Mild Steel Cutting/Pierce Parameter - Fiber Laser

[gotpho]

Hello everyone,

I'm new to the laser world and I recently got my hands on a fiber laser cutting head but I don't know how to get a good cut with mild steel. I have been successful with cutting up to 6 mm stainless steel but the mild steel has got me all puzzled. I seem to get a lot of dross/bubbles in the back of the cut and I'm pretty sure it pierced all the way through from the start.

My cutting conditions is as followed

Gas: Oxygen
Gas Pressure: 30-40 PSI
Cutting Speed: 15mm/sec
Pulse: 100 Hz, 10% duty Cycle

At this point, I think I got my cutting speed and gas pressure right and this may have to do with my pulsing parameters. From the literature I read, is it true that pulsing must always be on from the pierce to the finish cut? There's no need to switch from pulse to CW in mild steel? Also it seems most literature suggest higher frequency to 400 Hz and above. Is this what some of you guys do? Any advice?

Thank you,

gotpho

 

[RPosty]

i am not familiar with fiber lasers, but i know they will ask thickness of what you are cutting and the focal length you are using. Also post the make/Model of your Laser System. I would try lowering the Oxygen pressure or increasing the feed rate if this was one of my machines assuming you have proper focus. Someone who knows your machine and a lot more about process than me will be here shortly. I Fix them, so my knowledge of process is limited.

"I am stuck on Band-Aid brand, 'cause they are stuck on me"

 

[gotpho]

The fiber laser system is a YLS from IPGP and the cutting head is an old precitec head. The motion control system is an acs spiiplus. A lot of what I do is hard code the movement of the head. The system doesn't have any fancy piece options so I code the software to pierce 4mm away from the work piece and then tell it to come down 1mm standoff when cutting the workpiece.

Also the mild steel thickness is 6mm(1/4)

One of the main problem I see is the lava eruption from the piercing to the actual cut. Could this mean that the pierce wasn't successful so the material bounced back to the top?

 

[gotpho]

Well no one really replied but I seem to figure out the problem. Apparently, people do use CW when typically cutting mild steel and I found that some OEM cheat and use nitrogen instead of oxygen. The idea is that nitrogen is inert and the high pressure will help blow the molten material through the kerf like stainless steel.

I, however, believe that if I increased my spot size diameter, I could probably be able to cut thicker mild steel with oxygen. Currently I have a spot size of about 400 microns. I'm thinking maybe doubling the spot size will increase my depth of cut hence giving me more range for thicker material.

 

[JeanFreli]

First you need a buble nozzle; #1 or #1.2 depends of the result
.250 mild steel use oxygene, less expensive; .6 bar
Piercing have to be pulse
Speed; 74 inch\min
If you have dross under it it because of your protective lens dirty ...believe me it goes fast dirty if you don't cut tru.
Focal for mild steel is over; I use 2 to 2.2
Before you enter your plate in the machine spray anti-spatter over and wipe it everywhere on the plate to be uniform. A good anti-spatter will help you a lot on the piercing.