3D PRINTING - PART 1
The Next Big Thing
A Guide to Additive Manufacturing - SLA Using ProJet 6000MP
3D printing is not as new as you may think! How is that possible you might ask? With all the media coverage and electronic stores showcasing the various capabilities of this technology, it was only when the FDM patents finally expired in 2009 that it became more accessible to the general public. Every school, office or home now has a 3D printer that it’s become part and parcel of our everyday, much like Wi-Fi or social media it’s embedded in our lives that it is easy to believe it is a brand new innovation.
Truth be told the first 3D printing technology was Stereolithography (SLA) and was first implemented and patented as early as 1980. In fact the early 1980s gave rise to the three well known 3D printing techniques we have all come to know and love.
Stereolithography process involves filling a chamber with enough polymer resin. When activated the build platform (the area where the 3D printed part is created) lowers into the pool of resin, leaving a gap equal to one layer thickness between the platform and the top surface of the resin. Once this first stage is complete, the 3D printer begins to construct the parts geometry. A stationary UV laser is directed to X-Y canning mirrors. The mirrors redirect the laser beam for travel in the X-Y plane.
As the laser scans across the top surface of the resin, it imparts UV energy into the photopolymer, causing the material to solidify. The depth of curing is a function of the laser power and the travel speed. Longer laser times result in much deeper cure depths. Laser thicknesses range from 0.03 – 0.25mm.
The first layer that’s solidified is made entirely of support structures, a mechanical bond with the build platform. After constructing approximately 6.4mm of support structure, the first layer of part geometry is solidified. To create the parts geometry the laser traces the boundaries of the profile and then solidifies the internal area with overlapping passes in the X and Y axis. After a layer is complete, the build platform lowers by one layer thickness, and the liquid resin flows over the top of the part. To level the resin, a blade sweeps over the surface. In preparation for curing the next layer, sensors check the resin level and the laser power. The process repeats for subsequent layers until the part is fully complete. To remove the completed prototype, the platform is raised above the resin vat, and the platform, with the attached prototype is removed from the build chamber.
Once the excess polymer resin has drained from the part, the platform is transported to a wash station. Of course this is not always viable depending on the size of the platform in use. The ProJet6000 has a manageable size of 250 x 250 x 250mm allowing the removal of parts off the platform with a scrapper tool to be immersed into a bath of cleaning solution known as Isopropyl alcohol (IPA). Parts are left to soak for 10 to 20 minutes depending on the size and detail. However it is more effective to wear protective gloves and safety glasses and hand wash the parts using brushes in the solution to ensure resin is thoroughly removed. Some cleaning stations are equipped with their own automatic agitators to assist with this process.
While it is recommend soaking parts in IPA, it is important to never leave parts in the solution for longer than the recommended wash time, as cured resin is not resistant to IPA. For prints with thin walls, it is recommended leaving the parts in IPA for even less time.
Soften support material is removed using pliers or flush cutters along with any debris or defects created during the build stage. Ensure gloves and safety glasses are always worn for safety!
After cleaning, the polymerization process is completed in a UV post-curing chamber and the mechanical properties are stabilized. In this way, the parts receive the highest possible degree of strength and stability, which is particularly important for functional resins in the fields of engineering, dentistry and jewelry.
Below is a 1 meter tall Godzilla model which was sculpted digitally and sliced into sections to be 3D printed using clear resin on the ProJet6000. Click the image below to view the making of this piece: https://vimeo.com/190228131
Image – Nasser Samman 2016
5 Things to Consider When Designing a 3D Model for 3D Printing
Without being exposed to this medium, 3D printing let alone digital modelling can be overwhelming and very confusing. There are hundreds of software packages to choose from, a wide range of printing materials, and numerous printers with various printing technology capabilities. With all this in mind it is no wonder some people find the whole area overwhelming and intimidating. The following are some guidelines to assist in making the journey from concept to tangible outcome a positive experience.
1. Consider the Material Guidelines
As you’re probably familiar now, every printing material is different. They range from robust to weak, rigid or flexible, smooth or rough, heavy or light, etc. Although not always possible, but it is good practice to design a part with a specific material in mind. For example, if you design a multicolored product or feature and want to see this fabricated, there will be specific material-related design recommendations that will need to be taken into account such as, strengthening wall sections, exporting texture maps, etc. For colour 3D printing, please read 3D Printing Part 2 – Your True Colours A guide to 3D colour printing using the ZPrinter 650.
2. Tolerances for Interlocking Parts
For objects with multiple interlocking parts, design in your fit tolerance. Getting tolerances correct can be difficult, a useful guide is to use a 0.2mm offset for tight fit (press fit parts, connecters) and use a 0.4mm offset for lose fit (hinges, box lids). You will have to test it yourself with your particular model to determine the right tolerance for the product you are creating.
- Wall Thickness
This is one of the most crucial aspects and most overlooked when designing for 3D printing. It is not uncommon to spend countless of hours modelling an impressive design to 3D print, only to find the next day that parts or all of the model have collapsed and failed on the build platform. In some cases, wall thickness is too thin. Walls that are too thin make small parts on the model unable to be printed or very fragile and could break off easily.
- File Resolution
For 3D printing, the most common file format is STL (standard triangle language), which means that your design will be translated into triangles in a 3D space. There are other file formats that can be used when exporting a 3D model but STL is one of the most common. It is important to be aware of low and high resolution file exports. Low-resolution STL files results in large triangular data with a rough surface area resembling a more pixelated look to the final print. On the other hand, a high-resolution STL file results in a more refined smooth surface area with much smaller triangles, resembling more accurately to the digital model. However a file with a resolution that is too high can result in a file that is impossible to work with. It might also contain high level of detail that the 3D printer simply cannot print.
Its good practice to remember keeping file sizes below 100 MB when exporting.
- Software Versatility
With the many software packages on offer, it is worth exploring the one that best suits your design needs, but remember to not become reliant on one software alone. Some were designed for creating 3D prints, others are mostly used by 3D artists and their designs will require additional editing before they can offer a printable 3D model. For example, applying a wall thickness is automatic in some programs such as SolidWorks, while others work with surfaces such as 3ds Max, requiring additional work before 3D printing can commence. Being able to work from one package to the next will help identify the potential as well as the limitations of the software to help you make an informed selection and to ensure successful transition to the printing stage.