HIP involves isostatic compaction of powders (and other materials) at an elevated temperature. A water-cooled pressure vessel with an internal high-temperature furnace is employed. Pressures reach about 45,000 lbf/in2 (310 MPa) and temperatures about 3600°F (2000°C). Argon, nitrogen, or helium gas is pressurized and acts against the surfaces of the workpiece through a hemetically sealed glass or metal encapsulation. Because of the high temperatures involved, sheet metal, if used for encapsulation, must be refractory. Glass envelopes soften at the temperatures involved but still transmit the pressure to the ceramic material. Pressure and temperature are closely controlled. Electrical resistance heating is usually used. The method is advantageous for producing more complex shapes of parts than by regular hot pressing. Improved, more-uniform compaction for critical parts is an important advantage. The process is applicable to powder metals and cermets as well as ceramic powders and is used to remove voids in castings for critical parts such as turbine blades, to compact powder metal parts to almost 100 percent density of the metal involved and to bond dissimilar materials together.
HandBook of Manufacturing Processes, James G. Bralla p.287
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Hot Isostatic Press (HIP): The container is made of a high-melting-point sheet metal, and the pressurizing is high-temperature inert gas or a vitreous (glasslike) fluid. Common condition for HIP are pressure as high as 100 MPa (15 ksi) - although it can be three times as high - and at a temperature 1200 0C (2200 0F). The main advantage of HIP is its ability to produce having almost %100 density. Consequently, it has gained wide acceptance in making high-quality parts.
The HIP process is used mainly in making superalloy components for the aircraft and aerospace industries and in military, medical and chemical applications. It also is used to close internal porosity, to improve properties in superalloy and titanium-alloy castings for the aerospace industry, and as a final densification step for tungsten-carbide cutting tools and P/M tool steels.
(Kalpakjian S., Schmid S.R.,Manufacturing engineering and technology, 5th Edition, p. 494,495)
2) Vulcanization(Manufacturing)
The term vulcanization is derived from "Vulcan," the Roman fire god, its connection with regard to rubber being therefore the heat which causes rubber when mixed with sulphur, to assume entirely different physical and chemical properties. There are two general methods of vulcanization, namely, what is known as the " cold cure " and the " hot cure vulcanization." The former is effected by the use of a sulphur mono--chloride solution, which acts upon the rubber, and as it is a surface action, it may be employed only with very thin articles. This method is also allowed to take place by placing the articles to be vulcanized in the vapors of sulphur monochloride. The credit for this process belongs to Parkes, who, in 1S46, dipped thin strips of caoutchouc, for different lengths of time, in to a solution of 100 parts of carbon disulphide and 2.5 parts of sulphur monochloride. After dipping these strips, he quickly dried them at 78 deg. F. and then washed them in warm water. The process has been modified somewhat since his day but the essential features were known to him.
The credit for the " hot vulcaniza-tion " should be divided between Hancock and Goodyear, who independently discovered that rubber, when heated in contact with sulphur, changes its properties very materially. Thej' arrived at this conclusion, however, by slightly different means. Hancock in 1843 patented a process for vulcanization whereby he subjected sheets of rubber to the action of molten sulphur heated to a temperature of 284 deg. to 302 deg. F., when the rubber took up 10 to 15 percent of sulphur. Of course, these sheets had a great tendency to bloom, so he washed them with a solution of soda. At the same time Hancock was trying these experiments, Good-year was working along the same lines, only he was mixing the sulphur into the rubber, until he had a homo-geneous mixture which he subjected to a high temperature. Of course, the two results were similar, but Good-year's method being, in many ways, the easiest to control, is the one which has survived. Gerard found that it was possible to effect vulcanization by subjecting the rubber for three hours, under a pressure of four atmospheres in a solution of calcium pentasulphide, to a temperature of 265 deg. F. The articles are then removed and washed with warm water. They are well cured and will possess a velvety appearance. The length of time they must remain in such a bath, of course, is determined by the thickness of the articles to be vulcanized.
