How to Troubleshoot Plasma Cut Quality

How to Troubleshoot Plasma Cut Quality

Introduction

Like any cutting process, there are a lot of variables that affect plasma cut quality. Some of these variables include:

  • Torch Type
  • Torch Alignment
  • Condition of consumables
  • Arc Voltage, or cutting height
  • Gas Type
  • Gas Purity
  • Gas Pressure and Flow
  • Material Thickness
  • Material Composition
  • Surface Condition
  • Cutting Amperage
  • Nozzle orifice size
  • Cutting speed (i.e. Machine travel rate)

Most of these variables are interdependent, meaning that if you change one variable, it will affect the others. Figuring out how to fix cut quality issues can be difficult, so the following information was assembled to provide the usual solutions to some typical cut quality problems. To begin, select the most prominent condition:

  • Cut angle
  • Cut flatness
  • Surface roughness
  • Dross

Recommended cutting parameters will usually give the best cut quality, so refer to your system’s cut data manual for suggested parameter settings. Occasionally, conditions may vary and slight adjustments will be required. If so:

  1. Make small, incremental changes to gas flow and pressure.
  2. Adjust arc voltage in one volt increments, up or down as required.
  3. Adjust cutting speed in five percent increments or less until conditions improve.

Cut Angle

Negative Cut Angle

If the top dimension of a part is larger than bottom dimension, you have a “negative” cut angle. This can be caused by:

  • Misaligned torch
  • Bent or warped material
  • Worn or damaged consumables
  • Low arc voltage and/or
  • Cutting speed too low

Positive Cut Angle

When the top dimension is smaller than the bottom dimension, it is a “positive” cut angle. This is usually caused by:

  • Misaligned torch
  • Bent or warped material
  • Worn or damaged consumables
  • High arc voltage
  • Cutting speed too high, and/or
  • Improper amperage settings

Cut Flatness

Top And Bottom Rounded

This usually only happens when cutting thinner materials, less than 1/4 inch (6mm) thick. It is most often caused by over-powering the material, or using too much current (amperage) for the material thickness.

Top Edge Undercut

When the sides of the cut face are curve inward; it is most likely caused by cutting with the torch too close to the material. This results when the arc voltage is set too low for given material thickness.

Surface Finish

Process Induced Roughness

If you see irregularities in the cut face that are consistent, and may only appear in one axis, it is probably induced by the process. Likely problems include:

  • Worn or damaged consumables, and/or
  • Gas flow too high.

Machine Induced Roughness

When cut face irregularities are inconsistent, and often confined to one axis, then look for roughness induced by the machine motion. This could be caused by:

  • Dirty machine rails, wheels, rack, and/or pinion
  • Rails out of alignment
  • Wheels or bearings worn, damaged, or loose.

Dross

Dross happens. And there are lots of things that can affect dross performance. Modern plasma systems have a pretty wide range of dross-free cutting, so when you start to see dross forming on your parts, it usually indicates something is going wrong. There are several different varieties of dross, including High Speed Dross, Low Speed Dross, and Top Dross.

High Speed Dross

When the dross is small, but appears welded or rolled over on the bottom surface of cut part, it is usually caused by cutting too fast. This type dross is difficult to remove and may require grinding. It will often be accompanied by “S-shaped” lag lines, which also indicate that you are cutting too fast. Also, look at the arc voltage to see if it is too high.

Low Speed Dross

Low Speed Dross forms as larger globules on the bottom of the cut, but it usually pops off pretty easily. Try speeding up and/or adjusting the arc voltage higher to increase the cutting height.

Top Dross

This appears as splatter on top of the parts, and is usually easy to remove. It is most often associated with cutting too fast, or cutting too high (high arc voltage).

Intermittent Dross

If the dross is inconsistent, appears on top or bottom of the part, check for worn out consumables.

Other Factors Affecting Dross:

There are some other factors that can affect dross formation, most of which are related to the material itself. This can include material temperature, surface conditions such as heavy mill scale or rust, and material composition. For example, alloys containing high carbon levels will typically form more dross.

 

Intermittent Dross

If the dross is inconsistent, appears on top or bottom of the part, check for worn out consumables.

Other Factors Affecting Dross:

There are some other factors that can affect dross formation, most of which are related to the material itself. This can include material temperature, surface conditions such as heavy mill scale or rust, and material composition. For example, alloys containing high carbon levels will typically form more dross.

 

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