Abstract: When a laser pulse interacts with metal or semiconductor target, the coherent phonon, which is the coherent motions of lattice and molecule vibrations in solids, is excited by the interaction of electrons and high latitude electric field. It has unique properties of decaying in approximately several picoseconds and substance specific frequency. Owing to that, femtosecond laser processing is the local processing with little heat diffusion and little thermal damage to the target, due to the ultrafast time scales. We propose a novel femtosecond pulse ablation process with oscillation of the coherent phonon by femtosecond pulse train. The pulse train is shaped using Spatial Light Modulator (SLM), which shift the phase of the passing light. And coherent phonon oscillations are enhanced and decayed due to the controlling the shape of pulse train. It is able to activate the lattice motion for processing efficiently, and hence the target is expected to be ablated with high accuracy and less thermal damage.
Abstract: Carbon fiber-reinforced plastics (CFRP), which are now used in some aerospace applications, is difficult to cut and drill holes in. Moreover, no reports have focused on selecting a suitable drilling method for each aerospace part. This paper discusses many methods of hole generation for CFRP composites, including methods using traditional drill tools and non-traditional methods such as abrasive water jet (AWJ), laser beam and abrasive blast. We look at traditional cemented carbide material tools, polycrystalline diamond (PCD) tools, diamond-like carbon (DLC) coated tools and ceramic tools. Then, comparing the experimental results of these methods from the viewpoints of characteristics, efficiency, cost, and hole quality, we investigate each problem to select the suitable drilling method. As a result, we propose a novel method to strategically obtain the best solutions to generate holes in aerospace parts.
Abstract: Demand is increasing for the manufacturing and machining of small mechanical parts. We focus on using a multi-functional desktop-sized machine tool to meet such demands because power consumption is decreased when they are machined. However, few reports have focused on heat treatment among manufacturing processes, we investigate the laser heat treatment of small parts as a highly efficient and eco-friendly method and propose in-situ heat treatment on a desktop-sized machine tool using a low-power diode laser beam. We quenched a small thin steel plate with a 30 W diode laser source. Our proposed method makes it feasible to quench a small thin steel plate and effectively reduces the power consumption of in-situ heat treatment by a desktop-sized machine tool.
Abstract: In laser materials processing, trepanning optics are used to fabricate laser drilled holes of high aspect ratios (> 10) and controllable drill-hole conicity. However, trepanning optics available up to today are limited to circular trepanning geometries. Thus, only circular holes with drill-hole wall angles of rotational symmetry are feasible. Within this paper we will present a novel trepanning optic based on two piezo-actuatoric tip/tilt mirrors, being first of its kind, which allows arbitrary developments of propagation angle and lateral position of the laser beam, both being independent of each other. Consequently, the novel trepanning optic allows arbitrary drill-hole geometries such as circular, elliptical, rectangular etc. At the same time the drill-hole wall angle may be varied freely. Thus, asymmetric drill-hole wall angles are feasible such as tilt of the drill hole or wobbling of the drill-hole wall angle for instance. Demonstrative drill-holes of different shapes produced with an ultrashort pulsed laser prove the flexibility of the trepanning optic presented.
Abstract: Selective Laser Melting (SLM) is a direct fabrication of part through layer by layer powder deposition and successive laser beam irradiation based on Computer Aided Design (CAD) data. One of the important properties in SLM is thermal conductivity of metal powder. This is because the ability of metal powder to conduct heat will affect the consolidation process during SLM. In this paper, thermal conductivity of metal powders with different particle diameters and their mixture was analysed. Other than that, thermal conductivity of consolidated materials fabricated via SLM process was also studied. In order to measure the thermal conductivity of metal powder, a theoretically verified method which was previously developed by the authors was used. Determination of thermal conductivity of consolidated material was analysed using laser flash technique. It was found that the thermal conductivity of powder metal was influenced by bulk density and particle diameter of metal powder. In this study also, metal powders of different particle diameters were mixed with various volume ratios, and its effect was discussed. Thermal conductivity of the consolidated materials was also examined, and its relation to porosity was elaborated.
