【正文】 sites, primarily for autoclave curing. As other posite manufacturing processes are introduced in later chapters, additional tooling information specific to that process will be discussed, particularly in Chapter 8, since the fabrication of unitized structure is tooling intensive.Tooling for posite structures is a plex discipline in its own right, largely built on years of experience. It should be pointed out that there is no single correct way to tool a part. There are usually several different approaches that will work with the final decision based largely on experience of what has worked in the past and what did not work. The purpose of the bond tool is to transfer the autoclave heat and pressure during cure, to yield a dimensionally accurate part and there are a number of alternatives that will usually work. Although this chapter serves as an introduction to tooling, the interested reader is referred to a much more prehensive coverage. A shorter review of some of the key principles of be found in 6 also contain useful sections on posite cure tooling. ConsiderationsThere are many requirements a tool designer must consider before selecting a tooling material and fabrication process for a given application. Some of these requirements are listed in 。 however, the number of parts to be made on the too1 and the part configuration are often the overriding factors in the selection process. It would not make good economic sense to build an inexpensive proto type tool that would only last for several parts when the application calls for a long production run, 本科畢業(yè)論文32or vice versa. Part configuration or plexity will also drive the tooling decision process. For example, while welded steel tools are often used for large wing skins, it would not be cost effective to use steel for a highly contoured fuselage section due to the high fabrication cost and plexity.One of the first choices that must be made is which side of the part should be tooled, . ,the inside or outside surface as shown in a skin to provides the opportunity to produce a part with an extremely smooth outside surface finish. However, if the part is going to be assembled to substructure, for example, with mechanical fasteners, tooling to the inside or inner mold line (IML) surface will provide better at with fewer gaps and less shimming required. An example is the wing skin shown in , which was tooled to the IML surface to ensure the best possible fit to the substructure during assembly. Acaul plate is used on the bag side during cure to provide an acceptable OML aerodynamic surface finish. As shown in , this part contains severe thickness transitions on the IML surface.If the part were of constant thickness or contained little thickness variation, it might have then made more sense to tool it to the OML surface. Ease of part fabrication is another in ,it would certainly be easier to collate or layup the plies on the male tool shown than down inside the cavity of a female tool. Selection of the material used to make the tool is another important consideration. Several of the key properties of various tooling materials are given in Table ,reinforced polymers can be used for low to intermediate temperatures, metals for low to high temperatures, and monolithic graphite or ceramics for very high generally been made of either steel or aluminum. Electroformed nickel became popular in the early 1980s followed by the introduction of carbon/epoxy and carbon/bismaleimide posite tools in the ,in the early 1990s,a series of low expansion ironnickel alloys was introducted under the trade names Invar and Nilo.Steel has the attributes of being a fairly cheap material with exceptional durability. It is teadily castable and has been known to withstand over 1300autoclave CUIE cycles and still be capable of making good partsHowever, steed is heavy, has a higher coefficient of thermal expansion (CTE)than the carbonjepoxy parts usually built on it, and for large massive tooling it can experience slow heatup rates in an autoclave. When a steel tool fails inservice, it usually be due to a cracked weldment.Aluminum, on the other hand, is much .lighter and has a much higher coefficient of thermal conductivity. It is do much easier to machine than steel but is more difficult Part Outside Surface本科畢業(yè)論文33to produce pressuretight castings and weldment. The two biggest drawbacks of aluminum are: being a soft material, it is rather susceptible to scratches, nicks and dents, and it has a very high coefficient of thermal expansion. Aluminum tools are quite frequently hard anodized to improve the durability. Hard anodize coatings do tend to spall and flakeoff as the aluminum temper ages during multiple thermal cycles. Due to its lightweight and ease of mach inability, aluminum is often used for what are called form block tool. As shown in ,a number of aluminum form block tools can be placed on a large flat aluminum project plate, then the plate with all the parts is covered with a single vacuum bag for cure, a considerable cost savings pared to bagging each individual part. Another application for aluminum tools is matcheddie tooling, where all surface are tooled, as shown for the spar in .Electroformed nickel keel has the advantages that it can be made into plex contours and does not require a thick faceplate. When backed with an open tubulartype substructure, this type of tool experiences excellent heatup rate in an autoclave. However, to make an electroformed nickel tool requires that a mandrel be fabricated to the exact contour of the final tool.Carbon/epoxy or glass/epoxy tools ()also require a master or mandrel for layup, during tool fabrication. A distinct advantage of carbon/ epoxy tools is that their CTE can be tailored to match that of the carbon/ epoxy parts they build. In addition, posite tools are rela