Extensive Machining Research Articles

A Review on the Machinability Enhancement of Metal Matrix Composites by Modern Machining Processes.

These days, metal matrix composites (MMCs) are being widely utilized in automotive and aerospace industries as prominent alternatives to traditional materials. Owing to their elevated strength-to-weight proportion, exceptional fracture toughness, and lightweight design, they can be used in a variety of applications. MMCs undergo extensive machining while making parts and components out of them. The machining of monolithic materials, such as metals and alloys, is a widely used and established process in different industries, such as the aerospace, bio-medical, and automotive sectors. Because of the properties of the metal matrix and the strong reinforcement, MMCs provide unique challenges. Modern machining processes have been found to be superior in overcoming challenges and achieving improved machinability of MMCs. An overview of MMC machining with modern methods is provided in this article. This article first outlines MMCs and addresses the need for and difficulties associated with their machining. Next, it reviews previous investigations on the machining of MMCs employing modern methods like electrical discharge machining, laser machining, abrasive machining, and hybrid machining. Productivity and surface integrity issues, including delamination and roughness, etc., are discussed. When presenting the review, the benefits and drawbacks of modern processes are also taken into account.

Investigation of 300M ultra-high-strength steel deposited by wire-based gas metal arc additive manufacturing

300 M ultra-high-strength steel (UHSS) is widely used to produce landing gear components for aircraft. The conventional manufacturing route for these components involves extensive machining and significant material wastage. Here, the application of wire-based gas metal arc additive manufacturing to produce 300 M UHSS parts was investigated. In particular, the influence of torch shielding atmosphere on the process stability and material performance of 300 M UHSS was investigated. The shielding gases used for comparison are pure Ar, Ar with 2.5% CO2, Ar with 8% CO2, Ar with 20% CO2, and Ar with 2% CO2 and 38% He. It was found that the arc length decreased, the transfer mode changed from spray to droplet mode, and spattering became more severe as the CO2 proportion increased. Additionally, replacing Ar with He led to a broader arc core, and a slightly shorter arc length and maintained a spray transfer, which decreased spatter. The wall surface roughness followed the trend in spatter, becoming worse with the increasing CO2 proportion, and better with He addition. Adding CO2 and He in pure Ar significantly increased the bead and wall width. The microstructure and mechanical properties exhibited a strong location dependence in the as-built state, with fresh martensite and higher strength in the top region, and tempered martensite and better ductility in the reheated bulk. Generally, torch shielding gas composition appeared to have no significant effect on the microstructure evolution. This study provides a reference for the subsequent application of gas metal arc additive manufacturing to aircraft landing gear mass production to achieve a high deposition rate and process stability simultaneously.

Comparative Life Cycle Assessment of Injection Molded and Big Area Additive Manufactured NdFeB Bonded Permanent Magnets

Abstract Permanent magnets are expected to play a crucial role in the realization of the clean economy. In particular, the neodymium–iron–boron (Nd2Fe14B or NdFeB) magnets, which have the highest energy density among rare earth permanent magnets, are needed for building more efficient windmill generators, electric vehicle motors, etc. Currently, near-net shape magnets can be either made through sintering and compression molding with extensive post machining or directly through injection molding. However, injection molding has a loading volume fraction limitation of 0.65 for nylon binders. A novel method of manufacturing bonded permanent magnets with loading fraction greater than 0.65 has been demonstrated using big area additive manufacturing (BAAM) printers. As energy density is directly proportional to the square of the magnet loading fraction, magnets produced using BAAM printers require less volume and magnetic material compared to that of injection molded magnets on average. A comparative life cycle assessment shows that this difference in magnetic powder consumption nearly constitutes the difference in the environmental impact categories. Even after assuming recycled magnetic input, the BAAM magnets perform better environmentally than injection molded magnets, especially in the ozone depletion category. Since BAAM printers can accommodate even higher loading fractions, at scale, BAAM printers possibly can bring about a significant decrease in rare earth mineral consumption and environmental emissions. Furthermore, single screw extrusion enables BAAM printers to have high print speeds and allow them to be economically competitive against injection molding. Therefore, BAAM printed magnets show great promise in transitioning towards the clean economy.

