For users interested in 3D printing large parts, fused deposition modelling (FDM) is the most affordable and accessible technology, with an extensively growing range of printing materials. Matt Tyson explores the world of large-scale 3D printing and the technologies and materials used to reliably print large, functional parts, from 250mm all the way up to 25m long.

Most durable and engineering grade plastics can be printed reliably at moderate sizes, but when scaled, many of these materials become much harder to print without advanced printing systems or technologies. Compromises must be made between print time and resolution, and consideration should be given to the desired printing material.

It can be easy

Full-size 3D printing with some materials can be fairly straightforward. Polylactide (PLA) can be printed reliably at room temperature and has therefore maintained its reputation as the most popular 3D printing filament. When printing large parts, draughts can certainly cause shrinkage or warping, so a printer with enclosed sides is ideal and a heated bed or printing surface is recommended to maximise bed adhesion.

The main consideration when printing PLA at larger scales is minimising print time with larger layer heights/nozzles and ensuring your bed is perfectly levelled. These two factors are important when printing any material.

For most users interested in printing large and functional products, PLA just isn’t the right material. Certainly a tougher PLA material like PolyMax PLA would provide mechanical properties to rival acrylonitrile butadiene styrene (ABS), but many applications at this size also require heat resistance or UV resistance, which is not an inherent property of PLA. Without expensive industrial machines, it was difficult to print large parts with engineering materials, until now.

Nylon (PA) is one of the world’s most popular engineering materials. Nylon filaments have traditionally suffered from warping, but we can now print nylon easily with basic 3D printers. The reason is advanced material development and innovation.

Developed by Polymaker, the PolyMide series of nylon materials are unique and solve the core reason nylon materials warp during printing. Nylon is semi-crystalline. and during printing, other nylon materials crystallise too rapidly, forming internal stresses and cracking or warping. Polymaker developed new warp-free technology that controls the crystallisation rate; as the name suggests parts don’t warp at any size on both simple and industrial 3D printers alike.

With no enclosure required, excellent dimensional stability and the inherent strength and heat resistance associated with Nylon 6 66, PolyMide forms the building blocks for large-scale products like the LSEV car from XEV, or the air intake from Custom Import Arts. To print these parts in ABS or polycarbonate (PC) would require a more advanced printer.

Heat, heat, heat!

Almost all 3D printing materials can be printed without warping; the key is to understand what environment is required to print each material reliably when choosing your machine. Materials like ABS, PolyCarbonate and acrylonitrile styrene acrylate (ASA) require a high environmental temperature (50-70°C) when printing to maintain dimensional stability and prevent warping at large sizes.

Many 3D printers are enclosed and equipped with the specifications to print materials like ABS. A heated bed heats the printing environment, and an enclosure traps this heat while protecting from draughts. A 3D printer design with a compact enclosure can maintain an enclosure temperature around 40°C, good enough to prevent warping and cracking with some medium-sized objects.

At larger scales, the temperature inside the enclosure will be significantly lower as the heated bed must now heat a much larger area. If we were to print a 200mm squared part, an enclosed 500mm x 500mm x 500mm 3D printer will have a much harder time printing ABS than a 250mm x 250mm x 250mm printer. The key to 3D printing ABS, PC and ASA at large sizes is a printer with an actively heated chamber, a feature differentiating industrial and professional 3D printers.

With an actively heated chamber, internal stress in the plastic is released, preventing warping or cracking. It is important to note adding active heating to an existing 3D printer is not recommended as the electronics in many 3D printers aren’t rated for high-temperature environments.

Of course some customer requirements may be significantly larger than what industrial manufacturers currently offer, in these cases custom built solutions are common.

Massive 3D printing

Recently I visited the SCG 3D printer in Shanghai, an ambitious example of large-scale 3D printing and a successful collaboration between Coin Robotics and Shanghai Construction Group. Even though the current build volume of this massive printer is 144m cubed with a printing area 25m long, there is still room for expansion.

Unlike desktop and industrial 3D printers that feed a spool of plastic filament, the SCG feeds from three hoppers filled with plastic pellets. When printing at this size a single print can easily require 20-50kg of plastic, so spools of filament become impracticable.

The SCG 3D printer can print functional materials like ASA without warping and was recently used to print the first plastic 3D-printed pedestrian bridge. To print parts at this scale without warping, a unique approach was required, combining advancements in 3D printing technology, along with leading material development from Polymaker.

To prevent drafts and maintain heat, the SCG 3D printer is enclosed with a tent heated to 38°C. During my visit inside the SCG printer, a chair was being printed, so workers had also built a smaller tent with blankets to concentrate heat within the print.

