The “process chain” concept for the integration of multiple manufacturing processes has been attracting attention in the field of manufacturing in recent years. In a number of specialized fields, laser-based processes in particular are actively being studied, as their high flexibility allows them to be used not only as individual manufacturing processes but also in combination to develop new ones.
Most of the practical laser technologies involve heat, which can be used for thermal processing to change surface properties or for removal processing. In recent years, lasers have also been used as a heat source for additive manufacturing, as well as ultra-short-pulsed lasers being applied to non-thermal processes.
This special issue features various studies and reports that present the latest advances as well as current challenges in laser-based/assisted manufacturing. It includes nine related papers that indicate the possibilities and future of new laser processing technologies.
We deeply appreciate all the authors and reviewers for their efforts and contributions, and we also hope this special issue will encourage further research on laser-based/assisted manufacturing.
Since the semiconductor laser has a high conversion efficiency, it has many expectations for effective application. There are increasing application trials of processing at actual factories and jobsites. Moreover, it can currently be used as a heat source to directly conduct processing. This is called direct-diode laser (DDL). However, since there is almost no information regarding the DDL structure and beam mode, there are no scientific documents for the theoretical treatment of this heat source. This is considered to have interfered with the broad application for development. This research establishes the theoretical analysis of the semiconductor heat source for material processing, and we attempted to employ a simulation for processing. To verify the established theory, surface hardening and welding processing were performed as typical processing.
This paper presents a fabrication method of a two-dimensional (2D) diffraction grating with isolated photoresist pattern structures in order to reduce fluctuation in the grating pitch due to the thermal expansion. At first, theoretical calculations for the fabrication of a 2D diffraction grating with isolated photoresist pattern structures are carried out to estimate the influences of exposure and development time on the pattern structures to be fabricated through the pattern exposure and development process. A diode laser-based compact non-orthogonal two-axis Lloyd’s mirror interferometer system designed in a size of 500 mm × 840 mm is then built on a breadboard for stable mask-less interference lithography. Basic performances of the newly developed compact interferometer system are evaluated through the fabrication of 2D diffraction gratings to demonstrate the feasibility of the theoretical calculations and the developed lithography system.
Compared with traditional nanotexturing methods, an ultrashort-pulsed laser is an efficient technology of fabricating nanostructures called laser-induced periodic surface structures (LIPSS) on material surfaces. LIPSS are easily fabricated when the pulse duration is shorter than collisional relaxation time (CRT). Accordingly, ultrashort-pulsed lasers have been mainly used to study LIPSS, but they unstably irradiate while requiring high costs. Although long-pulsed lasers have low cost and high stability, the phenomena (such as the effect of pulse duration, laser wavelength, and heat) of the LIPSS fabricated using short-pulsed lasers with the pulse duration close to the maximum CRT, which is greater than femtosecond, have not been clarified. However, the nanosecond pulse laser has been reported to produce LIPSS, but those were unclear and ununiform. In this study, the short-pulsed laser with the pulse duration of 20 ps, which is close to the maximum CRT, was employed to clarify the effects of pulse duration and heat on the fabrication of LIPSS and to solve problems associated with ultrashort-pulsed lasers. First, a finite-difference time-domain simulation was developed at 20-ps pulse duration to investigate the effects of irradiation conditions on the electric-field-intensity distribution. Subsequently, experiments were conducted using the 20-ps pulse laser by varying conditions. The aspect ratio of the LIPSS obtained was greater than that of the LIPSS fabricated using ultrashort-pulsed lasers, but LIPSS were not fabricated at 355- and 266-nm laser wavelength. In addition, the short-pulsed laser experienced thermal influences and a cooling material was effective for the fabrication of LIPSS with high-aspect-ratio. This demonstrates the effects of pulse duration close to the CRT and heat on the fabrication of LIPSS.
The proposed paper is about the development of an integrated manufacturing process for smart 3D polymeric components, with electronics embedded, developed in the framework of research collaboration between the university partner and a group of SME. The system will be able to produce a polymeric structure by additive manufacturing technique, whereas a robotic system is integrated in the line to assemble electronic components onto the part while the manufacturing process goes on. A laser engraving station will process the component, providing micro- and nano-surface structuring, microcutting and microdrilling. Finally, another laser source is integrated in the system to weld electronic parts and circuits within the manufactured component. At the same time, the assembly of large size systems by welding small size components is allowed, and also a sealed atmosphere is ensured by welding a plastic cap onto the plastic structure.
