In the early days of rapid prototyping, product developers were ecstatic to have quickly produced parts that accurately indicated form and fit. But as compressed development cycles have placed more demands upon design engineers, they in turn demand more from their prototypes. They want RP parts that exhibit greater functionality, more durability, higher accuracy, and improved appearance. The key to meeting those demands is continued innovation in the realm of RP materials, and the companies that create such products have stepped up to the plate and delivered. In the past few years, the industry has witnessed an expanded range of RP materials that bring product designers ever closer to their ideal – making rapid prototypes that look and perform as well as production parts.

Rapid prototyping material choices are still somewhat limited as compared to injection moldable plastics and castable metals. While there are thousands of traditional thermoplastics on the market, for instance, only a few dozen grades of thermoplastics and photopolymers for additive plastic systems are available. However, the number of materials that mimic more common plastics is growing. Today, there are a number of prototyping variants of ABS, polypropylene (PP), polycarbonate (PC), and other materials. The menu of metal powders used in laser sintering also contains new options.

Some of the new materials challenge the conventional wisdom that RP parts are not as strong as production parts made by injection molding or casting. Impact resistance, elongation at break, flexural modulus, and other material properties have improved. New infiltrants, which infuse materials with enhanced physical and mechanical properties, are now available including glass-filled materials and flame retardant additives.

Beyond being sturdier, some of the new materials offer enhanced aesthetic features such as transparency, and new colors and shades. Several companies even offer soft elastomer materials.

3D Systems offers a polypropylene-like material that offers high flexibility.

Rapid prototyping is achieved by a wide range of technologies. Some of the more widely used ones include stereolithography (SL), which uses liquid photopolymers; Stratasys fused deposition modeling (FDM), which uses extruded polymer filaments; selective laser sintering (SLS), which uses powdered polymers and powdered metals; Objet Geometries’ PolyJet system that uses jetted photopolymers; and Z Corp. 3DP technology, which uses an adhesive to selectively bind polymer powders.

Each prototyping method has its own pluses and minuses. Stereolithography has a quality surface, but is typically not good for products that require long-term durability. FDM and laser sintering systems are better for durable, manufactured parts, but part accuracy isn’t as high as an SL system. A Z Corp. 3DP machine is fast, clean, and colorful, but parts can suffer from reduced durability and accuracy. However, the new materials that have hit the market have blurred these general lines, with improvements reducing some of the minuses of some, while playing up the strengths of others.

Stereolithography

A drill housing made with 3D System’s ABS-like Accura 55 material.

Stereolithography has been one of the more popular of the rapid prototyping methods, as it was first on the scene. With SL, prototypes are built by tracing a laser beam over a vat of liquid photopolymer. As the laser beam touches the material, the polymer immediately begins to solidify. After a layer is traced, it is lowered and covered with more liquid and the laser is traced back over the new layer of material to create the part’s second layer. In this way, successive layers of the photocurable resin are built up into a multidimensional part. The SL method tends to create parts with a good surface finish and fine detail, but they typically require a post-curing operation to complete the chemical process. Without this secondary curing, the chemical reaction that solidifies the material can continue, causing property changes to the material. Parts can warp and become brittle, and the useful lifetime of parts made from these types of resins are limited.

But new materials have been made available that solve some of these issues.

DSM Somos, of Elgin, Ill., has developed several new SL materials including the DMX-SL 100. Brian Bauman, technical service and product manager, says the material was designed to bridge the gap between prototyping and manufacturing. It delivers the accuracy of stereolithography with sintered-like durability and is targeted to applications that previously would have required SLS or FDM prototyping. It has impact strength of 0.8 J/cm, and a flexural modulus ranging from 2,000 to 2,400 megapascals (MPa). The DMX-SL 100 has the stiffness of standard ABS-type resins, but with more than twice the impact strength, plus up to 20 percent elongation at break, he says.

A power saw prototype made with Dimension 3D Printing’s ABS material.

Bauman says that to track durability, impact testing was conducted over a three-month period at temperatures of 30 DegC, 54 DegC, and 85 DegC. Prior to test, impact resistance was 0.8 j/cm, and after 3 months of impact testing, the results ranged from 0.49 j/cm for the 85 DegC test subject, to 0.6 for the 30 DegC test subject.

The company also introduced the WaterShed XC11122, which is a new colorless version of its ABS-like WaterShed 11120 material. It offers high stiffness, good elongation and water resistance. (Moisture absorption can affect a prototype’s mechanical properties and dimensions.) It performs like ABS, but looks more like glass with a slight green tint. The clear, water-resistant material has been given an FDA USP 23 Class VI approval that allows it to be used in a variety of medical applications.

Huntsman Advanced Materials, of The Woodlands, Texas, has also released a new, more durable stereolithography material. The ABS-type material, RenShape UltraClear SL7870, is a transparent material that includes heat deflection temperatures of up to 85 DegC, elongations at break as high as 30 percent, flexural strengths from 7,000 to 15,000 psi, and good humidity resistance (40 DegC and 90 percent R/H), says Harald Wiedemann, who heads strategic marketing for Huntsman. The material yields parts that are clear without blue or green tints. It is an antimony-free, low-viscosity, stable liquid that produces models and prototypes that are “as clear as glass” according to the CIELAB color scale system, he says. It is formulated to conform to FDA USP 23 Class VI standards for use in medical modeling and prototyping.

