Polyjet System

TEAM Lab Equipment: Polyjet 3D Printing

Basic Overview of Polyjet Printing:

Materials: Type: Proprietary acrylate based polymer. Rigid White & Flexible Translucent (which can be combined to achieve intermediate mechanical properties).  Alternatively, Rigid Translucent/Clear (Clear achieved with polishing)
Properties: Variable mechanical properties but moderately low yield stress at highest stiffness. Behaves much like standard acrylic, unless blended with flexible material.  Alternative materials can be rubber-like in mechanical properties, or clear/translucent.

Accuracy: Extremely high: 16/32 micron layer thickness, Overall 0.05mm to 0.15 mm accuracy (depending on geometry).  Smallest free-standing feature approximately 0.25mm to 0.3mm Support Structures:  Gel-Like secondary material (Removed with water jet).  

Maximum Build Dimensions: 10.2×10.2×7.9 inches (260x260x200 mm)(Both Systems, single or multimaterial)

Build Time: Total: 30 minutes – 5+ Hours (dependent on geometry & size)
*Turnaround time is workload dependent.  Expedited parts may come with an additional fee.

Cost: UC: (at cost) Standard Material (Rigid and Flexible):  $5/10 grams of build material + $3/10 grams of support material + $3/hr of build time + setup and cleaning fee. Clear Material:  $7/10 grams of build material + $4/10 grams of support material + $3/hr of build time + setup and cleaning fee. Outside UC: 32% Premium (above cost)

Pros: Extreme accuracy, Parts can be printed as functional assemblies, functional prototypes (or direct application in light-duty).  Variable mechanical properties.  Near limitless geometric configurations

Cons: Material (generally) not as strong as FDM, or SLA techniques. Cost is comparatively higher than FDM or SLA.

         *If outside UC, then 32% above the cost

 

In Depth Overview of Polyjet Printing:

Polyjet printing is a 3d deposition process that shares many similarities to traditional, 2D inkjet printing. However, instead of jetting droplets of ink onto paper, Polyjet printing deposits a UV curing liquid resin onto a build platform which is solidified immediately following the jetting process. This process is looped in successive layers. Upon completion of the print, a gel-like temporary support structure is removed via high-pressure water.

As the layer size is typically around 22 microns, this printing technology is capable of extreme precision in comparison to FDM printing, and is slightly better than SLA printing in terms of accuracy. However, the cost for this level of precision is that materials are significantly weaker, and more expensive.

Coupling this level of precision with a dedicated support structure permits the development of “printed assemblies,” whereby multiple pieces are held in suspension from one another with support structure, printed as one part, and separated after cleaning to reveal a functional part. As an example, note that the planetary gears depicted below were not assembled post-print, but were instead printed with support material isolating all components in the assembly.

Figure 1: Functional Planetary Gears, Printed as an Assembly after Cleaning (via 3space.us)

One of our polyjet printers is also capable of a unique property among 3D printers: multi-material printing. This process permits the use of two distinctly different build materials, which can be blended in defined ratios to achieve intermediate properties. For example, the system can work with a rigid polymer as its first build material, and a flexible polymer as its second polymer. These two materials can then be deposited onto a single “part” such that different areas of the print have different mechanical properties. Also, the two materials can be blended to achieve intermediates (in this case, one could modulate the stiffness of a body by using different ratios of the two base materials). This same technique can be used in opaque, and transparent/translucent materials to control the optical properties (as a second example).

Figure 2: Example of Multi-Material Polyjet Printing

Materials:

The materials this printing technology uses are all proprietary, with most being either acrylic, or vinyl derived.

The materials that we make most frequent use of are as follows:

Vero+: Rigid acrylic derived polymer, comes in white (stocked, VeroWhite+) or black (not typically stocked, VeroBlack+)

Figure 3: A Sample VeroWhite+ Print (via proto3000.com)

Tango+: Flexible vinyl “rubber like” polymer, comes in translucent amber (Tango+) or black (TangoBlack+).

Figure 4: Sample Tango+ Print (via Stratasys)

Gray60: Gray/Blue colored hybridized mixture between Vero, and Tango materials. Slighly enhanced impact strength, slightly less brittle than Vero alone. True Grey60 is a mixture between VeroWhite+ and TangoBlack+, but we often use VeroWhite+ and Tango+ to achieve the same mechanical properties in a White colored print.

