Desktop rapid prototyping

31 Jul, 2002 By: Mark Huxley,Steven Weisberg Cadalyst

Cuts costs and improves designs

Producing real physical models directly from 3D CAD models is possible through an increasingly automatic process called rapid prototyping. Rapid prototyping is very useful to those who design in 3D because it helps identify the need for significant changes earlier in the product development cycle. This in turn reduces cost and improves performance. If you still primarily use 2D designs, rapid prototyping is yet another reason to switch to 3D.

Figure 1. Not quite small enough to sit on your desk, this officefriendly rapid prototyping system, Z Corp.'s Z406, is roughly the size of an office copier.

The diverse areas in which rapid prototyping is used continues to grow and astound even long-time users. Examples include engine part mold masters, architectural scale models, medical implants, and even final products, such as the Invisalign orthodontic retainers. The adoption rate of rapid prototyping among engineers and designers follows closely that of 3D CAD use, although rapid prototyping is at a much earlier stage of popularity and time in the market.

In this article, we address a subsection of the rapid prototyping field that is generally less expensive ($7,500–$190,000) and more convenient for designers to use directly. This subset, known as office-friendly or desktop prototyping, is gaining popularity thanks to its use of more environmentally friendly materials and a significant reduction in physical machine size.

Most of the machines we found are larger than your average printer, more similar in size to a copying machine—still quite an office-friendly size (figure 1). For a broader perspective on rapid prototyping technology, please see our previous article in the May 2001 issue of Cadalyst as well as the Wohlers Report 2002.

This prototype is a full-size turbo charger housing that was built in 5 hours, 41 minutes, plus 30 minutes of finishing time, using a Z Corp. system. A monochrome version took 3 hours, 11 minutes to create. The model measures 8" x 6" x 5" and occupies 38 cubic inches. Material cost for the color prototype was $97.14, and $65.60 for the monochrome version.

Office-friendly 3D printers
Traditionally, rapid prototyping machines needed their own lab-type area because their operational characteristics (noise, fumes, possible contamination of resin, residue, UV-sensitive materials, and so forth) were not appropriate for the office. Labs provided extra electrical power, space for machines the size of industrial refrigerators, a separate area for noxious build materials, venting ducts for outgassing, and noise insulation from the office. Users also needed a fair amount of training to operate these machines properly.

Figure 2. In this example, reverse-engineering data was used to make a detailed 2D drawing.Figure 3. This 3D CAD model, created from the 2D drawing, was sent to the rapid prototyping system.
Figure 3. This 3D CAD model, created from the 2D drawing, was sent to the rapid prototyping system.Figure 5. The finished machine casting.

A goal of the rapid prototyping industry is to make a class of rapid prototyping machines that are as officefriendly as laser printers. Such units must be smaller and more movable than traditional systems, with no special venting or power requirements. User training should be minimal. The first generation of 3D printers with these characteristics is now available. A typical air-conditioned office is the assumed setting for these devices. Though some machines approach the size of a laser printer, it's still too soon to call them desktop rapid prototypers.

Delivering an office-friendly rapid prototyping system is more complicated than a paper printer because the user's final output requirements vary considerably. Rapid prototyping vendor 3D Systems divides the final outputs desired into five categories:

  • concept models
  • prototypes
  • patterns
  • tools
  • finished parts

Concept models, prototypes, and patterns are a strong suit of 3D printers, and some machines provide green parts that can assist in the rapid manufacturing realm. The relationship between price and functionality is not as clear as it used to be. Even so, the less-expensive office machines have not eclipsed their more expensive forebears.

Product development engineer Jim Pike at the Sturm division of the Sulzer pump company provided a real-world example of rapid manufacturing via rapid prototyping for a replacement impeller part (see figures 2–5, above). prototyping

This feature surveys the office-friendly offerings of four manufacturers of rapid prototyping systems. In addition, the box below shows some tabletop milling machines that can quickly produce metal parts and models.

Benchtop milling machines serve rapid prototyping roles

The MDX-650 (shown at right) and MDX-500 (not shown) benchtop milling machines from Roland DGA (www.rolanddga. com) quickly turn CAD files into 3D prototypes and molds. Powered by AC servo motors on all three axes, they mill ABS, modeling wax, aluminum, brass, and other nonferrous metals. With its optional rotary axis, the MDX-650 mills the full circumference of objects. Both mill as much as 200 per minute with no finishing required. The MDX-650 has a maximum work area of 25.56" x 17.69" x 6.06", and the MDX-500 has a maximum work area of 19.63" x 12.94" x 4.125".
The Roland MDX-15 (not shown) and MDX-20 (shown at left) desktop milling machines are ideal for jewelers and product designers working on a budget. They mill chemical wood, resin, aluminum, and brass and incorporate RAPS technology to scan with resolution up to 0.002". Maximum work area is 8" x 6" for the MDX-15 and 6" x 4" for the MDX-20. Both have a z-axis height of 2.38".

