Single-point Diamond Turning Process Research Articles

Online chatter detection for single-point diamond turning based on multidimensional cutting force fusion

Single-point diamond turning (SPDT) is an advanced ultra-precision processing technology that is widely used in machining optical surfaces and microstructures. However, due to insufficient stiffness or damping of the cutting system and the high strength of the workpiece material, chatter inevitably occurs in the machining process, resulting in inferior workpieces and short tool lives. Thus, chatter detection at the early stage is vital to avoid its adverse effects, and a multidimensional cutting force fusion-based online chatter detection method for SPDT is proposed in this work. According to the characteristics of each component of the cutting force in the chatter SPDT process, the stable frequency component is filtered out, and then an artificial constant offset is added. On this basis, the cutting force-based multidimensional information fusion signal and its derivative are set as the detection variables. The chatter detection indicator is developed based on the sum of squares of the detection variable’s frequency spectrum amplitude, with the chatter warning threshold being adaptively determined by the upper limit of the 95% confidence interval of the same indicator obtained from the measurement noises under air cuts. Experiments conducted under various cutting conditions prove that the proposed method can accurately and timely detect weak chatter, thereby preventing further severe chatter and its detrimental effects on the SPDT system.

Design and Analysis of Ultra-Precision Smart Cutting Tool for In-Process Force Measurement and Tool Nanopositioning in Ultra-High-Precision Single-Point Diamond Turning.

Ultra-high-precision single-point diamond turning (SPDT) is the state-of-the-art machining technology for the advanced manufacturing of critical components with an optical surface finish and surface roughness down to one nanometer. One of the critical factors that directly affects the quality of the diamond-cutting process is the cutting force. Increasing the cutting force can induce tool wear, increase the cutting temperature, and amplify the positioning errors of the diamond tool caused by the applied cutting force. It is important to measure the cutting force during the SPDT process to monitor the tool wear and surface defects in real time. By measuring the cutting force in different cutting conditions, the optimum cutting parameters can be determined and the best surface accuracies with minimum surface roughness can be achieved. In this study a smart cutting tool for in-process force measurement and nanopositioning of the cutting tool for compensating the displacements of the diamond tool during the cutting process is designed and analyzed. The proposed smart cutting tool can measure applied forces to the diamond tool and correct the nanometric positioning displacements of the diamond tool in three dimensions. The proposed cutting tool is wireless and can be used in hybrid and intelligent SPDT platforms to achieve the best results in terms of optical surface finish. The simulation results are shown to be almost consistent with the results of the derived analytical model. The preliminary results pave the way for promising applications of the proposed smart cutting tool in SPDT applications in the future.

Experimental investigation on the effects of magnetic field assistance on the quality of surface finish for sustainable manufacturing of ultra-precision single-point diamond turning of titanium alloys

Single-point diamond turning (SPDT) is the state-of-the-art technology for ultra-precision manufacturing of optical products with optical surface roughness down to 1 nm. The SPDT technology has an important role in advanced manufacturing of critical components in different fields of industry. In a SPDT process, different cutting mechanisms affect the optical surface generation and reduce the quality of the turned product. Different efforts have been undertaken to improve the machining conditions as well as optical surface generation mechanisms. Recently, the application of magnetic field assistance in non-conventional SPDT platforms has shown promising results in terms of improving the cutting stability as well as the quality of surface finish. The application of magnetic field assistance becomes more important in SPDT of hard-to-cut materials including titanium alloy. In this study, magnetic field assistance is used in SPDT of Ti-6Al-4V alloy. The machining results show that using this technique could significantly improve the machining conditions and the quality of optical surface generation. The magnetic field assisted SPDT with air coolant could successfully improve the quality of surface finish by 62.5% when compared to non-magnetic purely mechanical SPDT process in dry cutting conditions. Magnetic field assistance is a passive machining technique, environmentally friendly, and it can promote green manufacturing and clean production in ultra-precision SPDT applications.