Digital Materials: Mixture of Vero and Tango class materials, typically specified in shore hardness when soft enough to become flexible. Contact lab staff for details on available ratios.

Figure 5: Blended Material Spectrum - Flexible tango (left) Rigid VeroWhite+ (right) Intermediates between (via javelin-tech.com)

MED610: Rigid translucent (which can become clear when polished) material. Described as: “ideal for applications requiring prolonged skin contact of more than 30 days and short-term mucosal-membrane contact of up to 24 hours. Bio-compatible material has five medical approvals including cytotoxicity, genotoxicity, delayed type hypersensitivity, irritation and USP plastic class VI.”

Figure 6: Sample MED610 Print (via Stratasys)

Techniques:

Designing for Polyjet Printing:

The team lab requires two sets of files for each 3D printed part – the original parametric model file (Solidworks/Inventor/Fusion360/etc), and a millimeter scale STL file (point-mesh file)

Clearance between assemblies, General Fit and Finish

When printing assemblies in a fully assembled state, the minimum suggested clearance (gap) between two faces (to prevent accidental bonding, and permit cleaning) is 0.3mm.

Some finishing (sanding) may be required on high-precision faces, or in cases where a very smooth finish is required/desired.

Figure 7: A Multi-Body Print - One File Provided for Each Material (Rigid in white, and Flexible in gray), On Each Half of the Assembly. All Features Along Hinge Have Built-In Clearance

Wall Thickness

The minimum suggested wall-thickness for polyjet prints is equal to 0.3mm. Further, for free-standing features, it’s advised to limit the height-to-width ratio to less than 5:1 (for features less than 1mm in scale)

Figure 8: Thin, and Relatively Tall Walls Can Be Problematic For All Types of 3D Printers (via myplasticfurture.com)

Support Structure

Note that all prints will require support structure along the underside of the print, and where overhangs are present.

If a print has an internal cavity that is inaccessible from an outside face, that cavity will be filled with support structure that cannot be removed. If this is an issue, consider splitting the part such that the support can be removed, and bonding together afterwards (if necessary).

Figure 9: Polyjet Support Material Being Manually Removed From a Print (Via 3D Hubs)

Finish (Glossy Vs Matte)

The printer operates in two modes that ultimately influence surface finish:

“Matte” Finish Mode (default): The entire part is encapsulated in support material for a consistent nonreflective finish. These prints are generally more accurate (as the support material acts to stabilize the geometry). However, residual support material may take some gentle scrubbing to fully release (else the surface of the print may feel “soft”) when picked at.

“Glossy” Finish Mode: The print is only exposed to support structure where absolutely mandatory. This mode presents a smooth shiny finish on upward faces, but will appear different (“matte” finish) where support material is required (underside and overhangs)

Multi-material Prints

In cases where multiple materials are desired on a single print, multiple STL files must be supplied; specifically, at least one file per material type must be supplied. Further, each file must share the same coordinate system so that parts are properly registered in the printer’s deposition software.

Figure 10: A Multi-material print - One Solid Continuous Print with Flexible Bristles, and a Rigid Body

Preparing Files for Polyjet Printing:

The team lab requires two sets of files for each 3D printed part – the original parametric model file (Solidworks/Inventor/Fusion360/etc), and a millimeter scale STL file (point-mesh file)

Technical Specifications:

Layer thickness: ~20 microns

Maximum Build Size: 250x250x200mm

Typical accuracy: 20 to 85um for features below 50um, up to 200um for entire model (rigid materials)

Safety:

Unless otherwise stated, polyjet prints should not be assumed biocompatible. Further, additional processing is required to make a biocompatible print fully biocompatible.

Examples:

Figure 11: Organic, CT or MRI Derived Geometry is Easily Achieved through Polyjet Printing (via Stratasys)

Figure 12: A Polyjet Print (left) shown next to an FDM Print (right) (via 3dprototyping.com.au)

Figure 13: A Polyjet Skull Print Used For Surgical Pre-Planning

Sources and Resources:

Polyjet Technology Overview: http://www.stratasys.com/3d-printers/technologies/polyjet-technology

Polyjet vs SLA: https://blog.trimech.com/sla-vs-polyjet-technology-review

Prototyping with Polyjet Printing: https://www.protolabs.com/resources/design-tips/prototyping-with-polyjet-3d-printing/