Fundamentals of Laser Cutting and Its Processing System — Laser Cutting Equipment
II. Composition of Laser Cutting Equipment
2.1 Components and Working Principle of Laser Cutting Machine
A laser cutting machine consists of a laser emitter, cutting head, beam transmission assembly, machine tool worktable, numerical control (NC) system, computer (hardware and software), chiller, shielding gas cylinder, dust collector, and air dryer.
-
Laser Generator
The laser generator is a device that produces laser light sources. For laser cutting applications, most machines adopt CO₂ gas lasers which feature high electro-optical conversion efficiency and high power output, except for a few cases where YAG solid-state lasers are used. Not all lasers are suitable for cutting, as laser cutting imposes stringent requirements on beam quality.
-
Cutting Head
It mainly comprises components such as a nozzle, focusing lens, and focus tracking system.
The cutting head drive device is used to drive the cutting head to move along the Z-axis according to preset programs. It consists of a servo motor and transmission parts like lead screws or gears.
(1) Nozzle: There are three main types of nozzles: parallel type, convergent type, and conical type.
(2) Focusing Lens: To perform cutting using laser beam energy, the original beam emitted by the laser must be focused through a lens to form a light spot with high energy density. Medium and long focal length lenses are suitable for thick plate cutting and have lower requirements for the spacing stability of the tracking system. Short focal length lenses are only suitable for cutting thin plates below 3 mm; they have strict requirements for the spacing stability of the tracking system but can significantly reduce the required laser output power.
(3) Tracking System: The focus tracking system of a laser cutting machine generally consists of a focusing cutting head and a tracking sensor system. The cutting head integrates functions of beam guiding and focusing, water cooling, gas blowing, and mechanical adjustment.
The sensor is composed of sensing elements and an amplification control unit. Tracking systems vary completely depending on the type of sensing elements. There are two main types available: one is the capacitive sensor tracking system, also known as the non-contact tracking system; the other is the inductive sensor tracking system, also referred to as the contact tracking system.
-
Beam Transmission Assembly
External Optical Path: Reflective mirrors are used to guide the laser beam in the desired direction. To prevent malfunctions in the beam path, all reflective mirrors are protected by shields, and clean positive-pressure shielding gas is introduced to keep the mirrors free from contamination. A high-performance lens can focus a non-divergent beam into an infinitely small spot. A lens with a 5.0-inch focal length is commonly used, while a 7.5-inch lens is only applicable for cutting materials thicker than 12 mm.
-
Machine Tool Worktable
Main Machine Body: The machine tool section of the laser cutting machine is the mechanical part that realizes the movement of X, Y, and Z axes, including the cutting work platform.
-
Numerical Control System
The NC system controls the machine tool to achieve X, Y, Z-axis movements and regulates the output power of the laser at the same time.
-
Cooling System
Chiller Unit: It is used to cool the laser generator. A laser is a device that converts electrical energy into light energy. For example, the conversion efficiency of a CO₂ gas laser is generally 20%, with the remaining energy converted into heat. Cooling water removes excess heat to maintain the normal operation of the laser generator. The chiller unit also cools the external optical path mirrors and focusing lenses of the machine tool, ensuring stable beam transmission quality and effectively preventing lens deformation or cracking due to overheating.
-
Gas Cylinders
Gas cylinders include working medium cylinders and auxiliary gas cylinders for the laser cutting machine, which are used to supplement industrial gases for laser oscillation and supply auxiliary gases for the cutting head.
-
Dust Removal System
It extracts smoke and dust generated during processing and conducts filtration treatment to ensure that exhaust gas emissions meet environmental protection standards.
-
Air Cooling Dryer & Filter
It supplies clean, dry air to the laser generator and beam path, maintaining the normal operation of the beam path and reflective mirrors.
2.2 Cutting Torch for Laser Cutting
The structural diagram of a cutting torch for laser cutting is shown below. It is mainly composed of a torch body, focusing lens, reflective mirror, and auxiliary gas nozzle. During laser cutting, the cutting torch must meet the following requirements:
① The torch can eject a sufficient gas flow.
② The ejection direction of the gas inside the torch must be coaxial with the optical axis of the reflective mirror.
③ The focal length of the torch can be easily adjusted.
④ During cutting, metal vapor and splashes from the cut metal must not damage the reflective mirror.
The movement of the cutting torch is adjusted by an NC motion system. There are three scenarios for the relative movement between the cutting torch and the workpiece:
① The torch remains stationary while the workpiece moves via the worktable — mainly suitable for small-sized workpieces.
