TECHNICAL FIELD

The present disclosure relates generally to laser machining, and more particularly, to laser machining systems and methods using laser beams having uniform beam profile and narrow beam divergence for forming zero and negative taper machined cuts.

BACKGROUND

In laser machining, a laser beam generation device is used in conjunction with an optical system to direct the laser beam onto a workpiece that is to be machined. The impingement of the laser beam on the workpiece locally melts and/or vaporizes the workpiece material to produce or extend a hole or cut in the workpiece. The location of the laser beam impingement point on the workpiece may be controlled by moving one or both of the laser beam and the workpiece relative to one another to thereby control the geometry of the hole or cut.

Laser machining of workpieces often produce edges along the cut features that exhibit taper. One approach to avoid tapered edges is to use a special trepanning head to rotate the laser beam at a spot location with a fixed tilt angle. The part remains stationary. Such an approach is only good for small hole drilling. Another approach is to rotate the part physically while keeping the laser beam at the same incident angle, which need high precision CNC stage (usually 4-5 axis) and sophisticated control software to achieve a zero taper cut.

There is a need for laser machining systems and methods using laser beams having uniform beam profile and narrow beam divergence for forming zero and negative taper machined cuts.

SUMMARY

The present disclosure provides, in a first aspect, a method for laser machining a workpiece. The method includes directing, from an F-theta lens having a long focal length of greater than about 250 millimeters, a laser beam at a non-perpendicular beam tilt angle from an optical axis of the lens having a top-hat profile and a narrow beam divergence angle of between about 1 degree and about 3 degrees towards a workpiece disposed on a stage movable in at least an X-direction and a Y-direction, engaging the directed laser beam with the workpiece disposed in the usable field of view, moving the workpiece and the directed laser beam relative to each other, and removing portions of the workpiece with the directed laser beam to define a machined surface.

The present disclosure provides, in a second aspect, a laser micromachining system for laser machining a workpiece. The laser micromachining system includes a laser, a converter, an F-theta lens a stage, a beam steering device, and a controller. The laser is operable to generate a laser beam having a Gaussian profile. The converter is operable to convert the laser beam having the Gaussian profile into the laser beam having the top-hat profile. The F-theta lens has a long focal length of greater than about 250 millimeters. The stage is operable to support and move the workpiece movable in at least an X-direction and a Y-direction. The beam steering device is operable for receiving the laser beam having the top-hat profile and directing the laser beam through the F-theta lens at an angle from an optical axis of the lens towards the workpiece on the stage. The laser beam is directable over a range of angles from the optical axis of the lens defining a usable field of view having a perimeter and having a narrow beam divergence angle of between about 1 degree and about 3 degrees. The controller is operable to control motion of said stage and/or said beam steering device to orientate the laser beam having the top-hat profile through the F-theta lens and onto the workpiece removing portions of the workpiece with the directed laser beam to define a machined surface.

