Subsequent Machining Process Research Articles

Wire and arc additive manufacturing for strengthening of metallic components

Wire and arc additive manufacturing (WAAM), also known as wire arc directed energy deposition (WA-DED), offers valuable capabilities not only for manufacturing but also for strengthening and repairing aging components. This paper employs the finite element (FE) method to investigate the influence of deposition parameters on the strengthening efficiency of damaged steel plates strengthened by WAAM material. The study calibrates the inherent strain method (ISM) with thermo-mechanical analysis to accurately predict residual stresses (RS) in manufactured samples, demonstrating that the ISM enhances computational efficiency while effectively predicting RS. It thoroughly examines key parameters such as the deposition direction, maximum thickness, and the geometric configuration of the WAAM material, including shapes and in-plane dimensions. The results indicate that deposition perpendicular to the loading direction provides better performance compared to deposition along the loading direction as it induces less normal and through-thickness stresses. Furthermore, this research determines the optimal maximum thickness for the WAAM material, showing that an increase in thickness can lead to higher maximum tensile stresses at the interface between the newly WAAM material and the underlying base plate. The study also establishes the optimal in-plane dimensions for the WAAM material. The results suggest placing the maximum thickness of WAAM material near the damaged area and gradually decreasing it in two directions to ensure sufficient stiffness around the cracked area, while avoiding an abrupt change in stiffness. This approach generates appropriate compressive stresses around the crack tip and decreases maximum tensile stresses in the plate. The study further illustrates that employing a proper printing strategy without a subsequent machining process can effectively reduce the maximum tensile stress in the steel plate while minimizing material usage.

Optimization Milling Force and Surface Roughness of Ti-6Al-4V Based on Ultrasonic-Assisted Milling (UAM): An Experimental Study.

This study aimed to develop a longitudinal ultrasonic-assisted milling system to investigate the machinability of titanium (Ti) Alloy Ti-6Al-4V (TC4). Aiming at reduced milling force and enhanced surface quality, ultrasonic-assisted milling was investigated taking into account the following processing parameters: spindle speed (cutting rate) n, feed per tooth fz, milling depth ap, and ultrasonic amplitude A. A comparison was made with conventional milling. The results of univariate tests demonstrated that the ultrasonic amplitude had the most significant impact on the milling force along the z-axis, resulting in a reduction of 15.48% compared with conventional milling. The range analysis results of multivariate tests demonstrated that ap and fz were the dominant factors influencing the cutting force. The minimum reduction in the milling force in ultrasonic-assisted milling along the x-, y-, and z-axes was 11.77%, 15.52%, and 17.66%, respectively, compared with that in conventional milling. The ultrasonic-assisted milling led to reduced surface roughness and enhanced surface quality; the maximum surface roughness in ultrasonic-assisted milling was 25.93%, 36.36% and 26.32% in terms of n, fz, and ap, respectively. In longitudinal ultrasonic-assisted milling, the periodic "separation-contact" was accompanied by microimpacts, resulting in even smaller intermittent periodic cutting forces. Hence, regular fish scale machining mesh was observed on the processed surface, and the workpiece surface exhibited high cleanness and smoothness. The reasonable configuration of ultrasonic-assisted milling parameters can effectively improve the milling force and surface quality of Ti alloys and accumulate reference data for the subsequent machining process research.

Localized sinking electrochemical machining of pre-shaped convex structure on revolution surface using specifically designed cathode tool

Counter-rotating electrochemical machining (CRECM) is an effective method for machining thin-walled revolving parts with complex structures. However, it is difficult to achieve a desirable uniform straight sidewall during the CRECM of isolated convex structures with variable cross-sectional profiles, so a subsequent local machining process is necessary. In this paper, a localized sinking ECM method is proposed to locally machine a pre-shaped convex structure by CRECM. A mathematical model is established to analyze the anode shaping process. In addition, a special cathode tool is designed to control the junction mark between the subsequent dissolution regions and the surrounded non-machined areas. The simulation and experimental results indicate that the sidewall profiles of the convex structure can be improved remarkably. In lateral view, convex side wall taper is reduced from 21.81° to 3.05°, In front view, convex side wall taper is reduced from 6.45° to 0.28°, Furthermore, the junction mark can be effectively controlled to within 0.07 mm.