Design of Electro-optical Vibrometer for On-Machine Metrology in Hybrid Single-Point Diamond Turning

Single-point diamond turning (SPDT) is a machining process with high levels of profile accuracy and nanometric surface characteristics. SPDT is a leading technology in advanced manufacturing of ultra-precision optical components for critical applications. Different efforts have been undertaken to improve the cutting condition and optimize the machining parameters during SPDT. The implementation of on-machine metrology system (OMMS) has helped to improve the outcomes of SPDT in terms of machined profile accuracy and understand the effects of various processing parameters on optical surface generation. OMMS could be implemented in the hybrid SPDT platforms to effectively improve machining conditions by measuring and diagnosing, and providing testing procedures. Different sensors and principles have been used in the design and development of OMMS including laser-based optical systems. However, measuring the micrometric and nanometric parameters during diamond cutting is difficult to achieve at relatively low resolutions. The purpose of this study is to design and simulate an electro-optical vibrometer (EOV) for measuring machine-tool and workpiece vibration during the SPDT process. The proposed EOV has the capability of measuring, monitoring, and analyzing the vibration characteristics in different machining conditions. In addition, the designed system can communicate with the main control units of the hybrid SPDT platforms. Design specifications and simulation results have shown that the implemented mechanism is functional and has met requirements for a successful profiling vibrometry system that can be employed on SPDT machines.

Atomic-scale dissecting the formation mechanism of gradient nanostructured layer on Mg alloy processed by a novel high-speed machining technique

Severe plastic deformation (SPD)-induced gradient nanostructured (GNS) metallic materials exhibit superior mechanical performance, especially the high strength and good ductility. In this study, a novel high-speed machining SPD technique, namely single point diamond turning (SPDT), was developed to produce effectively the GNS layer on the hexagonal close-packed (HCP) structural Mg alloy. The high-resolution transmission electron microscopy observations and atomistic molecular dynamics simulations were mainly performed to atomic-scale dissect the grain refinement process and corresponding plastic deformation mechanisms of the GNS layer. It was found that the grain refinement process for the formation of the GNS Mg alloy layer consists of elongated coarse grains, lamellar fine grains with deformation-induced-tension twins and contraction twins, ultrafine grains, and nanograins with the grain size of ∼70 nm along the direction from the inner matrix to surface. Specifically, experiment results and atomistic simulations reveal that these deformation twins are formed by gliding twinning partial dislocations that are dissociated from the lattice dislocations piled up at grain boundaries. The corresponding deformation mechanisms were evidenced to transit from the deformation twinning to dislocation slip when the grain size was below 2.45 μm. Moreover, the Hall-Petch relationship plot and the surface equivalent stress along the gradient direction estimated by finite element analysis for the SPDT process were incorporated to quantitatively elucidate the transition of deformation mechanisms during the grain refinement process. Our findings have implications for the development of the facile SPD technique to construct high strength-ductility heterogeneous GNS metals, especially for the HCP metals.

Machinability analysis of quartz during single point diamond turning process based on finite element method: influence of ultrasonic vibration and micro-machining parameters

Quartz is one of the difficult-to-machine materials due to its low fracture toughness and high hardness. In this study, the machinability of this material during single point diamond turning (SPDT) was numerically investigated using finite element method (FEM). First of all, the accuracy of the FE model was verified based on the experimental data available in literature. Then, the machinability of quartz was analysed in terms of cutting force, tool/workpiece temperature and tool wear rate. Also, the influence of tool vibration on cutting force and tool wear rate was investigated. Furthermore, an empirical/mathematical model was developed to express the machining outputs as a function of the micro-machining parameters. The obtained results indicate the good performance of FEM in analysing the machinability of quartz during SPDT process.

Review of non-conventional technologies for assisting ultra-precision single-point diamond turning

Ultra-precision single-point diamond turning (SPDT) is a recent realm in advanced manufacturing of optical components with nanometric features. SPDT has various applications in different industry sectors including space science, biomedical engineering, military, defense, and optics. However, different factors negatively impact the outcome of SPDT process and limit the success of optical surface generation. In addition, standard SPDT is based on the pure mechanical action of cutting and is limited when it comes to turning brittle and hard-to-machine materials. These materials have low machinability, and cutting them with diamond tool has been affected by high tool wear, short tool life, and consequently low quality of optical surface finish. Non-conventional machining techniques have been implemented to assist the purely mechanical SPDT process in order to eliminate the existing limitations, reduce effects of influencing factors, and enable an optimized machining environment. Different methods have been developed and used for assisting the SPDT process. In this review paper, recent trends and advances in technologies used for assisting SPDT are surveyed. Studying constructive and destructive effects of these SPDT-assisted technologies could provide necessary information for using the best possible solutions in diamond turning of different materials while improving targeted parameters. In addition, studying the effects of assisting technologies could provide a good perspective on hybrid SPDT process limitations and possible solutions. Although various techniques and solutions have been developed, there are still limitations for enabling an ultimate turning process. The paper highlights the possible trend of new technologies related to SPDT. More attention needs to be given, especially, to the development of novel techniques to completely solve existing limitations and enable best SPDT performance. Future studies need to be focused on the development of hybrid SPDT platforms, based on suitable combinations of non-conventional technologies, to achieve the best possible quality in terms of optical surface generation.

