Finish Machining Research Articles

Optimization of end milling parameters for rough and finish machining of Al-4032/3%SiC metal matrix composite

Aluminum-based composites are known for better mechanical properties, superior corrosion performance, and light weight. Gradual increase in the reinforcement (SiC particles) produces improvement in several mechanical properties of Aluminum base alloy but adversely affects ductility. The present work depicts the end milling of the Al-4032/3%SiC composite. The investigation on the impact of end milling parameters has been attempted for rough and finish machining conditions. Two case studies (a) rough machining i.e., 100% weightage to material removal rate (MRR) (b) finish machining i.e., 80% weightage to surface roughness, and only 20% weightage to MRR have been investigated. Full factorial design with 3-factors at 3-level each has been used as the design matrix for conducting the milling experiments. Taguchi-based grey relational analysis (TGRA) has been adopted for the bi-objective optimization for finish machining. The significance of process parameters has been checked with analysis of variance (ANOVA).

In-situ measurement of machining part deflection with Digital Image Correlation

In the context of the aeronautics industry, aluminum alloy structural parts are manufactured in several stages, from forming processes and heat treatments to final machining. Some process steps may generate residual stresses. Thus, material removal during machining releases these residual stresses, which induces part deformation. Such deformations can lead to geometric nonconformity of the machined part. It is therefore essential to control this phenomenon. Due to the variability in residual stress distribution in each raw part, the modeling approaches must to be coupled with experimental measurements. This article thus aims to define a reliable experimental technique for measuring in-plane deformation of large aeronautical parts during their machining. The backbone of the technique relies on Digital Image Correlation (DIC), which enables the contactless measurement of part deformation during machining. Moreover, DIC provides a full-field measurement and a direct evaluation of part deformations. This work discusses more specifically problems related to the use of DIC during machining, the latter corresponding to a particularly harsh environment. Indeed, optical systems undergo undesirable movement and metal chips hide areas of the observed part. These unwanted events corrupt the results. In order to control these problems and consistently apply DIC part deformation measurement during machining, specific methods are proposed in this paper. Finally, DIC measurements are performed during the same machining sequence of two parts. The excellent agreement of the two measurements confirms the reliability of the technique. Finally, measurements are discussed, emphasizing the contribution they provide to the machining community.

Экспериментальные исследования влияния электрохимической размерной обработки на контактную усталость валков прокатных машин

The study results of the influence of the surface layer of forming rolls on their operational characteristics are presented, the results of comparative tests for contact fatigue of samples machined by grinding and electrochemical sizing are presented, the sequence of sample preparation for experimental studies is considered, recommendations on the choice of final machining method are formulated.

Machining parameters in WEDM of EN31 steel using Taguchi technique optimization

Wire electrical discharge machining (WEDM) is often used in the machining of conductive materials when precision is important. The current study looked at wire-cut electric discharge machining of EN31 steel. Taguchi's L27 orthogonal array was used to finish the investigation using various amounts of input parameters. This method was used to determine the optimal parameter combination. The experimental findings show that the machining model is correct, and Taguchi's approach meets the practical requirements. Surfaces having micro cracks and porosity, as well as poor surface quality, are produced by rough machining with WEDM. Finish machining yields a better surface finish (Ra) but at a slower rate (MRR). As a result, the Taguchi approach's purpose is to improve MRR while lowering Ra. To check the performance measures in terms of Surface Roughness, control parameters such as voltage applied, pulse width, pulse interval, and speed were used.

Chip formation and wear mechanisms of SiAlON and whisker-reinforced ceramics when turning Inconel 718

Inconel 718 has found use in many demanding applications due to its high temperature fatigue strength, hardness and low thermal conductivity. These material properties present a challenge to productive and high quality (surface finish) machining and promote rapid tool wear. The work presented here describes the chip formation and wear mechanisms of silicon nitride (Si3N4) based ceramic SiAlON and silicon carbide whiskers reinforced alumina (WRA) (Al2O3 + SiCw) round (RNGN) inserts, when turning solution-annealed Inconel 718 (27<HRC<30) with a 10% concentration cutting fluid. Four sets of cutting trials were conducted at a cutting speed of 250 m/min and another four at 300 m/min. The results show that using SiAlON turning inserts at a cutting speed of 300 m/min delivered the best results in terms of tool flank wear, total tool life, and work-piece surface finish. The morphology of the Inconel 718 chip, at cutting speeds above 250 m/min, presents an intense shear band localisation in the primary shear zone of the chip/tool interface, which leads to chip segmentation.