A testing fixture made from Dimension 3D Printing prototyping system.

At 3D Systems, Rock Hill, S.C., several new SL materials have been developed that are meant to offer greater durability, says Steve Hanna, stereolithography materials manager. These new products include the DuraForm XR3000, a translucent, white-in-color, material that has good chemical resistance and elevated impact strength.

The company also introduced three new products in its Accura product line including the Accura 48HTR, the Accura Extreme, and the Accura Bluestone. The Accura 48HTR is a ceramic composite material that is meant for high temperature applications of up to 130 DegC. The Accura Extreme features the aesthetics and properties of a grey-molded ABS or polypropylene production part. It has impact strength of 35 to 52 J/m, elongation at break of 14 to 22 percent, flexural strength of 52 MPa to 71 MPa, and flexural modulus of 1,520 MPa to 2,070 MPa. The Bluestone is a nanocomposite material that has a flexural strength of 124 MPa to 154 MPa, flexural modulus of 8,300 MPa to 9,800 MPa, and impact strength (Notched Izod) of 14 to 17 J/m.

Selective Laser Sintering

DSM Somos’ WaterShed XC11122 is a new colorless version of its ABS-like WaterShed 11120 material.

Selective laser sintering builds parts using powdered metal or plastic materials. A computer-guided laser is used to sinter or bond the powdered material together. The laser scans cross sections generated from a 3D digital file. As the laser moves, it fuses small particles of polymers and metals into a working prototype. The laser scans cross sections generated from a 3D digital file. After a cross section of the part is sintered, the powder bed is lowered and a new layer of material is deposited and sintered on top. It can make very complex geometries directly from digital CAD data.

Sintered parts can be porous and have a rougher surface finish compared to other prototyping parts, but can be modified to improve strength and surface finish.

Laser sintering allows designers to craft parts with varying wall thicknesses and allows the build of hollow structures with internal components, says Florian Pfefferkorn, a plastics product manager with EOS of Germany, a manufacturer of prototyping machines and materials.

A flexible keypad made with Objet Geometries Tango FullCure930 material.

EOS now offers a new plastic and a new metal material for SLS. The plastic is PrimePart DC, which is an impact-resistant polyamide with a tensile strength of 48 MPa. It has an elongation break at 50 percent, which Pfefferkorn says is about 50 percent greater than previously available materials. Pfefferkorn says that the PrimePart DC is based on a Nylon-12 material and offers good properties at low temperatures down to -30 DegC.

Versions are available that are glass filled and fire retardant.

The company is also working on a new material called PrimePart ST (soft touch), which is a soft material with an elongation of around 250 percent and a Shore hardness of A95/D35. Parts laser-sintered from this material are fully dense, so gas-tight products can be produced directly. Compared to other flexible laser-sintering materials available, PrimePart ST shows a four times higher tensile strength of 8 MPa.

Future plastic materials from EOS will offer a wider choice of colors. Its PA 2202 black is a polyamide material containing black pigments. The resulting parts are colored throughout their whole volume, which makes them resistant against scratches, abrasion, and dirt. The parts are well suited for mechanically stressed applications or dirty environments. The polymer in black will be the first choice for industries where this color of parts is relevant. PA 2203 grey is a further alternative in light grey.

For direct metal laser sintering, which builds parts from successive layers of fused metal powder, EOS now offers StainlessSteel PH1, which Michael Shellabear, vice president at EOS and a metals specialist, says offers hardness, corrosion resistance, and excellent mechanical properties that can match the traits of stainless steels currently in use. It has a tensile strength of around 1,100 MPa, which increases to about 1,300 MPa after post hardening.

Fused Deposition Modeling

EOS offers a variety of new materials including laser sintered plastic and metal powders. This EOS prototype is a sieve made from 17-4 stainless steel.

The FDM process uses a plastic filament to produce parts. The filaments are supplied in coil form and fed into a heated nozzle. As the nozzle moves over the build chamber, it deposits a thin bead of extruded plastic to form each layer of a part. The plastic hardens immediately after extrusion from the nozzle.

Stratasys of Eden Prairie, Minn., developed the FDM process and offers prototyping equipment and the prototyping materials to operate them. One of the newest materials offered by Stratasys is the ABS-M30, which Fred Fisher, product marketing manager for Stratasys, says is 25 to 70 percent stronger than standard Stratasys ABS. It has tensile strength in the range of 36 MPa, tensile modulus of 2,413 MPa, and elongation at break of 4 percent. Flexural modulus is in the range of 2,317 MPa, flexural elongation is 52 percent, and IZOD notched impact tests are about 139 J/m. The ABS-M30 material makes stable parts, that have no appreciable warping, shrinkage, or moisture absorption, he says. It can make parts that are durable enough for functional testing, installation, and end use. One of its most popular uses is for developing rapid tooling such as jigs, fixtures, and check gages.

