Editorial

6 pages, 215 KiB

Open AccessEditorial

Metal Machining—Recent Advances, Applications, and Challenges

by Francisco J. G. Silva

Metals 2021, 11(4), 580; https://doi.org/10.3390/met11040580 - 02 Apr 2021

Viewed by 1825

Though new manufacturing processes that revolutionize the landscape regarding the rapid manufacture of parts have recently emerged, the machining process remains alive and up-to-date in this context, always presenting itself as a manufacturing process with several variants and allowing for high dimensional accuracy [...] Read more.

Though new manufacturing processes that revolutionize the landscape regarding the rapid manufacture of parts have recently emerged, the machining process remains alive and up-to-date in this context, always presenting itself as a manufacturing process with several variants and allowing for high dimensional accuracy and high levels of surface finish [...] Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

Research

Jump to: Editorial, Review

21 pages, 12013 KiB

Open AccessFeature PaperArticle

On the Surface Quality of CFRTP/Steel Hybrid Structures Machined by AWJM

by Fermin Bañon, Bartolome Simonet, Alejandro Sambruno, Moises Batista and Jorge Salguero

Metals 2020, 10(7), 983; https://doi.org/10.3390/met10070983 - 21 Jul 2020

Cited by 11 | Viewed by 2855

Abstract

The joining of dissimilar materials in a hybrid structure is a line of research of great interest at present. Nevertheless, the machining of materials with different machinability requires specific processes capable of minimizing defectology in both materials and achieving a correct surface finish [...] Read more.

The joining of dissimilar materials in a hybrid structure is a line of research of great interest at present. Nevertheless, the machining of materials with different machinability requires specific processes capable of minimizing defectology in both materials and achieving a correct surface finish in terms of functional performance. In this article, abrasive water jet machining of a hybrid carbon fiber-reinforced thermoplastics (CFRTP)/Steel structure and the generated surface finish are studied. A parametric study in two stacking configurations (CFRTP/Steel and Steel/CFRTP) has been established in order to determine the range of cutting parameters that generates the lowest values in terms of arithmetic mean roughness (Ra) and maximum profile height (Rz). The percentage contribution of each cutting parameter has been identified through an ANOVA analysis for each material and stacking configuration. A combination of 420 MPa hydraulic pressure with an abrasive mass flow of 385 g/min and a travel speed of 50 mm/min offers the lowest Ra and Rz values in the CFRTP/Steel configuration. The stacking order is a determining factor, obtaining a better surface quality in a CFRTP/Steel stack. Finally, a series of contour diagrams relating surface quality to machining conditions have been obtained. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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12 pages, 6893 KiB

Open AccessArticle

Assessment of Chip Breakability during Turning of Stainless Steels Based on Weight Distributions of Chips

by Hongying Du, Andrey Karasev, Thomas Björk, Simon Lövquist and Pär G. Jönsson

Metals 2020, 10(5), 675; https://doi.org/10.3390/met10050675 - 21 May 2020

Cited by 3 | Viewed by 2765

Abstract

Currently, the available evaluation methods for determining the chip breakability in the industry are mainly based on subjective visual assessment of the chip formation by an operator during machining or on chips that were collected after the tests. However, in many cases, these [...] Read more.

Currently, the available evaluation methods for determining the chip breakability in the industry are mainly based on subjective visual assessment of the chip formation by an operator during machining or on chips that were collected after the tests. However, in many cases, these methods cannot give us accurate quantitative differences for evaluation of the chip breakability of similar steel grades and similar sets of machining parameters. Thus, more sensitive methods are required to obtain more detailed information. In this study, a new method for the objective assessment of chip breakability based on quantitative determination of the weight distribution of chips (WDC) was tested and applied during machining of stainless steels without Ca treatment (316L) and with Ca treatment (316L + Ca). The obtained results show great consistencies and the reliability of this method. By using the WDC method, significant quantitative differences were obtained by the evaluation of chips, which were collected during the machining process of these two similar grades of steel at various cutting parameters, while, visually, these chips look very similar. More specifically, it was found that the Ca treatment of steel can improve the chip breakability of 316L + Ca steel in 80% of cutting trials, since a fraction of small light chips (Type I) from this steel increased and a fraction of large heavy chips (Type III) decreased accordingly. Moreover, the WDCs that were obtained at different cutting parameters were determined and compared in this study. The obtained results can be used for the optimization of chip breakability of each steel at different cutting parameters. The positive effect of Ca treatment of stainless steel was discussed in this study based on consideration of the modification of different non-metallic inclusions and their effect on the chip breakability during machining. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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17 pages, 5053 KiB

