Limitations of 3D printing: why traditional processes still have an edge

Much of the conversation today surrounds the advantages of 3D printing, its increasing versatility and usefulness when applied to traditional manufacturing and nascent applications. This article is going to look at the alternative side of this and touch on the limitations of current 3D printing technologies.

Let’s take the four major plastic 3D printing technologies; FDM, SLA, SLS and Polyjet, a fifth CLIP is still currently not as widespread as these four.

FDM uses a heated nozzle to extrude material filament onto a build platform, building the model one layer at a time. Of all current technologies, FDM allows the greatest versatility in terms of material selection and is also probably the cheapest both in terms of equipment and process. But due to the extrusion build process, which creates the model one layer at a time, even on some of the more expensive machines these layers are 0.127mm which though very small is still visible to the human eye. If you want to get rid of this layered look you need to polish the part. Again the build process also impacts the accuracy of the part especially on the more affordable desktop printers and part strength is weak perpendicular to the build axis. The extrusion process and material filament diameter also mean fine detail is very difficult to achieve.

SLA is one of the older and more widely used 3D printing technologies. SLA has a smooth surface finish and allows for fine detail. SLA is limited in terms of materials though, and despite increasing choice on this front the ones available are still pretty far from production materials. The parts are generally quite brittle and will discolour over time. They are also susceptible to damage by moisture, heat, and chemicals. This limits the potential applications of parts made by SLA and means for the most part it is only useful for prototypes and models.  

SLS is a great choice for functional models and even production parts. The PA materials are tough and durable. That said you are again confronted with a lack of choice with SLS, the nylon PA materials are essentially all you have. The powder sintering process also means fine details are difficult to realise via SLS. The parts are porous and have a rough surface which is difficult to polish and paint (though not impossible).

Polyjet is a Stratasys technology that shoots very thin layers of liquid photopolymer to build complex, detailed parts with smooth surfaces. Polyjet also allows you to combine multiple colors and materials in one print so you can create over-molded parts or detailed display models. Despite multiple material choices available they are still all of the same ilk and as such are limited in terms of the properties, and like SLA materials not very durable. The build accuracy is different in different directions and due to the layered build process there is also a stepping effect on some surfaces.

Above are some of the technology specific limitations and there is also one major limitation facing all current 3D printing processes - the build size. All of these technologies are limited by the size of the machines and the larger they get the more issues you have with accuracy across the whole build table. It is possible to split and glue parts produced from FDM or SLA for example but again you are losing strength and accuracy.

Despite these drawbacks use of 3D printing in all manner of industries and applications is growing and will continue to do so at an increasing rate. There are plusses and minuses to all manufacturing processes and as long as you are aware of them before you make a selection you will reduce chances of a nasty surprise.

At HLH we have years of experience manufacturing parts from many different technologies and can advise you on the best fit for your project. For more information please get in touch at [email protected]