Diamond Machined Surface Research Articles

The Approach of Nanoscale Vision-Based Measurement Via Diamond-Machined Surface Topography

The Approach of Nanoscale Vision-Based Measurement Via Diamond-Machined Surface Topography

Ultra-Precision Machining: Cutting With Diamond Tools

Abstract This article is written as a tribute to Professor Frederick Fongsun Ling 1927–2014. Single-point diamond machining, a subset of a broader class of processes characterized as ultraprecision machining, is used for the creation of surfaces and components with nanometer scale surface roughnesses, and submicrometer scale geometrical form accuracies. Its initial development centered mainly on the machining of optics for energy and defense related needs. Today, diamond machining has broad applications that include the manufacture of precision freeform optics for defense and commercial applications, the structuring of surfaces for functional performance, and the creation of molds used for the replication of a broad range of components in plastic or glass. The present work focuses on a brief review of the technology. First addressed is the state of current understanding of the mechanics that govern the process including the resulting forces, energies and the size effect, forces when cutting single crystals, and resulting cutting temperatures. Efforts to model the process are then described. The workpiece material response when cutting ductile and brittle materials is also included. Then the present state of the art in machine tools, diamond tools and tool development, various cutting configurations used, and some examples of diamond machined surfaces and components are presented. A discussion on the measurement of surface topography, geometrical form, and subsurface damage of diamond machined surfaces is also included.

Any-degrees-of-freedom (anyDOF) registration for the characterization of freeform surfaces

This paper presents an any-degrees-of-freedom (anyDOF) registration method for the characterization of freeform surfaces. The method attempts to fill the research gap regarding traditional surface registration methods which are normally dedicated to solving the global optimization problem with all DOF but they lack flexibility. The proposed anyDOF method is capable of registering surfaces with any specified combination of DOF. This is particularly useful when some of the DOF are known to be unchanged according to the a priori knowledge. The anyDOF surface registration method is regarded as a typical optimization problem of finding the minimum distance from target surface to the reference surface, with constraints of the unwanted DOF. The problem is solved by the Levenberg-Marquardt method. Simulated experiments for a two-dimensional (2D) profile and a three-dimensional (3D) surface were undertaken, together with three measurement experiments including a fluid-jet polished surface, a bonnet polished surface and a diamond machined freeform surface. Experimental results show that the anyDOF registration method is highly flexible in the characterization of freeform surfaces.

Fabrication of 3D submicron to micro textured surfaces using backside patterned texturing (BPT)

This work presents a novel fabrication method for submicron to micro size textures on flat surfaces using the backside patterned texturing (BPT). The proposed method utilizes the pre-fabricated macro-features on the backside of work material, and thereafter the front side is face turned with a single point diamond tool to generate textured surfaces. Different from existing texturing methods, BPT produces textured surfaces from submicron to micro scale without any external gadgets such as vibration assisted machining or synchronized tool-spindle motion. The miniature feature arises on the diamond turned surface due to the induced residual stresses when the specimen is unleashed from the machine. To demonstrate the efficacy of the method, a series of machining experiments were conducted to fabricate various types of freeform surface textures like water-drop freeform, cylindrical freeform surfaces, etc. The fabrication methodology of different sizes of bumps with precisely controlled surface quality is illustrated. The texture profiles comprising the deformation height from hundreds of nanometer to few micrometers with mirror surface quality were successfully fabricated on the diamond machined surface. The experimental results suggest that the pre-fabricated pattern, workpiece thickness and machining condition play a critical role to determine the final shape and geometry of generated textures.

