Jin-Chen Hsu

On-line depth measurement for laser-drilled holes based on the intensity of plasma emission

The direct time-resolved depth measurement of blind holes is extremely difficult due to the short time interval and the limited space inside the hole. This work presents a method that involves on-line plasma emission acquisition and analysis to obtain correlations between the machining processes and the optical signal output. Given that the depths of laser-machined holes can be estimated on-line using a coaxial photodiode, this was employed in our inspection system. Our experiments were conducted in air under normal atmospheric conditions without gas assist. The intensity of radiation emitted from the vaporized material was found to correlate with the depth of the hole. The results indicate that the estimated depths of the laser-drilled holes were inversely proportional to the maximum plasma light emission measured for a given laser pulse number.

Characteristics of the effect of swirling gas jet assisted laser percussion drilling based on machine vision

In this paper, a machine vision-based system is used for in-situ monitoring and characterization of the effect of swirling gas jet assisted laser percussion drilling. Feasibility of laser percussion drilling on highly reflective materials, i.e., Al5052 with the implementation of assisting swirling gas jet, was explored. The influence of the gas jet type on the mechanism of material removal and resulting spatter is reported. The authors conclude that the swirling gas jet method greatly reduces spatter formation around the hole exit during the laser-drilling process. Consequently, in order to understand and monitor the gas jet effects in laser drilling, real-time in situ metrology is employed to observe the details. Compared with the results obtained when using a straight gas jet, laser drilling with a swirling gas jet reduces the drilled hole debris by 0.69 and increases the drilled hole efficiency by a factor of up to 1.5. Experimental results show that both the drilling depth and machining quality can be...

External Electric Field-Assisted Laser Percussion Drilling for Highly Reflective Metals:

In this study, an external electric field was employed during the laser percussion drilling on highly reflective materials. The laser-produced plasma was sputtered substantially, and the charged ions in the plasma plume were drawn by the electrodes. Different configurations of plate electrodes were proposed and investigated in this work to provide a simple, low-cost method that allows expelling the laser-induced plasma during the percussion drilling process. The electric field resulted from the potential that was applied across the two electrodes. This electrical perturbation produced a uniform electric field when the laser-generated plasma was created in the plane plate-charged capacitor. The electric field with different electrode configurations applied to the charged particles that are carrying the electrons was also simulated in this work. All processing work was performed in air under standard atmospheric conditions and in the absence of assisting process gas. The depth of the holes drilled when various types of electrode configurations were used was measured, and the results were used to evaluate the percussion drilling rate. Results show that vaporized debris is expelled by the applied electric field; hence, in optimal configuration the penetration depth can be increased by up to 91.1%.

Hybrid stamping and laser micromachining process for micro-scale hole drilling

ABSTRACT Micro-scale hole drilling on metallic sheets has been employed in a wide range of personal computing devices, such as smart phones and tablet computers. Laser machining, micro-electro-discharge machining, and chemical etching are the methods used for fabricating micro-scale holes. In this paper, we propose a hybrid sequential stamping and laser machining process. The alignment in the hybrid process is critical, and a patented device called the ball-cone-hole magnet was used in the experiments to achieve an alignment error of less than 1 µm. The fabrication results obtained by laser-only, stamping-only, and the proposed hybrid process were compared. The diameters of inlets and outlets, as well as the cross-section of holes, were compared herein. The surface roughness of the sidewalls’ inside holes was measured. The proposed hybrid stamping and laser machining process provides an alternative fabrication method for the micro-scale hole drilling process with better hole quality than a laser-only machining process.

Laser direct nano-structuring assisted by water droplets

Nano-structuring using laser direct writing technology has shown a great potential for industrial applications. A novel application of water droplets to this technology is proposed in this paper. With a hydrophobic layer and a controlled substrate temperature, a layer of randomly distributed water droplets with a high contact angle is formed on the substrate. These liquid droplets can be used as lenses to enhance the laser intensity at the bottom of the droplets. As a result, nanoscale holes can be fabricated on the substrate by controlling the laser energy density. We successfully fabricate holes with a diameter of 600nm at a substrate temperature of 12°C and a power density of 1.2×108 mW/cm2 in our experiments.

Nanostructure fabricated by laser direct writing with water droplets

Nanopatterning using near-field optics has shown great potential for industrial applications. A novel application of water droplets to this technology is proposed in this study. With a hydrophobic layer and controlled substrate temperature, a layer of randomly distributed water droplets with a high contact angle is formed on the substrate. These liquid droplets can be used as lenses to enhance the laser intensity at the bottom of the droplets. As a result, nanoscale holes can be formed on the substrate by laser ablation. We have fabricated holes with a diameter of 500nm at the substrate temperature of 12°C. The depth of the holes ranges from 0.1μm to 0.9μm, depending on the diameter of droplets.

Laser induced plasma detection by flat and circular interdigital electrodes in laser material processing

In this paper, we propose two new interdigital electrode designs, flat and circular, to increase the signal level and the detection sensitivity of laser-induced plasma.