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Laser Cutting and Its Processing System Fundamentals
Topic Introduction
To further broaden readers’ understanding of the role and industrial value of lasers and their processing systems in the field of industrial engineering, subsequent content will gradually introduce applications of lasers in other areas. This topic primarily covers the fundamentals of laser cutting and its processing systems. To distinguish from articles on laser welding, articles on laser cutting will use a purple cover, while those on laser welding will continue to use a red cover. Readers may choose content based on their interests. Articles on laser cutting and welding will be updated alternately.
1. Laser Cutting Principles, Characteristics, and Applications
1.1 Principles of Laser Cutting
Laser cutting uses a focused high-power-density laser beam to scan the workpiece surface. Within an extremely short time, the material is locally heated to thousands or even tens of thousands of degrees Celsius, causing the irradiated area to rapidly melt, vaporize, ablate, or reach its ignition point. Simultaneously, a high-speed gas jet coaxial with the beam blows away the molten material, creating a cut. If the blown gas reacts exothermically with the material being cut, this reaction provides additional energy for cutting. The gas also cools the cutting edge, reduces the heat-affected zone, and protects the focusing lens from contamination. Laser cutting is a thermal cutting process. A schematic diagram of the laser cutting principle is shown below:
Whether using a CO₂ laser or an Nd:YAG laser for cutting, the basic principles are essentially the same. In practical applications, a lens installed in the laser cutting head focuses the laser beam onto a very small spot (focal point). The power density at the focal point is extremely high. By adjusting the focal point to the workpiece surface, the material to be cut is melted or vaporized. A schematic diagram of the laser cutting zone is shown below:
The laser cutting process occurs on the surface at the end of the kerf, known as the ablation front. The laser beam and gas flow enter the kerf at this point. Part of the laser energy is absorbed by the ablation front, while part passes through the kerf or is reflected into the kerf space by the ablation front. The ablation front is heated, melted, or vaporized by the absorbed laser energy and the exothermic reactions during cutting, and is then removed by the gas flow. Some heat is conducted into the base material, lost through radiation, or carried away by convective heat transfer via the gas flow.
An important factor in laser cutting is the absorption of incident laser energy at the kerf’s ablation front, which is fundamental for effective laser cutting. Laser absorption depends on the polarization, mode, and convergence angle of the laser beam, as well as the shape and inclination angle of the ablation front, the properties of the material, and its degree of oxidation.
Laser cutting uses a high-energy laser beam to melt or vaporize the material at the kerf and employs a high-speed auxiliary gas jet to blow it away, completing the cut. The power density of laser cutting can reach 10⁴ to 10⁵ W/cm². CO₂ laser beams are commonly used as the laser source, with working powers ranging from 500 to 2,500 W. This power level is lower than that required by many household electric heaters. However, through lenses and mirrors, the laser beam is concentrated into a very small area. This high concentration of energy enables rapid local heating, causing the material to evaporate. Additionally, due to the extreme energy concentration, only a small amount of heat is transferred to other parts of the material, resulting in minimal or no deformation. Laser cutting allows precise cutting of complex-shaped blanks, which require no further processing.
Although high-power CO₂ lasers can cut carbon steel plates up to 25 mm thick, the plate thickness should generally not exceed 10 mm for high-quality cuts.
1.2 Classification of Laser Cutting
Laser cutting can use auxiliary gases to help remove melted or vaporized material, or it can operate without them. Based on the type of auxiliary gas used, laser cutting can be classified into four categories: vaporization cutting, fusion cutting, oxidation-assisted melting cutting, and controlled fracture cutting.
(1) Vaporization Cutting
A high-energy-density laser beam heats the workpiece, rapidly raising the surface temperature to the material’s boiling point within an extremely short time, preventing heat conduction from causing melting. The material begins to vaporize, with some material disappearing as vapor. These vapors are ejected at high speed. During vapor ejection, some material is blown away from the bottom of the kerf by the auxiliary gas stream as ejecta, forming a cut in the material. In the vaporization process, approximately 40% of the material disappears as vapor, while 60% is removed as molten droplets by the gas flow. Since the heat of vaporization is generally large, laser vaporization cutting requires high power and power density. Materials that cannot be melted, such as wood, carbon materials, and certain plastics, are cut using this method. Laser vaporization cutting is mostly used for very thin metal materials and non-metallic materials such as paper, fabric, wood, plastic, and rubber.
