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|3D PRINTING TECHNOLOGY IN EDUCATION ENVIRONMENT |

|Nenad Grujović1, Milan Radović1, Vladimir Kanjevac1, Jelena Borota1, George Grujovic2, Dejan Divac3 |

|1Faculty of Mechanical Engineering, University of Kragujevac, Sestre Janjic 6, 34000 Kragujevac, Serbia |

|2IBM UK Limited, 76/78 Upper Ground, South Bank, London SE1 9PZ, United Kingdom |

|3Faculty of Civil Engineering, University of Belgrade, Bulevar Kralja Aleksandra 73, 11000 Belgrade, Serbia |

|gruja@kg.ac.rs, radovic.milan@, vkanjevac@, jborota@, GeorgeAG@, ddivac@eunet.rs |

Abstract: This paper presents a result of a decade of teaching and research with students of Faculty of Mechanical Engineering in Kragujevac, Serbia, in an environment established for the course of Rapid Prototyping (RP). The environment is based on the 3D printing and 3D scanning technologies, and their relationship with other technologies. Special attention is devoted to “RepRap”, an open source project, and “RapMan”, a 3D printer based on that technology. The printer has been assembled, tested and brought to production form in Center for Information Technology located at the Faculty of Mechanical Engineering in Kragujevac. Experience gained in educational environment in Serbian faculty corresponds to reports of the printer use as an educational tool in many schools all over the Europe, in the first place in United Kingdom.

Key words: rapid prototyping, education

1. INTRODUCTION

Rapid Prototyping (RP) process can be represented as a succession of additive technological processes which allow the construction of complex objects. The input of the RP process is a 3D digital geometrical model [1] that can be realized either with a CAD program or via Reverse Engineering (RE) [3]. The RE is performed in two steps. First a 3D scan of an existing object is taken and then the results of the scan are appropriately elaborated.

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Fig.1. Basic steps of an RP process

The RP processes are now widely used in the industry because of their many advantages. An important characteristic of the RP processes is their relation to the RE which allows to replicate the existing parts of a product or a product in its integrity for which no technical documentation is available. The basic steps of every RP process are represented in the Figure 1: 3D modelling, data conversion and storage, data control and preparation, realization of the prototype and post processing. These steps can be repeated until a satisfactory level of quality is achieved.

2. 3D PRINTING TECHNOLOGY

In 2005 the company "Bits From Bytes" built the first release of their 3D printer RapMan which was soon upgraded into the Release 2.1 [6].The RapMan printer was based on a technology developed at the University of Bath as part of a project called RepRap. The first releases of the printer were made of a mechanical part only leaving to the end user to realize the control of the mechanical part based on the various solutions proposed by the RepRap project. In 2009 Bits From Bytes built the Release 3.0 of the printer RapMan which included also the electronic part that made it ready to print [7]. Shortly after the RapMan was adopted as part of the educational program in over 200 schools in the UK.

3D objects are made of layers of melted material laid on top of each other modelled to create the final object.

The materials that are most frequently used for 3D printing are ABS and PLA. ABS is derived from the petroleum (as the majority of the polymers) and PLA is derived from the starch and it can biodegrade under certain conditions (at 60 C in a slightly acid compost). Other materials that can be used are LDPE, HDPE, PP, uPVC, PVC, Nylon6, PMMA and many others.

The RapMan is a Computer Numerical Control (CNC) machine based on the extrusion of the plastic. The temperature at which the extrusion is performed depends on the type of the material used for the 3D printing. The extruded material has a shape of a thin “thread”. The 3D object is printed with the thread which draws the object layer by layer.

The figure 2 represents the process of 3D printing. The extruder caries the material used for printing up to the heater by pressing mechanism where the material is heated to reach the operating temperature and extruded to form a layer of the 3D object on the platform. The extruder can move along XY surface. After the first layer has been drawn, the platform is lowered in Z direction by the amount of the thickness of the drawn layer and everything is ready for the next cycle. The extruder and the platform are powered by a stepper motor whose movements are controlled by a set of parameters which define the temperature and the position of the heater, the extrusion speed, the layer thickness etc.

