Ductile Streaks Research Articles

Surface roughness of machined wood and advanced engineering materials and its prediction: A review

This article discusses the surface roughness of wood and advanced engineering materials after machining and its prediction. The topics are surface roughness of precision-machined advanced engineering materials, machining of WC and Inconel, rapidly solidified Al alloys, surface roughness of wood materials, and prediction of surface roughness. Findings include that ductile streaks on silicon and glass surfaces ground or lapped with inexpensive machines largely reduced the polishing time to obtain the required surface roughness. Abrasive jet machining could remove the patterns from recycled wafers and improve the surface roughness. The roughness of WC-Co coatings was significantly improved by using the method of fast regime fluidized bed machining. As beryllium is a toxic element, the rapidly solidified Al alloy may be a good insert material to replace BeCu. Higher bonding strengths resulted from rougher surfaces of wood samples. Wood samples had reduced bonding strengths after soaking in water. Optimum artificial neural networks (ANNs) with necessary inputs could accurately predict the roughness values. ANNs trained using particle swarm optimization and genetic algorithms could predict surface roughness better than typical ANNs. Minimum quantity lubrication is a hot research topic to minimize the amount of the fluid for cost and environmental considerations.

Achievement of Ductile Regime Machining in High Speed End Milling of Soda Lime Glass by Using Tungsten Carbide Tool Insert

Soda lime glass is widely used in optics, chemical apparatus, camera lens, micro gas turbines, light bulbs etc. on account of its high hardness, corrosion resistance, and excellent optical properties. These require high dimensional accuracy and flawless surface finish. However, soda lime glass is inherently brittle leading to subsurface crack propagation and fracture which compromise its functionality. To avoid these defects, the machining needs to be performed under ductile mode conditions. Therefore, this research investigates the viability and requisite conditions for achieving ductile regime machining (DRM) in high speed micro-end milling of soda lime glass. Machining was performed at high cutting speeds (30,000 to 50,000 rpm), feed rate (5 to 15 mm/min), and depth of cut (3 to 7 μm). A surface profilometer was then used to measure the surface roughness and a scanning electron microscope (SEM) used to scrutinize the resultant machined surfaces. The results demonstrate that ductile streaks and rounded gummy chips (without sharp or jagged edges) are produced in all runs. In addition, there are no subsurface cracks and the minimum surface roughness attained is 0.08μm. These indicate that DRM of soda lime glass is obtainable using high-speed micro end milling in a conventional end mill with tungsten carbide inserts.

Machining Characteristics in Cryogenic Grinding of SiCp/Al Composites

In this study, liquid nitrogen was applied to grind SiCp/Al composites with high volume fraction and large SiC particle at different levels of cutting conditions, and the effects of grinding depth and speed on grinding force, surface morphology, and surface roughness were investigated. At the same time, the effect of cryogenic cooling was also compared with that of conventional wet grinding. The experimental results indicated that cryogenic cooling is effective in enhancing supporting function of Al matrix to the SiC particles and improving surface quality. Additionally, the brittle fracture of SiC particles was suppressed and some ductile streaks on SiC particle could be observed.

Surface finish prediction models for precision grinding of silicon

Conventional grinding of silicon substrates results in poor surface quality unless they are machined in ductile mode on expensive ultra-precision machine tools. However, precision grinding can be used to generate massive ductile surfaces on silicon so that the polishing time can be reduced immensely and surface quality improved. However, precision grinding has to be planned with reliability in advance and the process has to be performed with high rates of reproducibility. Therefore, this work reports the empirical models developed for surface parameters Ra, Rmax, and Rt with precision grinding parameters, depths of cut, feed rates, and spindle speeds using conventional numerical control machine tools with Box–Behnken design. Second-order models are developed for the surface parameters in relation to the grinding parameters. Analysis of variance is used to show the parameters as well as their interactions that influence the roughness models. The models are capable of navigating the design space. Also, the results show large amounts of ductile streaks at depth of cut of 20 μm, feed rate of 6.25 mm/min, and spindle speed of 70,000 rpm with a 43-nm Ra. Optimization experiments by desirability function generate 37-nm Ra, 400-nm Rmax, and 880-nm Rt with massive ductile surfaces.

An experimental study on precision grinding of silicon using diamond grinding pins

Silicon substrates are difficult to grind to good surface finishes using conventional machining. Ductile mode machining is often required to have flawless machining but this requires the use of expensive machine tools. However, precision grinding using conventional machine tools could generate large amounts of ductile streaks on ground silicon surfaces under good machining conditions. High wheel rotation, slow feed rate, small indentations and small grain sizes are the practical requirements to realise precision grinding of silicon. Therefore, this study examines the feasibility of quantitative determination of the criteria to realise precision grinding of silicon on an NC milling machine with factorial experimental design. The result shows massive ductile streaks at depth of cut, 20 μm; feed rate, 6.25 mm/min and spindle speed of 70,000 rpm with a 43 nm Ra. Spindle speed affects mostly the surface finish. The combined effects of depth of cut and feed rate on Ra and Rt which add to the complexity in the precision grinding process are investigated.