(2) Fusion Cutting
The laser beam heats the metal material until it melts. When the power density of the incident laser beam exceeds a certain threshold, evaporation begins inside the material at the irradiated area, forming a hole. Once formed, this small hole acts as a black body, absorbing all incident beam energy. The hole is surrounded by molten metal walls. A non-oxidizing gas (such as Ar, He, N₂) is then blown coaxially with the beam through a nozzle. The strong gas pressure expels the molten metal surrounding the hole. As the workpiece moves, the hole translates synchronously along the cutting direction, forming a kerf. The laser beam continues to irradiate the leading edge of the kerf, and the molten material is continuously or intermittently blown out of the kerf. Laser fusion cutting does not require complete vaporization of the metal, requiring only about one-tenth of the energy needed for vaporization cutting. Laser fusion cutting is mainly used for materials that are difficult to oxidize or for reactive metals, such as stainless steel, titanium, aluminum, and their alloys.
(3) Oxidation-Assisted Melting Cutting
This principle is similar to oxy-acetylene cutting. It uses the laser as a preheating heat source and oxygen or other reactive gases as the cutting gas. The injected gas reacts with the cutting metal, releasing significant oxidation heat, while simultaneously blowing molten oxides and melt from the reaction zone, forming a kerf in the metal. Because the oxidation reaction generates substantial heat during cutting, laser oxygen cutting requires only half the energy of fusion cutting, and the cutting speed is much faster than both vaporization and fusion cutting.
The basic principles of oxidation-assisted melting cutting are as follows:
① Oxygen or other reactive gases are used. Under laser irradiation, the material surface is quickly heated to its ignition temperature and undergoes intense combustion with oxygen, releasing large amounts of heat. This heat creates vapor-filled holes inside the material, surrounded by molten metal walls.
② The combustion material transforms into slag, controlling the rate of oxygen-metal combustion. Higher oxygen flow rates accelerate the combustion reaction and slag removal. However, excessively high oxygen flow rates can cause rapid cooling of the reaction products (metal oxides) at the kerf exit, which negatively affects cutting quality.
③ The oxidation-assisted melting cutting process involves two heat sources: laser irradiation energy and the heat generated by the chemical reaction between oxygen and the metal. When cutting steel, the heat released by the oxidation reaction accounts for approximately 60% of the total energy required for cutting. Compared to inert gases, using oxygen as an auxiliary gas achieves higher cutting speeds.
④ In the oxidation-assisted melting cutting process with two heat sources, if the oxygen combustion rate exceeds the laser beam traverse speed, the kerf becomes wide and rough. Conversely, if the laser beam traverse speed exceeds the oxygen combustion rate, the resulting kerf is narrow and smooth. Laser oxidation-assisted melting cutting is mainly used for cutting steel and is the most widely applied cutting method.
(4) Controlled Fracture Cutting
For brittle materials susceptible to thermal damage, a high-energy-density laser beam scans the surface of the brittle material, causing localized evaporation and forming a small groove. Pressure is then applied, and the laser beam heating enables high-speed, controlled cutting. The brittle material fractures along the groove. The principle of this cutting process is that the laser beam heats a localized area of the brittle material, inducing a steep thermal gradient and severe mechanical deformation, which causes cracks to form. As long as a uniform heating gradient is maintained, the laser beam can guide crack generation and propagation in any desired direction.
Controlled fracture cutting utilizes the steep temperature distribution created by laser scribing to generate localized thermal stress in brittle materials, causing the material to break along the groove. It should be noted that this method is unsuitable for cutting sharp corners or angled edges. Cutting large enclosed shapes is also challenging. Controlled fracture cutting is fast and requires relatively low power; excessive power may cause surface melting and damage the kerf edges. Key control parameters include laser power and spot size.
