Machinery's Handbook, 31st Edition
616 ADDITIVE MANUFACTURING PLASTICS An example of the benefits of AM for fixtures is shown by a fixture needed for dimension and distortion measurement of investment casting for a household sweeper. Fabricating the fixture using a CNC machine would require delivery time of four weeks and cost $450 if it were made from aluminum, $350 if made from high-density polyethylene (HDPE). Producing the part from ABS plastic by FDM cost $50 and was delivered in one day. Similar savings of time and money are realized in AM production of plastic assembly jigs. For example, AM is being used on automotive assembly lines to produce low-run parts, such as jigs for emblem or medallion attachment. While AM processes and procedures currently are not capable of economically produc- ing the large numbers of components needed for full-scale automotive production, rapid evolution of AM processes and procedures will soon lead to mass (or serial ) production of small parts. In the meantime, AM is being used in the automotive industry to produce customized features, such as whimsical front-end “face” coverings, with shark skin, dim - ple, and whisker details. Race car and other custom shops have used AM for many years to produce custom spoilers for wind tunnel testing, vents to enhance engine performance, and other specialized parts. AM also is used to make parts such as air intakes and fender vents for luxury automobiles. For vintage vehicles, from cars to airplanes, AM software and systems can scan, analyze, and replicate outdated replacement parts. For this pur- pose, in addition to making plastic parts directly, plastic-based AM processes also are used to produce tooling for other manufacturing processes. Such applications of plastic AM include making patterns and molds for metal and com- posite casting and molding, as well as dies for sheet metal forming processes. FDM, SLS, and MJ processes can be used to produce thermoforming dies in much less time than machining aluminum (see Sheet Thermoforming on page 584) . One of the most visible applications is the use of SLA to print custom molds for thermoforming of Invisalign dental braces. Plastic tooling made by AM processes has enough strength to be used for forming sim- ple shapes in sheet metal. In one case, a nose gear failure during landing on an aircraft carrier at sea damaged two sheet metal parts in the nose of the plane, removing it from service. Replacement parts were not available, so two forming dies, used for forming such replacement sheet metal parts, were made by FDM at a seaside base and then flown to the carrier at sea. The aircraft was repaired and in service within a week, instead of waiting longer to receive replacement parts from the original equipment manufacturer or after - market parts supplier. SLA, FDM, and MJ processes also are used to produce injection molding tools for short runs between 100 and 1,000 parts (see Sheet Thermoforming on page 584) . A major advantage of making injection molding tools by AM processes is that conformal internal cooling channels can be printed into tools. Because the cooling channels have the same profile as the tool, heat is removed from the part rapidly and uniformly, reducing injection molding cycle time and improving quality by practically eliminating warping of molded parts. Patterns for sandcasting are being made by FDM to shorten time to mold production. While patterns are commonly made by machining aluminum or composition, using FDM reduces delivery time from weeks to days. The pattern materials must resist the heavy pressures and abrasion of sand impact during mold compaction around the pattern and be impervious to the binding agents and mold-release chemicals used in casting (see Pat- terns on page 1498) . ABS and Ultem patterns produced on FDM machines meet these conditions. Printed patterns may be sanded, smoothed by acetone treatment, or sealed with epoxy to provide a smoother finish. Plastic AM is also used to produce patterns for investment casting (see Precision Invest- ment Casting on page 1504) . Patterns are produced by SLA, SLS, and FDM processes, and then used in the conventional investment casting sequence of coating the pattern with plaster or refractory materials, melting or burning out the pattern material, and pouring liquid metal into the mold. Plastics have been developed for this purpose that leave very
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