Polishing metal surfaces is a demanding but monotonous task, and it is difficult to find skilled operatives. Polishing machines do not represent an adequate alternative because they cannot get to difficult parts of the surface. However, a new solution to this problem is provided by laser polishers.
Researchers at the Fraunhofer Institute for Laser Technology (ILT) in Aachen have developed a way of automating the polishing work: Dr-Ing Edgar Willenborg, group leader at the ILT, explains: "We do not polish the surface by hand with grinding and polishing media. Instead we use a laser. The laser beam melts the surface to a depth of about 50 to 100 micrometers. Surface tension ensures that the liquid metal flows evenly and solidifies smoothly."
Like in conventional grinding and polishing, the process is repeated with increasing degrees of fineness. In the first stage the researchers melt the surface to a depth of about 100 micrometers; in further steps they gradually reduce the depth. Willenborg adds: "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."
Laser polishing does not achieve the same surface smoothness as perfect hand polishing – hand polishers can achieve a roughness Ra of 5 nanometres, the laser at present can only manage 50 nanometres – but Willenborg still sees considerable market potential for the system: "We will concentrate on automating the medium grades: a roughness of 50 nanometres is adequate for many applications, including the moulds used for making standard plastic parts." The high-end levels of smoothness will therefore remain the domain of skilled hand polishers.
The potential time saved by laser polishing and the associated cost savings are enormous. Whereas a skilled polisher needs about 10 to 30 minutes for each square centimetre, the laser polishes the same area in about one minute. A prototype of the laser polishing machine developed by the scientists in co-operation with mechanical engineering firm Maschinenfabrik Arnold has already been built. Willenborg estimates that the system will be ready for industrial use in one to two years' time. At the Euromold trade show, to be held from 2-5 December 2009 in Frankfurt, Germany, the researchers will be presenting examples of three-dimensional surfaces polished by laser (Hall 8, Stand M114).
For more information, visit www.fraunhofer.de
