Patent ID: 7608799

Claim:
A laser welding process, comprising: welding overlapped steel plates with a solid state laser processing apparatus, said apparatus comprising: a solid-state laser oscillator for oscillating a laser beam, said oscillator comprising an exciter, a partial reflection mirror, first and second lenses, and an aperture having a controlled diameter for controlling a beam diameter of the laser beam; an optical fiber for guiding the controlled laser beam; and a processing head comprising a transfer optical system for focusing the guided laser beam, and for irradiating the guided laser beam to a surface of a workpiece to be processed; the laser welding process comprising: controlling the beam diameter by controlling the controlled diameter of the aperture such that a beam quality M 2 of the laser falls in a range of 85≦M 2 ≦105, wherein the laser beam has a first incidence angle θ 1 prior to entering the optical fiber, and a second incidence angle θ 2 after exiting the optical fiber, wherein θ 1 =tan −1 (A/2L)=A/2L, and θ 1 ≈θ 2 , wherein the beam quality M 2 is defined as M 2 =π×D×(θ 2 /1.5)/(2×λ), with D being the diameter of the optical fiber, wherein λ is a wavelength of the laser beam, wherein A is a diameter of the aperture, wherein L is a distance from the aperture to the optical fiber, wherein the transfer optical system comprises two spherical lenses, and wherein the two spherical lenses are plane-convex lenses.