Laser cutting requires the material to be “laser flat,” and not just ordinarily flat. The term laser flatness is specific to the laser cutting system and needs to be achieved accordingly. However, first, we will explore in laser cutting, why material flatness is essential and how the RDI Laser Blanking System can provide accurate laser flatness for coil processing.
Importance of Material Flatness in Laser Cutting Technology
The material must be properly flattened before it undergoes laser cutting. If laser cutting material flatness is not achieved as required, material can twist or distort while being cut. This can happen even with material that looks flat because of internal stresses that can cause the material to bend when the laser begins to cut it. On the laser cutting machine, when trying to hold a precise tolerance to a few thousandths of an inch, the material waving up and down due to a sheet that isn’t flat changes the dimensions during cutting.
Most laser cutting machines come with a capacitive height sensor – a sensor on the cutting head that can detect the distance between the nozzle and the surface of the material. Paired with the Z cutting axis, it helps maintain a proper cutting standoff. Such a technique enables the laser cutting machine to continue its work even as the material ripples; however, with more wavy material the accuracy reduces.
Since the Computer Numerical Control (CNC) directs the laser beam from a rigid framework and onto a straight line, the bending of the sheet can cause problems. Without laser cutting level material flatness, or the arc length of the wave in the material duly corrected, the laser optic and CNC cannot cut to precise accuracy. Therefore, it is imperative to ensure that the sheet is flat to begin with, as any dimensional inaccuracy caused by the height sensor correcting for the warping will still not be rectified in the downstream processing later.
Ways to Remove Internal Stress and Warp
Not just in downstream processes, the materials on a coil fed laser or a table laser are affected if the laser cutting material flatness is not guaranteed, and thereby impact the work of the laser cutter. RDI Laser Blanking Systems and table lasers use a capacitive height sensor that does allow for some correction due to minor fluctuations in material height. The RDI Laser Blanking System can even use this height compensation to process diamond tread aluminum material with the diamonds either facing up or down.
Nevertheless, frequent warping or distortion of the material can exceed the responses of the cutting head to react to the change. Relieving internal stress can cause the previously cut areas to spring up. In order to avoid this, nesting software, which is used to pack a series of parts onto material to be cut with the least amount of waste, can add a “cut feature avoidance” option to prevent such faults from occurring from the cutting head, by preventing the head from crossing over a region that had previously been cut. While this is a good option if intelligently applied, it can add time and processing costs to the cutting sequence.
Consequently, laser cutting material flatness is critical for the smooth running of the laser cutting machine. Such curves and warps that can cause a springing up slow down the processing time, as operators reduce the cutting speed to eliminate faults and poor edge quality. In case of laser cutting material flatness, the machine can run fast without interruptions of unnecessary processing holds caused by nozzle touches or sprung up material.
Usually, the operator has a “knee jerk” reaction to poor cutting quality caused by the rippling of the material. Instinctively, the operator slows down the laser cutting speed to allow the cutting head more time to react to wave in the material, and in turn, an increased cycle time. This does not only require the operator to go back to the nesting software step and activate the “cut feature avoidance” option to generate a new cutting path. Instead, this is a worse scenario where along with the cut feature avoidance and the time it adds, the material is so warped that it also needs a readjustment of the speed.
On table laser cutters, the material to be cut is pre-purchased as sheets from the suppliers. When the sheet is warped to the extent that the operator is stuck with no recourse, the only option is to slow down the speed along with the feature avoidance option, and hope that the parts are not too warped that they cannot be used in downstream processing.
Luckily, RDI Laser Blanking System has another built-in option to correct this dilemma: making coil correction at either the leveler, flattener, or straightener, and on the fly during the process.