1.3 Characteristics of Laser Cutting
Compared to other thermal cutting methods, laser cutting offers significant advantages, characterized by high speed and excellent quality. Specific features are summarized as follows:
(1) High Cutting Quality
Due to the small laser spot size, high energy density, and fast cutting speed, laser cutting achieves superior cutting quality. The kerf is narrow, and dimensional accuracy of cut parts can reach ±0.05 mm. The cut surface is smooth and clean, with surface roughness typically ranging from Ra 12.5 to 25 μm. Laser cutting can often serve as the final processing step, with kerfs generally requiring no further finishing before welding, allowing components to be used directly. After laser cutting, the heat-affected zone is very narrow, and the material properties near the kerf remain largely unaffected. Workpiece deformation is minimal, cutting precision is high, and the kerf geometry is favorable, typically exhibiting a regular rectangular cross-section.
Comparison of laser cutting, oxy-acetylene cutting, and plasma cutting methods (cutting material: carbon steel plate):
Cutting Method | Kerf Width (mm) | Heat-Affected Zone Width (mm) | Kerf Shape | Cutting Speed | Equipment Cost |
Laser Cutting | 0.2–0.3 | 0.04–0.06 | Parallel | Fast | High |
Oxy-Acetylene Cutting | 0.9–1.2 | 0.6–1.2 | Relatively Parallel | Slow | Low |
Plasma Cutting | 3.0–4.0 | 0.5–1.0 | Wedge-shaped and Tapered | Fast | Medium-High |
(2) High Cutting Efficiency
Due to the transmission characteristics of lasers, laser cutting machines are typically equipped with multiple CNC worktables, allowing the entire cutting process to be fully numerically controlled. Operation only requires changing the CNC program to accommodate different part shapes, enabling both 2D and 3D cutting.
(3) Fast Cutting Speed
Using a 1.2 kW laser to cut 2 mm thick low-carbon steel achieves a cutting speed of up to 600 cm/min. Cutting 5 mm thick polypropylene resin board reaches a speed of 1,200 cm/min. Using a 2 kW laser to cut 8 mm thick carbon steel achieves a speed of 1.6 m/min, while cutting 2 mm thick stainless steel reaches 3.5 m/min, with a small heat-affected zone and minimal deformation. Material does not require clamping or fixing during laser cutting, saving both fixture costs and auxiliary loading/unloading time.
(4) Clean, Safe, and Pollution-Free
During laser cutting, the cutting torch does not contact the workpiece, eliminating tool wear. Different part shapes require no tool changes—only adjustment of laser output parameters. The laser cutting process produces low noise, minimal vibration, and no pollution, significantly improving operator working conditions.
(5) Wide Range of Cuttable Materials
Compared to oxy-acetylene and plasma cutting, laser cutting can process a wider variety of materials, including metals, non-metals, metal-matrix and non-metal-matrix composites, leather, wood, and fibers. Different materials exhibit varying laser cutting adaptability due to their thermophysical properties and laser absorption rates. The following table shows the laser cutting characteristics of various materials using a CO₂ laser:
Laser Cutting Characteristics of Various Materials
Category | Subcategory | Material | Laser Absorption Capability | Cutting Characteristics |
Metals | – | Au, Ag, Cu, Al | Low laser absorption rate | Generally difficult to process; 1–2 mm thin sheets of Cu and Al can be laser cut |
Metals | – | W, Mo, Cr, Ta, Zr, Ti (high melting point) | High laser absorption rate | Thin sheets can be cut at slow speeds. Ti, Zr, etc., require Ar as auxiliary gas |
Metals | – | Fe, Ni, Pb, Sn | High laser absorption rate | Relatively easy to process |
Non-Metals | Organic Materials | Acrylic, polyethylene, polypropylene, polyester, PTFE | Transparent to white light | Most materials can be cut with low-power lasers. However, these materials are flammable, and cut surfaces may carbonize. Acrylic and PTFE resist carbonization. Nitrogen or dry air is commonly used as auxiliary gas |
Non-Metals | Organic Materials | Leather, wood, fabric, rubber, paper, glass, epoxy resin, phenolic plastic | Opaque to white light | Same as above |
Non-Metals | Inorganic Materials | Glass, fiberglass | High thermal expansion | Glass, ceramics, porcelain, etc., are prone to cracking during or after processing. Quartz glass thinner than 2 mm exhibits good cuttability |
Non-Metals | Inorganic Materials | Ceramics, quartz glass, asbestos, mica, porcelain | Low thermal expansion | Same as above |
Limitations of Laser Cutting: Due to limitations in laser power and equipment size, laser cutting can only handle medium-to-thin plates and tubes. Cutting speed decreases significantly as workpiece thickness increases. Laser cutting equipment is expensive, requiring a substantial initial investment.