NiP coating with an amorphous structure is a commonly used mold material for manufacturing resin optical components. However, due to the inhomogeneous deformation characteristics of amorphous alloys, chippings and burrs are easily produced at the edge of microstructures. Laser-assisted microcutting has proven to effectively inhibit the generation of these defects but the evolution of chip-deformation mechanisms with different laser power remains to be explored. In this study, a simulation of the temperature field under nanosecond laser irradiation was conducted and the laser-assisted cutting of NiP was considered, using the same irradiation parameters. Through the analysis of chip morphology under different conditions, it is found that the temperature in the deformation zone mainly affects the morphology of the secondary shear bands but has no effect on the number of nucleation in the primary and secondary shear bands. The proper temperature in the shear deformation zone can improve the deformation ability of the secondary shear band, thus making the shearing process more stable. This research will prove helpful to understand the material deformation mechanisms to guide the selection of laser parameters in the laser assisted cutting of amorphous alloy.
Titanium alloys are widely used for the hard tissue substitute implants. However, it is necessary to improve interfacial biocompatibility to reduce adhesion period. For improvement of biocompatibility of Ti-6Al-4V ELI alloys, texture and chemical composition on contact part with biological tissue play very important roles. In this research, micro texture was generated on the Ti-6Al-4V ELI alloy surfaces utilizing laser irradiation, in order to improve biocompatibility. The biocompatibility was evaluated by osteoblast cell culture assays. The results indicated the surface having micro texture improve biocompatibility as compared with untreated surface. This was considered in order the fact that the formed modified surface had hydrophilicity, thereby improving the cell compatibility, and the cell adhesion due to the complicated shape. In addition, mist of glycerophosphoric acid calcium aqueous solution was applied on the laser irradiated area. As result, micro texture including Ca and P elements was generated on the Ti-6Al-4V ELI alloy surfaces. When laser was irradiated, glycerophosphoric acid calcium aqueous solution was applied as mist flowed on the test pieces as droplet. The velocity of droplet fluid was relatively fast, so that laser irradiation was unhindered access to the surface of test pieces and the treatment was stable. In order to estimate biocompatibility, culture assays using osteoblast cells were conducted on the treated surface having micro texture including Ca and P elements. As results, it was clearly that biocompatibility of the specimen treated by laser with glycerophosphoric acid calcium aqueous solution mist more improved than either untreated specimen or treated specimen soaked in glycerophosphoric acid calcium aqueous solution.
The reduced density of the autogenous bone around metal medical implants forces joint replacement patients to undergo revision surgery. The loss of bone density is caused by a significant difference in the elastic modulus between implants and autogenous bone. Various studies have attempted to reduce the elastic modulus of the implant to close the large gap in the two moduli. Porous metal is a promising material for reducing the elastic modulus of implants, but it is difficult to fabricate a closed-cell structure like bone using conventional porous metal fabrication methods. In this study, porous Ti-6Al-4V was prepared by selective laser melting, then its porosity was evaluated by X-ray computed tomography. Additionally, tensile test specimens of the porous structure were prepared and the effect of pores on the tensile properties was evaluated. Depending on the energy density, the structure of the porous body was found to form both closed- and open-cell structures. In the tensile specimens that showed the most favorable results, the elastic modulus was reduced by approximately 90%, and the tensile strength exceeded that of the annealed material. This indicates that a metal implant that has a low elastic modulus while maintaining strength can be obtained.
This research proposes a method to achieve laser quenching and laser forming simultaneously. This technique uses a diode laser to produce thin steel sheet-assuming parts, such as springs and hinges. Energy and time are saved by combining the advantages of laser quenching, which has high input heat efficiency, and laser forming, which, unlike press molding, does not require metal molds. In this study, laser-quenching molding was performed for an entire thin steel plate, and the influence on warping was investigated. Furthermore, the proposed method was evaluated under repeated quenchings for different cross-sections of a workpiece. The results indicated that the technique prevented bending deformation during the next laser scan and reduced warping by increasing the second moment of area of the entire workpiece.
Functional surface creation technologies have garnered increasing attention over the years. These technologies can provide various functions to a material by establishing a fine structure on the material surface and responding to the needs of industrial products with distinguished functions or high values. In addition, by creating a “composite fine structure,” which is composed of two kinds of structures with different scales, the enhancement of functions and emergence of new functionalities can be expected. Hence, our study combined a micrometer-scale V-shaped groove structure using an ultra-precision cutting and nanometer-scale ultra-fine periodic structure (LIPSS) using a short-pulsed laser. Then, we clarified the creation principle and studied the functionality of the structure, specifically, its wettability. As a result, it was found that optical behavior inside the V-shaped groove changed; therefore, the composite structure changed depending on the groove angle, laser polarization direction, and number of times of irradiation. In addition, it was found that the water wettability changed depending on the type of formed micro-nano composite structures. Moreover, the wettability could be controlled by depending on how the structure is used.