Spectral analysis of surface roughness features of a lapped ultraprecision single-point diamond machined surface

Single-point diamond turning of soft metals could provide a much shiny surface with an optimal feed rate; however, the machining mark would be left on the machined surface, which caused the roughness cannot be neglected. If the feed rate is too small, the roughness of the surface could be improved but the reflectiveness would be decreased because of damaging the profile. Therefore, it is necessary to develop a lapping method to reduce the roughness by removing the machining mark, while the reflectiveness can be kept at the original level simultaneously. In this study, the novel lapping method, using strands of wool fibers to deliver the abrasive slurry to rub against the lens, was proposed for removing the machining marks on the mold of a lenticular lens by lapping without damaging the profile of the mold. Even though the normal pressure applied by the wool strands onto the mold surface is very low, the coefficient of friction would be increased significantly with the application of the abrasive slurry. The combined effect was to provide a relatively large shear force to lap the surface with a minimal normal force. Therefore, the proposed method could theoretically avoid damaging the lens while effectively removing the irregularities that appeared on the surfaces. In order to evaluate the proposed lapping method, we firstly lapped the machining marks with different lapping parameters (speed, grit size, time, and pressure) to find out the relationship between these parameters and roughness with the same profile of the mold. Secondly, the optimal lapping parameters were designed based on the above lapping results to deduce the best lapping solution for processing the machining marks. Thirdly, the lapped surface profile of the mold was test by optical profiling system, and the features of the surface can be categorized into various spectral distribution groups. Finally, by comparing the variation of the spectral distribution groups, it is verified that based on our proposed methodology, selective removal of surface spectral groups of features becomes possible.

Predictive Modelling of Cutting Force and its Influence on Surface Accuracy in Ultra-high Precision Machining of Contact Lenses

Abstract The successful application of contact lenses is heavily dependent on their form accuracy and surface integrity. Cutting forces play a key role in the diamond turning of contact lenses as they have direct influence on their form accuracy and surface integrity. In addition, the cutting forces are also important for other aspects of diamond turning of contact lenses such as tool wear. Therefore, the prediction of cutting forces in contact lens manufacturing is deemed essential for the sake of high quality optical surfaces. One way to manage the effect of the cutting force and reduce its negative effect on surface finish could be realised through optimisation and modelling techniques. There are several factors that affect the extent of the cutting force developed in diamond turning. An example of these factors is the selection of cutting parameters. The establishment of a statistical model for the reliable prediction of cutting forces which is linked to a specific optical quality characteristic could be a way for understanding the behaviour of cutting force and its effect. In this study, a cutting force model based on response surface statistical method is developed for reliably predicting the values of cutting force based on its relationship to cutting parameters in the high-precision machining of contact lenses. The model obtained from fifteen experimental tests determines the effects of cutting speed, feed rate and depth of cut on force and how various combinations of parameters affect cutting force and thus surface quality. Results indicate that feed rate is a significant factor in the generation of high cutting force and low surface roughness. The study concludes that high feed rates and high cutting speeds cause an increase in cutting force and thus adversely affect the quality of the diamond-machined surface in the high precision machining of contact lenses.

Nano texture generation in single point diamond turning using backside patterned workpiece

Abstract A nano-texturing method in single point diamond turning using backside patterned workpiece is presented. The back side of the workpiece is pre-machined to first create a pattern. The front side is then diamond turned on an ultra-precision lathe. After machining down to a certain thickness, periodic bumps and valleys that mirror the back side pattern start to appear on the front diamond machined surface. The periodic wavy/bumpy surfaces have nanometer depths, and possess mirror finish. The results suggest that this technique provides an alternative method to create optical features that are conventionally developed using tool-spindle synchronized cutting motions.

Optical Effects of Surface Finish by Ultraprecision Single Point Diamond Machining

The single point diamond turning process has been used extensively for direct optical surface fabrication. However, the diamond machined surfaces have characteristic periodic tool marks, which contribute to reduced optical performance such as scattering and distortion. In this paper, studies of the characteristics of diamond machined surface and scattering from the diamond machined surfaces are presented. Four different parameters, the first order optical diffraction, the zero order reflection, the surface roughness, and the residual tool mark depth, are used as indicators for the machined surface quality. Four sets of tests are presented showing the relationship between machined surface quality and machining conditions such as spindle speed, feedrate, and machining process. Finally, an empirical model is given based on the measurements.

