Key Engineering Materials Vols. 364-366

Abstract: The accurate thickness measurement of Ultra-thin rolling metallic foil has an important role in industrial or some special applications. Unfortunately, commercial thickness meters do not provide high precision measurements non-destructively. A new spectral-domain interferometric method for measuring absolute thickness of Ultra-thin metallic foil is proposed here. The thickness is measured by differential white light spectral interferometer. Two differential Michelson Interferometers (MI) are used as basic measuring system to obtain the spectral interference fringes on the spectrometers. The spectral interference between both beams, which shows up a periodic modulation of the source spectrum with the period dependent on the OPD, serves as an illustration of a technique for measuring both OPDs and displacements in a range dependent on the source spectrum width. Therefore, the interference fringes only depend on the OPD due to the thickness of metallic foil and are unrelated to the position of the foils in the system, which is insensitive to the vibration. The spectral interference fringes are resolved over a wide spectral range and the absolute thickness of metallic foil can be calculated by measuring the OPD with a modified extremum method based on the least root mean square (RMS) deviation. The theoretical analysis and preliminary experiments indicate that the technique can measure the thickness of foils in the range of 1μm to 80μm, and it requires less than 50ms within the single measurement. Experimental results are presented.

Abstract: Recently, the trends of industrial products move towards more miniaturization, variety and mass production. Micro drilling which take high precision in cutting work is required to perform more micro hole and high speed working. Especially, Micro deep hole drilling is becoming more important in a wide spectrum of precision production industries, ranging from the production of automotive fuel injection nozzle, watch and camera parts, medical needles, and thick multilayered Printed Circuit Boards(PCB) that are demanded for very high density electric circuitry. The industries of precision production require smaller holes, high aspect ratio and high speed working for micro deep hole drilling. However the undesirable characteristics of micro drilling is the small signal to noise ratios, wandering motion of drill, high aspect ratio and the increase of cutting force as cutting depth increases. In order to optimize cutting conditions, an experimental study on the characteristics of micro deep hole machining processes using a tool dynamometer was carried out. And additionally, microscope with built-in an inspection monitor showed the relationship between burr in workpieces and chip form of micro drill machining.

Abstract: novel time-domain error separation method which can reconstruct straightness profile of workpiece exactly for on-machine measurement has successfully been developed. The proposed method is based on difference measurement and can use two or three displacement probes. It possesses following characteristics: (i) adapting to long or short workpiece, (ii) assuming no prior knowledge, (iii) employing large shears, (iv) needing no accurate zero-adjustment of probes, and (v) reconstructing various surfaces including smooth, non-smooth, periodic and non-periodic profiles with no theoretical error. The shortest length which can be reconstructed exactly has been calculated in time-domain method. The theoretical analysis justifies the effectiveness of this method.

Abstract: In order to realize ductile machining of optical glasses using mono-layer nickel electroplated coarse-grained diamond grinding wheel, a novel conditioning technique features using a copper bonded diamond grinding wheels of 15m grain size dressed by ELID (electrolytic inprocess dressing) to condition the 46m grain sized diamond wheel has been developed. During the conditioning process, a force transducer was used to monitor the conditioning force, a coaxial optical distance measurement system was used to in-situ monitor the modified wheel surface status. White-light interferometry (WLI), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the conditioned wheel surface status as well as the ground optical glass surface topography correspondingly. The experimental result indicates that a minimized wheel radial run-out error of less than 2μm as well as the top-flattened diamond grains of constant wheel peripheral envelop profile were generated on a 5-axis ultra-precision machine tool. The grinding experiment proved that the well conditioned 46μm coarse-grained diamond wheel can be used in realizing the ductile grinding of optical glass BK7, which indicates that the newly developed conditioning technique is feasible and applicable to introduce the coarse-grained diamond wheels into precision machining of brittle and hard-to-machine materials.