Optimizing Processing Parameters and Surface Quality of TC18 via Ultrasonic-Assisted Milling (UAM): An Experimental Study.

This study conducted longitudinal ultrasonic-assisted milling (UAM) tests and optimized a combination of milling technological parameters to achieve high-quality machining of TC18 titanium alloy. The motion paths of the cutter under the coupled superposition states of longitudinal ultrasonic vibration and end milling were analyzed. Based on the orthogonal test, the cutting forces, cutting temperatures, residual stresses, and surface topographical patterns of TC18 specimens under different UAM conditions (cutting speeds, feeds per tooth, cutting depths, and ultrasonic vibration amplitudes) were examined. The differences between ordinary milling and UAM in terms of machining performance were compared. Using UAM, numerous characteristics (including variable cutting thickness in the cutting area, variable cutting front angles of the tool, and the lifting of the cuttings by the tool) were optimized, reducing the average cutting force in all directions, lowering the cutting temperature, increasing the surface residual compressive stress, and significantly improving the surface morphology. Finally, fish scale bionic microtextures with clear, uniform, and regular patterns were formed on the machined surface. High-frequency vibration can improve material removal convenience, thus reducing surface roughness. The introduction of longitudinal ultrasonic vibration to the end milling process can overcome the limitations of traditional processing. The optimal combination of UAM parameters for titanium alloy machining was determined through the end milling orthogonal test with compound ultrasonic vibration, which significantly improved the surface quality of TC18 workpieces. This study provides insightful reference data for subsequent machining process optimization.

Mapping of three-dimensional residual stresses by neutron diffraction in nickel-based superalloy discs prepared under different quenching conditions

Large interior residual stresses, generated during various thermomechanical treatments, could greatly affect not only the machining dimension precision during subsequent machining processes but also the structural stability under service in superalloy components. In this paper, neutron diffraction measurements have been carried out to characterize the three-dimensional residual stress distributions in IN718 superalloy discs quenched with different media, including water, oil, air and insulation. Three-dimensional residual stress maps have been derived in these specimens. It was found that, in the water-quenched, oil-quenched and air-cooled specimens, the residual stresses are compressive near the surface balanced by tension within the interior, with the peak magnitude stresses of 560 MPa, 480 MPa and 120 MPa, respectively. It was evidenced that there is no obvious residual stress in the insulation-cooled specimen. The corresponding Vickers hardness maps show a larger hardness at the core and smaller hardness near the surface in the water-quenched, oil-quenched and air-cooled specimens, whereas there is a larger hardness near the cylindrical surface and smaller hardness at the central axis in the insulation-cooled specimen, achieved by the differential cooling rate control. Our investigations show that the coordinated regulation of residual stress and microstructure and properties can be realized by reasonably selecting cooling media.

Microstructure impact on the machining of two gear steels. Part 1: Derivation of effective flow curves

A multiscale approach is presented here to investigate the effect of the ferrite-pearlite microstructure after annealing on the subsequent machining process of steel gears. The case-hardening steel 18CrNiMo7-6 and a cost efficient alternative with reduced Cr and Ni content have been studied. After detailed microstructure characterization, three different scales are defined: the nano-scale with pearlite, built of ferrite-cementite bi-lamellas, the micro-scale, which corresponds to a RVE of the ferrite/pearlite microstructure and the macro-scale. In order to derive the effective flow behaviour of pearlite, virtual uniaxial tensile and shear tests of the ferrite/cementite bi-lamella are performed at the nanoscale. The flow behaviour of the ferrite phase is described there by an extension of the Kocks-Mecking law suitable for large machining strains. Moreover, at the nanoscale, the effective flow curve of the ferrite matrix having either small MnS or NbC inclusions is determined. At the microscale, effective flow curves for both steel grades are derived from virtual tests on 3D RVE's of both steel microstructures and compared with experimental measurements.

