3D CAD/CAM and Rapid Prototyping applied for Malta Cross Mechanism fabrication
3D CAD/CAM AND RAPID PROTOTYPING APPLIED FOR MALTA CROSS MECHANISM FABRICATION Ciobanu Robert1, Donţu Octavian1, Besnea Daniel1, Cuţa Andrei Nicolae1, Doina Cioboata2, Nachila Costel2 1 Politehnica University of Bucharest Splaiul Independenţei, nr. 313, Bucharest, Romania 2 The National Institute of Research and Development in Mechatronics and Measurement Technique, Bucharest, Romania E-mail:
[email protected] Abstract - Integrating rapid prototyping and computer aided design technologies offers a way to obtain complex geometries in a fast and cost-effective manner. In this paper, a comparison between CNC manufacturing and Rapid Prototyping technology (FDM – Fused Deposition Modeling process), applied for a Malta Cross Mechanism fabrication, is presented. In the products development area, a substantial support is offered by models, as intermediaries of product configuration and technology design. The FDM process is based on the extrusion of heated feedstock plastic filaments(PLA- polylactide ) through a nozzle tip to deposit layers onto a platform to build parts layer by layer directly from a digital model of the part, and represents an alternative solution to traditional methods(CNC manufacturing) used to obtain mechatronics parts. Keywords: CNC milling, Rapid Prototyping, CAM fabrication, Fused Deposition Modeling.
1. Introduction The rapid prototyping opens new possibilities, which companies can use, according to the limit conditions, for shortening the design phases and improvement of product properties. The rapidly available models in order to verify a project as documentary material for talks or for research on the assembly and mounting possibilities, offer to the designer unknown ways till now. In the last years, a great number of RP innovative processes have been developed, which allow transformation of the conceived model of a complex product in a solid replica obtained in a short time. [1, 8, 9]
The RP techniques directly creat parts from a 3D CAD model, allowing both design improvement and diminishing of designing time and costs. Using the CAD model performed in CATIA (fig. 1), by opening of a working zone for CAM process in a CATPart or CATProduct document, the initiating of Malta Cross Mechanism execution process is determined in order to manufacture the part on the CNC (Computer Numerical Controlled) milling centre, or to create the STL (STereoLithography) file format for generating the G code program necessary to rapid prototyping [2, 3, 4, 5].
Figure 1: The CAD design of Malta Cross Mechanism
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3D CAD/CAM and Rapid Prototyping applied for Malta Cross Mechanism fabrication 2. Execution of Malta Cross Mechanism on CNC machine CATIA software has a powerful CAM – Computer Aided Manufacturing module to define and organize numerical command programs for the fabrication of parts represented by 3D models of wireframe or solid type, using manufacturing techniques on machines with until 5 axes.
The fabrication module has, also a post – processing engine for covering the entire manufacturing process, starting with the tool path generation and finishing with the NC code program[6]. In order to design the maltese cross mechanism fabrication, the module of prismatic processing for machining centres was chosen. The Z Level and tool changing operation are defined in fig. 2.
Figure 2: Definition of the Z Level and tool changing operation The execution process of Malta Cross Mechanism on CNC Milling machine is illustrated in fig. 3.
Figure 3: Execution stages of Malta Cross Mechanism on CNC machine 3. The Malta Cross Mechanism execution using Fused Deposition Modeling Process Fused deposition modeling (FDM) is one layered manufacturing technology that produces parts of complex geometry by the layering of extruded materials, such as polylactide-PLA. The process of material extrusion, also named Fused Deposition Modeling (FDM), pushes liquid material as thermoplastic polymer(polylactide-PLA in our case) which is initially in the raw form of a flexible filament, through a nozzle, along the path of the digital model onto a platform layer by layer. The molten material naturally cools and hardens, and a new layer can be then added on the top. The bonding between the individual roads of the same layer and of neighboring layers is driven by the thermal energy of the semi-molten material and diffusion.
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In FDM, as in other RP processes, the heating and rapid cooling cycles of the work materials will aggravate non-uniform thermal gradients and cause stress build-up that consequently results in part distortions and dimensional inaccuracy. Once the build process is completed, the FDM built part can be viewed as a laminate composite structure with anisotropic material properties. The mechanical properties of FDM parts are not only controlled by the build material, but also influenced by the selected fabrication parameters like printer settings, filament settings, print settings, properties of material, etc. In Fused Deposition Modeling process the main steps (fig. 4) taken to obtain the prototype are: CAD model design: in FDM process, like in all RP processes, the designer must create the 3D model of the part, starting from an existing model that have pass through a stage of optimization and requires changes, or can create a new model, for a new project.
