Precision Machining Process Research Articles

Finite Element Research of Cup Wheel Grinding Heat Based on Trochoid Scratch Model

Grinding is a highly precise machining process. However, excessive temperatures during grinding can result in adverse thermal effects on the machined material. In this study, cup wheel grinding was analyzed using a model that represents heat generation as a trochoid discrete heat source formed by the interactions between abrasive particles and the workpiece surface. With this approach, certain assumptions were made to facilitate analysis, including the modeling of abrasive grains as rigid point heat sources. Finite element simulations and experimental validations based on the trochoid model were conducted using COMSOL 6.2 software. These analyses evaluated the thermal behavior of cup wheel grinding under varying wheel speeds and feed rate ratios. The results revealed an asymmetrical distribution of the temperature field in cup wheel grinding. By examining both surface and subsurface temperature fields, this study provided a more comprehensive understanding of grinding heat. Furthermore, this investigation explored the influence of trochoid trajectories and process parameters on the temperature field, highlighting intersection and curvature thermal effects. These findings contribute valuable analytical methods and theoretical insights for controlling grinding heat in precision machining processes.

Retention and interfacial failure mechanism of single diamond grains in resin-bonded grinding tools

Abrasive grains and the associated bonding agent are the two significant components in the manufacturing of fixed abrasive machining tools. The material properties and interfacial bonding behavior between the grains and the bonding matrix determine machining performance. In precision machining processes with diamond abrasives, the primary failure modes of fixed abrasive tools are grain dislodgement and premature loss, leading to abrupt change in machining load and ultimately causing inaccurate and inefficient machining performance. This study develops a comprehensive model for understanding abrasive grain retention and interfacial failure mechanisms in resin-bonded diamond tools. Finite element analysis of a single diamond grain embedded in a resin matrix was conducted to examine the influence of the grain shape, protruding height, and orientation angle on critical interfacial failure force. A series of single diamond scratching experiments validated the model, revealing that the maximum retention force reached 43.56 N for grains with a 0.9 mm protruding height and a 60° orientation angle. The results also show that, within a specific grain size range, grain shape—quantified by the sphere deviation coefficient proposed in this paper, has the greatest impact on retention and failure behavior. Protruding height plays a secondary role, while the contribution of orientation angle is minimal. These findings provide valuable insights for the design, manufacture, and optimization of precision abrasive machining tools, particularly for applications requiring high precision and reliability.

Atomistic understanding on the surface formation mechanism of nanoscale scratches along different crystal orientations of silicon carbide

Single crystal silicon carbide has been widely used in many fields due to its excellent physical and chemical properties. However, these special properties of silicon carbide can lead to surface defects and subsurface damage in precision machining processes. In this research, high-speed scratching experiments and molecular dynamics simulations were used to study the surface formation mechanism of nanoscale scratches along the [1-210] and [1-100] crystal orientations of silicon carbide. For both the simulations and experiments, different scratching crystal orientations result in the formation of different amorphous patterns. The angle between the scratching orientation [1-210] and the amorphous pattern is 60°, while the angle between scratching orientation [1-100] and the amorphous pattern is 30°. The stress concentration during the scratching process along the orientations [1-210] and [1-100] is mainly located at the two edges and one edge of the amorphous patterns, respectively. The amorphous patterns along the < 1-210 > directions on the (0001) plane are caused by dislocations and slips on the {10-10} plane. This study reveals the material deformation mechanism and removal mechanism of silicon carbide along different crystal orientations scratching, providing theoretical guidance for the nanoscale machining of silicon carbide.

