Search

In this paper, both numerical and analytical method were developed for computing, in strip or plate rolling, the distribution of roll pressure, rolling force and rolling torque (from which also rolling power can be estimated), assuming an homogeneous deformation of the rolled material. Differently to other similar models present in literature, which solve the resulting rolling differential equation for the roll pressure, the model presented in this work solves the problem for the horizontal force. In this way it is possible to avoid the calculation of the derivative of material flow stress curve, which is not always analytically easy and possible (i.e. point material flow stress data). The proposed numerical model is based on the friction law proposed by Chen and Kobayashi while the analytical one is based on simple shear friction model and brings to useful analytical formulas for a quickly calculation of rolling torque and force. Moreover, a relationship between the shear friction factor and Coulomb friction coefficient in rolling was found. The developed models show good agreement with experimental measures, in terms of rolling force and torque, found in literature.

The reliability of a prosthetic implant needs durability, biocompatibility, and osseointegration capability. Accomplishing these characteristics, Ti-6Al-4V alloy is the main used material for implant fabrication. Moreover, it can be processed by additive manufacturing technique, permitting to meet the needs of patience-tailored, often complex shaped, prosthesis topologies. Once an implant is realized, it is finished by machining operations and its osseointegration capability is heavily influenced by the resulting surface roughness. Consequently, the assessment of this latter is mandatory to evaluate the prosthesis durability. This paper presents the analysis of surface roughness of Ti-6Al-4V micro-milled specimens produced by plastic deformation, selective laser melting, and electron beam melting processes. A central composite design was employed for planning the cutting tests. The comparison between surface roughness results and its values for enhancing osseointegration, firstly permitted to individuate the range of micro-milling suitable applications, which have been individuated as ball joints, bone plates, and screws. Next, the statistical analysis of the experimental measurements allowed the identification of the most influential micro-milling parameters together with the determination of the mathematical models of surface roughness by response surface methodology. The good comparison among calculated and experimental results revealed the reliability of the model, allowing the prediction of achievable surface roughness once micro-machining parameters are selected, or their optimization as a function of a desired surface roughness value.

Nowadays aerospace, microelectronics, biotechnology industries require small sized components with complex shape and high mechanical properties, often operating in aggressive environment. In this framework, Additive Manufacturing (AM) of Nickel-based superalloys is an interesting and cost effective process. Fewer design constraints and the weight reduction achievable through the topology optimization are the most relevant AM advantages. Furthermore, micro-scale features on the additively fabricated parts can be manufactured by using micro machining. Subtractive processes ensure to achieve high-precision mechanical coupling due to better surface finishes and tighter tolerances. A lack of scientific studies focusses on the material removal behavior of difficulty-to-cut alloys produced via Additive Manufacturing is evident. This work describes a machining analytical force models which considers the presence of ploughing- and shearing- dominated cutting regimes. The undefined cutting force model parameters and the Minimum Uncut Chip Thickness (MUCT) can be identified through proper experimental tests. The refinement procedure of the model was utilized to characterize Inconel 625 samples fabricated by LaserCUSINGTM. The cutting force data were elaborated with an iterative methodology based on a search algorithm. The model successfully predicted how the cutting force changes as a function of the process parameters.

In recent years, miniaturization of components has been concerned with several industrial fields including aerospace, energy, and electronics. This phenomenon resulted in increasing demand of micro-components with complex shape and high strength, often in high-temperature environment. Nickel-based superalloys such as Inconel 625 are a class of material suitable to aforementioned applications and can be successfully processed with Additive Manufacturing (AM). Moreover, micro-milling can be employed to manufacture micro-scale features on the additively fabricated parts or to achieve better surface finishes, as required for high-precision mechanical assemblies. In micro machining, it is possible to notice a lack of scientific study focusses on the material removal behavior of difficulty-to-cut alloys produced via Additive Manufacturing. This paper describes an analytical cutting force model suitable also for AM’d parts which considers the presence of ploughing- and shearing- dominated cutting regimes. A refinement procedure of the cutting force model was defined and applied by performing an experimental work on Inconel 625 samples fabricated by LaserCUSING™. A search algorithm was employed to develop an iterative methodology to determine the unknown cutting force model parameters. The model was successfully utilized to predict how the cutting force is affected as the process parameters change.

