Co2 vs fibre

[matthew knott]

Just a quick straw pole, who here thinks the main reason a fibre will directly engrave metal and a co2 won't (assuming low powers here) is the wavelength ?

[Scott Shepherd]

My thoughts are it's a power @ wavelength issue Matt. That could be 100% wrong, I don't know. But it's my understanding that at "X" power, "Y" wavelength will not penetrate metal. I suspect there is a curve where the power hits a point that it will penetrate.

Is that incorrect?

[Mary Ma]

My thoughts are it's a power @ wavelength issue Matt. That could be 100% wrong, I don't know. But it's my understanding that at "X" power, "Y" wavelength will not penetrate metal. I suspect there is a curve where the power hits a point that it will penetrate.

Is that incorrect?

Agree. Fiber is generally suitable for metal. co2 is more often used for non-metal materials. And that's partially because of the wave length.

[Dan Hintz]

My thoughts are it's a power @ wavelength issue Matt.

This ^^^^^^

A significantly smaller portion of energy is absorbed by metal at the CO2 wavelength compared to the fiber wavelength... enough power and you can still cut with CO2, but a fiber is more efficient.

[Keith Winter]

This ^^^^^^

A significantly smaller portion of energy is absorbed by metal at the CO2 wavelength compared to the fiber wavelength... enough power and you can still cut with CO2, but a fiber is more efficient.

Spot on. ^^

[Scott Shepherd]

I think many of us simply the statement by making comments like "It's the wrong wavelength, it won't penetrate", which a more accurate statement is "at 80W, that wavelength isn't going to penetrate".

[Jon Colley]

It's really 3 things:
- more energy in the 1060-1070nm wavelength is absorbed by metals vs. 10600nm ("normal" CO2)
- the smaller spot size gives a much greater energy density
- for marking lasers (usually pulsed; not CW or continuous wave), short pulses concentrate the energy over a much shorter time period which makes for more effective power (1mJ over 100ns = 10kW! ; 1mJ times 20kHz = 20W average power)

I wrote an article on this topic for Engraver's Journal back in 2011 if you want to read some more detail. It was not intended to be a scientific article but more of a practical explanation.

[Dave Sheldrake]

My thoughts are it's a power @ wavelength issue Matt.

A product of Energy Vs Time Vs Absorption rate (or reflective index)

The G100 pulsed 100watt CO2 cuts steel quite well so I would guess that 10^6 watts square inch energy is about right

[matthew knott]

Every one is kinda right except Jon , who is exactly right , the wavelength is not the biggest factor by a wide margin, a 100 watt continues wave fibre will not engrave metal , a 5 watt pulsed fibre will ! Its all about peak power and generally over 5kw for blasting metal. It's only a special type of fibre that's really 'good' at engraving , as it happens that's pretty much all that's ever used so it can be taken out of the equation. But I'm dealing with someone that has got hold of a 150watt yag and can't understand why it won't even cut thin aluminium when the job was done before on a 20 watt laser. It always seem the general consensus it's 'wavelength' is the key & it's not

[Scott Shepherd]

Yeah, I think there's about about 4 of you on here that understand the pulsed side of the equation :)

[Dan Hintz]

Every one is kinda right except Jon , who is exactly right , the wavelength is not the biggest factor by a wide margin, a 100 watt continues wave fibre will not engrave metal , a 5 watt pulsed fibre will ! Its all about peak power and generally over 5kw for blasting metal. It's only a special type of fibre that's really 'good' at engraving , as it happens that's pretty much all that's ever used so it can be taken out of the equation. But I'm dealing with someone that has got hold of a 150watt yag and can't understand why it won't even cut thin aluminium when the job was done before on a 20 watt laser. It always seem the general consensus it's 'wavelength' is the key & it's not

As I said earlier, energy absorbed is the key. Instantaneous energy absorbed, for sure, but still energy absorbed (and, of course, add "per unit of material" to that if you want to be ultra-precise). I'm not sure I would label it as a "special type" of fiber, however. A YAG can do the job if it's Q-switched, but you're certainly going to see much better numbers with something that can build up a much higher peak power (e.g., MOPA/MOFA). Wavelength is often used as a deciding factor because it appears like you're matching apples to apples, like saying a 250hp car is faster than a 200hp car (which can also be quite false), but the generalization is a reasonable one for most cases. You just have to make sure the assumptions being used for the rule of thumb still apply.

[matthew knott]

all true Dan, my point is the wavelength is NOT the most important factor, its a factor that has an effect but is genrally used as the deciding factor. its all semantics as even though the genralisation is wrong the outcome is right. fibres are better on metal and thats probably all that maters.
thanks for the feedback guys