Active compliance control of grinding process for stripping enameled copper wire

The hairpin motor is among the motors used in eco-friendly automobiles. Unlike the random-winding method, this method features a square cross-sectional enamel coil formed into several hundred hairpins inserted into the stator. This offers an increased space factor, which leads to enhanced motor power. With the growing use of hairpin motors, there is an increasing demand for automated equipment in their production. With an aim to improve the manufacturing quality of hairpin motors, many countries are conducting research and development. The process of enamel removal is one of the key steps in hairpin-forming equipment and can significantly affect the performance of the motor. A precise machining process technology is required to improve the enamel removal process, achieve higher enamel removal rates, and reduce wire loss rates. Grinding is a technique used for enamel removal. In this study, an adaptive control algorithm was applied to the grinding process to enhance the enamel removal machining performance. During the machining process, the vertical position of the spindle was controlled to maintain a consistent machining depth for tracking the target grinding force. An experimental setup, which included a system for measuring the spindle torque to calculate the grinding force in real time, was created. To validate the performance of the adaptive control technology, experiments were conducted using this setup. Furthermore, experiments were conducted to observe the changes in the grinding force ratio based on the conditions of the grinding wheel. The correlation between the grinding force ratio and tool condition was analyzed, and based on this, the feasibility of assessing tool condition and determining the timing for tool replacement through real-time monitoring of the grinding force ratio was confirmed.

Research on Cutting Edge form Factor of Milling Tool after Drag Finishing Preparation Based on Discrete Element Method

Cutting edge preparation is a precision machining process that improves the surface quality of cutting tools through the relative movement of abrasives and the tool. Research on removing materials in drag finishing can be greatly beneficial to tool manufacturing. This paper proposes the hypothesis that both abrasive wear and erosion wear act on the surface of milling tools and discusses the material removal models for abrasive wear and erosion wear. The influence of immersion depth, abrasive velocity, abrasive radius, and abrasive density on the material removal rate in two material removal forms is compared and validated by discrete element simulations. The results show that immersion depth has a greater impact on abrasive wear, while abrasive properties have a greater impact on erosion wear. The correlation between simulation results and theoretical models demonstrates the sensitivity of the two forms of wear on this surface to parameter change differences. Dragging finishing was conducted to verify the effectiveness of the simulation, and the effects of immersion depth, dragging velocity, and abrasive properties on the edge radius and form factor (K value) were studied.

Multi-layer phenomena in petawatt laser-driven acceleration of heavy ions

Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators. A particle-in-cell program (Smilei) is employed to simulate the entire process of Station of Extreme Light (SEL) 100 PW laser-accelerated heavy particles using different nanoscale short targets with a thickness of 100 nm Cr, Fe, Ag, Ta, Au, Pb, Th and U, as well as 200 nm thick Al and Ca. An obvious stratification is observed in the simulation. The layering phenomenon is a hybrid acceleration mechanism reflecting target normal sheath acceleration and radiation pressure acceleration, and this phenomenon is understood from the simulated energy spectrum, ionization and spatial electric field distribution. According to the stratification, it is suggested that high-quality heavy-ion beams could be expected for fusion reactions to synthesize superheavy nuclei. Two plasma clusters in the stratification are observed simultaneously, which suggest new techniques for plasma experiments as well as thinner metal targets in the precision machining process.

Analysis, Modeling and Experimental Study of the Normal Contact Stiffness of Rough Surfaces in Grinding

Grinding is the most important method in machining, which belongs to the category of precision machining processes. Many mechanical bonding surfaces are grinding surfaces. Therefore, the contact mechanism of grinding a joint surface is of great significance for predicting the loading process and dynamic characteristics of precision mechanical products. In this paper, based on the collected grinding surface roughness data, the profile parameters and topography characteristics of the asperity were analyzed, the rough surface data were fitted, the asperity profile was reconstructed, and the parabola y = nx2 + mx + l of the cylindrical asperity model was established. After analyzing the rough surface data of the grinding process, the asperity distribution height was fitted with a Gaussian distribution function, which proved that asperity follows the Gaussian distribution law. The validity of this model was confirmed by the non-dimensional processing of the assumed model and the fitting of six plasticity indices. When the pressure is the same, the normal stiffness increases with the decrease in the roughness value of the joint surface. The experimental stiffness values are basically consistent with the fitting stiffness values of the newly established model, which verifies the reliability and effectiveness of the new model established for the grinding surface. In this paper, a new model for grinding joint surface is established, and an experimental platform is set up to verify the validity of the model.

