Thursday, 15 May 2008


There are quite a few things to consider when deciding which rapid prototyping process to use and these are mainly to do with the way each different process works and the materials they use.

SLS machines are different from SLA machines in that they use a powerful laser to fuse together granules of material. The loose powder acts as a support for the parts, which means that no support structures have to be removed, and parts to be built can be stacked on top of each other filling the cube. The result is that SLS parts are generally cheaper than SLA parts due to the economies of scales from the build process. The materials SLS machines use can be either nylon or metal depending on the type of machine and there are different types of materials within those groups. Regarding nylon, you can have standard Duraform Polyamide material, which is tough with some flexibility, or if you need something more rigid there is 30% glass filled nylon. A new material on the market is Duraform EX plastic, which comes in black or natural (off white.) This material is more flexible than PA and is good for living hinges and snap fit designs. The self-coloured black version is also useful if you need coloured parts without the cost of painting and finishing. One of the drawbacks with SLS is the porosity of the parts due to the powder-based material. It gives the parts a rough, granular surface finish, which, granted can be rubbed down and painted but this takes hours and is expensive to do well. This is where SLA parts should be the choice if you need cosmetically superior finishes on your parts or if you need to go onto make vacuum castings. However, the choices don’t stop there! There are many different types of SLA material and also machines. Machines can come in 250mm x 250mm x 250mm sizes (as our machine at Martello) and also huge mammoth sizes (Materialise.) and in-between. Stereolithography as a process has proved itself to be the most effective in building accurate parts with good surface finish and durable enough to be used as masters for tooling. Masters need to be finished for vacuum casting and SLA’s are by far the best parts to work on. Other processes such as FDM parts are very difficult when it comes to finishing, as the parts tend to de-laminate. This adds huge amounts of extra time and cost onto the job, which is no good for us as a bureau building masters for tooling!

SLA materials come in quite a few varieties all with certain advantages. The watersheds are great for holding their shape, which was an issue with SLA’s originally and can be lacquered to produce clear parts. Si50 is a good resin, which comes in grey or blue and produces very plastic looking parts but is not any stronger than the watershed resins. More technical information is on our web site on the datasheets page.

The thing to remember is that there will be a process by which you can get your parts built cost effectively and accurately and the best thing to do is ask around for some advice if you’re not sure. We have referred many projects onto other companies because we recognised that our polyurethane resin vacuum casting process wasn’t the most suitable for certain parts. For instance, very thin parts without features such as ribs or bosses parts maybe cheaper using vacuum forming or thick walled large mouldings maybe be better using RIM (resin injection moulding.)


Beth said...

I agree that SLA and SLS are both effective prototyping techniques. Both offers superior inspection services that helps in improving the prototype. There is keen attention to dimensional measurements too, which helps researchers in determining the strengths and weaknesses of their output. Indeed, the engineer or architect needs to make informed choices to find the most suitable technique for a given project. Thanks!

rahul said...

The post is good and I agree with these points here.
EMS USA Company

Avikshit Saras said...

Very informative and really liked it.

Mozella M.Babich said...

Great Share!!

It is rare these days to find one technology vastly superior to another one for every single case, task or project.

This will not be one of those rare cases and most definitely both SLS and SLA will excel in specific cases.

When transparent or translucent parts are required, SLA is clearly the way to go. The same applies if you need to achieve a smooth surface or display tiny details on your print.

Summary of SLA strengths: accuracy, design flexibility
Summary of SLA weaknesses: material flexibility, material costs, production speed

On the other hand, if your design would use a lot of support material to cope with its intricacy, you need a seriously strong part, or you just want to save some money, then you may want to consider a SLS plastic print.

Summary of SLS strengths: accuracy, design flexibility, material flexibility, material cost
Summary of SLS weaknesses: manufacturing costs, production speed

EIDP Technologies is a great platform of 3D rapid prototyping.