Istraživanje o obradivosti aluminijuma 7075 u suvom okruženju

Aluminum is a light and soft material that is difficult to machine. It is the most produced non-ferrous metal and undergoes extensive machining for the development of a wide range of products. Advances in industry inspire the need to find sustainable ways of machining aluminum and its alloys using conventional machining processes. In the study reported in this paper, two sets of experiments were conducted to investigate the machinability of aluminum 7075 using a plain carbide tool under a dry environment, i.e., no lubrication. In the first set, four rough experiments were conducted where three important machining parameters, i.e., cutting speed CS (115-495 RPM), depth of cut DOC (0.8-1.5 mm), and Feed rate FR (0.08-0.2 mm/rev) have been varied at two levels each to check the behavior of responses or machinability indicators, i.e., surface roughness and tool wear, at machining parameters' highest and lowest values. Based on the results of the first set of experiments, the ranges and levels of parameters have been fixed in the second set for a detailed study of the machinability of aluminum. A total of nine experiments based upon Taguchi's robust design of experiment technique with orthogonal array L9 have been conducted where an additional machining parameter, i.e., machining time MT, has been introduced. The effect of machining parameters on tool wear and surface roughness has been studied in detail, and it is found that the dry machining of aluminum is possible without the early failure of the tool. Dry machining with low values of CS, DOC, FR, and medium MT is desirable for better machinability, i.e., minimum roughness and tool wear, an optimum combination of machining parameter cutting speed-115 RPM, depth of cut-0.8 mm, feed rate-0.12 mm/rev, and machining time-90 seconds. The findings of the present work will assist engineers and researchers in attaining quality, productivity, and sustainability while manufacturing parts and components from aluminum to be used in the automotive, defense, and aerospace sectors.

ATLAS 303

Abstract Atlas 303 is a free-machining austenitic stainless steel. It is primarily used when production involves extensive machining in automatic screw machines. The sulfur addition which is responsible for the improved machining and galling characteristics of Atlas 303 lowers its corrosion resistance to below that of type 304 austenitic stainless steel. Compared with the other austenitic grades, Atlas 303 has excellent toughness, although its sulfur content reduces its toughness slightly. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as heat treating, machining, and joining. Filing Code: SS-1351. Producer or source: Atlas Steels.

Titanium alloy components fabrication by laser depositing TA15 powders on TC17 forged plate: Microstructure and mechanical properties

The manufacturing of titanium alloy components is of great significance for many industrial applications. High-performance titanium alloy parts are generally produced by a serial operation of hot forging process and extensive machining. Recently, additive manufacturing (AM) technologies such as direct laser deposition (DLD) has been developed to produce net-shape components. In this study, the parts were fabricated by depositing TA15 titanium alloy powders via DLD process on forged TC17 titanium alloy plates. Microstructure, microhardness and tensile properties of as-fabricated sample were examined. By using digital image correlation (DIC), the strain fields as well as the global strain behavior of the tensile specimen have been analyzed. The sample consists of three typical zones: the laser deposited zone (LDZ), the forged substrate zone (SZ), and the heat affected zone (HAZ) with good metallurgical bonding. Superfine basketweave microstructure forms within β grains in LDZ and HAZ because of fast cooling rate. The as-fabricated specimens have good tensile properties with an average ultimate tensile strength of 1027 MPa and average elongation of 4.57%. Non-uniform local strain concentration occurs in LDZ, while no strain concentration is found in HAZ and SZ. The remarkable non-uniformity of plastic strain is ascribed to different microstructures.

Microstructural and Mechanical Analysis of High-Performance Parts Produced by Hybrid Additive Manufacturing of Powder LMD on Forged Base Components

Ti-6Al-4V is used as a high-performance material in many industries (mainly automotive and aerospace, but also the medical industry) and traditionally produced by hot forging, with subsequent extensive post-processing and machining, leading to a material yield far from 100 % [1]. New production chains, such as additive manufacturing, enable the near net shape production of high-performance parts, however, still with long production cycles and high manufacturing costs, especially for larger parts [2]. Therefore, an efficient and feasible production is often limited to low quantities and/or small pieces. In the present study, we propose a hybrid manufacturing route, combining additive laser metal deposition (powder LMD) on hot forged base components, enhancing material efficiency, but still enabling the production of industrial quantities. Primary investigations on the microstructure and mechanical properties of the material show results similar to conventional hot forged material, but reduce the number of processing steps and increase the material yield.In more detail, the relationship between the primary beta grain size and the secondary alpha phase characteristics was investigated and moreover, related to the cooling history of the material. Furthermore, the influence of the microstructure and phase characteristics on the mechanical properties of the material was analyzed. For the determination of the primary beta grain size, the programming language MATLAB as well as its integrated open-source toolbox MTEX were used, where a GUI has been developed for the reconstruction of the primary beta grain orientations and sizes from recorded EBSD data of the secondary alpha (Ti) phase, using the Burger’s orientation relationship (BOR, [3-7]).