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3D CAD/CAM and Rapid Prototyping applied for Malta Cross Mechanism fabrication
Figure 4 Fused Deposition Modeling main steps Convert CAD model into STL model: native CAD models are models with complex surfaces, large memory size and difficult to implement in an installation analysis of RP. Given this, the RP industry has developed the STL file format which transforms complex surfaces of 3D CAD model in plane triangular surfaces. In FDM process, the STL file is the most common interface between CAD and RP systems, and it is a description of the part to be performed through its component surfaces. Actually, the surface of 3D model is meshed with triangles, which share common sides and vertices. After obtaining the STL file, some parameters specific to the RP system are set for the machine control: Printer Settings, Filament Settings and Print Settings. (fig. 5) [9, 10]. The extrusion head is a compact subassembly, composed from the supply block with the deposition material, precisely controlled by PC, and the heating block, electronically controlled, which ensures the material melting (fig. 6). [1, 10]
Figure 6: Malta Cross Mechanism obtained through FDM process with aditional layer
Figure 7: The 3D model obtained through FDM process
4. Conclusions
Figure 5: Fused Deposition Modeling process Creating the prototype: the STL file created earlier is processed to divide the model into layers with a thickness below 0.4 mm usually (fig. 6). Post Processing: 3D model is removed from the working platform and is controlled by defects, cleared of excess material, paint, etc(fig. 7).
Rapid prototyping and CNC milling are different manufacturing techniques: one of them is an additive method, and the other one is a subtractive manufacturing method. Both of them use 3D CAD models and are layered fabrication techniques; machining is able to produce finer surfaces, more accurate and larger parts in a much wider variety of materials than RP processes. This is not nearly as automatic as with rapid prototyping (except on the simplest types of operations). Complex parts can take hours or days to program correctly. Further, the CAM programs themselves can be quite expensive. Contrary to the more complicated CAM programming and CNC machining, RP software and machines are generally simple and quick to use, resulting in significantly reduced fabrication time, needed to produce prototype parts. RP processes are generally quiet, non-dangerous
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3D CAD/CAM and Rapid Prototyping applied for Malta Cross Mechanism fabrication processes which can run in an office environment. This contrasts with machining, which generally needs a workshop or factory environment (noise, dust, liquids) and has a number of safety issues. Thus, the two types of technologies, additive and subtractive, continue to co-exist and be complementary in the 3D prototyping world. An intelligent user can choose which process will be best for a certain part, and even use both together. Acknowledgement: The work has been funded by the Sectoral Operational Programme Human Resources Development 2007-2013 of the Ministry of European Funds through the Financial Agreement POSDRU/159/1.5/S/132395 5. References [1] Amza Gh., s.a., Tratat de tehnologia materialelor, Editura Academiei Romane, Bucuresti, 2002.
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[2] Cosma S. Cosmin, Fabricarea implanturilor prin topire selectiva laser, Balneo-Research Journal, Vol.3, Nr.3, 2012 [3] Mircea M. Popovici, Modelarea virtuala 3D in constructia de masini, Editura Printech, Bucuresti, 2005. [4] Ionut. G. Ghionea, Catia V5, Aplicatii in ingineria mecanica, Editura Bren, Bucuresti, 2009. [5] Ionut. G. Ghionea, Proiectarea asistata in Catia V5, Elemente teoretice si aplicatii, Editura Bren, Bucuresti, 2007. [6] Besnea D., s.a., Tehnologii de fabricatie asistate de calculator pentru executia unor componente mecatronice, Editura Printech, Bucuresti, 2008. [7] Ciocirlea A., Paunescu R., Constantin V., Constantin M., Besnea D, Introducere in proiectarea asistata a structurilor mecanice, Editura Printech, Bucuresti, 2008 [8] E. Cerit & I. Lazoglu, A CAM-based path generation method for rapid prototyping applications, Int J Adv Manuf Technol (2011) 56:319–327 [9] 3D Systems Inc.- Thermojet Solid Object Printer User Guide [10] www.MakerBot.com
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