Fisher says the improved mechanical performance is derived not only from the resin, but the hardware that is building the part. He says that the mechanical properties are better in part because of the elevated temperature at which the FDM equipment extrudes the material (about 295 DegC), which helps to better bond the individual layers, creating a denser, less porous part.

A fan blade from DSM Somos SL prototyping material.

The Dimension division of Stratasys makes 3D printers that also employ the FDM technology. Jon Cobb, vice president of Dimension 3D Printer, also of Eden Prairie, says that the new ABSPlus material substantially increases the strength of parts over those made with traditional ABS materials. Previously, these materials represented about 70 percent of the strength of an injection-molded part, but the new material is about 90 percent of the value of an injection-molded part. He says unlike most models built with a 3D printer, the new material allows for snap/fit testing, and can be part of larger assembly in which other parts are bolted or screwed onto the component. In fact, the parts are so durable that about 15 percent of the models built with the material are used to create tooling such as jigs and fixtures.

With ABSPlus, no additional curing or other post processing is needed other than removing supports. The material is available in up to nine different colors.

Z Corp. 3DP

Stratasys offers durable materials for use in direct digital manufacturing applications. Shown is the FDM 900 prototyping machine.

Another popular 3D printer technology is one developed by Z Corp., Burlington, Mass., in which a layer of powdered polymer material is selectively bonded by the jetting of adhesive. One of the key advantages of this technology is its speed. Z Corp. says that its 3D printers are 5 times to 10 times faster than other RP technologies.

Another virtue of this method is the availability of colored materials and the ability to create a multicolored part in the same build.

Parts made with Z Corp. 3DP printers are typically smaller and less durable. They are generally used for concept modeling, and typically can only undergo very simple testing. It is the least costly variation of rapid prototyping technology and is often used as a quick and inexpensive concept model early in the design process. Parts made by this process that require a lot of handling can be given a post-fabrication infusion of a different material that makes the parts stronger.

The company has also been developing new materials to improve the functionality and strength of such parts. New to the company’s product line is the zp140, which is a monochrome 3D printed material that cures with a “quick mist with tap water.” The monochrome parts require no further treatment or equipment to reach their finished strength and harden in less than half of the time of previous materials. If stronger parts are required for fit and functional testing, the parts can be augmented with Z Corp. infiltrants.

The Huntsman UltraClear SL7870 is a transparent material that includes heat deflection temperatures of up to 85 DegC.

Z Corp. also introduced the zp131 material that, when infiltrated with Z-Bond material, is 50 percent stronger than when printed with previous materials. These stronger parts are good for fit and functional testing. They are 115 percent whiter than previous materials and are more uniform in color across a wider range of hues, and faster to harden, enabling the printing of finer details.

The company also offers a new material, dubbed Elastomeric Material, which has been optimized for infiltration with an elastomer to create parts with rubber like properties. The materials consists of a mix of cellulose, specialty fibers and other additives that combine to provide an accurate part that is capable of absorbing the elastomer and gives the parts their flexible, rubber like property.

PolyJet

A clear tray made with Huntsman UltraClear transparent material.

Objet Geometries, Rehovot, Israel, developed a technology called PolyJet, which jets a photopolymer. The print head on its machines selectively deposits the photopolmer, which is immediately cured by a UV light in the print head. Parts are built layer by layer, as with the other RP approaches. PolyJet technology provides high resolution, jetting layers as thin as 16 microns, permitting the fabrication of smooth, accurate, and highly detailed parts.

Last year the company introduced a new rubber like material, TangoPlus FullCure930, which has a Hardness ShoreA value of 27. The materials’ elongation to break is 218 percent, its tensile strength at break is 1,455 MPa, and its tensile modulus ranges from 0.146 MPa to 0.263 MPa. This translucent material joins previous members of the Tango elastomer family, TangoGrey and TangoBlack, which also offer specific levels of elasticity.

And just a few months ago, Objet unveiled a material called DurusWhite, FullCure430, which was formulated to simulate the toughness, strength, and flexibility of polypropylene. For toughness, it exhibits Izod Notched Impact of 44.22 J/m. For flexibility, it has elongation at break of 44.2 percent, and for strength it has a modulus of elasticity of 1,135 MPa. The mechanical properties of DurusWhite simulate polypropylene’s resistance to fatigue and enable snap-fit functionality, critical for products with hinging mechanisms.

A multiple-part, prototyped valve made with Z Corp.’s 3DP system.

All of these developments make it more complex for design engineers to choose an RP technology for their needs, since choices were often heavily influenced by limitations in associated materials. But, at the same time, these innovations provide more opportunities to produce RP parts that more closely match the intentions of the final production part, permitting thorough pre-production evaluations and tests that were previously unattainable.

For more information, email:
3D Systems, grahamj@3dsystems.com
Dimension 3D Printer, jroitenberg@dimensionprinting.com
DSM Somos, Brian.Bauman@DSM.COM
EOS, florian.pfefferkorn@eos.info
Huntsman Advanced Materials, magnus_wied@huntsman.com
Objet Geometries, info@2objet.com
Stratasys, Fred.Fischer@Stratasys.com
Z Corp., jtitlow@zcorp.com