Electric heating – Metal heating – By arc
Reexamination Certificate
2001-04-10
2002-12-10
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121700
Reexamination Certificate
active
06492617
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser cutter, and more specifically to a piercing device for a laser cutter that is highly efficient at carrying out the piercing operation performed to initiate a cutting operation.
2. Description of the Related Art
When employing a laser to cut a thick (6 mm or more) steel sheet, for example, it is the typical practice to perform a piercing operation first, followed by the intended cutting operation.
In general, as shown in
FIG. 7
, the piercing operation consists of irradiating a material
3
to be cut, such as a steel plate or the like, with a laser beam
2
from a cutting nozzle
1
; supplying an assist gas
4
along the same axis as the laser beam
2
, to heat and melt cutting material
3
; and expelling molten metal
6
using the kinetic energy of assist gas
4
from a pierced hole
5
which is formed in the cutting material
3
. When carrying out the piercing operation, a portion of the molten metal
6
accumulates around the periphery of the pierced hole
5
while another portion spatters onto sites away from the pierced hole
5
.
Oxygen is typically used as assist gas
4
. When the piercing operation is carried out using oxygen gas, high energy is produced due to oxidation of the steel plate material by the oxygen gas. Accordingly, this is advantageous to carrying out the piercing operation efficiently. A pulse oscillation of 100 Hz or less is typical as the radiating conditions for the laser beam
2
during piercing. However, by placing the laser in a continuous oscillation state, output of the laser beam
2
can be increased, enabling the formation of the desired pierced hole
5
in a shorter period of time. Thus, the time for performing the piercing operation can be reduced.
Various problems arise when the output of the laser beam
2
is increased, however. Namely:
a) The diameter of the pierced hole
5
increases
b) Bubbling of the molten metal
6
becomes excessive
c) Damage may be caused to the cutting nozzle
1
or the condensing lens due to b)
d) Spattered material adhering to the cutting material
3
increases
e) Poor cutting occurs when initiating the cutting operation due to d)
In light of these problems, attempts have been made in recent years to carry out the piercing operation at high speed by increasing the peak output of the laser beam pulse. However, since such problems as adherence of spattering to the lens or nozzle occurs, this has not fundamentally resolved the problem.
Attempts have also been made to prevent bubbling of the molten metal and adherence of spattering by controlling the output of the laser beam during the piercing operation. However, since the piercing speed is contingent upon the control speed, the improvement in speed has been limited.
The present inventors accordingly developed the laser cutter shown in
FIGS. 8 through 10
(Japanese Patent Application, Hei 9-29380).
This laser cutter has a side blow gas nozzle
10
provided at the side of a cutting nozzle
1
. The side blow gas nozzle
10
is a separate member from the cutting nozzle
1
and is held by a moving means
11
at the side of the cutting nozzle
1
. The side blow gas nozzle
10
jets a side blow gas (side assist gas)
12
at the piercing site (i.e., the site where the pierced hole
5
is to be formed). Accordingly, the jetting of side blow gas
12
jetted by the side blow gas nozzle
10
is slanted toward the optical axis of the laser beam
2
. The laser beam
2
radiates the cutting material
3
by traveling through a laser beam hole
7
which passes through the cutting nozzle
1
. Thus, the jetting of side blow gas
12
is inclined with respect to the assist gas
4
which is being jetted from the laser beam hole
7
. The moving means
11
has the structure as shown in
FIGS. 9 and 10
, and is for moving the side blow gas nozzle
10
, which it holds, closer to or further away from the piercing site.
In
FIG. 9
, the moving means
11
is a rotational driving member
13
that is attached above cutting nozzle
1
(i.e., at the upper part of FIG.
9
). Using the driving force of an electric motor for example, the moving means
11
supports the side blow gas
12
supply inlet side of the side blow gas nozzle
10
in a manner so as to be freely rotating about an axial line perpendicular to the optical axis of laser beam
2
. The rotational driving member
13
moves an end
14
of the side blow gas nozzle
10
near an end
15
of the cutting nozzle
1
during piercing, and rotates the side blow gas nozzle
10
during the cutting operation to move it away from the end
15
of the cutting nozzle
1
.
In
FIG. 10
, the moving means
11
is an elevational driving member
16
that is attached above the cutting nozzle
1
(at the upper part of FIG.
10
). Using the driving force of an electric motor for example, the moving means
11
supports the side blow gas
12
supply inlet side of side blow gas nozzle
10
in a manner so as to be freely elevating along the optical axis of the laser beam
2
. The elevational driving member
16
moves an end
14
of the side blow gas nozzle
10
near an end
15
of the cutting nozzle
1
during piercing, and elevates the side blow gas nozzle
10
during the cutting operation to move it away from the end
15
of the cutting nozzle
1
.
The numeric symbol
17
in
FIG. 8
indicates a side blow gas control mechanism. This side blow gas control mechanism
17
is provided with a pressure sensor
18
for measuring the supply pressure of assist gas
4
to the laser beam hole
7
; a level converting mechanism
19
that changes and sets the supply pressure of the side blow gas
12
in response to the measured pressure at the pressure sensor
18
; and a pressure adjusting mechanism
20
for adjusting the supply pressure of the side blow gas based on the pressure set by the level converting mechanism
19
. The pressure sensor
18
is attached to the cutting nozzle
1
and measures the pressure of the assist gas
4
inside the laser beam hole
7
.
In other words, at the side blow gas control mechanism
17
, when the measurement signal for pressure P
1
of the assist gas
4
, which is measured by the pressure sensor
18
, is input to the level converting mechanism
19
, the level converting mechanism
19
calculates a suitable supply pressure P
2
for the side blow gas
12
according to this pressure P
1
, and sends a directive signal to pressure adjusting mechanism
20
. As a result, the pressure adjusting mechanism
20
adjusts the supply pressure of the side blow gas
12
to the pressure P
2
.
The flow rate of the side blow gas
12
which is jetted from the side blow gas nozzle
10
must be adjusted to be within limits that do not impair the supply of the assist gas
4
to the piercing site, and which can promote formation of the pierced hole
5
by ensuring sufficient kinetic energy is imparted to the side blow gas
12
. This flow rate is determined based on the supply pressure P
2
of the side blow gas
12
with respect to the cross-sectional area of the gas flow path at the end of the side blow gas nozzle
10
from which the gas is jetted.
This laser cutting device performs the intended cutting operation on the cutting material
3
by moving the cutting nozzle
1
in three-dimensional directions using a driving mechanism not shown in the figures. The side blow gas nozzle
10
is also moved accompanying the cutting nozzle
1
at this time, and is typically disposed near the cutting nozzle
1
.
When cutting a thick plate using this laser cutting mechanism, the pierced hole
5
is first formed during the piercing operation, after which the process proceeds to the intended cutting operation. In the piercing operation, the side blow gas nozzle
10
is moved to the piercing site by the moving means
11
and maintained there. The assist gas
4
is jetted from the cutting nozzle
1
and the side blow gas
12
is jetted from the side blow gas nozzle
10
so that molten metal is removed as the pierced hole
5
is being formed by irradiating the cutting material
3
with
Kawakita Masato
Nagahori Masayuki
Numata Shinji
Evans Geoffrey S.
Scully Scott Murphy & Presser
Tanaka Engineering Works, Ltd.
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