Review of hybrid methods and advanced technologies for in-process metrology in ultra-high-precision single-point diamond turning

Single-point diamond turning (SPDT) is a leading machining technology for advanced manufacturing of high-accuracy optical components characterized by their nanometric surface characteristics. By employing SPDT, optical surfaces with roughness down to 1 nm could be machined. However, in a purely mechanical ordinary SPDT procedure, different factors may influence the outcome of the process and significantly affect the quality of the diamond-turned optical surface. In the last few years, non-conventional machining technologies have been successfully implemented on the basis of traditional mechanical SPDT for optical surface generation. These non-conventional methods assist the purely mechanical SPDT process to improve the diamond machining performance and machinability of various optical materials. They attempt to eliminate the process disturbances that occur during mechanical interactions between the tool and workpiece in order to further reduce the surface roughness indicator. Recently, the application of hybrid SPDT methods in optical surface generation has emerged, in which more than one non-conventional machining technique impact the workpiece surface during the mechanical interaction with the diamond tool cutting edge. Compared with conventional SPDT solutions, in a hybrid SPDT method, superior results in terms of optical surface quality could be obtained. In addition, development of intelligent SPDT solutions for achieving the best possible results in optical surface generation is a novel approach. In an intelligent SPDT solution, in addition to the hybrid machining methods, automatic control systems and advanced on-machine metrology systems need to be implemented on the diamond turning machine platform. This may help further improve the quality of optical surface by continuously performing in-process error diagnosing and consequently conducting in-process tuning of the diamond cutting parameters and optimizing the machining conditions. In this review paper, recent advances in ultra-precision SPDT based on hybrid methods, associated metrology systems, and their process control systems are surveyed. In addition, the effect of developed various hybrid SPDT methods and influencing factors that may affect optical surface generation have been discussed. At the end, guidelines for further developments of intelligent SPDT platforms by using hybrid SPDT methods, automatic process control, and in-process metrology solutions are proposed.

Review of single-point diamond turning process in terms of ultra-precision optical surface roughness

Ultra-precision machining is the recent realm subsequent to conventional precision machining processes. Recently, achieving nanoscale features on products has become important in manufacturing of critical components. One of the main objectives in advanced manufacturing of optics is to reach ultimately high precision in accuracy of optical surface generation. Through further development of computer numerical controlled machinery technology, single-point diamond turning (SPDT) has evolved rapidly and became a key step in the process chain of nano-machining. In SPDT, advanced and competitive technology for optical surface generation combined with ultra-precision fixtures and accurate metrological systems, high-precision surface machining with scales down to 1 nanometer, even less than 1 nanometer, are successfully achieved. Different engineering applications including medical, dental, defense, aerospace, computer science, and electronic components demand extreme smoothness and optical quality of the machined surfaces. However, there are limitations and drawbacks in SPDT process and surface generation using this technology. Different factors may significantly influence turning conditions, affect surface generation, and limit the outcome of the process. This paper attempts to provide a review of ultra-precision SPDT: technology and characteristics, manufacturing process, applications, machinable materials, and surface generation. Subsequently, influencing factors on surface generation are introduced and comprehensively discussed. Studying influencing factors on surface generation could enable setting optimized sets of machining factors and providing best possible machining conditions for generating high quality optical surfaces. Furthermore, limitations and drawbacks of standard structure SPDT process is discussed. Although a number of published studies have attempted to provide a good perspective of the SPDT process by looking into the effect of influencing factors on surface generation and existing limitations, more investigation needs to be undertaken to discover all destructive effects, origins, and influences in order to further extend the machinability of materials, reduce side effects, and improve the outcome of SPDT.