Effects of abrasive tools on surface finishing under brittle-ductile grinding regimes when manufacturing glass

This paper addresses the effects of bonds and grains of abrasive tools on the edge aspect of ground glass surface. Diamond grains and silicon carbide (SiC) grains combined with two bond types, i.e., resin and metal, were considered for this study. The surface edge characteristics were characterized using scanning electron microscope (SEM) and interferometer observations. In particular, the spectrum of arithmetic mean was investigated for distinguishing the different scales of analysis. Experimental results showed that the grinding forces vary sensitively with bond type and wheel velocity. Using diamond grains’ wheel, it was found that roughness level obtained with metallic bond is lower than that obtained with resin bond. However, using a resin-bonded wheel, two mechanisms of material removal were revealed according to grains’ type. (i) A partial ductile regime, i.e., ductile streaks and brittle fracture, obtained with diamond grains, and (ii) a fully ductile regime obtained with SiC grains. Thus, it was found that ground surface obtained using SiC grains’ wheel has a better roughness than that obtained using diamond grains wheel. Besides, SiC grains seem to lead to more marked streaks and form defects.

The novel bondless wheel, spherical glass chips and a new method of aspheric generation

Polished partial ductile mode ground surfaces that are the result of relatively low cost processes for ophthalmic, infra-red, and laser optics applications are discussed here. Surfaces obtained during generation of aspheric profiles on glass, Si and Ge have shown formation of massive ductile streaks, which reduce polishing time. A novel imaging technique has been developed to assess the quantity of ductile streaks formed during grinding. Yet another observation is the occurrence of spherical shaped glass chips, which appears to indicate the best cutting conditions. The development of a bondless diamond grinding wheel has resulted in surfaces where the quantity of ductile mode streaks is increased. Finally, a model for arriving at the optimum depth of cut is outlined.

Partial melting of slab window margins: genesis of adakitic and non-adakitic magmas

When a mid-ocean spreading ridge subducts, it typically splits apart at depth to form two tapered slab edges separated by asthenospheric mantle within a slab window. We examine the fate of the slab edges using simplified slab window geometries, specific thermal parameters, and assumptions regarding shear stress and slab hydration. Six fundamental zones of slab anatexis are identified and classified according to expected melt and restite compositions. Non-adakitic melts of granodioritic to tonalitic composition are generated along the plate edges at depths of 5–65 km, whereas adakitic melts form proximal to the edges at depths of 25–90 km. As anatexis proceeds, the subducted crust is converted to a migmatite of slab melt and eclogitic restite. Much of the migmatite may shear away from the slab and become incorporated into the mantle. The melts will rise and leave behind fragments of restite within mantle peridotite. If the peridotite is part of the overriding plate, then the restite fragments may become long-term residents of the continental lithospheric mantle. However, if the restite becomes entrained in the asthenosphere, it may undergo upwelling and melting, or flow away as ductile streaks to become long-term mantle heterogeneities. Slab windows are thereby identified as important sites for slab melting and geochemical replenishment of the mantle.

Ductile streaks in precision grinding of hard and brittle materials

Ductile streaks produced during diamond grinding of hard and brittle materials have aided the subsequent process of polishing. Two novel techniques were used to study the formation of ductile mode streaks during diamond grinding (primary process) of germanium, silicon, and glass. In the first technique, aspheric surfaces were generated on Ge and Si at conventional speeds (5000 rpm). In the second technique, diamond grinding of plano surfaces on glass and Si surfaces using high speed (100,000 rpm) was carried out. Form accuracy, surface finish and ductile mode grinding streaks are discussed in this paper. It was found that resinoid diamond wheels gave more ductile streaks than metal-bonded wheels but better form accuracy was obtained with the latter. Ductile streaks were obtained more easily with pyrex rather than with BK 7 glass thus necessitating very little time for polishing. Ductile streaks appeared in abundance on germanium rather than silicon. Both the novel grinding techniques were used on CNC machining centres.

Ductile or Partial Ductile Mode Machining of Brittle Materials

This paper reports ductile or partial ductile mode machining of silicon, glass and some advanced ceramics. Results are presented using scanning electron micrographs of the machined surfaces. Grinding and lapping operations using inexpensive machine tools could produce ductile streaks on surfaces of these brittle materials under good conditions. Manufacture of spherical glass lenses by the fracture mode or partial ductile mode grinding followed by partial ductile mode lapping and ductile mode polishing is fast and economical. Using partial ductile mode grinding and ductile mode polishing has also been very successful for manufacturing aspherical glass lenses. Reduced polishing time and improved surface quality are due to the presence of ductile streaks. Ground silicon, ZrO2 and Al2O3 also showed ductile streaks. Toroidal SiC surfaces ground with flat-face cup wheels indicated 100% ductile machining, and did not require polishing.

