Friction drilling solves the problem of screw connections at thin-wall thicknesses and replaces the welding nuts or attaching rivet nuts. The produced bushing and collar ( L b) are 2 to 4 times the workpiece wall thickness ( t), thus increasing the effective thread length and joint strength of the tapped joint. All work material from the hole contributes to forming the collar and the bushing. As the friction drill penetrates and pushes the material, some of the extruded material forms a collar around the upper surface of the workpiece, and the rest forms a bushing in the lower surface of the workpiece, as illustrated in Fig. This leads to a temperature rise of about half and two-thirds of the melting temperature of the work material, causing a decrease in the yielding point and softening of the work material, hence facilitating the plastic deformation to form the bushing. The friction drilling process depends on the heat generated from the friction force between the rotating conical tool and the workpiece. These characteristics make stainless steels hard to machine, and friction drilling offers in this case the solution.įriction drilling is distinguished by being dry and clean without applying coolant or generating chips (chip-less process). Materials like stainless steels are characterized by high toughness, low thermal conductivity, and high work-hardening coefficient. Graphical abstractįriction drilling is a novel, promising hole-making process compared to cutting or conventional hole-making processes. The longer effective thread length of the formed thread realized higher strength values than the cut thread. The elevated temperature associated with high plastic deformation during the processes resulting in fine grains with high hardness values were observed at the heat-affected zone. By comparing the performance of the three tools, it was noticeable that the friction drill Ø7.3 realized better results in terms of mean hole diametral oversize and mean cylindricity error. The analysis of variance (ANOVA) showed that the t/ d ratio was the most significant factor affecting the mean cylindricity error and the collar height. The effects of the ratio of workpiece thickness ( t) to tool diameter ( d T), rotational speed ( N), and feed speed ( f) on the hole diametral oversize ( U), cylindricity error, and collar height were studied. Tungsten carbide friction drills with diameters (Ø9.2, Ø7.3, and Ø4.5 mm) were used to perform the experiments. The experiments were conducted on difficult-to-cut material AISI 304 stainless steel workpieces with (2 and 3 mm) wall thicknesses. Finally, a tension test was performed to compare the performance of the form tapped thread with the conventionally cut thread. Due to lack of research related to the hardness macro- and microstructure of formed threads, experiments were conducted to investigate these important issues. The main purpose of this research paper is to improve the quality of the friction-drilled holes and formed thread by investigating the influence of the input working parameters that have not been investigated yet on the quality of the produced bores.
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