Parametric appraisal of mechanical property of fused deposition modelling processed parts
Introduction
Reduction of product development cycle time is a major concern in industries to remain competitive in the marketplace and hence, focus has shifted from traditional product development methodology to rapid fabrication techniques like rapid prototyping (RP) [1]. The RP process is capable of building parts of any complicated geometry in least possible time without incurring extra cost due of absence of tooling [2], [3]. Another advantage with RP is to produce functional assemblies by consolidating sub assemblies into single unit at the computer aided design (CAD) stage and thus reduces part counts, handling time, and storage requirement and avoids mating and fit problem [4], [5]. Although RP is an efficient technology, full scale application has not gained much emphasis because of compatibility of presently available materials with RP technologies [6], [7]. To overcome this limitation, one approach may be development of new materials having superior characteristics than conventional materials and its compatibility with technology. Another convenient approach may be suitably adjusting the process parameters during fabrication stage so that properties may improve. A good number of researchers have devoted towards the second approach [8], [9], [10]. Literature reveals that properties of RP parts are function of various process related parameters and can be significantly improved with proper adjustment. Since mechanical properties are important for functional parts, it is absolutely essential to study influence of various process parameters on mechanical properties so that improvement can be made through selection of best settings. The present study focus on assessment of mechanical properties viz. tensile, flexural and impact strength of part fabricated using fused deposition modelling (FDM) technology. As the relation between mechanical property and process parameters is difficult to establish, attempt has been made to derive the empirical model between the processing parameters and mechanical properties using response surface methodology. In addition, effect of each process parameter on mechanical property is analysed. In actual practice, the parts are subjected to various types of loadings and it is necessary that the fabricated part must withhold more than one mechanical property simultaneously. To address this issue, a desirability function approach has been adopted to optimize more than one response at a time.
Section snippets
Literature review
A study made by Es Said et al. [11] shows that raster orientation causes alignment of polymer molecules along the direction of deposition during fabrication and tensile, flexural and impact strength depends on orientation. Since semi-molten filament is extruded from nozzle tip and solidified in a chamber maintained at certain temperature, change of phase is likely to occur. As a result volumetric shrinkage takes place resulting in weak interlayer bonding and high porosity; hence, reduces load
Experimental plan
Fused deposition modelling (FDM) by Stratasys Inc., USA is one of the rapid prototyping (RP) processes that build part of any geometry by sequential deposition of material on a layer by layer basis. Unlike other RP systems which involve an array of lasers, powders, and resins, this process uses heated thermoplastic filaments which are extruded from the tip of nozzle in a prescribed manner in a semi molten state and solidify at chamber temperature. Strength of FDM processed component primarily
Experimental procedure
Tensile strength at break is determined according to ISO R527:1966 (Plastics: Determination of Tensile Properties). Fig. 1a shows the shape and dimensions of test specimen. Flexural strength at yield is determined as per ISO R178:1975 (Plastics – Determination of Flexural Properties of Rigid Plastics) standard for the specimen shown in Fig. 1b. Three point bending test is used for flexural strength determination. The specimen is supported by two supports and loaded in the middle by force until
Analysis of experiments
Analysis of the experimental data obtained from FCCCD design runs is done on MINITAB R14 software using full quadratic response surface model as given bywhere y is the response, xi is ith factor, k is total number of factors.
For significance check F value given in ANOVA table is used. Probability of F value greater than calculated F value due to noise is indicated by p value. If p value is less than 0.05, significance of corresponding term is established.
Discussions
Response surface plots for interaction terms are given in Fig. 3, Fig. 7, Fig. 10 for TS, FS and IS, respectively.
Optimization of process parameters
Above discussion shows that FDM process involves large number of conflicting factors and complex part building phenomena making it difficult to predict the output characteristics based on simple analysis of factor variation. Hence, to determine the optimal setting of process parameters that will maximize the tensile strength, flexural strength and impact strength, respectively, desirability function (DF) given by Eq. (7) is used.where di is the desirability defined for the i
Conclusions
Functional relationship between process parameters and strength (tensile, flexural and impact) were determined using response surface methodology. The process parameters considered are layer thickness, orientation, raster angle, raster width and air gap. The response surface plots involving interaction terms are studied and the reasons behind the observed response can be summarized as follows.
- 1.
Number of layers in a part depends upon the layer thickness and part orientation. If number of layers
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