Evaluation of tools and cutting conditions on carbon fibre reinforced laminates

The distinctive characteristics of carbon fibre reinforced plastics, like low weight or high specific strength, had broadened their use to new fields. Due to the need of assembly to structures, machining operations like drilling are frequent. In result of composites inhomogeneity, this operation can lead to different damages that reduce mechanical strength of the parts in the connection area. From these damages, delamination is the most severe. A proper choice of tool and cutting parameters can reduce delamination substantially. In this work the results obtained with five different tool geometries are compared. Conclusions show that the choice of an adequate drill can reduce thrust forces, thus delamination damage.

Influence of Cutting Conditions on Tool Life, Tool Wear and Surface Finish in the Face Milling Process

The main goal of this work is to study the influence of cutting conditions - cutting speed, feed velocity and feed per tooth - on tool life and surface finish of the workpiece in the face milling of flat surfaces. Aiming to achieve this goal, several milling experiments were carried out with different cutting speeds, feed velocities and feeds per tooth. In the first phase of the experiments, cutting speed was varied without varying feed velocity, which caused a variation in feed per tooth. In the second phase of the experiments, cutting speed and feed velocity were varied in such a way that feed per tooth was kept constant. Tool flank wear and surface roughness of the workpiece were measured as cutting time elapsed. The main conclusions of this work are that a) cutting speed has a strong influence on tool life, regardless of whether feed velocity or feed per tooth varies and b) an increase in surface roughness of the workpiece is not closely related to an increase in wear of the primary cutting edge.

Modelling Cutting States in Rough Turning of 34CrNiMo6 Steel

Rough turning is an important form of manufacturing cylinder-symmetric parts. Thus far, increasing the level of automation in rough turning has included process monitoring methods or adaptive turning control methods that aim to keep the process conditions constant. However, in order to improve process safety, quality and efficiency, an adaptive turning control should be transformed into an intelligent machining system optimizing cutting values to match process conditions or to actively seek to improve process conditions. In this study, primary and secondary chatter and chip formation are studied to understand how to measure the effect of these phenomena to the process conditions and how to avoid undesired cutting conditions. The concept of cutting state is used to address the combination of these phenomena and the current use of the power capacity of the lathe. The measures to the phenomena are not developed based on physical measures, but instead, the severity of the measures is modelled against expert opinion. Based on the concept of cutting state, an expert system style fuzzy control system capable of optimizing the cutting process was created. Important aspects of the system include the capability to adapt to several cutting phenomena appearing at once, even if the said phenomena would potentially require conflicting control action.

Microstructural, Mechanical and Tribological Characterisation of CVD and PVD Coatings for Metal Cutting Applications

The present thesis focuses on characterisation of microstructure and the resulting mechanical and tribological properties of CVD and PVD coatings used in metal cutting applications. These thin and hard coatings are designed to improve the tribological performance of cutting tools which in metal cutting operations may result in improved cutting performance, lower energy consumption, lower production costs and lower impact on the environment.  In order to increase the understanding of the tribological behaviour of the coating systems a number of friction and wear tests have been performed and evaluated by post-test microscopy and surface analysis. Much of the work has focused on coating cohesive and adhesive strength, surface fatigue resistance, abrasive wear resistance and friction and wear behaviour under sliding contact and metal cutting conditions. The results show that the CVD deposition of accurate crystallographic phases, e.g. α-Al2O3 rather than κ-Al2O3, textures and multilayer structures can increase the wear resistance of Al2O3. However, the characteristics of the interfaces, e.g. topography as well as interfacial porosity, have a strong impact on coating adhesion and consequently on the resulting properties.  Through the deposition of well designed bonding and template layer structures the above problems may be eliminated. Also, the presence of macro-particles in PVD coatings may have a significant impact on the interfacial adhesive strength, increasing the tendency to coating spalling and lowering the surface fatigue resistance, as well as increasing the friction in sliding contacts. Finally, the CVD-Al2O3 coating topography influences the contact conditions in sliding as well as in metal cutting. In summary, the work illuminates the importance of understanding the relationships between deposition process parameters, composition and microstructure, resulting properties and tribological performance of CVD and PVD coatings and how this knowledge can be used to develop the coating materials of tomorrow.

