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The conventional manufacturing chain for technical ceramics is too expensive for the production of small series or unique parts with complex designs. Hybrid machines that combine additive and subtractive processes can be an interesting solution to overcome this technology lock-in. However, despite the great interest in hybrid machines for metallic parts, there is a lack of data in the literature when it comes to ceramics. The purpose of this paper is to contribute to closing this gap. It is the first to evaluate the achievable geometrical tolerances according to ISO 2768-2 as well as the surface textures of composite zirconia parts shaped sequentially by pellet additive manufacturing (PAM, from ceramic injection molding feedstock) and finish milling. The green parts were then debinded and sintered to analyze the influence of these steps. Compared to the initial green parts, the sintered parts exhibited shiny and smooth surfaces with sharp edges. Flatness, parallelism and perpendicularity all achieved an H (fine) class, while the surface textures were significantly improved, resulting in arithmetic roughness (Ra) below 1.6 µm. [ABSTRACT FROM AUTHOR]

Knowing the tolerance interval capabilities (TICs) of a manufacturing process is of prime interest, especially if specifications link the manufacturer to a customer. These TICs can be determined using the machine performance concept of ISO 22514. However, few works have applied this to Additive Manufacturing printers, while testing most of the printing area as recommended takes a very long time (nearly 1 month is common). This paper, by proposing a novel part design called COMPAQT (Component for Machine Performances Assessment in Quick Time), aims at giving the same level of printing area coverage, while keeping the manufacturing time below 24 h. The method was successfully tested on a material extrusion printer. It allowed the determination of potential and real machine tolerance interval capabilities. Independently of the feature size, those aligned with the X axis achieved lower TICs than those aligned with the Y axis, while the Z axis exhibited the best performance. The measurements specific to one part exhibited a systematic error centered around 0 mm ± 0.050 mm, while those involving two parts reached up to 0.314 mm of deviation. COMPAQT can be used in two applications: evaluating printer tolerance interval capabilities and tracking its long-term performance by incorporating it into batches of other parts. [ABSTRACT FROM AUTHOR]

The performance assessment of additive manufacturing (AM) printers is still a challenge since no dedicated standard exists. This paper proposes a systematic method for evaluating the dimensional and geometrical performance of such machines using the concept of machine performance. The method was applied to an Ultimaker 2+ printer producing parts with polylactic acid (PLA). The X and Y axes of the printer were the most performant and led to narrower potential and real tolerance intervals than the Z axis. The proposed systematic framework can be used to assess the performance of any material extrusion printer and its achievable tolerance intervals. [ABSTRACT FROM AUTHOR]

The innovative Green Ceramic Hybrid Machining (GCHM) process sequentially combines milling with a cutting tool (GCM, Green Ceramic Machining) and laser beam machining (GCLBM) of a ceramic material (black Y-TZP in this study) at the green stage mainly to increase productivity, avoid taper angle limitations of laser beam machining, and obtain micro-features. The study focuses on the reliability and the repeatability of the properties of sintered parts obtained by three manufacturing processes (GCM, GCLBM, GCHM) to assess the performance of hybridisation. It turns out that GCHM is a compromise of both milling and laser beam processes; it increases the repeatability of the surface quality and it slightly reduces (less than 7%) the flexural strength by comparison to milling for a similar reliability. The study also highlights that the surface quality of GCLBM processed parts relies on of the surface generated by the previous operation. Milling that surface at the previous step is therefore recommended, corresponding to the sequence adopted by GCHM. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) opens new possibilities of obtaining ceramic green parts with a tailored complex design at low cost. Meeting the requirements of highly demanding industries (aeronautical and biomedical, for example) is still challenging, even for machining. Hybrid machines can solve this problem by combining the advantages of both additive and subtractive processes. However, little information is currently available to determine the milling parameters of additively fabricated ceramic green parts. This article proposes a systematic approach to experimentally determine the cutting parameters of green AM zirconia parts. Three tools, one dedicated to thermoplastics, one to composites, and a universal tool, were tested. The tool--material couple standard (NF E 66-520-5) was followed. The lower cost and repeatable generation of smooth surfaces (Ra < 1.6 µm) without material pull-out were the main goals of the study. The universal tool showed few repeatable working points without material pull-out, while the two other tools gave satisfying results. The thermoplastic tool ensured repeatable results of Ra < 0.8 µm at a four times lower cost than the composite tool. Moreover, it exhibited a larger chip thickness range (from 0.003 mm to 0.036 mm). Nevertheless, it generated an uncut zone that must be considered when planning the milling operations. [ABSTRACT FROM AUTHOR]

