A PRACTICAL APPROACH TO COMPARING ENERGY EFFECTIVENESS OF RAPID PROTOTYPING TECHNOLOGIES

Transcription

1 Proceedings of AEPR 12, 17th European Forum on Rapid Prototyping and Manufacturing Paris, France, June 2012 A PRACTICAL APPROACH TO COMPARING ENERGY EFFECTIVENESS OF RAPID PROTOTYPING TECHNOLOGIES Stefan Junk University of Applied Sciences Offenburg, Germany stefan.junk@hs-offenburg.de Samantha Côté University of Applied Sciences Offenburg, Germany samantha.côté@hs-offenburg.de ABSTRACT The examination of the energy efficiency of different Rapid Prototyping technologies does fundamentally support the choice of an energy-saving manufacturing method. Therefore in this contribution two common RP technologies are examined and compared with regard to their energy consumption. The consumption measuring of electrical energy was carried out during the complete production time. In addition the value of energy consumption was compared with the value of other resources consumed during the additive manufacturing process. Finally, measures for the increase of the energy efficiency and economizing possibilities are discussed. This practical approach allows the determination of the specific energy needed for the layer construction per volume unit and the comparison with specific stock removal energy of conventional manufacturing technologies. Hence the choice of a suitable manufacturing method for a component based on the criterion energy efficiency becomes possible. KEYWORDS Energy effectiveness, energy consumption, specific energy for layer construction

2 A practical approach to comparing energy effectiveness of RP technologies 1. INTRODUCTION The energy requirements both of a growing world population and of the industrial sector are continually on the rise. This puts a strain on the environment and leads to increased emissions, climate change and a scarcity of fossil resources [1]. For companies this not only means a rise in energy costs and a tightening of environmental regulations, as for example laid down in the Kyoto Protocol on international climate protection, but also a direct responsibility to increase sustainability by cutting back the negative effects of energy consumption. The potential for saving energy is enormous, with about half of the electricity being used by industry and commerce in Germany alone [2]. If companies take measures to save energy and apply it more efficiently, that in turn means a decrease in emissions and in the depletion of raw materials and puts less pressure on the environment. Energy used efficiently leads to a minimisation of energy costs, so that the competitiveness of the company and its products can be enhanced [1]. Apart from these challenges in the field of energy, companies are also being confronted with changes in market requirements. With many of today s products there is a demand for more variety and smaller quantities, as end consumers prefer individual rather than mass products. Technical progress means that the life-cycle of a product is considerably shorter, depending on the manufacturing sector. In order to satisfy the demands of the market, companies must customize their product development and product development time [3]. One way of doing this is by using Rapid Prototyping technologies. 2. PRESENTATION OF BOTH RAPID PROTOYPING TECHNOLOGIES EXAMINED Rapid Prototyping (RP) is the term used to describe the quick manufacture of samples or prototype construction parts in successive additive layers. The original material is strengthened or solidified layer by layer by applying energy to it. The separate layers are thereby bonded or fused. The original material may be powdery, fluid or solid. This depends on the chosen procedure methods [4]. For this reason two widely used methods were examined as examples: on the one hand "Fused Layer Modeling" (FLM) and on the other "3-Dimensional Printing" (3DP). 3DP is used at the University of Applied Sciences Offenburg for apprenticeship and research purposes and also provides a service for the economy of the region. As part of this study [5] a 3D-printer "ZPrinter Z450 " from the ZCorporation was used in the laboratory for Rapid Prototyping (Gengenbach campus). In addition a FLM printer "Dimension SST 1200es" was employed as a second RP system. The materials which were used and the energy required for each of the steps in production with 3DP are shown in Figure 1. In this procedure the CAD-model is first preprocessed by reading the data into the control computer, in which printing

