V.C. Venkatesh

Quantification of surface damage of tool steels after EDM

Abstract The surface transformation and damage in AISI O1, A2, D2 and D6 tool steels after EDM were investigated. The results show that the recast layer is composed of two distinct layers: a topmost layer solidifying inwards from the specimen surface and an intermediate layer solidifying outwards from the base of the molten metal. The depth of surface cracks is found to correlate well with the thickness of the white layer, the latter being a layer of rapidly solidified material which, depending on the tool steel material, may consist either primarily of the topmost recast layer, or both the topmost and a large part of the intermediate recast layer. The density of surface cracks, however, correlates better with the thickness of the overall recast layer. Attempts were made to quantify the depth of white (or damaged) layer with respect to the process parameters and surface roughness after EDM. It is found that with a fixed dielectric and flushing condition, the damaged layer correlates well with the pulse energy irrespective of the tool steel material. On the other hand, even though the thickness of the white layer increases with the surface roughness, the result shows considerably more scatter. Based on the present findings, ways of estimating the depth of the damaged layer produced by EDM are proposed.

Diamond Cutting of Silicon with Nanometric Finish

Abstract Micro-cutting is a viable alternative to grinding and polishing techniques in the fabrication of high quality brittle materials. Using different diamond tools with rake angles of 0 degree and −25 degree at different cutting speeds, taper cutting experiments were carried out with increasing depth of cut on silicon. The grooves formed were analyzed by Scanning Electron Microscopy and Optical Measurement Inspection System. Topographic details were studied using Atomic Force Microscope. For turned silicon surfaces with roughness value of Ra=23.8 nm and Rmax=140 nm, mirror surfaces of 1 nm roughness were achieved repeatedly by micro-cutting. The integrity of the resulting surfaces were then studied in detail by using Atomic Force Microscopy and Scanning Electron Microscopy. The results prove that the micro-cutting mechanism, proposed in theory, is justified in actual material removal in the range of nanometers.

Observations on Polishing and Ultraprecision Machining of Semiconductor Substrate Materials

Abstract Among the polishing techniques used for semi-conductor materials that are hard and brittle (Si), chemical-mechanical polishing (CMP) has many advantages and a few serious disadvantages too. For materials that are soft and brittle like GaAs, GaP, and InP, which have a very promising future, the CMP technique is now possible without the use of toxic agents. The elimination of the polishing process altogether, or a substantial reduction in polishing time is another strategy that has been successfully established by the use of electroyltic in-process dressing techniques (ELID). At the same time there are applications where profile requirements are not stringent like inexpensive night vision lenses, where partial ductile grinding and simple mechanical polishing are highly economical. Finally a simulated model for ultra precision grinding is presented here.

Performance evaluation of cemented carbide tools in turning AISI 1010 steel

In this paper, the performance of three cemented carbide cutting tools, two coated tungsten based cemented carbide — one with Al2O3 (black) outer layer and the other with TiN (golden), and an uncoated titanium based (silver grey) cemented carbide tool, with 80° — diamond insert shape were investigated during finish turning of AISI 1010 steel. The PCBNR tool holder, giving a side cutting edge angle of +15°, was used. Cutting tests were performed with constant depth of cut and at various cutting speeds and feed rates to investigate the performance of the tools under dry cutting conditions. Cutting forces and surface roughness were measured. The chips produced by the three type of tools during experimental trials were examined to determine the secondary shear zone, chip thickness and the angle of maximum crystal elongation. The tool which had the CVD with TiCN/TiC and PVD with TiN coating layer sequence performs best under the conditions tested, as lower forces with little variation were encountered, very good surface finish could be obtained and chips with minimum SSZ thickness could be produced, that contributed to low chip strain and therefore to low residual stresses on the workpiece surface.

Gloss and Surface Topography

Abstract Optical reflection and dispersion from surfaces are examined. Some of the early experiments are reviewed. This is followed by a consideration of conventional and more recent theoretical approaches. Applications of gloss are discussed with respect to manufacturing engineering and finally considerations of colour and surface interrogation by x-rays are given.

Semi-Ductile Grinding and Polishing of Ophthalmic Aspherics and Spherics*

Abstract Ductile grinding yields surfaces whose precision is far beyond that expected of ophthalmic requirements. This process requires machine tools and cutting tools that are manufactured to sub micron tolerances and which require clean rooms, thus making its cost prohibitive. While fracture mode grinding, followed by lapping and polishing have been successful, this paper presents results of semi-ductile grinding that is followed by reduced polishing time without an intervening lapping operation. Using conventional CNC machining centres and/or dedicated machines, silicon, germanium and glass were ground by metal bonded and/or diamond bonded diamond wheels followed by conventional polishing techniques.

A Heuristic Algorithm for Optimum Layout of Metal Stamping Blanks

Layout of metal stamping blank marks the first stage of a tool and die design. Traditionally, this is dependent on the skill of the craftsman who may spend many hours in achieving the final solution. In this paper, a heuristic algorithm is developed on a computer with user-friendly dialogues. The algorithm generates an optimum layout considering such factors as minimum material wastage, correct bridge width and grain orientation. In addition, it provides such information as recommendation on stock purchase policy, economic justification for a single or multiple-station operation and alignment of centre of pressure with press centre. Computer-generated solution compares very favourably with laborious trial-and-error industrial practices.

A Study of Chip Surface Characteristics during the Machining of Steel

Summary Carbide inserts of different geometry (SNG, CNMG, CNMG-MG, CPMP, and SPMP) with a variety of coatings [CVD TiN, PVD TiN, CVD (TiCN/TiC/Al 2 O 3 ), CVD (TiCN/TiC) + PVD TiN, CVD TiC, and TiN/Al 2 O 3 , …TiCN] were used to machine AISI 1018 steel at different speeds with and without a coolant. Three typical colors deep blue, blue, and golden brown were analyzed and found to contain varying amounts of oxide layers consisting of FeO, Fe 2 O 3 and Fe 3 O 4 . Chip roots from turning/drilling operations were studied for secondary shear/built-up edge formation, and temperatures calculated and related to chip color. Chip color classification, brightness, surface roughness, waviness, roundness, and chip strain were measured and evaluated.

Semi-ductile grinding and polishing of Pyrex glass

Abstract 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.

Generation of Parabolic and Toroidal Surfaces on Silicon and Silicon-Based Compounds Using Diamond Cup Grinding Wheels

Summary This paper presents the methods and experimental results using diamond cup wheels and CNC machining centers for grinding parabolic and toroidal surfaces made of Si and SiC, the former for use as a thermal imaging lens and the latter for synchrotron radiation facilities. Generation of aspheric surfaces, by zonal material removal, on Si using cup grinding wheels and a 5-axis machining center was investigated. Theoretical and experimental investigation of the grinding and material parameters that influence ductile grinding are discussed. Ductile grinding is possible with wheels having small grit size and with proper combination of feed and unit normal load; a resinoid bonded wheel promotes this more easily than a metal bonded wheel, though at the expense of profile accuracy. Profile analysis, surface integrity, and examination of grinding swarf using digital imaging are discussed. Also, generation of toroidal surfaces on SiC using metal-bonded cup wheels, a 3-axis machining center and a micro-displacement table with piezoelectric actuators was studied. Toroidal SiC mirrors were ground with good shape accuracy, mirror finish, and low surface roughness. The time consumed in the process is very short. The machines used are inexpensive and not specially designed for ultra-precision grinding.