Laser Induced Modifications of Carbon Nanotube Composite Surfaces

Carbon nanotubes epoxy composites have been processed with high power laser pulses and micro-machined with a single crystal diamond tool. The effect of the dispersion of the carbon nanotubes (CNTs, 0.4 wt %) in the epoxy resin and carbon nanotube interaction with the composite matrix have been probed using spectroscopic Raman mapping. While the micro-machined surface maintains a good electrical conductivity after machining, the surface is poorly conductive after laser ablation. Laser processing (power 150 J/pulse, 1064 nm) transforms the surface of the carbon nanotube nanocomposite up to a distance of 25 µm. AFM images show that the diamond machined surface reduces the composite surface roughness.

Fixed abrasive diamond wire machining—part II: experiment design and results

Experimental results from fixed abrasive diamond wire machining of wood and foam ceramics are presented. Three types of wood—pine, oak, and fir, and three types of foam ceramic—silicon carbide, zirconia, and zirconia toughened alumina, are tested. The research investigates the life of diamond wire and effects of process parameters on the cutting forces, force ratio, and surface roughness. A scanning electron microscope is used to study the worn diamond wire, machined surfaces, and debris. The diamond wire saw is demonstrated to be very effective in machining foam ceramics. The wire life for cutting wood at slow feed rates is low. The short tool life for dry cutting of wood indicates that more research in new fixed abrasive diamond wire and wire saw machining technologies is necessary.

Effect of surface condition and bonding pressure on quality of diffusion bonded high purity copper for linear collider accelerator structures

Tests have been carried out to assess the feasibility of diffusion bonding as a fabrication technology for vacuum tight joints in linear accelerator cells for the Next Linear Collider. High purity copper specimens were diffusion bonded over a range of temperatures from 400 to 1000°C, under high (3.45 MPa) and low (3.45 kPa) bonding pressures, and at two different diamond machined surface finishes. Experiments showed that diffusion bonds with strengths equal to, or greater than, that of silver brazed joints could be made at temperatures ≥700°C at the 3.45 MPa bonding pressure, or ≥800°C at the 3.45 kPa bonding pressure. Partial strength diffusion bonds were made at temperatures as low as 400°C at the high bonding pressure, whereas no bonding (zero strength) was observed at temperatures below 700°C at the low bonding pressure. Observations of the fracture surfaces of the diffusion bonded specimens showed that bonding begins by point asperity contact. At low bonding pressures, surfaces created by diamond turning of annealed copper specimens produce higher strength bonds than those created by diamond flycutting of unannealed surfaces, whereas at higher bonding pressures the effect of surface finish was less important.

Diffusion bonding and brazing of high purity copper for linear collider accelerator structures

Diffusion bonding and brazing of high purity copper were investigated to develop procedures for joining precision machined copper components for the Next Linear Collider (NLC). Diffusion bonds were made over a range of temperatures from 400 \ifmmode^\circ\else\textdegree\fi{}C to 1000 \ifmmode^\circ\else\textdegree\fi{}C, under two different loading conditions [3.45 kPa (0.5 psi) and 3.45 MPa (500 psi)], and on two different diamond machined surface finishes. Brazes were made using pure silver, pure gold, and gold-nickel alloys, and different heating rates produced by both radiation and induction heating. Braze materials were applied by both physical vapor deposition (PVD) and conventional braze alloy shims. Results of the diffusion bonding experiments showed that bond strengths very near that of the copper base metal could be made at bonding temperatures of 700 \ifmmode^\circ\else\textdegree\fi{}C or higher at 3.45 MPa bonding pressure. At lower temperatures, only partial strength diffusion bonds could be made. At low bonding pressures (3.45 kPa), full strength bonds were made at temperatures of 800 \ifmmode^\circ\else\textdegree\fi{}C and higher, while no bonding (zero strength) was observed at temperatures of 700 \ifmmode^\circ\else\textdegree\fi{}C and lower. Observations of the fracture surfaces of the diffusion bonded samples showed the effects of surface finish on the bonding mechanism. These observations clearly indicate that bonding began by point asperity contact, and flatter surfaces resulted in a higher percentage of bonded area under similar bonding conditions. Results of the brazing experiments indicated that pure silver worked very well for brazing under both conventional and high heating rate scenarios. Similarly, pure silver brazed well for both the PVD layers and the braze alloy shims. The gold and gold-containing brazes had problems, mainly due to the high diffusivity of gold in copper. These problems led to the necessity of overdriving the temperature to ensure melting, the presence of porosity in the joint, and very wide braze joints. Based on the overall findings of this study, a two-step joining method is proposed for fabricating the NLC structures. The structure would be assembled with pure silver braze inserts using a self-aligning step joint design, then the assembly would be vacuum diffusion bonded at 700 \ifmmode^\circ\else\textdegree\fi{}C and 3.45 MPa pressure to seal the critical inner portion of the assembly. Finally, during the same furnace cycle, the temperature would be increased to 800 \ifmmode^\circ\else\textdegree\fi{}C in order to react the silver with the copper to form a liquid braze alloy that would join and seal the outer portion of the cells together.

