MakingMachines that Make Buildings

Constructing aMobile 3D Printer for Concrete Elements

Bassam Daoud1, Johan Voordouw2

13DBuilder 2Azrieli School of Architecture and Urbanism, Carleton University1bassdaoud@gmail.com 2johan.voordouw@carleton.ca

This paper is both a fundamental and applied study of the multi-faceted designand fabrication issues related to the construction of a mobile 3D printer. Thepaper signifies the halfway point in a project initiated at the Azrieli School ofArchitecture and Urbanism at Carleton University starting in 2013. The printer,entitled 3DB, intends to print concrete elements for the Architecture, Engineeringand Construction industry. The printer frame was designed to fit within the bed ofa typical half-ton pick up truck or contract trailer. The paper describes thedesign, simulation and construction of the steel frame, gantry and extruder andmakes speculation on future research including improved design of the extruderand nozzle mechanism.

Keywords: Digital Fabrication, 3D Printing, Concrete Architecture, AdditiveManufacturing, Mobile Building Technology

INTRODUCTIONThis project conveys the design and constructionof a mobile concrete 3D printing platform. Enti-tled the 3DBuilder (3DB) this paper expresses thehalfway point towards an operational prototype. Theproject's intent is to build a printer capable of fabri-cating concrete elementswith amaximumvolumeof1800 x 1200 x 1000mm. The3Dprinting frame is con-structed to fit the bed of a standard half-ton truck orequivalent contracting trailer. Bassam Daoud, whilean M.Arch student, initiated the 3D printing projectin January 2013 as an independent research study.The project ran in parallel with the completion of hisM.Arch thesis. Johan Voordouw supervised the inde-pendent research project until Daoud's graduation.This project is ongoing as a post-M.Arch research ini-tiative. A fully operational prototype has an antici-

pated completion date in 2016.

SIGNIFICANCE3D printing is currently topical. There have been anumber of developments in relation to the Architec-ture, Engineering and Construction (AEC) industry.While a number of prototypes have been developedthe technology remains an emerging field. The crit-ical aspects regarding the success of this prototypeare: 1) the desire for a seamless concrete finish and 2)mobility and operability on-site.

The context within the emerging fabricationfield is quickly evolving. At this time, there aretwo overarching trajectories among researchers: 1)the large-scale contour crafting research by individ-uals such as Professor Behrokh Khoshnevis, Directorof Manufacturing Engineering Graduate Program at

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the University of Southern California (USC), recentpartnerships including Skanska, Foster + Partnersand Loughborough University with the work of Dr.Richard Buswell and Professor Simon Austin and thesecond trajectoryof development, 2) the increasinglyrefined large-scale building elements such as theDigital Grotesque byMichael Hansmeyer, thework ofRael San Fratello with the 3D printed house studiesand DUSwith the 3D Print Canal House. These explo-rations not only scale up existing technologies butare at the forefront of a new tectonic design culture.

The research team for the 3DB project aims fortwo possible outputs: 1) that the 3D printer wouldwork in the field in connection to 3D scanning tech-nology to resolve site specific printing requirementsand 2) the ability to print bespoke, digitally designedcomponents. This makes the mobile concrete 3Dprinter a versatile construction technology for bothconservation and new build projects.

STEEL FRAMEThe 3DBmachinewas designed in Autodesk InventorProfessional. The frame has a rigid all steel construc-tion. The undercarriage was inset to account for thewheel wells of half-ton pickup trucks and contractingtrailers. The platform is placed on heavy duty, indus-trial casters for ease of mobility. It is equipped withretractable and adjustable feet for the purpose of lev-eling and stability.

The project used Autodesk Simulation and In-ventor's structural simulation capabilities, eliminat-ing a number of design uncertainties. Inventor'sframe generating capabilities were critical in design-ing the structural layout and mechanical connec-tions of the frame. Structural and collapse sim-ulations were conducted to determine deflections,strengthen the weak points, and prevent joint fail-ures when the 3DB is printing an object and themax-imum volume of 2.16 cubicmeters is reached (1800 x1200 x 1000mm effective printing bed volume).

The frame is designed to handle the maximumcompressive weight in concrete of +- 4,600 kg dis-tributeddownwards at six points and supportedby four

leveling feet capable of handling +- 3,500 kg each.The results of the simulations helped determine thequantity, layout, and thicknesses of the steel mem-bers and optimize the overall strength-to-weight ra-tio. This allowed the frame to have a reduced num-ber of members with minimal wall thicknesses with-out compromising the required strength. The result-ing tubular steel frame is relatively lightweight andhas fullywelded connections formaximumstructuralstability and durability (Figs. 1-4).

Figure 1Cutting the steelelements prior towelding

Figure 2Welding the steelframe in the AzrieliSchool ofArchitecture andUrbanism shopfacilities

Figure 3Simulation of thesteel frame understress

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Figure 4The completedsteel frame

Figure 5The gantry

GANTRYThe 3-axis gantry mechanism (Fig. 5) was remodeledfromanopen-sourcewoodworking (Mechmate) CNCmachine. A series of modifications to the mecha-

nismwere designed in Autodesk Inventor to accountfor the deposition of heavy printing material. The Z-axis was modified with a re-designed Z-slide to sup-port the extended length of one meter. New brack-ets were added to connect a custom ordered retract-ing mechanism manufactured to specifications. TheY-sliderwas adjusted toaccommodate thenewZ-axiscomponents and the X and Y-axis members were re-sized to fit the frame. To eliminate possible obstruc-tions while the machine is operational or when theZ-axis is fully retracted within the opening of the Y-slider, further adjustments were made to clear thepath of the extruder, fittings, and the nozzle mecha-nism along the XYZ axis of travel. The Z-slide assem-bly was further modified by pushing its seating posi-tion backwards and by extending its stroke to allowfor a full retraction, thusmaximizing the overall effec-tive height of built objects.

