At present, components used in areas such as tool and die making
generally have to be painstakingly polished by hand – but a
recently developed automated process could soon offer a much faster
solution. Fraunhofer researchers unveil a machine tool that uses laser
polishing to give even complex 3D surfaces a high-gloss finish.
Millimeter by millimeter, the polisher uses grinding stones and
polishing pastes to polish the surface of a metal mold, working at a
rate of some ten minutes per square centimeter. This activity is
time-consuming and hence incurs a significant cost. What is more, many
companies are struggling to find new recruits for such a challenging
yet monotonous task.
But the era of laborious hand polishing could soon be over: In
collaboration with the companies Maschinenfabrik Arnold and S&F
Systemtechnik, researchers at the Fraunhofer Institute for Laser
Technology ILT have developed a novel type of machine tool which can
polish both simple and complex surfaces using laser beams.
"Conventional methods remove material from the surface to even it out.
Our method is different: It uses a laser to melt a thin surface layer
roughly 20 to 100 µm deep," says Dr.-Ing. Edgar Willenborg,
Section Head at the ILT in Aachen. "Surface tension – a property
that applies to all liquids – ensures that the layer of liquid
metal solidifies evenly."
Depending on the material, the project team can already produce
surfaces with an average roughness (Ra) of between 0.1 and 0.4
µm. "Hand polishing can still get better results than that,"
Willenborg admits, "but the point is that in many applications –
for example molds for glass-making, forming and forging tools – a
medium-quality surface is all that is needed". The new machine
developed at the Aachen-based ILT has the potential to save
considerable amounts of time and money in these areas:
The machine polishes surfaces up to ten times faster than a hand
polisher and is an excellent option for serial production and for
polishing small batches.
The new laser polishing system consists of a 5-axis gantry system plus
an additional 3-axis laser scanner, a design that enables the workpiece
to be accessed from all sides. Carefully arranged mirrors deflect the
laser beam to allow feed rates (the speed at which the laser beam moves
along the workpiece within a specified time frame) in excess of one
meter a second, even on small surfaces. An end-to-end CAM NC data chain
has also been developed which draws on a 3D CAD model of the component
to be polished. The beam path data is calculated on the basis of this
model. "For this step, we use conventional computer-aided manufacturing
(CAM) programs such as those used in milling processes. The advantage
is that companies are typically already running those kinds of programs
so the employees know how to use them," says Willenborg. The calculated
beam path data is then supplied to a special post-processing software
program developed at the ILT. This program configures more advanced
aspects – for example adapting the laser to the specific angle of
incidence and component edges in each particular case.
This new process technology also offers benefits in terms of machine
development: "The fact that we are working with a completely new
operating principle makes it much easier to construct the machines we
need," Willenborg says. "Unlike conventional polishing techniques,
laser polishing does not primarily rely on the rigidity of the machine
to achieve high component quality, but rather on the physics of surface
More information at http://www.ilt.fraunhofer.de/