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How To Achieve a Laser-Cut with Fine Edge Quality?

How To Achieve a Laser-Cut with Fine Edge Quality?

  • 2019/01/07

What is laser cutting ?

Laser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses, and hobbyists. Laser cutting works by directing the output of a high-power laser most commonly through optics. The laser optics and CNC (computer numerical control) are used to direct the material or the laser beam generated. A typical commercial laser for cutting materials involved a motion control system to follow a CNC or G-code of the pattern to be cut onto the material. The focused laser beam is directed at the material, which then either melts, burns, vaporizes away, or is blown away by a jet of gas,[1] leaving an edge with a high-quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials.

How to achieve a laser-cut with fine edge quality? what's the secret to burr-free laser cutting?

Every metal fabricator wishes to gain a burr-free laser cutting. Anyway the operators need to know exactly what has to happen when the laser cutting beam, assist gas, and workpiece interact to create the perfect cut edge,ensuring molten metal evacuates in the right way at the right time.

There are the guides:

1. making the right adjustments to the cutting parameters

focus spot too high in the cut can leave spiky dross; focusing too low in the cut yields slower cutting speeds and can leave beads, a telltale sign of “overflushing .”

It’s true that setting the standoff too high causes the assist gas to have trouble evacuating the molten metal cleanly and efficiently from the kerf

2.Assisted gas usage.

Cutting of  stainless steel, the N2 pressure can reach 2MPa , purity of 99.999%;A capacity for Carburetor is 50N3/H with design pressure 2.5MPA. When using with small cylinder of  N2 for cutting, a high pressure nitrogen meter is a must with range from 0 to 6MPa .

Nitrogen assist gas can make up 35 to 50 percent of the variable costs in laser cutting. it’s important to control that is necessary to  choose the smallest nozzle diameter you can use to obtain the desired quality and performance.

Oxygen Cutting Considerations

oxygen cutting for carbon steel using the exothermic reaction. Max pressure of O2 should reach 1Mpa and purity of at least 99.9%.

Oxygen-cutting carbon steel benefits from higher oxygen gas purity levels.oxygen purity level plays an important role. increasing oxygen global purity to 99.95 percent or above—to 99.98 or 99.99 percent—we can increase the cutting speed in production significantly, sometimes between 30 and 40 percent.

Any changes in the exothermic reaction, which can in turn affect the cutting performance. The exothermic reaction works in conjunction with the gas flow rate (much lower than in nitrogen cutting) to burn and evacuate molten material and slag. If that molten material and oxidized slag aren’t removed effectively, it remains as a burr on the cut edge

3.Nozzles for Fiber Laser Machine

It is necessary to use right nozzles  with right orifice and structures.

Pay attention to  the  spatter sticking on the nozzle’s edge or internal wall. The protruding spatter interrupts the gas flow dynamics and deflects that supersonic shock wave on the kerf. The shock wave makes the molten-metal evacuation erratic, and some metal cools before it exits the cutting area, solidifying while still hanging on to the bottom cut edge. In other words, you get a burr.

Most nozzles are cylindrical and very capable for a variety of sheet thicknesses. Some nozzles, suited for a narrow range of (usually thicker) material, have a convergent and divergent shape, designed to give the gas flow enveloping the beam a similar convergent and divergent, or hourglass, shape.

The hourglass shape of the beam as it enters and exits its focus point, along with the location and nature of the exothermic reaction when oxygen cutting, creates that characteristic cut edge seen on thicker plate. The thicker the material, the more difference you have in the gas dynamic and laser beam shape between the top and bottom surface of the cut. The edge is smooth on top and becomes rougher deeper in the cut, eventually turning into rough striations at the bottom.

Conclusion: Attaining a burr-free cut is about ensuring the beam parameters and gas dynamics work together to ensure the right amount of molten metal evacuates the kerf at the right time and in the right way.

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