Study of cutting forces on machinability properties of gray cast iron using new ceramics cutting tools

During gray cast iron cutting, the great rate of mechanical energy from cutting forces is converted into heat. Considerable heat is generated, principally in three areas: the shear zone, rake face and at the clearance side of the cutting edge. Excessive heat will cause undesirable high temperature in the tool which leads to softening of the tool and its accelerated wear and breakage. Nowadays the advanced ceramics are widely used in cutting tools. In this paper a composition special of Si3N4 was sintering, characterized, cut and ground to make SNGN120408 and applyed in machining gray cast iron with hardness equal 205 HB in dry cutting conditions by using digital controlled computer lathe. The tool performance was analysed in function of cutting forces, flank wear, temperature and roughness. Therefore metal removing process is carried out for three different cutting speeds (300 m/min, 600 m/min, and 800 m/min), while a cutting depth of 1 mm and a feed rate of 0.33 mm/rev are kept constant. As a result of the experiments, the lowest main cutting force, which depends on cutting speed, is obtained as 264 N at 600 m/min while the highest main cutting force is recorded as 294 N at 300 m/min.

Cutting performance of diamond coated Si3N4 tool during turning

Silicon nitride cutting tools have been used successfully for machining hard materials, like: cast irons, nickel based alloys, etc. However these cutting tools with diamond coating present little information on dry turning operations of gray cast iron. In the present work, Si3N4 square inserts was developed, characterized and subsequently coated with diamond for dry machining operations on gray cast iron. All experiments were conducted with replica. It was used a 1500, 3000, 4500 m cutting length, feed rate of 0.33 mm/rev and keeping the depth of cut constant and equal to 1 mm. The results show that wear in the tool tips of the Si3N4 inserts, in all cutting conditions, was caused by both mechanical and chemical processes. To understand the tool wear mechanisms, a morphological analysis of the inserts, after experiments, has been performed by SEM and optical microscopy. Diamond coated PVD inserts showed to be capable to reach large cutting lengths when machining gray cast iron. © (2010) Trans Tech Publications.

The cutting performance of sialon ceramic tools

The thesis deals with a research programme in which the cutting performance of a new generation of ceramic cutting tool material is evaluated using the turning process. In part one, the performance of commercial Kyon 2000 sialon ceramic inserts is studied when machining a hardened alloy steel under a wide range of cutting conditions. The aim is to formulate a pattern of machining behaviour in which tool wear is related to a theoretical interpretation of the temperatures and stresses generated by the chip-tool interaction. The work involves a correlation of wear measurement and metallographic examination of the wear area with the measurable cutting data. Four main tool failure modes are recognised: (a) flank and crater wear (b) grooving wear (c) deformation wear and (d) brittle failure Results indicate catastrophic edge breakdown under certain conditions. Accordingly in part two, the edge geometry is modified to give a double rake tool; a negative/positive combination. The results are reported for a range of workpiece materials under orthogonal cutting conditions. Significant improvements in the cutting performance are achieved. The improvements are explained by a study of process parameters; cutting forces, chip thickness ratio, chip contact length, temperature distribution, stress distribution and chip formation. In part three, improvements in tool performance are shown to arise when the edge chamfer on a single rake tool is modified. Under optimum edge chamfer conditions a substantial increase in tool life is obtained compared with the commercial cutting geometry.

Modelling the dynamics of cutting during turning

This thesis presents an approach to cutting dynamics during turning based upon the mechanism of deformation of work material around the tool nose known as "ploughing". Starting from the shearing process in the cutting zone and accounting for "ploughing", new mathematical models relating turning force components to cutting conditions, tool geometry and tool vibration are developed. These models are developed separately for steady state and for oscillatory turning with new and worn tools. Experimental results are used to determine mathematical functions expressing the parameters introduced by the steady state model in the case of a new tool. The form of these functions are of general validity though their coefficients are dependent on work and tool materials. Good agreement is achieved between experimental and predicted forces. The model is extended on one hand to include different work material by introducing a hardness factor. The model provides good predictions when predicted forces are compared to present and published experimental results. On the other hand, the extension of the ploughing model to taming with a worn edge showed the ability of the model in predicting machining forces during steady state turning with the worn flank of the tool. In the development of the dynamic models, the dynamic turning force equations define the cutting process as being a system for which vibration of the tool tip in the feed direction is the input and measured forces are the output The model takes into account the shear plane oscillation and the cutting configuration variation in response to tool motion. Theoretical expressions of the turning forces are obtained for new and worn cutting edges. The dynamic analysis revealed the interaction between the cutting mechanism and the machine tool structure. The effect of the machine tool and tool post is accounted for by using experimental data of the transfer function of the tool post system. Steady state coefficients are corrected to include the changes in the cutting configuration with tool vibration and are used in the dynamic model. A series of oscillatory cutting tests at various conditions and various tool flank wear levels are carried out and experimental results are compared with model—predicted forces. Good agreement between predictions and experiments were achieved over a wide range of cutting conditions. This research bridges the gap between the analysis of vibration and turning forces in turning. It offers an explicit expression of the dynamic turning force generated during machining and highlights the relationships between tool wear, tool vibration and turning force. Spectral analysis of tool acceleration and turning force components led to define an "Inertance Power Ratio" as a flank wear monitoring factor. A formulation of an on—line flank wear monitoring methodology is presented and shows how the results of the present model can be applied to practical in—process tool wear monitoring in • turning operations.

