Comparison of 3-D Printing Techniques Usable in Digital Landscape Architecture

Comparison of 3-D Printing Techniques Usable in Digital Landscape Architecture Wanda-Marie STEINHILP and Ulrich KIAS 1 Introduction In landscape architecture there are numerous situations where a two-dimensional plan is not sufficient. In a couple of situations you can operate with 3D computer graphics. However there are a lot of cases where 3D models would be preferable. A 3D model could show the planned subject more realistic whereby an assessment is easier and defects become visible. Furthermore the communication between clients and planners gets improved. Producing models manually is already popular in landscape architecture for a long time, especially in urban planning. The manual model making process is time-consuming and expensive. In disciplines like industrial design Rapid Prototyping has already become a common technique since a couple of years. Also in architecture these new techniques have been noticed while the professional practice of landscape architecture (at least in Germany) has not yet recognized Rapid Prototyping as a promising alternative. In order to promote 3D printing techniques in landscape architecture it is necessary to find out those techniques, which are most useful for the special tasks in landscape architecture. Based on a survey of German landscape architects knowledge and expectations concerning 3D printing a variety of existing prototyping techniques have been analysed and evaluated. The intention of the research was to figure out how far existing systems on the market could be applicable and useful for the diverse needs in landscape architecture. For each technique one representative system has been chosen in order to show its typical characteristics. The selection especially focused the aspect, that the system should be operated in a typical office environment. Because of the promising possibilities it is assumed that Rapid Prototyping is going to spread out during the next years as it was the case with the introduction of CAD and GIS years ago. Besides others like speed and cost arguments we can see especially 2 reasons why landscape architects should think about extending their toolbox by 3-D printing techniques: Speedy translation of GIS contour data into physical models Possibility to create complex 3D forms that are hard to model accurately with traditional modelling tools

174 W.-M. Steinhilp and U. Kias 2 What are 3-D printing techniques? For 3D printing techniques a lot of words exist in the domain-specific terminology. The most famous terms are Rapid Prototyping, Rapid Technologies and 3D Printing. The aim of all 3D printing techniques is to make a three-dimensional model, a tool or a functioning product from a 3D data file, mostly constructed by CAD software. The model, tool or product is build by deposing layers one upon the other and connecting them. All Rapid Prototyping techniques use one basic principle: The first step is to create a 3D data file of the model. Next the CAD data file gets transformed into a file format, which is readable by the Rapid Prototyping software. The most popular file format is STL (Surface Triangulation Language). It describes surfaces as a grid of triangles. Nearly all software solutions, which are typically used in landscape architecture, are able to write this file format. Unfortunately STL is not capable to transmit colour information. A major step in planning the construction process is the slicing, where all important parameters for producing the model in the respective machine get defined. Thereby the STL file gets split into layers, which are converted into instructions for the prototyping machine. Other important parameters are to position the model in the build chamber, to compensate little faults in the dataset and to generate necessary support structures. In the following construction process preparation key data like orientation in the build chamber, layer thickness and construction temperature will be fixed (SEEFRIED & SIGL, 2002). The next step is to build the model in the Rapid Prototyping machine. The building material will be applied layer by layer on a building platform. The material will be hardened inside the model borders. The next layer follows and gets connected with the precedent layer. This chronological order is repeated until the desired cast is achieved. 3 Selection of Rapid Prototyping systems Because of the fast development in Rapid Prototyping domain a selection has been made, covering the five most promising techniques for the field of landscape architecture. These techniques are Stereo Lithography, Laser Sintering, Laminated Object Manufacturing, Extrusion Processes and Three Dimensional Printing. For each technique one representative prototype system has been chosen. The selection especially focused the aspect that the system should be operated in a typical office environment. So the selected systems are particularly small and their build chamber is relatively spacious. Besides a theoretical analysis, 3 models standing for typical tasks in landscape architecture should be built by the different RP systems: A construction model showing some details of a typical open space scene, an urban design model and a landscape scene typical for landscape planning tasks incl. digital terrain data and draped aerial image (Fig. 1) were chosen. 3.1 Stereo Lithography In Stereo Lithography mostly liquid photo-curable monomer material (e.g. acrylic or epoxy resin) is exposed to a light source inside the model borders (SEEFRIED & SIGL, 2002). Due to the exposure to light a polymerisation is provoked layer by layer and the light-hardening material starts to cure (Fig. 2).

