Introduction

As a matter of fact, the new market realities require faster product development and reduced time to meet market demands (like: higher quality, greater efficiencies, cost reductions and an ability to meet environmental and recycling objectives) [1–3]. To reduce the product development time and cost of manufacturing, new technology of rapid prototyping (RP) has been developed [2]. Fused deposition modelling (FDM) is one of the RP technology which works on an “additive” principle where material in form of layers is extruded out of nozzle tip [3]. A plastic filament or metal wire is unwound from a coil and material is supplied to an extrusion nozzle [4]. Presently FDM fabricate parts are used for design verification, form and fit checking and patterns for casting processes and medicine application [5]. New materials for FDM are needed to increase its application domain especially in RT and rapid manufacturing (RM) areas [5]. A key requirement for any material to be used in FDM is compatibility of material with existing FDM setup without changing functional hardware/software of machine. Apart from compatibility, mechanical properties of material are also important to explore its industrial applications [6]. The development of alternative materials considering polymer, plastic, metal and composite made it a tough job as requirements of feed stock filament as well as FDM machine are very specific [7]. The literature review reveals that very less has been reported on development of feedstock filament other than ABS for FDM [5–8]. In previous reported studies feedstock filament was developed using iron powder and ABS powder in proportion of 10 % iron powder and 90 % ABS powder by volume with an aim to improve mechanical and thermal properties of filament wire [5]. Whereas, in another development process metal–polymer elements were chosen in varying volume fractions of metal powder as 5, 10, 20, 30 and 40 % for producing appropriate feed stock filament for FDM [6]. The results of these studies highlights that iron and copper powders as short fibre fillers were used because of good mechanical and thermal properties, as well as their capabilities of mixing and surface bonding with polymers [4]. Twin-screw extruder, with a screw diameter of 34 mm and L:D ratio of 34 and single screw extruder with a screw diameter of 30 mm and length of 800 mm were used to develop FDM filament (The diameter of the filament was controlled to fall in the range of 1.75–1.90 mm). Some studies highlighted that glass fibres were used to significantly improve the strength of an ABS filament at the expense of reduced flexibility and handle-ability [7].

Almost all reported literature highlights metal based composites with ABS combination that has been suggested for FDM feedstock filament [5–10] and no alternative to ABS has been explored in detail. The present research paper presents the development of nylon based wire as alternative of ABS material and composite material Al2O3 as matrix reinforcement for filament of FDM. The aim is to develop the new composite with desirable mechanical properties for RT applications and to study properties like tensile strength and percentage elongation of the wire formed.

Experimentation

In any development work, the most important task is to obtain maximum realistic information with the minimum number of well-designed experiments and factors affecting output of process, which must be optimised using Design of Experiments (DoE). Taguchi L9 OA has been used to design final control log of experimentation for the present study. Development of FDM feedstock filament wire has been carried out on single screw extruder as shown in Fig. 1.

Fig. 1
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Schematic of single screw extruder machine

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In the present research work, pilot experimentation, as shown in Table 1, has been conducted with an aim of selection of optimum input levels and nylon–Al2O3 used in granular form. Nylon granules (as shown in Fig. 2) was mixed with varying proportion of Al2O3 and then processed on extruder machine under controlled processing parameters. Based on pilot experimentations, levels of input parameters as shown in Table 2 were selected and mechanical properties were optimized.

Table 1 Results of pilot experimentation
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Fig. 2
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Nylon granules

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Table 2 Input parameters
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A total of 27 experiments were conducted and each experiment was conducted thrice under unchanged input levels to reduce experimental error. The control log of experimentation is given in Table 3. Figure 3 shows the finally developed wire. Mechanical tests were performed on the developed wire and compared with standard ABS wire supplied by manufacturer (OEM) thereafter.

Table 3 Control log of experimentation
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Fig. 3
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Developed wire

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Results and Discussion

The results obtained by final experimentation were analyzed by using signal to noise (S/N) ratio analysis. Results obtained from standard ABS wire are given in Table 4. All tests were conducted on universal tensile testing machine under controlled environment as per ASTM-D638 standard.

Table 4 Standard ABS wire average results
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Tensile Strength

Observations from experiments conducted are shown in Table 5, whereas Fig. 4a–c shows the variation of S/N ratio and tensile strength with respect to barrel temperature, screw head speed and percentage proportion of Al2O3 in nylon. Table 6 shows the S/N response for tensile strength. From Table 5, it was observed that the strength of developed wire was uniformly obtained at different positions of a long wire due to homogeneous mixing of alumina with nylon.

Table 5 Tensile strength results
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Fig. 4
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Variation of S/N ratio and tensile strength w. r. t. a barrel temperature, b screw head speed and c vol. proportion (%) of Al2O3 in nylon

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Table 6 S/N response to tensile strength data
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Percentage Elongation

Table 7 shows the results for elongation and Fig. 5a–c show the variation of S/N ratio and percentage elongation with respect to input variables, whereas, Table 8 shows the S/N response to percentage elongation data.

Table 7 Percentage elongation results
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Fig. 5
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Variation of S/N ratio and percentage elongation w. r. t. a barrel temperature, b screw head speed and c vol. proportion (%) of Al2O3 in nylon

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Table 8 S/N response to percentage elongation data
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The percentage contribution of different process variables in tensile strength and percentage elongation are represented by 3D Pie charts in Fig. 6. These results are valid for 95 % confidence level. It should be noted that in commercially used FDM machines, the operation cost is around 2.74 × 105 US$/m3 with ABS filament. The major part of this cost is attributed to patented ABS wire material. With this new development of nylon based filament, this cost is reduced to 0.7506 × 105 US$/m3 with flexibility of improved/controlled mechanical properties for tailor made RT/RM applications.

Fig. 6
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Pie charts showing percentage contribution of various parameters a tensile strength and b percentage elongation

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Conclusions

The outcome of present research work outlines the possibilities of alternative feedstock filament of FDM. However, precise control is required at each level of development process inclusive of testing. The flexible filaments of the new material have been successfully produced and processed in the existing FDM setup. Mechanical properties like tensile strength and percentage elongation has been increased significantly. The main conclusions are summarized as follows:

  1. 1.

    Nylon based feed stock filament for FDM machine has been developed and composite material provide good mechanical properties as compared to the conventional filament used.

  2. 2.

    It has been observed that tensile strength was maximum when, 5 % proportion of Al2O3 is mixed in nylon, barrel temperature being kept at 180 °C and screw head speed being 35 rpm. Similarly, in case of percentage elongation, optimized settings are at barrel temperature of 180 °C, screw head speed of 30 rpm and Al2O3 proportion 5 %.

  3. 3.

    Percentage contribution of different input parameters for tensile strength is: barrel temperature-56.34 %, screw head speed-24.52 % and Al2O3 proportion-2.22 %. In case of percentage elongation, contribution of different input parameters is: barrel temperature-53.88 %, screw head speed-25.72 % and Al2O3 proportion-6.92 %.