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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.

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.

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.

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.

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.

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.

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.

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.

Tube hydroforming process is a forming technique that consists of tubular workpiece deformation by means of hydraulic pressure and punches which guarantee the tube end feeding and sealing. In the last years, this technique found a large and rapid development thanks to its many advantages with respect to conventional processes: parts weight reduction, tighter dimensional tolerances, lower tool and die costs, less secondary operations. Besides, many lacks in the process knowledge still represent an obstacle and they are usually bypassed by trial and error methods. Therefore, lot of studies have been conducted to better understand the influence of the process parameters, such as pressure path, punch stroke or material behaviour on the process feasibility. In this paper a finite element model, validated by means of experimental tests conducted on a self designed hydroforming machine, was used for forecasting initiation and growth of defects in T-joints hydroforming. The conducted finite element analysis allowed to identify the aspects of the process which cause defects in tube hydroforming of T-joints. In this manner performance indicators to be used for developing a process optimising strategy were identified.

Technological progress has led to increased demand for small components with tiny features, which cannot be achieved through conventional machining. Industrial application of processes based on microcutting is limited by some issues concerning the geometrical scale. The process performance is significantly affected by milling machine, tool holder, tool, workpiece material microstructure, workpiece fixtures, and process parameters. At present, an ultimate micromachining assessment procedure is not available. This study aims to propose and conduct an experiment on a testing procedure for micromilling. The set up to be implemented and the output to be considered are defined and described. Three major stages are identified: estimation of the effective bandwidth of the load cell–tool holder system, the milling machine natural frequency measurement, and micromilling test execution. The entire procedure is performed, and its robustness is demonstrated. Keywords: Micromilling, Machine tool performance test, Tool run-out, Force analysis, Modal analysis