The following section describes work that is cur-rentlyongoingandwill continueuntil thecomple-tion of Phase 2 in 2016.

EXTRUDER DESIGNThe cement extruder is fed by a digitally controlledprogressive cavity pump. The extruder is capableof depositing bituminous mixtures of various densi-ties. This offers versatility in constructing concreteelements of various structural and aesthetic charac-teristics. This ongoing research was initiated in 2014.The research team has contacted a number of indus-try sources including individuals at the Carleton Uni-versity Science & Technology Center to advise on thedesign of the extruder and concrete mixtures.

The extrusion mechanism in composed of threemain assemblies:

1) A progressive cavity (PC) pump housed be-neath the printing bed used to feed the pre-mixedconcrete through the plumbing lines. The concretewould be mixed and fed to the pump via a standardopen hopper or an integrated auger hopper.

2) The material chamber attached to the Z-axis used to regulate the flow of the concrete bythe means of air compression with solenoid valves

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and/or flow metering systems. This allows the out-put from the extruder to be controlled electronicallywith great accuracy.

3) The nozzle release system has a digitally con-trolled directional output. It would be fitted with atrowelling mechanism used to shape the flow of thecementmixture. Themechanized nozzle would formthe extrusion as required eliminating the need forpost processing and conventional concrete surfacingmethods.

ASSEMBLY AND TESTINGAfter preliminary research, a progressive cavity wetpumping system was selected. A PC metering pumpfrom a leading manufacturer (Seepex Inc.) is cur-rently under consideration to be fitted and wiredto the control enclosure.The first iteration of thecompression chamber and mechanical nozzle sys-tem were designed in Inventor and will be fitted tothe Z-axis of the 3DB in late 2015. The design ofthe mechanism utilized readily available mechanicaland electronic automation components such as ac-tuators, linear motion systems, drive mechanisms,and electric motors and drivers. A number of theextruder's parts will be CNC milled and/or water-jetcut in aluminum such as the brackets and connec-tors, housings andmechanical joints. The anticipatedchallenges facing our initial test runs revolve aroundthe synchronization of the digital controllers of me-chanical movements with the material output of thecement mixtures along the printing bed. The con-trol software for the initial trials of themachinewouldbe ArtSoft's Mach3, along with a number of opensource applications used for the processing of three-dimensional models into G-Code. The later stages ofthe project would involve the development of morespecific codes and applications - such as direct oper-ability using grasshopper - to resolve more complexoperations of the 3DB printer. A dedicated controlapplication would be developed in the event whereadditional axis of travel are added to thematerial de-position apparatus. The nozzle release mechanismon the Z-axis could be refitted with additional mo-

tors/axis for swivel and rotation to numerically guidethe nozzle towards the desired position and angle.

FUTURE DEVELOPMENTSThe three-axis mechanism of the printer was se-lected for its solid welded sheet metal constructionand highly accurate drivemechanism intended to betransported and operated on-site. There is howeverroom for improvement to the gantry system in fu-ture stages of the project to enhance the printingspeed. Unlike conventional numerically controlleddrive mechanism, 3D printers require a fast acceler-ation to travel and deposit material efficiently alongthe X and Y-axis. The gantry and drive mechanismsusedmay as a result be further enhanced or replacedwith a faster and more efficient alternative suitablefor rapid additive manufacturing requirements.

The nozzle mechanism can be improved by ex-tending the angular reach of the nozzle's tip andtrowels. This requires the additionof twoormore axisof travel, placing thenozzle in anyprogrammable po-sition and angle relative to the work surface. The ad-ditional axis would provide a near limitless degree offreedom for the depositionmechanismand allow theprinter to extrude complex free form shapeswith op-timal accuracy and finish quality.

Further improvements could be made to thenozzle's tip itself. A simplified tip design that couldchange its physical characteristics using elasticmem-branes is being investigated. This could result ina wide variety of material extrusion configurationswithout resorting to complicated mechanized trow-eling systems.An alternative 360o swivel head withrotary joints is currently being designed. Once com-plete a series ofmechanical and Computational FluidDynamics (CFD) simulationswill be performed to testthe functionality of the unit and the material flowwithin it aswell as theprintedoutput. Thedigital pro-totyping of the nozzle mechanism will help manageuncertainties leading up to the fabrication and test-ing of the unit. The 360 degree swivel nozzle appara-tus could be coupled with the existing design for theextruder and used for the printing of highly complex

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geometric forms.

Figure 6The finished 3DBframe prior toelectricalinstallation

CONCLUSIONDigital fabrication undoubtedly offers enormous po-tential for the AEC industry. The 3DB project at-tempts to examine the implications of these devel-opments. It is both a fundamental and applied studyin understanding the technology that defines thisemerging field. As the use of 3D printers becomes in-creasingly normative in academia and practice it hasbecomeapparent to the research teamthat a founda-tional understanding is necessary. This project wasinitially undertaken out of a curiosity for emergingconstruction technology. It has now morphed into alarger study of the purpose of 3D printing for archi-tectural fabrication, its judicious necessity and cur-rent limitations. As the project progresses and the3DB becomes fully operational these ideas will con-textualize continuously and the limitations and op-portunities of such technology will continually betested.

The 3DB printing platform was successfully con-structed (Fig. 6) and has currently reached the it-erative stages of design and development commonwith research projects of its nature. Many of the deci-sionspresently examinedwill transformandprogressas the implications of such decisions transcend to af-fect the output of the machine in terms of fabricatedconcrete objects. In this sense, the implications ofthe project must be understood as two phases; one

that involves the creation of the machine prototype(3D printer) the second to make building prototypes(concrete elements).

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