In-Situ Calibrated Digital Process Twin Models for Resource Efficient Manufacturing

Abstract The chief objective of manufacturing process improvement efforts is to significantly minimize process resources such as time, cost, waste, and consumed energy while improving product quality and process productivity. This paper presents a novel physics-informed optimization approach based on artificial intelligence (AI) to generate digital process twins (DPTs). The utility of the DPT approach is demonstrated in the case of finish machining of aerospace components made from gamma titanium aluminide alloy (γ-TiAl). This particular component has been plagued with persistent quality defects, including surface and sub-surface cracks, which adversely affect resource efficiency. Previous process improvement efforts have been restricted to anecdotal post-mortem investigation and empirical modeling, which fail to address the fundamental issue of how and when cracks occur during cutting. In this work, the integration of in-situ process characterization with modular physics-based models is presented, and machine learning algorithms are used to create a DPT capable of reducing environmental and energy impacts while significantly increasing yield and profitability. Based on the preliminary results presented here, an improvement in the overall embodied energy efficiency of over 84%, 93% in process queuing time, 2% in scrap cost, and 93% in queuing cost has been realized for γ-TiAl machining using our novel approach.

Generic model of time-variant tool influence function and dwell-time algorithm for deterministic polishing

In computer-controlled optical surfacing (CCOS) techniques, the tool influence function (TIF) is generally assumed to be time-invariant; thus, two-dimensional convolution can be employed to compute the dwell time. However, the material removal rate is time-variant in some CCOS processes. This time-variant material removal rate makes it difficult to accurately model the TIF and leads to impracticality of the two-dimensional convolution algorithm. We herein establish a novel modelling framework of the TIF considering the time-variant material removal rate in CCOS based on a partial differential equation. An updated dwell-time algorithm is also proposed to address the inverse problem of freeform surface generation by using the established TIF. The proposed modelling technique is well demonstrated in magnetically driven internal finishing and abrasive jet machining. The results demonstrate that the model can precisely predict the polished profile against the polishing time, and the novel dwell-time algorithm outperforms the conventional convolution algorithm in terms of efficiency and accuracy. The modelling framework enables localised freeform surface generation and corrective polishing on internal surfaces. The proposed TIF model and dwell-time algorithm may be extended to other CCOS techniques to achieve better figuring accuracy, such as bonnet polishing, ion beam figuring, and plasma jet machining.

ФИНИШНАЯ АБРАЗИВНАЯ ОБРАБОТКА ТОНКОСТЕННЫХ ПЛАСТИН

The features of the final machining of thin-walled plates are given. The calculation scheme for the kinematic parameters of abrasive finishing of thin-walled easily deformable plates and the mathematical dependence for calculating the pressure on the lapping faceplates with the processed parts are determined. The aim of the work is to obtain an analytical dependence that establishes the relationship between the operating parameters and the conditions of the abrasive finishing process with the roughness of the working surface of the plates. The task, which the article is devoted to solve is theoretical and experimental studies of the influence of technological modes and conditions of abrasive finishing of plates with complex relative movement of parts and lapping on the roughness of the treated surfaces, as well as in the development of a methodology for determining rational modes and conditions of surface treatment of thin-walled plates. Theoretical research was carried out on the basis of the main provisions of mechanical engineering technology, grinding theory, theoretical mechanics, theory of elasticity and plasticity, probability theory and mathematical statistics. Experimental studies have been carried out according to standard methods in production and laboratory conditions using certified control and measuring equipment. The obtained data were processed using computer technology and presented in the form of empirical dependencies that are convenient for practical application.&#x0D; The originality of the work consists in obtaining mathematical dependencies for calculating the kinematic parameters and parameters of the contact interaction of abrasive particles with the treated surfaces of the plates, which allow determining the rational values of the ratio of the speeds of movement of the plates and lapping.

