Construction 3D Printing
SALEM is a form of Construction 3D printing, a relatively new method of Additive Manufacturing aimed at producing large objects for construction purposes. The general principle of Construction 3D Printing (C3DP) is the same as that of its much smaller desktop counterpart. A desired article for manufacture is designed using CAD software and is “spliced” into consecutive layers from the bottom of the model to the top using special software. These layers are then converted into manufacture instructions that tell the printer how to operate to reproduce that layer. The 3D printer then manufactures the desired article by printing out the model layer by layer according to the manufacturing instruction file (often referred to as a GCODE).
The materials printed by C3DP machines are typically cement or metals and the printers come in many shapes and varieties. These include rotary arms, robotic printers and overhead cranes to name a few styles. One of the best examples of current C3DP technology is a rotary arm printer designed by Apis Cor (see below).
Current C3DP Issues
One of the key issues with current C3DP machines is scalability. To print a larger structure, you generally need to build a larger printer which is more expensive and limits the ease of assembly or deployment of the printer. The Apis Cor printer for example, can only print within a circular envelope as wide as the print arms reach (about 8.5m).
Some C3DP companies, such as the Chinese company WinSun, have approached this issue by completing their prints in segments at a central location, then assembling the segments at location. There are two main issues with this solution. The first is that it requires transport of the segments to the final build location. This is cumbersome for large structures and prohibitive for building structures in uninhabited regions without transport infrastructure like roads and where it is difficult to erect craneage to lift and place the segments.
The second issue is that structures built in segments are inherently less structurally sound than a structure printed in one constant extrusion.
How SALEM works
SALEM works by triangulating the position of the Extruder based on the extension length of the Hoist cables and the relative positions of each Hoist. The Hoists can traverse the length of the Support Structure and will rise gradually as more layers are added to the printed cement structure. The Hoists can extend or retract the cables and by extending some cables and retracting others, it is possible to move the relative position of the Extruder in a fully controlled manner. This allows the Printer to print any shape within a 3-dimensional print envelope. The Printer could be capable of printing with millimetre accuracy once fully developed and will be capable of printing far more complex structures than current construction methods feasibly allow.
Each of the Supporting legs are composed of several standardised pieces. By adding or subtracting these grid pieces from the support the height of the printer can be adjusted. It is permissible to secure these Support Legs at any practical length apart, from as little as 2 meters separation, to upwards of 100 meters. When erecting the printer there are several calibration operations which set the starting positions of the Hoists, Support Legs and Extruder as well as identifies ground height and slope of the print envelope. This means that it is unnecessary to position the legs perfectly square as the print envelope is entirely relative.
Benefits of Construction 3D Printing
There are several benefits to construction 3D printing that have already been proven by many of the current C3D printers in development. The main benefits are:
- Cost – C3DP reduces the cost of building structures by minimising waste and significantly reducing the number of manufacturing steps required to manufacture a structure. Most construction 3D printers create structures by extruding cement meaning there is no preproduction of bricks and other building materials. The only material that needs to be prefabricated is the cement. All3dp.com states that Apis Cor was able to complete a demonstrative 3D Printed home for just over $10000 with the actual structure costing approx. $4335 to print. This is an order of magnitude cheaper than traditional bricklaying. As the process is largely automatic there is also a significant reduction in labour costs.
- Time – Construction printing minimises construction time to mind-blowingly low lead-times. There have now been multiple demonstrations wherein C3DP houses have been printed in less than 24 hours. Even factoring in a long printer assembly lead-time this still results in a staggeringly rapid build time as compared to traditional techniques.
- Customisability – 3D printing allows for greater design freedom than traditional construction techniques can feasibly achieve. It is possible to for example, integrate channels within the structure walls to control airflow more efficiently inside the structure. The design potential for C3DP is limited only by the architects imagination and the laws of physics.
- Ease of Manufacture – C3DP makes constructing buildings and other structures much simpler. Design and structural analysis can be done with CAD software and then printed out with very few secondary steps occurring in between. Simply design the structure, assemble the printer, then start the print. The printer is fully autonomous aside from quality control and some minor assembly tasks such as fitting lintels.
Benefits of SALEM
Due to the modular design, SALEM can be disassembled and compacted small enough to be transported by a single mini-van for smaller applications. As the Hoists are motorised and capable of travelling along the Legs it is also technically feasible to assemble the Printer using no overhead crane and, with the right tooling, could be assembled by just 2 people. This makes it an ideal concept for erecting permanent structures in hard to reach or uninhabited locations such as Mars where construction tools such as overhead cranes cannot be made readily available.
The travel speed of the Extruder is fixed only by the speed of the cable spool and the drying time of the cement meaning that extremely rapid printing speeds can be achieved. If we assume that it is at least possible to print at the same travel speed of the average human walking (about 1.6mph) it would be possible to extrude a 1000 sq. ft. structure in less than 24 hours. Another feature that decreases print time is a variable diameter Extrusion Nozzle enabling the Printer to outline the print using a thin cement layer, then fill the profile in using a thick cement layer, drastically reducing the total amount of Extruder movement required to complete a single layer whilst also improving the quality of structure definition.
Applications of SALEM
Putting aside the obvious, standard construction 3D Printing applications, SALEM has been designed with two special applications in mind:
Humans currently use approximately 1.5 Billion Hectares of land to feed ourselves. That is equivalent to around 36% of all arable land on planet earth. The UN predicts that by 2050 our population will grow to 9.7 Billion. If we assume the same agricultural density, we would then be using nearly 45% of all arable land to feed ourselves. It is clear that we must improve the amount of food grown per acre of land or risk collapsing the earth ecosphere.
Vertical Farming appears to provide a potential solution to this problem. The basic premise of Vertical farming is that instead of growing food in a 2D space like traditional farming, you grow in a 3D space. This is achieved by stacking crops on shelves and growing by artificial means. This is usually achieved with special grow lights and hydroponics.
The major issue with Vertical Farming is that it has a high start up cost and complexity compared to traditional methods. To grow food in this manner you must first create the facilities to do so. To keep costs low enough to be profitable, most Vertical Farming companies are relying on converting shipping containers or old unused warehouses to house their farms.
Where does SALEM come into this equation you ask? If it were possible to rapidly produce multi-story buildings using C3DP, you could in theory build industrial scale Vertical Farms for cheap enough to turn a profit. This is one of the key benefits of SALEM. It makes it possible to print out large scale structures without the need for difficult and resource heavy logistics, therefore making such facilities possible.
Off-world & Uninhabited Printing
There has been serious movement in recent years towards establishing human colonies off-world. Looking past the many challenges we face in getting humans to these distant places, we then have to consider how we might actually survive once we’ve arrived.
Moving mass from one planet to another is an extremely difficult and costly process. As such, we must keep the amount of mass sent from earth to other worlds as low as possible. We should look to use as much as possible from the worlds we arrive at to build our bases. It stands to reason then, that C3DP would be an especially useful concept for building bases on places such as the Moon and Mars. It turns out all the ingredients you need to produce cement are abundant in the Martian crust.
SALEM is perfect for this application as it has been designed to not require any overhead craneage to be erected. It should be possible to assemble a SALEM printer with just manual handling practices, some simple tooling and the printer itself. It also is fully customisable and theoretically self-calibrating making it more flexible for use in places where it is more difficult to do foundational ground prep.