Are you planning to purchase a laser cutter, but are doubting which one is best for stainless steel?
This page will tell you the key factors to consider when purchasing a laser cutting machine for stainless steel as well as the cost.
1 Stainless Steel Laser Cutting Speed
The cutting speed is determined by the thickness of the stainless sheet and the power of the laser. As stainless sheet thickness and laser power decrease, cutting speed increases.
Figure 1 depicts the cutting speed ranges for various powered lasers. To optimize cut quality, cutting speed must be balanced with other cutting parameters such as gas pressure and focal position.
The cut edge will have a regular striation pattern and no dross if the cutting speed is correct (Figure 2).
Figure 2 Good Cut – 10 mm Stainless Steel 304
If the cutting speed is too high, there is insufficient laser absorption into the material causing an increase in the melt viscosity and dross formation (Figure 3). The cut surface will have high frequency, fine striation lines.
Figure 3 Dross formed when cutting speed was increased by 30% for 10 mm Stainless Steel 304
If the cutting speed is too low, a large amount of dross will form on the underside of the cut (Figure 4) as well as the striation lines dragging towards the bottom of the cut.
Figure 4 Dross formed when velocity was reduced by 40% for 10 mm Stainless Steel 304
2 Stainless Steel Laser Cutting Edge Quality
When cutting with nitrogen as the assist gas, there are two different regions of the cut surface. There is a distinct transition in edge quality called the Boundary Layer Separation point.
This is the point at which the melt velocity decreases and melt thickness increases and after which an irregular striation pattern appears on the cut edge. Improved edge quality can be achieved by optimising the following: assist gas pressure, nozzle diameter, focal point position, and cutting speed.
The following parameters can improve the edge quality:
Focal point within material – this causes an increased spot size on the surface of the material and hence a wider kerf is produced so melt removal is easier and cut quality is improved. When cutting stainless steel, the focal position should be within the metal sheet (negative sign following standard practice). As the plate thickness increases, the focal position will decrease (i.e. further into the sheet) to provide the wider spot size.
Adjust cutting speed – striation pattern can be optimised and dross reduced with careful adjustment of speed.
Increase assist gas pressure – melt flow velocity increases so melt film thickness decreases and boundary layer separation occurs closer to the lower cut edge. Increasing the nozzle diameter also reduces surface roughness. However, the gain in cut quality has to be balanced with the added cost of nitrogen.
3 CUTTING RANGE
Fiber laser cutters can produce extremely precise and clean cuts very quickly for thin/medium stainless steel.
In general, the higher the laser power, the wider the range of sheet thicknesses that can be cut, however, there may be a point at which for a set sheet thickness and laser power, cut quality will start to deteriorate and dross formation may become significant.
It is always important to consider what your priority is: productivity or edge quality.
Table 1 provides the approximate sheet thickness ranges for different laser powers.