F400 Mild Steel Cutting

 

 

Objective:   Assess Preliminary cutting performance of laser cutting at 400watts in CW.

 

Method:  The 400watt laser was focused using a 2.5” Positive Meniscus lens. The F400 was fitted with a 2.5X expander that provided a 13mm spot size before final focusing optic.  80psi (1.33cfm) of Oxygen (99.998%purity) was used as an assist gas. The nozzle I.D. was .0345” and the standoff was set to .045”.   The focused spot size was .0032” and depth of focus was .047”. The power density of the F400 at 400watts and M2 of 1.1 power density was 48,600,000 w/in2.

 

                                     Mild Steel Thickness .1045”

                                                              

 

Figure 1                          

Kerf Width .0045” (Measured

On QA’s Optical Comparator)                 

 

 

             

                                              

 

                                                      

 

 

 

 

 

 

 

 

 

 

Figure 2

Mild Steel Thickness .1045”(Cut Surface)
   

 

 

                                  Mild Steel Thickness .25”(Cut Surface)

  Figure 3

 

 

 

 

Figure 4

 

 

 Figure 5

 

 

 

  Figure 6   

  Ref: Powell, j etc.: “ The Role of Oxygen Purity in Laser Cutting Of Mild Steel”

   ICALEO Proceedings, October 1992, Page 436, Published by LIA Orlando, Florida.

 

 

 

Discussion:

 

The cutting results showed that the F400 produces clean dross free cut edges in the thinner sheets of mild steel. Figure 1 shows with the quality of beam (low M2 number) the kerf width exhibits evenness and no changes in kerf width across the mild steel being cut. The striation pattern in figure 2 shows an even energy distribution, which is consistent with lasers that have a TEM 00 high purity mode with low M2 number. The striations are evenly spaced and the surface finish is consistent with high quality laser cuts.

 

 

 

 

Figure 3 shows some roughness in the striation pattern along with dross starting to be present at bottom of cut edge. This is to be expected with the thickness of steel being cut with power being used. With the F400 as you go up into .2” or thicker mild steel issues will arise such as slower speeds, quality of cuts suffering and other HAZ issues.  Figure 4 shows cutting speeds of mild steel between .1” and .25”. Figure 5 shows a 3D graphical representation of the same data. When Oxygen is used as an assist gas it will assist in the laser absorption process and, together with the exothermic heat, will result in typical gains between 20-40% increase in cutting speeds.  Figure 6 shows the effect of going to a lower purity of oxygen at 800watts and this data can be applied to different laser powers levels lower or higher.  The data above should give solid information on cutting speeds and qualities that can be expected when cutting mild steel with parameters used in the F400 tests