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Method of forming and blank thereforRelated Patent Categories: Metal Fusion Bonding, Process, Using Dynamic Frictional Energy (i.e., Friction Welding)Method of forming and blank therefor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060191978, Method of forming and blank therefor. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF INVENTION [0001] This invention relates to a method of material forming to produce shaped parts, and to a blank for use in such forming. The invention is particularly directed to the superplastic forming (SPF) process utilising certain materials, primarily metallic, which exhibit superplastic properties. [0002] BACKGROUND [0003] Superplasticity can be defined in various different ways, but generally it is a property exhibited by certain materials whereby they are able, at an appropriate temperature and strain rate, typically in the range 10.sup.-3S.sup.-1 to 10.sup.-4S.sup.-1, to undergo plastic deformation to very large (e.g. 200% or more) elongations under tension without rupture. High strain rate superplasticity may be defined as a minimum strain rate of 10.sup.-2S.sup.-1 and is typically found in materials produced by Equal Channel Angular Pressing (ECAP) or friction stir processing (FSP). Materials which possess superplastic properties may be formed, using processes such as SPF, into complex 3D shapes such as are needed in the aerospace and automotive industries. [0004] Several materials exhibit superplastic properties, but only a relatively small number find commercial applications. These include certain alloys of aluminum, of titanium of nickel and of magnesium. Various methods can be used to achieve the fine grain microstructure which is necessary for materials to exhibit superplasticity. Unfortunately these methods usually involve quite complex and expensive processing to convert a base material, which does not possess superplastic properties at all or only to a small extent, into one which does possess the required superplastic properties. For example, US patent application No 2002/0079351 describes a technique in which superplastic properties are generated locally in a parent metal using FSP. The blank thus created can thence be deformed to create a desired 3D article by a forming process such as forging, rolling, drawing, bending, extruding, gas forming, punching or stamping. That part of the blank which has been rendered superplastic by the FSP is sufficiently ductile to deform to the required shape whereas the remainder of the blank is not. [0005] Friction stir welding (FSW) is described, for example, in WO 93/10935 and is typically used to join two workpieces. The process involves plunging a rotating or reciprocating probe into the workpiece to be joined, and moving the probe along the line of the join. The heat generated by the frictional engagement of the probe with the workpieces generates an area of plasticised material which, after passage of the probe, joins across the join line to weld the workpieces together. SUMMARY [0006] In the present invention, we seek to achieve a blank which is functionally similar to that obtained in the process described in the above-mentioned US patent application No. 2002/0079351 in that it comprises a limited area within the parent metal which has superplastic properties and which thus, during a subsequent forming process, will readily deform to produce the required shape, leaving the remaining material either not deformed at all, or deformed only to a limited extent within its plastic capabilities. The technique of the present invention leads, however, to a number of advantages over the prior-art process, which advantages will become apparent in the following description. [0007] According to a first aspect of the invention there is provided a method of preparing a blank for superplastic forming, said method comprising the steps of joining at least one insert to a parent body by means of friction stir welding, at least one of the parent body and the insert or inserts being made of a material which has superplastic properties. [0008] Any suitable method of forming can be used, such as those listed above, but the preferred method is superplastic forming at elevated temperature with pressurized fluid, as will be described in more detail below. [0009] In accordance with a second aspect of the invention there is provided a blank for use in a superplastic forming process, said blank comprising a parent body and an insert joined thereto by means of friction stir welding, at least one of the parent body and the insert being made of a material which has superplastic properties. [0010] The use of the terms "parent body" and "insert" are not intended to imply any particular size relationship between the two, but are used simply to enable the two parts to be readily distinguished. It will, however, often be the case that the part of the blank that is superplastic will be the smaller in size since investigation has shown that, in many cases, it is only a relatively small proportion of a blank that is subjected to deformation, during the forming process, of sufficient magnitude to warrant the need for a superplastic material. Thus, fabricating the whole blank of superplastic material is often unnecessary and, since such materials are more expensive to produce, costs can be saved by using as little as possible of the superplastic material. However, we do not wish to exclude the possibility that the remainder of the blank is also of superplastic material and, indeed, the degree of superplasticity of the parent body, whilst normally