Improvement of surface laser damage resistance of KDP crystal under combined machining process

The nature of potassium dihydrogen phosphate (KDP) crystals leads to a hard manufacture for optical surface, especially in the application of an intensive laser system. We use single-point diamond turning (SPDT), magnetorheological finishing with water-dissolution (MRFWD), and ion beam figuring (IBF) to accomplish high surface quality and to inhibit surface defects meanwhile. According to the intensification of light field of 355-nm wavelength calculated by finite-difference time-domain method, the surface ripples of 2-μm spatial period created by SPDT process should be strictly treated. On the basis of SPDT, a series of processing and testing experiments are carried out on the samples for the best laser damage performance. The MRFWD developed with the measures of pressure depth control, fluid temperature control, and fluid PH value adjustment etc. can partly smooth out the ripples of critical frequency and maintain lower iron pollutions at the same time. These metal particles induce stronger light field modulations compared with the residual ripples from the simulation. As for IBF processing, the sample with removal depth of 100 nm exhibits the best laser damage performance in the experiment. The cleaning effects of IBF under optimized parameters combined with the better full aperture uniformity scanned by a photothermal absorption system after MRFWD finally decide the optimal processing procedure. And the surface damage threshold of KDP crystal increases from 4.98 J / cm2 after SPDT processing to ultimate 9.2 J / cm2 under the irradiation of 355 nm, 10 ns pulsed laser.

Analysis of the convergence rules of full-range PSD surface error of magnetorheological figuring KDP crystal.

A new non-aqueous and abrasive-free magnetorheological finishing (MRF) method is adopted for processing potassium dihydrogen phosphate (KDP) crystal due to its low hardness, high brittleness, temperature sensitivity, and water solubility. This paper researches the convergence rules of the surface error of an initial single-point diamond turning (SPDT)-finished KDP crystal after MRF polishing. Currently, the SPDT process contains spiral cutting and fly cutting. The main difference of these two processes lies in the morphology of intermediate-frequency turning marks on the surface, which affects the convergence rules. The turning marks after spiral cutting are a series of concentric circles, while the turning marks after fly cutting are a series of parallel big arcs. Polishing results indicate that MRF polishing can only improve the low-frequency errors (L>10 mm) of a spiral-cutting KDP crystal. MRF polishing can improve the full-range surface errors (L>0.01 mm) of a fly-cutting KDP crystal if the polishing process is not done more than two times for single surface. We can conclude a fly-cutting KDP crystal will meet better optical performance after MRF figuring than a spiral-cutting KDP crystal with similar initial surface performance.

A water dissolution method for removing micro-waviness caused by SPDT process on KDP crystals

Single crystals of potassium dihydrogen phosphate (KDP) are an irreplaceable optical material in laser-induced inertial confinement fusion (ICF), where they are used as electro-optic switches and for laser-frequency conversion. The KDP lenses used in ICF applications must be pristine, high quality, and have a surface roughness of less than 3 nm. Currently, single-point diamond turning (SPDT) is the primary method for performing ultra-precision machining on KDP crystals. However, after the SPDT process, the crystal surface exhibits micro-waviness and subsurface damage, both of which have adverse effects on the optical performance of the KDP elements, especially the laser-induced damage threshold. In this study, a new method of micro-dissolution polishing was developed, which is based on the solubility of KDP crystals in water, to achieve controllable material removal. A material removal function was formulated to describe the material removal in terms of both the path and parameters used to polish the SPDT-machined samples with a small polishing tool. An experimental study showed that this method is able to reduce the surface micro-waviness and surface roughness (from 6.205 to 2.107 nm) significantly. The method is also applicable to the polishing of other water-soluble materials.

Integrated finite element method and response surface methodology-based modelling and simulation of single point diamond turning of silicon

This paper presents an integrated finite element method-response surface methodology (FEM-RSM)-based approach for modelling and simulation of single point diamond turning (SPDT) operation of silicon. Initially, a two-dimensional nonlinear plain strain model of SPDT process has been developed by using FEM. The results predicted by the numerical model were validated with the experimental results available in the literature for similar process conditions and they found in good agreement. Detailed parametric studies were carried out using RSM to study the effect of cutting speed, rake angle, depth of cut and tool edge radius on machining forces. The RSM-based model was also validated by carrying out confirmation simulations and the model was found to be predicting good with mean prediction error of about 5%. It is felt that the proposed approach can be a good alternative to the costly, time consuming and tedious SPDT experimental study of silicon material.