Molecular dynamics study on martensitic transformation behavior of SLM-NiTi alloy induced by temperature and stress

Selective laser melting (SLM) technology is currently one of the most promising additive manufacturing technologies for complex metal components. NiTi alloy has been highly regarded in advanced applications due to its excellent shape memory and good biocompatibility. However, as a new material, SLM-NiTi alloy is far from being applied in actual advanced fields. In the actual processing, such as grinding, turning, polishing, electrical discharge machining, all involve changes in temperature and stress, Therefore, it is very important to study the martensitic phase transition caused by temperature and stress changes in the precision machining process of SLM-NiTi alloy. However, it is difficult to observe the martensitic phase transition changes directly in the actual processing, so the method of molecular dynamics is adopted in this paper. Moreover, in the process of preparing NiTi alloy by selective laser melting, the ratio of Ni to Ti is very important, which determines the final forming quality. Therefore, this paper studied the martensitic transformation behavior induced by temperature and stress under different nickel proportions, different initial temperatures and different model sizes, and expounded the variation laws of stress–strain, potential energy, volume and dislocation. The microstructure and shear strain were demonstrated on the atomic scale. The results show that temperature plays an important role in the martensite transformation of SLM-NiTi alloy, low temperature will largely inhibit martensite transformation, and high temperature will promote martensite transformation. The stress induced martensite reorientation in SLM-NiTi alloy is accomplished by the migration of the interface between different martensite variants. When the nickel content is 52% and 55%, there is no inflection point between volume and potential energy with the change of temperature, when the nickel content is 50.8%, there is an obvious jump between volume and potential energy. The research in this paper is helpful to guide the processing technology of SLM-NiTi alloy, and also broadens the application of additive manufacturing materials.

Influence of selective process interfering on the workpiece fixture dynamics in precision honing

In the area of precision machining processes, honing is of central importance for manufacturing high-precision functional components according to the current state of technology. This precision machining process usually represents the last machining step in the process chain and fulfills high requirements in terms of shape, dimensional and surface quality of less than 1 µm. Therefore, the knowledge of the process dynamics of the tool-workpiece fixture system is of major importance. This paper focuses on the process dynamics of the workpiece fixture in internal long-stroke honing for bore diameters less than 10 mm. In general, the dynamics of a moving system can be described by mass, stiffness and damping. These variables are experimentally included in the investigations as interfering variables in the workpiece fixture and the process dynamics are monitored using eddy current sensors. A gimbal-mounted workpiece fixture with four degrees of freedom is applied for this purpose. The aim of this work is the analysis of the dynamic behavior by variation of the interfering variables and the determination of the process limits. For this purpose, elaborate experiments are carried out and extensive results are presented.

Effect of flexible machining on subsurface damage and recrystallization of single crystal superalloy

Single crystal superalloy has gradually become the primary manufacturing material of advanced aero-engine turbine blades. However, it is easy to introduce subsurface damage and recrystallization to worsen the high-temperature service performance during the precision machining process. To investigate the effect of abrasive belt grinding on the subsurface damage and recrystallization of single crystal superalloy, a flexible adaptive continuous feed analysis model was established, which was confirmed by a series of flexible and rigid scratching experiments. The experimental results showed that the plastic deformation area generated by flexible scratch was smaller, but the slip area was larger. The recrystallization depth of flexible scratch was about 35 % lower than that of rigid scratch. The effective material removal rate of the flexible scratch was larger. The flexible reciprocating scratch verified the feasibility of the adaptive continuous feed model. And the recrystallization depth of flexible reciprocating scratch was about 47 % lower than that of rigid scratch. It indicates that the flexible machining method can not only reduce the recrystallization depth but also ensure material processing efficiency. It is expected to provide a theoretical basis and technical support for the high efficiency and low-damage machining of single crystal superalloy.

