Rapid prototyping technologies are quickly compressing the product development cycle. According to one manufacturer of aerospace parts, the development of a jet engine blade took one month rather than nine thanks to these technologies; an electronics manufacturer reports a 40% decrease in the time needed to design electric power systems; and general manufacturers claim they save at least 45% on the costs of tooling. These are just a few of the thousands of examples emerging today. While a number of rapid prototyping systems are available, the least expensive systems are 3D printers. For about $20,000 or less, you can purchase a 3D printer that will turn your CAD designs into three-dimensional objects overnight.

Contrary to most thinking, though, the deciding factor over your choice of 3D printing system is not cost. Instead, your choice will depend on the goals you have for your model; are you checking for form, fit, feel, or function, or some combination of these features? “What you plan to do with your model,” said Jon Cobb, vice president and GM, Stratasys Inc. Eden Prairie, Minn., “will dictate the type of material you select, which will influence the type of 3D printing system you need. If the model will only be viewed, you do not need a material that offers durability. For example, say you’re using a model to determine fit, such as whether a printed circuit board will fit into a cell phone shell. This goal will influence your material selection, which influences the choice of printing system.”

Based
on Objet’s breakthrough PolyJet Matrix™ Technology,the Connex500
simultaneously prints two FullCure model materials and creates 21 types
of Digital Materials. It can also print a single material from any of
the original seven FullCure model materials.

In general, 3D printing systems will let you:

     —Analyze form: How the model looks off the screen in multidimensional reality; whether it
meets the “look” desired by the client.
     —Analyze fit: How parts will fit together.

     —Analyze feel: How the finished product will likely feel in your hands.

     —Analyze function:Recent advances in some 3D printer systems use materials that let test models to obtain reliable data on how well the final product will perform desired or required functions and tasks. “If you use materials that are close enough to the final properties your part needs, then you can perform functional tests on the model,” said Neil Ranney, senior application engineer, Objet Geometries Ltd., Billerica, Mass. Alternatively, you can treat the printed part, for example coating it with a resin to give it properties similar to those needed by the finished part, such as stiffness and strength.

     —Control the costs of design modification and validate the design: It is inevitable that a design will go through changes. In general, though, 3D-printing systems help manage the costs of iterative designs because they are one of the fastest and least costly ways to obtain models. “With conventional modeling,” noted Dave Tedder, product manager,Z-Corp., Burlington, Mass., manufacturers must often invest in the development of tooling and fixtures before producing a model.” Plus, printers help you present your designs in the most intuitive way possible — as a physical three-dimensional model, which improves customer responsiveness and decisions. “Engineers gain confidence in their design after they have printed it or put it through a rapid prototyping process,” said Tedder. “These systems let you know whether you have a producible model; one that fits the requirements of the customer.”

The
ProJet™ HD3000 3-D Production System, from 3D Systems, is a new,
professional, high-definition 3-D Printer. It offers a large build
volume and part stacking and nesting capabilities for extended
unattended production runs. The company’s VisiJet® Materials’
portfolio, including direct-investment castable materials, works with
the new printer.

      —Faster feedback: Printers can produce your model in hours or a day, depending on its complexity, versus a week or more from contracted services. “3-D printers have helped move the modeling process out of the service bureaus and into the hands of the individual engineers,” continued Tedder.

     —Produce production-quality product: Also known as “Digital Manufacturing,” some printing systems offer the ability to produce thousands of plastic parts for use, not just examination.
     —Create parts at your desk: Several systems are small enough, and environmentally friendly enough to operate in an office rather than on a plant floor.
     —Eliminate noxious materials: Compared to other prototyping technologies, 3D printing usually eliminates toxic chemicals like those used in some stereolithography machines.

     —Reduce follow on processes: Products made with 3D printing systems usually require fewer post processing steps than parts made from more complex prototyping technologies. “Those additional processes, such as heating, curing, brushing off, and infiltration,” said Cobb, “are usually not compatible with an office environment.” Plus, plastic processes let you make parts that are impossible to mold. Each 3D printer manufacturer specializes in technologies or capabilities that affect the final model. On the other hand, while 3D printing can be viewed as an alternative to injection molding, in some cases printing does not have a cost advantage over molding. A service bureau or a 3D printer manufacturer can offer guidance. Also, when you have multiple goals, or models that must meet multiple criteria, service bureaus may be a better option.

Popular printing processes

One of the features these systems are often judged by is the object’s surface finish or feature detail, also termed the fidelity. “For example,” noted Cobb, “a powder technology will result in a model with a different look than an extrusion technology, and so on with all of the other printing methods.”

For a time, ink jet printing was the first and only 3D printing technology. Over the last twenty years, manufacturers have developed other processes that are classified as 3D printing. These include photopolymer, fused deposition modeling, and the latest–film layer deposition and film transfer imaging.

Ink jet printing has undergone several changes over the years. Typically, layers of a fine powder, such as plaster, cornstarch, or resins, are selectively bonded by “printing” an adhesive from the inkjet printhead in the shape of a cross-section determined by a CAD file.

Of 3D Systems Corp., Rock Hill, S.C., three printing technologies, one is based on ink-jet technology. “We work under an exclusive arrangement with Xerox Corp.,” said Abe Reichental, president and CEO, “and adapted one of their proprietary inkjet printers to deposit a hot melted plastic instead of ink through hundreds of tiny jets onto the build platform. But we also incorporated a phase change element; the system changes the material from a solid into a liquid that is jetted onto the platform. The material is then hardened and cured with UV light. Our phase-changed plastic material gives us extreme accuracy and the latitude to use different chemistries within the machine, including wax-like materials that can be used for sacrificial patterns in investment casting or micro-casting applications.”

