Net-shaped parts

One of the most desirable aspects of plastics and composites is the ability to make net-shaped parts. The same process that creates the material also creates the structure. The penalty for this advantage is that the process of curing a thermosetting plastic or composite part is irreversible. Any part that is not properly processed represents a loss of part, material and the money and time required to make that part, although larger parts are usually repaired if possible. Proper shape becomes a controlled property in addition to the bulk material properties, such as mechanical (stiffness or strength), physical (density, void content, etc.), chemical (degree of cure or carbonization, chemical resistance), electrical (resistivity, conductivity), or any combination of these. 

Bell, N., Wang, L., Sigmund, W., and Aldinger, R, Temperature-induced forming application of bridging flocculation to near-net-shape part production of ceramics,... 

Often, the advantages are in a better product with more uniform structure and/or reduction in final machining requirements (production of near-net-shape parts). 

Hot isostatic pressing of near-net-shape parts from refractory or super-alloy metal powders is applied for jet engine parts. In contrast, common metals can readily be formed by conventional methods such as casting, rolling, forging, or extrusion. Therefore, only recently have metal fabricators begun to look more closely at the feasibility of isostatic pressing. 

Many products, particularly the often very complex near-net or net shape parts (Fig. 6.11-9), which also include simpler gears, self-lubricating or high temperature bearings, bushings, retainer hubs, roller guides, thrust washers and discs, wire guides with molded-in holes, wear strips, and many more, are made on punch-and-die... 

Fig. 6.11-9 a) Complex near-net or net shape parts for wafer handling and processing, b) 1C (integrated circuits) handling and testing and other semiconductor manufacturing made ofVespel polyimide non-melt processable compound (courtesy, DuPont, Newark, DE, USA)... 

Fig. 6.11-8) can and will be machined to final tolerances, net or near-net shape parts (Fig. 6.11-9) must have so small density variations after pressing that they do not distort during heat treatment. Well granulated molding compounds, taking into consideration the above discussions, and the use of optimally designed dies will yield products that meet this requirement. 

Cold-formed Near-Net-Shape Parts Examples of Applications 3,3,1, Extrusion... 

Near-Net-Shape Manufacturing Light depth of cut applications with close tolerance requirements, such as near-net-shape parts, are well suited for cermets because of their unique performance characteristics. Technological advances in the forging and casting industries permit production of raw products that require minimal material removal during machining operation. 

Tho objectives of the program "Dispersion-Toughened Silicon Nitride" carried out within the scope of the Ceramic Technology for Advanced Heat Engines (CTAHE) program are to develop an advanced toughened silicon nitride composite and a process for near net shape part fabrication. The work on this program was Initiated In 1985. 

Figure 13 Development of a process for complex near net shape part fabrication (SisNa - 30 v/o SiC whisker composite—Forming injection molding Densification hot isostatic pressing)...

Chapters 9 through 11 all belong to a class of processes called liquid composite molding (LCM). In this class of processes, one usually transfers the resin from a reservoir into a network of fibers. The fiber network is formed from any type of reinforcement from random mat to woven, stitched, noncrimp and bidirectional fabrics. This class of processes is very attractive as one can make net shape parts from composites using continuous fibers and have good control over the orientation of the fibers so one can tailor the properties as required by the design. Usually thermoset matrices are used... 

There are a variety of processes to make silicon carbide particle-reinforced aluminiun, including powder metallurgy, stir casting, and pressure and pressureless infiltration. The last two, as well as remelt casting, can make net shape or near-net shape parts. 

Some of these processing technologies, such as injection molding, also have the ability to create near-net-shape parts. These processes often result in a part that is close to its final (net) shape, in a single operation. They offer high precision, and are accurate and repeatable. They also allow for fabrication of complex shapes. 

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