Stereolithography of plastic parts
Highlights
The key to successful prototyping with Stereolithography is material selection. The process is well proven and accuracies generally sufficient for most applications. However, choose the wrong material and disappointment looms.
Whilst all of the materials used in Stereolithography are process specific, they have evolved to emulate various production plastics. Thus the key is usually the production intent material, or at least the desired properties.
Plunkett Associates regularly accesses a full range of materials and process platforms, offering the latest technology, the largest platforms and the highest levels of resolution.
Whilst deliveries are always tailored to customer requirements, a typical turnaround would be 5 - 7 days.
Whilst Stereolithography is good for general purpose prototyping it should be evaluated against better functionality from laser sintering and even better accuracy from machining.
Process Features
Accuracy
Tolerances vary depending on material and supplier, however as a generality Stereolithography is still superior to most other RP processes.
Minimum Feature Size
Typically 0.25mm (this is resin dependent) unless using high resolution (HR).
Layer thickness
Typically 0.1 or 0.15mm, unless using high resolution (HR).
Bed sizes
Vary from 250 x 250 mm up to 650 x 750 mm allowing the single piece manufacture of a wide range of part sizes.
Post processing
Parts can be dressed to a high cosmetic finish for display purposes or to be used as a master for vacuum casting. Stereolithography parts may also be electroformed, ie plated with a thin layer of metal, to significantly increase their strength and hermetically seal the resin inside a metal shell. This can be used just to provide EMI/RFI shielding, but offers serious strength and stiffness benefits as well.
Description
Like most RP processes Stereolithography relies on the 3D CAD data of the component being resolved (sliced) into a series of layers that can then be sequentially recreated. A laser drawing on the surface of a tank of liquid resin that, when exposed to the laser light changes state from liquid to solid, forms each layer.
Parts are built on a support structure that anchors the developing part to the machine bed and must be manually stripped away afterwards.
The additive nature of the process permits almost any geometry to be created without concerns about 'access' that would be applicable to machining.
Clear Parts using Stereolithography
Stereolithography is capable of producing clear parts. For full details view the stereolithography of clear parts page.
Lightweight Structures
For thick walled parts and very large parts there can be process advantages to hollowing out the inside. TetraShell facilitates this and allows the addition of a mesh that can be fully customised.
Benefits range from basic process advantages to being able to create lightweight structures that utilise the full potential of additive manufacture.
Biocompatible Stereolithography
It is frequently necessary to produce biocompatible prototypes for clinical trials or early development testing. By specifying the use of Watershed (biocompatible) parts can be made that pass USP Class VI testing for biocompatibility and cytotoxicity as well as ISO 10993 Part 5 cytotoxicity and Part 10 irritation and sensitisation.
These parts are supplied with certificate of conformance, material lot traceability and double bagged to allow easy sterilisation.