High-precision Machining Processes Research Articles

Investigations on burr formation mechanisms and surface quality when micro-milling duplex stainless steel (UNS S32205)

Micromilling is a high-precision machining process that has been widely used to produce components or provide micro-characteristics on macro-sized parts. It is imperative that surfaces generated by micro-machining have high specifications and quality, translated as low surface roughness and a minimum number of burrs. Deburring processes are difficult to control, and the need to assure process quality motivated a study of this work focused on burr formation and surface quality when micromilling duplex stainless steel (UNS S32205). For this purpose, slots were machined using a 4-axis computer numerically controlled (CNC) micromachining center equipped with TiN-coated carbide microtools (381 µm diameter (0.015 inch)). Optimization experiments were performed in order to choose the most suitable cutting conditions. The measurements of burr height and surface roughness were made using a profilometer. In addition, milled slots were analyzed using a scanning electron microscope (SEM). The results showed that top burrs were dominant, and the main types presented on the up-milling side were feather burrs and primary burrs. On the down-milling side, burrs presented a rather irregular shape. The width of the root of the burr presented values very close to the size of the metallurgical phases of the material, and burrs formed at distances that are comparable to the spacing between both phases, such as, α-ferrite and γ-austenite. Surface roughness is higher when using increased cutting speeds, implying that lower speeds produce a measure of surface roughness in line with component specifications that appears to be dependent on the type of burr formed during milling and associated tool wear.

Review of the Causes of Wire Breakage and Its Mitigation During the Wire Electric Discharge Machining Process

Abstract Wire electric discharge machining (WEDM) is a widely used high-precision machining process. It has the capability of cutting high-strength alloys, namely, tool alloys, Hastelloy, and monel with very tight tolerance. Frequent wire breakage adversely affects the product geometric precision, surface integrity, and productivity of the manufacturing establishments. It is essential to understand the causes of wire breakage and to mitigate the frequency of its occurrence. This paper comprehensively reviews the experimental as well as theoretical research work reported on various aspects of wire electrode erosion such as the effect of heat generated in spark plasma, thermal stresses, wire rupture phenomena, and wire fatigue. It also presents important research findings on the causes of wire failure and advancements to reduce wire erosion and wire vibrations. The paper systematically and carefully examines the measures suggested to improve the wire life and depicts the development of various wire health monitoring and control systems. Overall, it presents useful insights and important guidelines for the efficient utilization of the wire EDM process by mitigating the causes of wire erosion and its failure. It will certainly help for the improvement of the precision machining capability of the WEDM process.

A High Efficiency and Precision Smoothing Polishing Method for NiP Coating of Metal Mirror.

The NiP coating has excellent wear and corrosion resistance, and electroless nickel-phosphorus coating is one of the best measures for surface modification of metal optical devices. The NiP layer could be processed by single-point diamond turning (SPDT). However, the periodic marks on the surface of the NiP coating processed by SPDT will lead to diffraction and stray light, which will reduce the reflectivity and image quality of the mirror. This paper studied smoothing polishing based on chemical mechanical polishing to remove turning periodic marks efficiently. Firstly, we studied the chemical corrosion and mechanical removal mechanism of smoothing polishing of the NiP coating through theoretical analysis. Then, the influencing factors of processing the quality of smoothing polishing are analyzed, and the optimal machining parameters and polishing slurry formula are formulated. Finally, through the developed process, the surface roughness of Root Mean Square (RMS) 0.223 nm is realized on the NiP coating, and an ultra-smooth surface that can meet the service accuracy of a hard X-ray mirror is obtained. Our research simplifies the high-precision machining process of the NiP coating and improves the machining efficiency. Therefore, it can be used as a new high-precision manufacturing NiP coating method.

SoC-Based Early Failure Detection System Using Deep Learning for Tool Wear

This study aims to implement a system-on-chip (SoC) detection system for tool wear monitoring and alarms for high-precision machining processes. The proposed deep learning approach is trained by the collected sensors from real performed in a three-axial computer numerical control (CNC) machine center combined with different conditions of spindle speed and tightening torque. The corresponding vibrational and sound signals were collected by a three-axial accelerometer and micro-electro-mechanical-system (MEMS) microphone, and then the tool flank wear was measured by a camera. In this study, the flank wear was designed for early detection according to the ISO 8688-2:1989 standard. A deep learning model with frequency spectrum inputs of the collected signals was developed for tool wear prediction. In addition, to treat the machining variation for detection, two sensor fusion approaches are presented and implemented on an SoC-board (Pocket Beagle) for landing and cost reduction. The corresponding average detection accuracies were approximately 99.7% and 87.75% for the single and merged models, respectively. The results demonstrated the effectiveness and performance of the proposed approach.

