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Expanding the reach of RP and RT

While rapid prototyping and tooling are not exactly new, they can still be classified as emerging technologies. As such, keeping up with the frequent breakthroughs and improvements to these methods can be daunting.

With an eye toward keeping our readers informed, IMM presents highlights of a conference on the benefits and risks of rapid technologies held at Euromold’99 (see February 2000 IMM, pp. 40-42). Organized by Terry Wohlers, Wohlers Assoc., the seminar presented findings on RP/RT methods currently in use, along with several case studies.

Wohlers opened the conference session by referring to RP as a child experiencing growing pains as it moves toward its adolescent years. "Slowed growth in the past three years has confused many," he says, "but compared to the CNC and machine tool markets, RP has done very well." He cites a recent success story at Caterpillar, in which the company was able to produce a tractor cab mock-up in 31/2 months using 32 RP parts. "They had never done this in less than a year before," he adds.

Currently, three segments of the industry appear the most dynamic, according to Wohlers. "First, there are 3-D printing applications, which produce inexpensive models for evaluation early in the design cycle when engineering changes are less costly," he says. "Next, some believe RP can and will be used for directly fabricating production parts in a layer-by-layer manner. This is known as rapid manufacturing. Finally, we have rapid tooling, the name adopted by the industry to describe RP-driven tooling and core and cavity inserts created directly from RP processes. As many as 20 methods of RT have developed over the past few years, so we are seeing a lot of interest in the area."

Replicating in 3-D
As a less costly variation of RP, 3-D printers are also easy to use and small enough to fit on a bench or tabletop. Their primary goal is to provide engineers with validation models early in the design process so that changes can be made upfront, and therefore, inexpensively. These systems function much like an inkjet printer, taking a solid CAD model and rendering it in a thermoplastic such as wax.

The beauty of these replicators is that most models can be produced in a day or less vs. the multiple days it may take to build a stereolithography model. "After a CAD solid model is created, the data often changes quickly during the concept phase of development," Wohlers says. "Expensive RP models just can’t keep up with the pace, and discourage designers from building them as concept models. With 3-D printing, time and cost obstacles are overcome."

On the other hand, the variety of materials available and better part quality give higher-end RP systems an edge over 3-D printers for demanding applications. Brock Hinzmann, director of SRI International’s TechMonitoring, lists some of the material improvements in a paper titled "The Personal Factory":

  • New epoxy materials—greater strength than early acrylic materials (produced for 3D Systems by Ciba).
  • Nylon and composite materials—greater toughness over the original acrylics or the epoxies (DTM Corp.).
  • Polymeric composites (Helisys).
  • ABS (Stratasys—some developed in partnership with 3M).
  • Material suppliers such as DuPont Somos (now DSM Somos), Japan Synthetic Rubber, and others also offer variations that can be soft, almost like rubber, or can be filled with additives that give other desirable properties.

Production Parts
Ready for yet another abbreviation? Try RM, for rapid manufacturing. Boeing/Rocketdyne did, and the results were amazing. ‘They used a DTM Sinterstation to produce 200 retainer parts for an electrical assembly, creating all of them within two days," Wohlers explains. "These were not models, but actual production parts in glass-filled nylon."

Wohlers speculates that RM may be the next frontier for RP. "While it’s unlikely that RM will ever reach the production capacity of injection molding or sheet metal stamping, there are those industries where low volumes are the norm. For example, consider the customized work of those who make prosthetic devices or replacement limbs, and the low-volume production of parts for space applications."

Another category where RM may triumph is that of nonappearance parts, those hidden from view. Currently, the surface finish of RP parts doesn’t meet most production standards, but as stair steps and layer thicknesses decrease, this issue may be less critical.

Mass customization also comes into play when looking at RM. Some experts predict that, for expensive products, the entire production run may consist of one product, customized to suit the end user. "While mechanical properties of RP materials don’t suit all products," says Wohlers, "some of the new epoxy resins, nylons, ABS, and composites offer impressive strength."

However, he cautions those interested in RM to watch as it develops. "One consideration is cleaning the parts and removing support structures. Also, the speed of fabricating production parts using an RP process will be critical to the success of RM. Finally, CNC machining will remain the technology of choice for many applications. It’s a proven and widely accepted option that offers a wide material selection."

Fast Tools
With an estimated $39 billion in sales worldwide, the tooling market appeals to many RP manufacturers. A host of new and seasoned companies have joined the fray, producing a wide variety of options for creating prototype and production tooling from RP processes.

Driving this growth are time-to-market pressures, especially critical for long-lead-time injection molds. "Developers see the opportunity to slash cost and time, with possibilities for prototype, bridge, short-run, and production tooling," says Wohlers. "In addition, RT offers the option of embedding conformal cooling lines in the mold to remove hot spots and reduce cycle times."

RT can be broken into two main categories: indirect and direct tooling. Indirect methods, which account for the majority of tools, start with an RP pattern and build the tool from it. Direct methods, of course, build the tool directly using an RP process. Joel Segal, formerly of Rover/BMW, David Tait, ARRK Product Development, and Philip Dickens, De Montfort University, summarized the existing methods being used for rapid tool construction.

