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Precision Plasma Cutting Method

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Plasma cutting technology has evolved into a high-precision and productive tool for the fabricator’s shop floor. A high-precision plasma system concentrates arc energy in a small area, in effect creating a sharper cutting tool while an increased plasma density creates a precision cut with a narrower kerf, less top-edge rounding, and less bevel. A high-precision plasma cutting means faster cutting, high-quality edges, and longer-lived consumables when compared to the first generation of precision plasma cutting technology.

A plasma cutting system provider can help fabricators determine the equipment features that make sense for their applications. According to the standards given by ISO 9013:2002, a high precision cut surface has the following characteristics:

  • Square face (less than 3-degree bevel)
  • Smooth, with nearly vertical drag lines
  • Little to no nitrides or oxides
  • Little to no dross, and what dross is present should be easy to remove
  • Minimal heat-affected zone and recast layer
  • Good mechanical properties in welded components

To appreciate the enormity of plasma technology developments, consider that even modern simulation methodologies cannot fully and efficiently model plasma arc behavior without considerably simplifying assumptions. Plasma cutting certainly has evolved from its birth in the laboratory to become a productive fabricating tool that plays a key role in many manufacturers’ success.

Precise torch height control also greatly controls electrode wear and cut precision. Height control is a function of arc voltage, which is directly proportional to the distance between the electrode tip and the plate. Advanced systems use voltage sampling to adapt for consumable wear, keeping the nozzle at the correct distance from the plate throughout the entire lifetime of the electrode. However, as the electrode wears, the arc becomes longer. Voltage sampling moves the torch progressively closer to the plate as the electrode wears, thus maintaining consistent kerf width and cut quality.

Use the following characteristics to evaluate cut quality of test parts, and remember to ask the plasma system vendor for the cut time and estimated cut cost per part for those test parts:

– Cut surface: A smooth surface free of dross and nitride contamination.

– Top edge rounding: is caused by the heat of the plasma arc at the top surface of the cut.

– Top spatter: Cutting too quickly or using a too high torch setting.

– Bottom dross: Easy-to-remove dross indicates cutting is too slow. Hard-to-remove dross indicates cutting is too fast.

– Kerf width: The kerf (or cut) width is related to tip orifice size, current setting, and torch height.

– Cut surface bevel angle: High-precision processes produce a bevel angle of 0 to 3 degrees, while conventional plasma produces larger bevel angles.

– Nitride contamination: When carbon steel is cut with air as the plasma gas, some of the nitrogen becomes absorbed into the cut surface, which then requires grinding before welding to eliminate porosity and the risk of nitrides at the grain boundary.

New beveling technology seamlessly integrates Precision Plasma Cutters, CNC, software, height control, bevel head, and gantry functions so fabricators can take full advantage of their plasma system and maximize productivity. New technology offers a high level of automation for the programmer by incorporating best-practice bevel cut sequences into CAD/CAM programming and nesting software. Therefore, the part program or nest represents the actual desired part geometry, without bevel compensations. This eliminates the need for trial-and-error programming. Instead, operators can quickly and easily make any necessary adjustments at the machine.

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