothing member 8 is supported at the
web 44 by a trim plate 46 and is held at the same by means of the
clamping screw 12. The legs 40, 42 and the web 44 are spaced apart
from the center portion 48 of the tool shaft 6 by approx. 0.5 mm,
wherein an adjusting screw 50 which is supported at the center
portion 48 is screwed into the leg 40. By means of the adjusting
screw 50 the pre-deflection of the smoothing tool 4 and the
stiffness of the parallel link 38 can be adjusted. In the shown
embodiment a seat 52 in which an elastomer member 54 is received
passes through the center portion 48. Said elastomer member 54 is
supported at the left-hand leg 43 of the parallel link 38 by a
first end portion via a mounting element 56 and at the second leg
42 of the parallel link 38 by its second end portion. The elastomer
body 54 serves as a damping element and for trimming the stiffness
of the smoothing tool 4. In an embodiment not shown an oil damper
is used instead of the elastomer member 54.
[0050] The pre-machining and the smoothing are carried out for
instance at two stations. When machining a connecting rod 1 (cf.
FIG. 1) the pre-machining is preferably performed by fine-boring by
a fine-hole drill head preferably adjustable in radial direction.
Said fine-hole drill head is initially preset according to the
theoretical setting at an appropriate measuring device, for
instance a tool presetting device. After that, the fine-boring is
carried out, wherein the machining is performed by means of machine
control or adjustment of the tool cutting edge, until the middle of
the tolerance range or another predetermined value within the
tolerance range is obtained. This actual dimension is then picked
up in the machine as zero dimension and said zero dimension is
transferred to a measuring device, a so-called master, and is
fixed. In the case of a tool change said zero dimension can be
directly picked up by the master and transferred in the machine by
means of machine tool control or adjustment of the cutting edge
(radial tool) to the fine-boring tool. This course of action
ensures that fine-boring is performed with maximum precision and
reproducibility so that a component geometry which meets even
maximum requirements and has a predetermined minimum roughness
depth (less than 1 .mu.m) is brought about by the subsequent
smoothing. As described in the beginning, the smoothing member 8,
preferably the diamond ball is inserted in a radially adjustable
infeed tool head. The control is designed so that the pressing
force or the surface pressure of the smoothing member 8 applied to
the surface to be machined can be controlled during machining so
that it remains within a predetermined tolerance range and thus
constantly a particular bias (approx. 10 .mu.m) is effective. This
bias is adapted to compensate also for small undesired ovals from
fine-boring.
[0051] The radially adjustable infeed head permits to machine also
surfaces having recesses--for instance for forming lubricating
slots etc. It is preferred to disengage the smoothing member in the
area of said lubricating slots by adjusting the infeed head so that
after passing said recess the smoothing member is not exposed to
impact stress, because it is engaged again only after having passed
said recess.
[0052] After performing the smoothing operation it is checked by a
measuring device whether the smoothing member 8 is still in
position and whether there is possibly wear which can then be
appropriately compensated. A respective measurement of wear is also
carried out during pre-machining (fine-boring), wherein the tool is
measured after each machining of a workpiece and possibly existing
wear is stored and compensated by a station-oriented wear
compensation (offset correction). This correction can be made using
a sliding mean value, wherein for instance during a tool change a
measuring unit rejection free of primary processing times is
performed with up-to-date reading and possible offset
correction.
[0053] FIG. 10 illustrates an embodiment of a smoothing tool 4 in
the form of a multi-purpose tool 58 having a pre-machining cutting
edge 60 which is practically responsible for fine-boring, wherein
in a subsequent step the smoothing member 8 can be engaged with its
ball segment by swiveling the tool 4.
[0054] According to FIG. 11 showing a side view of the
multi-purpose tool 58 from FIG. 10, it has turned out to be
especially advantageous when the pre-machining cutting edge 60 is
disposed approximately diametrically with respect to the smoothing
member 8 so that optionally the smoothing member 8 or the
pre-machining cutting edge 60 can be engaged by a swivel motion.
This shall be illustrated in detail hereinafter by way of FIGS. 12
and 13 showing the multi-purpose tool 58 engaged with the
pre-machining cutting edge 60 and engaged with the smoothing member
8, respectively.
