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Direct Digital Manufacturing

 

Many different industries are discovering the power of additive fabrication techniques

   

By Terry Wohlers
President
Wohlers Associates Inc.
Fort Collins, CO       
          

This robotic gripper has vacuum channels running through each of its legs. Components for the unit were first prototyped, then manufactured, using FDM (Fused Deposition Modeling). The robot that employs the gripper is used by an injection molder to hold and transfer 400–500-mm diam conical parts.

New methods of manufacturing are bringing about fundamental changes in the way products are designed and delivered. With advances in additive fabrication (AF) technology, it's now possible to conceive a product and deliver that product to a customer within days.

A growing number of manufacturing organizations of all sizes are using AF technology for custom and limited-edition replacement-part manufacturing, products, and short-run production. They are also using it to make patterns for production castings, as well as for jigs, fixtures, drill guides, and assembly tools used in manufacturing.

Direct digital manufacturing (DDM), also referred to by some as rapid manufacturing, is easiest to justify when the parts being manufactured are difficult to make by using conventional methods of manufacturing, which usually means they are complex. Such designs can be highly convoluted and, at times, impossible to manufacture by means of any other technology. DDM is best applied when production volumes are relatively low, because AF systems do not produce parts as rapidly as injection molding machines. Also, while the surface finish of AF parts has improved a lot, don't expect to see the surface finish that you obtain from a polished injection mold.

The biggest benefit of DDM is that tooling is not needed. This provides a great amount of design freedom, because you don't have to worry about removing the part from the tool. Also, you don't have to wait weeks or months for the tooling. Once the design is available, production can begin. What's more, you have the freedom to make design changes or offer variations of the product after production has started.

This direct metal laser-sintering equipment, the EOSINT M 270, can manufacture parts with a range of powdered metals, including maraging steel, stainless, cobalt chrome, and titanium.It's true, however, that DDM is typically not a good option for standard, low-priced products. AF machines are not inexpensive, so it's usually best to manufacture "cheap" products using more conventional techniques. Also, if the part being manufactured is large, such as an entire instrument panel for an automobile, DDM (rapid manufacturing) becomes difficult to justify in terms of time and cost. Material cost alone is considerable, because AF materials are many times more expensive than the standard materials used for manufacturing. Many new and impressive AF materials have been introduced over the years, yet they represent a small fraction of the materials available for conventional methods of manufacturing.

Despite some of the limitations of DDM, growth has been impressive. Over the past five years compounded annual growth has averaged 32%, according to Wohlers Report 2008, an annual study by our company that tracks developments and trends in AF technology and applications. The number of people and companies interested in exploring what DDM can do for them suggest that this trend will continue as organizations better understand the capabilities and limitations of a DDM strategy.

Many industries are embracing DDM. For years, the aerospace industry has been using AF to manufacture plastic enclosures, covers, housings, and other nonstructural parts. In fact, the international space station and the entire space shuttle fleet include hundreds of laser-sintered (LS) parts, and have done so for nearly a decade.

The largest and arguably most significant application in aerospace has been the production of highly complex air ducting for the F-18. Boeing and its contractors, such as On Demand Manufacturing (Oxnard, CA), have manufactured thousands of them over the past seven years. By using laser sintering, a highly complex duct can be manufactured in a nylon-grade material—usually in one piece—and tested, inspected, and shipped in one to two weeks. Previously, each duct would require the production and assembly of multiple parts, many requiring special tools, which could take months, depending on the method of manufacturing. The use of LS parts has dramatically reduced or eliminated tooling, inventory, labor, payload, and maintenance costs. These aircraft programs have been considered highly successful due to part-count reduction on each duct, cycle-time reduction for delivery to the aircraft, and the ease of redesign with laser sintering.

The commercial aerospace industry is also beginning to use laser sintering to make parts such as ducting for the Boeing 787. That aircraft contains more than 30 air ducts manufactured by laser sintering using FR-106 flame-retardant nylon from Advanced Laser Materials LLC (Belton, TX).

