Multi-Criterion Decision Method for Roughness Optimization of Fused Deposition Modelled Parts

Multi-Criterion Decision Method for Roughness Optimization of Fused Deposition Modelled Parts

Azhar Equbal (RTC Institute of Technology, India), Md. Asif Equbal (Cambridge Institute of Technology, India), Md. Israr Equbal (J. B. Institute of Engineering and Technology, India) and Anoop Kumar Sood (National Institute of Foundry and Forge Technology, India)
DOI: 10.4018/978-1-5225-9167-2.ch012

Abstract

Fused deposition modelling is an extrusion-based automated fabrication process for making 3D physical objects from part digital information. The process offers distinct advantages, but the quality of part lacks in surface finish when compared with other liquid or powder based additive manufacturing processes. Considering the important factors affecting the part quality, the chapter attempted to optimize the raster angle, air gap, and raster width to minimize overall part roughness. Experiments are designed using face-centered central composite design and analysis of variance provides the effects of processing parameters on roughness of part. Suitability of developed model is tested using Anderson-darling normality test. Desirability method propose that roughness of different part faces are affected differently with chosen parameters, and thus, hybrid approach of WPCA based TOPSIS is used to break the correlation between part faces and reduce the overall part roughness. Optimizing shows that lower raster angle, lower air gap, and larger raster width minimizes overall part roughness.
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Introduction

Additive manufacturing (AM) is a layer based automated fabrication process for making scaled three dimensional physical objects directly from 3D-CAD (computer aided design) data (Equbal et al., 2015). The part is fabricated by depositing the part material in a layerwise deposition principle following bottom up approach even in an office friendly environment (Mohamed et al., 2016). AM processes have the ability to produce any complex geometry of part in a less time span without any specific tooling. As per ASTM F2792-12a, AM processes are categorized into seven different categories (ASTM Designation, 2012). Fused deposition modelling (FDM) is an extrusion-based AM process that construct the 3D object directly from its part digital information. The part material is used in the form of strand or filament which is heated in a liquifier to semi-molten state before extruding it through a nozzle onto a table or a plateform provided in a bulid chamber. While depositing the material on plateform, the nozzle moves in three different axes thus creating a cross section of three-dimensional object (Sood et al., 2009). The material on deposition gets cools, hardens and bonds to the layer beneath it. Based on the layer thickness used the process is repeated up to the last layer. The different parts materials used for fabrication are ABS (acrylonitrile butadiene styrene), PC (polycarbonate), ABSi (high impact grade of ABS) and PC-ABS. The process also uses water works soluble support for ABS, ABSi and PC-ABS and breakaway support for PC and PC-ISO (BASSTM). Support material use can be easily breakaway by hand. It can build part in three different layer thicknesses that are 0.127mm, 0.178mm and 0.254mm. Process chain of part fabrication is as follows:

  • Step 1: 3D CAD model of part is made using any suitable CAD software.

  • Step 2: CAD model is converted into STL file format.

  • Step 3: Different processing parameters for part building and location of support structure is decided. The data generated is then changed to SML (Stratasys machine language) format and sent to hardware of FDM for part fabrication.

  • Step 4: Part is fabricated by layerwise deposition of materials in the build chamber.

  • Step 5: Once the part build is finished, it is taken out from the chamber and support material is removed by hand or some time by vibrations generated in ultrasonic bath.

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