② The workpiece remains stationary while the torch moves.
③ Both the torch and the worktable move simultaneously.
2.2.1 Cutting Head
The laser cutting head is located at the end of the beam transmission system, consisting of a focusing lens and a cutting nozzle.
Focusing lenses are mainly classified by focal length. Most laser cutting equipment is equipped with several cutting heads with different focal lengths. Taking CO₂ laser cutting as an example, common focal lengths are 127 mm (5 in) and 190 mm (7.5 in). A short focal length lens produces a small focal spot and short focal depth, which is conducive to reducing the kerf width and achieving finer cuts. A long focal length lens yields a larger focal spot and longer focal depth. Compared with short focal length lenses, long focal length lenses can provide a focused beam with laser energy density sufficient for material processing near the focal point. Therefore, short focal length lenses are mostly used for precision cutting of thin plates, while long focal length lenses are required for thicker materials to obtain adequate focal depth, ensuring minimal variation in spot diameter and sufficient power density within the cutting thickness range.
Focusing lenses are used to focus the parallel laser beam incident into the cutting torch, achieving a smaller spot size and higher power density. Lenses are made of materials that can transmit the laser wavelength. Optical glass is commonly used for solid-state lasers, while materials such as ZnSe, GaAs, and Ge are adopted for CO₂ gas lasers (since ordinary glass is not transparent to CO₂ laser beams), among which ZnSe is the most widely used.
For laser cutting, minimizing the focal spot diameter is desirable to increase power density and enable high-speed cutting. However, a shorter lens focal length results in a smaller focal depth, making it difficult to achieve a perpendicular cut surface when cutting thick plates. In addition, a shorter focal length reduces the distance between the lens and the workpiece, increasing the risk of the lens being contaminated by molten splashes during cutting and affecting normal operation. Therefore, the appropriate focal length should be determined comprehensively based on factors such as cutting thickness and cutting quality requirements.
2.2.2 Reflective Mirror
The function of the reflective mirror is to change the direction of the beam emitted from the laser. For beams from solid-state lasers, reflective mirrors made of optical glass can be used. In contrast, reflective mirrors in CO₂ gas laser cutting devices are usually made of copper or metals with high reflectivity. To prevent damage caused by overheating from laser irradiation during operation, reflective mirrors are typically cooled with water.
2.2.3 Nozzle
The nozzle is used to spray auxiliary gas into the cutting zone, and its structure has a certain impact on cutting efficiency and quality. Figure 4.11 shows common nozzle shapes for laser cutting; the nozzle orifice shapes include cylindrical, conical, and converging-diverging types.
The selection of the nozzle is generally determined through tests based on the material and thickness of the workpiece, and the pressure of the auxiliary gas. Laser cutting usually adopts coaxial nozzles (where the gas flow is coaxial with the optical axis). If the gas flow and the laser beam are not coaxial, excessive splashing is likely to occur during cutting. The inner wall of the nozzle orifice should be smooth to ensure unobstructed gas flow and avoid turbulence that may affect kerf quality. To ensure cutting stability, the distance between the nozzle end face and the workpiece surface should be minimized, typically ranging from 0.5 mm to 2.0 mm. The nozzle orifice diameter must allow the laser beam to pass through smoothly, preventing the beam from touching the inner wall of the orifice. The smaller the orifice diameter, the more difficult it is to collimate the beam. For a given auxiliary gas pressure, there is an optimal range of nozzle orifice diameters. An excessively small or large orifice will hinder the removal of molten products from the kerf and affect the cutting speed.
The influence of nozzle orifice diameter on cutting speed under fixed laser power and auxiliary gas pressure is shown in Figures 4.12 and 4.13. It can be seen that there is an optimal nozzle orifice diameter that achieves the maximum cutting speed. This optimal value is approximately 1.5 mm regardless of whether oxygen or argon is used as the auxiliary gas.
Tests on laser cutting of hard alloys (which are difficult to cut) show that the optimal nozzle orifice diameter is very close to the above results, as illustrated in Figure 4.14. The nozzle orifice diameter also affects the kerf width and heat-affected zone (HAZ) width. As shown in Figure 4.15, with the increase of nozzle orifice diameter, the kerf width increases while the HAZ width narrows. The main reason for the narrowing of the HAZ is the enhanced cooling effect of the auxiliary gas flow on the base material in the cutting zone.
