Stereolithography the answer to your prototyping needs

Stereolithography Machine

Advantages and Disadvantages of the Stereolithography Process

As a manufacturing tool, stereolithography is a process that has been a huge benefit to both fast prototyping and limited production runs and has helped many companies realise their designs quickly and accurately. Stereolithography was one of the first processes to be developed for rapid prototyping, and though it is among the oldest 3D printing methods, it is still well used today.

One of what is actually a group of several related processes that fuse liquid plastic into solid objects, the stereolithography (SL) process is an additive system that lends itself to the low-cost manufacture of prototype parts and is one of the most used means of realising pre-production parts in an economic way. The process employs specialist printers to form a thin layer of photopolymer – typically between 0.05-0.15 mm – is exposed above a perforated platform. A UV laser rasters across the layer on the perforated platform, effectively “painting” the pattern of the object being printed. The laser returns to its start position and the process starts again.  In this way, the component is built up layer by layer.

As a process, stereolithography has a number of distinct advantages, but it also has a few drawbacks that mean that it may not be ideal in all instances. Before you commit to a rapid-prototyping process, it is worth understanding the SL process’s pros and cons.

SL Process

Advantages of stereolithography

High precision: due to the thinness of each layer applied in stereolithography (0.05 to 0.15 mm) and the ultra-fine laser beam, it is possible to obtain prototypes with a very realistic finish and complex geometric features.

Fine detail:  Because each layer is so thin, extremely fine detail features can be created, including differences in wall thickness, threaded sections, high-tolerance holes and cut-outs and even textured surfaces.

High final part quality: despite the use of relatively low-cost materials such as photo-activated resins, parts made with stereolithography have good functional surface quality and are able to hold high tolerances.  Therefore, it is rare to have dimensional or texture failures using this process.

Adaptable finish: In stereolithography, the resulting parts generally have a smooth finish, with the option to choose between a number of resins for different renderings, but areas requiring a different finish can be created due to the nature by which the material is built up.  Therefore, textures can be added to the part as required.

Product size: With stereolithography, it is possible to create small parts with high definition, as well as larger parts up to two metres in size, while maintaining high precision. This flexibility means that there are few prototypes that can’t be created.  Furthermore, because high tolerance parts can be made, it is possible to make up complex assemblies from smaller parts.

Speed: By choosing the stereolithography method, you can usually obtain a part in anything from under an hour to about two days, because 3D CAD files are all that is required to launch a printing session. With base materials being relatively cheap to purchase and the low-powered laser cheap to run, this is a process that can be owned and run by even the smallest prototyping shops.

But there are also some disadvantages to the process too.

Stereolithography Prototypes

Disadvantages of stereolithography

Low strength: Stereolithography uses laid-up resinous materials to create space models that are functional prototypes and can be used to visualise a new part, but stereolithography does not allow parts that can be used for mechanical testing since they are generally quite fragile.

Limited life.  Because the resin is activated by UV light, further application of that end of the spectrum can create crazing and cracking in manufactured parts.  Therefore, parts made should be assumed to have only limited use.

Unit production: Because of the limitations outlined here, stereolithography is usually only seen as a pure prototyping process, and is not a viable solution for the mass-production of a part.  This means that you may have to run more than one type of process for the first prototypes and then create production runs, which can turn out expensive.

Put plainly, stereolithography has more advantages than disadvantages, but it is also a process that is limited by those disadvantages. That makes it a useful tool, but only within certain constraints.

Stephen Dyson

About The Author:

Stephen Dyson, special operations manager at Protolabs, on the advantages and disadvantages of the stereolithography process.

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