Machined Workpiece Surface Research Articles

Investigation on the optimal ultra-precision machining of nitriding mold steel by in-situ laser assisted diamond cutting

S136 (STAVAX ESR) mold steel is an advanced material for the optical mold industry. The precisely machined surface quality is essential for guaranteeing the excellent performance of molds. Diamond cutting is a high-efficiency machining technique in optical mold manufacturing. However, the chemical wear of diamond tool is a huge challenge in precisely machining steel mold due to the reaction between atoms C and Fe. In this study, the hybrid machining technique which combined the in-situ laser assisted diamond cutting (LADC) and plasma nitriding was used to machine S136 mold steel. Furthermore, the impact of the various machining conditions on the machined workpiece surface roughness Sa was comprehensively investigated by the Taguchi method (TM) and Response surface methodology (RSM). The experimental results of material characterization indicated that a 90 μm nitride layer was generated on the workpiece surface by plasma nitriding. Analysis of variance (ANOVA) results demonstrated that the feed rate and laser power had an important impact on the machined surface roughness Sa. According to the RSM, a precise mathematical model was developed which is explored by experimental investigations. The results showed that the optimal machining parameter combination by RSM generated the better surface quality of 6.393 nm in in-situ LADC of nitriding steel. This study provides a reference for mold steel ultra-precision machining technique and parameter optimization method for surface integrity.

Assessment of the roughness of the machined surface during pendulum surface plastic deformation

The influence of pendular surface plastic deformation mode on the roughness parameters of the machined surface of a cylindrical workpiece is studied. The optimal values of the processing mode parameters are determined. Keywords surface plastic deformation, roughness parameters, experimental study, device for pendular motion

Tribological Mechanism of Graphene and Ionic Liquid Mixed Fluid on Grinding Interface under Nanofluid Minimum Quantity Lubrication

Graphene has superhigh thermal conductivity up to 5000 W/(m·K), extremely thin thickness, superhigh mechanical strength and nano-lamellar structure with low interlayer shear strength, making it possess great potential in minimum quantity lubrication (MQL) grinding. Meanwhile, ionic liquids (ILs) have higher thermal conductivity and better thermal stability than vegetable oils, which are frequently used as MQL grinding fluids. And ILs have extremely low vapor pressure, thereby avoiding film boiling in grinding. These excellent properties make ILs also have immense potential in MQL grinding. However, the grinding performance of graphene and ionic liquid mixed fluid under nanofluid minimum quantity lubrication (NMQL), and its tribological mechanism on abrasive grain/workpiece grinding interface, are still unclear. This research firstly evaluates the grinding performance of graphene and ionic liquid mixed nanofluids (graphene/IL nanofluids) under NMQL experimentally. The evaluation shows that graphene/IL nanofluids can further strengthen both the cooling and lubricating performances compared with MQL grinding using ILs only. The specific grinding energy and grinding force ratio can be reduced by over 40% at grinding depth of 10 μm. Workpiece machined surface roughness can be decreased by over 10%, and grinding temperature can be lowered over 50 ℃ at grinding depth of 30 μm. Aiming at the unclear tribological mechanism of graphene/IL nanofluids, molecular dynamics simulations for abrasive grain/workpiece grinding interface are performed to explore the formation mechanism of physical adsorption film. The simulations show that the grinding interface is in a boundary lubrication state. IL molecules absorb in groove-like fractures on grain wear flat face to form boundary lubrication film, and graphene nanosheets can enter into the grinding interface to further decrease the contact area between abrasive grain and workpiece. Compared with MQL grinding, the average tangential grinding force of graphene/IL nanofluids can decrease up to 10.8%. The interlayer shear effect and low interlayer shear strength of graphene nanosheets are the principal causes of enhanced lubricating performance on the grinding interface. EDS and XPS analyses are further carried out to explore the formation mechanism of chemical reaction film. The analyses show that IL base fluid happens chemical reactions with workpiece material, producing FeF2, CrF3, and BN. The fresh machined surface of workpiece is oxidized by air, producing NiO, Cr2O3 and Fe2O3. The chemical reaction film is constituted by fluorides, nitrides and oxides together. The combined action of physical adsorption film and chemical reaction film make graphene/IL nanofluids obtain excellent grinding performance.

