Cutting Process

By Rahmat Azis Nabawi

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The cutting process is one of the most critical stages in steel fabrication, during which steel profiles and steel plates are cut according to the cutting lines established during the marking process. This operation plays a significant role in ensuring the dimensional accuracy of fabricated components, which directly influences the quality, fit, and structural performance of the final product.

Various cutting methods are employed in steel fabrication, each offering specific advantages depending on the material type, plate thickness, production requirements, and desired cutting precision. Selecting an appropriate cutting technique is essential for achieving high-quality fabrication results while improving productivity, minimizing material waste, and ensuring dimensional accuracy.

The most commonly used cutting methods include Hydraulic Shearing, Oxy-Fuel Flame Cutting, and Computer Numerical Control (CNC) Cutting. Each method has unique operating principles and applications, allowing fabricators to produce steel components efficiently while maintaining the required quality standards.

Hydraulic Shearing

Hydraulic shearing is one of the most widely used mechanical cutting methods in steel fabrication. This process utilizes hydraulic power generated by a hydraulic pump driven by an electric motor. Modern hydraulic shearing machines are equipped with programmable hydraulic control systems, allowing operators to perform cutting operations more efficiently, accurately, and safely.

Hydraulic shearing machines are capable of cutting steel plates with thicknesses of up to approximately 20 mm. Their operating principle is similar to that of a conventional guillotine shear. However, unlike conventional systems, the upper cutting blade is driven by two double-acting hydraulic cylinders, providing greater cutting force and improved operational stability.

The hydraulic actuators are installed on both sides of the machine and are directly connected to the upper blade. The machine also employs hydraulically operated back gauges (stoppers) to position the workpiece accurately before cutting. Multiple stoppers are arranged along the cutting area, allowing precise positioning even when cutting relatively narrow steel plates. This design improves dimensional accuracy while increasing production efficiency.

Figure 1. Hydraulic plate shearing machine.

Oxy-Fuel Flame Cutting

Oxy-fuel flame cutting is one of the most widely used thermal cutting processes in steel fabrication. The cutting action occurs through a chemical reaction between oxygen and heated steel. Before cutting begins, the workpiece is preheated using an oxy-fuel flame until it reaches a temperature of approximately 800–900°C. Once the required temperature is achieved, a high-pressure oxygen jet is directed onto the heated area. The oxygen reacts with the hot steel, producing molten iron oxide, which is then expelled by the oxygen stream to form the cutting groove.

Because iron oxide has a lower melting point than the base metal, it melts more readily and is blown away during the cutting process. This reaction enables the steel to be cut efficiently while maintaining acceptable dimensional accuracy. Oxy-fuel cutting is particularly suitable for carbon steel and thick steel plates commonly used in structural fabrication.

The quality of an oxy-fuel cut is generally evaluated based on several characteristics, including:

• A narrow cutting kerf.
• A smooth cut surface.
• Slag that can be removed easily.
• Slightly rounded upper edges of the cut.

According to the Japanese Welding Engineering Society (WES-2801), the surface quality of gas-cut steel depends on several factors, including oxygen purity, flame quality, cutting equipment characteristics, and appropriate cutting parameters. Proper adjustment of these variables is essential to obtain clean and accurate cuts.

Figure 2. Cross-section of an oxy-fuel cut (Harsono & Toshie, 1981).

Figure 3. Manual oxy-fuel flame cutting process.

Oxy-Fuel Cutting Procedure

To achieve a clean, accurate, and safe cut, the oxy-fuel cutting process should be performed according to the recommended operating procedure. Proper equipment setup and correct cutting techniques help improve cut quality while minimizing defects and material waste.

1. Mark the intended cutting line on the workpiece during the marking process.
2. Select the appropriate cutting tip according to the thickness of the steel plate.
3. Adjust the acetylene and oxygen gas pressures based on the selected cutting tip and material thickness.
4. Open both the oxygen and acetylene gas supply valves.
5. Ignite the torch by opening the acetylene valve first, followed gradually by the oxygen valve until a neutral flame is obtained.
6. Preheat the workpiece by positioning the flame approximately 2–4 mm above the steel surface.
7. Once the steel reaches a yellowish-red temperature, indicating that it is approaching its ignition temperature, open the cutting oxygen valve.
8. Move the cutting torch steadily along the previously marked cutting line while maintaining a constant travel speed.
9. Maintain a consistent torch-to-workpiece distance throughout the cutting process to ensure a smooth and uniform cut.

Oxy-fuel cutting equipment is generally classified into low-pressure and medium-pressure systems. Depending on production requirements, cutting operations may be performed manually or automatically. In automated cutting, the torch is mounted on a motor-driven carriage that follows the programmed cutting path, providing higher accuracy, improved productivity, and more consistent cutting quality.

Figure 4. Automatic oxy-fuel cutting using a Quicky cutting machine.

CNC Cutting

Computer Numerical Control (CNC) cutting is an automated cutting process that utilizes a computer-based control system to execute programmed cutting operations with high precision. CNC cutting machines interpret digital instructions (G-code and M-code) to control the movement of the cutting torch and produce components according to the specified design dimensions. Compared with manual cutting, CNC cutting provides greater accuracy, repeatability, productivity, and material utilization.

Modern CNC cutting systems are capable of performing different thermal cutting processes depending on the application requirements. The two most common cutting technologies integrated into CNC machines are oxy-fuel flame cutting and plasma arc cutting. These technologies enable manufacturers to produce complex shapes and high-quality cuts while minimizing production time and material waste.

Figure 5. CNC cutting machine.

Plasma Arc Cutting

Plasma arc cutting is one of the most advanced thermal cutting technologies used in modern steel fabrication. Unlike oxy-fuel cutting, which relies on the oxidation of steel, plasma cutting employs a high-temperature, high-velocity plasma jet to melt and remove metal along the cutting path. This process produces narrow kerfs, smooth cut surfaces, and excellent dimensional accuracy.

One of the major advantages of plasma arc cutting is its ability to cut electrically conductive metals that cannot be processed efficiently using conventional oxy-fuel cutting. These materials include stainless steel, aluminum alloys, copper alloys, and various other non-ferrous metals. Plasma cutting also offers significantly higher cutting speeds and produces a smaller heat-affected zone, making it particularly suitable for precision fabrication and high-productivity manufacturing.

Because of its speed, cutting quality, and versatility, plasma arc cutting has become one of the preferred cutting methods in modern fabrication industries, especially for applications requiring high precision, complex geometries, and efficient production processes.

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References

1. Harsono, W., & Toshie, O. (1981). Teknologi Pengelasan Logam. Jakarta: Pradnya Paramita.
2. Japanese Welding Engineering Society. (1980). WES 2801: Standard for Gas Cutting Surface Quality.
3. Jeffus, L. F. (2021). Welding: Principles and Applications (9th ed.). Cengage Learning.
4. American Welding Society. (2020). AWS Welding Handbook. Miami, FL: American Welding Society.
5. ASM International. (1993). ASM Handbook, Volume 6: Welding, Brazing, and Soldering. Materials Park, OH: ASM International.