Spray metal tooling. A three-part process for depositing metal onto a substrate. An energy source is used to melt the metal, and then a gas atomizes the molten metal and propels it onto a substrate (i.e. a pattern). Costs are typically less than 50 percent of conventional tooling, and lead times are 65 percent less. Geometry limitations exist due to line of sight issues. Work done at Pera (Melton Mowbray, England) has produced arc-sprayed steel tooling from RP patterns. Also, Ford is commercializing a patented process called Sprayform for steel production tooling.

RP/RT on the web

Not surprisingly, rapid prototyping and tooling sites are a significant presence in the Net universe. Many of the sites stem from universities that perform research in this area. Others are developed by companies providing RP/RT equipment. As with any evolving technology, research and development efforts are still going strong, and surfing the Web proves it.

Most of the research-oriented websites offer information on the various types of RP systems, along with links to manufacturers’ sites. Here are a few that IMM reviewed:

  • Wohlers Assoc.: www.wohlersassociates.com
  • Rapid Prototyping: www.cc.utah.edu/~asn8200/rapid.html
  • Rapid Tooling: www.cc.utah.edu/~asn8200/rt.html
  • NASA RP: nasarp.msfc.nasa.gov
  • Rapid Prototyping Center: www.rpc.msoe.edu

    In addition, we found an extensive list of RP technologies at the Rapid Prototyping Family Tree page (ltk.hut.fi/~koukka/RP/rptree.html). Compiled by Henri Koukka, a researcher at the Helsinki University of Technology in Finland, the list contains a key as to whether the method is commercially available, under research, or defunct. The table below, excerpted from this site, lists several systems that are currently available.

  • 3D Keltool. (3D Systems) Uses an SLA master pattern to create RTV silicone rubber molds, which are then filled with tool steel powder, tungsten carbide, and epoxy to form green parts. These are sintered and infiltrated with copper to form a fully dense mold insert. Benefits are a 20 to 30 percent faster cycle time than P-20 steel inserts, greater than one million-shot lifetime, and accuracy to within .2 percent. Inserts can be produced in as little as eight days.

    RapidTool. (DTM Corp.) Uses the SLS process to create solid inserts by fusing powders with a CO2 laser. For tooling, RapidSteel 2.0 material is used most often. This is a direct RT process in which there are two furnace cycles—one to sinter the steel particles, and the second to infiltrate with bronze. Segal notes that one company in England saved 21,000 euro (28 percent) and 10 weeks (80 percent) vs. a conventional tool by using this process for a telecommunications product.

    DMLS. (EOS) Direct Metal Laser Sintering, an RT method that produces metal tools by laser sintering metal powders. The latest material, DirectSteel 50-V1, has been used to produce injection mold inserts. Time and cost savings over traditional molds range up to 80 percent.

    ProMetal. (Extrude Hone Corp.) Another direct process in which solid objects are created by printing polymeric binder onto thin layers of metal using an inkjet printer. This green part is heated to 1200C to burn out the binder, and then is infiltrated with bronze for a fully dense mold insert. Beta tester Motorola in Ft. Lauderdale, FL is using this process to fabricate mold inserts. According to Tait, Motorola reports it is looking at ProMetal as a strategic option for future bridge tooling, and is targeting build time at four days, including sintering and infiltration.

    TABLE 1. Commercially Available RP technologies
    Material  General method Specific method  Providers 
     LIQUIDS  Photocurable liquids Curing by light through masks Solid Ground Curing (SGC)/Cubital Inc.
    Design-Controlled Automated Fabrication
    (DESCAF)/Light Sculpting Inc.
    Curing with a UV laser (single beam) Stereolithography (SLA)/3D Systems
    Stereolithography/Aaroflex Inc.
     POWDERS  Melting powder Sintering with a heat-transferring laser Selective Laser Sintering (SLS)/DTM Corp.
    Direct Metal Laser Sintering (DMLS)/EOS
    Melting with a heat-transferring laser Laser Engineered Net Shaping (LENS)/
    Optomec, Sandia National Laboratories
    Lasform/AeroMet
    Direct Metal Deposition (DMD)/
    Precision Optical Mfg.
     Binding by adhesives Methods based on MIT's 3-D printing 3D-Printing/Z Corp.
    ProMetal/Extrude Hone Corp.
     SOLID MATERIALS  Extrusion of melted material  Plastics Fused Deposition Modeling (FDM)/Stratasys
    Melted Extrusion Manufacturing (MEM)/
    CLRF, Tsinghua University
     Inkjet techniques Multi Jet Modeling (MJM)/3D Systems
    3D Plotting/Sanders Prototype Inc.
     SHEETS  Bond-first lamination  Cutting material with a laser Laminated Object Manufacturing (LOM)/Helisys Inc.




    Contact information
    Wohlers Assoc. Inc.
    Fort Collins, CO
    Terry Wohlers
    Phone: (970) 225-0086
    Fax: (970) 225-2027
    Web: www.wohlersassociates.com
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