Experiment and Discussion on Ultrasonic Vibration-Assisted Single Point Diamond Turning of Die Steels

Traditionally, single point diamond turning (SPDT) can not process ferreous metals because of acute tool wear. Ultrasonic vibration-assisted cutting(UVC) provides a promising solution for the problem. In this paper, for the aim of directly obtaining mirror surface on die steels, UVC method was used combining with SPDT process. Experiments were carried out on an ultra precision turning machine, cutting parameters and vibration parameters were well-chosen, and two kind of feed rates, two kinds of prevailing die steels were experimented. Mirror surfaces were successfully achieved on face turning, with the best roughness of Ra16.6nm. And the surface roughness, surface texture and tool wear in machining process were discussed.

Influence of temperature and crystal orientation on tool wear during single point diamond turning of silicon

Owing to the capricious wear of cutting tools, ultra precision manufacturing of silicon through single point diamond turning (SPDT) operation becomes a challenging task. It thus becomes non-trivial to understand the contribution of temperature and crystal orientation during the SPDT process in order to suppress tool wear. Molecular dynamics (MD) simulation is an appropriate tool to study nanoscale processes occurring at the femtosecond/picosecond timescale which cannot otherwise be studied experimentally or by the finite element method (FEM). Accordingly, MD simulation has been deployed with a realistic analytical bond order potential (ABOP) formalism based potential energy function to simulate the single point diamond turning operation of single crystal silicon in order to understand the influence of temperature and crystal orientation on the tool wear mechanism. Results showed the strong influence of crystal orientation on the wear resistance of a diamond tool; cubic orientation performed better than dodecahedral orientation. It was also observed that high pressure phase transformation (HPPT) in the cutting zone was accompanied by the formation of dangling bonds of silicon. Under the influence of cutting temperature, the newly formed dangling bonds of silicon chemically combine with the pre-existing dangling bonds on the surface of the diamond tool resulting in the formation of silicon carbide (SiC), the main appearance of which was evident at the tool flank face. Continuous abrasion of the diamond cutting tool with SiC causes sp3–sp2 disorder of the diamond tool. Hence, both these processes proceed in tandem with each other. The mechanism proposed here is in good agreement with a recent experimental study, where silicon carbide and carbon like particles were observed using X-ray photoelectron spectroscope (XPS) technology after machining a silicon wafer with a diamond tool.

Single Point Diamond Turning of Single Crystal Silicon Carbide: Molecular Dynamic Simulation Study

Silicon carbide can meet the additional requirements of operation in hostile environments where conventional silicon-based electronics (limited to 623K) cannot function. However, being recent in nature, significant study is required to understand the various machining properties of silicon carbide as a work material. In this paper, a molecular dynamic (MD) simulation has been adopted, to simulate single crystal β-silicon carbide (cubic) in an ultra precision machining process known as single point diamond turning (SPDT). β-silicon carbide (cubic), similar to other materials, can also be machined in ductile regime. It was found that a high magnitude of compression in the cutting zone causes a sp3- sp2 order-disorder transition which appears to be fundamental cause of wear of diamond tool during the SPDT process.

Broadband antireflective surface-relief structure for THz optics

The requirements for a broadband antireflective structure in the THz spectral region are derived. Optimized structural parameters for a surface-relief grating adapted to the spectrum of an intended THz pulse are deduced. The effect of a structure fabricated into Topas((R)) by a single-point diamond-turning process is demonstrated.

Measurements of Spindle Parameters on a Diamond Turning Machine to Nanometer Resolution(Precision positioning and control technology)

A single point diamond turning (SPDT) facility is utilized for the ultra-precision machining of planar surfaces, and aspheric mirror components for geo-orbital x-ray telescopes and x-ray microscopes. The spindle of the machine tool is encased in an ultra-precision hydraulic bearing, and the motion controller is programmable to nanometer resolution. The radii of diamond cutting tools, utilized in the SPDT process, approach nanometer accuracy. This combination of parameters produces planar and aspheric components with nanometer surface and shape quality. We examine the radial and axial motion of the spindle in the static and dynamic domains with an optical nanometer-resolution sensor. The sensing geometry is based on standard optical triangulation off the target surface, and the sensor can be calibrated in situ utilizing the position controller of the machine. We present results, which examine the parametric performance of the diamond turning operation. At 1000rpm we measured a minimum of approximately 35-nm rms radial and the axial spindle error motion.