Study on optimization of surface processing technology of silicon nitride bearing ring

Based on the difficult machining characteristics of silicon nitride materials, this manuscript focuses on optimizing the precision machining process of silicon nitride bearing components and improving the machining efficiency and quality of silicon nitride bearing components. Firstly, the mechanism of crack formation and propagation in hard and brittle materials under the action of abrasive particles is discussed in this paper, and based on this, a kinematic model of single abrasive grain cutting on hard and brittle materials is established. The effect of workpiece linear velocity, grinding wheel linear velocity, grinding wheel oscillation velocity and feed velocity on inner surface roughness of Si3N4 ring was discussed through grinding test. The experimental results show that the surface roughness can reach about Ra0.20 ∼Ra0.33 μm through a large number of grinding experiments by adjusting the combination of process parameters μm. On this basis, use the optimized process parameters calculated by the surface quality prediction model constructed in this manuscript to conduct grinding test again, and the surface roughness value reaches about Ra0.19 ∼Ra0.23 μm. The purpose of optimizing the process parameters is realized. Finally, the surface roughness can be further reduced and maintained at Ra0.05 ∼Ra0.06 μm by further superfinishing the surface after the process optimization with an oilstone. The research work of this manuscript realized the optimization of precision machining process of silicon nitride bearing ring and the rapid optimization of machining process through the established prediction model, which improved the precision machining efficiency of ceramic bearing components. Through the study of this manuscript, a process route of controllable processing of inner surface quality of Si3N4 ring is formed, from preliminary selection of process parameters by optimization model to precision grinding and then to ultra-finishing of whetstone, which provides theoretical reference for efficient and precise manufacturing of practical bearing components.

Methodology for the development of augmented reality applications for the elimination of errors in the interpretation of manufacturing drawings

Nowadays, precision machining processes have been widely used in the manufacture of products mainly focused on aerospace, automotive, mold manufacturing and various types of products that demand high production volumes, precision and surface quality. However, these manufacturing processes are not exempt from errors and failures during the machining process. Recent studies found that the main errors are due to the interpretation of the information in the manufacturing drawings due to lack of experience or training of the personnel. This research project aims to eliminate errors due to misinterpretation of information in Computer Numerical Control (CNC) machining processes through the implementation of a methodology to develop Augmented Reality (AR) applications for the interpretation of manufacturing drawings. Its main contribution is to provide virtual support to the operating personnel obtaining multiple benefits such as reducing downtime due to failures in the machining process, ensuring the optimal operation of the machines, avoiding collisions of the tools and ensuring the quality of the products.

Surface roughness prediction for turning based on the corrected subsection theoretical model

To obtain an accurate prediction model of surface roughness on the premise of low experimental cost in precision machining processes, this paper proposes two error correction models of the subsection theoretical model of arithmetic mean height roughness (Ra) in turning. The prediction performance of the two error correction models was evaluated by 25 groups of turning data of AISI1045 steel. The determination coefficient (R2) of the 10 random runs of the two correction models are both above 0.9, the mean squared error (MSE) is lower than 0.05, and the standard deviations (StdDev) of R2 and MSE are 0.01. The experimental results show that the two error correction models significantly improve the prediction accuracy and stability of the subsection theoretical model. Moreover, the influence of turning parameters and tool geometry on Ra based on the two correction models and the subsection theoretical model as well as the advantages and disadvantages of the three models is analysed, which provide an effective guidance for the selection of parameters and the prediction model in actual machining.

Influence of EDM Process Parameters on the Surface Finish of Alnico Alloys.