In terms of cutting accuracy and kerf surface roughness, CO₂ laser cutting does not surpass electrical discharge machining. Regarding cutting thickness, it cannot match flame or plasma cutting levels. However, the significant advantages mentioned above demonstrate that CO₂ laser cutting has already replaced and continues to replace some traditional cutting methods, particularly for various non-metallic materials. It is a rapidly developing and increasingly widely applied advanced processing method.
1.4 Application Scope of Laser Cutting
In industrial production, laser cutting technology is one of the most widely used laser processing methods, accounting for approximately 60% of all material laser processing applications.
Most laser cutting machines are operated via CNC programs or configured as cutting robots. As a precision processing method, laser cutting can cut almost all materials, including 2D or 3D cutting of thin metal sheets. Laser cutting is widely applied in electrical manufacturing, transportation machinery, petrochemicals, automotive manufacturing, engineering machinery, medical devices, decoration, packaging, and other industries.
In automotive manufacturing, laser cutting of spatial curves such as car sunroof openings has been widely adopted. Volkswagen AG in Germany uses a 500 W laser to cut complex-shaped body sheet metal and various curved parts.
In aerospace, laser cutting technology is primarily used for cutting specialized aviation materials such as titanium alloys, aluminum alloys, nickel alloys, chromium alloys, stainless steel, beryllium oxide, composite materials, plastics, ceramics, and quartz. Aerospace components processed by laser cutting include engine flame tubes, thin-walled titanium alloy casings, aircraft frames, titanium alloy skins, wing stringers, tail wall panels, helicopter main rotors, and space shuttle ceramic insulation tiles.
Laser cutting technology also has broad applications in non-metallic materials. The power required for laser cutting is relatively low; generally, continuous-wave CO₂ lasers below 1 kW are sufficient for cutting thin workpieces. It can cut not only hard and brittle materials such as silicon nitride, ceramics, and quartz but also flexible materials like fabric, paper, plastic sheets, rubber, and leather. For example, laser garment cutting saves 10%–12% of fabric and increases efficiency by more than three times.
The energy density of a laser beam is slightly lower than that of an electron beam, but the cutting capabilities of both are essentially similar. Compared to electron beam cutting, laser cutting can cut metal up to 25 mm thick in atmospheric conditions, using automated cutting equipment at very high speeds. The kerf is very narrow, the kerf angle is nearly vertical, and cut quality is excellent. Table 4.3 compares laser cutting with plasma cutting and oxy-acetylene cutting.Products suitable for CO₂ laser cutting can be broadly categorized into three types:
Category 1: Metal sheet metal parts where mold manufacturing is economically unfeasible, especially parts with complex shapes and small batch sizes, such as low-carbon steel plates up to 12 mm thick, stainless steel plates up to 6 mm thick, and non-metallic materials up to 20 mm thick. This saves mold manufacturing costs and lead times. Typical products cut with CO₂ lasers include elevator structural components, elevator panels, machine tool and grain machinery enclosures, various electrical cabinets and switchgear, textile machinery parts, engineering machinery structural components, and large motor silicon steel sheets. 3D spatial curve cutting is also used in automotive and aerospace industries.
