This study investigates the effects of electro-discharge parameters on the surface integrity in small-hole drilling. Discharge current, pulse on-time and pulse off-time were chosen as variable parameters. The gap voltage, dielectric flushing pressure, electrode rotation, electrode polarity and capacitance were taken as constant. Material removal rate, surface roughness, average white layer thickness, overcut and taper were taken as outputs for this study. Experiments were performed on DIN 1.2080 (X210Cr12) cold working tool steel, and ∅2 mm single-hole brass electrodes were used. The experimental results indicate that a compromise solution is required in selection of the electrical discharge machining parameters (i.e. discharge current, pulse on-time and pulse off-time) to maintain machining stability (melting–evaporation and removal of debris). As the stability is maintained during the process, dimensional accuracy increases and a better finish can be obtained with a reasonable machining time.

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Large vehicles, ships, and airplanes are made of hybrid structures with a combination of metal and composite materials. Aluminum and fiber composites are widely used in the aerospace, automotive, and marine industries due to their high strength/weight ratios. In these industries, adhesive joints are preferred as the primary method of forming structural joints. Although the use of adhesives in a combination with different materials provides many advantages over mechanical methods, efforts are being made to increase the strength of the adhesive connection. In this study, three different nanoparticles such as nanosilica, nanoclay, and multiwalled carbon nanotubes (MWCNTs) were added to a commercial epoxy adhesive (Araldite 2014), and the shear strengths of singlelap joints made of aluminum and glass fiber reinforced polymer composite were investigated. According to the experimental results, adding nanoparticles increased the strength of the bonded joints. The best increase was determined as 62% for the connection with 0.5 wt% MWCNTs added. On the other hand, the improvement in the bond with 1.5 wt% nanoclay was found to be 37.8%, while the improvement in the bond with 1.5% nanosilica was 43.3%. Failure types of samples after the mechanical tests were analyzed by taking macro and scanning electron microscopy images from the overlap sides.

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