Leonardo De Chiffre

Reliable tool life measurements in turning : an application to cutting fluid efficiency evaluation

Abstract The paper proposes a method to obtain reliable measurements of tool life in turning, discussing some aspects related to experimental procedure and measurement accuracy. The method (i) allows an experimental determination of the extended Taylors equation, with a limited set of experiments and (ii) provides a basis for the quantification of tool life measurement uncertainty. The procedure was applied to cutting fluid efficiency evaluation. Six cutting oils, five of which formulated from vegetable basestock, were evaluated in turning. Experiments were run in a range of cutting parameters, according to a 23–1 factorial design, machining AISI 316L stainless steel with coated carbide tools. Tool life measurements were associated to an estimation of their uncertainty, and it was found that by taking three repetitions the uncertainty calculated with a coverage factor of two was on average three times bigger than the experimental standard deviation.

Development and validation of a new reference cylindrical gear for pitch measurement

Abstract A new type of master gear, the Gauge Block Gear (GBG), was developed for the performance verification of coordinate measuring machines (CMMs), for the specific task of pitch and chordal tooth thickness measurement. Its main characteristic is the replacement of the teeth with gauge blocks to achieve direct traceability of the chordal tooth thickness. Mathematical models for the geometrical definition of cylindrical gears with involute toothing, data evaluation, and assessment of the task-related uncertainty, were formulated, and measuring strategies for CMMs were designed and implemented. The GBG was calibrated using the swing round method, and measurement uncertainties on chordal tooth thickness and total pitch deviation Fp were determined to be 0.9 μm and 1.4 μm, respectively. Assembly stability and flexibility of the artefact were verified with measurements performed on a CMM provided with general purpose software, one with dedicated gear measuring software, a form tester, and a conventional gear measuring center. Results confirm the correctness of the mathematical models developed to analyze CMM results as well as their compatibility with existing approaches. The Gauge Block Gear provides, therefore, for direct traceability of the chordal tooth thickness and allows the definition of the task-specific uncertainty of pitch and tooth thickness measurements of cylindrical gears as basis for the assessment of the metrological capability of measuring machines.

An industrial comparison of coordinate measuring machines in Scandinavia with focus on uncertainty statements

Abstract This paper describes an industrial comparison of coordinate measuring machines (CMMs) carried out in the Scandinavian countries from October 1994 to May 1996. Fifty-nine industrial companies with a total of 62 CMMs participated in the project and measured a comparison package with five items chosen to represent a variety of dimensions, angles, and other geometrical quantities. A tool holder, two gauge blocks, a straightedge, and a ring together with instructions on how to measure the items were produced and sent to each participant. Simple measurement tasks were observed to be carried out with good results for the majority of the participants; whereas, increasing the level of difficulty from simple length measurements to more complex geometrical quantities gave severe problems for some of the companies. This occurred even though the participants measured according to prescribed procedures. An important part of the intercomparison was to test the ability of the participants to determine measurement uncertainties. One of the uncertainties was based upon a “best guess” but nevertheless, many participants did not even report this uncertainty. Uncertainty budgeting was not used for measurements other than simple length. For each company, a comparison of their measurement ability with the reference laboratory and other Scandinavian companies was made possible. A network regarding CMMs was created in these Scandinavian countries.

Forming of Shape Memory Composite Structures

A new forming procedure was developed to produce shape memory composite structures having structural composite skins over a shape memory polymer core. Core material was obtained by solid state foaming of an epoxy polyester resin with remarkably shape memory properties. The composite skin consisted of a two-layer unidirectional thermoplastic composite (glass filled polypropylene). Skins were joined to the foamed core by hot compression without any adhesive: a very good adhesion was obtained as experimental tests confirmed. The structure of the foam core was investigated by means of computer axial tomography. Final shape memory composite panels were mechanically tested by three point bending before and after a shape memory step. This step consisted of a compression to reduce the panel thickness up to 60%. At the end of the bending test the panel shape was recovered by heating and a new memory step was performed with a higher thickness reduction. Memory steps were performed at room temperature and 120 °C so as to test the foam core in the glassy and rubbery state, respectively. Shape memory tests revealed the ability of the shape memory composite structures to recover the initial shape also after severe damaging (i.e. after room temperature compression). Compressing the panel at a temperature higher than the foam resin glass transition temperature minimally affects composite stiffness.

Surface and Interface Characterization

While the bulk material properties treated in Part C of this handbook are obviously important, the surface characteristics of materials are also of great significance. They are responsible for the appearances of materials and surface phenomena, and they have a crucial influence on the interactions of materials with gases or fluids (in corrosion, for example; Chap. 12), contacting solids (as in friction and wear; Chap. 13) or biospecies (Chap. 14), and materials–environment interactions (Chap. 15). Surface and interface characterization have been important topics for very many years. Indeed, it was known in antiquity that impurities could be detrimental to the quality of metals, and that keying and contamination were important to adhesion in architecture and also in the fine arts. In contemporary technologies, surface modification or functional coatings are frequently used to tailor the processing of advanced materials. Some components, such as quantum-well devices and x-ray mirrors, are composed of multilayers with individual layer thicknesses in the low nanometer range. Quality assurance of industrial processes, as well as the development of advanced surface-modified or coated components, requires chemical information on material surfaces and (buried) interfaces with high sensitivity and high lateral and depth resolution. In this chapter we present the methods applicable to the chemical and physical characterization of surfaces and interfaces.

