In modern manufacturing, the cutting of large plate materials (typically referring to metal plates with a width ≥ 6m and a thickness ≥ 10mm) is a fundamental process, facing core demands for low cost, large thickness, and compatibility with various common metals. Flame cutting, as a traditional and mature thermal cutting technology, remains the mainstream solution for cutting large carbon steel and low alloy steel plates due to its advantages of low equipment investment, simple operation, and ability to cut thick plates. Its core principle is to generate a high-temperature flame by mixing combustible gas and oxygen, locally heating the plate to its ignition point, and then using high-pressure oxygen to blow away the molten slag, achieving continuous cutting of the plate. It is widely used in many heavy industrial fields such as steel structures, shipbuilding, engineering machinery, and metallurgical processing, and is especially suitable for mass production scenarios where cutting precision requirements are not extremely high and high cost-effectiveness is pursued.
The core advantages of flame cutting for large sheet metal are concentrated in three points: First, it offers controllable costs and outstanding cutting capabilities for thick sheets. It requires no high-power laser source, resulting in low equipment purchase and maintenance costs. It can stably cut carbon steel and low-alloy steel with thicknesses of 10–150 mm, and some specialized equipment can cut plates thicker than 200 mm, making it the most economical solution for cutting thick metal sheets currently available. Second, it boasts strong equipment adaptability and a low operating threshold. Various structures such as gantry and floor-mounted types are available, and the cutting width can be flexibly expanded to 6–60 m. It supports one-time cutting of entire sheets and has low requirements for the surface finish of the sheet metal; minor rust and oxide scale do not affect cutting. Operators can learn to operate the equipment after simple training. Third, it offers high flexibility. Cutting speed and flame intensity can be adjusted according to processing needs, adapting to sheets of different thicknesses and materials, balancing mass production and customized processing requirements, giving it an irreplaceable position in the heavy industry sector.
Standard Process Flow
A standard flame cutting process for large sheet metal must follow a complete flow: “Pre-treatment—Programming and Layout—Equipment Preparation and Trial Cutting—Formal Cutting—Post-treatment.” Each step is closely linked, with key parameters such as heating temperature and oxygen pressure being crucial as they directly impact cutting quality and efficiency.
Sheet Metal Pre-treatment: Although flame cutting has relatively low requirements for sheet metal surface finish, basic pre-treatment is still indispensable. Severe oil stains, thick rust, and debris must be removed from the sheet metal surface to prevent oil from affecting flame temperature during combustion and rust from hindering slag removal. For severely deformed sheets, leveling is required (flatness ≤ 1mm/m) to prevent displacement and cut deviation during cutting. Finally, mechanical clamping or heavy-load positioning is used to ensure stability during the cutting process.
Programming and Layout: This is key to improving efficiency and reducing material waste. Operators import CAD drawings and use nested layout software to rationally plan the graphic layout, prioritizing large-sized components and filling in small-sized parts to maximize material utilization. Simultaneously, a scientific cutting sequence is set (inside to outside, short to long, small to large), allowing shrinkage allowance for thick plates and adjusting corner cutting speeds to avoid thermal deformation, preparing for subsequent cutting.
Equipment Preparation and Trial Cutting: A prerequisite for safe and stable cutting. Before formal cutting, a comprehensive inspection of the equipment status is conducted: verifying the pressure and purity of combustible gases (acetylene, propane, etc.) and oxygen to ensure no leaks and a stable supply; clearing any blockages from the cutting nozzle; and checking the integrity of the torch, gantry, guide rails, and safety devices. A trial cut is then performed using scrap material of the same material and thickness to verify that the flame temperature, cut quality, dimensional accuracy, and thermal deformation meet standards. Only after passing the test can formal cutting begin.
Formal Cutting (Core Process): Focusing on four key control points. First, preheat the cutting torch. Position the torch at the cutting point and preheat to the ignition point of the sheet metal (800–1000℃ for carbon steel) using a neutral or slightly oxidizing flame. Adjust the preheating time according to the sheet thickness. Second, adjust the flame. Avoid using a carburizing flame to prevent carbonization and cracking of the cut. Third, adjust the oxygen pressure according to the thickness (0.3–0.5MPa for 10–30mm, 0.5–0.8MPa for 30–100mm). Excessive pressure will result in an overly wide cut and too many burrs, while insufficient pressure will prevent complete penetration. Fourth, adjust the cutting speed. The thicker the sheet, the slower the speed (150–200mm/min for 20mm thick carbon steel, 50–80mm/min for 80mm thick carbon steel). Maintain a vertical torch and a 5–10mm distance between the nozzle and the sheet metal.
