Material Jetting

Material Jetting can be divided in two main groups of technologies:
Polyjet and Digital Wax .

Polyjet machines use a print head to jet a photopolymer-resin.
Micro-droplets are deposited on a build platform and UV-light is used
to cure/solidify the resin directly after deposition or subsequently.
Depending on the machine the print head or the platform moves.
The resin is only deposited in the cross-section of the part to be build.
When the first layer is finished the platform drops by one layer thickness
and the next layer is deposited. The top layer bonds with the layer underneath
and the part grows. To realize overhanging areas a support material is required.
The support material is jetted through separate  nozzles simultaneously when the
print head deposits the build material. At the end of the process the platform raises
up and the part can be taken off the build platform. The support material has to be
removed in following  step. Depending on the process and material a water pressure
cleaner, a hot oil/water bath or an oven is used to remove the support. Some manual
finishing might be required to remove support material from intricate design features.

Resolution
Polyjet machine offer a very good resolution.
Some machines are capable of up to 4000 dots/droplets per mm2 in XY and
over 300 dots/droplets per mm in the Z-axis.
The layer thickness ranges from about 15 to 30 micron.

Materials
The materials are special photo polymer resins. These materials are
usually distributed exclusively by the machine manufacturers only.
Material properties do vary. There are translucent and opaque materials.
Some machines are capable to print colored parts with up to 45 colors.
There are more temperature stable materials (80 degrees Celsius).
Wax and wax like materials can be used for casting applications.
There are rubber like materials but also materials with ABS-like properties.

Some machines are capable of processing two different build materials to create
parts with gradient properties. A part can be starting rubber like at one end
and change over to be made of a more ridged material at the other end.
There are also bio-compatible and wax like materials for medical and dental
applications available. So far there are no materials for long term dental fillings.

As the materials are cured with UV light the parts made age with UV exposition.
To make parts more stable and durable UV shielding coatings can be used.
Stratasys Connex3 build platform

Stratasys ObjetColored sample parts made on a Stratasys Connex3 system

Applications
Polyjet printers are applied in various industries.

Prototyping
The technology is ideal to create prototypes in product development.
Complex shapes and different materials can be prototyped to evaluate
a new design. For example the handle of a razor can be build in a ABS like
material and soft rubber fins are added. Material properties so close to the
ones of the production materials gives the prototype not just the right shape.
It adds the realistic feel and let the designers also evaluate the haptic.
Such a model  can be realized within just a few hours, even in an office environment.

Injection molding tools
Tools for low batch injection molding. This tools may last only for 30 parts
but the parts can be made of a real injection molding material. This means
real use properties on parts produced in low batch production. There are
huge efforts in R&D to extend the life-time of tools.

Stratasys injection molding tool
Stratasys injection molding tool

For your information
Injection molding tools are usually made of Tool Steel or Aluminium (Al) for
low batch production runs.
For example:
A steel tool costs ten thousands of dollars and lasts for hundred thousands of parts.
The same tool made of Al may cost a few thousand dollars and lasts for 5000 parts.
A tool made with Polyjet technology will cost only a few hundred dollars and it will last
for about 30 parts. This makes it a very interesting technique to substitute the high labor intensive silicone-vacuum-casting process.

Dental models

Dental labs are using polyjet machines to create upper and lower jaw models.
This models are used to create aligners via thermo forming. Different models
are created to move and align the teeth slowly step by step.

Drill guides for dental implants
Very similar is the application to create a jig to guide the drill into the ideal
location in the jaw to mount a dental implant.

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Digital Wax machines use a heated print head to jet a wax on a build platform.
When the material is deposited it it cools down and solidifies.
The wax is only deposited in the cross-section of the part to be build.
When the first layer is finished the platform drops by one layer and
the next layer is created. The top layer bonds with the layer underneath and
the part grows layer by layer.
To create overhanging areas a support material is required. The support material
is jetted through separate nozzles simultaneously when the print head deposits
the build material. The support material is usually a wax with a lower melting point
than the build material. This way the support material can me molten out of the
finished part.

Materials
The materials are synthetic waxes.

Resolution
Digital wax printers offer a very high resolution.
Some machines are capable of resolutions of up to 200 dots/droplets per mm
in X & in Y-axis and over 300 dots/droplets per mm in the Z-axis.
This is 5000 by 5000 dpi in XY and 8000dpi in Z-axis.

The layer thickness ranges from below 10 micron to about 80 micron.

Applications
Digital Wax printers can be found mainly in dental and jewelry industry.

Dental replacements, removeables and braces
Dental labs are using Digital Wax Printers since decades.
The dentist takes an impressions or an interoral scan.
The impression is cast in plaster and laser scanned or
the digital model is processed directly. A dental technician
creates a virtual coping or denture.
This digital model is created on the digital wax printer.
The part created is used for lost wax casting to create the
coping or removable, most likely in Cobalt-Chromium.
Patient specific braces
3M™ using the same process to manufacture patient specific
braces. The brackets are custom tailored and sit on the inside
of the the teeth. Here is a link to 3M Incognito™ Hidden Braces

 

Jewelry
From custom wedding bands to mass production. Digital wax printers
are ideal to create the models for lost wax casting of jewelry. This is why
this technology has been applied in this field for years and years.
Would you like to know more about this technology and its applications?
Contact us

 

 

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