3D systems
The company that started the rapid prototyping industry maintains a reputation for producing machines that generate accurate and functional parts.

3D Systems recently announced a new product called the InVision 3D Printer (figure 6) for the office-friendly rapid prototyping market segment. The InVision 3D Printer uses a new model material and support material (figure 7). The model material is a translucent, durable acrylic photopolymer blend appropriate for durable communication models and assembly analysis prototypes. The support material is a wax-based blend.

Figure 6. The InVision 3D printer produces models from 3D design data.
Figure 7. The 3D Systems' InVision 3D Printer makes models from a durable, acrylic photopolymer-based material that withstands the stresses of shipping and handling.

Part sizes appear to be in the same range as those produced by other midpriced rapid prototyping systems (see comparison table).

3D Systems' ThermoJet printer remains as a solution for investment casting and communication models. The ThermoJet provides less durable models but supports colors. InVision is available through the company's worldwide direct sales force and its network of channel partners, resellers, and distributors.

Solidscape positions its 3D printers as highly accurate machines that exceed concept model requirements to produce precise models and patterns. Models are accurate to one-thousandth of an inch per inch in the x-, y- and zdimensions. This enables an excellent surface finish with very fine feature detail. Little or no postprocessing is required. This precision comes at the expense of speed and potential part volume.

Two types of proprietary materials are available, and both are nontoxic. Support structures for the materials dissolve easily. The build material has a fast melt-out in casting and negligible thermal expansion. It leaves no ash or residue. The company estimates that at an 85% duty cycle, a typical user spends $200–$250 per month on materials.

Solidscape systems can run unattended for 72 hours. They have a small footprint and are about 5 tall. The only requirements are that the unit be in an air-conditioned room with standard power outlets.

Solidscape user Norm DePeau of Sturm, Ruger is very positive about his machine's contribution to rapid manufacturing: "This capability is invaluable as a complement to the investment casting process. Many customers are not prepared to invest in wax die tooling during the new product development phase. The Solidscape Pattern Master allows our casting operations to introduce customers to the use of castings with a significantly lower entry cost. The Pattern Master produces high-precision patterns that can be used directly in the investment casting process in place of the wax patterns normally generated from hard tooling (figures 8 and 9). As the project evolves and designs become firm, customers are better prepared to fund the hard tooling needed to produce investment castings."

Figure 8. Rapid prototyping components for firearms. The model is built from a green material, and the red material serves as the support structure.Figure 9. Once the supports dissolve, you can see the intricate parts that the Solidscape Pattern Master is capable of producing. Images courtesy of Sturm, Ruger & Co. Inc.

Stratasys is an established rapid prototyping vendor that made news early this year with the introduction of its Dimension 3D printer (figure 10). "Stratasys just released the Dimension to quickly create usable, functional models at the engineer's desk," said Mike Ontiveros of CAD/CAM Systems, a Stratasys reseller. "Confidentiality is of great concern, and the Dimension will keep intellectual property (design and mechanical technology) in house."

Figure 10. The Dimension printer uses two self-loading cartridges for the model and support materials.

This machine is very office-friendly. It uses a standard 110V AC power connection, is easy to network, and notifies you via e-mail, pager, or the Web when it completes a part. The material cartridges plug in much like toner cartridges —no chemicals, powders, or fumes.

With a base price of $29,900, it's currently the least expensive machine on the market, even with the optional annual maintenance plan (10% of price), although not by much. The Dimension is based on the proven technology found in the larger FDM (fused deposition modeling) machines that Stratasys makes.

The Dimension offers only one material choice, an ABS plastic with a tensile strength of 5,000psi. This is equal to or better than some other grades of commercially available ABS. Because of rapid prototyping build characteristics, the parts may be weaker in the x,y plane. This material produces very functional parts that can even be melted, if necessary, for shape or snap-fit tweaks. A fairly detailed pagersized part we saw took about 1.5 hours to build with a material cost of about $7.

Material cartridges contain an EPROM chip that tracks used and unused material to confirm that the necessary material for the part volume is available before the Dimension builds the model. You can switch cartridges midway through part building, if necessary. You can also pause the job to switch cartridge colors.

Dimension automatically builds breakaway supports. You must remove the supports by hand after the part is built. Cleanup involves a minimal amount of mess that is more office-friendly than that left by the powder used by some systems.