Rubber Manufacture- H. E. SIMMONS-pg 98
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Vulcanization
Vulcanization is a process generally applied to rubbery or elastomeric materials. These materials forcibly retract to their approximately original shape after a rather large mechanically imposed deformation. Vulcanization can be defined as a process which increases the retractile forces and reduces the amount of permanent deformation remaining after removal of the deforming force. Thus vulcanization increases elasticity while it decreases plasticity. It is generally accomplished by the formation of a crosslinked molecular network ( fig.1.)
According to the theory of rubber elasticity, the retractile force to resist a deformation isproportional to the number of network supporting polymer chains per unit volume of elastomer. A supporting polymer chain is a linear polymer molecular segment between network junctures. An increase in the number of junctures or crosslinks gives an increase in the number of supporting chains. In an unvulcanized linear high polymer (above its melting point), only molecular chain entanglements constitute junctures.
Vulcanization, thus, is a process of chemically producing network junctures by the insertion of crosslinks between polymer chains. A crosslink may be a group sulfur atoms in a short chain, a single sulfur atom, a carbon to carbon bond, a polyvalent organic radical, an ionic cluster, or a polyvalent metal ion. The process is usually carried out by heating the rubber, mixed with vulcanizing agents, in a mold under pressure.
(Mark, J., Erman, B., Eirich, F.R., Science and technology of rubber, 3rd Edition, pg.322)
3) Computer Aided Manufacturing(Manufacturing)
Computer Aided Manufacturing(CAM) is a widely used term in industrial literature, and it has various meanings. Here it is defined simply as those types of programmable automation which are used primarily on the factory floor to help produce products. The following sections provide functional descriptions of four CAM tools; robots, numerically machine tools, flexible manufacturing systems and automated materials handling systems.
Computerized manufacturing automation : employment, education, and the workplace. p.48
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Computer-aided manufacturing
Computer-aided manufacturing (CAM) involves the use of computers to assist in all phases of manufacturing a product. Because of the joint benefits, computer-aided design and computer-aided manufacturing often are combined into CAD/CAM systems. This combination allows the transfer of information from the design stage into the stage of planning for manufacture without the need to reenter the data on part geometry manually. The database devoloped during CAD is stored and processed further by CAM nto the necessary data and instructions for operating and controlling production machinery, material-handling equipment, and automated testing and inspection for product quality. CAD/CAM systems also are capable of coding and classifying parts into groups that have similar shapes using alphanumeric coding.
(Kalpakjian S., Schmid S.R.,Manufacturing engineering and technology, 5th Edition, p 1203)
4) Composite(Material)
Composite materials are multiphase materials obtained through the artificial com-bination of different materials in order to attain properties that the individual com-ponents by themselves cannot attain. They are not multiphase materials in which the different phases are formed naturally by reactions, phase transformations, or other phenomena. An example is carbon fiber reinforced polymer. Composite materials should be distinguished from alloys, which can comprise two more com-ponents but are formed naturally through processes such as casting. Composite materials can be tailored for various properties by appropriately choosing their components, their proportions, their distributions, their morphologies, their de-grees of crystallinity, their crystallographic textures, as well as the structure and composition of the interface between components. Due to this strong tailorability, composite materials can be designed to satisfy the needs of technologies relat-ing to the aerospace, automobile, electronics, construction, energy, biomedical and other industries. As a result, composite materials constitute most commercial engineering materials.
Deborah D. L. Chung, Composite Materials Science and Applications, pg 1.
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Composite 02.04.2011 23:47
Composites do not really constitute a separate category of materials; they are mixtures of the other three types. A composite is a material consisting of two or more phases that are processed separately and then bonded together to achieve properties superior to those of its constituents. The term phase refers to a homogeneous mass of material, such as an aggregation of grains of identical unit cell structure in a solid metal. The usual structure of a composite consists of particles or fibers of one phase mixed in a second phase, called thematrix.
Composites are found innature (e.g., wood), and they can be produced synthetically. The synthesized type is of greater interest here, and it includes glass fibers in a polymer matrix, such as fiber-reinforced plastic; polymer fibers of one type in a matrix of a second polymer, such as an epoxy-Kevlar composite; and ceramic in a metal matrix, such as a tungsten carbide in a cobalt binder to form a cemented carbide cutting tool.