3 Proceedings of AEPR 12, 17th European Forum on Rapid Prototyping and Manufacturing Paris, France, June 2012 is prepared with the help of the print software which controls the hardware. Then the model which has been sliced into separate layers is entered into the printer. This normally takes place in a file format which is dependent on the 3DP printer software. In the printer hardware a true 3D model is formed by joining and fusing layers of powdery material (plaster and synthetic materials) with a liquid binder. With coloured models the colour is added to the surface layer. Powder serves as a supporting agent for the construction part which at this point is described as a green body due to its unstable form. In a subsequent postprocessing procedure the superfluous powder, which can be used again untreated, is blown off by compressed air. Furthermore the construction part is infiltrated with a twocomponent synthetic resin, in order to increase its firmness and the brilliance of its colour. Now the finished part can be put to use. Figure 1 Diagram to illustrate the procedure in 3DP technology with the applied materials and energy In FLM, the second method of technology which was studied, plastic filaments were melted and ejected in a viscous state onto a support plate by means of a heated extrusion nozzle. Additionally a second plastic material was used for a supporting structure (support) which was later removed in an alkaline bath. 3. EXPERIMENTAL PROCEDURE Using both RP-Technologies two throttle valves were printed (one for each method with a volume of approx. 124 cm 3 ). The CAD-model of the throttle valve is shown in see Figure MEASURING SYSTEM At the same time the electrical power consumption of the machines during preparation, manufacturing and the subsequent postprocessing was measured. Measurements were carried out with the help of a Standby-Energy-Monitor "SEM16 + USB" from the company Nordwestdeutsche Zählerrevision NZR, Bad Laer (Germany). Thus the measured data was stored and transferred via USB to a Laptop to evaluate the data.

4 A practical approach to comparing energy effectiveness of RP technologies 3.2 MEASURING RESULTS OF 3D-PRINTING The diagram in Figure 3 shows an example of the measurements with 3DP technology. In the diagram it is possible to distinguish the three principal phases in manufacturing and notable peaks in power usage: Figure 2 Throttle valve as CAD-model (left), printed with 3DP (centre) and with FLM (right) Phase 1 Preparation: First the PC (control computer) and the 3D-printer which is to carry out the print job are switched on. The 3D-printer is warmed up to its operating temperature (1) and extracts superfluous powder from the pressure chamber by suction (2). Phase 2 Manufacturing: The component is printed layer by layer while the 3D-printer simultaneously creates a powder bed. (3) Figure 3 Characteristic curve of electrical power consumption with 3DP-technology Phase 3 Postprocessing: The 3D-printer extracts superfluous powder from the pressure chamber by suction (4). The printed components have to dry (5). When the components are removed from the powder bed loose powder must be

5 Proceedings of AEPR 12, 17th European Forum on Rapid Prototyping and Manufacturing Paris, France, June 2012 siphoned off manually. Some powder may still stick to the component (6). This residue must be blown off the component in a further construction chamber by means of an air jet (7). The experiment ends when the appliances are switched off (8). 3.3 MEASURING RESULTS OF FUSED LAYER MODELING FLM The curve for FLM technology (Figure 4), which can also be divided into three phases, shows similar characteristics: Phase 1 Preparation: When the PC is started up, the 3D-printer switched on and the interior of the printer begins to warm up, power consumption rises within a few minutes to approx. 1050W (1). With the warming up of the nozzles power consumption reaches approx. 1250W for two minutes then sinks again (2). Phase 2 Manufacturing: During the deposition and fusing of layers an average of approx. 580W is required (3). Phase 3 Postprocessing: With the heating of the alkaline bath to about 70 C for the removal of the supports power consumption rises and may peak at 1857W (4). After the necessary temperature in the alkaline bath has been reached consumption sinks again to around 260W (5). Figure 4 Characteristic curve of electrical power consumption with FLM technology 4. EVALUATION OF TEST RESULTS When 3DP technology is used energy consumption is between 1860Wh and 2161Wh, depending on the positioning of the construction part in the building chamber. This is equivalent to a "specific energy for layer construction" of approx. 55kJ/cm 3 or respectively 65kJ/cm 3. In this example, 4% of the total power

6 A practical approach to comparing energy effectiveness of RP technologies consumption is accounted for in the preparation stage, 44% in manufacturing and 52% in the postprocessing phase. In comparison 7791Wh was required in the manufacture of the same component with FLM. This is equivalent to a specific energy for layer construction of 180kJ/cm 3 or respectively 230kJ/cm 3 (depending on the proportional volume and filling level of the supporting material). Differences can also be seen in the greatly varying lengths of processing time 5h 38min with 3DP compared with 11h 56min with FLM. Figure 5 illustrates the required specific energy (proportionate to volume) whereby two conventional subtractive manufacturing technologies were compared. The values quoted in literature for specific energy consumption in conventional manufacturing technologies ( stock removal energy ) vary considerably, as they are strongly influenced by the setting of the machine and the materials used [6, 7]. Figure 5 Comparison of specific energy for layer construction of RP technologies and stock removal energy of conventional manufacturing technologies [6, 7] It now becomes evident that FLM technology consumes considerably more energy than 3DP technology. That can be explained by considering the operational procedure. With FLM the printer uses a great amount of energy in the preparation phase in order to reach an operating temperature of 270 C for the extrusion nozzle and jets as well as 70 C in the construction chamber, whereas the 3D-printer in 3DP technology merely needs a temperature of 38 C. In particular the length of time required for FLM is highly dependent on the geometrical shape of the construction part. In this procedure the jet must cover every single point on the layer, first printing the outer contours and then the interior surface. Increasingly complex construction parts lead to a rise in energy consumption and duration of the production process. In addition FLM-technology requires supportive structures, which must be removed after production in an alkaline bath heated to 70 C. In the postprocessing phase of the 3D-printer the construction parts dry within 90 minutes when warmed,

