Perpendicularity deviation of cut edges

Perpendicularity deviation is the perpendicular distance between the actual cut edge obtained and the specified shape and location of the cut edge. It defines both straightness

and flatness deviations. The results for the perpendicularity deviation of the cut edges are shown in figures 54, 55 and 56. Perpendicularity measurements were taken on both edges of each cut kerf and each data point in these figures was the highest measured value for the perpendicularity deviation of the edges for each cut kerf.

13.3.1 Disk laser

All the disk laser cut edges had perpendicularity deviations of less than 0.18 mm. The perpendicularity deviation tended to decrease with increase in cutting speed except for the 2.3mm sheet thickness where there was an increase in perpendicularity deviation at cutting speeds above 15m/min.

Disk Laser, Power 4000 W

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

0 5 10 15 20 25 30 35 40

Cutting speed (m/min)

Perpendicularity deviation, u, in mm

1.3mm sheet thickness 2.3mm sheet thickness 4.3mm sheet thickness 6.2mm sheet thickness

Figure 54. Perpendicularity deviation of the disk laser cut edges

13.3.2 Fiber laser

For the fiber laser cuts, the perpendicularity deviation was measured for each of the five cut edges per sheet thickness made at similar cutting conditions and at maximum cutting speed for each sheet thickness considered. The 1.3mm and 2.3mm sheet thickness cut edges had relatively small perpendicularity deviations (less than 0.08mm). The perpendicularity deviations of the 4.3mm and 6.2mm sheet thickness cut edges were higher than 0.08 mm but less than 0.18mm.

Fiber Laser, Power 4000 W

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

1 2 3 4 5

Range of identical cut kerfs for each sheet thickness

Perpendicularity deviation, u, in mm

1.3mm, Cutting speed 55 m/min 2.3mm, Cutting speed 27 m/min 4.3mm, Cutting speed 8,5 m/min 6.2mm, Cutting speed 4,5 m/min

Figure 55. Perpendicularity deviation of the fiber laser cut edges; for each sheet thickness, five cut kerfs were made under similar cutting conditions

13.3.3 CO2 laser

At a similar cutting speed and 1.3mm sheet thickness, the perpendicularity deviation of the CO2 laser cut edge (0.02mm) was lower than that of the disk laser cut edge (0.06mm).

Generally, the CO2 laser cut edges had a low perpendicularity deviation for all the four sheet thickness (1.3mm, 1.85mm, 4.4mm and 6.4mm) considered, with the maximum perpendicularity deviation of the 6.4mm sheet thickness cut edges being less than 0.16mm.

CO2 Laser, Power 4000 W

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

0 2 4 6 8 10

Cutting speed (m/min)

Perpendicularity deviation, u, in mm

12

1.3mm sheet thickness 1.85mm sheet thickness 4.4mm sheet thickness 6.4mm sheet thickness

Figure 56. Perpendicularity deviation of the CO2 laser cut edges

13.4 Surface roughness

The surface roughness (Ra) results are shown in figures 57, 58, and 59. The data points in these figures are the measured values for surface roughness in which the cut surfaces of sheet thickness less than 3mm have one roughness value for each cut surface while the cut surfaces of sheet thickness greater than 4mm have more than one roughness value.

The cut surfaces with sheet thickness less than 3mm showed uniform surface roughness throughout the cut thickness that is why only one roughness value was enough to describe the cut surface roughness. However, the surface roughness varied along the cut thickness of the cut surfaces with sheet thickness greater than 4mm therefore more than one roughness value was needed to describe the cut surface roughness.

13.4.1 Disk laser

Figure 57 shows the variation of the surface roughness (Ra) with cutting speed for the disk laser cuts and the different sheet thickness (1.3mm, 2.3mm, 4.3mm and 6.2mm). The 6.2mm sheet thickness showed a large variation between the surface roughness at the top of the cut thickness and that at the bottom of the cut thickness with the highest roughness being at the bottom of the cut thickness. The 4.3mm sheet thickness showed only a small difference between the roughness at the top and that at the bottom of the cut thickness.

The variation of surface roughness with cutting speed was not consistent probably because of the variation in other cutting parameters such as assist gas pressure for the different experiments. For instance at the various cutting speeds at which the 1.3mm sheet thickness was cut, the assist gas pressures were 8 bar, 15 bar and 20 bar and the assist gas pressures for the cutting experiments with 2.3mm sheet thickness were 6 bar and 20 bar for the various cutting speeds at which the 2.3mm sheet thickness was cut. The variations in cutting speed as well as the variations in assist gas pressure may have had a combined effect on the surface roughness variation shown in figure 57.

Disk Laser, Power 4000 W

0 2 4 6 8 10 12 14 16 18 20

0 5 10 15 20 25 30 35 40

Cutting speed (m/min)

Roughness, Ra (um)

1.3mm sheet thickness 2.3mm sheet thickness 4.3mm sheet thickness 6.2mm sheet thickness

Figure 57. Surface roughness of the disk laser cut surfaces

13.4.2 Fiber laser

The surface roughness results for the fiber laser cuts are shown in figure 58. Generally, the 1.3mm and 2.3mm sheet thickness were cut at higher cutting speeds (above 10 m/min) and showed a lower surface roughness compared with the 4.3mm and 6.2mm sheet thickness that were cut at lower cutting speeds (less than 10 m/min). The 2.3mm sheet thickness showed an increase in surface roughness at cutting speeds beyond 20m/min. The data points for the 4.3mm and 6.2mm sheet thickness in figure 58 include roughness values at the various positions on the cut thickness. The 4.3mm sheet thickness showed higher

surface roughness at the bottom than at the top of the cut thickness while the 6.2mm sheet thickness showed highest surface roughness at the middle of the cut thickness with lower roughness at the top and bottom of the cut thickness. Both the cutting speeds and laser powers were varying in these fiber laser cutting experiments and the highest cutting speeds for each sheet thickness were achieved at the highest laser power of 4000W. The assist gas pressure, focal length and focus position were kept constant for each particular sheet thickness at the various cutting speeds and laser power. This could be the reason for the fairly consistent variation of the surface roughness with cutting speed as seen for the 1.3mm and 2.3mm sheet thickness in figure 58.

Fiber Laser, Power 4000 W

Figure 58. Surface roughness of the fiber laser cut surfaces

13.4.3 CO2 laser

The CO2 laser cut surfaces generally had low surface roughness for all the four sheet thickness considered as figure 59 shows. Even the 4.4mm and 6.4mm sheet thickness showed a relatively uniform surface roughness throughout the cut thickness as there was no significant difference between the roughness at the top and that at the bottom of the cut thickness. There was no significant change in surface roughness for the range of cutting speeds considered which cutting speeds were actually quite close as figure 59 shows.

CO2 Laser, Power 4000 W

0 2 4 6 8 10 12 14 16 18 20

0 2 4 6 8 10

Cutting speed (m/min)

Roughness, Ra (um)

12

1.3mm sheet thickness 1.85mm sheet thickness 4.4mm sheet thickness 6.4mm sheet thickness

Figure 59. Surface roughness of the CO2 laser cut surfaces