Grinding of Single-Crystal Silicon Along Crystallographic Directions

This article studies the effect of grinding along crystallographic directions on the surface finish of single-crystal silicon. It also discusses new and/or improved processes for precision machining brittle materials, including silicon. Silicon samples were cut from (100) silicon wafers. These samples were then subjected to grinding along different crystallographic directions under the same experimental conditions. The surface roughness and the surface texture of these samples were then analyzed. The R a and R q values and the microphotographs of the ground silicon surfaces showed the dependency of surface finish on the grinding direction. Better surface finish was achieved when (100) silicon was ground along ⟨110⟩ directions. Samples ground along these directions also showed more ductile streaks on the silicon surfaces, compared with surfaces ground along the other directions.

Grinding of Aluminium-Based Metal Matrix Composites Reinforced with Al2O3 or SiC Particles

_m for rough grinding and 0.1–1 _m for fine grinding, a crossfeed of 3 mm and 1 mm for rough and fine grinding, respectively,while maintaining a constant table feedrate of 20.8 m min -1 . Surface integrity of the ground surfaces and subsurfaces was analysed using a scanning electron microscope and a profilometer. Grinding using a 3000-grit diamond wheel at depths of cut of 1 _m and 0.5 _m produced ductile streaks on the Al2O3 particles and the SiC particles, respectively. There was almost no subsurface damage except for rare cracked particles when fine grinding with the diamond wheel.

Grinding of alumina/aluminum composites

With the anticipated widespread usage of metal matrix composites (MMCs) in the near future, the machinability of high performance MMCs needs to be understood. This paper reports research results obtained from the grinding of aluminum-based MMCs reinforced with Al 2O 3 particles using grinding wheels having SiC in a vitrified matrix and diamond in a resin-bonded matrix. The issues discussed are surface roughness, grinding force, type and size of the abrasives, grinding conditions, and the consequential sub-surface integrity. The study used grinding speeds of 1100–2200 m/min, a grinding depth of 15 μm for rough grinding and 1 μm for fine grinding, and cross-feeds of 3 and 1 mm for rough and fine grinding respectively, while maintaining a constant table feed-rate of 20.8 m/min. The surface integrity of the ground surfaces and sub-surfaces were analyzed using a scanning electron microscope (SEM) and a profilometer. The surface finish values, R a, were scattered in the range 0.15–0.70 μm for the rough-ground samples, whilst a narrower range of 0.20–0.35 μm was achieved for the fine-ground samples. Smearing of aluminum on the ground surfaces was seen for rough grinding, but was negligible for fine grinding because all the Al 2O 3 particles of the ground surfaces were clearly visible when observed with the SEM. Grinding using a 3000-grit diamond wheel at depth of cut of 1 μm produced many ductile streaks on the Al 2O 3 particles. Both the Al 2O 3 particles and aluminum matrix were removed by micro machining. There were no cracks and defects found on the ground surfaces. There was almost no sub-surface damage, except for a rare cracked particle being found. Rough grinding with a SiC wheel followed by fine grinding with a fine-grit diamond wheel is recommended for the grinding of alumina/aluminum composites.

Surface finish of precision machined advanced materials

This paper studies the surface finish and integrity of glass, silicon, some advanced ceramics and aluminum-based metal matrix composites (MMCs) reinforced with ceramic particles, precision machined by various machining processes. The studies revealed that grinding/lapping operations using inexpensive machine tools can produce ductile streaks on glass and silicon surfaces under good grinding/lapping conditions. This resulted in significantly shortened polishing time to secure an acceptable surface finish. If there are several processes to manufacture a lens, each preceding process is very important for the successive processes. In order to reduce the total manufacturing time, it is preferable to obtain better ground/lapped surfaces with as many ductile streaks as possible in order to reduce the polishing time. Toroidal SiC surfaces ground with flat-face cup wheels indicated 100% ductile machining, and did not require polishing. Ground ZrO 2 showed a numerous ductile streaks. Plastic deformation was the major mechanism of material removal at high wheel speeds. Grinding of aluminum-based MMCs reinforced with Al 2O 3 or SiC particles using a 3000 grit diamond wheel at depths of grinding of 1 and 0.5 μm produced many ductile streaks on the Al 2O 3 and SiC particles, respectively. There was almost no sub-surface damage. The machines used for the experiments reported in this paper are not expensive ultra-precision machines.