Open AccessArticle

Predicting Continuous Chip to Segmented Chip Transition in Orthogonal Cutting of C45E Steel through Damage Modeling

by Ashwin Moris Devotta, P. V. Sivaprasad, Tomas Beno and Mahdi Eynian

Metals 2020, 10(4), 519; https://doi.org/10.3390/met10040519 - 17 Apr 2020

Cited by 7 | Viewed by 2393

Abstract

Machining process modeling has been an active endeavor for more than a century and it has been reported to be able to predict industrially relevant process outcomes. Recent advances in the fundamental understanding of material behavior and material modeling aids in improving the [...] Read more.

Machining process modeling has been an active endeavor for more than a century and it has been reported to be able to predict industrially relevant process outcomes. Recent advances in the fundamental understanding of material behavior and material modeling aids in improving the sustainability of industrial machining process. In this work, the flow stress behavior of C45E steel is modeled by modifying the well-known Johnson-Cook model that incorporates the dynamic strain aging (DSA) influence. The modification is based on the Voyiadjis-Abed-Rusinek (VAR) material model approach. The modified JC model provides the possibility for the first time to include DSA influence in chip formation simulations. The transition from continuous to segmented chip for varying rake angle and feed at constant cutting velocity is predicted while using the ductile damage modeling approach with two different fracture initiation strain models (Autenrieth fracture initiation strain model and Karp fracture initiation strain model). The result shows that chip segmentation intensity and frequency is sensitive to fracture initiation strain models. The Autenrieth fracture initiation strain model can predict the transition from continuous to segmented chip qualitatively. The study shows the transition from continuous chip to segmented chip for varying feed rates and rake angles for the first time. The study highlights the need for material testing at strain, strain rate, and temperature prevalent in the machining process for the development of flow stress and fracture models. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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15 pages, 13191 KiB

Open AccessArticle

Influence of Elastomer Layers in the Quality of Aluminum Parts on Finishing Operations

by Antonio Rubio-Mateos, Asuncion Rivero, Eneko Ukar and Aitzol Lamikiz

Metals 2020, 10(2), 289; https://doi.org/10.3390/met10020289 - 22 Feb 2020

Cited by 7 | Viewed by 2555

Abstract

In finishing processes, the quality of aluminum parts is mostly influenced by static and dynamic phenomena. Different solutions have been studied toward a stable milling process attainment. However, the improvements obtained with the tuning of process parameters are limited by the system stiffness [...] Read more.

In finishing processes, the quality of aluminum parts is mostly influenced by static and dynamic phenomena. Different solutions have been studied toward a stable milling process attainment. However, the improvements obtained with the tuning of process parameters are limited by the system stiffness and external dampers devices interfere with the machining process. To deal with this challenge, this work analyzes the suitability of elastomer layers as passive damping elements directly located under the part to be machined. Thus, exploiting the sealing properties of nitrile butadiene rubber (NBR), a suitable flexible vacuum fixture is developed, enabling a proper implementation in the manufacturing process. Two different compounds are characterized under axial compression and under finishing operations. The compression tests present the effect of the feed rate and the strain accumulative effect in the fixture compressive behavior. Despite the higher strain variability of the softer rubber, different milling process parameters, such as the tool feed rate, can lead to a similar compressive behavior of the fixture regardless the elastomer hardness. On the other hand, the characterization of these flexible fixtures is completed over AA2024 floor milling of rigid parts and compared with the use of a rigid part clamping. These results show that, as the cutting speed and the feed rate increases, due to the strain evolution of the rubber, the part quality obtained tend to equalize between the flexible and the rigid clamping of the workpiece. Due to the versatility of the NBR for clamping different part geometries without new fixture redesigns, this leads to a competitive advantage of these flexible solutions against the classic rigid vacuum fixtures. Finally, a model to predict the grooving forces with a bull-nose end mill regardless of the stiffness of the part support is proposed and validated for the working range. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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25 pages, 6121 KiB

Open AccessArticle

Sustainable Milling of Ti-6Al-4V: Investigating the Effects of Milling Orientation, Cutter′s Helix Angle, and Type of Cryogenic Coolant

by Asif Iqbal, Hazwani Suhaimi, Wei Zhao, Muhammad Jamil, Malik M Nauman, Ning He and Juliana Zaini

Metals 2020, 10(2), 258; https://doi.org/10.3390/met10020258 - 17 Feb 2020

Cited by 24 | Viewed by 3450

Abstract

Ti-6Al-4V, the most commonly used alloy of titanium, possesses excellent mechanical properties and corrosion resistance, which is the prime reason for the continual rise in its industrial demand worldwide. The extraordinary mechanical properties of the alloy are viewed as a hindrance when it [...] Read more.