This article deals with electrical discharge machining (EDM) of an alnico alloy, focusing on how key process parameters affect the surface finish. The experiments were conducted using a BP93L EDM machine. The Box–Behnken design was employed to study the effects of three factors, i.e., spark current, pulse-on time, and pulse-off time, each at three levels, on the surface quality. A specially designed system was employed to increase the effectiveness of the machining process by imparting an additional rotary motion to the tool and an additional rotary motion to the workpiece. The aim was to efficiently remove the eroded metal particles and create a surface with smaller craters. The workpiece surface roughness was measured with a Talysurf CCI lite non-contact profiler. During this precision machining process, the arithmetical mean height (Sa) was less than 1 µm. The surface quality was examined also using scanning electron microscopy (SEM) and optical microscopy (OM). The experimental data were analyzed by means of Statistica to determine and graphically represent the relationships between the input and output parameters.

Synthesis and polishing characteristics of a novel green GO/diamond hybrid slurry under ultrasonic technology

Ultrasonic polishing (UP), as an efficient and clean precision machining process, is increasingly applied in the hard and brittle material processing. To minimize the surface damage and polishing expenses, this paper aims to prepare novel graphene oxide/diamond hybrid slurries (GDS) by ultrasonication, and to investigate the UP mechanisms for silicon carbide (SiC) ceramics on UP and tribological experiments. Findings showed that GDS exhibited superior polishing performance compared to diamond polishing slurries. Moreover, the promotion effect of GDS was more obvious under UP. The surface roughness was improved by 31.62% after UP using GDS with a graphene oxide (GO) content of 0.1 wt%. On the one hand, the lubrication of GO reduce the wear and coefficient of friction. On the other hand, ultrasonic vibration induces stronger impact kinetic energy of abrasives to remove material and allows for a better uniform distribution of GDS to further enhance the lubrication characteristics of GO nanosheets. The application of GO in UP is a processing technology penetrating the manufacturing industry and even human life, laying the foundation for SiC nano-polishing.

Analysis of the Dynamic Behavior of a Structurally Optimized Gimbal-Mounted Workpiece Fixture in Precision Honing

Among the precision machining processes, honing describes a key technology for the manufacturing of high-precision functional components under high requirements. Manufacturing tolerances of less than 1µm in terms of shape, dimension and surface quality can be achieved. In order to fulfill the high requirements, the knowledge of the process control of the tool-device system is of major importance. In this context, this paper focuses on the optimization of the process dynamics in internal long-stroke honing for bore diameters less than 10mm. In general, the dynamics of a system can be determined by mass, stiffness and damping. In the following, an approach via the reduction of the mass of the workpiece fixture is pursued. For this purpose, the topology of a conventional gimbal-mounted workpiece fixture is optimized with simulation support and manufactured by means of Selective Laser Melting. The optimized workpiece fixture is investigated in a series of experiments and compared based on deep pre-investigations of the process dynamics in internal long-stroke honing. The aim is to present the effect of the mass reduction regarding the process dynamics and to elaborate on the potential for the honing process.

Approach and Development of a Methodology for Machining of Shapes in Cylindrical Bores by Precision Honing

In mechanical series production, honing is predominantly used to manufacture high-precision bores according to the current state of technology. This precision machining process usually represents the last machining step in the process chain and fulfills high requirements in terms of shape, dimensional and surface quality within narrow tolerances. Crucial for adherence to high requirements is the coaxial interaction between the honing tool and the workpiece. This paper examines the kinematics of the workpiece fixture in internal long-stroke honing. The focus is on changing the bore shape in contrast to coaxial machining by affecting the workpiece fixture. Controllable honing tools for machining a freeform in cylindrical bores as in combustion engines already exist, but they are mostly suitable for large components due to their size and complex structure. In this context, this paper develops and investigates an approach in the form honing process via the workpiece fixture for bore diameters less than 10mm. For this purpose, the movement dynamics and the degrees of freedom of the workpiece fixture are analyzed and affected by spring components to investigate the impact on the process dynamic and the resulting bore shape. Based on this approach, a gimbal-mounted workpiece fixture is modified with a load cell, leaf springs and equipped with eddy current sensors to monitor the process dynamic at the same time. The investigations focus on the analysis of the potential for machining non-cylindrical bores with an approach, to affect the kinematics of the workpiece fixture by mechanical components to provide a basis for the development of a controllable workpiece fixture. For this purpose, elaborate experiments are carried out and the first results on the bore shape are presented.

