Laser automates mould polishing

Researchers at the Fraunhofer Institute for Laser Technology (ILT) in Aachen have developed a way of automating the polishing of injection moulds by using lasers.

Polishing injection moulds is time consuming and monotonous but requires high levels of concentration as any blemish in the mould can render it useless.

A skilled worker may often need a whole week to polish a single metal mould and up until now it has not been possible to use machines for the work because they could not polish the curved parts of the mould.

Describing the new technique, Dr Edgar Willenborg, group leader at the ILT, said: ’The laser beam melts the surface to a depth of about 50 to 100um. Surface tension ensures that the liquid metal flows evenly and solidifies smoothly.’

As 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 100um, in further steps they gradually reduce the depth.

’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 Willenborg.

Laser polishing does not achieve the same surface smoothness as perfect hand polishing – hand polishers can achieve a roughness average - or Ra - of 5nm, while at present the laser can only manage 50nm, but Willenborg still sees considerable market potential for the system.

’A roughness of 50nm is adequate for many applications, including polishing the moulds used for making standard plastic parts,’ said Willenborg

The time gained by laser polishing and the cost savings achieved are enormous. Whereas a skilled polisher needs about 10 to 30min to polish each square centimetre of a mould, the laser polishes the same area in about a minute.

A prototype of the laser polishing machine, developed by the scientists in cooperation with Maschinenfabrik Arnold, has already been built. Willenborg estimates that the system will be ready for industrial use in one to two years’ time.