A novel calibration method for angular misalignment in independently controlled fast tool servo-based diamond turning

With significant technological progress in optics fields, such as VR and 3D sensing technologies, the demand for optical components with complex shapes (e.g., freeform surfaces) has expanded significantly in recent years. Ultra-precision diamond turning is one of the common manufacturing methods used for freeform optics. There are two tool-motion mechanisms for freeform diamond turning: slow tool servo (STS), which moves the entire tool rest, and fast tool servo (FTS), which only drives the diamond tool. In particular, high-frequency and long-stroke FTS units driven by a separate control system from the machine tool controller have recently been developed as a new trend in FTS-based diamond turning. However, this type of independent FTS control system causes a time delay between the machine tool instruction and the FTS tool motion. Even a millisecond-scale time delay can cause a considerable angular misalignment owing to the high rotation rate of the spindle, resulting in a micron-scale form error on the workpiece surface. In this paper, a novel method for precisely measuring the time delay from the machined workpiece surface and compensating for the misalignment based on the measured time delay was proposed. To measure the time delay, spherical dimples were machined on the workpiece surface by using STS and FTS. Subsequently, the angular misalignment and time delay were obtained by comparing the measured surface profiles at specific positions of the spherical dimples. Thus, the time delay can be measured with microsecond-scale accuracy. Based on the measured time delay, the shifted tool position along the spindle axis by the time delay was compensated to the ideal tool position by considering the cutting velocity. Consequently, the angular misalignment was completely eliminated, and submicron-level form accuracy was achieved. This calibration method of angular misalignment for an independent FTS unit is expected to significantly improve the accuracy of ultra-precision machining of freeform optics.

Multifractal parameterization of a periodic surface microrelief formed at the face milling. 1. The distribution of elements area of surface relief

The multifractal analysis (MFA) of the spatial microform area formed on the surface of steel C35 and aluminum alloy AA2024 at the face milling was implemented. The input information for the MFA was micro-images of the machined workpiece surface. Multifractal (MF) spectra and their main parameters are calculated for the surface of samples machined at various cutting conditions. Renyi’s numbers and fractal ordering parameters were chosen as the most informative MF parameters describing the surface structure. It is shown that the MF functions of the system correspond to their canonical forms. Quantitative relationships between the parameters of MF spectra for the surface area of microforms formed during machining surfaces of steel and aluminum alloy workpieces and the cutting conditions were obtained. The physical processes that are responsible for the formation of the observed MF spectra on the surface of the workpieces depending on feed and depth of cut at the face milling were discussed. The developed computational technique can be used to describe and analyze the state of spatial fractal structures formed on the surface of other materials.

Prediction of temperature field in machined workpiece surface during the cutting of Inconel 718 coated with surface-active media

Prediction of temperature field in machined workpiece surface during the cutting of Inconel 718 coated with surface-active media

Chip Formation and Orthogonal Cutting Optimisation of Unidirectional Carbon Fibre Composites.