By using direct metal laser-sintering to produce this blow mold for a promotional (giveaway) golf ball, the mold makers could incorporate conformal cooling to increase productivity and venting slits to avoid distortion.Companies are at the early phase of certifying metals for DDM (such as titanium alloys and cobalt-chrome) for aerospace applications. The goal is to use laser melting or electron beam melting (EBM) to produce complex and expensive parts like turbine blades. Currently, Morris Technologies (Cincinnati) is manufacturing turbine blades using several EOSINT M 270 machines from EOS (Novi, MI). The metal parts are being used on test rigs, and have not yet been permanently installed on aircraft.

In the medical industry, many metal parts have been produced and implanted into human beings. For example, Ala Ortho (Milan, Italy) has produced nearly 500 hip sockets in Ti6Al4V titanium alloy for implantation. Medical Modeling Inc. (Golden, CO) is the company that has produced the largest number of medical models for surgeons by additive fabrication. The group is also producing metal implants for patients. Both Ala Ortho and Medical Modeling use EBM machines from Arcam AB (Mölndal, Sweden).   

The dental industry is also embracing AF technology. Dental labs are typically small operations that provide crowns and bridges to dentists in a community. The delivery of a crown or bridge usually requires a week or two, and involves many manual steps by a skilled technician. A number of dental labs are looking to methods of additive fabrication to speed the process and increase profits. The market for crown and bridges in the US is said to be $8.5 billion annually.

Ex One LLC (Irwin, PA) has installed more than 30 Imagen RX-D machines at dental labs across the US. Using jetting technology licensed from MIT (Cambridge, MA), the machines deposit binder onto fine, gold-alloy powder to produce gold copings. (A coping is the main structure of a crown or bridge.) The copings are infiltrated with a lower-melt-temperature gold alloy to bring them to full density. They are then coated with porcelain to match the patient's teeth. Gold is the preferred material in the US for crowns that are mostly visible. A gold coping, coated with a very thin layer of porcelain, produces a much more realistic replacement tooth than dark metals.

Cobalt–chrome (CoCr), which is less expensive than gold, is used extensively in some parts of the world for dental copings, and can be produced on laser melting machines. With Selective Laser Melting from MTT (Stone, Staffordshire, UK), it's possible to manufacture 70 CoCr copings in 8 hr. An EOSINT M 270 machine can produce 380 CoCr copings in 20 hr. Using conventional manual methods of manufacturing, a dental technician can produce 8–10 crowns in one work day.

Demanding industries such as aerospace, medicine, and automotive are expected to become large markets for custom products produced by AF, but they have been relatively slow to adopt the technology for manufacturing because of regulatory issues, certifications, and legal liabilities. Less-demanding and less-technical industries, such as computer games, sculptures, home accessories, collectables, and corporate gifts, are embracing DDM with fewer obstacles. This activity is leading to interesting methods of design, manufacturing, and distribution worldwide. Many new business models, innovative companies, and R&D opportunities are developing as a result.

Many companies that manufacture, sell, or use AF systems are attempting to jump onto the DDM bandwagon. Some have discovered that the real money is in manufacturing, not prototyping. It has been estimated that only about 5–10% of a new product program is spent on design and prototyping, while the remaining 90–95% is spent on manufacturing.

It has not been easy for prototyping companies to transition to manufacturing. Such groups find that manufacturers play by a different set of rules. Securing a contract from an OEM to build prototypes has become routine at countless service providers, but these same OEMs are reluctant to award a manufacturing contact to a prototyping company. Some of these relatively small companies have secured the personnel and quality certifications to at least be considered. The most successful now look more like contract manufacturers than prototyping service bureaus.

About two years ago, Harvest Technologies (Belton, TX) began to focus on the aerospace production business, and is currently servicing multiple contracts, ranging from smallbatch production orders to multiyear military and commercial aerospace contracts. Harvest uses laser sintering to manufacture end-use production parts that are commonly assembled with procured fasteners, latches, seals, gaskets, and lenses, and are often finished with special paints and coatings. If service providers, such as Harvest, do a good job at meeting customer requirements, this business sector could present a much greater opportunity in the future.