MUELLER BRASS ALLOY C34500

Abstract Mueller Brass Alloy C34500 is a copper-zinc-lead (leaded brass) alloy that is suitable for applications requiring extensive machining before cold-forming operations such as swaging, flaring, severe knurling, or thread rolling. Melting temperature values corrected December 2020. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance as well as forming, heat treating, machining, and joining. Filing Code: Cu-908a. Producer or source: Mueller Brass Company. original 05/20, revised 12/20.

MUELLER BRASS ALLOY C34500

Abstract Mueller Brass Alloy C34500 is a copper-zinc-lead (leaded brass) alloy that is suitable for applications requiring extensive machining before cold-forming operations such as swaging, flaring, severe knurling, or thread rolling. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on high temperature performance as well as forming, heat treating, machining, and joining. Filing Code: Cu-908. Producer or source: Mueller Brass Company.

Hybrid manufacturing of components from Ti-6Al-4V by metal forming and wire-arc additive manufacturing

Abstract The manufacturing of components from the titanium alloy Ti-6Al-4 V is of great significance for many industrial sectors. The production of high-performance Ti-6Al-4 V components typically requires multiple hot forging steps and leads to parts with tolerances that need extensive machining to create the final shape. For many applications, net-shape technologies such as additive manufacturing (AM) could enable a higher material yield. However, with the part size, cost and processing time in AM rise rapidly. Thus, the advantages of AM and forging operations could be exploited by combining both processes to new hybrid process chains. The present study investigates the use of Wire-Arc additive manufacturing (WAAM) for hybrid manufacturing of Ti-6Al-4 V aerospace components. Two process routes are investigated that combine forming and AM processes. In the first process route, a WAAM process is used to generate a pre-shaped semi-finished part. The semi-finished part will then be forged using a single forming tool to obtain the final part contour. The second process route utilizes a conventionally forged pre-form, onto which features of the final workpiece are added using WAAM. The results confirm that hybrid technologies combining WAAM and forging are very promising for Ti-6Al-4 V part production. A jet engine blade produced by WAAM and subsequent forging shows microstructures typically produced in conventional processing of Ti-6Al-4 V alloy and exhibits tensile properties, which exceed the specification level of cast and forged Ti-6Al-4 V material. Features created by WAAM on forged pre-forms are shown to reach the mechanical properties required to combine both technologies. The combination of WAAM and forging may hence be used to develop new manufacturing chains that allow for higher material yield and flexibility than conventional forging.

Numerical Analysis of Different Fixation Strategies in Direct Energy Deposition Processes

Production of components through forming requires extensive machining, high tool costs and long manufacturing times. Wire Arc Additive Manufacturing (WAAM), a direct energy deposition process, uses conventional arc welding technology to generate complex near net shape 3D parts. In Wire-Arc Additive Manufacturing (WAAM), a moving heat source melts the electrode wire and deposits the metal on the substrate. The movement of the heat source creates different heating and cooling patterns at different locations and causes distortions in the substrate and the part. This work presents a method to minimize the distortions and residual stresses of the substrate during the WAAM process. A three-dimensional finite element model has been developed using the software LS-DYNA. With numerical simulation, different fixation strategies of the substrate are compared according to the total distortion and the stresses. The results show that the fixation strategy of the substrate has a great influence on the distortion as well as the residual stress distribution. The influence of edge fixation strategy in minimizing the deformations is more than the corner fixation strategy. Among the edge fixation, the transversal edge fixation strategy has been found to have greater influence in enhancing the geometrical accuracy of the substrate by reducing the undesired stress distribution.

