1. Field of the Invention
This invention relates to a laser beam machine for cutting the shape of a hole according to a machining program, and more particularly to a laser beam machine which is capable of cutting the shape of a hole with an enhanced cutting speed.
2. Description of the Related Art
Conventionally, to machine the shape of a hole through a plate material, such as a steel plate, by a laser beam machine, piercing, i.e. the machining of perforating a small hole, is first carried out, and then cutting is carried out along the shape of the hole.
FIGS. 7 (a) and 7 (b) show examples of conventional machining paths for cutting circular holes. FIG. 7 (a) shows a first example, while FIG. 7 (b) shows a second example. In the the case of FIG. 7 (a) example, the machining head starts to move from a start position A11, and once stops at a central position O11 of a circular hole 110, where laser beam irradiation is started to carry out piercing. After completion of piercing, cutting is started from the central position O11, and continued until the machining head reaches a point H11. From the point H11, the machining head moves along the circumference of the circular hole 110 until it comes to the point H11 again, where the machining head once stops, thereby completing cutting of the hole, and the laser beam irradiation is also stopped. Thereafter, the machining head moves to a final stop position Z11.
In the case of the FIG. 7 (b) example, the machining head starts to move from a start position A12, and directly reaches a point H12 on the circumference of the circular hole 110. The machining head once stops at the point H12, and then the laser beam irradiation is started to carry out piercing. After completion of piercing, cutting is started from the point H12, and the machining head moves along the circumference of the circular hole 110 until it comes to the point H12 again. At the point H12, the machining head once stops, thereby completing cutting of the hole, and the laser beam irradiation is also stopped, followed by the machining head moving to a final stop position Z12.
FIG. 8 (a) and FIG. 8 (b) show examples of conventional machining paths for cutting a slot and a square hole. FIG. 8 (a) shows an example of the machining path for the slot, while FIG. 8(b) an example of the machining path for the square hole. In the case of FIG. 8 (a), the machining head starts to move from a start position A13, and once stops at a central position O13 of a slot 120, followed by starting irradiation of the laser beam for piercing. After completion of piercing, cutting is started from the central position O13, and continued until the machining head reaches a point H13, from which the machining head moves along the periphery of the slot until it comes to the point H13 again, where the machining head once stops, thereby completing cutting of the slot. At the same time, the laser beam irradiation is also stopped. Thereafter, the machining head moves to a final stop position Z13.
In the case of FIG. 8 (b), the machining head starts to move from a start position A14, and once stops at a point I14 within a square hole 130, followed by starting irradiation of the laser beam for piercing. After completion of piercing, cutting is started from the point I14, and continued until the machining head moves to a point H14, from which the machining head moves along the periphery of the square hole 130 until it comes back to the point H14 again, where the machining head once stops, thereby completing cutting of the square hole. At the same time, laser beam irradiation is also stopped. Thereafter, the machining head moves to a final stop position Z14.
In all of the above examples of the machining path, the machining head stops two times, i.e. upon piercing and upon completion of cutting of a hole. Therefore, it is necessary to carry out deceleration and acceleration before and after stoppage of the machining head, requiring the longer time period for machining.
Especially, the machining path shown in FIG. 7 (a) is an ordinary one usually followed in cutting a circular hole, but the machining head undergoes a drastic or sharp turn at the point H11, requiring a rapid acceleration and deceleration on the drive mechanism side. Therefore, a slow-down of the feed rate is inevitable, requiring still the longer time period for machining.
As means for eliminating the above inconvenience in machining, a so-called running piercing is generally known. The running piercing dispenses with positioning of the machining head for piercing, through generation of a smooth path for the overall route for machining. That is, according to the running piercing, piercing is carried out without stopping the machining head at any intermediate point when the machining head is moved from a start position to a cutting start position on the periphery of a hole to be cut. This method of machining permits the drive mechanism to cause continuous cutting without requiring the same of a drastic acceleration and deceleration. Further, when the machining head cuts round the periphery of the hole and returns to the cutting start position, the machining head is caused to move further in an overlapping manner along the part of the periphery, and then move on the smooth path up to the final stop position. This also dispenses with positioning of the machining head in cutting off the hole, i.e. upon completion of cutting off the hole. Therefore, it is no longer necessary to carry out positioning of the machining head two times, thereby making it possible to realize a high-speed cutting process.
However, machining paths along which the running piercing is carried out as described above are complicated, and hence machining programs therefor are also complicated, requiring a long time period for programming.