The challenges and solutions to large scale 3D printing

Author: Matt Tyson/Wednesday, 13 March 2019/Categories: 3D Printing News

The challenges and solutions to large scale 3D printing

For users interested in 3D printing large parts, FDM 3D printing is the most affordable and accessible technology to scale with the added benefit of an extensively growing range of printing materials. Of course when scaling up, compromises need to be made between print time / resolution and considerations need to be made around the desired printing material.

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.

Let’s explore the world of large scale 3D printing and the technologies and materials used to reliably print large and functional parts. Of course the definition of a large 3d print is vague so we will be covering prints from 250mm all the way up to 25 meters long on the largest 3D printer in the world.

It can be easy!

Before we discuss the challenges (and solutions) related to large scale 3D printing, it is important to mention that full-size 3D printing with some materials can be fairly straight forward. PLA can be printed reliably at room temperature and for this reason has maintained its reputation as the most popular 3D printing filament. When printing large parts, drafts can certainly cause shrinkage or warping so a printer with enclosed sides is ideal and a heated bed or printing surface is recommended to maximize bed adhesion. 

The main consideration when printing PLA at larger scales is minimizing print time with larger layer heights / nozzles and ensuring your bed is perfectly leveled. 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 which rival ABS, but many applications at this size also require heat resistance or UV resistance which is not an inherent property of PLA. Without an expensive industrial machine, it was difficult to print large parts with engineering materials, until now.

Meet nylon (PA), one of the world’s most popular engineering materials. Nylon filaments on the market have traditionally suffered from warping so why can we now print nylon easily with basic 3D printers?

The answer is innovation and advanced material development in the heart of Shanghai.

 Parts for the LSEV Car printed in Polymaker PolyMide™ filament. 

Developed by Polymaker, the PolyMide™ series of nylon materials are unique and solve the core reason nylon materials warp during the printing process. Nylon is a semi-crystalline material and during the printing process other nylon materials crystallize too rapidly, forming internal stresses and cracking or warping. Polymaker developed their new warp-free™ technology which controls the rate of crystallization, this provides many benefits but 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, Polymakers PolyMide™ material forms the building blocks for large scale products like the LSEV car from XEV or air intake from Custom Import Arts. To print these parts in ABS or Polycarbonate (PC) would require a more advanced 3D 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 ASA require a high environmental temperature (50 °C-70 °C) when printing to maintain dimensional stability and prevent warping at large sizes.

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

As we scale the size of our 3D printer, 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 500 x 500 x 500mm 3D printer will have a much harder time printing ABS than the enclosed 250 x 250 x 250mm 3D printer. The key to 3D printing ABS, PC and ASA at large sizes is a 3D printer with an actively heated chamber, a key feature differentiating industrial and professional 3D printers.

 The INTAMSYS FUNMAT PRO is equipped with a heated chamber and advanced thermal system to print ABS and PolyCarbonate without warping.

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. For tips on printing ABS, ASA and PC materials on machines without active heating, visit our summary & tips section.

 Comparison between printing a medium sized part in PolyCarbonate with 100% infil on an enclosed desktop machine and an industrial machine with active heating.

With the right 3D printer we can print ABS, ASA and PC at all sizes and as easily as PLA and PolyMide™ CoPA
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!

Last month 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. This 3D printer is massive and even though the current build volume of this printer is 144 meters cubed with a 25 meter long printing area, there is still room for expansion. 

Unlike desktop and industrial 3D printers which feed a spool of plastic filament, the SCG feeds from 3 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 3d 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 from Coin Robotics and Shanghai Construction Group along with leading material development from Polymaker.

To prevent drafts and maintain heat the SCG 3D printer is enclosed with a tent which is heated to 38°C with heaters. 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 which blow 600°C of hot air onto the print reheating the print close to the materials glass transition temperature. The hot air guns combined with a unique extruder stamping system ensure perfect layer adhesion between the current and previous layer. During very large projects like the pedestrian bridge print, 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 with good mechanical properties so ASA is the optimal material. To print ASA at this scale, a significantly higher temperature in the enclosure would been required so Shanghai Construction Group hired Polymaker to develop an ASA material which can be printed without warping in the SCG printer.

Polymakers AS100GF which is an ASA with 12.5% glass fibers by weight was one of five materials tested. The glass fibers add strength and more importantly minimize the warping effect that plagues large 3D prints. 

Inside the SCG 3D printer I watched as a newer ASA from Polymaker with 20% glass fibers 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 too, afterwards these planks are removed from the print.

As covered in more detail in our pedestrian bridge article, 3D printing at this scale brings a host of challenges to solve many of which are shared when printing 25 meter or 1 meter long prints.

Summary & Tips

Printing objects at large scales isn’t always as straight forward 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 our top tips!

Print Time

As we print larger objects, the print time can rapidly increase if we don’t adjust our settings accordingly. Most 3D printers are equipped with a 0.4mm nozzle which is excellent for printing models and parts with. When we print larger parts, this level of detail is not required therefore a larger nozzle is an effective solution and minimizes print time in two ways.
With a larger nozzle (for example 0.8mm or 1.2mm) we can extrude thicker lines of plastic but we can also print with thicker layer heights, rapidly decreasing our print time. 

With larger nozzles, layer lines become more prominent and the smallest detail which 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.
 These two factors are important to consider when choosing your nozzle diameter.

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. 
Here are tips for those who have purchased a printer without active heating, and those interested in buying a large 3D printer.

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. Of course there are some tricks to 3D print high temperature materials 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 printers 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 minimize warping.

Take note of the filaments glass transition temperature, even if your parts are warping you should avoid heating the bed above this temperature. Yes the surrounding environment will be hotter but the increased bed temperature will affect other elements of your 3D print 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 maximize 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 infil will produce parts with less material and therefore less internal stress minimizing the risk of warping. For example parts printed at 100% infil will suffer from significant warping when compared to parts printed at 25%. Parts should still be printed with a moderate infil (above 20%) as parts printed with a very low infil are more susceptible to cracking.
Additionally you can modify your designs to maximize adhesion with 90° edges rather than fillets or chamfers and hollowing parts of the design.

In some cases these tricks can be used to minimize warping but of course we recommend annealing to release the internal stress which will maximize 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.

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