When printing parts the full length of the printer, each layer has already cooled significantly before the extruder returns to print the next layer. To combat this problem Coin Robotics engineered hot air guns that blow 600°C air onto the print, reheating it close to the material’s glass transition temperature. The air guns, combined with a unique extruder stamping system, ensure perfect adhesion between layers. During very large projects like the pedestrian bridge, workers also place blankets over the print to maintain a moderately high temperature.

Currently the projects printed with this machine require UV and weather resistance, plus good mechanical properties, so ASA is the optimal material. To print ASA at this scale, a significantly higher temperature in the enclosure would have been required so Shanghai Construction Group hired Polymaker to develop an ASA material that can be printed without warping in the SCG printer.

Polymaker’s AS100GF, an ASA with 12.5% glass fibres by weight, was one of five materials tested. The glass fibres add strength and more importantly minimise the warping effect that plagues large 3D prints.

Inside the SCG 3D printer I watched as a newer ASA from Polymaker with 20% glass fibres was being tested; I was told this will further reduce the coefficient of thermal expansion to maintain dimensional stability. To ensure the print adheres to the bed, ASA pellets are glued to wooden planks, which the first layer of the 3D print fuses to; afterwards these planks are removed.

Summary and tips

Printing large objects isn’t always as straightforward as purchasing a large 3D printer, importing a 3D file and clicking print. The nuances between materials become more defined when printing at large scales and considerations should be made regarding the turnaround time and materials you require.

If you are interested in large-scale 3D printing here are some tips.

Print time. With larger objects, print time can rapidly increase if we don’t adjust settings accordingly. Most 3D printers are equipped with a 0.4mm nozzle, which is excellent for printing models and parts. When we print larger parts, this level of detail is not required so a larger nozzle is an effective solution and minimises print time in two ways. A larger nozzle (for example, 0.8mm or 1.2mm) can extrude thicker lines of plastic, and can print thicker layer heights, slashing print time. Moreover, with larger nozzles, layer lines become more prominent and the smallest detail that can be printed changes. If a section of your project requires 1.6mm thickness, a 0.8mm nozzle will print 1.6mm with two 0.8mm lines, but a 1.2mm nozzle will only be able to print that section with a thickness of 1.2mm or 2.4mm. With a larger nozzle, more plastic is extruded per hour, so it is also important your extruder can reliably heat this extra plastic to avoid clogging or nozzle jams.

High-temperature materials. If you require high heat resistance, tensile strength or weather resistance, chances are the right material for your application will be susceptible to warping without a heated environment.

Tips for buying a large printer: Make sure the machine you are buying will be able to print the materials at the sizes you expect. In the printer specifications manufacturers only detail if the material can be printed and don’t cover what sizes can be achieved or the reliability to expect. A printer that can technically print ABS may not even print ABS parts that fill half or a quarter of the build volume without warping into the extruder and jamming. PLA is the most popular material and so the majority of 3D printer reviews are written from users who favour printing these less demanding materials. Paying the reseller/distributor to print a sample is a great way to test if the machine you are researching will reliably print the materials you require at the sizes you need.

Tips for users without active heating: There are many users who have already invested in 3D printers without active heating. There are some tricks to print at moderately large sizes in high-temperature materials like PC or ABS. There will always be a limitation on how big you can print without warping but sometimes you can push the printer’s capabilities to meet your needs.

The first key is to completely enclose your printer by closing all doors and lids and preheating the bed for 20 minutes to an hour. With long preheating times, it is sometimes possible to minimise warping. Take note of the filament’s glass transition temperature; even if your parts are warping you should avoid heating the bed above this temperature. The surrounding environment will be hotter but the increased bed temperature will affect other elements like strength and print quality. Without a controlled and heated environment, internal stresses will form during the printing process. With small 3D prints, the internal stress is enough to impact part performance but won’t impact dimensional stability so to maximise performance the internal stress can be released through annealing.

With large-scale 3D printing, parts will print with more material and therefore more internal stress, which when stronger than your bed adhesion or inter-layer adhesion will release in the form of warping or cracking. Printing with a lower infill will produce parts with less material and therefore less internal stress, minimising the risk of warping. For example, parts printed at 100% infill will suffer from significant warping when compared to parts printed at 25%. Parts should still be printed with a moderate infill (above 20%) as parts printed with a very low infill are more susceptible to cracking.

Additionally you can modify your designs to maximise adhesion with 90° edges rather than fillets or chamfers and hollowing parts of the design.

In some cases these tricks can be used to minimise warping but of course we recommend annealing to release the internal stress, which will maximise your part performance. If your part is still warping with these tips and you can’t afford a 3D printer with active heating, we recommend trying an engineering material like PolyMide CoPA.