The phenomenon of tool wear strongly affects the efficiency of machining and the quality of machined products. The experimental approach to investigate tool wear requires several time consuming tests. Finite Element Methods (FEM) can be utilized to predict tool wear and tool life as function of process parameters and tool geometry. The commercial software for Finite Element Analysis (FEA) are limited by the impossibility to update the geometry of the worn tool. This research utilizes a self-released subroutine in order to modify the tool geometry in DEFORM 3D simulations by considering the volume reduction of the tool. The model was validated with experimental data obtained by drilling tests on Inconel 718 using conventional metal working fluids (MWF). The correct profile of the simulated worn tool was individuated by comparing the prediction of the simulation with the real tool geometry. The FEM simulation allowed to predict how torque changes during the tool life. In a predictive maintenance perspective, the model can be implemented to optimize the tools replacement.

This paper deals with micro mechanical machining process of 17-4 PH stainless steel samples fabricated by selective laser melting. An analysis of the material removal behaviour during micro-milling operations for the selection of the optimal feed rate value was performed on 17-4 PH additive manufactured samples studying the variation of the specific cutting force as a function of the feed per tooth. The transition from shearing to ploughing regime was analysed by considering the variation of the specific cutting forces. The minimum uncut chip thickness was calculated to identify the transition between the cutting regimes (shearing, ploughing or their combination) that affects the final product quality in terms of surface integrity and dimensional accuracy. Moreover, the surface roughness and the burr extension were analysed as a function of the feed rate.

The change from a consolidated manufacturing practice to a new solution is often a complex problem because of the operative limits of technologies and the strict constraints of industrial parts. Moreover, the new process must reflect or enhance the characteristics of the product and, overall, it must be more competitive in performances and costs. Accordingly, the development of a new process is a multilevel and multivariate problem that requires a systematic and hierarchical approach. The present paper focuses on the development of a Tube Hydroforming process capable to replace the current practice for production of T-Joint parts made of AISI 316L for the water pipes market. In particular, the problem must withstand many process and product constraints. Therefore, it was split in three steps focused on specific aspects of the process: identification of process parameters and configuration, numerical optimization of the blank tube dimensions (length and thickness), experimental tests and final improvements. In particular, two numerical methods were implemented in the optimization step: the line&ndash, search method to approach to the optimum point and Bisection method to refine the search. These approaches allowed us to identify the optimum process configuration and, in particular, the optimal dimensions of the blank tube that allows one to achieve the product requirements with the minimum cost of material.

The micro machining technology is a widespread process in several industrial sectors, such as the electronics, the moulds fabrication, the biomedical field and the horology. The main advantages of micro-milling are the low material scrap, the high accuracy and repeatability, the possibility to manufacture small size features and the respect of the geometrical and dimensional tolerances. For these reasons, micro-milling is suitable to manufacture precision components in watchmaking industry. In the high-end horology field, high geometrical precision and elevated surfaces quality are key requirements. An optimal process parameters set should be identified to comply the very strict quality standards. This paper reports the results of an optimization performed to define how to make high-quality main-plates and bridges of wristwatch movement. The dimensions, the geometry and the surface finishing of holes, pins and pockets are the optimized wristwatch features. During the optimization, cutting speed, feed rate and depth of cut were varied and measurements of geometrical errors and roughness were performed to understand how the process parameters affect the final product quality. The experimental tests were conducted on “Nickel Silver” (CuNi18Zn20) samples by using an ultraprecision 5-axis milling center located in controlled environment. The surface roughness, the burrs extension and the geometrical errors were measured by using a multifocal 3D microscope, a coordinate measuring machines and an autofocus 3D laser probe. This study allowed to manufacture a wristwatch movement in conformity with the required technical characteristics.

This paper aims to model and simulate tool wear in drilling of Inconel 718 under two different cooling conditions, using an innovative numerical procedure. Although tool wear models can be implemented in most of finite element analysis (FEA) software to calculate the tool wear rate, there is a great limit due to the inability of all these software to update the geometry of the worn tool. In order to overcome this limitation, a subroutine able to modify the tool geometry based on a given tool wear model was developed and implemented in DEFORM 3D, an implicit FEA software. Experimental tests were performed to measure tool wear in drilling using conventional metal working fluids (MWF) and liquid nitrogen (LN2) cooling. Experimental data were used to calibrate the tool wear model and to validate the drilling models. A comparison between simulated and measured results demonstrated the suitability of the developed drilling model to predict tool wear under both MWF and LN2 cooling conditions. Therefore, the developed model can be efficiently used to evaluate the influence of the cutting conditions (including cooling conditions) on tool wear, minimizing the number of expensive and time-consuming tool wear tests.