GENERATION AND TEXTURE OF SURFACES IN ULTRAPRECISION CUTTING OF COPPER

The texture of diamond-machined optical-quality surfaces on polycrystalline metals is strongly influenced by the anisotropic elastic and plastic properties of the work material. Plunge-cut experiments were carried out on coarse-grained OFHC copper specimens to examine the correlations between surface topography, process forces, and the orientation of individual grains. Three distinct surface microtopographies were found on individual grains regardless of cutting speed and tool radius. These microtopographies are closely linked with different cutting force levels, which also appear to influence burr formation in the cutting process. The crystallographic orientations of individual grains, which reveal different microtopographies after machining, were determined by X-ray diffraction to correlate the generated surface texture with the material properties.

Pulsed laser-induced melting of precision diamond- machined Cu, Ag, and Au at infrared wavelengths

Threshold for characteristics of pulsed laser-induced damage have been measured on precision diamond-machined Cu, Ag, and Au surfaces at 10.6, 3.8, 2.7, and 1.06 μm wavelengths. Pulse lengths range from 2 μs to 9 ns, and focal spot diameters range from 238 to 52 μm. Comparison is made with melt thresholds calculated from one-dimensional heat flow considerations with a spot-size correction. The calculation incorporates waveform shape, as well as temperature-dependent absorption and thermal properties. Agreement is excellent for Ag, except at 1.06 μm, while agreement for Cu and Au is good only at 10.6 μm. Results suggest that disturbance of crystalline surface order has an important influence, especially at wavelengths shorter than 10.6 μm. A singular departure from calculated Cu and Au thresholds at 3.8 μm, using a multipeaked waveform, may have important implications for repetitively pulsed applications. For Cu at 10.6 μm, damage scales with pulse length according to the \sqrt{\tau} law provided the pulse length as appropriately defined.

An optical measurement of surface profile

With the recent advances in generating extremely smooth surfaces, new surface metrologies are needed to stay one step ahead. This paper describes a non-contact optical instrument for measuring surface profile with a height sensitivity of the order of 1 Å. The measurement technique, including pertinent design considerations, is outlined and measurements of polished and single point diamond machined surfaces are shown. The limitations as well as the potential impact of this technique are also discussed

Tool feed influence on the machinability of CO_2 laser optics

Influence of tool feed on reflectivity of diamond-machined surfaces was evaluated using materials (gold, silver, and copper) from which CO(2) laser optics are primarily produced. Fifteen specimens were machined by holding all machining parameters constant, except tool feed. Tool feed was allowed to vary by controlled amounts from one evaluation zone (or part) to another. Past experience has verified that the quality of a diamond-machined surface is not a function of the cutting velocity; therefore, this experiment was conducted on the basis that a variation in cutting velocity was not an influencing factor on the diamondturning process. Inspection results of the specimens indicated that tool feeds significantly higher than 5.1 micro/rev (200 microin./rev) produced detrimental effects on the machined surfaces. In some cases, at feeds as high as 13 microm/rev (500 microin./rev), visible scoring was evident. Those surfaces produced with tool feeds less than 5.1 microm/rev had little difference in reflectivity. Measurements indicat d that their reflectivity existed in a range from 96.7% to 99.3% at 10.6 microm.