The non-contact and precise performance of laser cutting provides advantages over dulling saw blades and large ragged plasma kerfs.
Mild steel pipe is commonly used in many applications ranging from machinery and equipment fabrication to industrial plumbing to sign posts and fencing. The walls of these pipes are often cut, notched, or drilled to obtain precision part fit-up for welded pieces and to provide accurately-located fastener holes or holes for various types of welded or threaded fittings.
Typical mechanical cutting or drilling methods, like saw blades and drill bits, dull quickly while thermal cutting methods, like plasma cutters, have a large and sometimes ragged cut kerf. This makes the non-contact aspect of laser processing very attractive for these types of applications. As with all other aspects of metal fabrication, care must be taken to determine the condition of the pipe prior to processing (clean, oily, or dirty), the grade of mild steel specified (1018, 1060, etc.), and the pipe thickness as all of these variables affect cut quality and speed.
For this particular application, 2-inch diameter, schedule 5 (0.065” thick) mild steel pipe was laser trepanned to create a series of 7.6 mm diameter holes. For this process, a Synrad 400 W laser from Laser Lines Ltd was used in conjunction with an XY table and cutting head outfitted with a 2.5” focal length lens that provides a 100 micron focused spot size. Pure oxygen gas assist at 6.9 bar (100 PSI) was sent through a 0.9 mm diameter nozzle to accelerate the cutting process and eject the molten steel. With this cutting setup, a series of 0.3” holes were successfully cut in the 1020 mild steel pipe at a rate of 30 millimeters/second. The resulting cut edges have minimal dross and heat affected zone.