Keywords

1 Introduction

In abrasive water jet machining, kerf top width and taper angle were influenced by the parameters such as transverse speed, standoff distance and mass flow rate [1]. The standoff distance has a predominant influence on the workpiece quality, and also the RMS and ACS values are lower when machining lower thickness workpiece [2]. In order to evaluate the Ra on the machined surface of MMC, increased in Ra value was observed due to increase in water jet pressure [3]. In the cases of slot cutting and piercing in MMC, the kerf taper will increase with increase in transfer rate and particle size but in the case of piercing kerf taper increases with increase in standoff distance [4]. On varying the abrasive mass flow rate, abrasive mesh size and jet impact angles on MMC found that erosion rate increases with increase in jet impact angles [5]. In machining of MMC, the depth of cut is higher when the mesh size is lesser due to lesser kinetic energy of the smaller size aggregate [6]. The machining aspects of MMCs were carried out in various non-conventional machining processes such as EDM, laser cutting and AWJM; in AWJM the mechanism of material removal was observed as ductile shearing and also there were no thermal damage and burr formation in the AWJM [7]. The process parameters of AWJM greatly influence its machining performance. It is widely classified into four types, namely [8] abrasive parameters: abrasive mass flow rate, abrasive size distribution, abrasive particle shape, diameter and hardness, etc.; [9] cutting parameters: standoff distance, impact angle, number of passes, traverse rate, etc.; mixing chamber and acceleration parameters: focusing nozzle length, focusing nozzle inside diameter, etc., and [10,11,12] hydraulic parameters: water flow rate, pump pressure, orifice diameter, etc. Each of these parameters has been investigated by several researchers using experimental trials and their optimum values have been found. These values become indispensable when one advances toward condition monitoring [13]. For any process to be completely automated and monitored, an in-depth understanding of the interaction between the machine, workpiece and tool is required. Hence, condition monitoring of AWJM is of primary importance for full automation. Condition monitoring is the continuous/periodic verification of few or all parameters of the system. It is usual to make sure that all system components are performing in close agreement to the optimum level or as a fault detection system [14, 15]. A comprehensive review on major research activity carried out so far by several researchers on condition monitoring of AWJM is also discussed here.

2 Experiment Details

2.1 MMC Casting Procedures

An electric furnace is used for preheating the reinforcements, and electric resistance furnace is used for melting the matrix material. MMCs are made by liquid-state stir casing process. The stir casting furnace is used for preheating the reinforcement of Si at the temperature of 700 °C. The trapezoid-shaped die is used for preparing the workpieces. The size of the workpieces is 10 mm diameter rods. Casted component (Al7074 alloy with 10% of SiC) is a poured in trapezoid-shaped die.

2.2 Microstructure

To study the microstructure of the specimens, they were cut and prepared as per the standard metallographic procedure. The specimen plates were prepared by grinding through 600 mesh size grit abrasives. Velvet cloth was polished by using 240, 400, 600 and 1000 mesh size to get the fine surface finish. After that specimens were further polished by using Nital reagent (etched). All these specimens were kept in dry air. The microstructure etched specimens were observed using optical microscope. The presence of SiC in the composites materials has been identified using microscope images captured with (Dewinter Metallurgical Microscope). It is observed from Fig. 1 the uniform distribution of SiC particles. This can be attributed to the effective stirring action and the use of appropriate process parameter.

Fig. 1
figure 1

Optical micrographs of MMCS

Full size image

2.3 Response Surface Methodology (RSM)

In this technique, the main objective is to optimize the response surface that is influenced by various process parameters. RSM also quantifies the relationship between the controllable input parameters and the obtained response surfaces.

If all variables are assumed to be measurable, the response surface can be expressed as follows:

$$Y = \, f\left( {X_{1} ,X_{2} , \ldots ,X_{n} } \right)$$

where

Y is the answer of the system and is the variable of action called factors.