different to that of the insert, may in certain circumstances be of a similar level to or equal to that of the insert. [0011] In most cases that region or regions of the blank which are to be subject to the greatest strain during the superplastic forming process will correspond to that region or regions of the blank which have said superplastic properties. However, there may be occasions when this is not the case; for example: [0012] 1) Where there is a need for a different alloy in a certain region; [0013] 2) Where a superplastic insert is present for purposes other than purely to accommodate strain--for example, an insert having a profiled thickness may be positioned not in the region of maximum expected strain, but where it is needed in order to maintain or enhance thickness. Alternatively, the primary purpose of the insert may be to provide a local fixing which may not correspond with the region of maximum expected strain. Still further, the insert may be required to actually provide a greater or a reduced thickness over a particular region in the finished product, and the position of this may be unrelated to the region of maximum expected strain during forming. [0014] In the preferred embodiment it is the insert that is formed of superplastic material, and the parent body is formed from a material which is either not superplastic at all, or is superplastic to a lesser extent. For simplicity of description, this arrangement will be assumed hereafter. Thus, during the forming process, there are two possibilities:-- [0015] 1) The parent body remains undeformed during the forming process, deformation only occurring within the insert; [0016] 2) Both the parent body and the insert are deformed during the forming process, but the insert is positioned in that region which requires an amount of deformation sufficient to warrant the use of a superplastic material, the remaining parts being deformed to a lesser extent than this. [0017] The blank may be formed of multiple inserts, each friction stir welded to the parent body. Some or all of these inserts may be made out of superplastic material. In addition, the or each insert may further be provided with means whereby it may perform a mechanical function, for example stiffening or providing a threaded bore for a fastening in the finished part. [0018] The, or each insert may be positioned in relation to the parent body in various different ways. For example an insert may simply abut one edge of the parent body and be joined along the abutting edge. Alternatively, the parent body may be cut out to receive the insert, either by way of slot opening into an edge of the parent body, or by way of a closed cut-out in the parent body. In a further alternative, the insert may overlie the parent body and be joined thereto, thus forming a two-layered composite structure in the area of the insert. Such an insert may more properly perhaps be referred to as a patch, since it is not "inserted" into an opening in the parent body. Thus the word "insert" as used herein should be construed with this in mind. Where a two-layered region is formed by a patch-type insert, care needs to be taken with the properties of the underlying material of the parent body; clearly the superplasticity of the two-layered structure is dictated by both layers, and if the plasticity of the parent body, at least in the region concerned, is not the same as or similar to that of the insert, then the overall superplasticity may be impaired. In a still further alternative, an insert and a patch may be used, by joining a patch in such a way as to wholly or partially overlie an existing insert thus forming, in effect, a composite insert comprising two layered parts. In practice, both parts of such a composite insert may be joined to the parent body in a single FSW operation. [0019] A particular benefit of friction stir welding as a joining method is that it is a solid state process in which there is no melting, unlike conventional fusion welding where melting occurs. Accordingly the superplastic properties of the or each insert are not impaired during the joining process; indeed in the immediate area of the join they may be enhanced. In addition the area of superplasticity may be extended for a short distance into the parent body (see the above-mentioned US patent application No. 2002/0079351). By contrast, fusion welding creates a cast material in the area of the join, together with heat-affected areas leading to reduced ductility. FSW also has the ability to produce joints between dissimilar materials including but not limited to aluminum and magnesium alloys. [0020] The, or each insert may or may not be the same thickness as the parent body. In one embodiment the insert is thicker than the parent body, but tapers at its edges so as to avoid a step where it joins the parent body. [0021] Such a step would be undesirable in the event that FSW is used since the FSW tool is normally waisted and thus a substantially equal thickness on each side of the join is desirable, although techniques for FSW welding of sheets presenting different thicknesses along the line of the join are now available. [0022] One or both surfaces of the insert may be contoured to achieve particular desired properties, as will be explained in more detail hereinafter. Continue reading about Method of forming and blank therefor... Full patent description for Method of forming and blank therefor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method of forming and blank therefor patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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