A diamond-like carbon (DLC) film, coated on an SKD11 (alloy tool steel) substrate, was shaped by plasma oxidation to form an assembly of DLC macro-pillars and to be used as a DLC-punch array that is micro-embossed into aluminum sheets. First, the SKD11 steel die substrate was prepared and DLC-coated to have a film thickness of 10 μm. This DLC coating worked as a punch material. The two-dimensional micro-patterns were printed onto this DLC film by maskless lithography. The unprinted DLC films were selectively removed by plasma oxidation to leave the three-dimensional DLC-punch array on the SKD11 substrate. Each DLC punch had a head of 3.5 μm × 3.5 μm and a height of 8 μm. This DLC-punch array was fixed into the cassette die set for a micro-embossing process using a table-top servo-stamper. Furthermore, through numerically controlled micro-embossing, an alignment of rectangular punches was transcribed into a micro-cavity array in the aluminum sheet. The single micro-cavity had a bottom surface of 3.2 μm × 3.2 μm and an average depth of 7.5 μm. A heat-transfer experiment in boiling water was also performed to investigate the effect of micro-cavity texture on bubbling behavior and the boiling curve.
The plasma oxidation printing (POP) was proposed as a digital manufacturing to shape the diamond-like carbon (DLC) thick film into a micronozzle on the tool steel substrate. Its head shape was first designed by computer-aided design (CAD) and printed onto DLC film by the maskless lithography. The unprinted DLC was removed in depth by the anisotropic etching. Fine circular nozzle with the inner diameter of 10 μm and the height of 10 μm was fabricated during the duration time of 3.6 ks. Different from the micromilling or the micro-electric discharging, the micronozzle geometry is directly fabricated from its CAD data. The micronozzle with the cross-star outlet was constructed without the change of processing procedure and without use of tooling.
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