Study on subsurface damage and recrystallization of single crystal superalloy in scratching with single diamond grain

Single crystal superalloy has gradually become the primary manufacturing material of advanced aero-engine turbine blades. However, it is easy to introduce subsurface damage and recrystallization in the precision machining process of this kind of material, and hence to worsen the high-temperature service performance of the parts. To explore its damage mechanism and influencing factors, a series of scratching experiments of single crystal superalloy with single diamond grain were conducted in this work. The examined results of the machined sample section by using a scanning electron microscope indicated that the subsurface damages include metallographic plastic deformation, slip band and transverse crack before heat treatment. Furthermore, cellular recrystallization observed in the surface layer mainly occurred in the metallographic plastic deformation zone after heat treatment. The experimental results revealed that the recrystallization depth increased with a rise in tool dimension and normal components of the scratching force. When the normal force is less than 20 N, the recrystallization depth scratched by the 80° tool is less than the critical safety value of 15 μm. Further analytical results indicated that improving the tool cutting performance and reducing the cutting force are beneficial to reduce the degree of recrystallization and subsurface damages. The research finding of this work is expected to provide a theoretical basis for the high efficiency and low damage machining of single crystal superalloy.

Analysis of Tool Wear and Roughness of Graphite Surfaces Machined Using MCD and NCD-Coated Ball Endmills.

The high-purity G5 graphite material is widely used for glass moulding and provides high hardness and brittleness because it is sintered to fine particles unlike other graphite materials. Hence, tool cutting of a G5 workpiece is performed by local fracture instead of plastic deformation of the machined surface. Although a diamond-coated tool with outstanding hardness is used to machine very hard graphite, the tool shows variability regarding the service life and machining performance depending on the grain size, even in the same machining environment. We investigated the wear and change trend of machined surface roughness considering microcrystalline diamond (MCD) and nanocrystalline diamond (NCD)-coated tools, which are generally used to machine graphite materials, and analysed their relation with coating. For rough machining, the MCD-coated tool, for which the delamination of coating occurred later, showed less wear and improved machined surface roughness. For precision machining, the NCD tool showed less tool wear rate relative to the cutting length, leading to a small difference in the machined surface roughness between the two tools. We conclude that if rough and precision machining processes are performed using the same cutting tool, the MCD-coated tool is advantageous in terms of service life, while the difference in roughness of the final machined surface between the tools is negligible.

Performance Evaluation of Low-Cost Vibration Sensors in Industrial IoT Applications

The recent development of low-cost accelerometers, driven by the Industrial Internet of Things (IIoT) revolution, provides an opportunity for their application in precision manufacturing. Sensor data is often of the highest consideration in any precision machining process. While high-cost vibration sensors have traditionally been employed for vibration measurements in industrial manufacturing, the measurement uncertainty affecting the accuracy of low-cost vibration sensors has not been explored and requires performance evaluation. This research focuses on the characterization of measurements from low-cost tri-axial micro electro-mechanical systems (MEMS) accelerometers in terms of identifying the parameters that induce uncertainties in measured data. Static and dynamic calibration was conducted on a calibration test bench using a range of frequencies while establishing traceability according to the ISO 16063 series and the IEEE-STD-1293-2018 standards. Moreover, comparison tests were performed by installing the sensors on machine tools for reliability evaluation in terms of digital transmission of recorded data. Both tests further established the relationship between the baseline errors originating from the sensors and their influence on the data obtained during the dynamic performance profile of the machine tools. The outcomes of this research will foresee the viability offered by such low-cost sensors in metrological applications enabling Industry 4.0.