ASSIST GAS CONTROL SYSTEM

Abstract: An assist gas control system for a CND laser machining apparatus is provided in which a laser machining apparatus and a numerical controller (CNC) are coupled together. When the laser machining is carried out, the kind of assist gas, mixing ratio, pressure and flow rate are instructed by machining program and controlled by a flow-rate control valve (32), a pressure control valve (33) and the like through a numerical controller (10). Since the kind of assist gas, mixing ratio, pressure and flow rate are instructed by the machining program and are automatically controlled, the operator is relieved from the need for the selection of assist gas, and various settings and adjustments, and thus it becomes possible to reduce the time for making preparation for the machining and to carry out the laser machining with precision. ABSTRACT An assist gas control method is provided for a CNC laser machining device including a combination of a laser beam machine and a numerical control apparatus (CNC). The kind, mixing ratio, pressure, and flow rate of assist gas are controlled by instructions from a machining program, and a numerical control apparatus (10) controls the kind, mixing ratio, pressure and flow rate of the assist gas by controlling a flow rate control valve (32), a pressure control valve (33), and other components, to perform laser machining. Since the kind, mixing ratio, pressure, and flow rate of assist gas are controlled by the instructions from the machining program and controlled automatically, an operator is not required to select, set or adjust the assist gas, whereby the preparation time for machining is shortened and laser machining can be carried out with a satisfactory precision.

