Direct digital manufacturing

Direct digital manufacturing, sometimes called additive, rapid, direct, instant, or on-demand manufacturing, is a manufacturing process which creates physical parts directly from 3D CAD files or data using computer-controlled additive and subtractive fabrication and machining techniques with minimal human intervention. When a small, low-cost device is used, it is also called desktop or personal manufacturing.

Additive manufacturing

Main article: additive manufacturing

Additive manufacturing is also referred to as Additive Freeform Fabrication, Rapid Prototyping, Layered manufacturing or 3D printing. This technique physically constructs or manifests 3D geometries directly from 3D CAD. The history of the process begins in the mid-1980s. It was originally known as Rapid Prototyping because the technology was used to make prototypes of parts without having to invest the time or resources to develop tooling or other traditional methods. As the process and quality controls have evolved, the market for additive manufacturing has grown to include production applications.

Additive Manufacturing or Direct Digital Manufacturing is an extension of Rapid Prototyping to real parts for use as final products (not prototypes). As of 2010, the equipment has become competitive with traditional manufacturing techniques in terms of price, speed, reliability, and cost of use. This has led to the expansion of its use in industry. There has been explosive growth in the sales and distribution of the hardware. A new industry has emerged to create software to enable more effective use of the technology, one use of which is the customization of products for consumers. The number of materials that the industry uses increased greatly in the decade to 2007. Modern machines can utilize a broad array of plastics & metals.

As the speed, reliability, and accuracy of the hardware improves, additive manufacturing may replace or complement traditional manufacturing in creating end-use products. One advantage often cited is that Additive manufacturing eliminates much of the labor associated with traditional manufacturing. Another often cited example is that production can make any number of complex products simultaneously so long as the parts will fit within the build envelope of the machine.

One of the main technologies used for additive manufacturing is Selective laser sintering, a process which uses laser energy to fuse material to create a solid object. Another technology is called Fused Deposition Modeling (FDM), which is commonly used for rapid prototyping but is becoming more and more popular in direct digital manufacturing.

The use of the technology is likely to grow. In 2007 a sub-$4,000 machine was presented. 3D printing bureaus have sprung up around the globe. The RepRap machine is a do-it-yourself rapid prototyping machine with limited use except for demonstration purposes, however, the machine is cheap to build and is constructed of commonly available materials.

Advantages

1. Energy efficiency: Only the energy necessary to form the part is expended, and waste is eliminated. This contrasts with conventional machining, in which energy is used to smelt metal into ingots, which become billet materials. These billet materials are then machined, removing a great deal of the material to produce the final part. The energy used to create the original block of material is wasted.
2. Low material waste: Since the process only forms the desired part, there is almost no waste formed, again in contrast to conventional machining. The absence of waste enhances energy efficiency, as energy is not used to transport or dispose of waste. With the elimination of traditional parts machining, petroleum-based cooling fluids are no longer a necessary waste byproduct.
3. Speed: Generally the actual 3D print process is far slower than traditional techniques, however, traditional techniques often require ancillary processes and procedures (intermediate steps) to form the final product. 3D printing technologies eliminate these steps. Considering this, products can be brought to market faster and sometimes cheaper by using 3D printing rather than traditional processes such as castings and forgings. Since no special tooling is required, 3D parts can be built in hours or days.
4. Complex Geometries: Additive manufacturing technologies allow designing to the process and the creation of more efficient designs without limitations of other processes. Internal passages and features can be created that could not be created with traditional methods.

Materials

METALS: A variety of metals are currently available including alloys of 17-4, 15-5 or 316L Stainless Steel, Maraging Steel, Cobalt Chromium (Stellites), Inconel 625 and 718, Aluminum alloys ( AlSi10Mg) and Titanium alloys (e.g. Ti6AlV4). Almost any alloy metal can be used in this process once fully developed and validated. These materials are not considered to be compliant with ASME specifications for the grades of metals they represent and are generally considered "approximately similar to" the material grades they mimic.

POLYMERS The variety of non-metallic materials used includes an array of photopolymers based on acrylics as well as an assortment of wax-like substances, polyamide powder (filled or not with glass/carbon fibers or aluminum) and even ABS plastic. It is important to note that many of these materials are not considered production-grade as they are brittle, lack good mechanical properties and generally age poorly. Also, the exact compositions of these materials is a closely guarded secret of the manufacturers.

Applications

Applications using this technology include direct parts for a variety of industries including aerospace, automotive, dental, fashion, military, medical and other industries that use complex parts of small to medium size. The Tooling industry uses it to make direct tooling inserts. In particular production of small batches or one off components. Often products can be optimized by taking complex geometries with multiple components in an assembly and simplifying it to fewer sub components and joints. This is one of the key advantages of the technology. Build volumes of existing equipment continue to grow and as the hardware becomes faster along with larger volumes, new uses become feasible.

Technologies

There are presently about 25 3D printing technologies (This list is not all inclusive). The oldest is layered object manufacturing. The next oldest is stereolithography. More recent technologies include selective laser sintering, selective laser melting, Direct Metal Laser Sintering (DMLS), inkjet technologies, fused deposition modeling, Polyjet matrix, laser cladding and many variations. All of these technologies take a 3D model, compute cross-sections of that model, and then deposit the cross-sections sequentially on top of each other until the final geometry is achieved. Overhanging parts are supported by a second material in many cases or by the material in powdered form such as in the case of Selective Laser Sintering.

To visualize how 3D printing works, consider a coffee cup. If you were to slice the coffee cup into wafer-thin layer like you would meat on a slicing machine at a Deli and save each layer and then re-stack them in order, you would re-create the shape of the original object. 3D printing accomplishes this by deposition of very thin layers on top of each other from sliced 3D models or CAD data within a computer system.

Varying the layer thickness affects the model surface finish and other parameters including but not limited to mechanical properties. Many methods have been devised to improve surface finishes; these usually slow down the printing process.

Direct Digital Manufacturing Usage

In 2006 there were approximately 50 commercially viewable examples of 3D printing being used for tooling or intermediate parts. The technology is still new and its use is directly dependent on users' knowledge of engineering to design a part and effectively use the printing equipment. The growth of the market is nevertheless fast, and was estimated in 2006 to be as high as 35% annually. As of mid 2011, online 3D printing service such as Sculpteo or Shapeways have over 44,000 items on display to be 3D printed on demand.

The earliest use of the term Direct Digital Manufacturing surfaced around 2004 by Digital Reality, Inc. The company purportedly holds a patent pending on a process for Direct Digital Manufacturing they call Made-To-Order Digital Manufacturing Enterprise. The company filed a non-publication request on the patent application.

See also

• Additive manufacturing
• Digital fabricator
• Direct metal laser sintering
• Rapid prototyping
• Solid freeform fabrication

Research centers developing these technologies

• SIRRIS

References

• Hopkinson, N. , Hague, R. , Dickens, P. (2005). Rapid Manufacturing (Abstract). Germany: Wiley-VCH.
• Wright, Paul K. (2001). 21st Century manufacturing. New Jersey: Prentice-Hall.
• Wohlers, T. (2011). Wohlers Report 2011. Wohlers Associates, Inc.
• Reinhardt et all. (2007) Freedom of Manufacturing by parallel batch production, technical and economical advantages for microsystems. Proceedings of the 1st European DAAAM International Young Researchers and Scientists Conference 24–27 October 2007 DAAAM