GB2309188A

GB2309188A - Laser beam machine

Info

Publication number: GB2309188A
Application number: GB9703780A
Authority: GB
Inventors: Hisao Tanaka; Takeshi Irino; Akira Ishimori; Akaru Usui; Shigehiro Yoshiyasu
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1995-02-28
Filing date: 1996-02-28
Publication date: 1997-07-23
Anticipated expiration: 2016-02-28
Also published as: GB2309188B; GB2309189A; GB2309189B; GB9703780D0; GB9703782D0

Description

LASER BEAM MACHINE The present invention pertains generally to laser beam machines and more particularly to their optical fiber wiring and beam output optical assemblies having improved structures.

It is known that a carbon dioxide gas (CO2) laser, which features high beam quality (i.e., light-condensing capability), is an excellent light source for use in laser beam cutting of metal plates and sheets. Various types of CO2 laser beam machines using mirrors and infrared-transparent optical fibers have thus far been proposed and developed for practical applications. On the other hand, yttrium-aluminum-garnet (YAG) lasers have been used in marking and trimming applications, for instance, because they have been able to provide good beam quality only in low-power ranges. However, recent technological advances have made it possible to develop YAG lasers which would offer as good beam quality as the CO2 lasers even at output power levels exceeding 100 W.As a result, it has become possible for the YAG lasers, which utilize visiblelight-transparent optical fibers featuring a high degree of operability and multi-purpose applicability, to achieve such cutting performance that is comparable to the CO2 lasers.

FIG. 2 is a perspective diagram illustrating a lightcondensing head positioning mechanism of a CO2 laser beam machine utilizing an infrared-transparent optical fiber, of which example is disclosed in Japanese Patent Application No.

57-124586. In FIG. 2, there are provided a flexible optical fiber cable 1 containing an infrared-transparent optical fiber measuring 10.6 iim in wavelength at CO2 laser connected to a laser oscillator (not shown) and a beam output optical assembly 2 connected to the end of the optical fiber cable 1.

Designated by the numeral 3 is a table on which a workpiece W, e.g., a piece of sheet metal, is fixedly mounted. Designated by the numeral 4 is a positioning mechanism for moving the beam output optical assembly 2 above the workpiece W in a twodimensional processing pattern. The positioning mechanism 4 includes a first carriage member 4-2 which moves along a pair of rails 4-1 and a second carriage member 4-3 which moves at right angles to the rails 4-1 along another pair of rails 4-4.

The beam output optical assembly 2 is mounted to the second carriage member 4-3.

Described in the following is how the CO2 laser beam machine of the above construction operates when marking a graphic or text pattern on the workpiece W. A marking process is commenced by first positioning the beam output optical assembly 2 just above a specified location of the workpiece W.

A controller (not shown) transmits a control signal produced in accordance with readily entered marking pattern data. This control signal controls opening and closing operations of a shutter provided inside a CO2 laser oscillator (not shown) in order to intermittently deliver and interrupt laser light. The laser light of an appropriate energy level transmitted to the beam output optical assembly 2 via the optical fiber cable 1 is switched on and off in this manner. The beam output optical assembly 2 is moved by the first carriage member 4-2 and second carriage member 4-3 of the positioning mechanism 4 above the workpiece W.When exposed to a laser beam radiated from the beam output optical assembly 2, resulting heat causes an exposed surface zone of the workpiece W to evaporate or melt so that the specified pattern is marked on the workpiece W in accordance with the movement of the beam output optical assembly 2 and the laser light switching on/off sequence.

The above-described CO2 laser beam machine employs an optical fiber for laser light transmission. Unlike laser machining systems using mirrors for laser beam transmission, this type of laser beam machine can not be used for cutting a steel plate, for instance, due to a large transmission loss of the 10.6 gm infrared-transparent optical fiber. Development of a low transmission loss optical fiber has therefore been awaited. YAG laser machining systems also have a similar problem. Although transmission loss of optical fibers used for carrying visible light is sufficiently low, output power of a YAG laser that can provide satisfactory beam quality is limited to a few tens of watts.