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Fig.2. 3D printing process of one layer [8]

The figure 3 shows the 3D object while the last layer is being printed. The objects realized via this process can be easily replicated and used in different ways [9]. It is also possible to enhance the hardness of the printed object the cyanoacrylate glue application.

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Fig.3. Scaffold - 3D printing process

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Fig.4. Parts printed at CIT, Kragujevac

The figure 4 shows some of the 3D objects printed in the Centre for Information Technology at the University of Kragujevac. Both the technic of 3D printing as well as the materials used in the printing are continuously being improved. The BFB 3000 represents the state of the art in the 3D printing and it has three extruders which can use three different materials.

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Fig.5. BitsFromBytes RapMan 3.1 at CIT, Kragujevac

3. PROTOTYPES CONSTRUCTION WITH 3D PRINTERS

The printing process of the RapMan printer needs to be prepared by CAM program. The CAM program analyses the 3D object and based on this analysis prepares the commands in G-Code language that will control the RapMan. There are two versions of CAM program for the RapMan. The first one is called Skeinforge [10] and is completely open-source. The Skeinforge is interoperable with all the operative systems used today and offers great possibilities for customisation in 3D printing. The drawback is its complexity and that it does not have any user interface defined. The second one is AXON [7] which is available free of charge by BitsFromBytes.

The AXON is based on the Skeinforge program and it has its own GUI. The drawback is that the AXON is interoperable only with Microsoft Windows Operative System.

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Fig.6. STL file at Netfabb Studio basic

The steps of prototypes construction are usually as follows: firstly a 3D model is built and stored in some format supported by the CAM packets (STL), all the imperfections are corrected and the format is translated by the CAM packet in the G-code. The model is eventually printed with the 3D printer.

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Fig.7. STL file at Axon Software

The AXON SW supports the STL format. The STL file may contain some errors caused by mistakes made during the phase of the 3D object modelling. These errors can be corrected with the application called Netfabb Studio shown in the picture 6 (the basic version of the application is free of charge whereas the professional version needs to be purchased). The basic version of Netfabb Studio can be used for correcting some simple errors in the STL files. For more complex problems errors the professional version is required [7]. After the STL file has been corrected, the file is imported in the AXTON SW (shown in the picture 7). The most important parameters that can be regulated by the AXTON SW are Layer Thickness, Temperature (at which the material is extruded) and Support Option (the support for printing of the objects in the air). The support is shown in the picture 8 in green.

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Fig.8. Model generated at CAM Skeinforge

When all the printing parameters are properly set, the STL file is translated in G-code which is stored on the SD card which is plugged in the 3 D printer. The 3D printer used in the Centre for the Information and Technology (CIT) at the University of Kragujevac is 3D printer RapMan 3.1. The 3D models are made in CAD starting from the reference models realised using the Reverse Engineering (RE) methods (i.e. by post processing of the Computer Tomography (CT) scans). The picture 9 shows the 3D print of the vertebra realised at the CIT as part of the course “Brza Izrada Prototipova” (Fast Prototypes Construction) [4]. The print is realised with the biodegradable material PLA. The time required for its construction was around 4.5 hours. After removing scaffold from platform, basic post-processing consists in careful removing its support. The dimensions of the printed objected were compared with the dimensions of the model generated with the SW and the comparison showed that the dimensions matched perfectly.

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Fig.9. Model of vertebra made at Center for Information Technology at Faculty of Mechanical Engineering, University of Kragujevac

The 3D prints built in this way can be used as both conceptual as well as functional parts. The 3D printers used at the CIT as part of classes of “Fast Prototypes Construction” course are RapMan 3.1 as well as ZPrinter 310 shown in the picture 10. The ZPrinter 310 [11] is an expensive professional 3D printer and requires greater costs for maintenance and material used in printing as well as longer printing time. Unlike the ZPrinter 310, the RapMan requires much lower costs but at the same time provides good basis of learning the techniques used for 3D printing which makes it a very interesting educational tool.