Micro milling process of CuZn37 brass is considered important due to applications in tool production for micro moulding and micro replication technology. The variations in material properties, work material adhesion to tool surfaces, burr formation, and tool wear result in loss of productivity. The deformed chip shapes together with localized temperature, plastic strain, and cutting forces during micro milling process can be predicted using finite element (FE) modeling and simulation. However, tool-workpiece engagement suffers from tool run-out affecting process performance in surface generation. This work provides experimental investigations on effects of tool run-out as well as process insight obtained from simulation of chip flow, with and without considering tool run-out. Scanning electron microscope (SEM) observation of the 3D chip shapes demonstrates ductile deformed surfaces together with localized serration behavior. FE simulations are utilized to investigate the effects of micro milling operation, cutting speed, and feed rate on forces, chip flow, and shapes. Predicted cutting forces and chip flow results from simulations are compared with force measurements, tool run-out, and chip morphology revealing reasonable agreements.

The objective of this study is to simulate tool wear in drilling of nickel-based alloys, in particular Inconel 718. When machining these kind of materials, the impact of the thermal and mechanical phenomena generated by tool wear on the surface integrity is of prime concern. For this reason, it important to study the influence of tool wear on tool life, on final part quality and on cutting force and power consumption. Tool wear is caused by several phenomena (adhesion, abrasion, erosion, diffusion, corrosion, fracture etc.) depending on selected cutting parameters (cutting velocity, feed rate, etc.). In some cases these wear mechanisms can be described by analytical models which are function of physical quantities involved in process (temperature, pressure and sliding velocity along the cutting surface). Usually, commercial FEM software allows to implement these tool wear models but without tool geometry update. To overcoming this limitation, a suitable subroutine considering tool geometry update was developed and implemented in SFTC DEFORM-3D FEA software to simulate tool wear in drilling of Inconel 718. A good agreement was obtained between the predicted and measured tool wear data.

Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are very promising materials, in particular, in the biomedical field where their unique properties of biocompatibility and wear resistance can be exploited for surgery applications, prostheses, and many other medical devices. While Additive Manufacturing is a key technology in this field, micro-milling can be used for the creation of micro-scale details on the printed parts, not obtainable with Additive Manufacturing techniques. In particular, there is a lack of scientific research in the field of the fundamental material removal mechanisms involving micro-milling of Co-Cr-Mo alloys. Therefore, this paper presents a micro-milling characterization of Co-Cr-Mo samples produced by Additive Manufacturing with the Selective Laser Melting (SLM) technique. In particular, microchannels with different depths were made in order to evaluate the material behavior, including the chip formation mechanism, in micro-milling. In addition, the resulting surface roughness (Ra and Sa) and hardness were analyzed. Finally, the cutting forces were acquired and analyzed in order to ascertain the minimum uncut chip thickness for the material. The results of the characterization studies can be used as a basis for the identification of a machining window for micro-milling of biomedical grade cobalt-chromium-molybdenum (Co-Cr-Mo) alloys.

Mechanical production greatly changed among the last decades. Nowadays, the need of higher accuracy and precision even for small details on the finished product makes micromachining a fundamental technology that can fulfill modern industry requirements. Micromilling is one of the most important and widespread microtechnology. This process is characterized by a great precision level even when high strength materials are machined. The understanding of tool deterioration and breakages causes is one of the main research challenges in micromilling field. Mechanisms that underlies these phenomena are different from those observed in conventional milling processes. The definition and the prediction of the tool-life are regulated by the ISO-8688 standard (part 1 and 2) for conventional milling process, but this standard actually is not referred to micromilling and a dedicated regulation has not been compiled yet. Therefore, this research work aims to investigate tool wear in micromilling process, in order to deepen the knowledge and better understand causes and mechanisms that lead to tool failure. Results are particularly focused on the correlation between flank wear and cutting force, and represents a base for a more complete study in this field aimed to provide fundamental knowledge for the development of a future standard that can fill the normative gap in tool-life criterion for micromilling processes.