7 Proceedings of AEPR 12, 17th European Forum on Rapid Prototyping and Manufacturing Paris, France, June 2012 independent of the geometry of their structure. Finally the parts are cleaned in a second chamber by the use of compressed air, which causes a high consumption of electrical energy. 5. CONCLUSION Energy input can be reduced in FLM-technology, by using as little supportive material as possible (e.g. through a better positioning of the construction part in the building chamber) or by employing synthetic materials with a low melting point. In addition the heating of the nozzles, the construction chamber and the alkaline bath to an operating temperature should be studied and possibly carried out more efficiently. With 3DP-technology the energy input can also be influenced by the positioning of the part in the construction chamber. In addition it is possible to examine the many various electrical components such as, for example, motors, the compressor or the heating system as to their efficiency when in operation. A comparison of the expense of the materials used in the production process as well as for electricity in both technologies reveals that the costs for 3DP only amount to about a third of the costs for FLM, which is illustrated in the segments of the circular diagrams in Figure 6. The largest share of the costs is allocated to the material of the model itself and the necessary support plate (in total approx. 80%). The costs for postprocessing by means of an alkaline bath (8%) and for electricity (approx. 3%) are fairly low in comparison. Figure 6 Comparison of the costs of the materials employed and energy consumption with FLM (left) und 3DP (right) With 3DP the costs can be divided basically between the powder and spraying of the binder (each approx. 48%). The resin used in infiltration takes up only 4% of the costs when used with conventional infiltration methods. However, it should be noted at this stage that for structures which are exposed to exceptional high stresses (e.g. in the rapid tooling of forming dies [8]) correspondingly high-strength infiltration materials are applied, which are much more cost-intensive. It is therefore important not only to study the question of energy efficiency but also to take other aspects of reducing material costs into consideration.

8 A practical approach to comparing energy effectiveness of RP technologies ACKNOWLEDGEMENTS Experiments on FLM were carried out in cooperation with the company t-c-w.de trade center ralph wagner e.k. ( in Lahr (Germany). REFERENCES [1] Pehnt, M.: Energieeffizienz. Ein Lehr- und Handbuch, ISBN , Springer-Verlag, 2010 [2] Ziesing, H.-J.: Energieverbrauch in Deutschland im Jahr 2010, Arbeitsgemeinschaft Energiebilanzen e. V., Berlin, 2011 [3] Gebhardt, A.: Understanding Additive Manufacturing: Rapid Prototyping - Rapid Tooling - Rapid Manufacturing, ISBN , Carl Hanser Verlag, 2011 [4] Zäh, M.F.: Wirtschaftliche Fertigung mit Rapid-Technologien: Anwender- Leitfaden zur Auswahl geeigneter Verfahren, ISBN , Carl Hanser Verlag, 2006 [5] Maier, O.: Untersuchung der Energieeffizienz von Rapid Prototyping Anlagen, Bachelor-Thesis, HS Offenburg, 2011 [6] Gentzen, J.: Anwendungspotentiale der Verfahren Schleifen, Superfinischen und Glattwalzen, in Hoffmeister, H.-W. und Tönshoff, H.K. (Hrsg.): Jahrbuch Schleifen, Honen, Läppen und Polieren, Vulkan-Verlag, 2004 [7] Fraunhofer-Gesellschaft: Fraunhofer-Institut für Werkzeugmaschinen und Umformtechnik - Projekte - Produkte, Online im Internet; URL nergieeffiziente_feinbearbeitung.html [Stand: ] [8] Junk, S., Taleb-Araghi, B.: New Developments in Rapid Tooling Using 3D- Printing with Plaster Powders, Fraunhofer Direct Digital Manufacturing Conference, DDMC, Berlin, 2012