Effect Of Focus Point On Cutting Mild Steel With Oxygen - Mazak STX SC L PLUS CONTROL Training Manual

EFFECT OF FOCUS POINT ON CUTTING MILD STEEL WITH OXYGEN

When the machine set-up procedure is performed the focus point of the lens is adjusted to a
specified position either above or below the surface of the material. When cutting mild steel the
focus point is raised higher as the thickness increases. Because thick mild steel requires lower
assist gas pressures than thinner gauges, the focus is raised to increase the kerf width allowing a
larger volume of gas to pass through the kerf.
a b
As seen in the example above, the higher focus point produces a wider kerf width ( a vs. B ) for
the given material thickness.
By using the g87 command the focus point can be raised or lowered to control the kerf width. If
the kerf is too small the cut will have dross. If the kerf is too large there will be self burning.
For cutting materials such as stainless steel and aluminum using nitrogen as the assist gas, the
ideal focus point is near the bottom surface of the given material thickness. For these materials
the g87 is always used to lower the focus. This is done for two reasons: 1) the focus is moved
closer to the bottom of the material, 2) the nozzle is closer to the material surface which allows
more gas to be forced through the kerf. Because the standard set-up requires an 0.040" gap, the
focus point can only be lowered about 0.030" before the nozzle is too close to the material.
Therefore, if the focus point needs to be lowered a significant distance below the surface of the
material, the machine must be refocussed to move the focus point further below the nozzle
.
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