This study presents a thorough experimental investigation utilising the design of experiments and analysis of variance (ANOVA) to examine the impact of machining process parameters on chip formation mechanisms, machining forces, workpiece surface integrity, and damage resulting from the orthogonal cutting of unidirectional CFRP. The study identified the mechanisms behind chip formation and found it to significantly impact the workpiece orientation of fibre and the tool's cutting angle, resulting in increased fibre bounceback at larger fibre orientation angles and when using smaller rake angle tools. Increasing the depth of cut and fibre orientation angle results in an increased damage depth, while using higher rake angles reduces it. An analytical model based on response surface analysis for predicting machining forces, damage, surface roughness, and bounceback was also developed. The ANOVA results indicate that fibre orientation is the most significant factor in machining CFRP, while cutting speed is insignificant. Increasing fibre orientation angle and depth leads to deeper damage, while larger tool rake angles reduce damage. Machining workpieces with 0° fibre orientation angle results in the least subsurface damage, and surface roughness is unaffected by the tool rake angle for fibre orientations between 0° to 90° but worsens for angles greater than 90°. Optimisation of cutting parameters was subsequently carried out to improve machined workpiece surface quality and reduce forces. The experimental results showed that negative rake angle and cutting at moderately low speeds (366 mm/min) are the optimal conditions for machining laminates with a fibre angle of θ = 45°. On the other hand, for composite materials with fibre angles of θ = 90° and θ = 135°, it is recommended to use a high positive rake angle and cutting speeds.

Tribological performance of phosphonium-based halogen-free ionic liquids as lubricant additives

In recent years, ionic liquids have shown great potential as an additive in lubricants. However, most of the explored ionic liquids for machining applications contain halogen-based anions, which are sensitive to moisture and have a tendency to produce harmful halogen acids (HX) after reacting with water/moisture. These acids are harmful to the environment and can corrode the working surfaces. This study investigates the effectiveness of halogen-free ionic liquids as potential additives to vegetable oil (canola oil). Two halogen-based ionic liquids (1-methyl 3-butylimidazolium tetrafluoroborate [BMIM BF4] and 1-methyl 3-butylimidazolium hexafluorophosphate [BMIM PF6]) and one halogen-free ionic liquids (trihexyl tetradecyl phosphonium bis (24,4-trimethylpentyl) phosphinate P6,6,6,14 [i(C8)2PO2]) were blended individually with canola oil. The percentage ratio of ionic liquid to canola oil is 1:99. Dynamic viscosity and contact angles of different lubricants were measured. Sliding tests were conducted in various conditions; dry, canola oil, and three different blends of ionic liquid with canola oil. Further, to connect tool-chip tribology with machining, turning experiments were carried out under similar lubricating conditions. Results show that the sliding friction, pin surface temperature, and wear were reduced by 48.1%, 44%, and 69.6%, respectively, due to better lubricating ability and spreading tendency of halogen-free ionic liquid blended with canola oil. The microscopic analyses of pin surfaces and the morphology of counter disc surfaces further supported better lubrication between the sliding pair. For P6,6,6,14 [i(C8)2PO2] ionic liquid blended with canola oil, the average cutting temperature and machined workpiece surface roughness reduces by 43.6% and 62.4% compared to dry machining.

Design and experiments of ultra-precision aerostatic turning machine tool

Ultra-precision turning is one of the commonly machining methods to obtain high-quality optical components. Ultra-precision turning machine tools are the industrial equipment that realize ultra-precision turning process. In this paper, a combined design, performance analysis and experimental verification are carried out to build an ultra-precision aerostatic turning machine tool (UPATMT), which adopts aerostatic support systems for the spindle system and the feed system. Firstly, the mathematical model and physical model of UPATMT are established, and the dynamic performance of UPATMT model is carried out and analyzed by finite element method. In addition, the electromechanical control system is simulated and analyzed to obtain better dynamic performance. Finally, the modal tests and turning experiments are carried out on a homemade UPATMT platform. The machined workpiece surface roughness is measured, the arithmetical mean deviation of the workplace surface roughness is Ra 7.4 nm, and the maximum peak valley height of workplace surface roughness Rz 34.4 nm. The results show that electromechanical coupling analysis can obtain high machining performance of UPATMT.