Tool wear state prediction based on feature-based transfer learning

Accurate identification of the tool wear state during the machining process is of great significance to improve product quality and benefit. The wear states of the same tool type and machining material have similarities during the machining process. By mining the data value of the historical machining process and analyzing the similarity of the procedure, the subsequent machining process can be predicted with the help of transfer learning. Therefore, this study proposes a tool wear prediction scheme based on feature-based transfer learning to realize the accurate prediction of the tool wear state. The genetic algorithm (GA) is used to select a subset of sensor features that are highly correlated with tool wear. Then, the source domain and target domain are constructed on the basis of the selected sensor features of the historical tool and the new tool during the machining process, respectively. In addition, features in the life cycle of the new tool are completed by feature-based transfer learning. After feature transfer, the maximum mean square discrepancy (MMD) method is used to evaluate the similarity of features, and the optimal feature subset is selected according to the evaluation result. Finally, the particle swarm-optimized support vector machine (PSO-SVM) model is applied to predict the tool wear states during the new tool machining. The effectiveness of the proposed tool wear scheme is verified by the cutting force and wear data of the tool life cycle under three different milling parameter combinations. Results with high accuracy show the advantages of the feature-based transfer learning method for tool wear state prediction.

Influence of a closed-loop controlled laser metal wire deposition process of S Al 5356 on the quality of manufactured parts before and after subsequent machining

This paper describes the interdependence of additive and subtractive manufacturing processes using the production of test components made from S Al 5356. To achieve the best possible part accuracy and a preferably small wall thickness already within the additive process, a closed loop process control was developed and applied. Subsequent machining processes were nonetheless required to give the components their final shape, but the amount of material in need of removal was minimised. The effort of minimising material removal strongly depended on the initial state of the component (wall thickness, wall thickness constancy, microstructure of the material and others) which was determined by the additive process. For this reason, knowledge of the correlations between generative parameters and component properties, as well as of the interdependency between the additive process and the subsequent machining process to tune the former to the latter was essential. To ascertain this behaviour, a suitable test part was designed to perform both additive processes using laser metal wire deposition with a closed loop control of the track height and subtractive processes using external and internal longitudinal turning with varied parameters. The so manufactured test parts were then used to qualify the material deposition and turning process by criteria like shape accuracy and surface quality.

Laser Powder Bed Fusion of Precipitation-Hardened Martensitic Stainless Steels: A Review

Martensitic stainless steels are widely used in industries due to their high strength and good corrosion resistance performance. Precipitation-hardened (PH) martensitic stainless steels feature very high strength compared with other stainless steels, around 3-4 times the strength of austenitic stainless steels such as 304 and 316. However, the poor workability due to the high strength and hardness induced by precipitation hardening limits the extensive utilization of PH stainless steels as structural components of complex shapes. Laser powder bed fusion (L-PBF) is an attractive additive manufacturing technology, which not only exhibits the advantages of producing complex and precise parts with a short lead time, but also avoids or reduces the subsequent machining process. In this review, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the microstructures, are reviewed. Then, the characteristics of defects in the as-built state and the causes are specifically analyzed. Afterward, the effect of process parameters and heat treatment conditions on mechanical properties are summarized and reviewed. Finally, the remaining issues and suggestions on future research on L-PBF of martensitic precipitation-hardened stainless steels are put forward.

Milling investigations and yield strength calculations for nickel alloy Inconel 625 manufactured with laser powder bed fusion process

