Laser Cutting Essentials: Optimal Parameters Guide

The main parameters for laser cutting include laser cutting power and speed, lens focal length and focal point position, nozzle shape and distance from the nozzle to the workpiece surface, as well as the type and pressure of the assist gas.

Laser Cutting Power and Cutting Speed

Cutting speed is a crucial parameter for cutting. During cutting, the cutting speed needs to be determined based on the laser power, gas pressure, and workpiece thickness. It increases with the increase in laser power and gas pressure, and decreases with the increase in workpiece thickness. For instance, when cutting a 6mm carbon steel plate, the cutting speed is 2.5m/min, while for a 12mm carbon steel plate, the cutting speed is 0.8m/min.

Lens Focal Length and Focal Point Position (Defocus Amount)

A smaller lens focal length results in higher power density but shallower focus, making it suitable for high-speed cutting of thin materials. Conversely, a larger lens focal length leads to lower power density but deeper focus, making it suitable for slow cutting of thick materials.

The defocus amount’s impact on the width of the cut is shown in Figure 5-3. Generally, the focal point is chosen to be located approximately 1/3 of the plate thickness below the workpiece surface, at which point the cut width is minimized.

Nozzle Shape and Nozzle-to-Workpiece Distance

(1) Selection of Nozzle Shape

The shape and size of the nozzle are crucial parameters affecting the quality and efficiency of laser cutting. Different cutting methods require different nozzle shapes. Common shapes for laser oxygen cutting nozzles are illustrated in Figure 5-4.

(2) Nozzle-to-Workpiece Distance

When the nozzle is too close to the workpiece surface, it affects the ability to blow away splattered molten slag. However, if the nozzle is too far from the workpiece surface, it can result in unnecessary energy loss. To ensure cutting stability, the distance from the nozzle end to the workpiece surface is generally controlled within 0.5 to 2mm.

Types and Pressure of Assist Gas

When using oxygen as the assist gas for cutting low carbon steel, intense oxidation reactions generate a large amount of heat, increasing cutting speed and thickness, and producing slag-free cuts. For cutting stainless steel, a mixture of oxygen and nitrogen is often used, resulting in better cut quality compared to using oxygen alone.

Increasing gas pressure enhances slag removal capability and can lead to higher cutting speeds. However, excessive pressure can result in rough cutting surfaces. See Table 5-1 for the main parameters and characteristics of laser cutting.

Table 5-1: Main parameters and characteristics of laser cutting