[0055] In FIG. 12 a radially feedable infeed head is shown into
which the multi-purpose tool 58 can be inserted. The infeed head is
in the form of a diaphragm tilting head 22 having a fork 24
adjustable in axial direction including a fork groove 26 extending
obliquely with respect to the longitudinal axis into which a pinion
28 of the tool head 30 immerses. Said tool head 30 is operatively
connected to a diaphragm 32 such that when the fork groove 26 is
displaced the tool head 30 is tilted and thus the smoothing tool
4--as shown in FIG. 12--or the pre-machining cutting edge 60--as
shown in FIG. 13--is engaged. That is to say, by appropriate
control of the diaphragm tilting head 22 the smoothing surface or
the pre-machining cutting edge 60 can be brought into a
predetermined position relative to the one of the surface to be
machined.
[0056] FIG. 14 illustrates a penetrating curve 62 of the smoothing
member 8 in response to the biasing force F. The force-penetration
depth characteristic extends relatively flatly having a gradient of
approx. 0.5 N/.mu.m. The smoothing tool 4 is preferably operated in
the deflection range of between 25 and 50 .mu.m and is adjustable
by a fixed stop. According to FIG. 14, the smoothing member 8
starts penetrating the surface of the component from a biasing
force of approx. 40 N. At a biasing force of approx. 75 N for
instance a penetration depth of 50 .mu.m is reached.
[0057] According to FIG. 15, an excellent surface quality allowing
for a roughness RZ of 0.8 can be obtained by the smoothing method
according to the invention--such roughness depths practically
cannot be attained by fine-boring.
[0058] FIG. 16 shows a concrete measurement of the roughness depth
by way of a curve 64, wherein the roughness after fine-boring is
shown on the right and amounts to approx. 2.5 to 4 .mu.m. By the
smoothing method according to the invention, a roughness depth
shown on the left of less than 1 .mu.m, for instance of 0.7 .mu.m,
can be obtained. The connecting rod eyes 2 manufactured in this way
(cf. FIG. 1) have an excellent quality and have proven themselves
in tool-life tests so that the use of conventional bearing bushes
is no longer required. It has turned out that the roundness
vis-a-vis fine-bored contours can be further improved by the
smoothing method according to the invention. Almost any contours,
for instance round recesses, elliptic recesses (ellipsis approx. 10
.mu.m) or contours which are trumpet-shaped in longitudinal
direction can be formed by the tool according to the invention.
[0059] Of course, the method and the smoothing tool 4 are not
restricted to the use in connecting rod eyes 2 but can also be used
for other surfaces having a high surface quality. The method
according to the invention and the smoothing tool 4 can also be
employed in machining cylinder bores, wherein the prescribed
lubrication slots (spiral-shaped, diamond pattern . . . ) can be
formed in the circumferential walls. The method according to the
invention and the smoothing tool 4 can be used as an alternative of
honing which requires considerable efforts in terms of machine
tools and control.
[0060] As explained in the beginning, the invention is especially
suited also for use with workpieces in which segregations occur in
the area of the circumferential walls of the bearing recesses. As
said segregations are formed substantially in the central
circumferential area in workpieces forged of round bars, in
accordance with the invention a circumferential groove is
introduced into said center portion of the circumferential walls.
Said groove can have a width of one or more millimeters, for
instance about 3 mm, in the case of a connecting rod, the depth
merely amounting to a fraction of the width. So the wear behavior
of the workpiece can be improved already with grooves having a
depth of between 1 .mu.m and 5 .mu.m. I.e. the width of the groove
and the depth of the groove are designed, according to the
invention, at a ratio of more than 100:1, preferably more than
1000:1. The groove can be formed by precision-turning or else
according to the method as set forth by the invention by smoothing.
In the latter case, the groove can be initially pre-machined by
precision-turning and then be finished by smoothing. On principle,
it is also possible to form the groove by smoothing only.
[0061] Of course, the method according to the invention can also be
used for oval bearing recesses (connecting rod eyes) or for a
cross-section deviating from the circular shape, because
practically any shape of recess can be tracked by the infeed head.
The principal advantage of a circumferential groove machined by
smoothing resides in the fact that a clean oil passage is formed in
which a continuous oil film is formed without cut-off so that the
wear behavior of the workpiece or the bush-less connecting rod is
further improved. Due to the small depth of the groove, it is also
referred to as micro-groove.
[0062] The invention relates to a method and a smoothing tool for
finishing surfaces as well as a workpiece that is machined by
smoothing. In accordance with the invention the surface that is to
be machined is smoothed by a shaping process with the aid of a
convex smoothing tool.
[0063] Although the best mode contemplated by the inventors of
carrying out the present invention is disclosed above, practice of
the above invention is not limited thereto. It will be manifest
that various additions, modifications and rearrangements of the
features of the present invention may be made without deviating
from the spirit and the scope of the underlying inventive
concept.
* * * * *