Tool cutting force modeling and wear estimation of micro -end-milling operations

The applications of micro-end-milling operations have increased recently. A Micro-End-Milling Operation Guide and Research Tool (MOGART) package has been developed for the study and monitoring of micro-end-milling operations. It includes an analytical cutting force model, neural network based data mapping and forecasting processes, and genetic algorithms based optimization routines. MOGART uses neural networks to estimate tool machinability and forecast tool wear from the experimental cutting force data, and genetic algorithms with the analytical model to monitor tool wear, breakage, run-out, cutting conditions from the cutting force profiles. ^ The performance of MOGART has been tested on the experimental data of over 800 experimental cases and very good agreement has been observed between the theoretical and experimental results. The MOGART package has been applied to the micro-end-milling operation study of Engineering Prototype Center of Radio Technology Division of Motorola Inc. ^

Tool cutting force modeling and wear estimation of micro-end-milling operations

The applications of micro-end-milling operations have increased recently. A Micro-End-Milling Operation Guide and Research Tool (MOGART) package has been developed for the study and monitoring of micro-end-milling operations. It includes an analytical cutting force model, neural network based data mapping and forecasting processes, and genetic algorithms based optimization routines. MOGART uses neural networks to estimate tool machinability and forecast tool wear from the experimental cutting force data, and genetic algorithms with the analytical model to monitor tool wear, breakage, run-out, cutting conditions from the cutting force profiles. The performance of MOGART has been tested on the experimental data of over 800 experimental cases and very good agreement has been observed between the theoretical and experimental results. The MOGART package has been applied to the micro-end-milling operation study of Engineering Prototype Center of Radio Technology Division of Motorola Inc.

Brittle and ductile removal modes observed during diamond turning of carbon nanotube composites

Ultraprecision diamond turning was used to evaluate the surface integrity of a carbon nanotube (CNT) composite as a function of the cutting conditions and the percentage of CNT in the epoxy matrix. The effects of cutting conditions on the chip morphology and surface roughness were analysed. The results showed that an increase in the percentage of CNT may influence the mechanism of material removal and consequently improve the quality of the machined surface. When smaller quantities of CNT (0.02 and 0.07 wt %) are present in the matrix, microcracks form within the cutting grooves (perpendicular to the cutting direction). This indicates that the amount of CNT on the epoxy matrix may have a direct influence on the mechanical properties of these materials. Chips removed from the CNT composite samples were analysed by scanning electron microscopy in order to correlate the material removal mechanism and the surface generation process. The area average surface roughness Sa was influenced by the material removal mechanism (Sa ranging from 0.28 to 1.1 mu m).

Phase transformation and residual stress probed by Raman spectroscopy in diamond-turned single crystal silicon

Single-point diamond turning of monocrystalline semiconductors is an important field of research within brittle materials machining. Monocrystalline silicon samples with a (100) orientation have been diamond turned under different cutting conditions (feed rate and depth of cut). Micro-Raman spectroscopy and atomic force microscopy have been used to assess structural alterations and surface finish of the samples diamond turned under ductile and brittle modes. It was found that silicon undergoes a phase transformation when machined in the ductile mode. This phase transformation is evidenced by the creation of an amorphous surface layer after machining which has been probed by Raman scattering. Compressive residual stresses are estimated for the machined surface and it is observed that they decrease with an increase in the feed rate and depth of cut. This behaviour has been attributed to the formation of subsurface cracks when the feed rate is higher than or equal to 2.5 mu m/rev. The surface roughness was observed to vary with the feed rate and the depth of cut. An increase in the surface roughness was influenced by microcrack formation when the feed rate reached 5.0 mu m/rev. Furthermore, a high-pressure phase transformation induced by the tool/material interaction and responsible for the ductile response of this typical brittle material is discussed based upon the presented Raman spectra. The application of this machining technology finds use for a wide range of high quality components, for example the creation of a micrometre-range channel for microfluidic devices as well as microlenses used in the infrared spectrum range.