4. CONCLUSION

The modern RP systems have been developed based on the proven and improved technologies and therefore can be widely used in the industry. On the other side, the so called open source solutions such as RapMan are more suitable for the research work and the education. Despite being a relatively new technology in the industry, the RapMan technology played a big role in reaching some important targets dictated by the modern market such as shortening the length of TTM (Time To Market) and lowering the cost of the final product which made this technology much more interesting to the industry and created a need for skilled engineers in the fields of RP and RE.

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Fig.10. ZPrinter 310 System at CIT, Kragujevac

The course “Rapid Prototyping” created at the University of Kragujevac has been awarded as the best course in Serbia as part of WUS Austria CDP program because of its importance and quality [4].

There are great potentials for application of this technology in many other even non-technical fields such as art and design, geography etc. This makes it a very interesting subject to be thought in schools the same way it was done in the past with the Information Technology. The co-authors of this paper are the students and lecturers at the University of Kragujevac.

REFERENCES

1] HARRISON P. (2003), Rapid Prototyping user guide, Faculty of computing Sciences and Engineering, De Montfort University, Leicester.

2] TRAJANOVIĆ M., MANIĆ M., MIŠIĆ D., VITKOVIĆ N. (2005), Expert system for selection of 3D scanning methods of physical objects (In Serbian), YU info 2005, Kopaonik

3] TRAJANOVIĆ M., MANIĆ M., MIŠIĆ D., VITKOVIĆ N. (2006), The use of reverse engineering techniques on the example of swindler spoon (In Serbian), YU info 2006, Kopaonik

4] GRUJOVIĆ N. (2005), Brza izrada prototipova-rapid prototyping (In Serbian), WUS Austria CDP+ 141-2004, Faculty of Mechanical Engineering, Kragujevac

5] TRAJANOVIĆ M., GRUJOVIĆ N., MILOVANOVIĆ J., MILIVOJEVIĆ V. (2008), Računarski podržane brze proizvodne tehnologije (In Serbian), Faculty of Mechanical Engineering, Kragujevac

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8] GIBSON I, ROSEN DW, STRUCKER B. (2009), Aditive Manufacturing Technologies: Rapid Prototyping to Direct Digital manufacturing, s.143-156. Springer New York Heidelberg Dordrecht, London

9] PHAM D.T., GAULT R.S. (1998), A comparison of rapid prototyping technologies, International Journal of Machine Tools and Manufacture, Elsevier Science, (ISSN 0890-6955), Volume 38, Number 10, October 1998, s. 1257-1287

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ACKNOWLEDGMENT: The part of this research is supported by Ministry of Science in Serbia, Grants III41007.

Correspondence

Nenad Grujović, Full Professor, PhD

Department for Applied Mechanics and Automatic Control, Faculty of Mechanical Engineering, University of Kragujevac, Sestre Janjić 6, Kragujevac, Serbia

gruja@kg.ac.rs

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Milan Radovic, student

Faculty of Mechanical Engineering, University of Kragujevac, Sestre Janjić 6, Kragujevac, Serbia

radovic.milan@

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Vladimir Kanjevac, student

Faculty of Mechanical Engineering, University of Kragujevac, Sestre Janjić 6, Kragujevac, Serbia

vkanjevac@

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Jelena Borota, Dipl. Eng.

Faculty of Mechanical Engineering, University of Kragujevac, Sestre Janjić 6, Kragujevac, Serbia

jborota@

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George Grujovic, Dipl. Eng.

IBM UK Limited, 76/78 Upper Ground, South Bank, London SE1 9PZ, United Kingdom

GeorgeAG@

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Dejan Divac, Senior Research Associate, PhD

Institute for Development of Water Resources "Jaroslav Černi", 80 Jaroslava Černog St., 11226

Beli Potok, Serbia

ddivac@eunet.rs

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