Micromachining is a key technology in contemporary society, due to the new requirements of the modern industry. The need of higher accuracy and precision, even for details on the finished product (which may also have very small dimensions), can be fulfilled only with micromechanical machining. Among this family of technologies, micromilling is one of the most important and widespread: the potential of this process is due to the great precision level that can be obtained, when machining high strength materials too. One of the main challenges launched by micromilling concerns the understanding of the processes that generate breakages and deterioration of the tool, and the study of their causes, that are usually different from those observed in conventional milling processes, for which the definition and the prediction of the tool-life are regulated by the ISO-8688 standard (part 1 and 2). This standard is not referred to micromilling and a dedicated regulation has not been compiled yet. In this article the results of an experimental campaign, made to investigate the tool wear in micromilling process, are presented. The aim of the work is to provide fundamental knowledge for the development of a future standard that can fill the normative gap. In particular, results describe that the flank wear evolution follows the typical trend characterized by the decreasing, constant and increasing tool wear slope regions. Cutting force, roughness and tool corner radius evolution are related with tool wear. In particular, a statistical analysis based on the Pearson correlation coefficient is presented in order to quantify the correlation between the flank wear and the considered parameters. Details about the influence of feed rate and mill type in flank wear evolution are also provided. Furthermore, results show that flank wear could actually be used for a tool-life criterion in micromilling processes.

Casting metal products are characterized by undesired void defects due to the shrinkage occurring during the solidification of molten material. In order to deliver safe and sound components satisfying the customer requirements, these defects need to be reduced or if possible eliminated. Hot metal forming processes can be used for this purpose therefore, the calibration of their parameters is a fundamental task. In this paper a study of the void closure during hot rolling of 316L stainless steel slabs coming from continuous casting has been conducted. The effects of the hot rolling main parameters (i.e. percentage of reduction, cooling time, and side of reduction) on void closure index have been investigated by means of FE analysis. Data coming from experimental tests performed by Cogne Acciai Speciali S.p.a. were utilised to validate the model and the research results. A correlation between void closure indexes and the residual voids along the hot rolled slabs axis was found for AISI 316L stainless steel. Moreover, new geometric indexes depending on the rolling parameters were defined. Also in this case a correlation between these new indexes and the void closure was found.

The aim of this article is to study the influence of a Ti6Al4V microstructure on cutting forces during the micromilling process. Samples were annealed above the β-transus at three different temperatures—1020, 1050, 1080°C—and then cooled in a furnace, air, and water, in order to produce different Widmastatten microstructures. Micromilling tests were carried out on heat-treated samples, and the cutting forces were measured by means of a load cell. The results were correlated to the sample microstructures, which were thoroughly investigated by means of an optical microscope, X-ray diffraction, and microhardness measurements.The highest cutting forces were observed for soft and ductile furnace-cooled samples, suggesting that the most important factor affecting workability is the material ductility, while hardness is a less relevant parameter.

Because of the improvement of machine-tool and tool performances in micro cutting field, the interest on these processes is increasing. Therefore, researchers involved in micro manufacturing processes focused their attention on these types of processes with the aim of improving the knowledge on the phenomena occurring during micro cutting operations. The objective of this work is to develop a modelling procedure for forecasting cutting forces in micromilling considering the tool run-out and the cutting tool geometry. The designed modelling procedure combines information coming from a force model, an optimization strategy and some experimental tests. The implemented force model is based on specific cutting pressure and actual instantaneous chip section. The tool run-out and the cutting tool geometry were considered in the analytical model. The adopted optimization strategy was based on the Particles Swarm strategy due to its suitability in solving analytical non-linear models. The experimental tests consisted in realizing micro slots on a sample made of Ti6Al4V. The comparison between experimental and analytical data demonstrates the good ability of the proposed procedure in correctly defining the model parameters.

