Source: {"pile_set_name": "USPTO Backgrounds"}

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 P1 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 P2 for the side blow gas 12 according to this pressure P1, 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 P2.
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 P2 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 the laser beam 2. When the desired pierced hole 5 is formed, the jetting of the side blow gas 12 from the side blow gas nozzle 10 is stopped, and the side blow gas nozzle 10 is withdrawn from the piercing site. At the same time, jetting of the assist gas 4 from the cutting nozzle 1 is continued and the intended cutting operation using the laser beam 2 is initiated.
In the piercing operation, as the molten metal 6 and spattering is generated, they are gradually blown away from the piercing site because the flow rate of the side blow gas 12 is two-fold or more greater than that of the assist gas 4. Thus, the molten metal 6 and spattering does not adhere to the cutting material 3 or the cutting nozzle 1. In other words, in the piercing operation, the pierced hole 5 is formed as the molten metal 6 and spattering are simultaneously being removed from the cutting material 3 when the molten metal 6 and spattering is generated. Accordingly, the molten metal 6 does not adhere around the pierced hole 5, so that the intended pierced hole 5 can be obtained. Since the adherence of the molten metal 6 and spatter to the cutting material 3, the side blow gas nozzle 10, and the condensing lens incorporated in cutting nozzle 1 are also prevented, there is no concern that poor cutting will occur during the intended cutting operation. Thus, the quality of the cut product is improved.
Thus, in this novel laser cutter, the adherence of molten metal or spatter on the cutting nozzle and the cutting material is prevented, so that piercing can be carried out quickly.
However, the side blow gas may not be stably supplied to the piercing site. For this reason, it is difficult to pierce a steel plate having a thickness of 20 mm or more in which a large amount of spattering occurs during piercing. When the piercing of a 20 mm or thicker steel plate is performed, a large amount of spattering occurs which adheres to the cutting nozzle and the lens. As a result,