A typical laser cladding machine for additive manufacturing consists of a laser source, a processing head, a numeric control, and an enclosure. Material can be added in the form of a wire or a powder feed. The necessary laser power depends on the material and the targeted deposition rate. Typically, 0.5–3 kW near-infrared diode, fiber, or disk lasers are used. The machine presented here has a 680 W diode laser, six independent axes of movement, and a build volume of 1000 × 1500 × 1000 mm (W×H×D). It is equipped with a coaxial powder-based processing head. For process control, a pyrometer and a computer-vision system are in place (see Fig. 1.1).
Starting from the laser beam source, the laser light is guided to the process head via an optical fiber. There, the beam propagates through a converging lens that collimates the beam. The beam is reflected at a dichroitic mirror at a 45° angle. The mirror is transmissive for the pyrometer and the camera wavelength. The combined process and sensor beams are focused on a substrate. The workpiece is melted locally and through an annular nozzle. Shield gas and metal powder are added coaxially. Moving the process head results in weld beads, which can be oriented in the x and y direction. Volumetric buildup is created by stacking layers and remelting previously printed material.
Materials that can be processed by laser cladding are manifold. The main requirement is availability as powder or wire, depending on the used technique. One of the advantages of powder-based materials is that the material composition can easily be modified (see Fig. 1.2) (Neef et al. 2019). Even in situ alloys of incompatible materials like metals and ceramics can be achieved. Printable, atomized metal powder can range from structural steel to special nickel superalloys like CMSX-4 and PWA 1426 (Alfred et al. 2018). Furthermore, due to the free control of the powder mass flow, high-resolution parts can be manufactured. In contrast,wire-based laser cladding processes are used for coarser structures. It is a cleaner process since less material is lost by powder overspray. Generally, metal wires are available at lower costs, but with their fixed metallurgic composition, variations of additives can only be done by coating the surface of the wires (Gehling et al. 2019). Powder properties like particle size and distribution in conjunction with their morphology dictate the flowability of the powder due to the possible interlocking of individual grains. Compared to powder bed processes, laser cladding is less sensitive to variations of these properties and allows for heterogeneous powder compositions.
An overview of common additive manufacturing materials can be seen in Table 1.1.