The introduction of machine tools specifically designed and industrialised for micro cutting processes, the development of high performance micro tools, and the possibility of easily realising complex shaped surfaces have increased the competitiveness and the industrial interest on these processes. Consequently, many researchers are studying the phenomena involved in the mechanics of micro cutting processes. This paper is focused on the micro drilling process for difficult to cut materials. An experimental analysis, consisting tool life tests, was performed with the aim of highlighting limits and advantages of this cutting process. Three hard-to-cut alloys, namely AISI 310H stainless steel, Hastelloy C22 and Inconel 625 nickel based alloys, were tested. By using standard micro drills, holes 500 μm diameter with two different depths were realised by utilising peck drilling strategy. The final results showed that, differently from macro scale cutting, the workability of hard-to-cut materials at micro scale is mainly affected by the material ductility rather than its hardness.

Continuous casting products contain void defects due to the shrinkage occurring during solidification. These defects, having different and irregular shapes and sizes, are located and distributed within the material depending on casting conditions. In order to deliver safe and sound products, these voids must be reduced during the subsequent hot forming processes, but it becomes very difficult when slabs are directly hot rolled without any previous forming processes (i.e., cogging), so obtaining a cheaper and more sustainable process chain. Many studies on voids closure present in literature are based on the evaluation of a process parameter called "stress triaxiality ratio". Aim of this research is to optimize the hot rolling process performed to reduce shrinkage voids of the billet due to casting. In particular, the results of a study on voids closure during hot rolling of stainless steel slabs (AISI 316L) coming from continuous casting process are reported. A FE analysis of the effects of the main process parameters of hot rolling on the "voids closure index" were investigated. Afterwards, experimental tests were performed to validate the research from an industrial point of view. A correlation between the void closure index and the final residual void percentage along the rolled slabs was found.

In recent years, innovative materials such as carbon nanotube composites are finding growing interest in several industrial sectors, from sports and leisure to electronics, automotive, aircraft, and defence. The reinforcing influence of the carbon nanotube is of prime interest. However, technological issues concerning the production methods and the manufacturing processes of carbon nanotube components limit the industrial application of this innovative and interesting material, especially whether small features are required. For this reason, manufacturing strategy involving new production technologies must be designed and developed. This paper studies the challenges of a manufacturing chain based on two manufacturing processes: injection moulding and micro milling. A case study based on these innovative processes is reported and discussed. The propagation chain effect and the influence of each considered process parameter on cutting force and geometrical accuracy of the features (the key characteristics of the process chain) were assessed by means of statistical analysis of variance (ANOVA). The ANOVA analysis demonstrated that cutting forces in micro milling are mainly influenced by the material and percentage of carbon nanotubes, while the main parameter influencing the geometrical accuracy of micro features is the matrix material.

The interest in the application of Carbon Nanotube (CNT) composites is recently increasing in several industrial sectors. The main reason for this growing attention is the reinforcing effect of the CNTs. However, the composite use is limited by technological issues concerning the manufacturing processes when small features are required. A multistage process chain could exploit the advantages of suitable processes to enhance the control of the filler orientation. This paper investigates the feasibility of milling micro features on micro injected specimens of POM/CNT and LCP/CNT composites. Design of Experiment is used to study a suitable experimental design to investigate the influence of the material and the process parameters on the machinability and the feature geometry. POM-based composites showed a better machinability and allowed a fabrication of more accurate features, while LCP showed high cutting forces and the presence of diffused burrs, preventing the fabrication of very small features.

In the last years researches on thixotropic materials have been developed in order to introduce this new technology in manufacturing processes. For instance, when considering high pressure die-casting, several applications are present in literature mainly related to low melting point alloys (Al and Mg) because of the limited die life experienced when casting higher melting materials. In this case, semi-solid metal forming allows to work at lower temperature with subsequent increase in die life and reduction in production costs, combined with lower porosity level in the casting. On the other hand, in the case of conventional forging, semi-solid processing needs higher performance materials and/or coatings for the mould because of the working temperatures; however, the advantages of obtaining near net shape part in a single step, with reduced machining and finishing costs, make the semi-solid technology competitive. The present paper deals with the thixoforging of aluminum 6061 alloy, whose semi-solid feedstock material was obtained by ultrasound treatment. The application of ultrasonic waves to liquid or solidifying alloys has been already demonstrated to be an effective technique for the obtainment of globular microstructure. Along with a refining effect, ultrasound can also produce a series of beneficial effects, such as hydrogen degassing or oxide and non-metallic inclusion removal, which all improve mechanical properties of the component. The aim of this research was to investigate the influence of process parameters on final forged part quality. The solid fraction percentage as a function of temperature was measured by differential scanning calorimetric analysis. The geometry of the die was properly designed and optimized by FEM simulation in order to be suitable for forging semi-solid material, allowing a comparison with conventional forging process. 14 K-type thermocouples were used for monitoring the temperature of top and bottom dies; an instrumented 100 ton press was also equipped with load cells to acquire the forging force. A deep metallurgical analysis of the forged parts was performed in order to evaluate their mechanical properties and quality.