The goal is to optimize the response variable y. In this work, the response y is MRR and Ra.

2.4 Box–Behnken Design

In this study, the Box–Behnken experimental design was chosen for finding out optimized WEDT parameters and regression equations which gives the relationship between the response functions (MRR and Ra) and variables pulse on time, voltage, spindle speed and pulse off time. Box–Behnken design is rotatable second-order designs based on three-level fractional factorial designs. The geometry of a Box–Behnken design is shown in Fig. 2.

Fig. 2
figure 2

Box–Behnken design

Full size image

Reason for the selection of Box–Behnken design over central composite design is for fewer no. of input factors (here four) and lesser no. of experiments are required than central composite design.

2.5 Level Input Parameter Using RSM

See Tables 1 and 2.

Table 1 AWJM input parameters
Full size table
Table 2 Observation results
Full size table

3 Result and Discussion

See Table 3.

Table 3 Box–Benkhen L29 I/O parameter
Full size table

3.1 Response Surface Methodology

See Fig. 3.

Fig. 3
figure 3

Response surface of MRR (Al 7075 + 10% SiC) for various combinations

Full size image

3.2 Analysis of MRR for Al 7075 + 10% SiC

Table 3 (S. No. 1–9) indicates that MRR values are achieved by varying abrasive mesh size (#80–#120) and abrasive flow rate (240–440 g/min), while water jet pressure and traverse rate are varied at different levels of combinations. Among the combinations, it is observed that high water jet pressure and low traverse rate result in high MRR of 647 mm3/min. From the analysis (Table 3, S. No. 1–54 and Fig. 4), it is observed that the combinations of input process parameter and their levels such as low abrasive mesh size, high abrasive flow rate, high water jet pressure and low traverse rate result in high MRR( 648 mm3/min) for Al 7075 + 10% SiC. It is observed that higher MRR is achieved with size (#80) and lower MRR is achieved with size (#120). Due to the fact that smaller size of abrasive is likely to possess lesser kinetic energy than resulting in lower MRR, higher size of abrasive is likely to possess higher kinetic energy than resulting in higher MRR.

Table 4 Analysis of variance table for MRR (Al 7075 + SiC 10%)
Full size table
Fig. 4
figure 4

Response surface of DoC (Al 7075 + 10% SiC) for various combinations

Full size image

The relationship between the input process parameter and the response (MRR) for MMC is expressed in the form of regression equation, and it is given below.

$$\begin{aligned} & {\text{MRR Al 7}}0{\text{75}} + {\text{1}}0\% {\text{ SiC}} = + {\text{3977}}.{\text{58}} - \left( {{\text{28}}.00*{\text{MS}}} \right) - \left( {{\text{5}}.{\text{43}}*{\text{AFR}}} \right) \\ & \quad + \left( {{\text{4}}.{\text{98}}*{\text{WP}}} \right) - \left( {{\text{24}}.{\text{21}}*{\text{TR}}} \right) - \left( {{\text{8}}.{\text{14E}} - 00{\text{3}}*{\text{MS}}*{\text{AFR}}} \right) \\ & \quad - \left( {0.0{\text{3}}0*{\text{MS}}*{\text{WP}}} \right) + \left( {0.{\text{25}}*{\text{MS}}*{\text{TR}}} \right) + \left( {{\text{8}}.{\text{25E}} - 00{\text{4}}*{\text{AFR}}*{\text{WP}}} \right) \\ & \quad + \left( {0.0{\text{31}}*{\text{AFR}}*{\text{TR}}} \right) + \left( {0.0{\text{25}}*{\text{WP}}*{\text{TR}}} \right) - \left( {0.0{\text{15}}*{\text{MS2}}} \right) \\ & \quad + \left( {{\text{3}}.{\text{42E}} - 00{\text{3}}*{\text{AFR2}}} \right) - \left( {0.0{\text{15}}*{\text{WP2}}} \right) - (0.0{\text{79}}*{\text{TR2}}) \\ \end{aligned}$$