GRINDING OF NICKEL-BASED SUPER-ALLOYS AND ADVANCED CERAMICS

This paper studies grinding of Inconel 718, Hastelloy, and some advanced ceramics. A newly developed ultra-high-speed grinding machine and a conventional grinding machine were used for the experiments. The ultra-high-speed grinding machine is equipped with a specially designed and built spindle unit that can run up to 200 m sec−1 and deliver a maximum output of 12 kW. The surface roughness and residual stress values of the ground super-alloys and advanced ceramics were measured using a profilometer and a residual stress analyzer, respectively. The ground surfaces were also assessed using a scanning electron microscope. The effect of h m (undeformed chip thickness) on surface topography of the difficult-to-machine materials was also investigated. A higher grinding wheel speed produces a smaller cutting depth and undeformed chip thickness, and thus smaller grinding force, decreased residual surface stress, and better surface finish. High productivity and good surfaces with ductile streaks could be obtained by employing ultra-high-speed grinding, even at very large wheel depths of cut such as 400 μm, without cross feed.

Diamond Turning and Grinding of Aluminum-Based Metal Matrix Composites

This paper reports research results obtained from diamond turning and grinding of aluminum-based MMCs reinforced with either SiC or Al2O3 particles. Both polycrystal diamond (PCD) and single crystal diamond (SCD) tools were used for turning the MMCs at depths of cut ranging from 0 to 1.6 um. Diamond grinding wheels were used to grind the MMCs at depths of cut from 0.1 to 1 µm. Besides die depth of cut, ductile-mode turning of the reinforcing particles might also be affected by the orientation of the particles. Grinding using a 3,000-grit diamond wheel at depths of cut of 1 and 0.5 µm produced ductile streaks on the Al2O3 particles and the SiC particles, respectively. There was almost no subsurface damage except rare cracked particles. At the same depth of cut, the surfaces ground with the diamond grinding wheel revealed more ductile streaks on the reinforcement ceramic particles than those obtained from SCD turning.

Machining of Glass Molds for Manufacturing Plastic Lenses

This paper reports research results on machining of glass molds for manufacturing plastic lenses. Aspherical and spherical plastic lenses are produced by replicating them on glass molds that are first ground (milled) and then lapped and polished. Results of surface texture analysis using the Form Talysurf instrument are presented together with scanning electron micrographs of the machined surfaces. Microstructure analysis conducted using scanning electron microscope reveals ductile streaks on ground (milled) and lapped glass surfaces. Polishing time versus surface roughness curves indicate the familiar knees, after which an increase in polishing time does not improve the surface finish. A moire deflectometer was used to observe fringe patterns on polished surfaces, in order to distinguish between acceptable polished surfaces and defective surfaces.

Partial-Ductile Grinding and Reduced Polishing for Ophthalmic Glass Molds

Plastic lenses are manufactured by the classical replication technique where two glass molds are assembled in a jacket and liquid plastic is injected into it. The glass molds are fabricated conventionally by fracture mode grinding, followed by lapping, and Finally polishing. This paper presents an alternative fabrication process using partial-ductile grinding, followed by a short polishing in an industrial polishing machine. The partial-ductile surfaces were generated on a laboratory ultra-precision machine using Fine grit resinoid-bond diamond wheel and they were compared to the glass molds prepared by industry. The results showed that (i) as much as 100% ductile streaks (fully ductile grinding) can be obtained in the ultra-precision ground surface and (ii) a net saving of 55 seconds polishing time if only 60% of ductile streaks on the glass mold surface was used prior to polishing.

Semi-ductile grinding and polishing of Pyrex glass

Semi-ductile grinding followed by simple mechanical polishing is an economical process for producing a mirror-like surface for hard and brittle Pyrex. A fine-grit resinoid-bonded diamond wheel was used to generate large amounts of ductile streaking to improve the surface quality and reduce the polishing time. The ground samples were polished with diamonds and/or cerium oxide to analyse the effect of the abrasives, the polishing pad and the pressure on the surface produced. The microstructure of the ground sample was investigated using a scanning electron microscope whilst the polished surface was analysed using an atomic force microscope. The results of this study show that: (i) as much as 85% of ductile streaks were found on the ground surface; and (ii) the cerium oxide polishing process yields the best surface, the latter having a roughness of 8.7 nm after 2 min of polishing, with very few fine hair-line scratches.

Partial-Ductile Grinding, Lapping, and Polishing of Aspheric and Spherical Surfaces on Glass

This paper discusses partial-ductile-mode grinding, lapping and polishing of aspheric and spherical surfaces on glass. Industrial manufacture of glass lenses usually involves three operations: grinding (known as milling in the optical industry), tapping, and polishing. The fracture mode of material removal is dominant in the grinding process. While these three operations have been successful for machining spherical lenses, aspheric lenses have been manufactured in the absence of the lapping process, because of the considerable amount of ductile mode of material removal in grinding. The parameters that helped identify and solve problems in manufacturing were surface roughness, micro-fractures and ductile streaks on glass surfaces, and interferometric fringes.