Improvement In Dimensional Accuracy Research Articles

로어투스의 롤오버 및 금형 면압 저감을 위한 하프블랭킹 공정 설계

In recent years, automotive seat components have been manufactured by the fine blanking process, allowing an improvement of dimensional accuracy at sheared surface in series production. However, the rollover has increased and die failures have occurred more frequently when manufacturing gears by fine blanking. Consequently, important goals for manufacturing seat recliner parts with gears have been to decrease the rollover as well as to improve the tool life. In this study, the half blanking and shaving processes were introduced to improve aforementioned problems for the lower tooth, the main component of a seat recliner. For this purpose, the half blanking process was optimized using the finite element (FE) analysis and design of experiment (DOE). The optimized conditions resulting from this study were an offset of 0.2 mm, a clearance of 0.1 mm and a penetration depth of 4.5 mm. Fine blanking experiment conducted under the optimal condition resulted in a rollover depth decrease from 1.9 to 1.3 mm, and no die failure occurrence.

Step-width adjustment in fabrication of staircase structures

Three-dimensional structures increasingly find applications in various devices such as diffractive optical elements, photonic element, microelectromechanical systems, etc., and are often fabricated by e-beam lithography. Their performance is known to be highly sensitive to their dimensions. Therefore, it is critical to achieve high dimensional accuracy for the desired characteristics. However, as the feature size in three-dimensional structures decreases down to nanoscale, the lateral development of the resist and the proximity effect due to electron scattering can make dimensions of the written features in a device substantially different from the target dimensions. In this study, this issue is addressed for staircase structures; specifically, minimizing the difference between the target and the actual widths of each step. Through computer simulation and experiments, it has been shown that significant improvement in dimensional accuracy, especially the step widths of the staircase structures, can be achieved by the proposed practical width-adjustment scheme.

Force Modeling in Laser-Assisted Microgrooving Including the Effect of Machine Deflection

Laser assisted mechanical micromachining is a process that utilizes highly localized thermal softening of the material by continuous wave laser irradiation applied simultaneously and directly in front of a miniature cutting tool in order to produce micron scale three-dimensional features in difficult-to-machine materials. The hybrid process is characterized by lower cutting forces and deflections, fewer tool failures, and potentially higher material removal rates. The desktop-sized machine used to implement this process has a finite stiffness and deflects under the influence of the cutting forces. The deflections can be of the same order of magnitude as the depth of cut in some cases, thereby having a negative effect on the dimensional accuracy of the micromachined feature. As a result, selection of the laser and cutting parameters that yield the desired reduction in cutting forces and deflection, and consequently an improvement in dimensional accuracy, requires a reliable cutting force model. This paper describes a cutting force model for the laser-assisted microgrooving process. The model accounts for the effect of elastic deflection of the machine X-Y stages on the forces and accuracy of the micromachined feature. The model combines an existing slip-line field based force model with a finite element based thermal model of laser heating and a constitutive material flow stress model to account for thermal softening. Experiments are carried out on H-13 steel (42 HRC (hardness measured on the Rockwell ‘C’ scale)) to validate the force model. The effects of process parameters, such as laser power and cutting speed, on the forces are also analyzed. The model captures the effect of thermal softening and indicates a 66% reduction in the shear flow stress at 35 W laser power. The cutting force and depth of cut prediction errors are less than 20% and 10%, respectively, for most of the cases examined.

Accurate control of remaining resist depth for nanoscale three-dimensional structures in electron-beam grayscale lithography

In electron-beam (e-beam) grayscale lithography, a three-dimensional (3D) structure is transferred onto the resist or substrate. In either case, accurate control of the remaining resist depth and, accordingly, profile is critical for successful fabrication of the structure. Usually, the remaining resist depth control is guided by the empirically derived dose (or exposure)-depth relationship using a two-dimensional model. However, such an approach may require multiple calibrations and also lead to significant dimensional errors for nanoscale structures due to the depth-dependent variation of exposure and the nonlinearity between exposure and developing rate. In this study, a resist developing model is incorporated into e-beam dose control schemes in order to take the exposure variation and nonlinearity into account. Through computer simulation, it has been demonstrated that significant improvement in dimensional accuracy may be achieved by including the 3D resist developing model in the e-beam dose control for fabricating nanoscale 3D structures.