Generally, it is necessary to eject an assist gas together with a laser beam through a coaxial nozzle to realize a high-quality cutting process. Different assist gases are used for different types of workpiece. As an example, oxygen is most often used for steel plates and stainless steel plates.

In this example, it is possible to increase the cutting speed and reduce the amount of dross (i.e., waste product deposits caused in cutting operations) by increasing the gas pressure.

Also effective for making efficient use of laser beam energy, increasing the cutting speed and reducing thermal distortion is to converge the laser beam on as small a spot as possible. It is a common practice in laser beam machining to construct beam output optical systems in consideration of the above aspects.

FIG. 3 is a cross-sectional view showing the structure of a conventional beam output optical assembly 2 used in YAG laser beam machines which employ optical fibers transparent to visible light. In FIG. Q , designated by the numeral 1 is an optical fiber cable containing an visible-light-transparent optical fiber in a flexible protective jacket. The beam output optical assembly 2 comprises a nozzle centering mechanism 12, a beam output optical assembly housing 2-1 provided with an assist gas inlet 15, a collimator lens 14 and a condenser lens 13. Designated by the numeral 11 is an optical fiber joint which connects the optical fiber cable 1 to the beam output optical assembly 2.The optical fiber joint 11 comprises an optical connector 11-1 including a plug ll-la and a receptacle ll-lb. The receptacle ll-lb is screwed to one end of the beam output optical assembly housing 2-1. Mounted to the beam output optical assembly housing 2-1 at the opposite end to the optical fiber joint 11, the nozzle centering mechanism 12 includes a nozzle 12-1, a first nozzle holder 12-2, nozzle adjusting screws 12-3 mounted on the first nozzle holder 12-2 and a second nozzle holder 12-4.

Operation of the beam output optical assembly 2 of FIG.

3 is now described. The laser light transmitted through the optical fiber cable 1 is emitted from the end of the optical fiber at the optical connector 11-1 of the optical fiber joint 11. The laser light propagates through the air in a diverging pattern until it reaches the collimator lens 14, which brings the laser light into a parallel beam. The condenser lens 13 causes the parallel beam to converge so that the laser beam outgoing through the nozzle 12-1 is focused on the surface of a workpiece W. Before starting a cutting operation, a machine operator carries out an adjustment for aligning the laser beam with the center of the nozzle 12-1 by turning the nozzle adjusting screws 12-3. With this adjustment, an assist gas injected from the assist gas inlet 15 is uniformly blown onto a currently processed spot to accomplish a successful cutting oEEeration.

The aforementioned conventional beam output optical assembly 2 has at its foremost end the nozzle centering mechanism 12. This increases the physical dimensions of the beam output optical assembly 2 and limits the machining area. In

accovod:Xt wttk tke invention, a laser beam machine comprises an optical fiber cable for transmitting laser light; a beam output optical device for emitting the laser light delivered through the optical fiber cable; and a nozzle centering mechanism provided between the optical fiber cable and beam output optical device for aligning the optical axis of the optical fiber cable with that of a nozzle of the beam output optical device.

This arrangement makes it possible to reduce the orifice size of the nozzle, providing not only the capability to process a small area but also an enlarged machining area.

The nozzle centering mechanism may comprise a movable member to which the optical fiber cable is fixed; a holder for retaining the movable member; and a fixing device provided on the holder for moving the movable member at right angles to the laser light path and fixing it in a desired position.

In this configuration, the laser light path is aligned with the nozzle by shifting the movable member by operating the fixing device. This also makes it possible to reduce the orifice size of the nozzle, providing not only the capability to process a small area but also an enlarged machining area.

Preferably, a surface area of the movable member that is kept in contact with the holder is coated with a lowfriction material.

This arrangement serves to facilitate nozzle centering operation.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: FIG. 1 is a cross-sectional view of a beam output optical assembly used in a laser beam machine according to a preferred embodiment of the invention; FIG. 2 is a perspective diagram illustrating a positioning mechanism of a conventional C02 laser beam machine; and FIG. 3 is a cross-sectional view of a beam output optical assembly used in a conventional TAG laser beam machine.