Additive manufacturing processes such as laser powder bed fusion (LPBF) are progressively implemented in industry due to increased flexibility and ability to produce complex geometries. However, the required dimensional and surface quality cannot be achieved even tough nearly fully dense net-shaped components are manufactured. Precision surfaces for design requirement can only be achieved with subsequent machining processes. Therefore, in this paper, milling investigations on nickel alloy Inconel 625 workpiece samples that were built using LPBF-based additive manufacturing process have been conducted. The samples were fabricated using different layer-to-layer scan strategy rotations. The side milling experiments were performed on machining of surfaces in horizontal (XY) and vertical (Z) orientations. It was observed that machining forces were influenced by the relative engagements of cutter feed direction and workpiece built directions. When milling cutter was fed against the vertical direction, lower peak forces with higher deviations were recorded. On the contrary, feeding the milling cutter along the vertical build direction resulted in higher peak forces with lower deviations. By using metal cutting principles, shear yield stress and yield strength at each milling case and relative engagements were identified. The results indicate that the yield stress is higher along the horizontal (XY) orientation and affects the milling forces and it is lower vertical (Z) build direction however, a scan strategy rotation of 90° layer-wise built provides an increase in yield strength as well as at higher cutting speeds due to strain-hardening behaviour of additively fabricated Inconel 625 material.

Preheating and thermal behaviour of a rotating cylindrical workpiece in laser-assisted machining

Laser-assisted machining is a widely used technique for preheating workpiece to reduce cutting forces and promote machinability in metal machining, thereby enhancing manufacturing quality and productivity. In setting laser-assisted machining parameters, the current practice typically relies on trial-and-error approaches. The uncertainties thereof could lead to adverse outcomes in product manufacturing, thus negating the potential benefits of this machining method. A clear understanding of workpiece thermal behaviour under laser spot heating is pivotal to developing a systematic basis for determining required preheating levels and optimised cutting variables for laser-assisted machining. In achieving this, the experimental methods are recognised to be largely impractical, if not tedious, due to instrument limitations and practicality of suitable non-intrusive measuring methods. Conversely, numerical methodologies do provide precise, flexible and cost-effective analytical options, warranting potential for insightful understanding on the transient thermal impact from laser preheating on rotating workpiece. Presenting such an investigation, this article presents a finite volume-based numerical simulation that examines and analyses the thermal response imparted by laser spot preheating on a rotating cylinder surface. On a rotating frame of reference using the ANSYS Fluent solver, the numerical model is formulated, accounting for transient heat conduction into the cylinder body and the combined convection and radiation loses from the cylinder surface. The model is comprehensively validated to ascertaining its high predictive accuracy and the applicability under reported laser-assisted machining operating conditions. The extensive parametric analyses carried out deliver clear insight into the dynamics of thermal penetration occurring within the workpiece due to laser spot preheating. This facilitates appropriate consideration of laser preheating intensity in relation to other operating variables to achieve necessary material softening depth at the workpiece surface prior to setting out on the subsequent machining process. Building upon the data generated, a practically simpler and cost-effective preheating parametric predictor is synthesised for laser-assisted machining using neural network principles incorporating the Levenberg–Marquardt algorithm. This predictive tool is trained and verified as a practical preheating guide for laser-assisted machining for a range of operating conditions.

Evaluation of Residual Stress Distribution and Relaxation on In Situ TiB₂/7050 Al Composites.

Interior residual stresses induced by quenching may cause distortion during subsequent machining processes. Hence, various strategies have been employed to relieve the interior residual stress, such as stretching, post treatment, and other techniques. In this study, the stress distribution inside TiB2/7050 Al composite extrusions was investigated and the effects of different methods on relieving the quenching-induced stress were compared. Firstly, three TiB2/7050 Al composite extrusions were treated by stretching, stretching and heat treatment, and stretching and cold treatment processes, respectively. Then, the multiple-cut contour method was employed to assess the residual stresses in the three workpieces. Experimental results indicate that the interior stress of TiB2/7050 Al composite extrusions after stretching ranges from −89 MPa to +55 MPa, which is larger than that in 7050 aluminum alloy, which ranges from −25 Pa to +25 MPa. The heat treatment performs better than the cold treatment to reduce the post-stretching residual stress, with a reduction of 23.2–46.4% compared to 11.3–40.8%, respectively. From the stress map, it is found that the stress distribution after the heat treatment is more uniform compared with that after the cold treatment.

