Hypertherm HT4400 HySpeed Plasma Arc Cutting System - Manual (Page 90)

OPERATION
HT4400 Instruction Manual 4-31
2
Piercing Height
Piercing height should be higher than the cutting height to prevent pierce splatter from building up on the front of
the nozzle and/or shield. An initial pierce height that is too high will increase the dwell time of the pilot arc on the
nozzle. As a rule, the pierce height should be 1.5 to 2 times as much as the cutting height (torch-to-work distance).
Pierce Delay
The pierce delay function can be set externally from the CNC controller in the form of a pierce complete signal.
Ramp Down
At the end of a cut, the plasma (current and gas flows) must be allowed to ramp down to an off state before the
torch is retracted from the workpiece. If the arc blows out without ramping down, life of the consumables is
decreased.
This is particularly a problem when cutting smaller parts. When the torch reaches the end of the cut and the smaller
or drop part (center) falls away from the workpiece, there is no metal under the torch to provide ramp down. How-
ever, in this situation arc blow out does not always occur. Sometimes the arc can stay attached to the edge of the
hole long enough to ramp down, removing only a small divot from the workpiece.
If a ramp down error occurs, try modifying the lead-out at the end of the cut:
• Reduce the cutting speed and use no lead-out.
• Stop the cut before reaching the end of the part - the ramp down of the current and gases will complete the
cut.
Running the torch off the edge of the plate will produce the same condition.
Note that in some cutting conditions, it may be difficult to achieve the full benefits of the LongLife process.
Electrode Life
1. To obtain maximum life from your consumable parts, program the lead-out of the cut so that the arc can
remain attached to the plate until the ramp-down process is complete.
• When cutting drop-parts (the part that drops away is production material and the plate remaining on the
cutting table is scrap), program the lead-out into the scrap area.
• When cutting a hole (the part that drops away is scrap), program the lead-out along the kerf so that the
arc can remain attached to cut edge until ramp-down is complete.
2. Use a chain cut if possible.
3. Purge the gas lines before cutting.
Nozzle Life
1. Do not lead out to the drop part, which will cause the arc to stretch.
2. Purge the gas lines to clean the plasma chamber before cutting.
3. Make sure the torch does not dive to the plate during cutting.