Tolerance molding

Noryl HMC3008A 30% glass-, mineral-, carbon-fiber-reinforced 248°F (120°C) HDT at 264 psi (1.82 MPa) UL-94 V-0 rating static dissipative for tight-tolerance molding... 

Dimensional accuracy in molding The ability to produce warpfree, high-tolerance molded parts. 

The inherent anisotropic shrinkage of acetal resin has created close-tolerance molding prob-... 

A special attribute of these processes is the abiHty to pre-position reinforcement, inserts, and core materials for stiffening ribs. Gel coatings can be apphed to the mold surface to eliminate post-mold finishing. Because both surfaces of the part are formed in a mold to close tolerances, accurate assemblies are possible, which is a requirement for many automotive or tmck body appHcations. 

To obtain satisfactory moldings with good surface appearance, contamination, including that by moisture, must be avoided. For good molding practice, particularly with the more polar styrene copolymers, drying must be part of the molding operation. A maximum of 0.1 wt % moisture can be tolerated before surface imperfections appear. 

Sand Casting. Sand casting is the most popular method of molding for cast copper alloys. It is the least expensive near net shape process, and pattern costs are low. Dimensional tolerance capabiUties vary widely and are the least accurate when compared with other methods of casting. 

Some plastics, such as the TSs and in particular the TS-RPs (RTSs), can produce products with exceptionally tight tolerances that practically meet zero tolerances. In injection or compression molding of relatively thin to thick and complex shapes, tolerances can be held to less than 0.001 in. or to even zero, as can also be done using hand layup RP fabricating techniques. 

Table 3-6 Examples of dimensional tolerances for injection molded TP products... 

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