Control Algorithm of Precision Machining

Due to more and more private customized non-standard design and precision manufacturing, as well as strict requirements for green environmental protection and sustainable economic development mode, it is challenging to realize the synchronous meeting of energy-saving optimization requirements in the processing process of high-precision workpiece. A new semi-automatic machining optimization system is proposed in this paper. The system is based on the high-precision 3D computer files of the workpiece to be processed and the laser thermophysical system. At the same time, the processing parameters are optimized based on the high-precision algorithm. The innovative contents of the high-precision optimization system include: (1) reciprocating fast high-frequency program design. Its single cycle task is: "core data acquisition, data in-depth analysis / machining precision refinement, key machining parameters recalibration", in order to maximize the process adaptability of the optimization system designed in this study in the highprecision machining process of different types of workpieces. (2) A new green energy-saving and environmental protection model, using primary chemical degreasing and laser derusting processing to get the most accurate 3D scanning files of parts waiting for processing, minimize the process error, so as to maximize the material and energy efficiency. In the calculation of the energy model, the most scientific consumption of coolant is considered.

Performance analysis of rough surface hybrid thrust bearing with elliptical dimples

Surface roughness is inherent to all machining processes. Therefore, even a high precision machining process renders micro-roughness to some extent on the surface of conventional materials. The asperities height of many rough engineering surfaces follows Gaussian distribution. The surface roughness on the bearing surface may significantly affect the bearing performance. Surface texturing is emerging as a new technique to improve the tribological behavior of the mating surfaces. Usually dimensions/height of micro-roughness is of order of the depth of surface textures in fluid film bearings. Neglecting micro-roughness while numerically simulating a textured surface bearing may generate inaccurate bearing performance data. In presented work, finite element simulation of textured surface hybrid thrust bearings has been performed. Surface texture is provided over thrust pad in the form of regular arrays of elliptical dimples. A parametric optimization is carried out to determine optimum attributes of elliptical dimple (axis, depth, texture length and orientation) so that the load-carrying capacity and fluid film stiffness should be maximized and film frictional power losses should be minimized. Use of textured surface (with optimum elliptical dimple attributes) results into a significant enhancement in load-carrying capacity (91.3%), film stiffness coefficient (+98.8%) and reduction in frictional power losses (−48.3%). It is also observed that elliptical dimple and micro-roughness (transverse orientation) generate synergistic effects in further enhancing the load-carrying capacity (+101.4%) and film stiffness coefficient (+112%) of the bearing.

Preliminary Design of Two Dimensional Vibration Assisted Machining System for Multi-Axis Micro-Milling Application

Vibration assisted machining (VAM) is a method that is widely used in improving the performance of machined products. External vibrations with high frequency to ultrasonic range along with an meso-micrometer amplitude are given to the cutting tool or workpiece. This will result in a periodic separation phenomenon, hence reducing the cutting force which has positive impacts on increasing tool life and machined surface quality. Among the high-precision machining processes, micro-milling which has the ability to produce complex components with 2D and 3D features, can also be applied with the vibration assisted method, known as vibration assisted micro-milling (VAMM). Based on the direction of vibration given in the machining process, there are 1D VAMM with linear vibrations and 2D VAMM with circular or elliptical trajectory vibrations. However to date, neither developed 1D nor 2D VAMM systems are still limited to the research of planar surfaces cutting using linear movement axes, meanwhile vibration assisted in inclination cutting of micro-milling using the rotational movement axes is still very rare. Therefore the purpose of this paper is to present the preliminary model in designing a 2D VAMM system for a 5-axis micro-milling machine. The system is powered using piezoelectric actuators as the vibration-producing actuators.

