Is Direct-Digital Manufacturing Right For You?

Additive fabrication technology has moved beyond prototyping. These four indicators can help manufacturers decide whether to consider direct-digital manufacturing (DDM) for their operations.

Article From: 11/14/2008 Modern Machine Shop, ,

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additive fabrication

FDM was used to produce this component for pill-dispensing machines sold to pharmacies directly from a CAD model. Each machine is customized according to customer needs, so the cost of injection molding such components would be prohibitive.

Fused Deposition Modeling

This diagram demonstrates the fused deposition modeling (FDM) process. Solid plastic is melted and extruded through nozzles no thicker than a human hair. The nozzles lay fine beads of molten plastic layer-by-layer to build parts directly from a 3D CAD model.

Additive manufacturing processes such as stereolithography have become popular for rapid prototyping of new product designs. That said, additive fabrication has moved beyond simply proving out designs, says Joe Hiemenz, public relations manager for Stratasys (Eden Prairie, Minnesota).

Recent developments in these manufacturing techniques have led to the advent of direct-digital manufacturing (DDM), in which an additive process constructs end-use parts. According to Mr. Hiemenz, this trend is especially evident in manufacturing jigs, fixtures and other tools used in production and assembly processes. It is also being used to create custom components as well as medical and dental parts. He says that’s because DDM processes such as fused-deposition modeling (FDM), developed by Stratasys, can be faster, more affordable alternatives to manufacturing such parts via machining or injection molding. The FDM process melts solid plastic and extrudes it through nozzles about as thick as a human hair (approximately 0.005 inch). Those nozzles lay fine beads of molten plastic layer-by-layer to quickly build parts directly from a 3D CAD model.

But how do you know if FDM or another additive manufacturing process is right for you? Mr. Heimenz suggests targeting applications that have one or more of these four attributes.

• Low Production Volume—DDM is most appropriate for parts produced in quantities of less than 3,000 per year. This is one reason that DDM is increasingly used in applications for jigs, fixtures and other tools used in the assembly process. For example, a large automotive manufacturer may produce hundreds of custom tools but need only 30 to 40 of each design. DDM can help such manufacturers avoid the high costs and lengthy waiting times involved in traditional methods such as machining injection molds or in bidding out that work. Small manufacturers producing components in low volumes can benefit in similar ways.

• High Design Complexity—Although DDM can be used to produce simple objects, the cost and time advantages are more pronounced when parts have complex shapes, intricate designs or numerous features. Additive processes such as FDM are insensitive to design complexity. Building material up layer-by-layer to complete the part eliminates problems such as creating internal cavities and complicated 3D contours. It also doesn’t require the workpiece to be set up or refixtured multiple times. However, parts requiring very tight tolerances (greater than ±0.005 inch) may require additional finishing work.

•  High Probability Of Change—Design changes can be expensive and time-consuming when using traditional subtractive manufacturing processes. On the other hand, DDM allows freedom to redesign at will. Manufacturing a revised design is simply a matter of modifying the CAD data, exporting a new programming file and starting the machine. There is no additional cost for rework or retooling, and there is no interruption in production schedules. In this way, DDM serves as a bridge to production—it provides flexibility to change a product’s design after its launch. This also explains why manufacturers of custom products, such as those in the medical and dental fields, have been early adopters of DDM.

• High Startup Investment—All subtractive manufacturing processes involve substantial investment of labor, time and money for toolpath creation, fixtures, molds and machinery. For example, a single injection mold can cost $75,000 or more and take anywhere from 8 to 16 weeks to manufacture. FDM has no tooling costs, and the waiting period for the first production parts may amount to only a few hours or a few days at most. This not only minimizes new-product startup investment, but can translate to better cash flow, improved profit and decreased debt for a company. Lowering the initial investment also opens the door to more product introductions.

Mr. Heimenz says that while manufacturers using traditional machining and/or fabricating techniques can make parts from virtually any plastic, DDM processes are somewhat limited in this area. Additive technologies such as FDM and stereolithography, for example, can use only certain formulations of plastic, so they may not be useful for parts that  require certain thermal or strength properties. However, if your application is open to being converted to select plastics, additive processes such as FDM are worth considering.

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