Abstract: Recently, cutting has replaced grinding in the finish processing of hardened steel. However, tool damage is a major problem in high-efficiency operations that use high-speed cutting and high feed rate conditions instead of the present cutting conditions. Therefore, the examination of a new cutting technique that can realize high-efficiency cutting is desired. In this study, the effects and efficiency of driven rotary cutting are investigated in the finish turning of carburized hardened steel. Based on the results, flaking occurs at the cutting edge at a short cutting length of 0.2 km using single-point turning. On the other hand, even if the cutting length amounts to 1.5 km, the tool wear width without flaking is small in the case of a driven rotary tool. Additionally, the tool wear is uniformly distributed along the circumference of the cutting edge. Furthermore, based on an examination of high-efficiency processing by increasing the feed rate, it is clarified that a feed rate of 0.3 mm/rev is the optimum condition from the viewpoint of wear resistance and surface roughness. Additionally, even if the cutting length amounts to 5.0 km for this condition, the flank wear width is as small as 0.04 mm, and the tool wear progresses gradually.
Abstract: To obtain an ultra-precision surface, this research developed a new type of magnetic finishing tool, “Ultra-precision Magnetic Abrasive Slurry”, for a magnetic field assisted internal finishing process. This ultra-precision magnetic abrasive slurry is made to mix simply the super-minute abrasive grains, super-minute globular iron particles, and oily grinding liquid. When the internal finishing was executed, the automatic mixing phenomenon of the Ultra-precision Magnetic Abrasive Slurry is caused, at the same time, super-minute abrasive grains and minute iron particles were uniformly distributed to the magnetic abrasive slurry. It was confirmed that a smooth mirror internal finishing for a SUS304 stainless steel tube is able to be achieved, by using the Ultra-precision Magnetic Abrasive Slurry that consists of the globular carbonyl iron particles (6μm in mean diameter) and diamond grains (0.25~0.75μm in mean diameter) and the oily grinding liquid. In this study, we examined the influence that the rotational speed of the magnetic pole exerted on the finishing characteristic. The results showed that the ultra-precision surface is successfully made, and the surface roughness has been improved from 320nm Ra to 3.37nm Ra .
Abstract: We demonstrated high adhesive fluoropolymer/copper interface through combination of atmospheric pressure plasma with liquid phase self-assembly. However, there are some disadvantages in atmospheric pressure plasma technique, such as small processing area due to the localized plasma and high gas temperature. Medium pressure plasma process has some advantages over atmospheric pressure plasma systems. A large plasma volume and low gas temperature, available for surface treatment of polymer material, can be easier obtained at medium pressure than at atmospheric pressure, which can result in a higher overall productivity. In this paper, we investigated the adhesion strength of electroless copper plated layer formed on poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) surface modified by combination of medium pressure helium plasma irradiation and aminated acrylic polymer grafting. The 90° peel test result for copper plating film formed on the treated PFA films showed the adhesion strength of 0.44 N/mm without increasing the surface roughness.
Abstract: Open-air type numerically controlled plasma chemical vaporization machining (NC-PCVM) is promising technique to fabricate the ultra-precision optical components and to finish the functional materials. The objective shape is fabricated by controlling the scanning speed of the localized plasma because removal volume is proportional to the dwelling time of the plasma on the workpiece surface. To achieve deterministic figuring with shape accuracy of nanometer level, it is essential to keep volumetric material removal rate (MRR) constant during and batch to batch processing. The removal rate is proportional to the density of fluorine radical generated by plasma. So, we control the electric power to keep the removal rate constant during the process based on the fluorine atomic density obtained by optical emission actinometry. We report the relationship between MRR and fluorine atomic density measured by optical emission actinometry.
Abstract: Focusing neutron beam with wide wavelength range is an indispensable technique used to compensate for weak signals from tiny samples in various experiments using pulsed neutron beam generated from high intensity proton accelerator facilities, such as J-PARC. Aspherical supermirror device is one of the most effective optical devices for focusing neutron beam with wide wavelength range since it has no chromatic aberration. Stack of aspherical supermirror enables us to focus neutron beams with wide divergence. Thin mirrors with a millimeter thickness are required to minimize the absorption loss of incident neutron beams since the thickness of a mirror shadows the reflective area of the other mirrors. Previously, we developed a fabrication process of a precise millimeter-thick elliptical supermirror. This process consists of noncontact figuring by the numerically controlled local wet etching technique, the finishing of surface without degrading mirror shape by low-pressure polishing, and the ion beam sputter deposition of NiC/Ti multilayers on both sides of the mirror substrate to compensate for film stress. In this paper, we report fabrication of elliptical supermirror with a thickness of 1 mm and development of multiply-arranged neutron focusing mirror device using stacked 4 fabricated elliptical supermirror with a thickness of 1mm.