This acetabular cup was built by the Italian company Adler Ortho using Arcam's EBM S12 machine.Some AF equipment manufacturers have made a strong commitment to DDM. In fact, laser-sintering machine manufacturer EOS says that 100% of its future product development will be focused on e-Manufacturing, a term the company uses for DDM. Currently, a number of companies are using LS machines from EOS for custom-product manufacturing and short run production. Meanwhile, Stratasys (Minneapolis) is positioning itself and its fused deposition modeling (FDM) technology for the manufacture of fabrication and assembly tools, such as jigs, fixtures, and drill guides. Vacuum maker Oreck Corp. (New Orleans) uses FDM to reduce fixture production costs by up to 65%. Previously, some fixture projects would cost more than $100,000, so the savings can be substantial, according to Bill Fish, senior model maker at Oreck.

Some believe that DDM requires high-end AF systems. While it's true that most industrial examples of DDM use expensive systems, low-end machines designed mainly for concept modeling and visualization are also employed for DDM. For example, Mydea Technologies (Orlando, FL) has used its Dimension 3-D printer to produce 200 ABS parts per day for a major European car manufacturer. The part is a "cap" that is permanently installed onto an audio system. To date, Mydea has received orders for 2000 and 5000 pieces.   

Cornell University's (Ithaca, NY) open-source development called Fab@Home has been used to create an assortment of objects. The Fab@Home system is available as a snap-and-screw-together kit that produces parts using a syringe and nozzle system. Alternatively, one can download the open-source design, instructions, and software for free and then purchase the individual parts and build the system. So far, variations of the system have been used to produce polymer structures, conductive wiring embedded in structural materials, elastomer strain gages, complete batteries, soft actuators, organic polymer transistors, electromechanical relays, engineered living tissues, and dense stainless parts (with furnace sintering). The Fab@Home system does not produce fine-looking parts, at least not yet, but part quality is expected to improve as users fine-tune the system for specific materials. More than 150 systems have been built and installed worldwide, mostly for experimental, research, and educational use.

Growing human body parts is one of the most exciting possibilities arising from DDM. Already, Anthony Atala, MD, of Wake Forest University (Winston-Salem, NC) has used a 3-D inkjet printer originally developed at Clemson University (Clemson, SC) to produce living structures such as pulsating heart valves. The 3-D printer is used to deposit living cells, a biodegradable scaffold to give the body part shape and structure. The cells are taken from the patient, so there's little chance of his/her body rejecting the growing tissue. Wake Forest has licensed the technology to Tengion (East Norriton, PA), a company that hopes to manufacture bladders, kidneys, heart valves, and other body parts and tissue.

The AF industry faces multiple obstacles to wide-scale adoption of DDM, especially in the aerospace, automotive, and medical industries. Among them are the needs for process controls and closed-loop feedback systems that can improve repeatability. Currently there can be too much variation from part to part and system to system, when consistency in mechanical properties and dimensional accuracy is required. Most of the machines were developed for prototyping, so equipment manufacturers are working to bring them up to manufacturing- quality standards.

These challenges present opportunities for universities and research organizations worldwide to develop and enhance AF methods, subsystems, and materials. One of the biggest areas of focus is expected to be on the front and back-ends of the process. For example, it's necessary to develop special software and procedures that streamline the process of organizing and ensuring data quality of hundreds or thousands of parts, such as dental crowns or game characters. Each job must be removed from the system with minimal human intervention, a task that can be tricky when powder or solid support material is involved. Developing and refining the pre and post-processing steps are as important as the fabrication process.

The availability of a wide range of AF systems is allowing people to experiment with the manufacture of custom and limited-edition products. A surprising number of individuals and organizations are giving DDM a try, because the risk of doing so is low. A second industrial revolution is beginning to unfold.

 

This article was first published in the January 2009 edition of Manufacturing Engineering magazine.


Published Date : 1/1/2009

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