Category 2: Patterns, logos, and lettering made of stainless steel (typically ≤3 mm thick) or non-metallic materials (typically ≤20 mm thick) for decoration, advertising, and service industries. Examples include patterns for art photo albums, company and institutional logos, hotel and shopping mall signage, and various text displays at stations and public venues.
Category 3: Special parts requiring uniform kerfs. The most common example is die boards used in packaging and printing industries. Grooves 0.7–0.8 mm wide are cut into 20 mm thick wooden templates, into which blades are embedded. These templates are mounted on die-cutting machines to cut pre-printed packaging boxes. Another recent application in China is oil screen pipes. To prevent sand from entering oil pumps, uniform kerfs 0.3 mm wide are cut into alloy steel pipes with wall thicknesses of 6–9 mm, with perforation hole diameters not exceeding 0.3 mm.
From the perspective of production unit types, one category includes large and medium-sized manufacturing enterprises producing products requiring extensive sheet metal blanking and cutting, possessing strong economic and technical capabilities. The other category includes job shops specializing in outsourced laser processing services without proprietary products. These shops meet the processing needs of small and medium-sized enterprises and play a demonstrative role in promoting laser cutting technology. In the 1980s, Chinese laser processing stations primarily engaged in laser heat treatment. From the 1990s onward, laser cutting gradually increased. In recent years, more and more enterprises have adopted CO₂ laser cutting technology.
Beyond the applications mentioned above, laser cutting continues to expand into new areas:
① Using 3D laser cutting systems or industrial robots to cut spatial curves, developing various 3D cutting software to accelerate the process from drawing to part cutting.
② To improve productivity, developing specialized cutting systems, material handling systems, and linear motor drive systems. Current cutting system speeds have exceeded 100 m/min.
③ To expand applications in engineering machinery and shipbuilding, cutting thickness for low-carbon steel plates has exceeded 30 mm. Research specifically focuses on nitrogen-assisted cutting of low-carbon steel plates to improve kerf quality for thick plates.
Expanding the application fields of CO₂ laser cutting and solving technical challenges in new applications remain important tasks for engineers and technicians.
1.5 Laser Cutting of Different Metal Materials
(1) General Considerations for Metal Materials
Although almost all metal materials exhibit high reflectivity to infrared wavelengths at room temperature, CO₂ lasers emitting far-infrared beams (10.6 μm) are successfully used for cutting many metals. Metal materials have poor absorption of 10.6 μm laser beams, with initial absorption rates of only 0.5%–10%. However, when metals reach a molten state, their absorption rates increase sharply, typically reaching 60%–80%.
(2) Carbon Steel
Laser cutting of carbon steel plates can achieve thicknesses up to 25 mm. Using oxidation-assisted melting cutting, kerf widths can be controlled within satisfactory limits. Thin plates can achieve kerf widths as narrow as approximately 0.1 mm.
(3) Alloy Steel
Most alloy structural steels and alloy tool steels can achieve good cut edge quality using laser cutting. When oxygen is used as the processing gas, the cut edges may experience slight oxidation. For plates up to 4 mm thick, nitrogen can be used as the processing gas for high-pressure cutting, preventing edge oxidation. For plates over 10 mm thick, special polar plates and surface oil coating can yield good results. For high-strength steels, proper parameter control produces straight, slag-free cut edges. However, tungsten-containing high-speed tool steels and hot-work die steels are prone to erosion and slag adhesion during laser cutting.
(4) Stainless Steel
For industries primarily dealing with thin stainless steel sheets, laser cutting is an effective processing method. By strictly controlling laser cutting heat input, the width of the heat-affected zone at the cut edge can be limited, preserving stainless steel’s excellent corrosion resistance. Oxygen can be used when edge oxidation is acceptable. Nitrogen produces oxidation-free, burr-free edges requiring no post-processing. Applying a thin oil film to the plate surface improves piercing performance without reducing processing quality.