Milling of an Aluminium Matrix Composite Using MCD-Tipped Tools with Adjusted Corner and Minor Cutting Edge Geometries

Aluminium matrix composites (AMCs) represent suitable materials for lightweight design applications. The abrasive ceramic reinforcements typically require diamond cutting materials to prevent excessive tool wear. In milling with diamond cutting materials the influence of cutting parameters was already examined to a significant extent. Investigations concerning the effect of modified tool geometries are limited and the potentials with regard to the geometrical and physical surface properties are unclear. Accordingly, experimental investigations in milling of a 10 vol.% SiC particle-reinforced aluminium wrought alloy EN AW-2017 T4 were addressed. The effect of modified corner and minor cutting edge geometries were investigated based on mono crystalline diamond (MCD)-tipped tools to benefit stable process conditions. The results indicated achievable areal roughness values in the range around 0.2μm. Especially the application of the lowest cutting edge angle and a trailing minor cutting edge led to strong fluctuations of the surface parameters. The lowest valley void volumes were achieved with an arched minor cutting edge. Generally, finish machining led to stronger compressive residual stresses compared to the state prior to machining. The strongest increase was achieved using a corner radius combined with a straight minor cutting edge. It is concluded that reduced effective radii generating the surface enable an acceptable surface structure and strong compressive residual stresses and should be addressed in further investigations.

A research on the mechanism and model of surface micro-damage in grinding hardening

Grinding hardening can obtain hardening effect besides fine machining effect on the surface of workpiece. A certain degree of surface micro-damage will be formed during grinding hardening process which mainly contains micro-crack, melting coating, decarburization, and surface scratch. In order to study the micro-damage of grinding hardening, the paper carries on a grinding hardening experiment and the characteristics of micro-damage are observed. The generation mechanism of micro-crack is revealed. It is formed by the accumulation of dislocation pile-up in the condition of grinding hardening process. When the grinding depth reaches a certain value, the surface micro-crack will be produced obviously and become more serious with the increasing of grinding depth. Other micro-damage containing surface melting coating, decarburization, and surface scratch are also studied and their relevance with micro-crack is revealed. Based on the grinding hardening theory and pile-up dislocation theory, a model for micro-crack of grinding hardening is established. The calculating result of the model accords with the experimental result in general.

Multicut technology used in WEDM machining of Mar-M247

Wire electrical discharge machining (WEDM) technology is often used for the final machining of parts to the required surface quality without further finishing operations. At the same time, WEDM has a significant advantage over other machining technologies, and in the fact, it is possible to machine all materials, regardless of their hardness or toughness, it only needs to be at least electrically conductive. Aviation nickel superalloy Mar-M247, which is usually machined to the final form by parts using WEDM, was the subject of research in this study. In order to find the optimal setting of machine parameters (Pulse on time, Pulse off time, and Discharge current) for multicut machining, an extensive design of experiment was performed with a total of 54 circles, which optimized the cutting speed in the first and second cuts and the topography of the machined surface was taken into account in the third cut. Subsequently, an analysis of the topography and morphology of the machined samples was performed, including an analysis of the condition of the subsurface layer. The study also included the analysis of the lamella in a transmission electron microscope. It was found that with the maximization of the cutting speed in the third cut, the surface topography deteriorates proportionally, but it also leads to the complete removal of all cracks formed in the first cut.

Effects of TVSR process on the dimensional stability and residual stress of 7075 aluminum alloy parts

Abstract Residual stress generated during the blank forming and machining process significantly influences the dimensional stability of the mechanical parts. The equivalent bending stiffness and thermal vibration stress relief (TVSR) are two factors that affect the deformation of thin-walled workpiece. To increase the machining accuracy, on the one hand, increase the equivalent bending stiffness in manufacturing, and on the other hand, usually conduct the stress relief process to reduce the residual stress in manufacturing. In the present study, morphology optimization and TVSR process are conducted on a thin-walled part Specimen B of 7075 aluminum alloy to control the residual stress and machining deformation before finish machining. As a contrast, Specimen A is machined in one step. The deformations vary with time of Specimen A and B are measured. The corresponding finite element model is built to further study the stress and distortion during the machining process. Results showed that (1) deformation decreased with the increase of equivalent bending stiffness, compared with Specimen A, the maximum deformation of Specimen B decreased by 58.28%. (2) The final maximum deformation of Specimen B can be reduced by 38.33% by topology reinforcement to improve the equivalent stiffness and TVSR to reduce the residual stress.

