Deep Narrow Grooves Research Articles

Electrochemical Milling of Deep-Narrow Grooves on GH4169 Alloy Using Tube Electrode with Wedged End Face.

Deep-narrow grooves (DNGs) of nickel-based alloy GH4169 are extensively used in aerospace industry. Electrochemical milling (EC-milling) can manufacture special structures including DNGs by controlling the moving path of simple tool, showing a flexible process with the advantages of high machining efficiency, regardless of material hardness, no residual stresses, burrs, and tool wear. However, due to the inefficient removal of electrolytic by-products in the inter-electrode gap (IEG), the machining accuracy and surface quality are always unsatisfactory. In this paper, a novel tube tool with wedged end face is designed to generate pulsating flow field in IEG, which can enhance the removal of electrolytic by-products as well as improve the machining quality of DNG. The flow field simulation results show that the electrolyte velocity in the IEG is changed periodically along with the rotation of the tube tool. The pulsating amplitude of electrolyte is changed by adjusting the wedged angle in the end face of the tube tool, which could affect the EC-milling process. Experimental results suggest that the machining quality of DNG, including the average width, taper of sidewall, and surface roughness, is significantly improved by using the tube tool with wedged end face. Compared with other wedged angles, the end face with the wedged angle of 40° is more suitable for the EC-milling process. DNG with the width of 1.49 mm ± 0.04 mm, taper of 1.53° ± 0.46°, and surface roughness (Ra) of 1.04 μm is well manufactured with the milling rate of 0.42 mm/min. Moreover, increasing the spindle speed and feed rate can further improve the machining quality of DNG. Finally, a complex DNG structure with the depth of 5 mm is well manufactured with the spindle speed of 4000 rpm and feed rate of 0.48 mm/min.

Electrochemical milling of narrow grooves with high aspect ratio using a tube electrode

Abstract Metallic narrow grooves with high aspect ratio, referred to here as deep narrow grooves (DNGs), are used widely in precision instruments, medical devices and other industries. However, because DNGs are usually less than 4 mm in width with depth-width ratio (aspect ratio) more than 2, it remains extremely challenging to machine them with high precision and efficiency, especially for blind (i.e., closed-end) cases. Therefore, this paper proposes a novel method of electrochemical milling using a tube electrode to fabricate a DNG by single-pass milling. A multi-physics coupling model, including a gas-liquid two-phase flow field and an electric field, was built to investigate the flow field distribution in the inter-electrode gap as well as the current density distribution at the DNG edge with different electrolyte pressures. Related experiments were also conducted. The simulation and experimental results indicated that a higher pressure was associated with a high electrolyte velocity, and had a significant influence on the machining process. First, the high electrolyte velocity in the inter-electrode gap could enhance the mass transfer and improve the sectional profile of the DNG. Second, when the electrolyte flowed out, the high electrolyte velocity could overcome self-gravity and reduce the accumulation at the edge of the DNG, which decreased the electrolyte volume fraction in the two-phase flow field at the DNG edge. Thus, the current density distribution at the outlet edge was decreased, and the corner radius at the edges of the DNGs was reduced. Then, systematic experiments were performed with different machining parameters (including electrolyte pressure, pulse parameters and feeding speed) to investigate their influence on the DNG dimensions; with the optimized parameters of an electrolyte pressure of 0.9 MPa, applied voltage of 12 V, pulse frequency of 9 kHz, pulse duty cycle of 40 % and feeding speed of 0.36 mm/min, a complex narrow groove of width 1.32 ± 0.02 mm (mean ± standard deviation) and depth 8.05 ± 0.01 mm was well fabricated with single-pass milling, and the aspect ratio reached 6.1, showing a high precision and efficiency machining method.

Experimental research on improving accuracy of electrochemical machining of deep narrow grooves

Deep narrow metal grooves have wide application prospects in the field of aeronautics and astronautics. Electrochemical machining (ECM) has a unique advantage in the fabrication of deep narrow grooves due to its advantages of no cutting heat, no cutting force, and high machining efficiency. But, there is significant stray current corrosion in the side wall of the deep narrow groove, which restricts the enhancement of the processing accuracy. In the interest of improving the processing accuracy of the deep narrow groove, the effects of compound feed and matching of pulse and oscillation (MOPAO) on the average current density distribution of the deep narrow groove side wall were studied based on finite element analysis (FEA) of the electrostatic field. The finite element simulation results show that the homogeneity of the deep narrow groove could be significantly improved with the increment of the oscillation amplitude, and the processing accuracy could be improved by prolonging the pulse turn-off time. Moreover, contrast experiments on the deep narrow groove ECM were carried out based on a self-developed ECM system. The experimental results indicate that the matching of pulse and oscillation can remarkably improve the processing accuracy, and smaller average groove width and better groove width uniformity can be obtained in comparison with the compound feed. Moreover, the maximum groove width is 2.78 mm, the minimum groove width is 2.73 mm, the length-width ratio reaches 11:1, and the depth-width ratio reaches 9:1 using the machining mode of MOPAO.