2.3 Parameters of Laser Cutting Equipment
2.3.1 Torch-driven Cutting Equipment
In torch-driven cutting equipment, the cutting torch is mounted on a movable gantry and moves horizontally along the gantry beam (Y-axis). The gantry drives the torch to move along the X-axis, while the workpiece is fixed on the worktable. Since the laser and the cutting torch are arranged separately, the laser transmission characteristics, parallelism along the beam scanning direction, and stability of the reflective mirrors are all affected during the cutting process.
Torch-driven cutting equipment can process large-sized workpieces. It occupies a relatively small floor area for the cutting production zone and can be easily integrated with other equipment to form a production line. However, its positioning accuracy is only ±0.04 mm.
The typical structure of torch-driven cutting equipment is shown in Figure 4.19. A continuous-wave CO₂ laser cutting machine is adopted, with the distance from the laser to the cutting torch being 18 m. To ensure that the change in beam diameter over this transmission distance does not interfere with cutting operations, the combination of oscillator mirrors must be carefully designed.
The main technical parameters of torch-driven cutting equipment are as follows:
- Laser Output Power: 1.5 kW (single-mode), 3 kW (multi-mode)
- Torch Stroke: X-axis 6.2 m, Y-axis 2.6 m
- Driving Speed: 0–10 m/min (adjustable)
- Torch Z-axis Floating Stroke: 150 mm
- Torch Z-axis Adjustment Speed: 300 mm/min
- Maximum Size of Processed Steel Plate: 12 mm × 2400 mm × 6000 mm
- Control System: Integrated NC Control Mode
2.3.2 XY Table-driven Cutting Equipment
In the XY table-driven cutting equipment, the cutting torch is fixed on the frame, and the workpiece is placed on the cutting table. The cutting table moves along the X and Y axes according to NC commands, with an adjustable driving speed typically ranging from 0–1 m/min or 0–5 m/min. Since the cutting torch remains stationary relative to the workpiece, it minimizes the impact on laser beam alignment and centering during the cutting process, ensuring uniform and stable cutting performance. When equipped with a small-sized cutting table featuring high mechanical precision, the machine achieves a positioning accuracy of ±0.01 mm and excellent cutting precision, making it particularly suitable for the precision cutting of small components. Additionally, larger cutting tables with an X-axis stroke of 2300–2400 mm and Y-axis stroke of 1200–1300 mm are available for processing large-sized workpieces.
The main technical parameters of the XY table-driven cutting equipment are as follows:
- Laser Source: CO₂ gas laser (semi-closed straight-tube type)
- Laser Power Supply: Input voltage 200 VAC; Output voltage 0–30 kV; Maximum output current 100 mA
- Laser Output Power: 550 W
- Cutting Table Stroke: X-axis 2300 mm, Y-axis 1300 mm
- Cutting Table Driving Speed (Step-adjustable): 0.4–5.0 m/min, 0.2–2.5 m/min, 0.1–1.3 m/min, 0.05–0.6 m/min
- Torch Z-axis Floating Stroke: 180 mm
- Maximum Size of Processed Plate: 6 mm × 1300 mm × 2300 mm
- Control System: Numerical Control (NC) Mode
2.3.3 Dual-driven Cutting Equipment (Torch & Table)
The dual-driven cutting equipment (torch & table) falls between the torch-driven and XY table-driven cutting machines in design. The cutting torch is mounted on a gantry and moves horizontally along the gantry beam (Y-axis), while the cutting table is driven longitudinally. This hybrid design combines the advantages of high cutting precision and space-saving efficiency. With a positioning accuracy of ±0.01 mm and an adjustable cutting speed range of 0–20 m/min, it is one of the most widely used cutting machines on the market. Larger models of this machine offer a Y-axis stroke of 2000 mm and an X-axis stroke of 6000 mm, enabling the cutting of large-sized workpieces.
The laser oscillator is mounted on the gantry alongside the cutting torch. This configuration delivers exceptional precision when cutting circular holes. The machine also boasts high production efficiency: it can cut 46 circular holes (10 mm in diameter) per minute on a 1 mm-thick steel plate.
2.3.4 Integrated Cutting Equipment
In an integrated cutting machine, the laser source is installed on the frame and moves longitudinally with it, while the cutting torch is integrated with its drive mechanism to move horizontally along the frame beam. The machine uses numerical control to cut various shaped components. To compensate for the optical path length variation caused by the horizontal movement of the cutting torch, an optical path length adjustment module is usually equipped. This module ensures a homogeneous laser beam within the cutting area and maintains consistent cutting surface quality.
Post time:
Dec-17-2025
