Manufacturing techniques

The materials engineer has control over three factors that affect the cost of a product (1) component design, (2) the material(s) used, and (3) the manufacturing technique(s). These factors are interrelated, in that component design may affect which material is used, and both component design and the material used influence the choice of manufacturing technique(s). Economic considerations for each of these factors are now briefly discussed. 

Some fraction of the cost of a component is associated with its design. In this context, component design is the specification of size, shape, and configuration, which affects in-service component performance. For example, if mechanical forces are present, then stress analyses may be required. Detailed drawings of the component must be prepared computers are normally employed, using software that has been generated for this specific function. 

A single component is often part of a complex device or system consisting of a large number of components (a television, an automobile, a DVD player/recorder, etc.). Thus, design must take into consideration each component s contribution to the efficient operation of the complete system. 

The approximate cost of a product is determined by this up-front design, even before the product has been manufactured. Thus, a creative design and the selection of appropriate materials can have a significant impact later on. 

Component design is a highly iterative process that involves many compromises and trade-offs. The engineer should keep in mind that an optimal component design may not be possible because of system constraints. 

The earliest commercial methods used sluny polymerizatiOTis with liquid hydrocarbon diluents, like hexane or heptane. These diluents carried the propylene and the catalyst. Small amounts of hydrogen were fed into the reaction mixtures to ccmtrol molecular weights. The catalyst system consisted of a deep purple or violet-colored TiCls reacted with diethyl aluminum chloride. The TiCls was often prepared by reduction of TiCU with an aluminum powder. These reactions were carried out in stirred autoclaves at temperatures below 90°C and at pressures sufficient to maintain a liquid phase. The concentration of propylene in the reaction mixtures ranged between 10 and 20%. The products formed in discrete particles and were removed at 20-40% concentrations of solids. Unreacted monomer was withdrawn from the product mixtures and reused. The catalysts were deactivated and dissolved out of the products with alcohol containing some HCl, or removed by steam extraction. This was followed by extraction of the amorphous fractions with hot liquid hydrocarbons. 

Later bulk polymerization processes were developed where liquid propylene was either used as the only diluent in a loop reactor or permitted to boil out to remove the heat of reaction. The second was done in stirred vessels with vapor space at the top. More recently, gas-phase polymerizations of propylene were introduced. The technology is similar to the gas-phase technology in ethylene polymerizations [15] described in Sect. 6.1. 

Once the component is laid up on the mould, it is enclosed in a flexible bag tailored approximately to the desired shape and the assembly is enclosed usually in an autoclave, a pressure vessel designed to contain a gas at pressures generally up to 1.5 MPa and fitted with a means of raising the internal temperature to that required to cure the resin. The flexible bag is first evacuated, thereby removing trapped air and organic vapours from the composite, after which the chamber is pressurised to provide additional consolidation during cure. The process produces structures of low 

The VARTM is a hquid resin infusion process and is currentiy considered by the aircraft industry to be the favoured low cost manufacmring process for the future. It is an autoclave-free process that has been identified as reducing the cost of component processing. It is reported that dimensional tolerance and mass measurements are comparable with stitched RFI autoclave panels. A conventional blade stiffened test panel (3 X 2 ft with 4-in-high blades 0.5 in thick) has been manufactured recently at NASA by using the VARTM method, achieving a reasonable quahty. 

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Optical Techniques. The most important tool in a museum laboratory is the low power stereomicroscope. This instmment, usually used at magnifications of 3—50 x, has enough depth of field to be useful for the study of surface phenomena on many types of objects without the need for removal and preparation of a sample. The information thus obtained can relate to toohnarks and manufacturing techniques, wear patterns, the stmcture of corrosion, artificial patination techniques, the stmcture of paint layers, or previous restorations. Any art object coming into a museum laboratory is examined by this microscope (see Microscopy Surface and interface analysis). 

Year Synthetic gemstone CAS Registry Number Manufacturing technique... 

Dyes for WORM-Disks. Regarding their memory layer, dye-in-polymer systems show advantages over metal layers in their higher stabiHty, lower toxicity, lower heat conductivity, lower melting and sublimation temperature, and simpler manufacturing technique (substrate coating by sublimation or spincoating). 

Mechanical Properties and Structural Performance. As a result of the manufacturing process, some cellular plastics have an elongated cell shape and thus exhibit anisotropy in mechanical, thermal, and expansion properties (35,36). Efforts are underway to develop manufacturing techniques that reduce such anisotropy and its effects. In general, higher strengths occur for the paraHel-to-rise direction than in the perpendicular-to-rise orientation. Properties of these materials show variabiUty due to specimen form and position in the bulk material and to uncertainty in the axes with respect to direction of foam rise. Expanded and molded bead products exhibit Httie anisotropy. 

The advent of newer polyurethane materials is expected to lead to a new generation of cardiovascular devices. The characteristics of polyurethanes, combined with newer manufacturing techniques, should translate into direct medical benefits for the physician, the hospital, and the patient. This field offers exciting growth opportunities. 

Review the motor requirements and specifications to make sure that all the unnecessary, nonstandard, special features have been eliminated. Each special requirement such as nonstandard mounting dimensions and nonstandard bearings should be eliminated unless it can be demonstrated the feature is cost effective. In actual practice, many special features are specified because of an isolated case of trouble that occurred years ago. Likewise, some special features may become obsolete through changes in refinery or chemical plant practice or through improved manufacturing techniques. 

First part qualification. First part qualification is a process performed the first time a new bonded assembly is manufactured or the first time a new tool is used to manufacture a bonded assembly. First part qualification provides assurance that all of the aspects that control bond assembly quality, such as the design dimensions, detail part manufacturing techniques, tool dimensions, layup procedures and autoclave cure cycle parameters are correct and will produce a bond assembly that meets the engineering requirements. 

Fluid catalytic cracking and hydrocracking are two additional processes that are often encountered. There are many other processes used in refineries not mentioned here. The list above is intended only to emphasize the wide diversity of processing which is common to petroleum refinuig and to introduce in a very general way some of the more important of these processes. Also it must be emphasized that only fundamental principles of refinery operations have been discussed and modern manufacturing techniques vary widely from company to company. 

The basic questions of The What, The Why, and The How of composite materials and structures have been addressed. Much more could be said about, for example, polymers, metals, ceramics, and carbon used as matrix materials. Also, many more composites manufacturing techniques are available. Moreover, many more examples of effective use of composite materials in structures do exist. However, an introduction to each topic has been provided, and hopefully, those introductions will suffice for the purpose of giving background on composite materials prior to studying their mechanics. 

The sintered metal units have uniform permeability with void spaces approximately 50% by volume for some metals and manufacturing techniques. The pore sizes can be graded to remove particles from 1 micion to 20 microns for liquids and smaller sizes when used in gaseous systems. (See Figure 4-77B.)... 

Figure 10-10L. Various fin manufacturing techniques used by Profins, Ltd., Finned and Plain Tubes bulletin. (Used by permission Profins, Ltd., Burdon Drive, North West Industrial Estate, Peterlee, Co. Durham SR82HX, England.)...

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