Experimental research on process stability in pulsed electrochemical machining of deep narrow grooves with high length-width ratio

With respect to deep narrow groove structures with high length-width ratio and high depth-width ratio (particularly when the ratio is greater than 10), the cathode rigidity and flow-field stability deteriorate during the electrochemical machining (ECM) process. To improve the machining efficiency and process stability of deep narrow grooves with high length-width ratio, a hollow slice cathode with stiffeners was designed and optimized to meet the rigid requirements using the method of one-way fluid-solid coupling finite element analysis. Additionally, the effects of cathode stiffener size, stiffener distribution, and cathode vibrating feed mode on the flow field in the machining gap were investigated using the flow-field simulation analysis method. The simulation results indicate that cavitation and electrolyte starvation in the machining gap are avoided with a reasonable stiffener design, and the renewal of electrolyte in the machining gap is improved with a reasonable vibration motion. Contrast experiments were performed based on the simulation results. The experimental results verified that the optimal design of stiffeners and the reasonable cathode vibration improve the stability of the flow field. Moreover, process stability and machining efficiency of ECM of deep narrow grooves with high length-width ratio improve with the adoption of the optimal vibrating feed parameters.

Extension of the double-ellipsoidal heat source model to narrow-groove and keyhole weld configurations

The double-ellipsoidal heat power density model proposed by Goldak, has been widely used as the basis for modelling heat transfer in arc welding operations for more than thirty years. This approach has proved to be extremely effective for a wide range of arc welding operations. However, the application of a double-ellipsoidal heat power density distribution is less appropriate for keyhole-laser or electron-beam welding operations, or in situations where arc welding takes place within deep narrow grooves. In this paper the double-ellipsoidal distribution is extended to a double-ellipsoidal-conical heat power density model in order to accurately describe transient temperature fields for a wider range of geometries and welding processes. The new extended model was validated through comparing predicted welding thermal cycles with those measured for a single pass electron beam weld, as well as those measured in a multi-pass narrow groove gas-tungsten-arc weld. In both cases, excellent agreement was obtained between predicted and measured thermal transients.

IR birefringence in artificial crystal fabricated by anisotropic etching of silicon

Periodic structures of deep narrow grooves with vertical walls have been fabricated by liquid anisotropic etching of silicon. It has been shown experimentally that the medium obtained behaves as a negative uniaxial crystal with an optical axis parallel to the wafer plane and exhibits an extremely high optical anisotropy in the mid-IR spectral range. The difference in the effective refractive indices for the ordinary and extraordinary rays, Δn, is about 1.5.

Characterization of III-V materials by optical interferometry

Digital interference microscopy is a new measuring technique with submicron horizontal resolution and nanometric vertical resolution, that can be used for the three-dimensional analysis of surface defects and device features in many microelectronics applications on bulk materials and epitaxial layers. In this paper we show how certain defects can be analysed on III-V materials and devices using two different interferometric techniques. The choice of the technique depends on the height and the slope of the surface features to be measured. We show that small defects less than λ/2 in height, or surfaces with shallow continuous slopes upto one or two microns high are best profiled with the phase stepping technique (PSM) because of the high vertical resolution of 1 nm and the higher speed and precision. This is illustrated by studies of the surface polish of InP wafers, defects after chemical etching of tin doped InP, defects on an epitaxial layer of GaAs on InP and quantum dot structures on GaAs. For measuring devices which contain mesas and grooves with step heights greater than λ/2, the peak fringe scanning (PFSM) method is the better choice. The vertical resolution is slighthly less (4 nm), but the vertical range is higher (upto 15 μm) as demonstrated with the measurement of an etched groove in laster/detector device on a quaternary layer on InP, and MESFET device on GaAs. Compared with electron microscopy and the new near field scanning techniques, digital interference microscopy has the advantages of ease of use and speed of analysis and being able to resolve certain problems that are difficult or not possible by other means, such as profiling deep narrow etched grooves, or measuring the relief of a surface hidden under a transparent layer. The main disadvantages are that the horizontal resolution is limited to the resolving power of the objective and that errors due to variations in the optical properties of the sample need to be taken into account

Directional solidification cells with grooves for a small partition coefficient.

Using the asymptotic matching procedure of Dombre and Hakim, we determine properties of the steady-state cellular structures with deep narrow grooves observed in directional solidification experiments. The method is valid in the experimentally relevant region of small partition coefficient and finite P\'eclet number. An extension of the Scheil equation for the grooves is given, and the importance of conservation in determining the groove closing is pointed out.

Can surface-enhanced raman scattering be caused by waveguide resonances?

The amplitude of the standing wave within each channel of a rough metallic surface consisting of a set of deep narrow grooves is shown to increase dramatically at certain (resonant) frequencies thereby leading to abnormal optical absorption and large field enhancement within the channels. Adsorbed molecules located therein might account for the SERS signals observed with quenched Ag films.

Laser-machined GaP monolithic displays

The feasibility of producing electrically and optically isolated monolithic devices from planar GaP p-n junction material by the use of laser-machining techniques has been demonstrated. By machining deep narrow grooves through the p-n junction and around the areas to be contacted, it is possible to produce monolithic displays without the use of photolithography or critical etching steps. The resultant mesa devices have excellent optical definition and electrical properties. As an illustration of the technique, small (2.5-mm-high) monolithic seven-bar numerics have been fabricated from green-emitting GaP. This laser-machining technique should be applicable to other semiconductor materials and devices such as GaAs lasers.