(5) Aluminum and Its Alloys
Laser cutting of aluminum and its alloys operates under the fusion cutting mechanism. Auxiliary gases primarily remove molten products from the cutting zone, typically achieving good kerf quality. For certain aluminum alloys, attention must be paid to preventing intergranular microcracks on the kerf surface. Despite aluminum alloys’ high reflectivity and excellent thermal conductivity, laser cutting can process aluminum up to 6 mm thick, depending on alloy type and laser power. Oxygen produces a rough, hard cut surface, while nitrogen yields a smooth surface. Pure aluminum is very difficult to cut and requires a “reflection absorption” device in the system; otherwise, reflection can damage optical components.
(6) Copper and Its Alloys
Pure copper, due to its extremely high reflectivity, is essentially unsuitable for CO₂ laser cutting. Brass (copper alloy) cutting requires higher laser power, using air or oxygen as auxiliary gas, and can only cut thin sheets. Both pure copper and brass exhibit high reflectivity and excellent thermal conductivity. Brass plates up to 1 mm thick can be cut with nitrogen; copper plates up to 2 mm thick can be cut using oxygen as the processing gas. Cutting pure copper and brass requires a “reflection absorption” device; otherwise, reflection damages optical components.
(7) Titanium and Its Alloys
Pure titanium couples well with focused laser beam energy. Using oxygen as auxiliary gas produces intense chemical reactions and fast cutting speeds but may create an oxide layer at the cut edge and potentially cause burning. Using air as auxiliary gas ensures cutting quality. Titanium alloys commonly used in aircraft manufacturing exhibit good laser cutting quality. Although slight slag may appear at the bottom of the kerf, it is easily removed. Titanium plates are cut using xenon or nitrogen as processing gases.
(8) Nickel-Based Alloys
Also known as superalloys, many varieties exist, most of which can undergo laser oxidation-assisted melting cutting with good kerf quality. Laser cutting equipment can cut stainless steel plates up to 4 mm thick. Adding oxygen to the laser beam enables cutting of carbon steel plates up to 25 mm thick, though a thin oxide film forms on the cut surface. Maximum cutting thickness can reach 30 mm, but dimensional tolerances of cut parts are larger.
Material absorption of the laser beam plays an important role in the initial heating stage. Once a small hole forms inside the workpiece, the black-body effect of the hole causes the material to absorb nearly 100% of the beam energy. In practice, surface condition effects on beam absorption can be exploited to improve cutting performance. For example, applying an absorbing coating to aluminum surfaces significantly increases cutting speed.
Room-Temperature Absorption Rates of Different Metals for Different Laser Wavelengths
Metal | Absorption Rate (20°C) – Ar (0.5 μm) | Absorption Rate (20°C) – Ruby (0.7 μm) | Absorption Rate (20°C) – Nd:YAG (1.06 μm) | Absorption Rate (20°C) – CO₂ (10.6 μm) |
Aluminum | 0.09 | 0.11 | 0.08 | 0.019 |
Copper | 0.56 | 0.17 | 0.10 | 0.015 |
Gold | 0.58 | 0.07 | — | 0.107 |
Iridium | 0.36 | 0.30 | 0.22 | — |
Iron | 0.68 | 0.64 | — | 0.035 |
Lead | 0.38 | 0.35 | 0.16 | 0.045 |
Molybdenum | 0.48 | 0.48 | 0.40 | 0.027 |
Nickel | 0.40 | 0.32 | 0.26 | 0.030 |
Niobium | 0.58 | 0.50 | 0.32 | 0.035 |
Platinum | 0.21 | 0.15 | 0.11 | — |
Rhenium | 0.47 | 0.44 | 0.28 | — |
Silver | 0.05 | 0.04 | 0.04 | 0.014 |
Tantalum | 0.65 | 0.50 | 0.18 | 0.144 |
Tin | 0.20 | 0.18 | 0.19 | 0.034 |
Titanium | 0.48 | 0.45 | 0.42 | 0.080 |
Tungsten | 0.55 | 0.50 | 0.41 | 0.026 |
Zinc | — | — | — | — |
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