Design and Investigate of Flushing System for Electrical Discharge Machining (EDM) Application

Electrical Discharge Machining (EDM) is high precision machining process in which no actual contact between the workpiece and electrode during sparking. Dielectric fluid play a role as flushing medium and semiconductor between workpiece and electrode to stabilization and controlled spark gap ionization condition. In real condition, nozzle flushing system in EDM machine not able to complete remove debris formed during machining and affect the machining performance. Improper flushing due to lack of guideline at setup position of nozzle and inlet pressure caused low material removal rate, irregular tool and higher cost on raw material. To overcome this problem, the design and investigate of flushing system in EDM application is required. The design and investigation undergo by simulation of ANSYS Computational Fluid Dynamics (CFD) with a virtual experiment to accurate prediction of flushing performance. The influence of nozzle size and inlet pressure supplied on flushing efficiency were analyzed to avoid improper flushing on die-sinking EDM process. The simulation and experiments clarified that the higher inlet pressure, P=0.20 bar and larger nozzle diameter, D=6mm resulting in higher total pressure which is 2647.16 Pa. Furthermore, the streamline of velocity and eddy viscosity contour in the work tank using to analyze the turbulence zone by nozzle flushing obtained by the CFD analysis. The condition in case 5 (D=5mm, P=0.15 bar) is more efficiency on debris removal rate based on the result of high total pressure on machining zone and eddy viscosity contour showed the turbulence zone only formed area near to outlet of system. The model results have been shown good agreement with experiment and co-relation data.

A New Type of Aerostatic Thrust Bearing Controlled by High-speed Pneumatic Valve and a Novel Pressure Transducer

The current research work presents a low cost, efficient and innovative active aerostatic thrust bearing which is controlled through a combination of the Arduino board, feedback transducers and high-speed valves. The purpose is to make low cost, compact active aerostatic thrust bearing with overall small dimensions and compact size. A prototype design is done in solid works with small dimensions and components are produced with the help of the high precision machining process. There are two high-speed electropneumatic valves which are controlled through pulse width modulation techniques. These high-speed electro-pneumatic valves modify the supply pressure of aerostatic bearing to achieve desired air height gap. There are two novel pressure sensors which provide a feedback signal for control. The test bench to perform experiments has been explained. The performance of the proposed aerostatic bearing is checked both in open loop and closed loop configuration with respect to static and dynamic conditions.

Advances in Rotary Ultrasonic-Assisted Machining

Rotary ultrasonic-assisted machining (RUAM) processes have been recognized as leading, non-traditional, high-precision machining processes that have been recently developed to machine a vast range of advanced, hard-to-machine, brittle materials like reinforced composites, ceramics, and metallic alloys to a very high surface finish in an efficient and cost-effective manner. As the field of materials engineering further progresses in search of materials with very high hardness and resistance to wear for use in the biomedical, energy, aerospace, automobile, and optical industries, so too must the machining processes progress in order to fulfill the demand for manufacturing the components. RUAM processes have been shown to reduce cutting forces and improve tool life during machining of very hard and brittle materials so far. Therefore, from the very first implementation of ultrasonic energy for higher-quality machining in the late 1920s to today’s advanced computer numerical control RUAM 5-axis machining centers, this review examines the development history, the working mechanisms, and the critical performance of each RUAM process, which influence the process outputs. The advancements, applications, limitations, and future perspective of RUAM processes are also discussed in detail with the aim of providing clear insight into the future of RUAM, for further development and to extend the range of its applications.

Influences of control error and setting error on machining accuracy of internal gearing power honing

As a high efficiency and high precision machining process, internal gearing power honing is often used in gear finishing after heat treatment. In order to improve the machining accuracy of internal gearing power honing, this paper analyzes the influence law of motion control error and machine setting error on tooth surface contour error. First, the tooth surface of the honing wheel and the workpiece gear is established by using homogeneous coordinate transformation and meshing principle. Second, the tooth surface of the workpiece with the control error and the setting error is constructed. The contour error and the sensitivity matrix of the tooth surface are also put forward. Finally, two numerical examples and an experiment are used to study the influences of control error and setting error on the machining accuracy of workpiece gear tooth surface. The research results can provide reference and precondition for the error compensation and improvement of machining precision of internal gearing power honing.