An integrated macroscopic model for simulating SLM and milling processes

Due to their flexibility to also build up highly complex geometries, Additive Manufacturing (AM) processes are increasingly applied. Although near net-shape components can be manufactured using, for example, the Selective Laser Melting (SLM) process, the required surface quality can often not be achieved. In order to manufacture contact areas or functional surfaces, subsequent machining processes can be used to achieve the required accuracy in shape and dimension as well as the desired surface quality. In order to reduce the experimental effort during process design and optimization, simulation systems that are able to efficiently model both processes are required. In this paper, an empirical geometry-based model for SLM and milling processes will be presented. Due to the usage of an empirical model, based on the analysis of a set of reference structures, the simulation of macroscopic geometries can be achieved and used in subsequent milling simulations. Furthermore, an experimental validation of the combination of the two simulation models will be presented.

THE EFFECT OF ALTERNATIVE CUTTER PATHS ON FLATNESS DEVIATIONS IN THE FACE MILLING OF ALUMINUM PLATE PARTS

In this paper the relationships between the alternative machining paths and flatness deviations of the aluminum plate part, were presented. The flatness tolerance of the main surface of the plate part has crucial meaning due to the assembly requirement of piezoelectric elements on the radiator. The aluminum bodies under investigation are the base part of the radiators with crimped feathers for the train industry. The surface of the aluminum plate part was milled using three different milling strategies: along of longer or shorter side of workpiece and at an angle of 45°. The aluminum bodies were machined on milling centre ecoMILL 70 DMG MORI. The flatness deviation measurements were carried out on the Coordinated Measuring Machine Altera 7.5.5 Nikon Metrology NV. These measurements were made during the manufacturing process of the radiator, namely after machining, however, before the process crimping of feathers. The results that were obtained enables the validation of assumed milling path strategies in connection of the subsequent machining and assembly processes.

Numerical analysis of temperature field and structure field in horizontal continuous casting process for copper pipes

To efficiently utilize energy, refrigeration industries, including air conditioning, have put forward higher and higher requirements for the performances of copper pipes used for heat exchangers. Horizontal continuous casting of pipe blank is a key process in production of copper pipes, and optimization of its technological parameters has positive effects on improving the structure uniformity of casting blank. The stability of the performances of pipe blank also directly influences the quality of subsequent machining process. In this paper, numerical analysis was carried out for the temperature field and structure field during solidification of pipe blank in the crystallizer for horizontal continuous casting, and the steady-state sump depth and morphology in the crystallizer for continuous casting, which could be used to evaluate production safety, were obtained. Quantitative analysis was conducted for the laws of influence of different casting technological parameters, such as cooling water flow rate, withdrawal speed, and casting temperature, on the sump morphology in the crystallizer for casting blank and the final distribution of structure field in casting blank. Metallographic experiment was carried out for casting blank, and the results were compared visually with the structure field from simulation calculation, to provide measurable reference bases for further optimizing the horizontal casting technological parameters for copper pipes.

The influence of phase transformation hardening on continuous laser processing of notches for fracture splitting of a C70S6 connecting rod

The dynamic process of local material microstructure and hardness of continuous laser grooving for fracture splitting of a C70S6 connecting rod was studied. According to the phase transformation characteristics of C70S6 steel during laser processing, the coupling calculation between the transient temperature field and phase transformation process of continuous laser grooving was carried out, and then the phase transformation process and phase compositions in the heat affected zone (HAZ) was obtained. The research results showed that the HAZ was composed of martensite and pearlite as well as residual austenite after continuous laser grooving, and the generation of the martensite in the HAZ is beneficial to the subsequent splitting process; meanwhile, the hardening effect of continuous laser grooving is remarkable on the HAZ, and the requirement for the cutting tool and technique used at the subsequent machining process for the fine boring of the big end hole should be higher.

Cutting Simulations of Two Gear Steels with Microstructure Dependent Material Laws

Within this work, a multiscale approach is presented investigating the effect of the ferrite-pearlite microstructure after annealing on the subsequent machining process of a steel gear. The case-hardening steel 18CrNiMo7-6 and a cost efficient alternative with reduced Cr and Ni content have been studied. Based on an advanced microstructure characterization an effective Johnson-Cook hardening law is derived for both steel grades via homogenization and is used in subsequent orthogonal cutting simulations based on the Coupled Eulerian-Lagrange approach. Machinability predictions are validated by comparing with cutting experiments proving the adopted multiscale approach.

