U.S. patent application number 12/291735 was filed with the patent office on 2009-06-04 for method for hardening groove walls of the ring groove of a steel piston.
Invention is credited to Achim Fedyna, Christian Peschke.
Application Number | 20090139610 12/291735 |
Document ID | / |
Family ID | 40377371 |
Filed Date | 2009-06-04 |
United States Patent
Application |
20090139610 |
Kind Code |
A1 |
Fedyna; Achim ; et
al. |
June 4, 2009 |
Method for hardening groove walls of the ring groove of a steel
piston
Abstract
A method for hardening groove walls of the ring groove of a
steel piston by a laser beam consists of conducting process gas
that contains oxygen onto a groove wall of the steel piston, and
putting the steel piston into rotation. The groove wall is
irradiated with the laser beam until an oxide layer has formed on
the groove wall. Subsequently, the feed of the process gas is
turned off, and the groove wall is heated and hardened, in tracks.
The degree of heat conductivity of the groove wall is improved by
the oxide layer on the groove wall, thereby bringing about faster
heating and hardening of the groove wall. The reflectivity of the
groove wall is also reduced in this way, so that only little light
is reflected by the groove wall onto other regions of the groove,
so that these regions are not unintentionally heated and
hardened.
Inventors: |
Fedyna; Achim; (Bopfingen,
DE) ; Peschke; Christian; (Stuttgart, DE) |
Correspondence
Address: |
COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Family ID: |
40377371 |
Appl. No.: |
12/291735 |
Filed: |
November 13, 2008 |
Current U.S.
Class: |
148/280 |
Current CPC
Class: |
C21D 9/0068 20130101;
B23P 15/10 20130101; C21D 1/09 20130101; C21D 2221/00 20130101 |
Class at
Publication: |
148/280 |
International
Class: |
C23C 8/04 20060101
C23C008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 16, 2007 |
DE |
10 2007 054 736.8 |
Claims
1. A method for hardening groove walls of the ring groove of a
steel piston that is mounted so as to rotate about its piston axis,
by means of a laser beam directed at a groove wall, the method
comprising the following steps: conducting process gas that
contains oxygen onto the groove wall of the steel piston; putting
the steel piston into rotation; irradiating the groove wall
surrounded by the process gas with the laser beam, until an oxide
layer has formed on the groove wall; turning off a feed of the
process gas; and heating and hardening the groove wall by means of
the laser beam, in tracks.
2. The method according to claim 1, wherein the process gas
consists of a mixture of argon and oxygen.
3. The method according to claim 1, wherein the process gas
consists of a mixture of nitrogen and oxygen.
4. The method according to claim 1, wherein the process gas
consists of a mixture of nitrogen, argon, and oxygen.
5. The method according to claim 1, wherein at least approximately
1% oxygen is mixed into the process gas.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Applicants claim priority under 35 U.S.C. 119 of German
Application No. 10 2007 054 736.8 filed Nov. 16, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for hardening groove walls
of the ring groove of a steel piston.
[0004] 2. The Prior Art
[0005] German Patent No. DE 103 37 962 A1 describes a method for
laser hardening of groove walls of the ring grooves of a steel
piston, in which a laser beam having a wavelength of less than 5
.mu.m is used in order to achieve a degree of absorption of the
laser beam energy that is suitable for hardening. The laser beam
furthermore has to be directed at the groove to be hardened at a
sufficiently great incidence angle. It is disadvantageous, in this
connection, that there is only a small selection of laser sources
that generate laser radiation at a wavelength of less than 5 .mu.m.
Furthermore, the selection of a sufficiently great incidence angle
is limited by the geometry of the ring groove, i.e. by the groove
wall that lies opposite the groove wall to be hardened, depending
on the position of the laser source relative to the steel
piston.
SUMMARY OF THE INVENTION
[0006] It is therefore on object of the invention to avoid these
disadvantages of the state of the art. This object is achieved by a
method for hardening groove walls of the ring groove of a steel
piston that put into rotation about its piston axis, by means of a
laser beam is directed at a groove wall. The method includes the
following steps: [0007] conducting process gas that contains oxygen
onto the groove wall of the steel piston, [0008] putting the steel
piston into rotation, [0009] irradiating the groove wall surrounded
by the process gas with the laser beam, until an oxide layer has
formed on the groove wall, [0010] turning off the feed of the
process gas, and [0011] heating and hardening of the groove wall by
the laser beam, in tracks.