Comparison of 3D Printing Techniques Usable in Digital Landscape Architecture 175 Fig. 1: Computer animations of the models (software: AutoCAD Civil 3D, ArcScene / ArcGIS, aerial image: Bayerische Vermessungsverwaltung 2009, digital terrain data: Nationalparkverwaltung Berchtesgaden) Fig. 2: Principle of Stereo Lithography (based on NEEF ET AL., 2005) At the beginning of the building process the platform sinks by one layer thickness into the build chamber, which is filled with the liquid base material. This makes the liquid flow over the platform. The wiper smoothes this first layer. An UV laser is reflected by a mirror so that the liquid monomer starts to cure upside the building platform. Next the platform sinks again by one layer thickness into the liquid and the process iterates until the model is completed (GEBHARDT, 2003). Attached support structures must be removed (GRIMM, 2004). Support structures are installed if the model contains overhangs, which can not be built on top of a liquid. Also shrinking processes are reduced by support structures. In order to harden the model completely, it will be put into an UV oven. The tested Stereo Lithography system Eden 250 works with a special form of Stereo Lithography, called Polymer Printing. Here the basic material is sprayed onto the platform through a print head. It is immediately hardened by an UV lamp which avoids post processing in an oven. With the deposit of model material, for overhangs and hollows a support material will be used in the same time. The support material is removable by water jetting or alkaline bathing. Its size and its process allow a use of the system Eden 250 in

176 W.-M. Steinhilp and U. Kias Fig. 3: Construction model, built with the system Eden 250 by ALPHAFORM AG an office environment. Models can be build up to the size of 250*250*200 1 mm. Separate parts of larger models can be glued together afterwards. Similar to other Stereo Lithography systems the Eden 250 works very precisely. Surface quality and fidelity are very high. Due to the slight layer thickness from 0,016 to 0,030 2 mm the building process takes a long time. For the construction model in Fig. 3 the distributor RTC estimated 83 h 3 building time. Although even in case of ramps no lamination is visible. The base materials, which are available in different colours and with different properties, are accordingly expensive. For this reason the system is suitable in landscape architecture for exceptional tasks with high detail requirements. So the system could become important if offered to the companies as a print service. 3.2 Laser Sintering In contrast to Stereo lithography Laser Sintering uses powdered or granulated base material, starting to sinter by the treatment with energy sources mostly a carbon dioxide laser. 1 2 3 Information from Mr. Kräutner, managing director, RTC, Mettmann, questionnaire about printing system specific characteristics from 19.08.2009. Information from Mr. Kräutner, managing director, RTC, Mettmann, questionnaire about printing system specific characteristics from 19.08.2009. Production cost and time calculation, RTC from 01.09.2009.

Comparison of 3D Printing Techniques Usable in Digital Landscape Architecture 177 Fig. 4: Urban design model, built with the system Formiga P100 by EOS GmbH In Laser Sintering the base material is transported by a blade from a supplying container into the build chamber. While the platform in the build chamber is going to sink the bottom of the applying container gets lifted. After disposing one layer of base material the energy source will be conducted over the layer. The energy starts the sintering process inside the desired area (SEEFRIED & SIGL, 2002). Because of the bed of powder or granulate no support structures are necessary. The Sintering process requires high temperatures, which leads to long cooling periods. Compared with other Laser Sintering systems the chosen system Formiga P100 is particularly compact and could be installed in normal rooms (GEBHARDT, 2007). However for using in offices the machine with its component parts such as unpacking and sieving station is too big and too complex. Separate parts up to the size of 200*250*330 4 mm can be built. Concerning landscape architecture applications the Formiga P100 is a very exactly working system. The base material polyamide, which has a high strength and elasticity, as well as the fine diameter of the laser enable wall thicknesses of as little as 0,4 5 mm to be built. Consequently no modification for building fine balustrades, furniture and beds in the urban design model has been necessary. Also during post-processing the model rests unhurt (Fig. 4). The material is non-transparent matt and white. The result has a slightly rough surface caused by the particle size. The production costs of the three models 4 5 Information from Mr. Salzberger, Manager Application, Technical Center Europe, EOS GmbH, Krailing, E-Mail from 17.08.2009. Information from Mr. Pfefferkorn, Product Manager P, EOS GmbH, Krailing, talk at 06.07.2009.