Another manufacturer of ink-jet type printers is ZCorp. These systems spread layers of powder onto a bed and use a binder to solidify, or “print” those areas pertinent to the model. The powder is 99% of what the final part will be. “We selectively print over that powder,” said Tedder. “The tanks are not really inks, they are binders. The system spreads binders in specific areas over the powders to create the part.” This process is quick because it happens over a wide area. In addition, you can print several parts simultaneously through their arrangement on the large print bed.

Z-Corp. uses off-the-shelf industrial grade HP print heads with multiple nozzles. Within the industry, each company uses different printheads, each comprised of a varying number of nozzles.

The company also offers several powder/binder/infiltrant systems. These include composites for printing strong, high-definition parts; investment casting material for quick part fabrication that can also be dipped in wax to produce investment casting patterns; and direct casting material for sand casting molds for non ferrous metals. Printed models can be sanded, drilled, tapped, painted and electroplated.

The ability to print colors is another differentiator for Z-Corp. One printhead is dedicated to a clear binder while others deposit cyan, magenta, and yellow colored binders.

In a photopolymer system, the machine feeds liquids, usually some type of photopolymer through an ink-jet type printhead. UV light, which can be mounted in the printhead, cures each layer as it is deposited. Many of these systems use a large printhead to cover a wide area.

Objet Geometries use photopolymers, but their systems deposit these materials a bit differently than other systems. One of the Objet Geometries’ systems uses simultaneous jetting, which they call a polyjet matrix.

A
Dimension 3D printer was instrumental in helping engineers at Neptec
Design Group, a prime contractor to NASA, print a 3D model of damage
aboard the Endeavour. The model provided visual representation of the
tiles and was used to evaluate the damage to the shuttle’s Thermal
Protection System.

“Model materials vary from translucent to rigid, hard opaque materials. They are available in several colors, and flexible resins offer different ranges of flexibility. “Our technology jets two model materials simultaneously,” said Ranney. “These two materials create a third combination material, which we refer to as digital materials because the machine creates them in real time. It’s like taking a rigid material and an elastomeric material and making a composite material. A flexible resin can give a model a tougher feel with flexible movement.” Each composite digital material offers specific values for tensile strength, elongation to break, and even Shore A flexibility.

The resins are not mixed within the printheads. Instead, the printheads, which are next to each other, print out one resin and then the other. When the resins hit the build platform, they start to mix, creating a third material. Such an arrangement suits parts that require both rigid and flexible plastics, and lets you remove steps from some build process, such as printing and then gluing several pieces together. You can load 3D data into a system and assign different materials to the parts. The dual-jet process can combine materials in several ways, enabling the simultaneous use of two different rigid materials, two flexible materials, one of each type, any combination with transparent material, or two jets of the same material.

The idea is to get the model closer to the feel of the final production part. “Each material has mechanical properties that engineers would choose,” continued Ranney. “A blue material for example, may have higher heat deflection capabilities. A white material may prove to be best against moisture.” The materials come in colors to easily identify the mechanical properties.

The system uses eight print heads for the required resolution. Four printheads handle the support material, two printheads handle one model material, and two other printheads handle the other model material. Objet offers data sheets with information on the various properties that arise from the multiple combinations. A gel-like material that supports complicated geometries is easily removed by hand or water jet processes.

In Fused Deposition Modeling (FDM) printing systems, a bead of plastic is extruded out of a nozzle creating a part line by line. DimensionPrinting Systems, Eden Prairie, MN, use an extrusion technology that takes a filament of ABS plastic and deposits it layer upon layer. The software automatically plots a precise deposition path. The plastic is fed into an extrusion head, heated to a semi-liquid state and accurately deposited in layers as fine as 0.010-inch (0.254 mm) thick. Usually, no post processing is needed.

Dimension uses a proprietary program that adds in any support structures needed in the model. You can queue up models, pull off the first model after it’s completed, and the system begins the next model in the queue. The support structures either break away or dissolve in a warm solution.

The plastic material is housed in cassettes in the form of filament string. The material is extruded out to a dimension that is about the width of a human hair and printed. The prototyping chamber is set at around 90F, enabling the material to fuse almost instantly after deposition. A typical model from one of the systems has about 85% of the strength typically associated with ABS plastic from an injection-molded part.

Recently, printer manufacturers have begun to offer new printing technologies. 3D Systems, for example, recently introduced a system that uses film transfer imaging (FTI), found in its VFlash desktop modeler. In film transfer imaging, a thin layer of material is dispensed onto a reciprocating film carriage. The carriage, which looks like an oversized camera film cassette, reciprocates in a motion similar to that of film in a camera. At each reciprocating movement, the cartridge brings a fresh layer of material onto the build surface, which is then imaged with UV flash photography one layer at a time. 

3D
printers, like those from Z-Corp., will let you see in three dimensions
the results of analyses, or allow you to model internal structures in
designs.

Resolution

You will hear the term resolution used to describe the fine detail possible with these printing systems. Each printing manufacturer, however, defines resolution differently. In some cases, it is defined as layers of thickness, which often run 100 microns (0.1 mm).

Other systems use dots per inch (dpi) to describe X-Y resolution. This term would describe the number of individual dots of ink a printer or toner can produce within a linear one-inch (2.54 cm) space. Most systems are comparable to high-quality laser printers. The “dot” is around 50 to 100 microns, (0.05 to 0.1 mm) in diameter.

In summary, each 3D printing system handles specific modeling requirements. Your choice depends on the goals of your model.

MPF