Estudo comparativo do comportamento de diferentes ferramentas na fresagem de aços duplex

A maquinagem por arranque de apara é, na actualidade, um dos processos de fabrico mais utilizados e de maior relevo no panorama da indústria metalomecânica mundial. Para além da forte evolução que se tem registado ao longo das últimas décadas nos equipamentos ligados à maquinagem, também as ferramentas têm visto o seu desempenho fortemente melhorado, graças essencialmente ao desenvolvimento de revestimentos finos, mono e multicamada, que têm proporcionado o conjunto de propriedades mais indicado a cada situação. Por outro lado, os aços inoxidáveis duplex têm registado um forte incremento na sua aplicação, a qual requer, em muitos casos, o uso da maquinagem para a obtenção das formas necessárias. Tendo em consideração estes dois factores, o presente trabalho visa, essencialmente avaliar qual a ferramenta mais adequada para trabalhar este tipo de ligas, em função do tipo de maquinagem e condições de corte. Para tal, foram utilizadas diferentes ferramentas dotadas da mesma geometria, e seleccionados parâmetros que constituíssem um denominador comum entre os valores indicados pelos diferentes fabricantes. Foram consideradas apenas condições de maquinagem com utilização de fluido de corte e realizados percursos de corte previamente determinados na fresagem, utilizando fresas de topo em condições de maquinagem de alta velocidade. A análise comparativa recaiu sobre a qualidade da superfície gerada por maquinagem, avaliada através de perfilometria, e o desgaste registado por cada uma das ferramentas utilizadas.

Empirical models for quantification of machining damage in composite materials

Dissertação para obtenção do Grau de Doutor em Engenharia Mecânica

Keraamisten teräpalojen käyttö niukkaseosteisten terästen lastuamiseen normaaleissa toimitustiloissa

Tämän tutkimuksen tavoitteena oli tutkia keraamisten kääntöterien soveltuvuus niukkaseosteräksille ja M-käsittelyn vaikutus teränkestoaikoihin. Lisäksi tavoitteena oli tutkia keraamiseosten erityisominaisuudet ja muodostaa käsitys keraamisilla kääntöterillä sorvaamisen erityisvaatimuksista. Kirjallisuusosassa selvitettiin tutkimushetkellä saatavissa olleet keraamiset teräaineseokset ja niiden ominaisuudet sekä selvitettiin keraamisten kääntöterien viimeaikaiset kehitystrendit. Lastuamistutkimus toteutettiin standardin ISO 3685:1993 mukaisesti, minkä lisäksi mitattiin lastuamisvoimat ja tehtiin kokeessa käytetyille terille lastunmurtokoe. Koemateriaalit olivat Imatra Steelin GreenCut, Hydax 25, M-käsittelemätön 42CrMo4 ja M-käsitelty MoC410M. Kokeissa käytetyt kääntöterät olivat eri valmistajien alumiinioksiditeriä, titaanikarbidiseostettuja alumiinioksiditeriä, kuituvahvisteisia ja yksi puhdas titaanikarbidiseosteinen terä. Koetulosten perusteella hyvän teränkestoajan saavuttamiseksi on tärkeää valita oikea keraamiseos ja sille soveltuvat parametrit. Oikein valituilla parametreilla M-terästä sorvattaessa tulokset ylittävät kovametalleilla saavutettavissa olevat arvot. Tulosten perusteella niukkaseostettujen terästen sorvaus onnistuu hyvin keraamisilla kääntöterillä, mutta kovametallisorvaukseen verrattuna syöttöä on laskettava ja lastuamisnopeutta lisättävä. Tämän työn tuloksia voidaan soveltaa sopivissa olosuhteissa toteutettavassa kappaletavaratuotannossa. Sovelluksen onnistuminen vaatii tukevat työstöolosuhteet ja riittävien lastuamisnopeuksien saavuttamisen.