Visualisation of FDM prototypes.

Gajdos, Ivan ; Slota, Jan ; Spisak, Emil 等

1. INTRODUCTION

Using rapid prototyping methods we are able to obtain real concept about new product. Rapid prototyping (RP) meets the current needs in the industry to shorten design cycles and improve the design quality. Fused deposition modeling (FDM) is one of the key technologies of RP (Anitha et. al, 2001). With prototype there is possibility to make mechanical and assembly tests and get almost real representation of new developed product. One of the most suitable methods for preparing plastic prototypes is FDM method, that is commercially available as Dimension printers from Stratasys, making prototypes from ABS polymer (Pahole et. al, 2005). One limit of using FDM for preparing prototypes of plastic parts is that these parts are typically thin walled and with the width of extruded fibre (0,511 mm) it is almost impossible to create walls thinner than 1mm or these walls are very brittle. (e.g. snap fit). Another issue with FDM prototypes is surface quality which is dependent on layer thickness (typically 0,254 mm) and build angle (fig. 1).

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Aim of the paper is to show possibility preparing virtual CAD model of FDM prototype, which can be subsequently used for identify possible build problems, find optimal build angle or for FEM analysis.

2. CREATING VIRTUAL FDM PROTOTYPE

To create virtual CAD model of FDM prototype it is necessary to know paths of printer extrusion head and cross section of extruded fibre. Based on these entry data it is possible to create CAD model with "extrusion feature" in modelling software.

2.1 Analysis of fibre cross-section

Fibre extruded trough printer head has circular cross-section (whit diameter (0, 38 mm), but with whit contact previous layer, the cross-section section is deformed) as shown in figure (2) (Pandey et al., 2003). The visual analysis of specimen broken in (3) -point bending test has shown that shape of contact surface between two fibres lying in two layers over each other, has square shape with dimension 0,33x0,33 mm (fig. 3).

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Based on dimensions obtained from figure 3a, we can determine simplified shape of fibre cross-section in FDM prototype (fig. 3b). The shape of fibre cross-section in not exact as in real FDM prototype but sufficient to prepare CAD model of this prototype.

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2.2 Paths analysis of printer extrusion head

Rapid prototyping processes produce models layer-by-layer. Hence, the geometric model must be first sliced into layers before the physical rebuilding process. Therefore, the slicing algorithm plays a very important role in RP systems. (Haipeng, P. & Tianrui, Z., 2007).

The layer in FDM prototype is created by fibre extrusion from printer head. The path for printer head is for Dimension SST printer defined in "*.CMB" file, generated with help of Catalyst 4.3 software from "*.STL" file.

After loading STL part model into Catalyst 4.3., are generated layers with modelling and support material and printer extrusion head tool paths. Screenshots are made from each layer and saved as pictures in jpeg format figure 4, with decreased colour depth to 1 bit (black and white).

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From these source images with all layers of the model (converted to 1 bit depth), are prepared data in "*.DXF" format, using IMG2CAD 7.0. Possible bugs in tool paths (fig. 4 right),are manually fixed in AutoCAD 2007 . Fixed tool path in DXF file is consequently imported as sketch into ProE Wildfire 3.0. This sketch then serve as path for "SWEEP--PROTRUSION" function (fig. 5) with the cross-section from figure 3 (right).

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Using all imported data (from DXF file) for sweeping cross-section from figure 3, we obtain one layer from FDM prototype as a part from ProE Wildfire 3.0. After preparing all the layers is made assembly of virtual FDM prototype (fig. 6)

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3. EXPERIMENT

Visualized FDM prototype model as a CAD model can be used as base for FEM analysis and results of analysis compared with tested specimen. . For this purpose was used specimen for 3-point bending test according to ISO EN 178:2001 (figure 7).

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The results for 3-point bending test are shown in figure 8, where strong anisotropy of bending strength depending on layer orientation can be observed.

For the A-specimen (fig. 7), was also prepared FEM analysis of 3-point bending test, to compare virtual FDM model whit experimental results.

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FEM analysis was carried out in CosmosExpress and the visual comparison of result is displayed in figure 9.

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4. CONCLUSION

In this paper was presented one approach for visualization of FDM prototypes. Ability to prepare virtual CAD model of FDM prototype, can help identify possible build problems, find optimal build angle or for FEM analysis.

FEM analysis can be used to find out optimal part orientation especially in large expensive prototypes when customer has demand on strength specific area of the part.

Disadvantage of this method are high time demands to prepare virtual FDM model and high demands on computer performance for FEM simulation. The next step in reengineering proposed procedure is to prepare software which could extract tool paths directly from "*.CMB" file and save them in DXF format.

5. REFERENCES

Anitha, R.; Arunachalam, S. & Radhakrishanan, P. (2001): Critical parameters influencing the quality of prototypes in fused deposition modeling In: Journal of Materials Processing Technology, No. 118, p. 385-388.

Bohacek, M. (2008): Vizualizacia modelov prototypov vyrobenych metodou FDM, Diploma work--Technical university in Kosice, Kosice.

Haipeng, P. & Tianrui, Z. (2007): Generation and optimization of slice profile data in rapid prototyping and manufacturing. Journal of Materials Processing Technology, Vol. 187-188, p. 623-626.

Pahole, I.; Drstvensek, I.; Ficko, M. & Balic, J. (2005): Rapid prototyping processes give new possibilities to numerical copying techniques. Journal of Materials Processing Technology 164-165, p. 1416-1422.

Pandey P.M.; Venkata Reddy N. & Dhande S.G. (2003): Improvement of surface finish by staricase machining in fused deposition modeling In: Journal of Materials Processing Technology, No. 132(2003), p. 323-331.