178 W.-M. Steinhilp and U. Kias estimated by the system manufacturer EOS 6 are competitive compared to other systems which work less exactly. 3.3 Laminated Object Manufacturing This system works with sheets of foil deposited on top of each other. The sheets get sticked together inside the model borders and the machine cuts the foils to the size of the model. The parts of the foils, which are not inside the model borders, serve as support structures. The redundant material is cut into small pieces and has to be removed when the model is finished (ZÄH, 2006). The chosen system is called PLT-20 Katana. It is about as big as a copier and has got a build chamber of 180*280*150 mm 7. This system promises the fastest building process and uses paper for the building process, which can be disposed easily. The price of the PLT-20 Katana of US$35000 8+9] is the lowest among the presented systems. For the building of massive parts such as simple terrain models the system could be useful. The produced parts are not very strong. This is the reason why the removal of the support paper structure is difficult in case of delicate model parts. While removing the support structures in the urban design model the trunks of the trees would presumably break away. Anyhow it is worth to be considered to produce parts of the model separate or to simplify the model components. 3.4 Extrusion Processes Meltable base materials are fed through a heated injector or print head and than deposited on a building platform (WESTKÄMPER & WARNECKE, 2006). While leaving the injector the material cools down and stiffens. In case of overhangs or hollows the material can not be deposited in the air. Therefore this technique needs support structures. The model material and the support material are different in their properties and get deposited at the same time (GEBHARDT, 2003). The chosen system Dimension SST 1200es uses a special structure for massive elements, which saves up to 70% 10 of material. Its size qualifies the system as a desktop version. Also the building chamber of 254*254*305mm 11 is relative spacious. Compared to the other systems the Dimension is beside the PLT-20 Katana part of the lower price segment. A Clean station is part of the base equipment of the Dimension. There the support structures of the models get washed out. The fact that it is possible to dye the base material allows different coloured layers in the model. The Dimension SST 1200es works with 6 Production cost and time calculation, EOS GmbH from 19.08.2009. 7 Website of Kira Europe: Modellbeispiele. URL: http://www.kira-katana.com/katana.htm [28.08.2009]. 8 Website of Desktop Engineering: Technology for Design Engineering. August 2006, URL: http://www.deskeng.com/articles/aaacnh.htm [28.08.2009]. 9 Website of Castle Island s: Worldwide Guide to Rapid Prototyping. A Designer Friendly Solution: Kira s Katana. URL: http://home.att.net/~drdipstik/inr/inr068.htm [04.08.2009]. 10 Information from Mr. Pietrzok, sales manager of FDM 3D-Printing Technologie, alphacam GmbH, Schorndorf, questionnaire about printing system specific characteristics from 17.08.2009. 11 Information from Mr. Pietrzok, sales manager of FDM 3D-Printing Technologie, alphacam GmbH, Schorndorf, questionnaire about printing system specific characteristics from 17.08.2009.

Comparison of 3D Printing Techniques Usable in Digital Landscape Architecture 179 Fig. 5: Construction model, built with the system Dimension SST 1200es by alphacam GmbH layer thicknesses of 0,25-0,33mm 12. The material is deposited in filament form. That s why the model surfaces have a visible striation. In case of inclines the model shows a slight lamination, which is visible at the ramp of the construction model (Fig. 5). Nevertheless the Dimension SST 1200es could describe all three models in a good way. 3.5 Three Dimensional Printing A very promising technique of Rapid Prototyping, especially in landscape architecture, is the Three Dimensional Printing. Like Laser Sintering Three Dimensional Printing works with a bed of powder, which takes over the support function for overhanging parts of a model. In contrast to Laser Sintering the material stiffens by an ink jetted binder, which glues the particles together. Mostly the systems of Three Dimensional Printing utilize a powder of starch and cellulose or gypsum together with a water-based binder. The size of the chosen system ZPrinter 450 (with a building chamber of 203*254*203 mm 13 ) is comparable to the size of a plotter. Because of an integrated and closed powder system, the ZPrinter 450 produces hardly any dust. It is possible to completely recycle 12 Information from Mr. Pietrzok, sales manager of FDM 3D-Printing Technologie, alphacam GmbH, Schorndorf, questionnaire about printing system specific characteristics from 17.08.2009. 13 Information from Mr. Schröttenhammer, sales manager of WDV GmbH, Garching, questionnaire about printing system specific characteristics from 22.07.2009.

