Taper in fibre laser

[collins8991]

Hi Guys,

On a Amada FLC-AJ and experiencing taper across 1.2mm stainless. It's taper of 0.025mm, 0.6mm deep which then tapers back in - similar to a hour glass form.

Tried adjust focus with no huge beneift.

Any suggestions greatly appreciated!

 

[MacGyverS2000]

Where is your focal point? I'm going to guess 0.6mm into the material?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[collins8991]

New to all this so excuse my ignorance but how do you know were the focal point is in the material?

 

[Foostrap]

Should be indicated in your cut conditions at the machine.

 

[collins8991]

oh yes sorry. It's set at 1.0. I focused the lense with this material for the narrowest kerf width and went from there. Adjust the focus point doesn't seem to give me a much better result?

 

[MacGyverS2000]

The smallest kerf also means the most pronounced hourglass shape. Keep that in mind when choosing focal lengths.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[collins8991]

Really? So if I have the focal point lets say 0.6 deep in a 1.2mm thick material in theory I should get a hour glass taper? And is there any point above or below which can minimise the taper? Also do ye think adjust powers etc would have any influence? New to this technology.

 

[MacGyverS2000]

This is what a laser beam looks like after the focal lens:
[image

http://www.spikenzielabs.com/SpikenzieLabs/Laser_How_To_files/Picture 17.png

]

The longer the focal length, the more stretched out the hourglass. A really short focal length will show a very pronounced hourglass, particularly in thicker metals (and the loss of processing energy shows when you try to use a short focal length lens with a thick substrate).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[collins8991]

I see. So if I can produce a longer focal length I should be able to minimise the taper of the hourglass? So the focal point is dictated by the lense position above the material, but what conveners the focal length?

 

[MacGyverS2000]

As your focal length increases, you also lose power density because the focal point (the waist of the hourglass) gets wider. You'll have to either increase power, or slow down your speed.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[collins8991]

Ok. So as I increase the focal length the actual focal point, that width increases. And i adjust the focal point by moving the lense up or down but how do you adjust the length? Or is that the actual distance from the top of the sheet to the lense? Sorry about the basic questions - new to this technology!

Also Power, Freq and Duty - if you reduce duty (that's the on/off time of the beam per cycle?) would you increase frequency to allow for that gap between beams?

 

[MacGyverS2000]

The focal length (distance from lens to beam waist) is determined by the lens. Due to physics, the beam waist increases in size slightly with increases in focal length. For example, a 1.5" lens might have a spot size of 3 mils, a 2" spot of 5 mil, and a 4" spot of 7 mils.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[collins8991]

So would I be right in saying the larger the focal length, the less pronounced the hourglass effect of the laser beam is which would minimize the taper - however this would result in a larger kerf or beam waist and a lower power density?

 

[MacGyverS2000]

Correct on all counts...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[collins8991]

Great. Thank for the help, much appreciated!

 

[MacGyverS2000]

BTW, I should mention... the spot sizes I mentioned earlier were for CO2 wavelengths. Figure a rough order of magnitude smaller spot sizes for fiber.

Dan - Owner

http://www.Hi-TecDesigns.com