Properties of a composite depend on its components, the physical shapes of the components, and the way they are combined to form the final material. Some composites combine high strength with light weight and are suited to applications such as aircraft components, car bodies, boat hulls, tennis rackets, and fishing rods. Other composites are strong, hard, and capable of maintaining these properties at elevated temperatures, for example, cemented carbide cutting tools.
(Mikell P.Groover, Fundamentals of Modern Manufacturing , materials,processes, and systems third edition page 10)
5) Polymer-matrix Composite(Material)
Polymer-matrix composites (abbreviated PMC) can be classified according to whether the matrix is a thermoset or a thermoplastic polymer. Thermoset matrix composites are traditionally far more common, but thermoplastic-matrix composites are currently the focus of rapid development. The advantages of thermoplastic-matrix composites compared to thermoset-matrix composites in-clude the following:
Lower manufacturing costs:
· No cure
· Unlimited shelf-life
· Reprocessing possible (for repair and recycling)
· Fewer health risks due to chemicals during processing
· Low moisture content
· Thermal shaping possible
· Weldability (fusion bonding possible).
Better performance:
· High toughness (damage tolerance)
· Good hot/wet properties
· High environmental tolerance.
The disadvantages of thermoplastic-matrix composites include the following:
· Limitations in relation to processing methods
· High processing temperatures
· High viscosities
· Prepreg (collection of continuous fibers aligned to form a sheet that has been impregnated with the polymer or polymer precursor) is stiff and dry when a solvent is not used (i.e., not drapeable or tacky)
· Fiber surface treatments less developed.
Fibrous polymer-matrix composites can be classified according to whether the fibers are short or continuous. Continuous fibers have much more effect than short fibers on the composite’s mechanical properties, electrical resistivity, thermal conductivity, and on other properties too. However, they give rise to composites that are more anisotropic. Continuous fibers can be utilized in unidirectionally aligned tape or woven fabric form. Polymer-matrix composites are much easier to fabricate than metal-matrix, carbon-matrix, and ceramic-matrix composites, whether the polymer is a ther-moset or a thermoplastic. This is because of the relatively low processing temper-atures required to fabricate polymer-matrix composites. For thermosets, such as epoxy, phenolic, and furfuryl resin, the processing temperature typically ranges from room temperature to about 200°C; for thermoplastic polymers, such as poly-imide (PI), polyethersulfone (PES), polyetheretherketone (PEEK), polyetherimide (PEI), and polyphenyl sulfide (PPS), the processing temperature typically range from 300 to 400°C.
Fibrous polymer-matrix composites can be classified according to whether the fibers are short or continuous. Continuous fibers have much more effect than short fibers on the composite’s mechanical properties, electrical resistivity, thermal conductivity, and on other properties too. However, they give rise to composites that are more anisotropic. Continuous fibers can be utilized in unidirectionally aligned tape or woven fabric form. Polymer-matrix composites are much easier to fabricate than metal-matrix, carbon-matrix, and ceramic-matrix composites, whether the polymer is a ther-moset or a thermoplastic. This is because of the relatively low processing temper-atures required to fabricate polymer-matrix composites. For thermosets, such as epoxy, phenolic, and furfuryl resin, the processing temperature typically ranges from room temperature to about 200°C; for thermoplastic polymers, such as poly-imide (PI), polyethersulfone (PES), polyetheretherketone (PEEK), polyetherimide (PEI), and polyphenyl sulfide (PPS), the processing temperature typically range from 300 to 400°C.
Deborah D. L. Chung, Composite Materials Science and Applications, pg 24.
