Literature review
2.2 Influence of wire electrode on machining precision and product quality
There have been numerous efforts to improve the product quality and geometrical accuracy of WEDMed components by optimizing the process conditions (Gupta and Jain (2014b), Gupta and Jain (2014b), Puri and Deshpande (2006)). The wire electrode also plays a significant role in deciding the surface quality and geometrical precision of the machined products. The influence of wire electrode and various other processing parameters on
cryogenically treated Ti-6Al-4V alloy material was investigated (Khan et al. (2019)).
Pramanik and Basak (2019) observed that higher values of wire tension reduced the fatigue life of WEDMed Ti-6Al-4V alloy and then remained almost constant with a further rise of wire tension. Microstructural characterization of machined workpiece surfaces concluded that wire electrode material diffused into the workpiece, covering almost 90% of the surface with approximately 10-20 µm of melted material thickness (Mouralova et al. (2018)).
Unstable machining conditions like high discharge energy, narrow interelectrode gap, and low pulse off-time caused higher contamination of workpiece surface with wire electrode material (Abhilash and Chakradhar (2020a)). Mouralova et al. (2020) made an extensive study on the WEDM of pure molybdenum material and performed defect analysis on the surface and sub-surface layers, morphological characterization, and percentage diffusion of electrode material on the machined surface. Silver-coated brass wire showed better performance in terms of reduced surface roughness (Ra) and minimum wire damage as compared to the conventional brass wire electrode during WEDM of Maraging steel 300 (Sen et al. (2018)).
Several authors have worked to determine optimized wire parameters viz. wire speed, wire tension, wire feed rate on a wide range of materials to achieve favourable machining output without wire breakage (Manjaiah et al. (2014), Owhal et al. (2020)). The vibration of the wire tool is also affected by these wire parameters, which determines the quality and precision of the produced parts (Tang et al. (2019)). Wire tension strongly influences workpiece Ra, MRR, and microhardness of the workpiece but no significant effect on the kerf width of stainless steel material (Chaudhary et al. (2019)). An increased value of wire tension minimizes the corner errors of the workpiece; however very large values of wire tension produced larger angles than desired. The effect of wire tension on the geometrical accuracy of the final component is also dependant on the workpiece thickness (Kirwin et al.
(2018)). Banu et al. (2020) employed the one factor at a time (OFAT) approach and design of experiment (DOE) approach for dry micro WEDM operation of SS304 stainless steel and concluded that the wire tension, wire feed, and wire velocity should be kept at an optimized constant value to achieve stable machining without wire ruptures. Increasing wire feed plays a significant role in minimizing geometrical inaccuracies and improving the product surface quality (Gupta and Jain (2014)). On the contrary, it was noted that comparatively lower
values of wire feed rate provided better precision accuracy for thinner workpieces (Kirwin et al. (2018)). A decreasing value of wire feed rate also reduces the spark gap value during WEDM operation (Deshmukh et al. (2019)). Qu et al. (2002) evaluated the effects of wire feed rate and rotational speed to obtain the best surface finish and roundness during cylindrical WEDM process. A particle swarm optimization algorithm was developed to demonstrate the role of wire tension and wire feed rate on the wire wear ratio (Nain et al.
(2018a)). It was further found that pulse on-time accelerated the rate of wire erosion during machining. Wire speed plays a very strong role in determining the kerf width (KW) and workpiece Ra of WEDMed components (Sneha et al. (2018)). A wire offset in the range of 0.169–0.173 mm, could further enhance the geometrical precision of the machined components (Farooq et al. (2020)). An effective wire radius compensation methodology was developed to determine the wire location for accurate and precise machining (Lin and Liao (2009)).
The information presented in this section highlights the importance of wire parameters on the machining output. The untimely failure of the wire tool disrupts the machining efficiency and productivity. Thus, the prediction and prevention of wire rupture is a potential research area and needs proper study. The following sections review various methodologies developed to prohibit the occurrence of wire failure and maintain the machining precision of the products.
Observations
The wire electrode is a small but essential element of the WEDM machine. Researchers worldwide have carried out detailed analysis on the influence of wire parameters like wire tension, wire feed, wire geometry and wire material on the machining efficiency and productivity. High values of wire tension minimized the corner errors in the machined components. Studies reported that the role of wire feed on geometrical accuracy and surface quality of the final products depends on the workpiece thickness. Wire speed plays a significant role in determining the extent of erosion undergone by the wire electrode. Sharp temperature gradients generated during the discharge phenomenon cause wire erosion, which degrades the wire strength and diminishes the product quality. Thus, optimal combination of the wire parameters viz. wire tension, wire feed, wire speed needs to be maintained to obtain
the desired machining output without wire breakage. A scant literature is available on the detrimental influence of wire wear on product precision and quality. The damages undergone by the wire tool need to be minimized in order to achieve sustainable and efficient machining.