Investigation on Cutting Force and Temperature of Cutting Cu<sub>50</sub>Zr<sub>50</sub> Metallic Glass by Molecular Dynamics Simulation

Metallic glasses have a variety of excellent properties compared with the majority of conventional crystalline alloys, and have a broad application prospects in the military, aerospace and sports equipment. Cutting, as an efficient and high-precision machining process, is expected to be an important processing method for metallic glasses. Currently, investigation on cutting metallic glasses is in a nascent stage. Although the machining precision of several tens of nanometers has been achieved, its cutting mechanism remains unclear. In this paper, a molecular dynamics simulation of orthogonal nanometric cutting of metallic glass Cu50Zr50 was carried out.The material deformation, cutting force, and workpiece temperature distribution were studied at microscopic scale. It is found that the deformation accumulation first occurred on the tool rake face. Then with the cutting progressing, materials underwent stable plastic deformation in the shear zone. Analysis on cutting force shows that in the initial material deformation process the cutting force increases rapidly until the cutting process is stabilized, , and then it is reduced to a stable value. Finally, the temperature change of the workpiece during cutting was calculated, and the result shows that the maximum temperature reaches the glass transition temperature. Further, the radial distribution function analysis of workpiece was used to confirm the occurrence of the glass transition.

Surface Alterations Produced in Grinding of Austempered Ductile Iron

The technological advances achieved in recent decades have allowed to obtain cast parts of ductile iron with no metallurgical defects and of complex shapes and dimensions very close to the final ones. Heat treatments have enabled to obtain ADI within a wide range of mechanical properties. After properly choosing the processing variables, the most suitable combination of strength and toughness can be attained for each application. When restrictive dimensional or shape accuracy is required, a high precision machining process, such as grinding, is used. This process induces significant temperature gradients and surface plastic deformations which could affect the surface characteristics. The aim of this paper is to analyze the effects of grinding on power consumption, surface characteristics, roughness and distortion on ADI plates grade 2 and 5. The results indicate that it is possible to achieve excellent surface finishes with moderate power consumption and low residual stresses and distortions.

Air Thin-Walled Parts Machining Precision Control

With the development of the aviation industry, the aircraft's increasingly high performance requirements, the overall application of thin-walled structural components became more widespread. However, due to the complex structure parts, thin wall, high precision machining process was complexity, the cutting force, cutting heat, clamping force under the influence of other factors, prone to machining distortion, and with the lower part wall thickness, decreased in rigidity, it was difficult to ensure processing quality. In this paper, we proposed several effective aviation thin-walled parts machining precision control program to solve the problems in the processing of machine structural characteristics of thin-walled parts .The results of experiments and production practice proved that these methods effectively control the air thin-walled parts machining precision machining to meet quality requirements, while reducing the processing time, improve processing efficiency, it was convenient and efficient processing methods.

Characterization of Cutting Force Induced Surface Shape Variation in Face Milling Using High-Definition Metrology1

High-definition metrology (HDM) systems with fine lateral resolution are capable of capturing the surface shape on a machined part that is beyond the capability of measurement systems employed in manufacturing plants today. Such surface shapes can precisely reflect the impact of cutting processes on surface quality. Understanding the cutting processes and the resultant surface shape is vital to high-precision machining process monitoring and control. This paper presents modeling and experiments of a face milling process to extract surface patterns from measured HDM data and correlate these patterns with cutting force variation. A relationship is established between the instantaneous cutting forces and the observed dominant surface patterns along the feed and circumferential directions for face milling. Potential applications of this relationship in process monitoring, diagnosis, and control are also discussed for face milling. Finally a systematic methodology for characterizing cutting force induced surface variations for a generic machining process is presented by integrating cutting force modeling and HDM measurements.

Recent Advances in Ultraprecision Diamond Turning of Non-Rotationally Symmetric Optical Surfaces

Firstly, the superior performance and industrial application prospects of non-rotationally symmetric (NRS) optical surfaces are detailed. Secondly, those high precision machining processes to generate NRS optical surfaces are overviewed, it’s been stressed that fast tool servo (FTS) based diamond turning has been the most promising, cost-effective, and high precision machining process to generate NRS surfaces. Finally, the recent research progress in FTS based diamond turning of NRS optical surfaces is remarked, both the tool trajectory generation and the FTS actuation techniques are discussed, the limitations of the existing researches are disclosed, and then the academic and technological researches to be urgently carried out are suggested.

