Researchers at the Fraunhofer Institute for Laser Technology ILT in Germany have helped develop a machine tool that can polish both simple and complex surfaces using laser beams. The machine is intended to replace laborious hand polishing that moldmakers typically use on metal molds.
“Polishing removes material from the surface to even it out. In contrast, the machine tool uses a laser to melt a thin surface layer roughly 20 to 100-µm deep,” says Section Head at the ILT Edgar Willenborg. The machine tool consists of a five-axis gantry and three-axis laser scanner, which lets it access workpieces from all sides. Mirrors deflect the laser beam for feed rates greater than 1 m/sec, even on small surfaces.
The laser beam is directed by CAM data that comes from the 3D CAD model of the component being polished. “We use conventional CAM programs such as those used in milling processes,” says Willenborg. “That’s because most companies already run that kind of software, so employees already know how to use it.”
The calculated beam path data then moves to postprocessing software developed at the ILT, which handles more-advanced aspects of the polishing technique. For example, it adapts the laser to the specific angle of incidence and component edges in each particular case.
Depending on the material being polished, the machine tool can produce surfaces with average roughnesses (Ra) of 0.1 to 0.4 µm. “Hand polishing can still get better results,” says Willenborg. “But certain jobs — such as molds for glassmaking and forming and forging tools — just need a medium-quality surface. For these cases, the new tool could slash production costs. According to researchers, the machine tool polishes surfaces up to 10 times faster than a hand polisher and is a good option for small batches.
The new technology also advances machine development. “Unlike conventional polishing, laser polishing does not primarily rely on the machine’s rigidity for high component quality,” says Willenborg.” Instead, the technique relies on a property that applies to all liquids — surface tension. Surface tension ensures the layer of liquid metal solidifies evenly.”
According to the Fraunhofer Institute, the polishing machine will soon be ready for market launch. It will be showcased for the first time at this year‘s EuroMold event
(November 29 to December 2).