Process Parameters For Laser Cutting

Numerous parameters influence the laser cutting process, some dependent on the technical performance of the laser source while others are variable. Today's focus is on the process parameters affecting the beam and focal point in laser cutting:

 

Laser Cutting Principle

 

Laser cutting involves focusing a high-power laser onto the surface of the workpiece to melt or vaporize it. Assisted by cutting gas, molten slag is blown away as the cutting head traverses the workpiece surface, forming a kerf that separates the material.

 

Laser Output Power and Mode

 

1. Laser Output Power

Laser output power directly impacts the performance of the laser cutting machine. Generally, as plate thickness increases, higher laser power is required. For cutting the same material at the same thickness, greater laser output power enables faster cutting speeds and smoother cut edges. However, once the output power is determined, the cutting speed must be optimized for the specific material and thickness to achieve the best results. Both excessively fast and excessively slow speeds can adversely affect laser cutting outcomes.

 

2. Laser Output Mode

 

Laser beam quality distribution is categorized into single-mode and multi-mode. Single-mode occurs when beam energy density concentrates at a single focal point, while multi-mode exists when two or more points exhibit maximum energy density. In cutting applications, the focused spot significantly impacts cut quality. Single-mode lasers feature a finer fiber core, superior beam quality compared to multi-mode lasers, and a Gaussian energy distribution with peak density at the center. The three-dimensional representation resembles a sharp, rounded peak.

 

Multimode lasers feature a thicker fiber core, resulting in lower beam quality compared to single-mode lasers. Their energy distribution is more uniform across the spot, with a three-dimensional image resembling an inverted cup. The steepness of the edges indicates that the multimode distribution is significantly steeper than that of the single-mode distribution.

 

Single-mode lasers excel in thin sheet processing, while multi-mode lasers perform better on thicker materials. Comparing the two is not meaningful as they represent distinct fiber laser configurations-much like vehicles: sedans suit highways, while SUVs handle off-road terrain. Yet sedans can traverse mountains, and SUVs can navigate roads. Thus, selecting single-mode or multi-mode depends entirely on the end-user's specific processing requirements.

 

Focus Size, Depth of Focus, and Focus Position

 

1. Focus Size and Depth of Focus

 

In laser cutting, the focus position significantly impacts cutting results. Different materials or thicknesses require corresponding focus positions during laser cutting.

 

In laser cutting, focal spot size and depth of focus are crucial factors affecting cutting quality and efficiency. A short-focus lens produces a relatively small spot diameter and short depth of focus, resulting in high power density at the focal point. This facilitates high-speed cutting of thin materials with superior precision. Conversely, a long-focus lens yields a larger focal spot diameter but a longer depth of focus. Provided sufficient power density is maintained, this configuration is better suited for cutting thicker workpieces.

 

2. Typical Relationship Between Focus Position and Cutting Surface

 

When cutting thin plates, the focus is generally positioned at the workpiece surface. For thick plates, the focus typically penetrates approximately 1/3 to 1/4 of the plate thickness, residing within the negative defocus range. When cutting carbon steel, the focus is positioned above the plate surface. As plate thickness increases, the focus moves further away from the surface, residing within the positive defocus range.