View Full Version : what's right focus lens for laser die cutting machine with 300-400w co2 laser tube

leland huang
07-04-2016, 2:35 AM
Hi all,
we are making one head laser die cutting machine, sample machine is 300w combined laser tube(3 pcs 120w laser tube combined together). Now we want to make 400w (3pcs 150w laser tube combined). But for 300w machine, we tried many times for different focus lens, say F120, F100, F70, but seemed cutting result is not perfect, for whole 18mm thick board 110*90cm, about 5-7 section is not cut through. The image is for cigaret box, very complicated, say picture atttached.


So any one knows better about the right focus lens?

Leland Huang
Liaocheng Shenhui Laser Equipment Co., Ltd

Rodne Gold
07-04-2016, 3:50 AM
Assuming an 8mm beam from the tubes , you would need around a 220mm focal lens to get an 18mm depth of focus , however your power density might not be enough for an 18mm cut into wood as your spot size will increase

Dave Sheldrake
07-04-2016, 4:26 PM
Are you phase stacking? How are you dealing with the cancellation effect? What combiner are you using?

leland huang
07-05-2016, 4:26 AM
In theory the focus spot should be inside of the die board, but we tried, no way to cut it through. Finally the focus spot is 4-7mm above the board. Most of die board is cut through, only several section not cut through. We tried F120,F100,F70 lens, F120 and F70 lens can not cut as well as F100 lens.

About laser power, we were told by laser tube factory 300w is enough to cut 18mm die board and they showed me working video. But finally it can not cut perfectly. So we are planing to make new machine with 400w laser tube. About the voltage, we use transformer to get 240v so that to provide stable and enough voltage.

300w machine can cut 2mm ss steel at speed of 25mm/s, but to cut die board, seemed not enough. We will try 400w soon.

leland huang
07-05-2016, 4:30 AM
Pls see the picture of combined laser tube.340256 I'm not technician, so can not understand your words well.

Rodne Gold
07-05-2016, 4:43 AM
When I was in china at the factory , the machines cutting thick die board worked from the top and the bottom of the sheet --ie one laser cutting top , the other the bottom

Dave Sheldrake
07-05-2016, 12:06 PM
Try circular polarising and phase stacking by means of a Phase retarding mirror, it will be a lot more efficient. You are getting 300 watts thermal, but not 300 watts effective ERP unless the directionals are stacked properly (given that it is very hard to phase stack 3 DC generated beams)

leland huang
07-06-2016, 2:52 AM
It was me to show boss this design, which was told by one of my customer. I sold this type to Pakistan. It is two laser head, only two pcs 150w laser tube, but it cuts well, but not easy to adjust light path since it has two laser heads.
Blanka sold one or two sets, I sold two sets, other workmates sold some, total no more than 30 sets. All response hard to adjust light path.

leland huang
07-06-2016, 3:12 AM
You said it. it has 3 reflector mirrors, each reflect reduces light power. The light from laser tube is round circle, but after first reflecting, it will be oval. Who knows what shape it is after 3 times reflecting? But seemed no better way but changing laser tube direction to use one reflector or no reflector.

If voltage is 220v, when laser tube works, the voltage becomes to only 196v. So we use transformer to provide 240v, when laser tube works, the voltage is about 216v. Then it cuts better.

Dave Sheldrake
07-06-2016, 6:56 AM
It's to do with the polarisation of the beam, if you point two or more lasers at the same spot and the beam phases aren't stacked properly you will get 300 watts thermal but not 300 effective radiated power. Folded resonators are common on big machines and RF units but don't work well in DC units.

You need a phase retarding mirror and a beam combiner, this is why the F220 tube from Bj EFR uses a circular polarising mirror after the output coupler (although due to heat the F220 has a habit of blowing up quite quickly)