FIG. i is a cross-sectional view of a beam output optical assembly 2 used in a laser beam machine according to one

embodiment of the invention. In FIG. 1, elements designated by the numerals 1, 2, 2-1, 11, 11-1, ll-la, ll-lb, 12-1, 13, 14 and 15 are identical or equivalent to those used in the earlier-described conventional laser beam machine.

Their detailed description is therefore omitted here.

Referring to FIG. I , designated by the numeral 31 is a nozzle centering mechanism for centering the nozzle 12-1, designated by the numeral 31-1 is a movable cylinder to which the receptacle ll-lb is fixed, and designated by the numerals 31-2 and 31-4 are first and second holders, respectively, for retaining the movable cylinder 31-1. There are four adjusting screws 31-3 provided at 900 angular intervals around the second holder 31-4 for securing the movable cylinder 31-1 in position.

Designated by the numeral 31-5 is a low-friction coat (e.g., Teflon polymer) covering such surface areas of the movable cylinder 31-1 that are kept in contact with the first and second holders 31-2 and 31-4.

Discussed in the following is how the construction of the embodiment works. This embodiment differs from the conventional arrangement in that the nozzle centering mechanism 31 is located between the optical fiber joint 11 and collimator lens 14. Operation of the nozzle centering mechanism 31 is now described in detail. The receptacle ll-lb which is mated with the optical connector 11-1 is fixed to the movable cylinder 311 by screws. The movable cylinder 31-1 is secured by the first holder 31-2 and second holder 31-4 which is provided with the adjusting screws 31-3. There is provided a gap between the movable cylinder 31-1 and a cylindrical wall of the second holder 31-4 where the adjusting screws 31-3 are fitted. The second holder 31-4 is screwed onto the beam output optical assembly housing 2-1.The movable cylinder 31-1 can be moved at right angles to the axis of laser light by means of the adjusting screws 31-3 provided on the second holder 31-4. The movable cylinder 31-1 is fixed in position after its exact alignment with the optical axis has been accomplished.

The laser light emitted from the optical fiber cable 1 is converged through the nozzle centering mechanism 31, collimator lens 14, condenser lens 13 and nozzle 12-1 and directed to a workpiece W together with an assist gas.

Although the beam output optical assembly 2 is so designed that the laser light emitting end of the optical fiber cable 1 and the center of the nozzle orifice align with the optical axis, small misalignment occurs due to variations in manufacturing processes. Needless to say, the converged laser light should pass the center of the nozzle orifice to obtain a high cutting speed and satisfactory cut surface quality. The fixing position of the optical fiber cable 1 is adjusted by turning the adjusting screws 31-3 provided on the second holder 31-4 to minimize the misalignment due to manufacturing variations.

As seen above, the nozzle centering mechanism 31 is provided between the optical fiber joint 11 and collimator lens 14 in this embodiment. This arrangement makes it possible to reduce the orifice size of the nozzle 12-1, providing not only the capability to process a small area but also an enlarged machining area. In addition, nozzle centering operation is made easier thanks to the low-friction coat 31-5 covering sliding areas of the movable cylinder 31-1.

Claims

Claims:

1. A laser beam machine comprising: an optical fiber cable for transmitting the laser light; beam emitting means for emitting the laser light delivered through the optical fiber cable; and nozzle centering means, provided between the optical fiber cable and the beam emitting means, for aligning the optical axis of the optical fiber cable with that of a nozzle of the beam emitting means.

2 A laser beam machine as claimed in claim 1, wherein the nozzle centering means comprises: a movable member to which the optical fiber cable is fixed and which moves at right angles to the laser light path; holding means for holding the movable member; and fixing means, provided on the holding means, for moving the movable member at right angles to the laser light path and fixing it relative to the holding means.

3. A laser beam machine as claimed in claim 2, wherein a surface area of the movable member that is kept in contact with the holding means is coated with a low-friction material.

4. A laser beam machine substantially as described with reference to Figure 1 of the accompanying drauings.