Although more typically used for marking, the nanosecond pulsed fiber laser is also ideally suited to metallic cutting. They are low cost, compact, reliable and require no maintenance. The scanner based cutting process can be applied to a wide variety of materials ranging from ferrous and non ferrous metals as covered in this application note, but also ceramics, polymers and even carbon composites. This application note specifically looks at metallic materials including copper, brass, aluminium, titanium, stainless steel and silver, and shows examples of these materials cut with a pulsed fiber laser.
The short pulses and relatively high peak powers that can be achieved with a pulsed fiber laser with its directly modulated seed MOPA designs gives it the ability to be an effective cutting tool.
As an alternative to standard cw type cutting the pulsed fiber laser can be used in a multi pass vaporisation type cutting process using a scanner to repeatedly pass over the cut line removing a small amount of material per pass. No nozzle or assist gas is required. This technique offers a flexible, accurate and very affordable solution. The equipment is basically a simple laser marking system!
The cutting speeds that can be achieved varies quite considerably from >10 m/min for thin foils to <10mm/min for thick >1mm materials. For cutting thicker materials special techniques that effectively widen the kerf width must be employed such as cut line off-setting or beam wobbling. Compared to conventional laser cutting these speeds may be slow but for many applications the low capital cost and the flexibility offered by ns pulsed fiber laser cutting/marking systems are highly attractive.
Results show that effective cutting can be achieved with all of SPI’s pulsed laser models SM/HS/HM, but each exhibits slightly different cutting characteristics and selection is very much dependant on the material and the desired output. For example for very narrow kerf widths the high beam quality and small spot size of the SM is best suited, while for thicker materials the higher peak power and slightly larger spot size HM generally produces better results.
The use of aluminium in pure and alloyed form is widely used and small intricate parts can be cut in relatively thick material.(Image 1) The surface finish does not have a significant impact as brushed and anodised parts can be cut equally well. Sections up to 2mm thick can be successfully cut however the effective cutting speed can be low.
Stainless steel is a widely used material particularly in the medical industry where there are significant fine cutting requirements. Cutting speeds of >20mm/min can be achieved with good quality in 0.5mm thick 304 grade material using a simple scanner system. However, using a 40W HM laser with a fixed cutting head and coaxial assist gas >1.5m/min cut speeds in 200µm stainless steel can be achieved (Image 2).
Thin titanium sheet can also be readily cut, for engineering applications care would be required to ensure that edge oxidation did not degrade the cut edge quality. However, for less technically functional applications such as ornamental jewellery the process is ideal, and can be combined with colour marking.
Highly Reflective materials
Copper, brass, silver and gold have an extremely high reflectivity and conductivity and are therefore considered difficult materials to cut. High power densities are required to initiate the cutting process and this is readily cut with ns fiber lasers.
Brass is a material that is typically considered to be difficult to cut with lasers and is often used as a test material to develop parameters for cutting gold. With sufficient peak power in the pulses excellent cut quality can be achieved in relatively thick material up to 1mm with 20W HS and 2mm with 40W HM (Image 4).
The cutting of copper has many applications particularly in the electrical and electronics areas particularly of foil type materials. Although a highly reflective and conductive material the high peak power couples into the material enabling high precision burr free cutting (Image 5). An emerging application is the cutting of copper deposited tracks on PCB boards where there are requirements to selectively cut conductive tracks on the boards.
The cutting of precious metals such as silver and gold are increasingly being done using pulsed lasers. The ability to do intricate patterns with very low material wastage is highly attractive to the jewellery sector. As an example a high quality ornately patterned silver disk of 20mm diameter has been cut using a 20W HS laser (Image 6).
Nanosecond pulsed fiber lasers are ideally suited to vaporisation cutting applications. These examples show a diverse range of metallic materials can be successfully cut showing the extreme versatility of these laser sources.