The wear detection of mill-grinding tool based on acoustic emission sensor

The monitoring of tool wear plays an important role in improving the processing efficiency and reducing the production cost of enterprises. This paper is focused on the detection of electroplated diamond mill-grinding tools by using the acoustic emission sensor. The wear stages of mill-grinding tools are divided into three parts, namely initial wear stage, normal wear stage, and severe wear stage. The characteristic parameter method and the waveform analysis method are applied to analyze the acoustic emission signals. The wear characteristics of the tool and workpiece in different wear stages are observed and analyzed. The results indicate that the acoustic emission waveform is relatively stable in the initial wear stage, and the continuous acoustic emission signal is dominated. Moreover, the diamond abrasive grains are mainly worn and slightly broken in the normal wear stage, and there are some pits on the machined workpiece surface after the initial wear stage. In the severe wear stage, most of the abrasive grains are broken or broken in a large area, and there are burst acoustic emission signals in the waveform.

Оптимизация режимов плоского шлифования деталей малой жесткости типа колец и призматических стержней

The study introduces an algorithm and method for optimization of flat grinding modes for low-rigidity workpieces such as rings and prismatic rods. The proposed solution ensures the specified quality of the machined surface at the maximum process efficiency. The required flatness tolerance of the machined surface is provided at the second stage of optimization modes by limiting the value of the maximum elastic deformation. The variable parameters are the cutting forces, magnetic field attraction of the machine table, and the bending rigidity of the workpiece. The study introduces mathematical models to determine maximum elastic deformation of workpieces when fixing and machining, outlines the conditions for ensuring the required flatness tolerance of the machined workpiece surface, taking into account the maximum elastic deformation of the low rigidity workpiece under the influence of the magnetic field of the machine tool and the radial component of the cutting force.

Performance Study of EDM Process Parameters Using TiC/ZrSiO4 Particulate-Reinforced Copper Composite Electrode

Electrical discharge machines (EDM) are widely employed in machining components containing complex profiles of hard-to-cut and machining materials. However, the fabrication-of-tool time for the EDM process is excessively high in the traditional machining method, which significantly affects the machining rate. Therefore, in this paper, a powder metallurgy (PM) technique is employed to fabricate the tool electrode using copper (Cu), titanium carbide (TiC), and zirconium silicate (ZrSiO4) for different combinations. An L18 orthogonal array (OA) is planned using the following input parameters: three types of tools (Cu, Cu90, Cu80), peak current (PC) [A], pulse on time (PT) [µs], and gap voltage (GV) [V]. The performance of EDM is evaluated through the material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). The process parameters are optimized using two different techniques: the technique for order of preference by similarity to the ideal solution (TOPSIS) and grey relational analysis (GRA). TOPSIS and GRA optimization techniques produce the same optimal parametric solution for less TWR, SR, and higher MRR with the combination of the Cu90 tool, E8 APC, 15 µs pulse PT, and 75 V GV. Based on the ANOVA table of TOPSIS, pulse on time plays a major role, contributing 46.8 % of the machining performance; peak current shows the most significant contribution of 39.3 % of the machining performance using GRA values. Furthermore, the scanning electron microscope (SEM) image analyses are carried out on the machined workpiece surface to understand the effect of tools on machining quality.

Effects of Sequential Operation with Heat Treatment and Mechanical Milling on Work Hardening for Superalloy GH4169

Engineering components are usually manufactured with sequential production processes. Work hardening due to previous production processes affects the machinability of the workpiece in subsequent operations. In this research, the surface work hardening of a workpiece manufactured by two sequential processes with heat treatment/milling (HT + M) and milling/heat treatment (M + HT) of superalloy GH4169 was investigated. First, the surface microstructure characteristics, including plastic deformation and grain size of the machined workpiece surface processed by the two sequential processes, were quantitatively presented. Then, the microhardness on the machined workpiece surface and its cross-section was measured and analyzed. Finally, a surface microhardness calculation model considering twin boundary deformation was proposed. Here, we also present the microstructure evolution principle of the machined workpiece surface by the two sequential processes. It was found that the degree of work hardening of HT + M machining was 179%, whereas that of M + HT was only 101%. The research results can be applied to the optimized selection of process sequence for manufacturing superalloy GH4169.

