Koike Aronson Inc./Ransome, Arcade, N.Y., supplies advanced cutting machines, welding positioning equipment, portable welding and cutting machines and gas apparatus. For more information, visit www.koike.com.
Plasma Systems Deliver Better Bevels
Plasma beveling has improved by leaps and bounds compared to past plasma beveling techniques.
Today’s new high definition auto-gas plasma systems, with enhanced torch designs, can produce better bevels. With their increased ability to control the taper angle of the plasma arc, more accurate bevel angles can be achieved to tolerances of 0.5 to 2.5 degrees, depending on the plasma power source.
Plasma torch consumable designs accommodate 45-degree shield caps. This design is necessary when trying to produce a 45-degree bevel because the arc length is reduced as the torch leans to a 45-degree angle. This allows for better control of the arc voltage by maintaining a much more precise torch-to-work distance. New plasma torch designs have precise gas flow, consumable tolerance, integrated ohmic contact, gas mixtures, CNC diagnostics, tapered consumables and retaining cap water cooling.
New high-definition plasma systems offer up to 400 amps using oxygen and air when cutting mild steel. This allows a bevel to be cut in 2-inch mild steel at plus or minus 45 degrees. When cutting any bevel type, proper amperage is a must to achieve sharp measurable edges and consistent lands. Too much amperage results in rounding of the edges and inconsistent lands, as too much heat is produced.
Typical bevel types that can be achieved with high-definition plasma are Y-bevel, X-bevel, K-bevel and V-bevel types. The K-bevel is the most difficult to cut. The first pass must be a negative cut followed by the land cut and finished with the positive cut. This process provides the least amount of rollover and a very clean bevel face.
The CNC monitors the arc voltage in real-time motion, producing precise and smooth height control. All the beveling process codes are automatic and do not have to be set manually, which reduces operator error.
With the introduction of new high-definition plasma systems, machine design has become more critical than ever. Proper engineering is required to produce smooth, accurate and stable motion, taking into account the machine frequency, linear motion, AC servo technology, planetary or harmonic gearboxes and bevel head design. Higher torque is required for machine acceleration, which involves more than just oversizing the drives.
The bevel head should be designed not only to execute the proper bevel angle, but to perform small corner loops for best plate utilization. The bevel head should incorporate tilt, rotation and height control motors away from the plasma cutting surface to ensure that heat and slag remain away from these components to eliminate component failure.
A common focal point is necessary for proper bevel angles, land sizes and physical part size. Bevel head alignment is most critical as this relates to the common focal point as well. Ease of alignment must be designed into the bevel head so that operator or maintenance personnel can quickly align the plasma torch to the common focal point and get the machine running as quickly as possible, reducing downtime.
The main driver of plasma beveling is the offline programming software. Imbedded beveling tables contain all of the necessary parameters for ease of programming—the specific bevel type, plate thickness, plate type, plasma amperage and desired bevel angle—which speeds up the process for the programmer. Most common bevel types can be selected very easily and posted to the machine for cutting. The machine operator just needs to make sure that the proper consumables are installed and that the plate is properly aligned.
Another critical component of plasma cutting is the cutting table surface, which must be flat and level. If the plate is not level and flat, then the focal point changes, which affects the bevel and also the land placement. Table slats should be changed more frequently to maintain the proper flatness.