Laser polisher achieves surface smoothness of 50nm

Polishing metal surfaces is a demanding, but monotonous, task. Polishing machines are not believed to be adequate alternative for experts because they cannot get to difficult parts of the surface.

However, the Fraunhofer Institute believes it has a solution to the problem in the form of laser polishers. Researchers at the Fraunhofer Institute for Laser Technology (ILT) in Aachen have developed a way of automating the polishing work. "We do not polish the surface by hand with grinding and polishing media. Instead, we use a laser," said Dr Ing Edgar Willenborg, group leader at the ILT. "The laser beam melts the surface to a depth of about 50 to 100µm. Surface tension ensures the liquid metal flows evenly and solidifies smoothly." The process is then repeated with increasing degrees of fineness.
In the first stage, the researchers melt the surface to a depth of about 100µm, but the depth is reduced in further steps. "We can set the melting depth by means of various parameters: the laser output, the speed at which the laser beam travels along the surface and the length of the laser pulses," said Dr Willenborg. While laser polishing does not achieve the same surface smoothness as perfect hand polishing – hand polishers can achieve a roughness Ra of 5nm, while the laser can only manage 50nm – Dr Willenborg sees considerable market potential. "We will concentrate on automating the medium grades: a roughness of 50nm is adequate for many applications, including the moulds used for making standard plastic parts."

Graham Pitcher

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