**4. CNC-imprinting of textures to metals, polymers, and glasses**

Both the DLC-coating die and the nitrogen supersaturated mold were utilized for CNC-imprinting the mother micro−/nano-textures on the dies into various work materials. The DLC-die was utilized in the cold and warm CNC-imprinting processes. The nitrogen supersaturated AISI420 mold was used in the hot CNC-imprinting process.

**CNC-imprinting of textures to aluminum alloy.** The CNC stamping system in **Figure 7** was utilized to imprint the star-shaped texture on the DLC-coating die onto the AA1060 aluminum alloy plate with the thickness of 1 mm and the as-rolled surface roughness. **Figure 14a** shows a star-shaped replica that is imprinted onto the aluminum plate by coining the micro-textured DLC punch. The original star-shaped emblem in **Figure 10** corresponds to the imprinted replica in **Figure 14a** in the mirrorinverse reflection. In parallel with the geometric imprinting from the microtextures

*Femtosecond Laser Micro-/Nano-Texturing to Die Substrates for Fine Imprinting to Products DOI: http://dx.doi.org/10.5772/intechopen.105795*

### **Figure 14.**

*Micro−/nano-textured AA1060 aluminum alloy plate by CNC-imprinting in cold. a) CNC-imprinting of the star-shaped emblem including the micro−/nano-textures onto the as rolled aluminum alloy plate with the thickness of 1 mm, and b) optical microscopy image of the star-shaped emblem.*

on the DLC-die to the plate, the color-grating and surface plasmonic brilliance are also duplicated on this aluminum plate. This reveals that the intrinsic color grating and surface plasmonic brilliance to micro−/nano-textures on the DLC-die can be reproduced on any metallic work product surfaces by the means of accurate imprinting.

Surface decoration observed in **Figure 14** in a similar manner to **Figure 10**, reveals that the mother micro−/nano-textures are accurately imprinted onto the aluminum alloy plate and that the microstructure reproduced on the product surface is responsible for the similar surface decoration to the textured DLC-die. Let us investigate the microstructure of replica textures imprinted onto the plate. **Figure 15** depicts the SEM image on the micro−/nano-textures imprinted onto the AA1060 aluminum alloy plate with varying magnification from a) to d). A-zone in **Figure 15a** turns to be **Figure 15b**, B-zone in **Figure 15b** turns to be **Figure 15c**, and C-zone in **Figure 15c**

### **Figure 15.**

*SEM image on the micro−/nano-textures imprinted on the AA1060 aluminum alloy plate with varying the magnification from a) to d).*

turns to be **Figure 15d**. In contrast to the mother micro−/nano-textures in **Figure 12**, the micro-textures in **Figure 15a** and **b** are just in the mirror-image reversal to the mother textures on the DLC-die in **Figure 12a** and **b**. Simply comparing **Figure 15c** and **d** to **Figure 12c** and **d**, the nanotextures are laterally aligned in **Figure 15c** and **d** against the longitudinal alignment of mother nanotextures in **Figure 12c** and **d**. This difference comes from the plastic flow of polycrystalline aluminum alloy with an average grain size of 20 μm into the DLC-die micro-cavities, to be discussed later.

**CNC-imprinting of textures to PET.** A PET (Poly-Ethylene Terephthalate) film was employed as a polymer work material for warm CNC-imprinting of mother textures on the DLC-die. In a similar manner to imprinting onto the aluminum alloy sheet, the DLC-die was indented into the PET film with a thickness of 0.2 mm. In this warm imprinting process, the thermocouple was embedded into the lower die. This die temperature was varied and optimized to search for the appropriate holding temperature (TH) and holding time (Ti). In the following experiment, TH = 290°, and Ti = 90 s.

**Figure 16** depicts the center part of the star-shaped replica imprinted onto the PET film. Micro-edges of textures in the DLC-die were indented into PET film to form the micro-grooves. This proves that originally tailored textures on the DLC-die are accurately reproduced onto the polymer products by this warm imprinting process.

**CNC-imprinting of textures to phosphorous glasses.** A phosphorous glass type L-PHL2 has been widely utilized as a work for the fabrication of functional optical lenses and DOE. It is characterized by a low glass transition temperature of 381°C and low softening point of 440°C. The flow stress of this glass significantly decreases between these two temperature points; the hot mold stamping process makes use of this temperature range to shape the glass preform to an optical element and lens.

In this hot imprinting process, a cylindrical L-PHL2 preform with a diameter of 5 mm was used as a work and mold-stamped at 440°C for 90 s. **Figure 17** compares

### **Figure 16.**

*Optical microscopy image on the micro−/nano-textures imprinted onto the PET film by compression of the DLC-die.*

*Femtosecond Laser Micro-/Nano-Texturing to Die Substrates for Fine Imprinting to Products DOI: http://dx.doi.org/10.5772/intechopen.105795*

**Figure 17.**

*A phosphorous glass type L-PHL2 preform before and after hot imprinting with the use of nitrided and lasertextured AISI420 mold.*

the L-PHL2 preform before and after hot imprinting process. The micro−/nano-textures were shaped onto the preform surface in **Figure 17b**. Three-dimensional surface profilomer was also utilized to measure this surface profile.

**Figure 18** shows the measured surface profile of L-PHL2 glass after CNCimprinting. With comparison to the mother surface profile of DLC-die in **Figure 11**, both profiles are corresponding to each other with fairly good geometric compatibility in its peak-to-valley. This compatibility is dependent on the filling process of glass material work into the cavities of nitrided AISI420 mold. To be discussed in later, the imprinting process control has much influence on this filling process.

The wettability test was performed to investigate the surface property change before and after micro-texturing onto the L-PHL2 glasses by CNC-imprinting. As shown in **Figure 19a**, the swelling on the textured surface proves that the original hydrophilic glass surface changes to be hydrophobic. As measured in **Figure 19b**, the contact angle changed from 60° before imprinting to 114° after imprinting. The surface property of glasses can be controlled from the original hydrophilicity to the hydrophobicity by imprinting the tailored micro−/nano-textures.

**Figure 18.**

*The preform surface profile shaped by hot imprinting the laser-textured mold. a) Bird view of preform surface profile, and b) preform surface profile scanned in the x-axis.*

### **Figure 19.**

*Wettability on the textured L-PHL2 glasses by CNC-imprinting. a) A pure water droplet on the textured L-PHL2 glass surface, and b) hydrophobic surface with a contact angle of 114°.*