180 W.-M. Steinhilp and U. Kias Fig. 6: Urban design model, built with the system ZPrinter 450 by 4dconcepts GmbH the unglued powder 14. So the operation in offices is uncomplicated. The binder can be dyed as the print head includes ordinary HP ink jet technology. So the system is able to print fully coloured models. Therefore it is especially interesting for terrain models with draped aerial images but also for any other tasks in landscape architecture. The manufacturer describes the build material as eco-friendly. The cost of the base material is not very high and the process is not time-consuming. For the building process of the construction model 9h40min 15 are estimated; for the urban design model in Figure 6 it is 7h44min 16. Because of the minor stability of the printed models, they should be removed carefully from the build chamber. For increasing the model stability it is possible to infiltrate a special liquid after the building process. Thus for modelling delicate constructions other techniques such as Extrusion Processes could be more suitable. For the professional practice in landscape architecture it is often sufficient to work out the models in a more abstract way in order to fit the restrictions of this Rapid Prototyping Technology. A very convincing aspect of the system is the sophisticated and user friendly concept of the software. 14 Information from Mr. Schröttenhammer, sales manager of WDV GmbH, Garching, questionnaire about printing system specific characteristics from 22.07.2009. 15 Information from Mr. Schröttenhammer, sales manager of WDV GmbH, Garching, E-Mail from 22.07.2009. 16 Production cost and time calculation, 4dconcepts GmbH from 05.08.2009.

Comparison of 3D Printing Techniques Usable in Digital Landscape Architecture 181 4 Conclusions and Outlook The research comes to the conclusion that there is not one single system best suitable for all existing tasks in landscape architecture. Each of the systems has some advantages but also drawbacks. Techniques which operate with high precision, such as Stereo Lithography or Laser Sintering, are convenient for tasks with special needs of detailing. These tasks are not daily routine in landscape architecture. Those techniques could become important in future if offered to the offices as a print service by specialised companies. Small prototyping systems using fast printing techniques, such as Extrusion Processes or Three Dimensional Printing, are appropriate to be used directly in landscape architecture offices. Working models and fast presentation models require high speed and low cost. Besides, for an office-based application, it is important that there is sufficient know-how and a well fitting software solution, which covers the whole process from the creation of the file up to the printed model. Concerning this aspect there is still some work to be done in order to improve the workflow between landscape architectural software and Rapid Prototyping software. References Gebhardt, A. (2003): Rapid Prototyping. München: Carl Hanser Verlag, 379. Gebhardt, A. (2007): Generative Fertigungsverfahren. 3. Aufl. München: Carl Hanser Verlag, 499. Grimm, T. (2004): User s Guide to Rapid Prototyping. Dearborn, Michigan: Society of Manufacturing Engineers, 404. Neef, A., Burmeister, K. & S. Krempl (2005): Vom Personal Computer zum Personal Fabricator. Hamburg: Murman Verlag GmbH, 133. Seefried, M. & M. Sigl (2002): Rapid Technologien Status Quo. In Zäh, M. & G. Reinhart (2002): Rapid Technologien. Anspruch Realität Zukunft. Westkämper, E. & H.-J. Warnecke (2006): Einführung in die Fertigungstechnik. 7. Aufl. Wiesbaden: B. G. Teubner Verlag, 296. Zäh, M. F. (2006): Wirtschaftliche Fertigung mit Rapid-Technologien. Anwender-Leitfaden zur Auswahl geeigneter Verfahren. München / Wien: Carl Hanser Verlag, 259.