Machinery's Handbook, 31st Edition
ADDITIVE MANUFACTURING PLASTICS 617 small amounts of ash to contaminate the investment casting. In addition, because loads on patterns for investment casting are low, the patterns are made in the form of a shell with a honeycomb internal structure, reducing the amount of material in the pattern. Tooling for composite layups is increasingly being made by FDM because of their rapid turnaround. Various approaches are used to heat and pressurize the composite layers into a finished part, such as a blade for a wind turbine. (See Reinforced Plastics on page 587 for curing practices used in plastic composite forming.) ABS and PC can withstand curing process temperatures up to 270°F (132°C) and pressures up to 100 psi (690 kPa). For greater temperatures and pressures, FDM tools made from ULTEM 1010 are used. Some of the largest parts made by AM processes are composite layup tools using the FDM process with filament containing chopped graphite fibers. Use of such filament drastically reduces thermal distortion and sagging during production of large parts. The largest of these 3D printers has a production envelope of length, width, and height, respectively, of 20 by 7.5 by 6 feet (6 by 2.3 by 1.8 meters). This process supports segmented printing of prototype vehicles and even building parts. Production of parts by AM is useful in several ways beyond prototyping. In some cases, a duplicate of the actual part can be made by AM and used to set up assembly jigs or in- spection fixtures while waiting for the first article from a molding or casting process. In addition, AM parts can be used as a bridge to production by accelerating rapid product changes, enabling short runs to gain market insertion without having to wait for conven - tional tooling and mass production. A further use of AM is providing spare parts, particularly for systems near the end of their lifecycle, if their inventory has been depleted. This capability is important for ma - chinery, such as older amusement park rides, that have been in operation for decades. Pro - duction of legacy and other on-demand parts on location for defense systems is a similar opportunity.
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