Abstract: This paper introduces a rotary three-torch flame cutting machine that can simultaneously cut the contour of a part and create a K-shaped welding bevel. The hardware and software design of the CNC system of this cutting machine are discussed in detail. Keywords: Flame cutting machine, rotary three-torch, welding bevel, CNC system 1 Introduction In China, factories and enterprises process tens of millions of tons of steel annually into parts of various shapes using thermal cutting equipment. For carbon steel, oxy-fuel cutting is the primary method. The widespread use of CNC flame cutting machines has not only greatly improved cutting efficiency but also increased material utilization by several percentage points, resulting in considerable socio-economic benefits. However, currently used CNC flame cutting machines are generally only two-axis linked control machines, equipped with only one torch perpendicular to the steel plate plane. Therefore, they can only cut parts with arbitrary contours but cannot cut welding bevels on these parts. In reality, parts often require welding after cutting, necessitating an additional welding bevel cutting process to ensure welding quality. To address this issue, this paper proposes a CNC flame cutting machine with a rotary three-torch based on an industrial PC. The cutting machine is controlled by a three-axis linkage of X, Y, and C. The X and Y axes control the movement trajectory of the three rotating torches, while the C axis controls the rotation angle of the three rotating torches, which rotates with the changes in the X and Y axis coordinates (Figure 1). This allows the cutting machine to cut the contour of the part along with the welding bevel. After cutting, welding can be performed simply by cleaning the slag, avoiding the need for the additional welding bevel process. [align=center] Figure 1 Schematic diagram of the rotating three torches[/align] 2 Design of CNC System Hardware The hardware block diagram of the CNC flame cutting machine's CNC system is shown in Figure 2. It mainly includes an industrial PC, a motion control card, and a servo system. The industrial PC is the core of the CNC system, responsible for calculating the cutting machine's movement trajectory (coarse interpolation) and managing the entire system. The motion control card is inserted into the expansion slot of the industrial PC, connecting to the servo system to control the cutting machine's movement trajectory (fine interpolation). On the other hand, it is connected to the machine tool operation panel and the relay controlling the air source. Through the operation panel, the position of the machine tool can be adjusted, and the machine tool can be commanded to start, pause, or return along the original cutting trajectory. It can also accelerate and decelerate the cutting speed. Through the relay, the oxygen and acetylene gas can be controlled to switch on and off. The servo system can be a stepper servo system or a fully digital AC servo system. [align=center] Figure 2 Hardware block diagram of CNC system[/align] The motion control card is designed by ourselves. It mainly includes decoding circuit, oscillation circuit, I/O port circuit, pulse control circuit, interrupt circuit, and opto-isolated input/output circuit. The decoding circuit provides an interface address range for the motion control card, which can be changed via a DIP switch; the oscillation circuit provides a fixed-frequency pulse source for the pulse control circuit on the motion control card; the I/O port circuit consists of two 8255 parallel port chips, whose main function is to output the cutting machine's air source control signal and input the machine tool button signal; the pulse control circuit consists of three 8254 counters, each controlling a servo motor of one axis; the interrupt circuit is designed to provide hardware interrupt signals for the control program; the opto-isolated output/input circuit isolates the industrial PC power supply from the external power supply, reducing interference from the external power supply to the computer. The principle of the motion control card design is shown in Figure 3. [align=center] Figure 3 Schematic diagram of the motion control card[/align] 3 Design of CNC System Software The CNC system software consists of two parts: the first part, the CAD/CAM module, implements the automatic graphic programming function; the second part, the CNC module, implements the cutting machine's motion trajectory and air source control function. The module framework of the two parts is shown in Figure 4. [align=center]Figure 4 System Software Block Diagram[/align] 3.1 Automatic Programming System Design Unlike traditional automatic programming systems, this paper adopts a graphical automatic programming system. During programming, there is no need to edit the part source code. Simply arrange the parts to be cut in the AutoCAD environment, and the system can automatically convert the graphics into CNC code, thus avoiding repetitive information input and improving programming efficiency and reliability. 3.1.1 Editing Part Graphics This module utilizes a localized AutoCAD graphics software. Programmers input and edit graphics in the AutoCAD environment, set the drawing frame size according to the size of the raw steel plate, arrange the parts to be cut within the drawing frame, and add cutting leaders. 3.1.2 Extraction of Graphic Data and Planning of Cutting Path The AutoCAD system provides an interface file with other high-level languages.