The application of artificial intelligence and increasing high-speed computational performance is still not fully explored in the field of numerical modeling and simulation of machining processes. The efficiency of the numerical model to predict the observables depends on various inputs. The most important and challenging inputs are the material behavior of the work material and the friction conditions during the cutting operation. The parameters of the material model and the friction model have a decisive impact on the simulated results. To reduce the expensive experimentation cost that gives limited data for the parameters, an inverse methodology to identify the parameter values of those inputs is suggested to potentially have data of better quality. This paper introduces a novel approach for the inverse identification of model parameters by implementing the Efficient Global Optimization algorithm. In this work, a method relying on a complete automated Finite Element simulation-based optimization algorithm is implemented to inversely identify the value of the Johnson–Cook (JC) parameters and Coulomb's friction coefficient correlatively, where the objective function is defined as minimizing the error difference between experimental and numerical results. The Ti6Al4V Grade 5 alloy material is considered as a work material, and the identified parameters sets are validated by comparing the simulated results with experimental results. The developed automation process reduces the computation time and eliminating human errors. The identified model parameters value predicts the cutting force as 169 N/mm (2% deviation from experiments), feed force as 55 N/mm (7% deviation from experiments), and chip thickness as 0.150 mm (11% deviation from experiments). Overall, the identified model parameters set improves the prediction accuracy of the finite element model by 32% compared with the best-identified parameters set in the literature. [ABSTRACT FROM AUTHOR]

Although much research has been carried out in the field of the milling of GFRP (Glass Fibre Reinforced Polymer) composites, the complexity of the process is such that it is still not mastered in many industrial cases. The current work is aimed at studying the influence of three different geometries of PCD (PolyCrystalline Diamond) and cemented tungsten carbide cutting tools during the up-milling of GFRP composites at fixed cutting conditions (vc = 502 m/min and vf = 420 mm/min). Delamination, cutting forces and tool wear are compared at the fresh and worn states, and the correlation between the lifespan and the cost of the cutting tool is analysed. The main wearing phase of the tools was performed under the conditions of production in the facilities of a company (Sobelcomp, Loncin, Belgium). The results indicate that the PCD tool with the straight edge, inclined peripheral tooth shape produces the smallest total cutting force and less delamination (shortest and lowest number of delaminated fibres) at both fresh and worn states. Moreover, the grinding ability of PCD makes the cutting tool cost per part lower than for cemented carbide. The PCD tool is therefore the best option to mill GFRP parts. [ABSTRACT FROM AUTHOR]

Manufacturing of advanced ceramic parts exhibiting complex geometries is laborious and expensive. Traditionally, the machining is carried out on a so-called 'green ceramic': a compact composed of ceramic powder held with the help of a binder. This difficulty is due not only to the composition of the material, but also to the lack of methods that determine optimal machining parameters. The goal of this paper is to apply the method based on ductile material behavior to determine a feed rate working range to ensure a machining quality. Indeed, a previous study demonstrated the limits of this method in determining cutting speed. In this case, two material removal mechanisms are observed: a mechanism dominated by pulling of the material and a proper machining mechanism. This demonstrates that the specific cutting energy is a reliable indicator for machining quality assessment. In the studied case, the recommended machining parameters to ensure quality machining of Y-TZP green ceramic with a 3 mm diameter cylindrical tool are: a cutting speed of 250 m/min, a feed per tooth of 0.037 mm/tooth, an axial depth of cut of 0.7 mm, and a radial depth of cut of 3 mm. [ABSTRACT FROM AUTHOR]