Elastic-properties measurement at high temperatures through contact resonance atomic force microscopy

Miniaturization of products and need for further improvement of machines performance introduce new serious challenges in materials characterization. In particular non-destructive mechanical testing in the sub-micrometer scale is needed to better understand and improve micro-manufacturing operations. To this regard, some open issues are of particular interest: low depth of penetration, high lateral resolution and measurements at elevated temperatures. An interesting solution is given by acoustic microscopy techniques, which can be successfully implemented for advanced research in surface elasticity, allowing fast direct and non-destructive measurement of Young’s modulus and related surface parameters. In this work an instrument set up for Contact Resonance Atomic Force Microscopy is proposed, where the sample with is coupled to a heating stage and a piezoelectric transducer directly vibrate the cantilever during scanning, in order to allow exploitation of high resolution measurements at relatively high temperatures. Such instrument set up was undergone a set of calibration experiments in order to allow not only qualitative but also quantitative characterization of surfaces. The work was completed with a feasibility study with mechanical and topography measurements at temperatures as high as 150°C, with lateral resolution lower than 100 nm.

Acoustic emission-based in-process monitoring of surface generation in robot-assisted polishing

The applicability of acoustic emission (AE) measurements for in-process monitoring of surface generation in the robot-assisted polishing (RAP) was investigated. Surface roughness measurements require interruption of the process, proper surface cleaning and measurements that sometimes necessitate removal of the part from the machine tool. In this study, stabilisation of surface roughness during polishing rotational symmetric surfaces by the RAP process was monitored by AE measurements. An AE sensor was placed on a polishing arm in direct contact with a bonded abrasive polishing tool, and a cylindrical workpiece in Vanadis 4E steel was polished in 40 polishing passes from an initial turned surface roughness Ra = 3.1 µm down to Ra = 0.07 µm. The polishing task was performed in five intervals and after 4, 8, 20, 30 and 40 passes, the resulting surface roughness was measured. The results show a decreasing trend in measured AE signal power and RMS, which is well qualitatively correlated with the development of surface roughness during polishing. The trend allows the identification of an asymptote representing the process completion (stabilisation of surface roughness), reliable for correct in-process determination of the process endpoint. This makes it possible to reliably determine the right time for changing the polishing media to finer abrasive when applying a given set of parameters is no longer effective to create a smoother surface, thus improving the efficiency of the process. The findings enabling automatic detection of optimal process endpoint allow intelligent process control, creating fundamental elements in development of robust fully automated RAP process for its widespread industrial application.

Dimensional metrology for process and part quality control in micro manufacturing

Micro manufacturing has gained interest over the last decade as the demand for micro mechanical components has increased. The need for dimensional metrology at micro scale is evident both in terms of quality assurance of components and products and in terms of process control. As critical dimensions are scaled down and geometrical complexity of objects is increased, the available measurement technologies appear not sufficient. New solutions for measuring principles and instrumentation, tolerancing rules and procedures as well as traceability and calibration are necessary if micro manufacturing is to develop into industrial manufacturing solutions. In this paper the application of dimensional precision metrology to both component and process quality control will be demonstrated. The parts investigated are micro injection moulded polymer parts, typical for the field of micro manufacturing.

Control of AFM tip wear

Atomic force microscopes can provide extremely high resolution imaging of surfaces; nevertheless due to non-ideal shape and size of the probe tip, distortions are present. The amplitude of these distortions is not constant: in fact, tip shape evolves with time, since physical effects and dynamic interactions produce wear. The possibility of foreseeing tip wear rate is of great help whenever quantitative analyses are needed, reducing the time needed for tip-investigation and allowing for a proper deconvolution operation. In this paper, a new strategy for monitoring and modelling tip wear in contact mode AFM is presented. Evolution of tip shape was observed by reverse imaging of a scanned nanostructured topography, periodically repeated throughout tip lifetime. An algorithm for tip deconvolution is presented in the paper.

A Simple Model Linking Surface Roughness with Friction Coefficient and Manufacturing Cost

A simple theoretical model linking surface micro geometry, friction and manufacturing cost is presented. Combining a basic geometrical relationship of plastic deformation of workpiece surface asperities by a hard tool with an assumption of adhesive friction, the friction coefficient of a soft, rough surface sliding against a hard, smooth tool surface can be calculated, linking surface roughness with friction coefficient. The simple model can also link the cost related to manufacturing with a surface characterized by a given friction coefficient value. Results are presented from tests carried out to verify the simple model. Several test pieces were manufactured by turning, or grooving, an aluminum alloy and brass using different feeds, tool nose radii, and tool nose angles, achieving different surface profiles. The surfaces were characterized using a stylus profilometer and a digital microscope. The static friction coefficient was determined in terms of angle of repose using a rotary table. The experimentally determined values of the friction coefficient were compared with those predicted from feed, tool radius, and asperity angle. The tests have shown a good reproducibility, and a clear determination of the friction coefficient was possible. However, due to the low normal loads involved in this set up, the influence from the surface roughness was not clear. Further investigations are therefore proposed.