With the established technique of laser in precision micromaterial processing, the fabrication of cardiovascular metallic stent with high quality has now become feasible. From the actual CAD design and FEM analysis of the stent fabrication, the need for the surface modification properties becomes essential in enduring its extended life duration. This paper describes the current status as well as fabrication of such metallic stent of length 20 mm and dia. 2.1 mm with an annular tube thickness of 0.2 mm, by using the short pulse Nd-YAG laser. Fine structures with slit width of 0.1 mm and pitch better than 0.2 mm are created with sharpness and low roughness in the cut surface. Some features on improving the surface characteristics of the cut surfaces of the stent, excimer laser coronary angioplasty and ultrasound ablation of plaque as well as a few techniques on preventing restenosis are well documented.
In the stent theory for the medical applications, especially in coronary heart disease, the metallic stent of high quality demands the ability for precision micromaterial processing. It possesses an inherent advantage of adequate radio opacity. This paper describes the current status as well as fabrication of such metallic stent of length 20 mm and dia. 2.1 mm with an annular tube thickness of 0.2 mm, by using the short pulse Nd-YAG laser. Fine structures with slit width of 0.1 mm and pitch better than 0.2 mm are created with sharpness and low roughness in the cut surface. Some features of the reduced heat affected zone and dross removal process of the cut surfaces are also discussed.
In the stent theory for the medical applications, especially in coronary heart disease, the metallic stent of high quality demands the ability for precision micromaterial processing. It possesses an inherent advantage of adequate radiopacity. This paper describes the current status as well as fabrication of such metallic stent of length 20 mm and dia. 2.1 mm with an annular tube thickness of 0.2 mm, by using the short pulse Nd-YAG laser. Fine structures with
slit width of 0.1 mm and pitch better than 0.2 mm are created with sharpness and low roughness in the cut surface. Some features on the reduced heat affected zone and dross removal process of the cut surfaces of the stent as well as a few techniques on preventing restenosis are well documented.
In the recent past years, developments in the rapid prototyping of various parts have taken new dynamic turns in manufacturing technology. Besides the use of new materials, unrelenting demands for the downsizing of miniature components in the micro-domain have expanded the application area of the rapid prototype product. Their requirements with reduced time lag have forced the manufacturers to adopt and develop innovative techniques which meet these demands. In order to overcome this problem, several techniques, predominantly laser stereolithography, have successfully been used in Japan for the past several years to generate a complex micro-/macro part of polymer resin based in two- or three-dimensional domains. The main disadvantage of this process is that they consist of two or more steps for producing metallic/metal-matrix composite microstructures. But recently developed new technologies of selective laser sintering/generating and ballistic particles manufacturing processes offer the possibility of the direct generation of these microstructures in a single step process. The last two processes actually have limitations on the feature size produced, due to the minimum size of the molten droplet. But the selective laser sintering technique can bind the particles by melting together at the interfacial grain contact area only and thus producing smaller feature sizes. Based upon these techniques, the present paper aims to review the current status and the future prospective of laser assisted rapid prototyping in Japan.
For the last decade processing application with the Nd:YAG laser operating int eh UV, visible and IR region has taken a new dynamic turn in the micro technology. It has covered a wide range of applications in microelectronics, semiconductors and screen printing as well as in the medical industries. From laser ablation to marking and from precision cutting to micro welding, it has opened a new horizon of industrial needs in micro technology. Of these, processing with the UV radiations have a unique characteristics of ablation and allow the production of small micrometers order microstructures, but their industrial application has yet to be established. On the contrary, processing with the IR radiations usually considered as thermal processing covers mainly precision cutting of stencil mask for screen printing technology, micro processing of metallic stents for medical therapy and various other microstructuring applications. In all these processes, due to different scale length of the beam interaction time with the material, various physical phenomenon are encountered that ultimately affect the quality of the end product. The present paper elaborates a few of these basic processes and explores the possibilities of current and new application areas.
In the emerging field of micro robotics and micro- electromechanical systems, the requirement of complex mechanical parts is gaining much importance. On one hand, the overall size and shape of the product is becoming continuously smaller and more complex, whereas the new product demand/offer is increasing manifold. In order to overcome this problem, the new organizational structure of the compete process for the product development as well as the new technology is necessary. This paper highlights the various processes viz. Micro-stereolithography of polymer resin, selective laser sintering of metallic powder as well as melting processes using lasers for the rapid prototyping of 3D parts in micro domain.