Influence of heat treatments on microstructure evolution and mechanical properties of Inconel 625 processed by laser powder bed fusion

This study investigated the mechanical behaviour and microstructure of as-built and heat-treated Inconel 625 (IN625) samples processed by laser powder bed fusion (LPBF). This process offers freedom in design to build complex IN625 components in order to overcome extensive machining. However, post heat treatments must be performed to obtain specific mechanical properties to match industrial requirements. For this purpose, different heat treatments were performed on IN625 samples, and through hardness measurements, three different heat treatments were selected, as optimised conditions. A direct ageing, a solutioning and a solutioning followed by ageing treatments were chosen to study the effects of these specific heat treatments on the microstructure and tensile properties, comparing them to those of as-built condition. The tensile properties of as-built and selected heat-treated IN625 samples showed superior values to minimum requirements for wrought IN625 alloys, whereas the investigation on the microstructures and fracture surfaces of as-built and heat-treated IN625 contributed to an understanding of the tensile properties evolution. The high tensile strength of as-built samples essentially derived from very fine dendritic structures mainly below 1 µm with high dislocation density and nanometric MC carbides. The high tensile properties of ageing treatments performed at 700 °C for 24 h, whether directly aged or post-solutioning, were found to be primarily dependent on γ" phases (10–30 nm) and M23C6 carbides formation. By contrast, the tensile properties of solution-treated IN625 samples at 1150 °C for 2 h showed higher ductility coupled to lower strength than other conditions, due to the grain growth.

Manufacturing of intermetallic Mn-46%Al by laser powder bed fusion

Laser powder bed fusion (LPBF) provides an excellent opportunity to use custom powders for complex objects without extensive machining. This opportunity is attractive for brittle and hard intermetallics, but is challenging due to cracking, anisotropy, and the formation of non-equilibrium phases. The present investigation is focused on a development of the process parameters for pre-alloyed Mn-46 at.%Al gas atomized intermetallic powder, which is a promising magnetic material. A hierarchical approach involving optimization of the process parameters for a single track, a single layer, and then a 3D specimen was applied. The manufacturing of single tracks was performed at scanning speeds of 0.06-3.4 m/s and laser powers of 50-350 W. Test parameters guaranteeing stable single track with constant width and height, and sufficient remelting depth were selected for further manufacturing. Surface morphology, chemical composition, crack density and distribution, and the microstructures in the final materials were investigated. It was shown that the consists mostly of the ε-phase with some amounts of equilibrium γ2 and β phases and the ferromagnetic τ-phase. The presence of the ε-phase shows a potential to use heat treatment to form τ-phase magnetic phase in AM Mn-46 at.%Al. Future investigations will clarify the applicability of LPBF to manufacture Mn-46%Al for magnetic applications.

Bayesian Learning-Based Model-Predictive Vibration Control for Thin-Walled Workpiece Machining Processes

Thin-walled flexible workpieces are known to be the most commonly used flexible elements in mechanical structures and machines in the industries of aerospace, national defense, integrated circuit production, and so on. The bottleneck of improving machining quality of thin-walled flexible workpieces lies in the workpiece deformation during machining processes. We hereby establish a machining platform for thin-walled flexible workpieces and develop a purely data-driven Sparse Bayesian learning-based method to predict the future deformation merely by using historical displacement information. Accordingly, a dual-mode predictive controller is developed to mitigate the machining vibrations, and the quality of the workpiece surface has been thus substantially improved. Finally, the superiority and effectiveness of our proposed method are demonstrated through extensive machining experiments of thin-walled flexible workpieces.

Powder bed binder jet 3D printing of Inconel 718: Densification, microstructural evolution and challenges☆

Traditional manufacturing of Inconel 718 components from castings and thermomechanical processing routes involve extensive post processing and machining to attain the desired geometry. Additive manufacturing (AM) technologies including direct energy deposition (DED), selective laser melting (SLM), electron beam melting (EBM) and binder jet 3D printing (BJ3DP) can minimize scrap generation and reduce lead times. While there is extensive literature on the use of melting and solidification based AM technologies, there has been limited research on the use of binder jet 3D printing. In this paper, a brief review on binder jet additive manufacturing of Inconel 718 is presented. In addition, existing knowledge on sintering of Inconel 718 has been extended to binder jet 3D printing. We found that supersolidus liquid phase sintering (SLPS) is necessary to achieve full densification of Inconel 718. SLPS is sensitive to the feedstock chemistry that has a strong influence on the liquid volume fraction at the processing temperature. Based on these results, we discuss an empirical framework to determine the role of powder particle size and liquid volume fraction on sintering kinetics. The role of powder packing factor and binder saturation on microstructural evolution is discussed. The current challenges in the use of BJ3DP for fabrication of Inconel 718, as well as, extension to other metal systems, are presented.

