The difference between the collimation mirror and the focusing mirror of laser cutting machine
Laser cutting machine from the energy fiber out of the light, it is a point light source, is a divergence angle (θ), if we put this point light source in the optical fiber collimator focus, we know: from a focus mirror (quasi-direct mirror, which is actually the focus mirror in turn) emitted by the focus of light, after the focus of the mirror into a parallel light Then after this quasi-direct mirror out of the beam diameter is how large, the formula is 2f*tag (1/2*θ), such as the divergence angle is 10°,f=150mm, then the beam from the quasi-direct lens diameter of =2*150*tag (5°) =26.2466mm. After the optical fiber collimator, the laser enters the optical fiber cutting machine’s focus mirror, in general, the collimation lens focal length ÷ focus lens focal length = focus after the energy density relative to the previous density ratio, for example: collimation lens focal length is 75mm, focus lens focal length is 150mm,75÷150=1/ 2, this means that after the focus of the lens focus on the area of the spot compared to the point from the energy fiber from the light source of the area of a large one-fold, the energy density is the original 1/2.
First, we will doubt: energy density concentration is not better? Why reduce light energy density?
There are several main reasons:
1, if the focal length of the lens is shorter, the focus of the lens of the more shallow focal depth, the focal depth will easily lead to cut;
2, the shorter the focal length, the smaller the focus point, the smaller the slit, the smaller the seam is not conducive to cutting out of the slag drop, resulting in a cut.
So we generally try to use the focal length between 120-150mm to do the optical fiber cutting machine focusing mirror.
Second, the question comes again, why do not we use the long focal length of the collimator mirror?
Here are two reasons:
1, with long focal length of the optical fiber collimator lens, the need for larger lens diameter, will lead to mechanical design more trouble;
2, the long-focal length of the optical fiber collimator will lead to the focus of the optical fiber cutting machine focus is very sensitive, once the focus of the lens away from the focal point will be a little bit of the phenomenon appears, which is our general fiber cutting machine focus generally in: 60-100mm between the reasons.