Abstract: In order to keep the stability of tool’s removal function, it is required that the anastomosis be tight between the tool and workpiece surface in Computer-controlled Optical Surfacing (CCOS). In this paper, the influence of tool’s character on anastomosis status is firstly studied. The relation model on the ratio of radius to thickness, Young's modulus of the tool, normal asphericity and normal arc height of workpiece surface is established, and the macroscopical condition of tight anastomosis is derived in aspheric optics machining. According to the microcosmic distribution of surface error, the mathematical relation between anastomosis error and removal rate is researched. In the end, the influence rule of anastomosis status on the convergence ratio of residual error is analyzed in machining zone. Based on the conclusion of machining instance, it is found that workpiece material would be fast removed in middle contact zone when the peak value of tool’s removal function locates in its center position.

Abstract: The shearing processes such as the blanking and piercing of sheet metals have been often used to prepare workpiece for subsequent forming operation. The sheared plane plays an important role in the shearing products’ dimension precision and their functions. The quality of sheared plane is affected not only by the material characteristics but also by the process parameters. In the current study, the finite element method is used to investigate the shearing process of sheet metals. Then, the neural network was employed to construct the relationship model of shearing process parameters related to the fracture depth of sheared plane, such as blank holding force, die corner radius, punch-die clearance, friction factor and punch speed,. The result and approach obtained from this study would be beneficial to stamping industries because they provide the reference for the prediction of shearing process.

Abstract: The work aims to present a novel press system, and to investigate its feasibility by performing a kinematic study. Firstly, the new design is proposed, which is composed by a motor, a constant speed coupling, a gear reducer, a generalized Oldham coupling, and a slider-crank mechanism. Secondly, its structural sketch is drawn, and its kinematic dimensions are obtained by studying its motion geometry. Then, a design example is given for illustration. Moreover, the solid model of the design is established, and then the validity of the design is verified by kinematic simulation using ADAMS software. Finally, the effects of different link ratios on the output motion are examined by conducting a number of simulations. The results of simulations show that the new design can produce more flexible output motion than a mechanical press. In addition, it has the advantages of lower cost, high reliability, and lower energy consumption, compared to a servo press.

Abstract: Stainless steel and other ferrous metals are normally classified as not diamond turnable for the unacceptable tool wear caused by the thermal-chemical reaction between diamond and ferrous metals. In the present research, stainless steel specimens were plasma nitrided at a relatively low temperature (<450oC) to prevent the depletion of Cr content at the austenite matrix and to give a hardened layer where Fe atoms are bonded to nitrogen atom to form γ’-Fe4N. Diamond turning experiments were subsequently carried out under the following machining conditions: single crystal diamond tool, cutting speed up to 180 m/min, cut depth up to 5μm and light mineral oil as the cutting fluid. The results showed that, given the same machining conditions, while rapid tool wear and poor surface finish were obtained when turning the as-received stainless steel, surfaces with Ra better than 3nm and no obvious tool wear were achieved when turning the plasma nitrided specimens

Abstract: Many research works have been focusing on nanoimprint technology due to the recent potential mass production for the nanostructure applications. For optical or display application, a nanoimprint mold of large area becomes one of the thorniest techniques since it takes much time to fabricate the whole mold with nanostructure and it may make the beginning nanostructures inconsistent with the final ones. In order to fabricate the nanostructure mold of large area in a short time, the plasma process forming nanostructures on silicon substrate and the electroforming process are explored in the current study. Well-aligned nanotip arrays of 4 inch silicon were fabricated by electron cyclotron resonance (ECR) plasma process using gas mixtures of silane, methane, argon, and hydrogen. The resultant tips have nano-scale apexes, approximately ~1 nm, with high aspect ratios, nearly ~15, which were achieved by simultaneous SiC nano-mask formation and dry etching during ECR plasma process. Next, the nickel mold of nanostructures is made from silicon nanostructures through the electroforming process by using Nickel Sulfamate. The total thickness of the nickel mold is 120 μm after a 10-hour-long electroforming process. The nanostructures of 100 nm diameter holes are successfully obtained. Nanoimprint process is proceeded by the nickel mold and the reflectance of the PMMA after imprinting at 160 °C has the lowest value, 0.2 %, compared with the other results for the incident optical wavelength of 550 nm. The large-area imprint mold with high-aspect-ratio nanotip arrays of sub-micron diameter is fabricated and is proofed by the optical application.