Technology of laser deposition of narrow bead overlays using solid and flux-cored wires

摘要

The use of high-power diode laser in the process of surfacing with a wire filler material makes it possible to deposit high quality, narrow beads on both flat surfaces and working edges of, say, tools. High quality of overlays feed is a decisive one when the weld- face quality is considered. Too low a rate results in a drop-melting mode of the wire and produces a very uneven weld face, the uneveness corresponds to the instants at which separation of drops of the molten metal from the wire end takes place (Fig 4). Increase of the rate to over the optimal value produces, for the given wire and power of the laser beam, an overlay characterised by partly melted wire elements which then appear on the weld face (Fig 5). Similarly, the quality of the weld face is affected by the location of the wire terminal with respect to the laser beam focus. As the depth of advance of the wire into the laser-beam increases, the surface of it absorbing laser radiation, also increases. The mode of the wire melting changes from continuous to interrupted droplet-form, and a considerable uneveness in the weld face is produced (Fig 4). With a solid wire it becomes possible to locate its terminal within the boundary of the laser-beam at about 1/3 of its length (Fig 3). A further shift of the wire terminal into the laser beam results in the droplet mode of its melting. Positioning of a flux-cored wire on the edge of the laser-beam focus will produce an overlay with fragments of partially melted elements of the wire, just as will be the case when the wire is shifted along the transverse axis of the laser beam focus (Fig 5). Overlays with smooth and even weld faces were deposited only when the wire terminal was located at about 1/3 of the focal length (Fig 3). The very small difference between the width of the laser beam focus, and the wire diameter calls, in both cases, for the positioning of the wire terminal exactly in the middle of the focus width. Even a minimal change in the location of the wire end will immediately produce a deterioration in the quality of the deposited overlay by leaving partly melted elements of the wire protruding from the weld face (Fig 5).