Description: The present invention relates to an assist gas control method for a laser machining device. CNC laser machining devices comprising a combination of a laser beam machine and a numerical control apparatus (CNC) are now in practical use, and since the function of the numerical control apparatus (CNC), in particular, enables a workpiece having a complex shape to be machined at a high speed, the CNC laser machining devices are used not only for cutting metal but also for a surface treatment of metal, such as welding, alloying of a metal surface, amorphous treatment of a metal surface, and the like. An assist gas is widely used in metal machining to prevent contamination of the lens of the laser machining device, protect the workpiece from machining splash, promote the machining of metal, and the like. In this operation, however, the kind, pressure, and flow time of the assist gas are selected, set, and adjusted by an operator in charge of the machining, according to working instructions or bases on the operators judgment. Therefore, problems arise in that a considerable time is required before starting laser machining and that a defective machining may occur due to, for example, an error by the operator. JP-A-61-123495 discloses an assist gas control method for a laser machining device including a combination of a laser beam machine and control means, the method comprising controlling a kind, pressure, and flow rate of an assist gas by a machining program during laser machining, the control means being a numerical control apparatus (CNC); and, according to the invention, such a method is characterized in that the method comprises storing in the CNC, independently of the machining program, a look-up table comprising data representing different combinations of pressures and flow times of a pre-flow of the assist gas, and pressures and flows times of a post-flow of the assist gas; designating in the machine program an assist gas parameter (Q); in the execution of the program addressing the look-up table by the assist gas parameter (Q) to recall the stored data; and controlling the pre-flow and post-flow of assist gas in accordance with the recalled data. The kind (mixing ratio), pressure, and flow rate of assist gas are controlled by instructions from the machining program, and thus the assist gas is controlled automatically, whereby the operator need not select, set or adjust the assist gas. Furthermore, the pressure and flow time of the assist gas pre-flow before machining and the pressure and flow time of the assist gas post-flow after machining are instructed by the machining program. Therefore, the pre-flow and post-flow are controlled automatically, and thus the operator need not set or adjust the pre-flow and post-flow. The kind (mixing ratio), pressure, and flow rate of assist gas, and the pressures and times for the pre-flow and post-flow are controlled by the instructions from the machining program, and thus all of the assist gas control is executed automatically. Therefore, the operator is not required to do any setting and adjusting, etc., of the assist gas. In the accompanying drawings: FIG. 1 is a block diagram illustrating an embodiment of the present invention; FIG. 2 is a diagram showing the relationship between time and pressure of a pre-flow and a post-flow; and FIG. 3 is a diagram illustrating a data table for the assist gas. An embodiment of the present invention will be described with reference to the drawings. In Figure 1, 10 represents a numerical control apparatus (CNC) for controlling laser machining. Note, the figure shows only the portions pertinent to assist gas control and those parts relating to control of various axes and a laser oscillator are omitted. Numeral 11 denotes a gas control means for controlling the flow rate and pressure, etc., of the assist gas, referred to hereinafter, 12 denotes a memory for storing a machining program and parameters, etc., for laser machining, 13 a flow rate control means for controlling the flow rate of the assist gas, and 14 a pressure control means for controlling the pressure of the assist gas. Numeral 21 designates a display for displaying the flow rate and pressure, etc., of the assist gas in accordance with instructions from the gas control means 11. A CRT or liquid-crystal display may be used as the display 21. Designated at 22 is a keyboard by which data, such as the kind, pressure, and flow rate, etc., of the assist gas, is input. The input data is stored in the memory 12, and is read out for laser machining. A machining program is read out by a tape reader, not shown, or is input through the keyboard 22, and is once stored in the memory 12. When carrying out machining, the data is read out and output from the gas control means 11 as instructions specifying the kind, flow rate, and pressure, etc., of the assist gas. Numeral 31 represents a gas supply unit including gas cylinders containing assist gases, valves for selectively delivering the gases, a mixing machine for mixing various assist gases, and other components. In accordance with instructions from the gas control means 11, the kind and mixing ratio of the assist gas are defined, and related solenoid valves are controlled to deliver an assist gas as instructed. Designated at 32 is a flow rate control valve, the opening of which is controlled by a voltage instruction from the flow rate control means 13 to control the flow rate of the assist gas. Numeral 33 designates a pressure control valve, the opening of which is controlled by a voltage instruction from the pressure control means 14 to control the pressure of the assist gas. Denoted at 34 is a flow sensor for detecting the flow rate of the assist gas at the output side of the flow rate control valve 32, and 35 denotes a pressure sensor for detecting the pressure at the output side of the pressure control valve 33. Numeral 36 designates a flow rate indicator, which receives a voltage output from the flow sensor 34 and amplifies the same to be displayed on a display incorporated therein. At the same time, the voltage signal is converted into a digital signal, which is output to the gas control means 11. The gas control means 11 supplies the signal to the display 21, which then displays the flow rate of the assist gas. The digital signal is also supplied to the flow rate control means 13, which compares the digital signal from the flow rate indicator 36 with an instruction value from the gas control means 11, and controls the flow rate control valve 32 such that the flow rate of the assist gas becomes equal to the instruction value. Numeral 37 denotes a pressure indicator, which receives a voltage output from the pressure sensor 35 and amplifies the same to be shown on a display incorporated therein. Simultaneously, the pressure indicator converts the voltage signal into a digital signal, which is supplied to the gas control means 11. The gas control means 11 supplies the signal to the display 21, to cause a display of the pressure of the assist gas thereon, and to the pressure control means 14. The pressure control means 14 compares the digital signal from the pressure indicator 37 with an instruction value from the gas control means 11, and controls the pressure control valve 33 such that the pressure of the assist gas becomes equal to the instruction value. Numeral 41 denotes a reflection mirror for reflecting a laser beam 43 from a laser oscillator 50 toward a lens 42. The lens 42 focuses the laser beam 43, reflected by the reflection mirror 41, onto a workpiece 45. Denoted at 44 is an assist gas which protects the lens 42 from splashes produced during machining and facilitates the machining of the workpiece 45. Now, an example of a machining program will be described. The instruction form the machining program is as follows: G32 P1 Q2 ; where "G32" is the G code for controlling the assist gas, and "P1" indicates the kind of assist gas, which, for example, can be defined as follows: P0 stoppage of assist gas P1 oxygen P2 nitrogen P3 air P4 argon The gas used may be a mixture of these gases, if necessary. "Q2" is data read from machining data tables previously stored in the memory 12, and indicates the pressure and flow rate, etc., of the assist gas. These tables are prepared beforehand in accordance with the material and thickness of a workpiece to be machined, and the kind of machining, such as cutting, welding, surface treatment (alloying or amorphous treatment of metal surface) or the like. The pre-flow and post-flow used in laser machining will now be described. During laser machining, the assist gas must flow not only during the actual machining but also before and after the machining, for predetermined time periods, regardless of whether cutting, welding or a surface treatment is to be carried out. The flow of assist gas before machining is called a pre-flow, and the flow after machining is called a post-flow. FIG. 2 shows the relationship between the time and pressure of the pre-flow and post-flow. In the figure, time is indicated along the abscissa, and the pressure of the assist gas along the ordinate. Time tw represents the actual machining time, and in this case, the pressure of the assist gas is Pw. During a time tp before machining, a pre-flow of assist gas with a pressure Pp is effected, and during a time ta after machining a post-flow is effected with a pressure Pa. Of these values, the machining time tw is determined by actual workpiece machining, whereas the other data is previously stored, as machining data, in the memory 12, in specified locations depending on the material and thickness, etc., of the respective workpieces. The data is denoted by Q and a numerical suffix, and is read out in the machining program as an instruction, such as "Q2", to perform machining. FIG. 3 shows an example of the table. The data in the table is denoted by numerical suffix to Q, and represents the pressure and time for the corresponding assist gas. The data must be previously obtained by measurement and stored in the memory 12. In the foregoing description, the data for the assist gas is stored together in the table to be read afterwards; alternatively it may be output from the program as an independent instruction, as in the case of the kind of assist gas, if necessary. As described above, the kind, mixing ratio, pressure, and flow rate of the assist gas are controlled by instructions from the machining program, and thus the assist gas is automatically controlled. Therefore, the operator need not select, set, or adjust the assist gas, and thus the preparation time for machining is shortened and setting and adjustment errors are eliminated. Furthermore, the pressure and flow time of the assist gas pre-flow before machining and the pressure and flow time of the assist gag post-flow after machining are controlled by the instructions from machining program to automatically control the pre-flow and post-flow. Therefore, the operator is not required to set and adjust the pre-flow and post-flow, and thus the preparation time for machining is shortened and setting and adjustment errors are eliminated. The kind, mixing ratio, pressure, and flow rate of the assist gas and the pressure and time for the pre-flow and post-flow are controlled by the instructions from the machining program to carry out the entire assist gas control automatically. The operator therefore need do nothing about the setting and adjustment, etc. of the assist gas, whereby the preparation time for machining is reduced, errors occurring when setting and adjusting the assist gas are eliminated, and machining suited to the material, thickness and other machining conditions can be carried out.

Claims: An assist gas control method for a laser machining device including a combination of a laser beam machine and control means, the method comprising controlling a kind, pressure, and flow rate of an assist gas by a machining program during laser machining; the control means being a numerical control apparatus (CNC); and characterised in that the method comprises storing in the CNC, independently of the machining program, a look-up table comprising data representing different combinations of pressures and flow times of a pre-flow of the assist gas, and pressures and flows times of a post-flow of the assist gas; designating in the machine program an assist gas parameter (Q); in the execution of the program addressing the look-up table by the assist gas parameter (Q) to recall the stored data; and controlling the pre-flow and post-flow of assist gas in accordance with the recalled data.

Inventors: ARAI TAKEJI FANUC MANSION HARI, ARAI, TAKEJI FANUC MANSION HARIMOMI 3-309
Applicants: FANUC LTD, FANUC LTD.
Application year: 1988
Main classification: B23K26
IPC codes: G05B19, B23K26