improving laser cutting finish

[engtobe]

I am looking into improving the surface finish of a cut when we use the laser on 3/8" to 1/2" thick material.

Mainly I find that the piece that is being worked on becomes to hot and that when he finish goes ugly on it.

My general idea is to prevent the part from becoming to hot. Or would this cause a to big temperature difference and increase my problem.

I don't know much on this subject, it would be appreciated if someone could helps me or refer me to website, book,etc.

 

[1plus1]

Many factors contribute to a good finish on a laser cut. Proper parameters or cutting data(Wattage power,duty, frequency,continous wave), feed rate, oxygen assist gas pressure, lens focus, clean lens, nozzle centering(alignment),and proper nozzle tip. A focal length of 7" is better than a 5" on 3/8 or thicker carbon steel, if your laser can accept a lens change. A properly tuned laser and clean internal bend mirrors that are aligned help the cut, also. A water assisted cut helps, if the laser has this option. It would help if I knew the type of laser you have and the wattage. Also the dimensions of the part. I have operated three lasers since 1991 and each has a different "style" of cutting. I assume you have a laser of about 2000 watts. You may want to check with the manufacturer of your laser to find the proper parameter setting for your laser. Most have a process engineer or Tech who will help you. Also check your lens. If it is dirty or heavily spotted, clean it properly or replace it. Change the nozzle tip if necessary. Make sure the beam is centered in the nozzle opening(called nozzle centering or alignment).Also check the focus position. I have found that setting the focus at a small minus setting increases the kerf size and allows the assist gas to blow out more slag for a smoother cut. Try different feed rates, oxygen pressure, and small focal point changes combinations on a small test square to find a good setting.

 

[engtobe]

ok, great info.

But I now realize that I was not precise enought in my question.Sorry about that!!

We are able to get good finish when we do a contour. But when is time to do holes ( round or squared) in the middle of the part we cannot get the desired result.

It seem like the part becomes to hot localy and the metal just blow out.

The machine is an Amada lasemac 1212(2000 watts)

The piece we are presently working on, is about 3.5" by 2.5", the contour as a nice finish but the two 0.5" square hole we do in the middle have an ugly finish.

Does anyone have an idea on how to solve this?

thank you in advanced

 

[1plus1]

I am somewhat familiar with Amada lasers. I assume the laser uses cutting data sheets. Small square or round holes are tricky in thick metals, but not impossible. You will have to experiment on a scrap piece first. You cannot use the same cutting data on the contour and the holes,it generally won't work. Heat is a factor. In your program you will have to assign a different cutting data for the holes , then use the cutting data you presently use to cut the contour. I can only give you some general idea to start from, then you will have to experiment a little and make a combination of changes in the cutting data sheet. First of all, slow the feedrate down to 5 - 25 ipm, power 1500-1800 watts,frequency 700-1300, duty (big factor here) 20-50%. Focal point .039 to .079. Use edge data for good square corners. Gas pressure and other factors can stay the same as your contour data. What your trying to do is cut out the holes with laser "bursts" so the area is not heated to high and has a lot of dross. The parameters I gave you are not absolutes. Maybe a feedrate above 25 ipm will work and a duty cycle of 70% will work. The point is you will have to find that right combination of feedrate, power,frequency,and duty to make a good small hole. Good luck.

 

[aamoroso]

Are you using a lead in on the holes or are you pecking in and cutting on the contour of the hole. You may try messing with different lead-in lengths to allow the heat to disperse before cutting the profile.

I am not positive but I believe we peck and contour at different settings (are programming is all automated so I don't pay much attention but I believe we use different sub programs for pecking and contouring).

Fill what's empty. Empty what's full. And scratch where it itches.