Laser Turning – New Technology

A tweezer for microsurgery, manufactured using laser turning technology. The hole in the tip measures just over 0.1 mm in diameter. Photo: GFH

Some materials wear out tools quickly: diamonds, for example. They can ruin any turning tool in no time. Ceramics are also a real challenge, as even the hardest milling heads quickly lose their edge. Or carbon: due to its abrasive properties, it rapidly dulls even the best drills. Laser beams, however, can help. They stay sharp—no matter what. For a long time, lasers have been used for cutting, drilling, and structuring across large parts of the manufacturing industry. GFH GmbH from Deggendorf is now expanding the range of laser applications with a new technique: laser turning.

“With this process, the surfaces of conventionally turned parts can also be finished.” Florian Lendner, Member of the Executive Board at GFH. Photo: GFH

A pulsed laser with about 50 W of power is used for the process. The pulse duration is in the picosecond or even femtosecond range, with a frequency between 200 kHz and 1 MHz. “This means that the high energy of a pulse acts on the workpiece for a very short time,” explains Florian Lendner, a member of GFH’s management team. “As a result, material is vaporized at the desired spot before melting effects or thermal changes in the surrounding area can occur.”
Similar to traditional turning, in laser turning, the workpiece also rotates around its own axis. “This is the only way to guarantee a rotationally symmetric shape of the final product,” says Lendner. A technical challenge was the varying diameters of the workpiece and the associated differences in track speeds. Normally, this would result in an uneven distribution of laser pulses: closer to the axis, there would be more energy input than at the outer areas. This would lead to thermal effects or insufficient material removal. “We solved this problem by not orienting the pulse frequency based on time, but on distance. So instead of emitting a pulse every 10 ns, for example, it’s every 10 µm,” Lendner explains. The value is always fine-tuned to ensure the process is efficient while remaining athermal.
Additionally, the removal tool—the laser beam—also rotates. This is made possible by a special trepanning optic. Its design is explained in the graphic on the left (top section): the outgoing laser enters a tube. Inside, it passes through cylindrical lenses. The entire tube is set into fast rotation by a finely balanced precision spindle, causing the laser beam to rotate as well. It traces a perfect circular path, with up to 30,000 revolutions per minute. By controlling the entry angle and position into the tube, the output angle of the beam can be precisely adjusted. A focusing lens is used to set the diameter of the circular path on the workpiece, which can be reduced to as small as 25 µm. This tool is then guided laterally onto the rotating workpiece (see graphic on the left, bottom section).
Currently, this process is being used to manufacture medical devices, among other things. Using a microsurgical tweezer (see photo at the bottom right) as an example, Lendner illustrates the extensive possibilities of laser turning: “First, the outer contour is roughly shaped with a slight excess. The laser parameters are set so coarsely that several 10 mm ³ of material can be removed per minute.” Any particles or vapors that might arise are extracted laterally. “Afterward comes the fine machining,” the 32-year-old explains. With the right choice of laser parameters, outer radii of just 20 µm can be turned. And the surface roughness (Ra) can be reduced to less than 0.1 µm.
The subsequent splitting of the tweezer body into two halves is also done by the laser. The same applies to any holes in the tweezer tip. What starts as a turning tool can be quickly transformed into a cutting blade, drill, or even a milling head without needing to reposition the workpiece.

The trepanning optics uses lenses and a precision spindle to create a rapidly rotating laser spot. Here, it functions as a drill. Photo: GFH

A major advantage of GFH’s technology is that drilling and cutting can be performed truly perpendicularly to the workpiece. “In conventional laser drilling, this is not easily achievable. There is always an angular deviation of at least five degrees,” says Lendner. “This is due to the Gaussian energy distribution of the laser and shadowing at the edge of the hole.” If neither the workpiece nor the laser optics is angled at a defined angle, a conical hole rather than a cylindrical one results. This effect can be easily addressed with the trepanning optics: it’s sufficient to adjust the entry angle of the laser beam accordingly. This works up to a maximum ratio of hole diameter to depth of 1:10. The optics even allow for undercuts, meaning negative wall angles. Another benefit is that very delicate pins or needles can be turned. Unlike in traditional lathes, there is no mechanical force exerted, so the workpiece is not pushed away or broken.

In turning, the rotating laser spot is guided from the side onto the rotating workpiece. Photo: GFH

The machine basis consists of the GL.evo and GL.compact machining centers from GFH. According to Lendner, they are characterized by their very precise yet highly dynamic kinematics. “This allows the laser to be positioned with an accuracy of ± 1 µm on the workpiece, despite accelerations of up to 20 m/s². The five axes— including two rotary axes in the workpiece clamping—enable longitudinal turning, cross-section turning, cross-plan turning, as well as spherical and contour turning.”