In today’s situation with high needs for care, a transfer work, among various assisting works, produces particularly large physical burden. The burden could result in not only diseases including waist pain but also resignation of care workers. A nursing lift used to reduce the burden lifts up a care receiver by using a wire or mechanical structure, causing sway. The sway not only makes the care receiver uncomfortable but also causes a risk of unintentional collision. To prevent such a situation, carers need to assist care receivers by holding them while simultaneously operating equipment and paying attention to the care receivers, which is not preferable from a viewpoint of work safety. In this study, we experimentally analyzed and discussed sway of a person when he/she is lifted up. On the basis of an analysis result, we propose an automatic control method of dynamical speed change for safe lifting works, which is applicable to ordinary nursing lifts.
The medical and bio-engineering fields have been increasingly using information and communication technology. To introduce robots into surgical procedures, data on surgical operations are required. Several studies have tried the creation of data on living tissues for mechanical actions, which makes determining the mechanical characteristics of living tissues vital, but few have been commonly used. Therefore, we previously developed a sensing system that uses a hydraulic-driven micro mechanism to measure the force applied to an object when it is touched. Micro force sensors are necessary for various manipulations requiring careful operation. Unfortunately, the measurement accuracy of sensors tends to reduce with the reduction in sensor size. The proportional output in conventional force sensors, such as piezoelectric sensors, also decreases when the size of the sensor is reduced. However, a micro force sensor using a hydraulic-driven micro mechanism can obtain a large output even when it is small. Our system uses Pascal’s principle to measure small forces acting on the end effector. We propose methods for identifying the mechanical characteristics of certain viscoelastic materials similar to those used in a living organ. A hydraulic-driven micro device pushes an object and measures the reaction force and its displacement. We have used two types of micro devices, micro cylinder and micro bellows. Its stiffness and viscosity coefficient are obtained through calculations using Kelvin-Voigt and Zenner models. Discrete displacement and load data are applied to the estimated model, and the mechanical characteristics of the materials are identified as a minimized value between the estimated value and experimental one. We conducted experiments using the proposed identification methods on viscoelastic materials, and the results indicate that the value provided from the Kelvin-Voigt model was near the truth value.
High precision is required for thin substrates used in the manufacturing processes for semiconductor devices and flat panel displays, and the required precision for substrate warp becomes more stringent every year. However, it is difficult to remove the warp efficiently utilizing the current grinding and polishing methods. One of the causes is deformation of the substrate during clamping. For this reason, a freezing pin chuck has been developed as a clamping technology that does not deform the substrate. A freezing pin chuck that uses the adhesion of frozen liquid can be designed with a substrate clamping force that can withstand the processing force. In this study, we developed a correction processing system that utilizes a freezing pin chuck to remove the warp of the thin substrate. The developed correction processing system can perform the grinding and polishing processes while clamping the substrate without deformation using a freezing pin chuck, and has a non-deformation clamping capacity that suppresses substrate deformation to 1/10 or less for a substrate with an initial warp of 100 μm. In addition, the newly devised additional application method has made it possible to increase the clampable warp by approximately twice that of the ordinal application method, and improves the clamping force. The results of the grinding and polishing experiments revealed that the correction processing system can obtain the same planarized profile as that when a vacuum pin chuck is utilized, while cooling the substrate surface during processing to 5°C or less, and also demonstrated that it can be applied to correction processing.
The present work demonstrates that exactly manufactured references for joining, mounting, and metrology purposes are crucial in the effective assembly of high-quality optical systems. Based on the alignment turning of spherical and aspherical lenses, the proposed approach can be transferred to non-rotational symmetric elements such as prisms, active components (e.g., laser diodes), and freeform mirrors. The complexity of the optical component decides whether on-machine metrology or specific measurement setups need to be used to determine the position and orientation of the references with respect to the optical function. The resulting correction data are considered during the machining process. The subsequent correction cycle realizes mounting and metrology references down to sub-micron precision using diamond-machining techniques. This approach facilitates the assembly of demanding optical systems and even freeform arrangements in a predictable and passive manner. Different machining setups as well as the corresponding metrology approaches are demonstrated, and results are presented for representative components. The effectiveness of the approach is discussed using rotationally symmetrical lens systems and a snap-together freeform mirror system.
In ultra-precision diamond turning of freeform optics, it is necessary to obtain submicron-level form accuracy with high efficiency. In this study, we proposed a new method for the quick measurement and compensation of tool contour errors to improve the form accuracy of the workpiece. In this method, the nanometer-scale contour error of a diamond tool is quickly and precisely measured using a white light interferometer and then compensated for, before machining. Results showed that the contour of a diamond tool was measured with an error less than 0.05 μm peak-to-valley (P-V) and the feasibility of error compensation was verified through cutting experiments to create a paraboloid mirror and a microlens array. The form error decreased to 0.2 μm P-V regardless of the contour error of the diamond tools when cutting the paraboloid mirror, and that of the microlens array was reduced to 0.15 μm P-V during a single machining step.