The aerospace, automotive, and electronic industries are finding increasing need for components made from silicon carbide (SiC) and silicon nitride (Si3N4). The development and use of miniaturized ceramic parts, in particular, is of significant interest in a variety of critical applications. As these application areas grow, manufacturers are being asked to find new and better solutions for machining and forming ceramic materials with microscopic precision. Recent advances in laser machining technologies are making precision micromachining of ceramics a reality. Questions regarding micromachining accuracy, residual melt region effects, and laser-induced microcracking are of critical concern during the machining process. In this activity, a variety of nondestructive inspection methods have been used to investigate the microscopic features of laser-machined ceramic components. The primary goal was to assess the micromachined areas for machining accuracy and microcracking using laser ultrasound, scanning electron microscopy, and white-light interference microscopic imaging of the machined regions.
Carbon nanocomposites consist of thermoset and thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, an Yb:KGW solid-state femtosecond laser and an Nd:YVO4 solid-state nanosecond laser were used to micromachine oxidized multi-wall carbon nanotube (MWCNT) doped morthane. The experimentation studied the relationship between various laser-processing parameters including laser pulse duration, pulse energy, beam scanning speed, and average power. The processing consisted of cutting channels into the materials using 1048 nm wavelength at 400 fs pulse duration, 1064 nm wavelength at 40 ns pulse duration, and 355 nm wavelength at 35 ns pulse duration. Additionally, the effects of oxidized MWCNT fill percentage were considered. The material removal rate was quantified for each experimental condition. The experimental results are discussed in terms of material removal rates, machining quality, and achievable feature size.
A considerable amount of work has recently been applied to the development of laser processing techniques for a wide variety of applications. With regard to aging aircraft, laser processing techniques could play a role in inhibiting crack growth and extending the life of structural aircraft components. The basic concept involves the application of a sharply-focused, moderate power laser beam to a local microscopic defect site that has been detected through advanced NDE techniques. The defect could be pitting corrosion site, a fretting region, or even a microcrack site. The laser would be raster-scanned across the defect, re-melting the site locally to a level where the sharp features of the defect are smoothed out, or perhaps re-melted completely to eliminate the flaw site altogether, thereby reducing stress concentration levels in the material. In order to test the feasibility of this basic concept, a series of measurements were made to study the effect of microscopic laser treatments applied to artificial defects in Al-2024-T3 aluminum and Ti-Al6-4V titanium. The major results of the study showed a moderate to significant level of fatigue life enhancement for engineered notches in the 1 mm size range. The laser treatmen approah may provide an opportunity for 'healing' structural defects in aerospace materials that would otherwise require expensive and time-consuming part replacements in aging aircraft structures.
Carbon nanocomposites consist of thermoset or thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This new and innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, direct diode and Nd:YAG solid-state lasers were used to transmission weld -carbon nanocomposite materials. The experimentation was focused on exploiting the infrared absorbing characteristics of the carbon nanocomposites. Polyetheretherketone (PEEK) based polymer was used in the initial experimentation to quantify weld strength. The experimentation included a complete analysis of the transmission characteristics of the base polymer at 810 nm and 1,064 nm wavelengths, an optical microscope view of the weld cross-section, and transmission welding experimentation. The transmission welding experimentation studied the relationship between average power, travel speed, and weld peel strength. A micro-channel welding experiment was also completed using a polycarbonate (PC) based polymer. The experimentation qualified the minimum feature size that could be joined. The resulsts show that the carbon nanocomposites can be welded in a similar way to carbon black filled materials. The carbon nanocomposites exhibited higher peel strengths at lower average laser power at both 810 and 1064 nm. The carbon nanocomposite material exhibited a unique characteristic of being able to be machined and welded by the same laser wavelength.
Carbon nanocomposites consist of thermoset and thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This new and innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, Nd:YAG and Nd:YVO4 solid-state lasers were used to micromachine carbon nanocomposite thermoplastic materials. Experimentation was completed to compare the ability to laser micromachine carbon nanomaterial, carbon black, and unfilled polyurethane. The experimentation studied the relationship between repetition rate, travel speed, and material removal rate. The processing consisted of cutting channels into the materials using an Nd:YVO4 laser at 1064, 532, and 355 nm wavelengths. The material removal rate and groove width were quantified for all wavelengths and compared versus the experimental variables. Trials were also completed on laser machining deep channels using an Nd:YAG laser and polyetheretherketone (PEEK) filled with carbon black and carbon nanofiber. The results of the experimentation show similar material removal rates for carbon black and carbon nanofiber filled polyurethane. The PEEK material exhibited high aspect ratio channels with both carbon black and carbon nanofiber fillers. Laser micromachining of polymers whcih were previously unmachinable using infra-red has been demonstrated.
Liquid crystal polymer (LCP) is a new and innovative material being used as an alternative to polyimide in the flexible circuit industry. LCP has many intrinsic benefits over polyimide including lower moisture absorption and improved dimensional stability. However, LCP is very resistant to chemical milling or etching. As a result, other methods for processing the material are being investigated including laser micromachining. In this paper, three frequency converted diode-pumped solid-state (DPSS) Nd:YVO4 lasers at 355 nm were used to micromachine a LCP film and a copper/LCP laminate. Of them, two are Q-switched lasers operating in the nanosecond regime and the other a mode-locked laser in the picosecond regime. The Q-switched lasers can be operated at pulse repetition rates of 1 to 300 kHz while the mode-locked system is operated at 80 MHz. The micromachining experiments consisted of cutting the 50 μm thick LCP film, cutting the 18 μm thick copper on the film, and drilling micro-vias through both the copper coating and the film substrate. The laser/material interactions and processing speeds were studied and compared. The results show that, compared to polyimide film of the same thickness, LCP film can be more efficiently processed by laser micromachining. In addition, each laser has a unique advantage in processing LCP based flexible circuit materials. The Q-switched lasers are more capable of processing the copper coating while the mode-locked laser can cut LCP film faster with the smallest kerf width.