This paper reports the results obtained during a research project funded by the Italian Government and involving several Italian Universities (PRIN INTEMA). The activities have been focused on side impact bar manufacturing by means of Tube Hydroforming process (THF). Punch movement paths and fluid pressure curve were optimized by means of FEM software (LS-DYNA) to guarantee tube sealing and material feeding during the tube deformation. The side impact bar geometry was optimized till reaching the shape guaranteeing the obtainment of safe parts with the best compromise in terms of final part geometry and thickness reduction. Different fluid pressure and punch movement paths were investigated. Once accomplished all the simulations and identified the best working solution, experimental tests were performed setting the process parameters according to the values defined during the simulation phase. Good agreement between FEM and experimental results were highlighted.

In cutting field, residual stress distribution analysis on the workpiece is a very interesting topic. Indeed, the residual stress distribution affects fatigue life, corrosion resistance and other functional aspects of the workpiece. Recent studies showed that the development of residual stresses is influenced by the cutting parameters, tool geometry and workpiece material. For reducing the costs of experimental tests and residual stress measurement, analytical and numerical models have been developed. The aim of these models is the possibility of forecasting the residual stress distribution into the workpiece as a function of the selected process parameters. In this work the residual stress distributions obtained simulating cutting operations using a 3D FEM software and the corresponding simulation procedure are reported. In particular, orthogonal cutting operations of AISI 1045 and AISI 316L steels were performed. The FEM results were compared with the experimental residual stress distribution in order to validate the model effectiveness.

Hard turning technique is considered an attractive alternative to traditional finish grinding operations because of the high flexibility, the capability to achieve comparable workpiece quality, the ability to achieve higher metal removal rates and to operate without the use of coolants. Nevertheless, the surface integrity effects of hard turning need to be better understood due to their influence on the life of machined components. In particular, the formation of a usually undesirable white layer at the surface, and dark layer below it, especially in presence of tool wear, need further investigation. This work deals with the experimental investigation of the effects of tool wear and cutting regime parameters (cutting speed and feed rate) in white and dark layers formation when hardened AISI 52100 bearing steel is machined. In particular, an experimental campaign has been conducted by orthogonal turning tests on disks made of AISI 52100 hardened steel using PCBN inserts. Experimental results are documented including quantification of tool wear and microstructure investigation of the machined surfaces. The results show that cutting regime parameters and, especially, tool wear affect white and dark layers formation.

The growing interest of several industrial fields (biomedical, medical, electronic, defence, aerospace, etc) on miniaturized components leads to an increased interest on micro cutting processes. When approaching these processes, phenomena that can be neglected in macro scale become predominant. For this reason material microstructure, material and geometry of the tool, machine-tool and process parameters must be correctly defined. Another aspect of interest in micro scale cutting is the definition of tests for qualifying the process performance. The present paper aims to propose a testing procedure for evaluating the performance of a micromilling process considering the machine-tool, tool-holder, tool and workpiece fixtures chain. This procedure is based on a series of micro channels realized by consecutive steps. A case of study is reported. The results allows to better understand the performances of the process and of the chain composed by the machine-tool, the tool-holder and the tool.

The interest on micro cutting processes is proved by the attention of industries on this topic. This trend moves the researches on micro cutting toward different aspects. A modelling procedure for forecasting cutting forces in microcutting, considering all phenomena involved in micro scale, can be of interest for industries allowing the evaluation of process quality. This paper deals with modelling of cutting forces in micromilling operations of channels. The proposed procedure is a combination of a force model based on specific cutting pressure and instantaneous chip section, estimated considering the tool run-out contribution, an optimisation strategy (particles swarm optimisation), and data coming from experimental tests realised on a sample of titanium alloy (Ti6Al4V). The comparisons between experimental and analytical data, and the evaluation of the uncertainty of the calibrated model show the good ability of the proposed procedure for defining analytical model for force prediction in channels micromilling.