Effect of aging and finish machining on the surface integrity of selective laser melted maraging steel

Purpose The present study aims to investigate the effect of finish machining and aging processes on the surface integrity of the selective laser melted (SLM) maraging steel samples and compared them with those obtained conventionally. Design/methodology/approach Finish machining and aging were applied on the SLM and wrought maraging samples to investigate and compare their microstructural and mechanical properties such as surface roughness, microhardness and wear resistance. Findings After applying aging and finish machining treatments, the surface roughness &lt;1 µm, microhardness (542Hv) and wear resistance (COF 0.578) of SLM samples were similar to their wrought counterparts. Compared to finish machining, the effect of aging was more significant on the microhardness and the wear resistance, regardless of sample type. Originality/value The knowledge of post-processing is essential to enhance the functional performance of the SLM samples. Aging and finish machining were applied for the first time to evaluate the surface integrity of the SLM prepared maraging steel and compared it with the wrought samples.

Multi-pass adaptive tool path generation for flank milling of thin-walled workpieces based on the deflection constraints

In multi-pass flank milling of thin-walled workpieces, deflections of both the workpiece and tool caused by the cutting force jeopardize the geometrical accuracy of the machined part, which is particularly problematic when cutting hard materials, such as titanium super-alloy used for blades on jet engines, as the due cutting force will be exceedingly large. Traditionally, to mitigate the deflection, machining parameters such as feed rate and depth-of-cut are set as constants and selected extremely conservatively, thus severely prolonging the total machining time. In this paper, aiming at reducing the total machining time while refraining the deflection of both the tool and in-process workpiece, we present a new multi-pass tool path generation method for flank milling of thin-walled workpieces at semi-finish and finish machining stages. In our method, both the feed rate and depth-of-cut are allowed to vary in each pass, and they are simultaneously maximized while subject to the given limits on the deflections of both the tool and in-process workpiece as well as the kinematical limits of the machine tool itself. A practical semi-greedy algorithm is then proposed to solve the formulated global optimization problem which includes both the finite element analysis for calculating the workpiece deflection and the meshing operation. Both computer simulation and physical cutting experiments are performed to demonstrate that a substantial saving (over 20%) in total machining time could be realized by the proposed method.

High precision in-situ monitoring of electrochemical machining process using an optical fiber Fabry–Pérot interferometer sensor

This article proposes a method to monitor the machining depth during the electrochemical machining process using an optical fiber. The fiber was inserted and fixed coaxially in the center of the tool electrode with its axis perpendicular to the surface of the workpiece, and an Fabry–Pérot cavity formed between the fiber tip and the workpiece was used to monitor the machining depth. By analyzing the reflected spectrum, the inter-electrode gap was calculated. The sensing mechanism was discussed in depth, and two different methods to obtain the inter-electrode gap was introduced. One of the methods has a theoretical precision of 4.45 nm, but a time-consuming spectrum alignment process is required. Another method can use a simple program but has a lower theoretical precision of 2.16 μm, and a precision of 11.05 μm during the experiment. Several groups of experiments with still tool electrode were implemented, and the machining depth-time curve was given. By comparing the final machining depth measured by our sensor and profilometer measurement, a difference of smaller than 4% was observed. This difference may be because of the change of the refractive index of the electrolyte during the machining process. This technique significantly improves the monitoring precision, and real-time monitoring is possible. This monitoring technique may provide a further understanding of the machining process and has a potential to increase machining accuracy to micrometer or even sub-micrometer scale.

Microstructure effects on the machinability behaviour of Ti6Al4V produced by Selective Laser Melting and Electron Beam Melting process