Hardening of Steel Perforated Tape by Nd:YAG Laser

One of the directions of application of the perforated metal material is their use as cutting elements in the production of processing tools. In this case it is necessary to carry out hardening of cutting surfaces to increase their hardness. One of the methods of hardening metals could be laser treatment. Therefore, the present work is a study of the effect of Nd:YAG laser radiation on the microstructure and hardness of fragments formed from steel perforated tape. Different laser scan speeds (doses) were used in the experiments. The results have shown that the increase the microhardness of 30-40% after the laser treatment of steel perforated tape in the surface layer in a depth range up to 1 μm take place. The studies of microstructure of fragments formed from steel perforated tape have shown the reduction of the structure size and the presence of a thin oxide compounds, which is consistent with the results on nanoindentation. Hardening of the metal by laser radiation is carried out without surface melting which eliminates the change of macroroughness and the need for subsequent machining process.

Polygonal model based cutter location data generation with offset error compensation

Purpose As manufacturing technology has developed, digital models from advanced measuring devices have been widely used in manufacturing sectors. To speed up the production cycle and reduce extra errors introduced in surface reconstruction processes, directly machining digital models in the polygonal stereolithographyformat has been considered as an effective approach in rapid digital manufacturing. In machining processes, Cutter Location (CL) data for numerical control (NC) machining is generated usually from an offset model. This model is created by offsetting each vertex of the original model along its vertex vector. However, this method has the drawback of overcut to the offset model. The purpose of this paper is to solve the overcut problem through an error compensation algorithm to the vertex offset model. Design/methodology/approach Based on the analysis of the vertex offset method and the offset model generated, the authors developed and implemented an error compensation method to correct the offset models and generated the accurate CL data for the subsequent machining process. This error compensation method is verified through three polygonal models and the tool paths generated were used for a real part machining. Findings Based on the analysis of the vertex offset method and the offset model generated, the authors developed an error compensation method to correct the offset models and generated the accurate CL data for the subsequent machining process. The developed error compensation algorithm can effectively solve the overcut drawback of the vertex offset method. Research limitations/implications The error compensation method to the vertex offset model is used for generating the CL data with the using of a ball-end cutter. Practical implications On the study of CL data generation for a STL model, most of the current studies are focused on the determination of the offset vectors of the vertexes. The offset distance is usually fixed to the radius of the cutter used. Thus, the overcut problem to the offset model is inevitable and has not been much studied. The authors propose an effective approach to compensate the insufficient distance of the offset vertex and solve the overcut problem. Social implications The directly tool paths generation from a STL model can reduce the error of surface reconstruction and speed up the machining progress. Originality/value The authors investigate the overcut problem occurred in vertex offset for CL data generation and present a new error compensation algorithm for generating the CL data that can effectively solve the overcut problem.

클라우드 기반 3D 프린팅 활용 생산 시스템 통합 연구

After the US government declared 3D printing technology a next-generation manufacturing technology, there have been many practical studies conducted to expand 3D printing technology to manufacturing technologies, called AMERICA MAKES. In particular, the Keck Center, located at the University of Texas at El Paso, has studied techniques for easily combing the 3D stacking process with space mobility and expanded these techniques to simultaneous staking techniques for multiple materials. Additionally, it developed convergence manufacturing techniques, such as direct inking techniques, in order to produce a module structure that combines electronic circuits and components, such as CUBESET. However, in these studies, it is impossible to develop a unified system using traditional independent through simple sequencing connections. This is because there are many problems in the integration between the stacking modeling of 3D printers and post-machining, such as thermal deformations, the precision accuracy of 3D printers, and independently driven coordinate problems among process systems. Therefore, in this paper, the integration method is suggested, which combines these 3D printers and subsequent machining process systems through an Internet-based cloud. Additionally, the sequential integrated system of a 3D printer, an NC milling machine, machine vision, and direct inking are realized.