Micromachining processes deal with the production of parts characterized by features in the micro range (i.e., with dimension lower than 1 mm). Several works are present in literature analyzing the tool behaviors, the material influence on the process, and the machine design. In fact, the downsize of the process up to the microscale needs a full review of all the knowledge coming from the meso and macro scale. As a consequence, machines suitable for micromachining processes were recently introduced in the market. Usually, these machines are classified by the classical gantry layout structure supported by a granite frame and, in order to guarantee the needed requirements of precision and accuracy in the micro scale, they are based on fluid-supported axes and active and/or passive vibration control systems. This paper proposes a new concept design: a high precision machine (HPM) based on an innovative layout exploiting a differential mechanism with three motors for two degrees of freedom using pulleys and metal belts. This new layout exhibits relevant advantages. The most significant is that all the worktable servo drives, that moves along x and y axes, are ground-fixed. This allows to isolate the working area of the machine from the servo drives. The system of pulleys and belts holding the working table slides on air bearings in order to minimize the micro vibrations induced by all the drives. A further peculiarity of the machine consists of the double z-axis each of them is motorized by a micrometer slide with linear absolute encoder. The first z-axis is equipped with a spindle for performing micro machining processes (drilling and milling). The second z-axis is equipped with a laser head for micro ablation. The servo drives of the two z-axes are controlled by the same control system of the worktable. Another important feature of the proposed layout is that the differential configuration of the xy mechanism admits the use of a constant speed signal to each control reference with no output displacements. This allows to guarantee non-inversion of motion of the servo-drives and so the avoidance of problems due to backlash and/or static friction. Drives are controlled by position and speed control loops with PID architecture, anti-windup and feed forward strategies. Controllers have been tuned by the use of a genetic algorithm applied to a dynamic model of the system. As a general consideration, the quality of the investigated micro machining processes can be improved with the designed machine structure.

The possibility of predicting the amount of the tool wear in machining processes is an interesting topic for industries, since tool wear affects surface integrity of the final parts and tool life is strictly connected with substitution policy and production costs. The definition of models able to correctly forecast the tool wear development is an important topic in the research field. For this reason in the present work, a comparison between response surface methodology (RSM) and artificial neural networks (ANNs) fitting techniques in tool wear forecasting was performed. For developing these predictive models, experimental values of tool wear, obtained by longitudinal turning operations with variable cutting parameters, were collected. Once selected, the best configuration of the two previously mentioned techniques, the resultant errors with respect to experimental data were estimated and then compared. The results showed that the developed models are able to predict the amount of wear. The comparison demonstrated that ANNs give better approximation than RSM in the prediction of the amount of the flank wear (VB) and of the crater wear (KT) depth. The obtained results are interesting not only from a scientific point of view but also for industries. In fact, it should be possible to implement the best model into a production manager software in order to correctly define the tool change during the lot production.

In these last years, the demand of shaped aluminium bottles and cans was continuously growing. The main problem is related to the fact that normally these objects have very thin thickness and a high strain-hardened material due to the deforming production steps (deep drawing and ironing). In the present paper, a study about the residual formability of cylindrical can is reported. In particular, a first characterization of the flow stress of the ironed component and the identification of the maximum deformation reachable with the hydroforming process were carried out. On the base of these preliminary results, the feasibility of hydroforming aluminium can, namely a small bottle for soft drink, has been investigated. The process is similar to tube hydroforming, even if the bottom part of the can is closed and air is used instead of liquid. The main problems to be solved were related with the possible breakages of the cylindrical body during hydroforming. The process success depends on the material characteristics, the diameter and thickness of the preformed cylindrical body, the shape, the geometry and the dimensions of the final part and the media pressure. The research aims to study the process feasibility and to prove the ability of the simulation software in forecasting the material behaviour. All the simulation phases are supported by experimental tests aiming at validating the finite element method model and to realize sound prototypes of Al soft drink bottles. In such a way, it is possible to have a reliable tool to help the designer in optimizing the process and in identifying new feasible shapes.