Mandrel drawing and plug drawing of shape-memory-alloy fine tubes used in catheters and stents

Drawing technology used to fabricate tubule catheters and stents for medical use, in which shape-memory and superelastic characteristics are applied, was studied. Processing conditions, improvement of dimensional accuracy and reduction of the roughness of the inner surface of the tube, which are required for the fabrication of small-diameter and thin-walled tubes, were examined by drawing experiments and using a finite-element method. Since the plastic formability of the shape-memory-alloy is extremely low, the possibility of fabricating high-quality fine tubes by mandrel drawing and plug drawing was examined. We determined an optimal shape for the plug, with which breakage frequency during plug drawing is suppressed to as low as possible, using a finite-element method, and fabricated plugs used in the experiments, based on the obtained optimal shape. For mandrel drawing in which a copper wire was used as a mandrel, drawing formability, change in the wall thickness of the drawn tubes was examined. We clarified that the fabrication of fine tubes used in catheters and stents is possible by means of plug drawing and mandrel drawing.

Software compensation of rapid prototyping machines

This paper addresses accuracy improvement of rapid prototyping (RP) machines by parametric error modeling and software error compensation. This approach is inspired by the techniques developed over the years for the parametric evaluation of coordinate measuring machines (CMM) and machine tool systems. The confounded effects of all errors in a RP machine are mapped into a “virtual” parametric machine error model. A generic artifact is built on the RP machine and measured by a master CMM. Measurement results are then used to develop a machine error function and error compensation is applied to the files which drive the build tool. The method is applied to three test parts and the results show a significant improvement in dimensional accuracy of built parts.

Near net shape manufacturing of ceramics

Reduction of shrinkage during fabrication of ceramic components is of particular importance for reduction of machining costs, improvement of dimensional accuracy as well as uniformity of microstructure and properties of complex shaped components. Processing techniques based on infiltration of fluid phases into porous preforms, reactions between condensed constituents in a green compact and porosity redistribution methods involving novel biomimetic approaches are considered. Basic limitations of novel near net shape techniques will be discussed and potential applications are introduced.

Coordinated Position Control of Multi-Axis Mechanical Systems

Position coordination of multi-axis mechanical systems is studied. Under the assumption that the coordination objective can be represented by smooth functions of the positions of the multiple axes control systems, a necessary coupling effect can be introduced to each axis by the proper choice of a Lyapunov-like function. The resulting, control law requires the knowledge of the desired trajectories and their time derivatives as well as actual position and velocity information. Implementation of the proposed control algorithm on a CNC feed drive system shows significant improvement in dimensional accuracy during high speed contouring.

Identification of Interelectrode Gap Sizes in Pulse Electrochemical Machining

Pulse electrochemical machining offers significant improvements in dimensional accuracy as compared with conventional electrochemical machining. One primary issue in pulse electrochemical machining is to identify and control the interelectrode gap size. This paper presents an identification method for the gap size by in‐process analysis of machining current pulses. Stochastic modeling and analysis of the current pulses reveal two gap indicators: pulse signal variance and damping ratio. The variance has a linear relationship with the gap size within a commonly used gap range of 0.10 to 0.20 mm for a wide range of pulse durations. The damping ratio has been found to be highly correlated with the gap size. Laboratory experiments confirm the feasibility of this method under unevenly distributed gap conditions. The process mechanism underlying these findings is also discussed.

Improvement of Dimensional Accuracy and Total Productivity by Air Impact Molding

Improvement of Dimensional Accuracy and Total Productivity by Air Impact Molding