This study proposes a new manufacturing technology to innovate traditional research approaches regarding bolting. Three bolts composed of different manufacturing materials—aluminum alloy (AA), die steel (DS) and stainless steel (SS)—are successfully 3D printed, and the desired geometric profile is achieved with high precision. Prior to printing, the digital file of the prototype (PT) bolt is obtained by a 3D laser scanning system, which is then processed to be recognizable to a 3D printer. Afterwards, mechanical tensile tests and digital image correlation (DIC) tests are carried out. The mechanical testing results indicate that the AA bolt has a relatively low strength, whereas the ultimate strength and stiffness of the DS bolt and SS bolt are greater than those of the PT bolt. It is worth highlighting that the peak strength of the DS bolt is approximately twice that of the PT bolt; thus, the advantage of the DS bolt is emphasized.
3D printing is an additive manufacturing measure and this method is a revolutionary technology that is can very likely change our cognition in terms of manufacturing. In 3D printing, products are built through a layer-by-layer, bottom-up method; this seemingly small distinction—adding material rather than subtracting material-means everything (Campbell et al. 2011). The use of 3D printing presents a plethora of advantages, such as eliminating assembly lines, enabling complex geometries, shorter development time, manufacturing labor reduction, increased product customization, and decreased energy consumption.
In terms of bolt printing, however, limited research exists. In 2018, Song et al. printed a tunnel model containing 3D printed lining and rock bolts to investigate the influencing mechanism of faults near tunnels. Nevertheless, the lining model and rock bolts model were printed by an FDM printer with PLA material (Song et al. 2018), which could not accurately reflect the real bolt or lining from the geometry or mechanical perspectives. To the best of the authors knowledge, no scholars have previously carried out research related to the manufacturing of bolts via 3D printing. In the neighboring field of metal manufacturing and processing, many metallic materials have been investigated for feasibility in 3D printing (Martin et al. 2017; Ngo et al. 2018), and it is believed that this type of procedure can greatly shorten the trial and error time when designing a metal workpiece. The existing literature has proven that 3D printed metal components have finer microstructures than traditionally manufactured parts, and most importantly, the yield and ultimate strengths can also be improved via 3D printing (Herzog et al. 2006). The technique for metal parts manufactured by 3D printing is already mature, and this methodology can assist relevant studies of bolt support in underground space engineering.