Electric heating – Metal heating – By arc
Patent
1991-11-04
1992-12-08
Albritton, C. L.
Electric heating
Metal heating
By arc
21912178, B23K 2600
Patent
active
051700310
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of bonding a covering layer onto a substrate For example, the invention is particularly applicable to cladding a substrate with a different material or compound.
Cladding by arc welding by various processes such as manual metal arc, submerged arc, flux cored wire, is well-known, as are techniques using controlled or inert atmospheres such as TIG and MIG welding. In general, in all arc welding there is a significant melting of the base material or substrate and typically some 30% of the base material is mixed with the deposited material. This dilution of the cladding changes its chemical composition and may lead to deleterious properties in terms of strength, corrosion or wear resistance and so forth. It is common practice in such arc welding to deposit the cladding in a series of layers, each of which picks up some material from the prior layer. Thus, where the pick-up is of the order of 30%, then in a multilayer deposit the third pass may only contain some 3% of the original substrate. Other techniques for achieving low dilution include adding a filler wire, which may be preheated, by a process such as TIG or plasma arc welding operated to result in a relatively low penetration of the substrate. Other variants on these techniques are aimed at obtaining minimal penetration of the substrate with a relatively thick deposit to reduce the overall dilution to, say, 3% in one operation.
Other cladding methods avoid fusion of the substrate, such as brazing or diffusion bonding a clad layer to a substrate, or friction surfacing where the consumable electrode is deposited as a plasticised layer on the substrate. These various techniques are not necessarily applicable to all sizes of component from small components clad with thin layers to very large components of surface dimension more than 1 m square. Among the difficulties experienced are obtaining a sufficiently even deposit or even adhesion to the substrate, or with large components providing the total power input required for heating and cladding in a single operation.
In accordance with the present invention, a method of joining a covering layer to a substrate comprises placing part of the covering layer on the substrate with the remaining part of the covering layer spaced from the substrate so as to expose a region of contact between the covering layer and substrate; causing a focussed power beam to impinge on the contact region so as to bond or fuse the substrate and covering layer together; and thereafter
a) moving the spaced part of the covering layer towards the substrate so as to change the position of the contact region;
b) causing the focussed power beam to impinge on the new contact region so as to cause bonding or fusion; and,
c) repeating steps a) and b) until the covering layer is bonded or fused to the substrate and is characterised in that the beam is traversed along the contact region in step (b); and in that step (a) is carried out in a non-continuous stepwise manner.
A new approach is proposed in which a focussed power beam is directed at a closing gap arranged between the covering or cladding layer and the substrate, such that the respective surfaces are heated to effect a bond or fusion weld which is progressively propagated in a direction substantially normal to the axis defined by the closing gap along the surface to be covered or clad. The invention enables a covering layer to be bonded or fused to the substrate with substantially no dilution or contamination of the covering layer by the substrate material at the outer or exposed surface of the covering layer.
Examples of suitable power beams include laser beams and electron beams.
Preferably, the focussed beam produces a softened or melted zone which has a relatively high depth/width ratio, for example in excess of 5/1 in the direction of the beam axis compared with normal to the substrate surface. Thus, the width is the degree of melting sideways with respect to the beam (which is normally slightly larger than the beam dimension at focus). In these cas
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Dawes Christopher J.
Russell Derek J.
Albritton C. L.
Novack Martin M.
The Welding Institute
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