Ti-6Al-4V, the most commonly used alloy of titanium, possesses excellent mechanical properties and corrosion resistance, which is the prime reason for the continual rise in its industrial demand worldwide. The extraordinary mechanical properties of the alloy are viewed as a hindrance when it comes to its shaping processes, and the process of milling is no exception to it. The generation of intense heat flux around the cutting zones is an established reason of poor machinability of the alloy and unacceptably low sustainability of its machining. The work presented in this paper attempts to enhance sustainability of milling Ti-6Al-4V by investigating the effects of milling orientation, cutter’s helix angle, cutting speed, and the type of cryogenic coolant and lubricant on the sustainability measures, such as tool damage, cutting energy consumption, process cost, milling forces, and work surface roughness. It was found that micro-lubrication is more effective than the two commonly used cryogenic coolants (carbon dioxide snow and liquid nitrogen) in reducing tool wear, work surface roughness, process cost, and energy consumption. Furthermore, down-milling enormously outperformed up-milling with respect to tool wear, work surface quality, and process cost. Likewise, the high levels of cutter’s helix angle and cutting speed also proved to be beneficial for milling sustainability. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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24 pages, 5696 KiB

Open AccessArticle

Effects of Tool Edge Geometry on Chip Segmentation and Exit Burr: A Finite Element Approach

by Muhammad Asad

Metals 2019, 9(11), 1234; https://doi.org/10.3390/met9111234 - 18 Nov 2019

Cited by 13 | Viewed by 3158

Abstract

The effects of different tool edge geometries (hone and chamfer (T-land)) on quantitative measurement of end (exit) burr and chip segmentation (frequency and degree) in machining of AA2024-T351 are presented in this work. The finite element (FE) approach is adopted to perform cutting [...] Read more.

The effects of different tool edge geometries (hone and chamfer (T-land)) on quantitative measurement of end (exit) burr and chip segmentation (frequency and degree) in machining of AA2024-T351 are presented in this work. The finite element (FE) approach is adopted to perform cutting simulations for various combinations of cutting speed, feed, and tool edge geometries. Results show an increasing trend in degree of chip segmentation and end burr as hone edge tool radius or chamfer tool geometry macro parameters concerning chamfer length and chamfer angle increase. Conversely, the least effects for chip segmentation frequency have been figured out. Statistical optimization techniques, such as response surface methodology, Taguchi’s design of experiment, and analysis of variance (ANOVA), are applied to present predictive models, figure out optimum cutting parameters, and their significance and relative contributions to results of end burr and chip segmentation. Various numerical findings are successfully compared with experimental data. The ultimate goal is to help optimize tool edge design and select optimum cutting parameters for improved productivity. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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18 pages, 5738 KiB

Open AccessArticle

Parametric Analysis of Macro-Geometrical Deviations in Dry Turning of UNS A97075 (Al-Zn) Alloy

by Sergio Martín Béjar, Francisco Javier Trujillo Vilches, Carolina Bermudo Gamboa and Lorenzo Sevilla Hurtado

Metals 2019, 9(11), 1141; https://doi.org/10.3390/met9111141 - 24 Oct 2019

Cited by 8 | Viewed by 2335

Abstract

Macro-geometrical deviations play a very important role in the functionality and reliability of structural parts for aircraft. The use of environmentally friendly techniques, such as dry machining, may negatively affect these deviations. Despite its importance, there is a lack of research that analyzes [...] Read more.