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Polymer Matrix Composite (PMC)
A polymer matrix composite (PMC) consists of a thermoset or thermoplastic resin matrix reinforced by fibers that are much stronger and stiffer than the matrix. PMCs are attractive because they are lighter, stronger, and stiffer than unreinforced polymers or conventional metals, with the additional advantage that properties and form can be tailored to meet the needs of a specific application. High-performance fiber reinforcements are of the highest interest for military and aerospace composite applications; these incude carbon fibers and such organic fibers as aramids, liwuid crystalline polymers, and ultrahigh-molecular-wieght polyethylene. (High Performance Structural Fibers For Advanced Polymer Matrix Composites, National Research Council, p.1)
Preform Molding
In preform molding, a dry mat of the reinforcing material is performed to the approximate shape of the part and placed into the open mold. Resin is added to the perform, and the mold halves are then pressed together and heated to cure the part. During the process the resin flows, impregnating the perform, and becomes hard. The cured part is removed after the mold is opened (often with the assistance of knockout pins that are built into the mold). In a variation on the standard method, preimpregnated chopped fibers are blown onto the perform and then cured.(Handbook of Composite Reinforcements, Lee, p.323)
Pulforming
Thepultrusion process islimited to straight sections of constant cross section. There is also a need for long parts which continuous fiber reinforcement that are curved rather than straight and whose cross sections may vary throughout the length. The pulforming process is suited to these less regular shapes. Pulforming can be defined as pultrusion with additional steps to form the length into a semicircular contour and alter the cross sestion at one or more locations along the length. After exiting the shaping die, the continuous workpiece is fed into a rotating tabe with negative molds positioned around its periphery. The work is forced into the mold cavities by a die shoe, which squeezes the cross section at various locations and forms the curvature in the length. The diameter of the table determines the radius of the part. As the work leaves the die table, it is cut to length to provide discrete parts. Resins and fibers similar to those for pultrusion are used in pulforming. An important application of the process is production of automobile leaf springs. (Fundamentals of Modern Manufacturing, 4th Edition, Groover, p.340)
Side-by-Side Mills (in Roll Forming)
Mills with the side-by-side arrangement of the stands are commonly used as rail-and-structural steel and heavy-section mills.
The side-by-side mills are less costly, but have a substantial drawback. Roll speed is the same in all the stands; as strip length increases after each pass, the final stand becomes a bottleneck. Because of this, the rolling rate in these mills is quite low.(Iron and Steel Production, Bugayev, p.167)
Previous Description
Polymer Matrix Composite (PMC)
A polymer matrix composite (PMC) consists of a thermoset or thermoplastic resin matrix reinforced by fibers that are much stronger and stiffer than the matrix. PMCs are attractive because they are lighter, stronger, and stiffer than unreinforced polymers or conventional metals, with the additional advantage that properties and form can be tailored to meet the needs of a specific application. High-performance fiber reinforcements are of the highest interest for military and aerospace composite applications; these incude carbon fibers and such organic fibers as aramids, liwuid crystalline polymers, and ultrahigh-molecular-wieght polyethylene. (High Performance Structural Fibers For Advanced Polymer Matrix Composites, National Research Council, p.1)
Preform Molding
In preform molding, a dry mat of the reinforcing material is performed to the approximate shape of the part and placed into the open mold. Resin is added to the perform, and the mold halves are then pressed together and heated to cure the part. During the process the resin flows, impregnating the perform, and becomes hard. The cured part is removed after the mold is opened (often with the assistance of knockout pins that are built into the mold). In a variation on the standard method, preimpregnated chopped fibers are blown onto the perform and then cured.(Handbook of Composite Reinforcements, Lee, p.323)
Pulforming
Thepultrusion process islimited to straight sections of constant cross section. There is also a need for long parts which continuous fiber reinforcement that are curved rather than straight and whose cross sections may vary throughout the length. The pulforming process is suited to these less regular shapes. Pulforming can be defined as pultrusion with additional steps to form the length into a semicircular contour and alter the cross sestion at one or more locations along the length. After exiting the shaping die, the continuous workpiece is fed into a rotating tabe with negative molds positioned around its periphery. The work is forced into the mold cavities by a die shoe, which squeezes the cross section at various locations and forms the curvature in the length. The diameter of the table determines the radius of the part. As the work leaves the die table, it is cut to length to provide discrete parts. Resins and fibers similar to those for pultrusion are used in pulforming. An important application of the process is production of automobile leaf springs. (Fundamentals of Modern Manufacturing, 4th Edition, Groover, p.340)
Side-by-Side Mills (in Roll Forming)
Mills with the side-by-side arrangement of the stands are commonly used as rail-and-structural steel and heavy-section mills.
The side-by-side mills are less costly, but have a substantial drawback. Roll speed is the same in all the stands; as strip length increases after each pass, the final stand becomes a bottleneck. Because of this, the rolling rate in these mills is quite low.(Iron and Steel Production, Bugayev, p.167)
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