Combustion Driven Powder Compaction Green Manufacturing Enables Higher Performance Parts

Abstract Conventional manufacturing from wrought bar stock typically involves extensive machining, creates significant material waste (scrap metal), and requires numerous steps to obtain the final part geometry. As a more efficient alternative, powder metallurgical (PM) processes are now available to cost effectively fabricate both simple and complex shapes with minimal material waste. Combustion driven higher pressure powder compaction (CDC) for near-net or net shape manufacturing was recently developed. It offers a unique way of forming near-net or net shape high-density powder metal components both cost effectively and at relatively higher compaction pressures than other PM processes.

Integrated approach to robotic machining with macro/micro-actuation

A novel integrated approach to high-accuracy machining with industrial robots is presented in this paper. By combining a conventional industrial robot with an external compensation mechanism, a significantly higher bandwidth of the control of the relative position between the tool and the workpiece can be achieved. A model-based feedback controller for the compensation mechanism, as well as a mid-ranging control architecture for the combined system with the robot and the compensation mechanism are developed. The system performance is evaluated in extensive machining experiments, and the workpiece accuracies achieved are quantified and compared to the corresponding results obtained with state-of-the-art approaches to robotic machining. It is shown that the proposed approach to machining offers significantly higher accuracy, up to eight times improvement for milling in steel, where the required process forces, and thus the exhibited position deviations of the robot, are significant.

An assessment of residual stresses on 316LN SS machined plates by hole-drilling strain-gage method

Type 316LN stainless steel (SS) is used as a major structural material in the construction of fast breeder reactor (FBR) in India. For fabrication of various components from thick 316LN SS plates, extensive machining is often necessary. It is known that machining can introduce residual stresses in the components and can affect the dimensional stability of the components in service at high temperature of 550°C (823 K). For this, the effect of machining on the residual stress distribution was studied on type 316LN SS plate material. The residual stresses introduced in the plate surfaces by two different machining sequences are measured and compared with the residual stresses present in the plate before machining. The residual stresses were measured by hole-drilling strain gage method. The residual stresses in the as-received 316LN SS plate are found to be compressive in nature. However, the machined 316LN SS plates shown tensile residual stresses transverse to the machining direction and compressive residual stresses along the machining direction.

EVALUATION AND COMPARISON OF LUBRICANT PROPERTIES IN MINIMUM QUANTITY LUBRICATION MACHINING

Minimum Quantity Lubrication (MQL) machining involves the application of a minute amount of an oil-based lubricant to the machining process in an attempt to replace the conventional flood coolant system. Understanding the correlations between fluid properties and MQL performance can help in selecting lubricants from a variety of choices without going through extensive machining tests. This study compared nine different MQL fluids in terms of their physical properties, wettability, tribological properties (lubricity and extreme pressure (EP) properties), mist characteristics and machinability to determine the correlation of measured properties and MQL drilling and reaming performance. Results show that low fluid viscosity, high mist concentration, large mist droplet diameter and high wettability were best correlated with good machinability. Although it is difficult to draw strong relationships, the optimal machining in a mild cutting condition was found with the low viscosity fluids, which may also have the highest mist concentration, largest drops and best wettability.

Extraction of flank wear growth models that correlates cutting edge integrity of ball nose end mills while machining titanium

The application of titanium alloys are increasingly seen at aerospace, marine, bio-medical and precision engineering due to its high strength to weight ratio and high temperature properties. However, while machining the titanium alloys using solid carbide tools, even with jet infusion of coolant lower tool life was vividly seen. The high temperatures generated at the tool–work interface causes adhesion of work-material on the cutting edges; hence, shorter tool life was reported. To reduce the high tool–work interface temperature positive rake angle, higher primary relief and higher secondary relief were configured on the ball nose end-mill cutting edges. However, after an initial working period, the growth of flank wear facilitates higher cutting forces followed by work-material adhesion on the cutting edges. Therefore, it is important to blend the strength, sharpness and surface integrity on the cutting edges so that the ball nose end mill would demonstrate an extended tool-life. Presently, validation of tool geometry is very tedious as it requires extensive machining experiments. This paper illustrates a new feature-based ball-nose-end-mill–work interface model with correlations to the material removal mechanisms by which the tool geometry optimization becomes easier. The data are further deployed to develop a multi-sensory feature extraction/correlation model to predict the performance using wavelet analysis and Wagner Ville distribution. Conclusively, this method enables to evaluate the different ball nose end mill geometry and reduces the product development cycle time.