Fatigue performance of surface ground and wire electrical discharge machined TiNi shape memory alloy

Fatigue performance is a major consideration for critical aerospace components. The influence of surface grinding and rough/finish wire electrical discharge machining (WEDM) on the high cycle fatigue performance of a binary Ti50.8-Ni49.2 shape memory alloy was assessed. The effect of machined workpiece surface integrity in terms of surface roughness and subsurface microhardness on the fatigue results was also evaluated, in addition to fractography analysis. Testing was performed using a tensile-tensile regime at an elevated temperature of 150°C with specimens in the austenitic phase. Ground samples showed the highest fatigue strength of 390 MPa at run-out of 1.2 × 107 cycles, while finish and rough WEDM specimens were 21% and 57% lower respectively, despite the finish WEDM surfaces having significantly lower roughness. This was likely due to the presence of tensile residual stresses following WEDM. All of the S-N curves however exhibited a relatively flat response with no clear indication of endurance limits. This implies that the different machining processes/conditions affected the fatigue strength of the material, but not the overall trend/shape of the fatigue curves.

Optimization of CNC Milling Parameters for Complex 3D Surfaces of SIMOLD 2083 Alloy Mold Core Utilizing Multiobjective Water Cycle Algorithm

In this article, an effective multiobjective optimization approach is exploited to search for the best milling parameters for CNC for complex 3d surfaces of SIMOLD 2083 alloy mold core. To improve the quality responses, the cutting factors are optimized by a combination of Taguchi method (TM), response surface method (RSM), and multiobjective water cycle algorithm (MWCA). Firstly, the design for initial series experiments of the cutting factors was generated via the TM. Thereafter, the regression models between the cutting factors and the surface roughness of the machined workpiece surface as well as milling time are formed via applying the RSM. Moreover, analysis of variance and sensitivity analysis are also executed to define the influences and crucial contributions of cutting parameters on the surface roughness and milling time. The results of analysis of variance showed that the factors which have main effects on surface roughness were spindle speed (42.42%), feed rate (29.40%), and cutting depth (6.59%), respectively. Meanwhile, the feed rate with the influence of 92.6% was the most significant factor in controlling the milling time. Ultimately, based on mathematical models, the MWCA is performed to define the optimal factors. The optimal results indicated that the optimized surface roughness was about 0.260 μm and the milling time was roughly 1012.767 (s). In addition, the errors between forecasted results and experimental verifications for the surface roughness and milling time are 2.04% and 5.39%, respectively. Therefore, the results of experimental verifications are suitable with the forecasted results from the proposed optimization method. These results depicted that the proposed integration approach can define effectively the optimal cutting factors for CNC milling and expand to apply for complex multiobjective optimization problems.

Tool deterioration of 316 stainless steel in dry down-milling using carbide insert

Machining of difficult-to-cut material such as 316 Stainless Steel has become a vital concern in machining industry. This is due to its mechanical properties of high hardness which leads to the high tendency of cutting tool breakage. Hence, the understanding of thorough progression of cutting tool deterioration is crucial, so that a better improvement of machining 316 Stainless Steel could be established. Thus, a series of documented experiments had been conducted to monitor and understand the tool deterioration of coated tungsten carbide insert in dry down-milling of 316 Stainless Steel. It was observed that the cutting tool started to deteriorate after the second pass of milling experiments and achieved VB = 0.3 mm after the sixth pass on average. Two types of tool deterioration mechanisms were identified which were tool wear and chipping. However, it was observed that the most predominant mode of tool deterioration was flank wear (tool wear). Cutting tools deteriorated gradually due to blunting and rubbing of tool edge over the surface of machined workpiece. .