[0012] In one embodiment, a mixture of argon and oxygen is used as
the process gas. Alternatively, a mixture of nitrogen and oxygen
can be used as the process gas. Or, a mixture of nitrogen, argon,
and oxygen can be used as the process gas. Preferably, at least
approximately 1% oxygen is mixed into the process gas.
[0013] Because the groove wall surface of the steel piston that is
to be hardened is colored with iron oxide, its heat conductivity is
increased to such an extent, and furthermore its reflectivity is
reduced so greatly that the laser light can be radiated onto the
groove wall surface to be hardened at any desired angle of
incidence, independent of its wavelength.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] 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.
[0015] In the drawings, wherein similar reference characters denote
similar elements throughout the several views:
[0016] FIG. 1 shows a device for laser hardening of the wall of a
groove for a piston ring; and
[0017] FIG. 2 shows an enlarged representation of the piston ring
groove, the lower wall of which is being hardened by a laser.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] Referring now in detail to the drawings, FIG. 1 shows a
laser source 2 attached to a holder device 1, which source, as
shown in an enlargement in FIG. 2, directs a laser beam 3 at the
lower wall 10 of the upper ring groove 11 of a piston 5 made of
steel, for an internal combustion engine. Ring groove 11 is
provided for a compression ring not shown in the figures. Steel
piston 5 is mounted on a turntable 6, by way of a clamping holder
12, to rotate about its piston axis 13. Turntable 6 is attached to
a foundation 7 having an electrical drive device not shown in the
figure, by which the turntable is put into rotation, under
electrical control.
[0019] Furthermore, a gas line 8 is attached to holder device 1 and
to a stand 9, by which line process gas is passed in the direction
of upper ring groove 11, by way of a gas jet 4, which particularly
surrounds the region of lower wall 10, which is to be
laser-hardened, with the process gas.
[0020] A diode laser or an Nd:YAG laser can be used as the laser
source 2, for example. Using this, in the present exemplary
embodiment of the invention, lower wall 10 of ring groove 11 for
the compression is hardened, because this wall is exposed to
increased stress during engine operation, by the compression ring.
However, any surface of piston 5 that is subject to great
mechanical stress can be hardened using the method according to the
invention.
[0021] In this connection, the small focus of laser beam 3 heats
lower surface 10 of ring groove 11 of piston 5 that is put into
rotation by means of turntable 6, in tracks. A cooling medium for
bringing about the cooling of the heated track that is required for
the hardening process is not necessary, since very rapid
temperature equalization between the heated track and the adjacent
piston material, steel, occurs, bringing with it automatic
quenching, which brings about good hardening of lower groove wall
10.
[0022] During this hardening process, the process gas is passed
onto lower groove wall 10 by way of gas jet 4; it can consist of a
mixture of argon and oxygen, of nitrogen and oxygen, or of argon,
nitrogen, and oxygen. Within the scope of comprehensive
experiments, good results were achieved with a process gas mixture
consisting of 1% oxygen and 99% nitrogen.
[0023] The groove wall surface hit by laser beam 3 colors as the
result of oxide formation, whereby iron oxide (Fe.sub.2O.sub.3) is
formed on the surface. As a result, an improvement of the heat
conductivity of the surface irradiated by the laser occurs, for one
thing, thereby accelerating the heating of this surface and thus
improving the degree of effectiveness of the laser. For another
thing, the coloring of the groove wall surface by iron oxide
reduces the reflectivity of this surface, thereby reducing the
intensity of the laser beam 3' reflected by groove wall 10 and
shown with a dotted line in FIG. 2 to such an extent that groove
root 14 hit by it is no longer sufficiently heated so that it is
hardened. It is undesirable to harden groove root 14, i.e. the edge
between groove wall 10 and groove root 14, because hardening of
these regions reduces the basic impact resistance of the piston
material in these regions to such an extent that cracks can form
here during engine operation.
[0024] The method according to the invention for hardening groove
wall 10 has the additional advantage that the angle of incidence
.alpha. formed by groove wall 10 and laser beam 3 can be selected
as desired, and is selected in such a manner that the size of the
hardness penetration zone is optimally adjusted for the best
possible hardening result.
[0025] 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.
REFERENCE SYMBOL LIST
[0026] .alpha. angle of incidence [0027] 1 holder device [0028] 2
laser source [0029] 3, 3' laser beam [0030] 4 gas jet [0031] 5
piston, steel piston [0032] 6 turntable [0033] 7 foundation [0034]
8 gas line [0035] 9 stand [0036] 10 lower wall, groove wall [0037]
11 upper ring groove [0038] 12 clamping holder [0039] 13 piston
axis [0040] 14 groove root
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