Improve cut quality on metal with these plasma cutting tips

Posted on 31/03/2016
Posted by Hypertherm

The following reference guide offers several solutions to help improve cut quality on metal. It is important to try and work through the suggestions provided – as often there are many different factors to consider:

  • Type of machine (e.g. X-Y table, punch press, motorized track, robot)
  • Plasma cutting system (e.g. air plasma system, oxygen plasma, high definition class plasma)
  • Motion control device (e.g. capability of the CNC machine and torch height control)
  • Process variables (e.g. cutting speed, cut height, choice of consumables)
  • External variables (e.g. material variability, gas purity, operator experience)

It is important to consider all of these factors when attempting to improve the appearance of a cut.

Step 1: Is the plasma arc cutting in the appropriate direction?

The squarest cut angles are always to the right side, with respect to the forward motion of the torch.

  • Check direction of the cut
  • Adjust the cutting direction, if needed

The plasma arc typically spins clockwise with standard consumables.

Contour:

  • Torch travels clockwise
  • Good side of the cut is to the right side of the torch, as it travels forward

How torch travels

Internal feature (hole):

  • Torch travels counter-clockwise
  • Good side of the cut is to the right side of the torch, as it travels forward.

Plate with internal hole

Plate with internal hole

Step 2: Was the correct process selected for the material and thickness being cut?

Refer to the cut charts in the Operation section of the Hypertherm Instruction Manual.

Example cut chart

Be sure to follow the specifications in the cut charts:

  • Select the appropriate process for:
    • Metal type
    • Metal thickness
    • Desired cut quality
    • Productivity goals
  • Select correct plasma and shield gas if using a dual-gas plasma cutting system
  • Select correct parameters for:
    • Gas pressures (or flow rates)
    • Torch-to-work distance and arc voltage
    • Cutting speed
  • Confirm the correct consumables (tips) are being used and verify the part numbers

Example consumables

Note: Generally, lower amperage processes offer better angularity and surface finish; however, cutting speeds will be slower and dross levels will be higher.

Step 3: Are the consumables worn?

  • Inspect consumables for wear
  • Replace worn consumables
  • Always replace the nozzle and electrode at the same time
  • Avoid over-lubricating o-rings

Note: Use genuine Hypertherm consumables to ensure maximum cutting performance.

Step 4: Is the torch square to the workpiece?

  • Level the workpiece
  • Square the torch to the workpiece (both from the front and side of the torch)

Torch square to workpiece

Note: Check to see if material is bent or warped; in extreme cases this limitation cannot be corrected.

Step 5: Is the torch-to-work distance set at the proper height?

  • Adjust torch-to-work distance to the correct setting
  • If using arc voltage control, adjust voltage

Note: As consumable parts wear, arc voltage settings need continual adjustment to maintain torch-to-work distance.

Torch-to-work distance can impact angularity

Negative cut angle: torch too low; increase torch-to-work distance
Positive cut angle:
torch too high; decrease torch-to-work distance

Note: A slight variation in cut angles may be normal, as long as it is within tolerance.

Step 6: Is the cutting speed set too fast or too slow?

  • Adjust cutting speed, as needed

Note: Cutting speed may also impact your dross levels.

High-speed dross: Cutting speed too fast (arc lags behind), reduce cutting speed
Low-speed dross: Cutting speed too slow (arc shoots ahead), increase cutting speed
Top spatter: Cutting speed too fast, reduce cutting speed

Note: In addition to speed, both material chemistry and surface finish can impact dross levels; as workpiece heats up, more dross may form on subsequent cuts.

Step 7: Are there problems with the gas delivery system?

  • Identify and repair any leaks or restrictions
  • Use properly sized regulators and gas lines
  • Use pure, high-quality gas
  • If manual purge required, such as with the MAX200, confirm purging cycle was completed
  • Consult the gas distributor

Step 8: Is there torch vibration?

  • Make sure that the torch is secure to the table gantry
  • Consult OEM; table may require maintenance

Step 9: Does the table need to be tuned?

  • Check and ensure that the table is cutting at specified speed
  • Consult OEM; table speed may need tuning

 

Posted on 31/03/2016
Posted by Hypertherm

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