Metal fusion bonding – Process – Using only pressure
Patent
1992-12-11
1994-09-20
Ramsey, Kenneth J.
Metal fusion bonding
Process
Using only pressure
29525, 295252, 403 11, 403 21, 403369, B23P 1100
Patent
active
053482107
DESCRIPTION:
BRIEF SUMMARY
This invention relates to joints, and concerns in particular joints in which the bond between two surfaces is caused by friction and other intersurface forces jamming the two together.
There are many ways in which one article can be joined (or jointed) to another, and those appropriate for use in any particular case will generally depend upon the circumstances. For example, two pieces of wood can be joined by nails or screws, or by some cunningly shaped interlocking joint, with or without glue, while two pieces of metal can be glued, soldered, brazed, welded, bolted, riveted . . . and so on. It is even possible to make good joints that are held together simply by the friction between the two parts. For instance, the pegs holding the strings of a violin stay in place purely by friction between the side of each peg and the side of the hole it is pushed into, and friction, or "interference", fits of one metal article onto another are quite common, examples being the securing of a gear-ring to a fly-wheel, typically as used in an automobile engine, and of a metal tire to a railway wheel. A friction joint usually has only shear strength, thus resisting motion in the "plane" of the join (such as might be caused by torsional or push-off forces), and effectively no tensile strength, thus not resisting pulling forces normal to the join. Indeed, such joints show no residual tensile strength if the forces maintaining the two bodies together are removed, and usually fall apart. Nevertheless, this can be perfectly acceptable provided the application, and specifically the physical design of the joint itself, allows for this. Thus, a joint between a rod- or shaft-like member and a body fitting, collar-like, around it, as in a violin string peg fitting into the hole in the neck of the violin, is quite satisfactory; the pegs lock tight against rotation even though they pull out quite easily.
A type of joint that involves friction in its formation, though it does not use friction as the bonding force, is the friction weld, where the two parts are rubbed repeatedly and rapidly against each other (typically several hundred times in a few seconds) until the friction between the touching surfaces makes them hot enough for their material to soften and then to mix when the rubbing is stopped and the two faces are forced/forged together (with forces of the order of tons per square inch (or a few hundred Newtons per square millimeter), expelling any contaminated remnants from the original surfaces)--to cause complete fusion between the bodies--to give a true weld (molecular interpenetration) of one part to the other. It is possible, but not common, to employ some form of friction promoter--a fine abrasive grit such as carborundum (alumina) or sand (silica)--between the two surfaces; once they are heated up, however, the promoter is squeezed out as the two surfaces are pushed/forged together (again with considerable "upsetting" deformation) to make the weld itself. A welded joint made in this way has, like any true weld in which the material of the two parts has actually interpenetrated, both shear (sideways) and tensile (lengthways) strength, which may well be an advantage, but suffers from the considerable disadvantage that the two parts must be heated to a relatively high temperature, which will result in heat-affected zones either side of the joint in which the basic state and physical condition of the material may be significantly changed.
Another type of metal-to-metal joint involving friction during formation, but without the generation of high temperatures within the bulk metal, is the cold pressure weld, especially that form thereof known as the cold pressure shear weld. To produce reliable results with this method, the surfaces must be carefully pre-conditioned (by wire brush cleaning immediately before assembly, or preferably nickel plating).
In an ordinary cold pressure weld the two pieces to be joined are forged together with a force sufficient to cause between 30% and 60% surface enlargement at the interface (as with f
REFERENCES:
patent: 3144710 (1964-08-01), Hollander et al.
Ball Burnishing Machine Tools Limited
Ramsey Kenneth J.
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