Measurement of tool internal temperatures in the tool–chip contact region by embedded micro thin film thermocouples

Sensors capable of providing fast and reliable feedback signals for monitoring and control of existing and emerging machining processes are an important research topic, that has quickly gained academic and industrial interest in recent years. Generally, high-precision machining processes are very sensitive to variation in local machining conditions at the tool–workpiece interface and lack a thorough understanding of fundamental thermomechanical phenomena. Existing sensors to monitor the machining conditions are not suitable for robust in-process control as they are either destructively embedded and/or do not possess the necessary spatial and temporal resolution to monitor local tool internal temperatures during machining at the cutting tip/edge effectively. This paper presents a novel approach for assessing transient tool internal temperature fields in the close vicinity of less than 300 μm of the tool cutting edge. A revised array layout of 10 micro thin film micro thermocouples, fabricated using adapted semiconductor microfabrication methods, has been embedded into polycrystalline cubic boron nitride (PCBN) cutting inserts by means of a modified diffusion bonding technique. Scanning electron microscopy was used to examine material interactions at the bonding interface and to determine optimal bonding parameters. Sensor performance was statically and dynamically characterized. They show good linearity, sensitivity and very fast response time. Initial machining tests on aluminum alloys are described herein. The tests have been performed to demonstrate the functionality and reliability of tool embedded thin film sensors, and are part of a feasibility study with the ultimate goal of applying the instrumented insert in hard machining operations. The microsensor array was used for the acquisition of tool internal temperature profiles very close to the cutting tip. The influence of varying cutting parameters on transient tool internal temperature profiles was measured and discussed. With further study, the described instrumented cutting inserts could provide more valuable insight into the process physics and could improve various aspects of machining processes, e.g. reliability, tool life, and workpiece quality.

Statistical quality control through process self-induced vibration spectrum analysis

The first part of this study (Carnero et al., Mechanical Systems and Signal Processing, 24:1138–1160, 2010) analysed the influence of the process variables and work cycles on the quality of the bearings manufactured in an automotive bearing plant. The study was focused on the analysis of the overall vibration reading produced by the contact between the tool and the part. An analysis of variance was conducted on the overall vibration readings, which reflected that high-frequency vibration displacements are sensitive to process setup variables as well as the quality of products manufactured. Nevertheless, it was also observed that overall vibration values are not sufficient to analyse the relationship between the mechanical behaviour (vibration) and final quality obtained from high-precision machining processes. In this article, therefore, a new study is conducted based on spectral vibration measurements. A new experiment has been designed taking as input variables the diameter and the rotating speed of the tool. The selection criterion is based on the strong influence of these two variables on high-frequency vibration displacement and quality of parts (chattering, measured in terms of Lob A and Lob B). Two identical grinding machine tools were used during the experimental phase. Output variables are high-frequency displacements and high- and low-frequency chattering. The statistical analysis used in the new experiments determines spectral bands of the process in which vibrations induced by tool–part contact relates to development of lobes in the part to be identified. The study allows identification of vibration bands that are suitable for control in order to guarantee quality of the parts produced. To achieve that goal, the concept of spectral identity of the processes has been introduced to incorporate vibration induced by the process itself in the spectrums and to differentiate that process vibration from other mechanical vibration sources.

HIGH-PRECISION MEASUREMENT OF TOOL-TIP DISPLACEMENT USING STRAIN GAUGES IN PRECISION FLEXIBLE LINE BORING

Precision displacement measurement is a critical element to achieve active control for high-precision (e.g. 5 μm) flexible line boring. Since current measurement methods are difficult to apply in this application, a new measurement method has been developed. This paper presents a new strain-gauge-based method for the high-precision vibration measurement of a beam. This method is based on the fact that the vibration displacement can be expressed in terms of an infinite number of vibration modes and be related to the measured strains through the strain–displacement relationship. By placing multiple sets of strain gauges, multiple modes can be taken into account to achieve high-precision measurement. Both simulation and experimental results were obtained and are provided for validation. From these results, it can be concluded that this new measurement method is applicable to high-precision flexible line boring, enabling active control to compensate for the tool-tip displacement to achieve a high-precision machining process.