Macro-geometrical deviations play a very important role in the functionality and reliability of structural parts for aircraft. The use of environmentally friendly techniques, such as dry machining, may negatively affect these deviations. Despite its importance, there is a lack of research that analyzes them as a function of the cutting parameters in the case of aluminum alloys for aeronautical purpose. In this work, the cutting speed and feed influence on several macro-geometrical deviations (parallelism, straightness, circular run-out, roundness, concentricity, total circular run-out and cylindricity) in dry turning of UNS A97075 alloy was analyzed. The main novelty of this work lies in the use of high slenderness parts used in further fatigue tests. The results showed that feed seems to be the most influential parameter in most of the deviations studied. In addition, the parts with lower rigidity exhibited higher sensitivity to change with the cutting parameters. Finally, different parametric models were proposed to obtain the geometrical deviations as a function of the cutting parameters. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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14 pages, 2697 KiB

Open AccessArticle

Sustainable High-Speed Finishing Turning of Haynes 282 Using Carbide Tools in Dry Conditions

by Antonio Díaz-Álvarez, José Díaz-Álvarez, José Luis Cantero and Henar Miguélez

Metals 2019, 9(9), 989; https://doi.org/10.3390/met9090989 - 06 Sep 2019

Cited by 9 | Viewed by 2456

Abstract

Nickel-based superalloys exhibit an exceptional combination of corrosion resistance, enhanced mechanical properties at high temperatures, and thermal stability. The mechanical behavior of nickel-based superalloys depends on the grain size and the precipitation state after aging. Haynes 282 was developed in order to improve [...] Read more.

Nickel-based superalloys exhibit an exceptional combination of corrosion resistance, enhanced mechanical properties at high temperatures, and thermal stability. The mechanical behavior of nickel-based superalloys depends on the grain size and the precipitation state after aging. Haynes 282 was developed in order to improve the creep behavior, formability, and strain-age cracking of the other commonly used nickel-based superalloys. Nevertheless, taking into account the interest of the industry in the machinability of Haynes 282 because of its great mechanical properties, which is not found in other superalloys like Inconel 718 or Waspaloy, more research on this alloy is necessary. Cutting tools suffer extreme thermomechanical loading because of the high pressure and temperature localized in the cutting zone. The consequence is material adhesion during machining and strong abrasion due to the hard carbides included in the material. The main recommendations for finishing turning in Haynes 282 include the use of carbide tools, low cutting speeds, low depth of pass, and the use of cutting fluids. However, because of the growing interest in sustainable processes and cost reduction, dry machining is considered to be one of the best techniques for material removal. During the machining of Haynes 282, at both the finishing and roughing turning, cemented carbide inserts are most commonly used and are recommended all over the industry. This paper deals with the machining of Haynes 282 by means of coated carbide tools cutting fluids (dry condition). Different cutting speeds and feeds were tested to quantify the cutting forces, quality of surface, wear progression, and end of tool life. Tool life values similar to those obtained with a lubricant under similar conditions in other studies have been obtained for the most favorable conditions in dry environments. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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11 pages, 3733 KiB

Open AccessArticle

Effects of Machining Parameters on the Quality in Machining of Aluminium Alloys Thin Plates

by Irene Del Sol, Asuncion Rivero and Antonio J. Gamez

Metals 2019, 9(9), 927; https://doi.org/10.3390/met9090927 - 24 Aug 2019

Cited by 9 | Viewed by 2745

Abstract

Nowadays, the industry looks for sustainable processes to ensure a more environmentally friendly production. For that reason, more and more aeronautical companies are replacing chemical milling in the manufacture of skin panels and thin plates components. This is a challenging operation that requires [...] Read more.

Nowadays, the industry looks for sustainable processes to ensure a more environmentally friendly production. For that reason, more and more aeronautical companies are replacing chemical milling in the manufacture of skin panels and thin plates components. This is a challenging operation that requires meeting tight dimensional tolerances and differs from a rigid body machining due to the low stiffness of the part. In order to fill the gap of literature research on this field, this work proposes an experimental study of the effect of the depth of cut, the feed rate and the cutting speed on the quality characteristics of the machined parts and on the cutting forces produced during the process. Whereas surface roughness values meet the specifications for all the machining conditions, an appropriate cutting parameters selection is likely to lead to a reduction of the final thickness deviation by up to 40% and the average cutting forces by up to a 20%, which consequently eases the clamping system and reduces machine consumption. Finally, an experimental model to control the process quality based on monitoring the machine power consumption is proposed. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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15 pages, 3343 KiB

Open AccessArticle

Feasibility Study of Hole Repair and Maintenance Operations by Dry Drilling of Magnesium Alloy UNS M11917 for Aeronautical Components

by Fernando Berzosa, Beatriz de Agustina, Eva María Rubio and J. Paulo Davim

Metals 2019, 9(7), 740; https://doi.org/10.3390/met9070740 - 30 Jun 2019

Cited by 5 | Viewed by 2532

Abstract

Magnesium alloys are increasingly used due to the reduction of weight and pollutants that can be obtained, especially in the aeronautical, aerospace, and automotive sectors. In maintenance and repair tasks, it is common to carry out re-drilling processes, which must comply with the [...] Read more.