3.3 Analysis of DoC for Al 7075 + 10%SiC

Table 5 (S. No. 1–9) indicates that DOC values are achieved by varying abrasive mesh size (#80–#120) and abrasive flow rate (240–440 g/min), while water jet pressure and traverse rate are varied at different levels of combinations. Among the combinations, it is observed that high water jet pressure and low traverse rate result in high DOC of 29 mm (Table 3 S. No. 3). Due to the fact that smaller size of abrasive is likely to possess lesser kinetic energy than resulting in lower DOC, higher size of abrasive is likely to possess higher kinetic energy than resulting in higher DOC. Similarly, it is observed that increased water jet pressure and decreased traverse rate lead to increased DOC and further observed that increases in abrasive flow rate and abrasive particle size result in higher DOC.

Table 5 Analysis of variance table for DoC (Al 7075 + SiC 10%)
Full size table

3.4 Analysis of Surface Roughness for Al 7075 + 10% SiC

Table 6 (S. No. 1–9) indicates that fine surface finish values are achieved by varying abrasive mesh size (#80 – #120) and abrasive flow rate (240–440 g/min. From the analysis (Table6, S. No. 1–54 and Fig. 5), it is observed that the combinations of input process parameter and their levels such as low abrasive mesh size, high abrasive flow rate, high water jet pressure and low traverse rate result in better surface finish (2.1 µm) for Al 7075 + 10% SiC. Due to the fact that smaller size of abrasive is likely to possess lesser kinetic energy than resulting in better Surface finish, higher size of abrasive is likely to possess higher kinetic energy than resulting in better surface finish. Similarly, it is observed that increased water jet pressure and decreased traverse rate lead to better surface finish, and further observed that increases in abrasive flow rate and abrasive particle size result in better Surface finish.

Table 6 Analysis of variance table for surface roughness
Full size table
Fig. 5
figure 5

Response surface of surface roughness (Al 7075 + 10% SiC) for various combinations

Full size image

4 Conclusion

In this present work, an attempt is made to investigate the material removal rate, depth of cut and surface roughness of AWJM, for various input parameters. In this study, aluminum alloy (AL7075) is reinforced with 10% SiC by using stir casting process. The experiments are conducted using RSM with Box–Behnken design. The signification AWJM process parameters and their levels are identified for achieving higher MRR, DoC and fine surface roughness. This investigation revealed the choice of #80 mesh size garnet for achieving the higher MRR of AWJM in Al7075 + SiC. MMCs can depend on the size of SiC particulate in MMCs. Hence, the combinations of input process parameter and their levels are recommended for higher MRR from the analysis of optimal value that are abrasive mesh size (#80), abrasive flow rate (440 g/min), water jet pressure (275 MPa) and traverse rate (60 mm/min), and the minimum MRR can be achieved by high abrasive mesh size (#120), abrasive flow rate (240 g/min), water jet pressure (125 MPa) and traverse rate (120 mm/min). Similarly, higher DoC is achieved with size (#80) and lower DoC is achieved with size (#120). Due to the fact that smaller size of abrasive is likely to possess lesser kinetic energy than resulting in lower DoC, higher size of abrasive is likely to possess higher kinetic energy than resulting in higher DoC. Similarly, it is observed that increased water jet pressure and decreased traverse rate lead to increase DoC, and further observed that increases in abrasive flow rate and abrasive particle size (µm) result in higher DoC. It is observed that better surface finish is achieved with size (#80), and rough surface finish is achieved with size (#120). Due to the fact that smaller size of abrasive is likely to possess lesser kinetic energy than resulting in better surface finish, higher size of abrasive is likely to possess higher kinetic energy than resulting in better surface finish. Similarly, it is observed that increased water jet pressure and decreased traverse rate lead to better surface finish, and further observed that increases in abrasive flow rate and abrasive particle size result in better surface finish.