As part designs become increasingly complex, there is a corresponding growing desire to emulate that complexity in the prototyping stage. A novel technology developed by Objet Geometries, Rehovot, Israel, makes that possible to an unprecedented degree. The company’s PolyJet Matrix technology, first employed in its Connex500 system, can simultaneously jet two different materials with different mechanical properties, permitting the prototyping of co-injected or overmolded parts. In addition, the system can blend those two materials in different proportions on the fly, enabling the fabrication of a multiple-material model in a single build.

The core of Objet’s PolyJet technology is the selective jetting of a liquid photopolymer from a movable print head. A UV light embedded in the print head cures the photopolymer immediately after it is dispensed. The print head also dispenses a gel-like support material that permits the fabrication of complicated geometries with overhangs and undercuts. After the prototype part is built, the support material is removed by hand and water jetting. A key advantage of the PolyJet process is its resolution, the ability to create a layer as thin as 16 microns. The technology has been used in the company’s Eden machines for several years.

What is new with PolyJet Matrix is the deployment of eight print heads in a single printing block that enables the dispensing of two different model materials. Each print head includes 96 nozzles, with each nozzle measuring 50 microns in diameter. Two of the eight print heads are designated for each of the two materials to be jetted. The remaining four print heads jet the support material. (See Fig. 1.) As with the original PolyJet system, PolyJet Matrix cures the material as it is laid down, so parts can be handled immediately after fabrication without any secondary processing required.

Fig. 2. A prototype of a handheld GPS device demonstrates the ability to emulate an overmolded part by printing a rubber-like material over a rigid material in the same run.

Objet has developed a range of materials and any two of them can be used in combination with Connex500 PolyJet Matrix system, including:

• Two different rigid materials.
• Two different flexible materials.
• A rigid material and a flexible material.
• A transparent material and an opaque material.
• A white material and a dark material.

So, in the case of using a rigid and a flexible material, one could, in a single build process, create a prototype that emulates a rigid plastic part overmolded with a soft elastomer, without any secondary operations required to produce the look and feel of such a part. (See Fig. 2.)

More importantly, through controlled variable deposition of the two materials, the system can lay down a blend of both, creating a composite material with properties different from either of the two base materials. By applying the materials in different proportions, a whole range of composites are possible.

Fig. 3. A model of an electric guitar made from black and white rigid model materials and Digital Material with different gray scales.

Objet refers to this concept as Digital Materials and has thus far identified a variety of such combinations, each with a designated number and each providing a specific set of mechanical and visual properties. The selection of a specific Digital Material is made by the user through dedicated software that determines the appropriate parameters for jetting the materials. The software implements the creation of the Digital Material automatically during the build process.

So in the case of using a rigid material and a rubber-like material, one could specify different levels of Shore A hardness values for different sections of the same part.

The same concept applies to the visual aspects of a part. One could, for example, use a black material and a white material in different combinations to create different shades of gray in the same part. (See Fig. 3.) In this two-color scenario, one could also simulate the printing of logos, nameplates, and legends on a part.a

Fig. 4. All eight razors were printed simultaneously on a single run, but each with slightly different materials offering different mechanical properties, allowing the product designer to choose the level of flexibility that best serves the objective.

The Connex500 machine has a build volume of 500 mm x 400 mm x 200 mm (19.7 in. x 15.7 in. x 7.9 in.), permitting the printing of large models or multiple smaller models on the same tray. Using Digital Materials for smaller parts, one can actually build different versions of the same part simultaneously. For example, Fig. 4. shows eight prototype razors that were printed simultaneously in a single run, but each with different degree of flexibility. This would allow the product designers to test and bend each one to see which version best meets the desired objective.

For designers of complex, multi-material plastic parts, the new system enables the printing of prototypes that come very close to the production part in terms of mechanical and visual properties, providing a much enhanced ability to evaluate form, fit and function.

For more information, email: info@2objet.com