In the present investigation a series of orthogonal hard turning tests were conducted to study the effects of tool wear and cutting parameters (cutting speed and feed rate), on white and dark layer formation in hardened AISI 52100 bearing steel, using PCBN inserts. Experimental results were presented including quantification of tool wear and microstructure analysis of the machined surfaces. The experimental results were compared with a newly developed finite elements (FE) model that enables to capture the effect of cutting conditions and tool wear on the microstructural changes occurring at the machined surface. The results showed that cutting regime parameters and, especially, tool wear affect noticeably white and dark layers formation.

The present paper reports the results obtained investigating surface work hardening in turning as a function of cutting speed, feed rate and tool wear. An experimental campaign was carried out using AISI 304 steel as workpiece material. Pipes 4 mm thick were machined under orthogonal cutting conditions. Tools with flat rake surface were adopted and dry cutting conditions were taken into account. Cutting speed and feed rate were varied and the tool wear was monitored using a CNC visiomeasuring machine. The tool wear was related to the workpiece strain hardening. Starting from micro Vickers test data, an analytical model representing the strain hardening behavior along a workpiece section was defined. In addition, a Fortran subroutine for the simulation of strain hardening by means of a 2D FEM code was implemented.

This paper deals with Incremental Sheet Forming (ISF) a sheet metal forming process that knew a wide development in the last years. A lot of experimental and simulative researches have been conducted in this field with different aims: to study the sheet formability and part feasibility; to define models able to forecast the final sheet thickness; to understand how the sheet deforms and how formability limits can be defined. Another very important issue is related with the tool path optimization. In fact, the process is characterized by high springback which causes dimensional defects. When IF is performed by a robot, the capabilities of the technology is improved in terms of obtainable shapes (it is possible to use the 6 degrees of freedom of the robot), but the shape errors seem to be higher due to the lower robot stiffness in comparison with CNC machine. In this work the comparison between two different ISF configurations, tool mounted on a CNC machine or tool mounted on a robot, is reported. A suitable geometry was investigated working different sheet material types and sheet thicknesses. The results in terms of geometrical accuracy and sheet deformation have been analyzed in order to define advantages and disadvantages of these two techniques. An analysis on the process forces has been carried out too.

This work deals with tool wear simulation. Studying the influence of tool wear on tool life, tool substitution policy and influence on final part quality, surface integrity, cutting forces and power consumption it is important to reduce the global process costs. Adhesion, abrasion, erosion, diffusion, corrosion and fracture are some of the phenomena responsible of the tool wear depending on the selected cutting parameters: cutting velocity, feed rate, depth of cut, …. In some cases these wear mechanisms are described by analytical models as a function of process variables (temperature, pressure and sliding velocity along the cutting surface). These analytical models are suitable to be implemented in FEM codes and they can be utilized to simulate the tool wear. In the present paper a commercial 3D FEM software has been customized to simulate the tool wear during turning operations when cutting AISI 1045 carbon steel with uncoated tungsten carbide tip. The FEM software was improved by means of a suitable subroutine able to modify the tool geometry on the basis of the estimated tool wear as the simulation goes on. Since for the considered couple of tool‐workpiece material the main phenomena generating wear are the abrasive and the diffusive ones, the tool wear model implemented into the subroutine was obtained as combination between the Usui’s and the Takeyama and Murata’s models. A comparison between experimental and simulated flank tool wear curves is reported demonstrating that it is possible to simulate the tool wear development.

The present paper deals with incremental sheet forming (ISF), a metal forming process developed in the last 20 years. Main advantages characterising this technology are its high flexibility and the possibility of reducing development times and costs. ISF consists of a simple hemispherical tool, moved by a CNC machine or a robot, which locally deforms a metal sheet moving along a defined path. The desired part profile can be obtained using three ISF techniques: single point incremental forming (SPIF) and two points incremental forming (TPIF) with either negative or positive die. In this work, a part, whose geometry was chosen to be representative for sheet formability through ISF, was formed considering the different ISF techniques. Moreover, the influence on the produced part of the adopted tool path step depth increment was investigated. Experimental tests were conducted and the results were analysed in terms of forming forces, material formability, process accuracy and final part thickness.