INTRODUCTIONStereolithography, or SLA, is used to create solid, plastic, three-dimensional (3-D) objects from CAD drawings in a matter of hours. This amazing process provides a fast, easy way to turn 3D CAD drawings into physical objects which can be tested for form, fit, and (depending upon material selection) function.
Boedeker Plastics provides quality plastic materials and parts machined from these materials in our CNC machine shop. However, for some customers or situations, a long leadtime may be too slow. In such cases, SLA provides a fast and accurate solution for product development, demonstration, and initial testing. In high resolution mode, a smaller diameter laser beam and thinner layers result in the highest accuracy available.
SLA EQUIPMENTStereolithography, also known as 3-D layering or 3-D printing, is accomplished using a special SLA machine containing a computer-controlled laser and a tank of light-curable plastic, or photopolymer. This machine has four important parts:
A tank filled with several gallons of liquid photopolymer. The photopolymer is a clear, liquid plastic.
A perforated platform immersed in the tank. The platform moves up and down in the tank as the printing process proceeds.
An ultraviolet laser
A computer that drives the laser and the platform
THE SLA PROCESSThe basic Stereolithography process consists of the following steps:
A 3-D model of an object is created in a CAD program. (NOTE: See "STL FILES" section below.)
Special computer software "cuts" the CAD model file into thin layers -- typically five to 10 layers per millimeter of part thickness.
The 3-D printer's ultraviolet laser "paints" one of the layers, exposing the top surface of the liquid plastic in the tank and hardening it. The photopolymer is sensitive to ultraviolet light, so wherever the laser touches the photopolymer, the polymer hardens.
The platform drops down into the tank a fraction of a millimeter, then the laser "paints" the next layer on top of the previous layer.
This process repeats, layer by layer, until the 3-dimensional plastic model is complete.
Depending upon the size and number of objects being created, the laser might take a minute or two for each layer. A typical run might take six to 12 hours. Runs over several days are possible for large objects. The maximum size for the machine is an object 10 inches (25 cm) in each of three dimensions ... 10 x 10 x 10.
When the process is complete, the SLA machine raises the platform with the completed 3-D object. If the finished object is small, several can be produced at the same time, sitting next to each other on the tray.
Once the run is complete, the finished objects are rinsed with solvent to remove all uncured plastic and then "baked" in an ultraviolet oven that thoroughly cures the plastic.
STL (STereoLithography) FILESThe .STL file format has become SLA industry's standard CAD export format and is required to interact with stereolithography machines. This format approximates the surfaces of a solid model with small triangles and was designed to give the proper amount of model detail required to operate the Stereolithography machines.
Virtually all of today's modern CAD software programs are capable of producing an STL file. For the user, the process is often as simple as selecting File, Save As, STL. Contact us if you need more detailed instructions for your particular CAD system.
SLA ACCURACYSLA parts may be built using normal or "high" resolution. Normal resolution is typically defined as an SLA part build using a .010" or larger laser beam diameter and .004" or greater layer thickness. Building parts in this manner results in the most cost-effective build, but may not catch all of the tiny features of small parts or tools. Normal resolution SLA can manufacture parts with tolerances of +/- .005 to .006 inches. This is the standard resolution available at most suppliers.
High resolution is defined as an SLA part build using a .003" - .004" diameter laser beam and/or a layer thickness less than .004". Building parts with the smaller laser beam diameter results in parts with sharp corners and the thinnest possible walls. Thin layers reduce the cleanup required to smooth out contours or to polish tooling masters. High resolution SLA can manufacture parts with tolerances of +/- .002 to .003 inches. This build style results in the most accurate, highest quality parts available in the industry, but it is also slower and more expensive than normal resolution.
SLA MATERIALSA number of excellent photopolymer materials are now available for SLA rapid prototyping. Each material has unique properties which can be used to simulate more traditional plastics or metals for rapid prototypes.
Some SLA resins mimic traditional engineering plastics such as PBT or ABS, with toughness and durability that make the resulting SLA parts suitable for mechanical testing and evaluation. Other SLA resins have properties similar to polypropylene, with fine features and details that can provide accurate test parts. If higher temperatures are needed, new SLA resins provide heat deflection resistance up to 220°F (105°C) as compared to traditional limits of 130°F (55°C). And, for near-metal performance, ceramic-filled SLA resins can be used to make parts with superior stiffness and high temperature resistance. The high stiffness also provides mechanical foundation for structural Nickel plating ... the resulting parts have a composite structure with mechanical and thermal performance approaching that of metal.
New SLA resins are constantly being developed and refined to extend the mechanical and thermal performance of SLA parts.
SLA MODEL FINISHINGWe offer a number of different choices for the finishing of your models and masters. The finish levels range from a simple "clean and cure" of the raw model, through various levels of sanding and blasting surface treatments, all the way to a completely smooth, painted and/or polished surface. Contact us to discuss your model finish needs ... your costs will vary depending upon the choice of finishing.
Contact us directly to discuss your needs and match them with our SLA capabilities.
Our experienced sales staff can review your part requirements
and recommend the best possible solution for your needs.