Additive Manufacturing (AM) is gaining widespread attention over the last decade in the areas of product development and prototyping, across aerospace and medical domains. Nevertheless, the built parts are near-net shaped that usually require a machining finish to improve the surface quality and operational life.The current study aims to document the machinability behaviour of the Ti6Al4V parts fabricated by the AM process, which is based on powder bed fusion, namely, Selective Laser Melting (SLM) and Electron Beam Melting (EBM). Further, machinability parameters are correlated with the microstructure and mechanical properties of the material. Face milling operation is performed under finishing conditions to study the response on the cutting forces. The effect of Hot Isostatic Pressing (HIP) and the influence of the build direction on microstructure and machinability have been investigated for the two AM processes. The effect of crystallographic textures and microstructure morphology of α and reconstructed prior β phases on the mechanical properties was studied using shear tests. It was observed that the SLM process primarily produced homogenous and fine α lath structures with less grain boundary α (αGB) grains, leading to low shear resistance and hence generated low cutting forces. On the other hand, the EBM process produced microstructures with variable morphologies, including more grain boundary alpha (αGB) grains and widmenstatten structures which resulted in a higher shear resistance and forces. The results show a striking influence of the microstructure induced by the type of the AM process, build orientation, and the subsequent heat treatment on the shear resistance and their ability to be machined. Further, the crystallographic textures were not strong for both processes and seem not to impact the machining process. The results highlight a strong “process – property” link which demands optimization of the cutting process for the type of the AM process and the resulting microstructure.

Influence of Thermochemical Treatment on the Surface Properties of Finish Turned Wire Arc Sprayed 17Cr Steel Coatings

Structural features of thermal spray coatings, e.g., porosity, can be beneficial as oil retention volumes in tribological systems in order to improve emergency running properties. While thermal spray coatings can already have a considerable degree of porosity depending on the coating conditions, the finish machining, e.g., by turning, has a significant influence on the final surface properties. Effects like near-surface deformation and subsequent closing of pores during the machining process should be prevented. In the present study, the influence of thermochemical surface hardening on the surface topography of wire arc sprayed 17Cr steel layers after finish turning was investigated. Successful surface hardening by gas nitriding was shown by light microscopic and phase analyses. The surface properties after the various treatment steps were characterized by the surface roughness parameters Ra and Rz, the valley void volume Vvv, and the Abbott curves. A rise of the valley void volume can be beneficial in tribological applications in which a suitable oil retention volume is required. Accordingly, a thermochemical treatment combined with an appropriate subsequent finishing process is suitable to significantly influence the surface properties of thermal spray steel coatings.

Assessment of process parameters and performance enhancement through a novel suction flushing technology in RµEDM

ABSTRACT Reverse micro electro-discharge machining (RµEDM) is a promising and cost-effective technology for fabricating unconventional shaped single and arrayed micro-pins of high aspect ratio. However, dimensional inaccuracies, poor surface finish and long machining time are of great concern. An experiment-based detailed investigation of process parameters for analyzing various machining responses has been performed in this article. Taguchi’s L16 orthogonal array design of experiments has been used to frame out the experimental runs. Discharge voltage, capacitance and feed rate have been considered as process parameters whereas, material removal rate, taper root angle, surface roughness and machining time as responses for the fabrication of a single micro-pin. Additionally, the feasibility of a novel high-pressure suction flushing technology implemented for RµEDM has been demonstrated. The performance of this technology is verified for better surface quality and lesser machining time. It is observed that by using the proposed suction technology, along with the suitable parametric settings, the micromachining time significantly improved (~20%) while fabricating an arrayed micro-pins in elliptical cross-sections profile.

Effect of Cold Pressing and Aging on Reduction and Evolution of Quenched Residual Stress for Al-Zn-Mg-Cu T-Type Rib

The preparation of the Al-Zn-Mg-Cu T-type rib consisted of forging, quenching, cold pressing, aging and the final machining processes, and the evolution of residual stress played a significant role in its properties and accuracy. Numerical models were established to investigate the evolution and distribution of residual stress for the T-type rib during the quenching and cold pressing processes. The results showed that the distribution of residual stress at the stiffened area is asymmetrical, which is different from the symmetrical distribution at the smooth area. The cold pressing is beneficial for the reduction of residual stress. The stepwise cold pressing resulted in the heterogeneous distribution of residual stress at the stiffened area and the overlap region. Three comparative T-type ribs were conducted, and their residual stresses were measured using X-ray diffraction and the contour method. A stress reduction of 50% can be obtained at the surfaces of the T-type rib through cold pressing followed by the aging process. The reduction of the maximum tensile stress at the stiffened area of the T-type rib was 42% and 50% for the cold pressing and aging, respectively, which increased to 54% and 60% at the smooth area. The mechanism of the stress reduction during the cold pressing and the aging processes was discussed.

Influence of LPBF Parameters and Strategies on Fine Machining of Pre-Built Bores

Influence of LPBF Parameters and Strategies on Fine Machining of Pre-Built Bores