Magnesium alloys are increasingly used due to the reduction of weight and pollutants that can be obtained, especially in the aeronautical, aerospace, and automotive sectors. In maintenance and repair tasks, it is common to carry out re-drilling processes, which must comply with the established quality requirements and be performed following the required safety and environmental standards. Currently, there is still a lack of knowledge of the machining of these alloys, especially with regards to drilling operations. The present article studies the influence of different cutting parameters on the surface quality obtained by drilling during repair and/or maintaining operations. For this propose, an experimental design was established that allows for the optimization of resources, using the average roughness (Ra) as the response variable, and it was analyzed through the analysis of variance (ANOVA). The results were within the margins of variation of the factors considered: the combination of factor levels that keep the Ra within the established margin, those that allow for the minimization of roughness, and those that allow for the reduction of machining time. In this sense, these operations were carried out in the most efficient way. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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Review

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49 pages, 17379 KiB

Open AccessReview

Characteristics and Wear Mechanisms of TiAlN-Based Coatings for Machining Applications: A Comprehensive Review

by Vitor F. C. Sousa, Francisco José Gomes Da Silva, Gustavo Filipe Pinto, Andresa Baptista and Ricardo Alexandre

Metals 2021, 11(2), 260; https://doi.org/10.3390/met11020260 - 04 Feb 2021

Cited by 70 | Viewed by 5339

Abstract

The machining process is still a very relevant process in today’s industry, being used to produce high quality parts for multiple industry sectors. The machining processes are heavily researched, with the focus on the improvement of these processes. One of these process improvements [...] Read more.

The machining process is still a very relevant process in today’s industry, being used to produce high quality parts for multiple industry sectors. The machining processes are heavily researched, with the focus on the improvement of these processes. One of these process improvements was the creation and implementation of tool coatings in various machining operations. These coatings improved overall process productivity and tool-life, with new coatings being developed for various machining applications. TiAlN coatings are still very present in today’s industry, being used due to its incredible wear behavior at high machining speeds, high mechanical properties, having a high-thermal stability and high corrosion resistance even at high machining temperatures. Novel TiAlN-based coatings doped with Ru, Mo and Ta are currently under investigation, as they show tremendous potential in terms of mechanical properties and wear behavior improvement. With the improvement of deposition technology, recent research seems to focus primarily on the study of nanolayered and nanocomposite TiAlN-based coatings, as the thinner layers improve drastically these coating’s beneficial properties for machining applications. In this review, the recent developments of TiAlN-based coatings are going to be presented, analyzed and their mechanical properties and cutting behavior for the turning and milling processes are compared. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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28 pages, 7145 KiB

Open AccessReview

Recent Advances in Turning Processes Using Coated Tools—A Comprehensive Review

by Vitor F. C. Sousa and Francisco J. G. Silva

Metals 2020, 10(2), 170; https://doi.org/10.3390/met10020170 - 23 Jan 2020

Cited by 60 | Viewed by 5720

Abstract

Turning continues to be the largest segment of the machining industry, which highlights the continued demand for turned parts and the overall improvement of the process. The turning process has seen quite an evolution, from basic lathes using solid tools, to complex CNC [...] Read more.

Turning continues to be the largest segment of the machining industry, which highlights the continued demand for turned parts and the overall improvement of the process. The turning process has seen quite an evolution, from basic lathes using solid tools, to complex CNC (Computer Numerical Control) multi-process machines, using, for the most part, coated inserts and coated tools. These coatings have proven to be a significant step in the production of high-quality parts and a higher tool life that have captivated the industry. Continuous improvement to turning coated tools has been made, with many researches focusing on the optimization of turning processes that use coated tools. In the present paper, a presentation of various recently published papers on this subject is going to be made, mentioning the various types of coatings that have recently been used in the turning process, the turning of hard to machine materials, such as titanium alloys and Inconel, as well as the interaction of these coatings with the turned surfaces, the wear patterns that these coatings suffer during the turning of materials and relating these wear mechanisms to the coated tool’s life expectancy. Some lubrication conditions present a more sustainable alternative to current methods used in the turning process; the employment of coated tool inserts under these conditions is a current popular research topic, as there is a focus on opting for more eco-friendly machining options. Full article

(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)

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