Cut Quality - Lincoln Electric FineLine 12864 Operator's Manual

FineLine 300HD Plasma System

5.2 Cut Quality

Before the optimum cutting condition can be achieved on a particular material type
and thickness, the machine operator must have a thorough understanding of the
cutting characteristics of the System. When the cut quality is not satisfactory, the
cutting speed, torch height, or gas pressures may need to be adjusted in small
increments until the proper cutting condition is obtained. The following guidelines
should be useful in determining which cutting parameter to adjust.
Note: Before making any parameter changes, verify that the torch is square to
the workpiece. Also, it is essential to have the correct torch parts in place and
to ensure that they are in good condition. Check the electrode for excessive
wear and the nozzle and shield cap orifices for roundness. Also, check the
parts for any dents or distortions. Irregularities in the torch parts can cause
cut quality problems.
A positive cut angle (top dimension of piece smaller than the bottom dimension)
usually occurs when the torch standoff distance is too high, when cutting too
fast, or when excessive power is used to cut a given plate thickness.
A negative cut angle (top dimension of piece larger than the bottom dimension)
usually occurs when the torch standoff distance is too low or when the cutting
speed is too slow.
Top dross usually occurs when the torch standoff distance is too high.
Bottom dross usually occurs when the cutting speed is either too slow (slow-
speed dross) or too fast (high-speed dross). Low-speed dross is easily
removed, while high-speed dross usually requires grinding or chipping off.
When using oxygen as the shielding gas, bottom dross can sometimes be
removed by increasing the shield gas pressure. However, increasing the shield
pressure too much can cause cut face irregularities (see below). Bottom dross
also occurs more frequently as the metal heats up. As more pieces are cut out
of a particular plate, the more likely they are to form dross.
When using oxygen as a shielding gas, cut face irregularities usually indicate
that the shield gas pressure is too high or the torch standoff distance is too low.
A concave cut face usually indicates that the torch standoff distance is too low
or the shield gas pressure is too high. A convex cut face usually indicates that
the torch standoff distance is too high or the shield gas pressure is too low.
Note that different material compositions have an effect on dross formation.
If the material is not being completely severed, the likely causes are that the
cutting current is too low, the travel speed is too high, the gas pressures are
incorrect, the incorrect gas types are selected, the incorrect consumables are
installed in the torch, or the consumables are worn.
This information is subject to the controls of the Export Administration Regulations [EAR]. This information shall not be provided to
non-U.S. persons or transferred by any means to any location outside the United States contrary to the requirements of the EAR.
Page 64 of 118
BK8053-000107 Rev A.01