In general, all common cutting methods such as plasma, oxyfuel, waterjet and laser can be used for bevel cutting. Not only flat sheets, but also geometric work pieces can be processed in this manner with V, Y, and K chamfers. Variable chamfers can also be used, which are necessary for a variety of welding processes.
3 Criteria for ideal Bevel Cutting
1. Precisely calibrated tools
Precisely calibrated tools form the basis for precise chamfers. There is often the misconception that it is sufficient to collect data and calibrate the tools based on the data alone, either mechanically or by manually entering the corresponding correction values into the machine control. However with this procedure, the angular deviation of the burner can hardly be brought under the 0.5 mm limit – not to mention the high costs which are obtained in the purely mechanical setting.
At this point, the new rotator MicroStep® R5 is set up. The entire calibration process runs completely automated and eliminates deviations in hundredths of a millimetre. By independently -tensioning the torch holder of the bevel cutting head it is ensured that the deviation even after burner collision is not greater than 0.5 mm.
The rest is handled with the control of the calibration: Here the exact endpoints of the burner tip at different rotation (X, Y and Z coordinates) are measured. Based on the measured deviations, the controller calculates the necessary correction values , which are automatically applied the next cutting process. This automatic calibration system (ACTG® – Automatic Calibration of Tool Geometry) provides a completely new quality in terms of bevel cutting. It significantly improves the precision and dimensional stability of the cutting process, makes lengthy mechanical adjustments unnecessary and significantly increases the productivity of the system.
2. Adaptive Height Control
To achieve the highest possible precision on a cut part, it is important to accurately maintain the distance from the burner tip to the surface of the material that is to be processed. The so-called cutting height is measured on the arc voltage – which in simple 2D sections is not a problem.
However, when bevelling comes into play there are a lot of other influencing factors that influence the ideal distance from the burner tip to the surface of the material. The inclination angle of the torch to the material, the strength of the cutting current and the flow rate of the plasma gases must be adapted. MicroStep® has developed the method of adaptive level control (ATHC® – Adaptive Torch Height Control) which allows all required parameters in bevel cutting to be automatically adjusted by software so that at any time a perfect bevelled cut can be implemented.
3 Adaptive bevel angle compensation
Different section joints in bevel cutting in cross section
In addition to the factors mentioned above, the precision of the cut work pieces is also highly influenced by the formation of section joints, which is created when cutting with the plasma arc. Illustrated in the accompanying figure is the cutting of the shape with a current of 260 A at different inclination angles (15 °, 30 ° and 45 °). As can be seen in the figure, the bevel angle is not identical to the respective opposite sides of the section joints. This is partly due to the shape of the arc, which is not exactly perfectly cylindrical. At the same time there is a formation of slag and thereby the rounding off of the top edge of the negative side, in contrast to the lower edge of the positive bevel, which remains sharp. This leads to the need for further corrections. One is to tilt the angle of the burner and the other relies on the size of the tools used, in such a way that the ready-cut part receives the exact desired dimensions.
These corrections are respectively different, when it involves the contours of the positive tool respectively the negative tool. Both of which are influenced by the angle of inclination of the burner, as well as the strength of the cutting current. To minimize deviations caused by the “natural condition of the plasma arc “, all systems are equipped with a MicroStep® R5 Rotator cutting system with the Adaptive bevel angle compensation (ABC® – Adaptive Bevel Compensation). This correction system ensures precision and dimensional accuracy of bevel cutting with plasma , together with the automatic calibration system described above (ACTG) and the adaptive level control (ATHC).