Nano-lubricant influence on surface residual stresses in hard milling

Residual stress could be induced by machining processes like milling which can greatly affect the fatigue life of fabricated parts, especially in dynamic loading conditions. In metal cutting operations, machining induced residual stresses can be explained in the terms of machining forces and temperatures of the cutting zones. This thermo mechanical loading along with the resulted metallurgical changes are the main sources of residual stresses generation at the surface of machined workpiece. Researchers have proved the superior properties of nanofluids over the conventional coolants to reduce the intensity of thermo mechanical loading in machining process which will affect the residual stresses caused by machining. Therefore, in this paper, silver nanoparticles in the water-soluble oil have been used for reducing the mechanical and thermal loads in the milling process. The cutting forces, temperature of the cutting zone, surface roughness and the residual stress of machined surface have been measured experimentally in milling of hardened steel AISI 4140 for various nanoparticle’s concentration, feeds and cutting speeds. Results show that increasing the concentration of Nano-particles in base fluid from 0.5 to 3.0% wt., will make machining surface residual stresses more compressive averagely by about 66.67% compared to conventional cutting fluid.

Recent progress in flexible supporting technology for aerospace thin-walled parts: A review

Thin-walled parts are widely used in the aerospace industry owing to their light weight and high specific strength. However, due to the low rigidity of thin-walled parts, elastic deformation and chatter easily occur, which seriously affect the machining accuracy and workpiece surface quality. To solve this problem, several supporting technologies have been reported in recent years. This paper reviews the recent research progress of flexible supporting technologies in the aerospace field by classifying them based on different principles and characteristics. The principle, progress, advantages, and limitations of the technologies are expounded by systematic comparison and summarized. Finally, the challenges and future development trends of flexible supporting technology, which will provide guidelines for further research, are discussed.

Управляемые шпиндельные опоры как инструмент обеспечения качества обработки

The purpose of the work is to provide conditions for machined workpiece surface quality control based on the use of gas-magnetic supports in machine-tool systems (on example of the 3K227A internal grinding machine). To model the trajectory of tool and workpiece mutual movement the methods of nonlinear dynamics are used. The literature data on the problem are analyzed and experimental studies are carried out. Based on the considered issues of controlling the dynamic stability of technological systems under machining by means of contactless controlled gas-magnetic supports of spindle units, a scheme for adaptive control of the machine-tool system is proposed. It allows in many respects to eliminate external mechanical effects on the technological system, internal vibrations caused by drives and moving parts, as well as to compensate temperature deformations of the spindle unit frame and body. An adaptive control system based on gas-magnetic supports of the spindle assembly and the workpiece, as well as the control systems of the position of workpiece and tool (on example of 3K227A internal grinding machine) are demonstrated in action. The gas-magnetic support control system developed at Komsomolsk-na-Amure State Technical University makes it possible to set the position of the rotor axis with the accuracy of 0.1 microns. The study results obtained lead to the conclusion that the control of two adaptive links on the gas-magnetic supports, i.e., the spindle assembly of the tool and the spindle assembly of the workpiece, allows to achieve a rotation accuracy of up to 0.2 microns. The methods of nonlinear dynamics make it possible to construct an attractor (trajectory) of the tool tip movement in the real time, which provides a possibility to affect the input parameters of the machining process and thereby to control the output parameters. In addition to this, the control system of machine-tool system dynamic stability is applicable to other processing types as well, including edge cutting machining.

Learning-Based Prediction of Pose-Dependent Dynamics

The constantly increasing demand for both, higher production output and more complex product geometries, which can only be achieved using five-axis milling processes, requires elaborated analysis approaches to optimize the regarded process. This is especially necessary when the used tool is susceptible to vibrations, which can deteriorate the quality of the machined workpiece surface. The prediction of tool vibrations based on the used NC path and process configuration can be achieved by, e.g., applying geometric physically-based process simulation systems prior to the machining process. However, recent research showed that the dynamic behavior of the system, consisting of the machine tool, the spindle, and the milling tool, can change significantly when using different inclination angles to realize certain machined workpiece shapes. Intermediate dynamic properties have to be interpolated based on measurements due to the impracticality of measuring the frequency response functions for each position and inclination angle that are used along the NC path. This paper presents a learning-based approach to predict the frequency response function for a given pose of the tool center point.