Electric heating – Metal heating – By arc
Patent
1996-02-15
1998-06-02
Walberg, Teresa J.
Electric heating
Metal heating
By arc
21912184, B23K 2614
Patent
active
057603685
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laser beam machining method of cutting a workpiece by means of a laser beam, and more particularly, to a laser beam machining method suited for cutting a mild steel sheet or the like at a high speed.
2. Description of the Related Art
Laser beam machining is a method of vaporizing or melting material of a workpiece by irradiating onto very small portions of the same a high-density-energy laser beam which is obtained by generating an extremely coherent, monochromatic light and then converging the light by a condenser lens. The laser beam is excellent in controllability, which enables the laser beam machining to be employed in cutting complicated shapes, very small articles with high accuracy, and so forth, under the control of a numerical control unit. To carry out such laser beam machining more efficiently, there has been employed a method of using oxygen as an assist gas for accelerating the melting of material of a workpiece. This assist gas helps not only to accelerate the melting of steel of a workpiece by adding heat of oxidation to heat of the laser beam, but also to blow off and remove molten steel from the worked part.
The chemical reaction caused by the assist gas of oxygen is shown in the following thermochemical formulas:
In cutting a mild steel sheet, the use of punching press or plasma rather than a laser beam would enable faster cutting. However, punching press and plasma cutting have the following problems: The former is not suited for cutting very small articles with high accuracy. The latter, which is capable of very high-speed cutting, has an adverse effect on the environment and causes serious wear of various kinds of machine components as well. For this reason, there is a demand for a method of speeding up laser beam cutting, since the laser beam cutting neither has any adverse effects on the environment nor causes serious wear of machine components, and further is excellent in cutting very small articles with high accuracy.
When an attempt is made to speed up laser beam cutting by increasing the laser output power, however, the rate of rise of the cutting speed becomes extremely low after the cutting speed has reached a specific value. The specific value of the cutting speed at which the rate of rise of cutting speed turns very low is called a saturated cutting speed.
FIG. 4 is a diagram showing the relationship between the laser output power and the cutting speed exhibited when oxygen is used as an assist gas. In the illustrated case, a mild steel sheet having a thickness of 1.0 mm is used. As shown in FIG. 4, the cutting speed increases in proportion to the laser output power until the latter reaches a value of 2 kW, but there is hardly any increase in the cutting speed after the laser output has exceeded 2 kW. The cutting speed of 8 m/min attained when the laser output power is 2 kW is a saturated cutting speed of the present case.
As is understood from the above, it is difficult to gain the cutting speed beyond the saturated cutting speed, even if the laser output power is increased. One possible reason for incapability of increasing the cutting speed is that the rate of removal of molten metal by an assist gas does not keep up with the cutting speed any longer.
If a higher-pressure oxygen gas is supplied as the assist gas to solve the above problem, an excessive oxidation reaction occurs, which increases molten part and hence increases the volume of molten metal to be removed. This prevents the cutting speed from being increased, and what is still worse, causes degraded quality of cut surfaces.
As a result, even a laser beam machine which is capable of emitting a laser beam with a high output power cannot cut at a higher speed than the saturated cutting speed, and instead performs cutting at a lower speed than it can achieve, which prevents the machine from delivering performance to its full capacity.
SUMMARY OF THE INVENTION
The present invention has been made in view of these circumstance, and t
REFERENCES:
patent: 4945207 (1990-07-01), Arai
patent: 5578228 (1996-11-01), Beyer et al.
patent: 5609781 (1997-03-01), Kaga et al.
Fanuc Ltd.
Mills Gregory L.
Walberg Teresa J.
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