This paper describes two processes for the 3D microstructuring of metallic/metal-matrix composite parts by using pulsed Nd-YAG laser. (1) In the first part, laser microcladding process is discussed. The effect of beam interaction time and the relationship between various layers are considered. The results show that in this case the beam interaction time greatly affect the structural development of the product with respect to its strength and quality. (2) In the second part, selective laser sintering with the one and two components metallic powders shall be discussed. The results show that due to the surface contact only, the feature size obtained with the one component solid state sintering is smaller compared to the two metal liquid phase sintering of the metallic powder, comprising of high and low melting point. The influence of the processing conditions on the type of phases and the microstructure evaluation are considered. Successful attempts were also made in creating the fine structures with the metal-matrix composite powder materials. A few examples are demonstrated briefly.
With the established technique of laser in science and industry, its applications have become diversified in the micro- and macro-processing areas. Three potential lasers CO2/Nd- YAG/Excimer operating in the ir and uv region have been applied in various domains covering different spectrum of industrial applications. Of this the processing with the CO2/Nd-YAG lasers usually considered as thermal processing covers mainly cutting/welding and surface modification areas. Whereas the excimer laser operating in the uv region and having a unique characteristics of cold ablation, allows the production of small um order microstructures. In all these processes the beam interaction time with the material greatly affects the structural development of the end product. The present paper elaborate a few of these basic processes and explore the possibilities of current and new application areas.
An ablation wave from materials based on laser supported detonation and laser supported combustion has been created by exposing them with laser. The purpose of this study is to analyse the mechanism of the ablation wave using a high speed streaked camera and to realize more precise microprocessing by controlling the wave. The laser used in this experiment was an ultraviolet XeCl excimer laser of high photon energy with a wavelength of 308nm, a maximum pulse energy of 500mJ, a pulse width of 30ns and a maximum frequency of 50Hz. The high speed streaked camera had a resolving power of 100ps. Metal-ceramics functionally graded materials (FGMs) were selected as sample materials. An experimental system of laser microprocessing was constructed and the behavior of the ablation wave from FGMs were observed. The experimental results showed that the mechanism of the ablation wave from FGMs was a photochemical reaction with thermal interaction.
In this paper two processes of microfabrication technology are investigated. In the first part, laser generating process which is largely affected by the beam interaction time is described. In the second part, selective laser sintering of metallic powder shall be discussed. The results show that the two metal liquid phase sintering is most effective in the selective laser sintering of the metallic powder comprising of high and low melting point. Whereas in the generating process the beam interaction time greatly affect the structural development of the product with respect to its strength and quality. A few examples are demonstrated briefly.
In the present work, the results of laser cladding by galvano scanning and modulated beam using the CO2 and Nd-YAG lasers are presented. The results are compared with the stationary beam. It is realized that the scanning frequency as well as the modulation effects were found to have significant effects on solidification and microstructural development process. The results indicate that the dendrite structure shall be fine at higher frequency or low duty modulation condition, compared to the coarse structure at lower frequency or high duty modulation condition. A shallow bead width as wide as 10 mm was obtained in a single pass. Macro- and micro- crossection, EPMA and microhardness profile have been employed to characterize the cladding. The results are correlated with the cladding quality. Microstructure, hardness, dilution etc. are discussed as a function of the processing parameter. Because of the high solidification rate a fine dendrite structure is developed in the cladding zone. A few of the actual results and EPMA analysis of the laser cladding of stellite 6 on 12 Cr-Ni turbine blade as shown in the figure are presented.
Potential applications such as hard facing of engine valve seat, turbine engine blade shroud interlock and leading edge of steam turbine blade, with controlled dilution have stimulated the use of laser cladding recently. In this paper, based on the laser beam interaction time, the microscopical study of dendrite structure formation in laser cladding of stellite number 6 on mild steel and Cr-Ni base materials is investigated. The effect of the various parameters such as heat input, beam interaction time, scanning frequency and transverse speed are considered. The applications in the rapid prototyping industries are also discussed.
The modulation and duty cycle effects on Al-alloy welding with high power Nd-YAG laser are investigated. Micro- structural characterization of the low and high duty welds with wave modulation identified the differences in the weld morphology. Welding depth, undercut and strength of fusion zone are discussed as a function of the processing parameters.
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