Fine piercing of micropatterns into metallic sheets has become an engineering issue in the stamping industries. Plasma nitriding-assisted printing was proposed as a solution for forming a microtextured surface on die materials. AISI420 die material was employed for this plasma printing. First, maskless patterning was used to print two dimensional micropatterns onto a mirror-polished AISI420 stainless steel surface. The unprinted surface area was selectively nitrided; the negative micropattern of the original prints changed to nitrogen supersaturated AISI420 areas. This die surface was dipped into 20% HCl solution for chemical etching. Since the nitrogen supersaturated areas had high corrosion resistance against this etching, only the printed parts were selectively etched, leaving a hardened AISI420 punch head after etching. These selective nitriding characteristics were demonstrated in experiments. A cylindrical punch array with a diameter of 50 mm was fabricated as a punch for piercing microtextures into thin AISI304 stainless steel sheets.
The effectiveness of the punching process to form the nano metric cutting edge of microtools was investigated in this study. To achieve improvement of tool wear and stability of shared surfaces. An argon ion irradiation beam for finishing the cutting edge of a micropunch of nanometric size was developed. Firstly, the cutting edge radius of the micropunch was decgreased from the micrometric to nanometric scale. Secondly, chipping of the WC-Co alloy at the cutting edge of the micropunch was decreased using on ion beam irradiation micropunch. Moreover, the shear droop length in the punched hole was decreased by using ion beam irradiation micropunch. Therefore, ion beam irradiation can effectively improve the cutting edge quality of a micropunch with no apparent damage.
Precision blanking processes suppress shear droop, fracture, and burr generation on a cut blank surface. However, as the blank size becomes extremely small, as in a microgear, the technology involved becomes extremely difficult. In the previous report1), the authors fabricated microgears by finish blanking and extrusion blanking, evaluated their cut surfaces, and confirmed the effectiveness/advantage of extrusion blanking. However, in the previous study, because of concerns about tool breakage due to punch and die interference, which is a problem of negative clearance processing, the extrusion process comprising two steps was stopped at 90 % of the plate thickness in the first step, and the remaining 10 % that was blanked in the second step became a fractured surface. Therefore, in this experiment, with the aim of preventing such fracture, extrusion processing was additionally carried out to the very limit of 99 % of the plate thickness where the punch and the die were almost in contact, and the plate was severed in the second step. Measurements of the constituent ratio of the whole cut surface, the geometry, and the surface roughness of the cut surface were performed. As a result, the fractured surface could be suppressed, and few burrs were observed.
A plasma-nitrided SKD11 punch-die pair was developed for the fine piercing process under nearly zero clearance. A high-density plasma-nitriding system was utilized to nitride the SKD11 punch to have a surface hardness of up to 1600 HV. The annealed SKD11 die substrate was shaved into a core die by accurate piercing with this nitrided punch. After the shaping and plasma nitriding of the shaved core die, both the punch and core die were placed into the cassette die set for piercing experiments under nearly zero clearance. Electromagnetic steel sheets with a thickness of 0.5 mm were prepared to describe the shearing behavior in piercing. The piercing load and stroke histories were measured with increasing number of shots. The engineering durability was also discussed to describe the wear of the punch and die. Fine piercing with smaller burr heights and fractured surface area ratios under the dry condition was put into practice using the plasma-nitrided punch and die-core set with rational compliance under nearly zero clearance.
Femtosecond laser machining was utilized to form the micro/nanotextures on mold material to transform a hydrophilic surface to a superhydrophobic one. The mold surface was segmented into unit cells by laser microtexturing; at the same time, each segment was nanotextured to have nanoscaled ripples by laser-induced periodic surface structuring (LIPSS). The micro/nano-textured SUS420 molds were hydrophobic with high contact angles and repellency. Each mold was fixed into a cassette die set for mold stamping of the phosphate glass specimens. The induction heating unit was utilized for this hot mold stamping at above the glass transition temperature. The static contact angle of the optical glass surface increased two fold from 56° to 114°.
A new microjoining system of plasma surface activation and intelligent heat induction processes has been developed. This microjoining process consisted of two steps. Eight stainless steel-sheets each with a thickness of 0.01 mm was surface activated by argon and hydrogen plasmas for 600 s. The passivated oxide film thickness was reduced by this surface activation. In the second step, the stack of eight stainless steel-sheets was accurately hot-stamped and joined into a mechanical element. The intelligent induction heating unit was utilized to accomplish uniform heating of the whole stack up to 1073 K for 60 seconds. Concurrent with heating, the stack was hot-stamped and held by 30 MPa for 1800 seconds. The miniature products and members such as a micropump were fabricated by this microjoining process as an alternative process that enables as to lower the joining temperature, shorten the duration time and to reduce the production cost for high qualification of metallic micropumps.