Additive manufacture of metal parts in industry always involves building an object layer by layer, usually from powder and most frequently using a laser.
The method that has become synonymous with additive manufacturing in people’s minds and in the media looks like this: In a powder bed, a laser fuses metallic powder to form layers of material. The process occurs in a chamber flooded with inert gas. It is called selective laser melting (SLM) or powder bed fusion.
The process creates highly complex components with internal structures or components that are the image of their internal strains. Material is consolidated exactly where it is required to accept and conduct stresses.
SECOND CAREER FOR LMD
Many components, however, do not have internal channels, cavities, and complex power flows. In addition, it is often favorable to apply additional material to existing components – adding a threaded mating surface to a pipe, for instance. In the past, a pipe would have been manufactured with a larger diameter than required and then everything except the connection would have been milled away. Or let’s say you wanted to change the surface geometry of a tool. In these cases, a different process becomes attractive.
Laser deposition welding, also known as laser metal deposition (LMD), inserts the filler material – powder or wire – directly into the melt pool formed by a laser beam, creating a layer of beads welded to each other.
The powder-based version is particularly promising, as it is 3D – capable: many layers build up to produce a body that – because the metal powder is supplied coaxially to the laser beam – can grow in every direction.
VOLUME AND SPEED
What makes deposition welding so exciting as a second additive process is not only the fact that the equipment technology is already fully developed and available, but – and more especially – the deposition volume and speed it can achieve.
With volumes of up to 500 cubic centimeters an hour, it beats conventional manufacturing processes not only from a technological perspective but often in terms of cost-effectiveness, too. And it imposes scarcely any restrictions on developers with respect to combining materials: it can produce almost any kind of sandwich structures and graded layers.
The process is carried out on the component in the ambient air. This reduces non-productive and setup times and means that even large components can be processed. All this reduces the costs per part.
HOPES AND REALITY
Despite the huge potentials of additive manufacturing, skeptics point to many obstacles. The materials are still relatively expensive and the building an object layer by layer is very time consuming.
Heat input, melting times, cooling times, the volume that can be processed – all these things put limits on speed. And then there is the whole business of programming the process. Although the CAD model contains all the necessary data for the component, the machine still needs to be shown a path – from the first welding line to the last dash of powder – and the thermophysical processes in the workpiece have to be taken account of.
At some point in the future, the software will be able to calculate this path on its own. But only now are engineers are laying the groundwork for this capability.
FOR FUNDAMENTAL RESEARCH
This fundamental research is being supported by the European Union, which is sponsoring development collaboration between the European Space Agency (ESA), eight universities, and 19 companies, including TRUMPF.
The objective of the AMAZE project is to manufacture metal components up to two meters tall using additive methods by 2016 – with zero waste. The aim is for production costs to be only half those of conventional processes. TRUMPF is heading and coordinating the laser deposition welding project group.
David J. Jarvis, head of new materials and energy research at ESA and chief coordinator for AMAZE, observes: "When talking about laser additive manufacturing, our conversation must without fail include laser deposition welding. It is an interesting way to conduct repairs, rescue components, and augment existing parts."
TRUMPF Laser- und Systemtechnik GmbH
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