The setup software for Windows is easy to use. Another program in the machine handles status and administration of the part. Setup parameters include:

  • Part orientation
  • Slice thickness
  • Part build type (solid, thin-walled, thick-walled)
  • Support type (dense, sparse)
  • Preview build paths
  • Finished part notification options

Stratasys sells its rapid prototyping machines through resellers in the United States and directly abroad.

Z Corp. "The earlier in the design process you can build concept models, the earlier you can resolve problems and issues," explained rapid prototyping reseller Mark Kemper of EMS USA. "Companies in the past would build concept models only near the end of the design cycle because of the time and cost of either using an outside service bureau or buying their own equipment. When the average part takes ten hours to build and costs $1,000 or more, how many would you build? When a part takes three hours to build and costs $20, you can afford to do many more models and do them earlier in the process.

"With Z Corp.'s full 3D color capabilities," he added, "users can analyze engineering data such as CFD, FEA, mold flow, and other analysis results right on their model." See figures 11 and 12 (below) for examples.

Figure 11. The cell phone analysis was performed with Moldflow software, then molten plastic flow characteristics were transferred to a Z Corp. rapid prototyping system via a VRML file. Image courtesy of EMS.Figure 12. Turbine blades were analyzed with FEA software, and the stress colors were built into this Z Corp. rapid prototyping model. Image courtesy of EMS.

Z Corp. earned its strong reputation as a leader in the 3D printer market. The company claims to have the fastest 3D printers in the world with the capability to produce a handheld part in less than an hour. They were also the first to provide full-color models. Color information displayed in software analysis packages is passed via VRML files to complement the STL file used for geometry.

Z Corp. attributes its relatively low product prices to using off-the-shelf components. These machines also have low operating costs. The company offers three different models for $33,500, $66,500, and $175,000. The first two are the size of an office copier and connect to computers via a serial port.

Two types of materials are currently available (a starch-based powder and a plaster) that enable the machines to produce concept models, prototypes, and patterns.

You can switch materials in a 20- minute, two-step process. First, you vacuum out the first powder, which you can reuse. Second, switch the binder over and purge the old resin.

The only complaint we heard about the material is that the powder is a little messy when you take it out of the machine, so you'll need a small cleanup area.

Penetrating and sealing models with a material similar to Superglue can result in a small amount of harmless outgassing with an odor that is not noxious or irritating.

In the United States, Z Corp. machines are available directly from the vendor and through resellers. Internationally, they are sold through distributors.

Service Bureaus remain important
Owners of 3D printing systems frequently report that they obtained rapid prototyping models through service bureaus before they bought their own systems. Many still use these outside resources to produce types of rapid prototyping models that their in-house systems can't create. In some cases, this may simply be due to the hassle and cost associated with switching out one material type for another.

Todd Grimm, marketing manager for dedicated rapid prototyping service bureau Accelerated Technologies, noted in a recent paper that choosing the right technology for your desired end product is difficult to do without hands-on experience. A good service bureau guides inexperienced rapid prototyping customers through selecting the right material and prototyping method.

"I think service bureaus will always exist because many companies require very few parts, and even with the low prices of 3D printers, they could never justify spending the money," explained reseller Mark Kemper.

Figure 13. A Z Corp. system took 6 hours, 44 minutes to produce this fullscale hydraulic pump case that masures 8" x 10"x 7". Part volume is 43 cubic inches, and materials cost $71.87. Finishing the part required another 45 minutes of work.

"What 3D printers have done is open a whole new market of small- to medium-size companies that could benefit from rapid prototyping but could never make a $100,000-plus investment in the technology. In addition, material costs used to be $10 or more per cubic inch. Z Corp.'s 3D printers can build parts for about $1.50 per cubic inch and do it 10 times faster [than was previously possible]," he said (figure 13).

Wohlers Associates maintains a list of service providers. Castle Island maintains a worldwide rapid prototyping directory.

Some online marketplaces, such as, let you request rapid prototyping quotes from different service providers. Other sites, such as, provide quotes from a single vendor based on part files you upload.

Rapid manufacturing with rapid prototyping
"[Rapid manufacturing] offers a lot of potential for small batches of parts because the cost and delivery time can be very attractive," noted Kemper. "For example, Z Corp.'s new Z Cast Direct Metal Casting and some new resins codeveloped with Vantico allow customers to make more functional metal parts. Other concept modelers—3D Systems' ThermoJet, for example— have always been good at the investment casting process. 3D Systems has also joined with DSM Somos to form a new company, OptoForm. OptoForm will develop advanced digital manufacturing technology that will build actual parts from composite plastic, ceramic, and metal. Such technology will eliminate the need for hard tooling.

On the flip side, Kemper notes that "traditional methods such as NC machining have also been moving forward. Machine tools continue to come down in price, while high-speed machining and automated CAM systems are more powerful than ever."

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