The demand for inert bioceramics is always increasing in the dental field. Yttrium oxide tetragonal zirconia polycrystals (Y-TZP) are oxide ceramics which are currently used because of their interesting mechanical properties due to a toughening transformation. Industrially speaking, machining of the ceramic before sintering (green body) is very common because it allows a better productivity and it reduces crack probability during the sintering process. The goal of this paper is to determine the behavior of green ceramic during the machining operation. This study is carried out on several blanks with different binder percentages. The specific cutting energy (SCE) and the surface quality (Ra and Rz) are determined for several cutting speeds. The SCE follows a logarithmic evolution when the cutting speed increases. Despite this increase, the Ra are relatively stable whatever the cutting speed and the binder percentage. At a low cutting speed, a higher Rz value is observed caused by pullout of material. The increase of cutting speed allows to stabilize the Rz value whatever the binder percentage. This study shows that the green ceramic has a pseudo-plastic behavior whose machinability depends mainly on the interaction between the material and the cutting edge of the tool, so unlike pre-sintered ceramic or metallic part cutting speed has a low influence on the quality of the machined part. [ABSTRACT FROM AUTHOR]

The machining industry raises an ever-growing concern for the significant cost of cutting tools in the production process of mechanical parts, with a focus on the replacement policy of these inserts. While an early maintenance induces lower tool return on investment, scraps and inherent costs stemfromlate replacement. The framework of this paper is the attempt to predict the tool insertsMean Up Time, based solely on the value of a cutting parameter (the cutting speed in this particular turning application). More specifically, the use of the Cox Proportional Hazards (PH) Model for this prediction is demonstrated. The main contribution of this paper is the analytic approach that was conducted about the relevance on data transformation prior to using the Cox PH Model. It is shown that the logarithm of the cutting speed is analytically much more relevant in the prediction of the Mean Up Time through the Cox PH model than the raw cutting speed value. The paper also covers a numerical validation designed to show and discuss the benefits of this data transformation and the overall interest of the Cox PH model for the lifetime prognosis. This methodology, however, necessitates the knowledge of an analytical law linking the covariate to the Mean Up Time. It also shows how the necessary data for the numerical experiment was obtained through a gamma process simulating the degradation of cutting inserts. The results of this paper are expected to help manufacturers in the assessment of tool lifespan. [ABSTRACT FROM AUTHOR]

Dystamill is an open-source framework, available for free on the Internet, that allows its user to perform milling simulations from a model of the machine tool dynamics, a description of the cutting tool, a representation of the workpiece and a cutting force model. First developed as a program to study the stability of milling operations, the C++ code was ported into a library so that it can now be coupled with a multi-physics engine or used standalone. Restricted to 2D12 cases, achievable cutting operations include contouring, slotting and face or pocket milling since the tool only moves in a plane perpendicular to its revolution axis. Dystamill permits computing the machining forces applied on the tool and generating the geometry of the machined workpiece. Achieving dynamic simulations in a row for various cutting conditions enables determining the chatter stability lobes needed to choose optimal cutting parameters. The C++ library is composed of 12 modules interacting with each other to model the milling studied case, involving namely a modelling of the tool and the machined surface, a cutting force model and a representation of the system dynamics through a modal model. It is completed with a GUI that generates an input file for Dystamill while the post process of the results can be carried out by Matlab™. Born from a Ph.D. thesis, Dystamill was tested and validated on numerous test cases from the literature and real experiments. This paper is an opportunity to shed light on the functions and algorithms of Dystamill. In the hope that it will be useful for users, this document presents the Dystamill library, namely its modules are described from a technical point of view. An early example is built up and validated through real measurements. Finally, the capabilities of Dystamill are illustrated by comprehensive examples leading to the chatter stability lobes. [ABSTRACT FROM AUTHOR]

This paper is concerned with the extension of the minimal coordinates approach to flexible bodies. When using minimal coordinates, the number of configuration parameters corresponds exactly to the number of degrees of freedom and they can be chosen arbitrarily as far as there is a one-to-one relationship between the configuration of the system and the configuration parameters. In the rigid case, the equations of motion are obtained from the description of the translational and rotational motion of a frame attached to each body in terms of the chosen configuration parameters, and from the forces acting on each body. The extension to the simulation of flexible bodies naturally leads to a description of the motion of a flexible body from the one of its nodes. However, the relationship between the latter and the full internal motion of the body is not unique and is the subject of various developments. It was then proposed for the sake of generality to systematically treat flexible bodies as superelements, implemented according to the corotational approach, with a floating corotational frame. This allows to model any flexible body from its mass and stiffness matrices obtained from any available finite element code. Moreover, it doesn’t impose any restriction on the kinematics of the nodes which can then be expressed indifferently from absolute or relative coordinates as usually encountered with minimal coordinates. After a description of the adopted framework, the paper develops the equations of motion. Some test examples are presented, where the proposed approach will be compared to the ones obtained with the classical body reference frame approach and results from the literature. In some cases, the influence of the chosen corotational frame is analysed. The examples confirm that the corotational formulation should be restricted to flexible bodies involving only small deformations and rotational velocity. It is also shown that modelling can be adapted to improve the quality of the results. [ABSTRACT FROM AUTHOR]