Post-cutting treatment: Ensure product meets standards. Use lifting equipment or manual unloading to avoid bumps and deformation; clean burrs and slag inclusions from the cut edges (through grinding and air gouging), and inspect and repair defects such as cracks and delamination; perform dimensional checks on the cut parts to verify deviations from the drawings, and finally apply rust prevention treatment to prevent the cut edges from rusting.
Key Considerations for Equipment Selection
Appropriate equipment selection is a prerequisite for ensuring effective flame cutting and improving production efficiency. The following points should be considered in conjunction with the needs of cutting large sheet metal:
Equipment Structure: Prioritize gantry-type (high rigidity and stability, suitable for batch processing in fixed locations) or floor-mounted type (flexible, adaptable to ultra-large sheet metal, can be spliced from 6m onwards);
Cutting Torch and Nozzle: Select heavy-duty cutting torches and adjustable nozzles to adapt to cutting sheet metal of different thicknesses;
Gas Supply System: Equipped with stable pressure reducing valves, flow meters, and gas leak alarms to ensure a safe and stable gas supply;
Cutting Bed: Adopt heavy-duty welding and aging treatment to resist thermal deformation and ensure long-term processing accuracy;
Auxiliary Configuration: For batch production scenarios, automatic loading and unloading, waste sorting systems, and CNC systems can be added to improve automation and cutting accuracy, and adapt to the processing of complex components.
Frequently Asked Questions
While flame cutting is a mature technology, various problems can arise in practical applications, requiring targeted solutions to ensure cutting quality:
Incomplete cutting of thick plates, severe slag inclusions: This is often caused by insufficient preheating, low oxygen pressure, nozzle blockage, or excessive cutting speed. Solutions include extending preheating time, increasing oxygen pressure, cleaning the nozzle, and reducing cutting speed.
Excessively wide kerfs and excessive edge burrs: This is related to excessively high oxygen pressure, slow cutting speed, and improper nozzle-to-plate distance. Adjustments include adjusting oxygen pressure, increasing cutting speed, and correcting nozzle distance.
Severe thermal deformation of large plates: This is caused by an unreasonable cutting sequence, concentrated heat input, and unleveled plates. Solutions include optimizing the cutting sequence, using intermittent cutting, allowing for shrinkage allowance, and pre-leveling the plate.
Cracks in the kerf: This is mainly caused by excessively high carbon content in the plate, insufficient preheating, and inadequate cooling after cutting. Solutions include selecting appropriate flame parameters, extending preheating time, and slow cooling after cutting.
Unstable Flame: Caused by gas pressure fluctuations, insufficient gas purity, or nozzle blockage. This requires checking the gas supply system, replacing with qualified gas, and cleaning the nozzle.
Application Areas
Flame cutting of large sheet metal is widely used in various heavy industries, especially suitable for applications requiring thick, low-cost, and rough machining: steel structure construction (10–80mm thick carbon steel plate beams, trusses, etc.), shipbuilding (30–150mm thick low-alloy steel plate ship plates, bulkheads, etc.), engineering machinery (20–100mm thick structural components), metallurgical processing (steel billet and plate cutting), and power equipment (rough machining of thick plates for boilers and pressure vessels). It is an indispensable basic cutting process in heavy industrial production.
Overall, flame cutting of large sheet metal occupies an important position in heavy industry due to its advantages of low cost, strong cutting capability for large thicknesses, ease of operation, and wide adaptability. It is the preferred solution for rough machining of large carbon steel and low-alloy steel plates. Its equipment investment and maintenance costs are far lower than laser cutting, enabling the cutting of plates thicker than 10–200mm, and adapting to the processing of plates of different sizes and shapes. With the upgrading of CNC technology, its automation level and cutting accuracy are continuously optimized, further expanding its application scenarios. Although it has limitations such as lower cutting accuracy than laser cutting, a larger heat-affected zone, and unsuitability for materials like stainless steel, it still has irreplaceable value in large-thickness cutting scenarios where precision requirements are not extreme and high cost-effectiveness is prioritized. In the future, combined with energy-saving, environmentally friendly, automated, and intelligent technologies, flame cutting will achieve more efficient, environmentally friendly, and precise large-plate cutting, providing support for the high-quality development of the manufacturing industry.
