When to choose SLA over other 3D printing technologies

Prototype Projects says: SLA (stereo lithography apparatus) is one of five 3D printing technologies that we have in-house at Prototype Projects. The reason we have so many is that none is ideal for every application. Unlike prototyping bureaux that specialise in one technology, we have several so we can offer the optimum to suit any given component and the customer’s requirements.

SLA 3D Printers at Prototype Projects

What is SLA?

SLA is a 3D printing (rapid prototyping/additive manufacturing) process that builds parts one layer (or slice) at a time by using a tiny spot of laser light to cure a photopolymer liquid resin. The position of the laser spot is computer-controlled in the X and Y axes. After each layer is cured, the bed descends in the Z axis. When each layer is cured, it also fuses to the layer beneath, resulting in material properties that are very close to being isotropic. The small diameter of the laser spot, in combination with the tight control of the X, Y and Z axis movements, enables intricate parts to be built with high resolution.

SLA materials

SLA is compatible with a wide variety of different UV-sensitive photopolymer resins. However, we have selected a range of SLA materials that enables us to build parts with the characteristics required by our customers.

  • Accura ClearVue: water-clear, with good moisture resistance and similar properties to polycarbonate. The material benefits from USP Class VI capability for limited patient contact applications.
  • Accura 25: cream-coloured with good flexibility and similar properties to polypropylene.
  • Accura Xtreme: grey-coloured, with similar properties to ABS.

Parts made from any of these three materials can be lacquered or painted, and be tapped or have inserts installed.

Pros and cons of SLA

There is no ‘silver bullet’ for 3D printing, no single process that is ideal for every application – though SLA is a great ‘all-rounder’ that can be used for most applications. All 3D printing processes have pros and cons (advantages and disadvantages) compared with alternatives. For SLA, these can be summarised as follows.

Advantages of SLA are:

  • Excellent for accurate parts with complex geometry and fine detail
  • Smoother surface finish than most other 3D printing technologies
  • Parts have excellent strength and rigidity (depending on material)
  • Parts have near-isotropic material properties
  • Good long-term dimensional stability, thermal resistance and water resistance (depending on material)
  • Can be used for parts where limited patient contact is required (Accura ClearVue only)
  • Minimal finishing required (typically removal of support structures and witness marks, followed by washing in a cleaning solution and UV curing)
  • Parts can be finished by sanding and lacquering or priming and painting
  • Best process for model making
  • Internal surfaces can accept a blackout/EMI/RFI coating
  • Relatively large parts can be built
  • Versatile process

Disadvantages of SLA are:

* Not as quick as DLP
* Equipment and consumables are more expensive than for technologies such as SLS
* Support structures are required; these add to the build time and cost, and need to be removed afterwards
* Surfaces are not perfectly smooth so, depending on the application, further hand-finishing may be required

Typical applications for SLA prototype parts

The following applications are typical of those for which we use SLA. However, the list is not exhaustive.

  • Proof-of-principle models where part function is critical
  • Prototype parts for functional testing
  • Parts for prototype medical devices and drug delivery devices where patient contact is required
  • Master patterns for vacuum casting
  • Development of assembly systems
  • Presentation models
  • Concept models

When would we not use SLA?

The following are examples of applications for which we would not normally use SLA, though there can be exceptions.

  • End-use parts requiring durability
  • Low- or medium-volume production parts
  • Parts where low cost is more important than high accuracy
  • Parts where exceptionally fine detail is required (measured in microns)
  • Production of elastomeric parts

SLA capability

Our years of experience with SLA machines from 3D Systems have proven them to be high-quality, reliable printers that build finely detailed, accurate parts. We now have nine of 3D Systems’ SLA 3D printers, giving us great versatility, a fast response, the ability to build parts of different sizes, and a choice of materials.

We currently operate eight SLA machines. Build volumes range from 250 x250 x 250mm up to 508 x 508 x 534mm.

This SLA capacity means we can meet our customers’ needs for SLA parts at short notice. For projects with tight timescales, we offer an Express 3D printing service, with parts shipped within one working day. On the other hand, for teams working with limited budgets, we offer an Economy 3D printing service with shipping in eight working days. In between these two, our Standard service ships parts within three working days.

In all cases, we never compromise on quality to meet either tight deadlines or the need for economy. Material, build orientation and finishing operations are always selected to meet the customer’s requirements.

Conclusion

SLA is a very versatile technology for 3D printing prototype parts. The materials we use produce parts that are sufficiently strong and durable for functional testing and for helping to prove (or disprove) a product’s design. SLA’s relatively high cost-per-part and restricted choice of materials mean the technology is not suitable for every application. Nevertheless, the high quality, accuracy and speed make it a very popular choice for 3D printing prototype parts.

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