Simulation of manufacturing processes also called virtual manufacturing plays a key role for the optimisation of productivity. Among all the manufacturing processes, machining operations are often unavoidable because most of the mechanical parts need to be machined during their production cycle, at least for finishing operations. The development of machining simulation is still challenging due to large strains, strain rates and temperatures needing complex material flow stress laws for example. In order to model industrially relevant situations, macroscopic approaches are often used to keep a reasonable simulation time. The simulation of milling operations at a macroscopic level combines a mechanistic model of the cutting forces, a numerical model of the dynamic response of the machine tool and a geometric model predicting the shape of the machined part. A numerical integration procedure is used to obtain the time history of the forces and the vibrations occurring during machining. This paper presents two different approaches for the consideration of the cutting force into the integration procedure and discusses the time step selection used to perform this numerical integration. By taking the evolution of the cutting force into account through a single integration step, it is possible to increase the time step. For a given precision, it is possible to reduce the computation time by a factor up to ten using this approach. [ABSTRACT FROM AUTHOR]

Simulation of manufacturing processes (also called virtual manufacturing) is an important research topic in order to optimize the added value of the manufacturing chain. The mastering of these techniques allows companies to remain competitive on the market. Machining operations are very complex to simulate numerically due to the severe conditions undergone by the material (high strain, very high strain rates, high temperature,...). In addition, the rising need of micro-manufacturing techniques creates new challenges in numerical simulation. Indeed, some physical phenomena neglected for traditional machining simulation need to be taken into account for accurate simulation when the feedrate is fairly low (size effect, minimum chip thickness, material heterogeneity,...). New developments are thus needed to unlock the full benefits of these techniques. The aim of this paper is to enhance the classical mechanistic cutting force model for milling operations with small diameter tool by considering the effect of the heterogeneity of the material. The variability of the response during a test on fixed conditions (cutting tool, machined material and cutting parameters) is taken into account to develop a model whose parameters can evolve during a given operation. The statistical dispersion of cutting forces observed during experimental test is measured and modeled as a random perturbation of the force. The effects of this perturbation on the stability of milling operations are then demonstrated by means of numerical simulation. [ABSTRACT FROM AUTHOR]

Purpose ? The purpose of this paper is to highlight the need for degradation data in order to improve the reliability and the mean residual life estimation of a specific item of equipment and to adapt the preventive maintenance tasks accordingly. Design/methodology/approach ? An initial reliability model which uses a degradation-based reliability model that is built from the collection of hitting times of a failure threshold. The proposed maintenance model is based on the cost/availability criterion. The estimation of both reliability and optimum time for preventive maintenance are updated with all new degradation data that are collected during operating time. Findings ? An improvement for the occurrences of maintenance tasks which minimizes the mean cost per unit of time and increases the availability. Practical implications ? Inspection tasks to measure the degradation level should be realized at least one time for each item of equipment at a specific time determined by the proposed methodology. Originality/value ? The introduction of a criterion which helps the maintainer to decide to postpone or not the preventive replacement time depending on the measured degradation level of a specific item of equipment. [ABSTRACT FROM AUTHOR]

The simulation of the cutting process becomes a key aspect on production optimization. The search for optimal cutting parameters by simulation can be a very effective way of reducing the tuning time of the process and can demonstrate potential cost reduction. As the simulation of the microscopic behavior of the cut is still difficult to perform, most of the prediction techniques are based on mechanistic models of the cutting forces, whose parameters are deduced from experimental tests. The runout of the tool can be a parasite effect that lowers the precision of the identification of the cutting forces parameters. This paper shows the improvement of an identification algorithm given by the modeling of radial runout effect on the undeformed chip thickness. Two different models of cutter runout have been used and tested on experimental measurement performed on a static dynamometer. The adequacy between simulation and experiment is good and allows reliable prediction of cutting forces for different cutting conditions. [ABSTRACT FROM AUTHOR]