Rapid prototyping with lasers using metal powder jets

Rapid Prototyping is an important part of modem development sequences, where a variety of solutions is available nowadays, ranging from ultrafast machining via casting technologies, laminated objects manufacturing, also with lasers, to stereolithography and laser sintering. Most of these processes suffer from certain restrictions, either in terms of raw material, geometry or quality of the finished workpiece. In particular, laser sintering leads to structures with a low density that reduces the strength of the part considerably. Since the individual powder particles are only molten at their surface and adhere thus to each other, only in small regions of the surface leaving the majority of the grain mass unmolten and resulting in a faint lattice that must be filled with an additional material to reach the necessary strength. A different solution offers the Blown Powder Process, where a jet of e.g. metal powder is directed towards the surface of the workpiece in the focus of a laser beam, thus melting each metal particle totally and producing practically molten droplets that settle on the momentary surface of the workpiece, thus being welded to the latter. Since all the material delivered to the workpiece is perfectly molten and resolidified, very dense structures with a high strength comparable to the strength of the initial unpowderized material are obtained, as experiments carried out by the authors with different powderized materials have shown. It has also been demonstrated that the latter process can be used to generate nearly arbitrary 3D geometry. A lot of effort has been invested by the authors to avoid the influence of the direction of the necessary relative motion between laser, powder jet and workpiece and also to reduce the roughness of the surface generated by the actual process. Further experimental investigations will be devoted to the clarification of the range of materials, where the actual process can be applied and to the generation of practical parts followed by testing of their strength, fatigue properties and wear.