What are the material choices for SLA 3D printing? 

SLA remains the best 3D printing technologies for many applications, despite being one of the first to be commercialised in the late 1980s.

With SLA (stereolithography apparatus), a computer-controlled UV laser traces a path on the surface of a photopolymer (light-curing liquid resin). After the laser has cured each ‘slice’ of the part, the bed descends by a distance equal to the layer thickness, then the laser cures the next layer. This process continues until the complete part has been 3D printed.

The material properties of finished parts relate to the resin used. Today, dozens of resins are available, many of which are similar to each other. We have selected three different resins to meet our customers’ diverse needs. These three are supplied by 3D Systems and have been optimised for use on the 3D Systems SLA 3D printers we operate. Build volumes (XYZ) range from 250 x 250 x 250 mm to 508 x 508 x 534 mm, but note that we do not run all materials on all 3D printers.

Each of the three materials we use has its own characteristics, yet all three build non-porous parts with isotropic material properties.

We recommend that customers decide what material properties their prototype or end use part requires before choosing the 3D printing technology. Let us look at the material choices for SLA that we use in terms of their material properties and typical applications.

Accura ClearVue

Accura ClearVue is a clear material with properties similar to polycarbonate. If parts are polished and lacquered, they become glass-clear, so this material is a popular choice for prototyping parts such as automotive lights. As well as having high optical clarity, Accura ClearVue is also very resistant to moisture and has good accuracy and durability. Accuracy will, of course, depend on factors such as the part’s size and geometry, the features being 3D printed, and the support structures that are used during the build process.

Key material properties are a flexural modulus of 1980-2310 MPa, flexural strength of 72-84 MPa, tensile modulus of 2270-2640 MPa, tensile strength of 46-53 MPa and an elongation at break of 3-15%.

Customers typically specify Accura ClearVue for prototyping clear functional prototype parts, as well as parts that would ultimately be injection moulded in opaque engineering plastics with similar mechanical properties. Accura ClearVue can also be extremely useful for 3D printing clear casings that enable internal mechanisms to be viewed, or clear manifolds for assessing fluid flows, for example. Clear parts for presentation models are frequently 3D printed in Accura ClearVue.

Depending on the operating environment, Accura ClearVue can be suitable for end use parts where polycarbonate-like properties are required.

Another important application area for this resin is in medical devices, as it has USP Class VI capability for parts requiring patient contact.

SLA is our preferred technology for producing master patterns for vacuum castings. Accura ClearVue can be suitable for this, depending on the specific part requirements.

Thanks to Accura ClearVue’s inherent properties, parts can be drilled, tapped, machined, and adhesively bonded. Depending on the thread size and whether the assembly is likely to be dismantled and reassembled multiple times, screws can be used directly in tapped holes or threaded inserts provide better durability. In addition, snap-fits can be 3D printed with Accura ClearVue provided care is taken with the detailed design.

Accura 25

Accura 25 possesses material properties that are similar to polypropylene. Part accuracy is marginally better than for Accura ClearVue, finished parts are similarly durable, while moisture resistance is slightly lower (but still good). The resin is cream-coloured, which is usually fine for functional prototype parts. If required, however, parts can be lacquered or primed and painted.

As you would expect, material properties are different from those for Accura ClearVue. Accura 25 has a flexural modulus of 1380-1660 MPa, flexural strength of 55-58 MPa, tensile modulus of 1590-1660 MPa, tensile strength of 38 MPa and an elongation at break of 13-20%.

Accura 25 is usually selected for making functional prototypes of parts that will ultimately be injection moulded from polypropylene. Provided the operating environment is not extreme, Accura 25 is suitable for 3D printing reasonably durable end use parts.

Other applications for this resin include concept models, presentation models and master patterns for vacuum casting.

Parts can be drilled, tapped, machined, and adhesively bonded. Screws can be used in tapped holes or threaded inserts. Accura 25 is better than Accura ClearVue for 3D printing snap fits.

Accura Xtreme

Accura Xtreme has material properties that are similar to those of ABS, so parts are stiffer than those made of Accura 25. Parts are very accurate (on a par with Accura 25) and as durable as those made from Accura ClearVue and Accura 25. Moisture resistance is similar Accura 25, so not as good as Accura ClearVue. Accura Xtreme is a grey material that can be painted if the part’s aesthetic is important.

Material properties for Accura Xtreme are as follows: flexural modulus of 1520-2070 MPa, flexural strength of 52-71 MPa, tensile modulus of 1790-1980 MPa, tensile strength of 38-44 MPa and an elongation at break of 14-22%.

Accura Xtreme is very versatile; parts can be used for concept models, presentation models, functional prototypes, vacuum casting master patterns and end use applications.

As with Accura ClearVue and Accura 25, parts made from Accura Xtreme can be drilled, tapped, machined and bonded, and snap-fits can be 3D printed.

Finishing options for SLA parts

Secondary finishes can improve a part’s aesthetics or functionality, so the choice of finishes relates primarily to the intended use. To some extent the finish depends on the material, the obvious point being that Accura ClearVue parts are often polished to take full advantage of this material’s high optical clarity.

When parts are for functional prototypes or functional end use applications, it is often sufficient to remove any support structure and some or all the witness marks, clean the parts and cure them in a UV oven. If necessary, parts can also be sanded or lightly bead blasted to improve the surface finish, with the subsequent option of a coat of clear lacquer or paint.

If appearance is important, ‘A’ surfaces can be hand-sanded, painted to give a satin, gloss or textured finish, or a soft-feel rubberised coating can be applied.

Bead blasting Accura ClearVue parts results in a frosted appearance. Alternatively, surfaces can be polished and lacquered to simulate glass or injection-moulded polycarbonate. Vacuum metallisation can be applied to polished surfaces to make them highly reflective. Clear parts are seldom painted in their entirety, but they are sometimes masked prior to painting to leave unmasked areas transparent.

All three of the materials we use for SLA 3D printing can have a blackout/RFI/EMC coating applied to internal ‘B’ surfaces, which can be for prototype or end use parts.

When customers request Express Delivery (parts dispatched the next working day), secondary finishing options are restricted to light bead blasting only. A wider choice is available for the Standard Delivery service (shipped in three working days) or Economy Delivery service (eight working days).

Alternative materials

Earlier we said that customers should determine what material properties they require in a part before choosing a 3D printing technology, regardless of whether they need additive prototyping (AP) or additive manufacturing (AM). If the required properties cannot be met by Accura ClearVue, Accura 25 or Accura Xtreme, remember that we offer alternative materials with other technologies.

Talk to us

SLA is a versatile 3D printing technology and we have chosen a set of materials to meet our customers’ needs for prototype and end use parts. Talk to one of our specialists about material choices for SLA by contacting us on 01763 249760.