Development of innovative TCT saw blades for high speed cutting of metallic alloys

The subject covered in this thesis concerns the development of an innovative PVD coated multipoint cutting tool with cemented carbide brazed inserts for high-speed cutting of ferrous alloys. The aim of the research was to optimize the properties of the constituent materials in order to maximize their durability and provide a constant level of surface finishing of the machined parts. Fast cutting technologies are nowadays spreading because of the high productive rate that they guarantee, but on the other side wear is more severe with high speed cutting. Tungsten Carbide Tipped (TCT) saw blades are typically used in wood cutting but since 30 years are gradually taking the place of traditional band saws due to the higher cutting speed that are possible to reach and thanks to a better surface finishing on machined surfaces. The research work that was part of an industrial project was divided into three steps: 1. characterization of cemented carbide grades for application in machining 2. optimization of the cutting geometry 3. development of a tailored CAE – PVD coating. The first part of the research work involved the study of literature in order to define the most suitable grades of cemented carbide for experimentation and to define some possible coating composition and architectures. Both plain grades and mixed grades with secondary Ti and Ta carbides were chosen, the relations among hardness, toughness, grain size and wear resistance were investigated through microstructural and mechanical characterization; finally discs made of cemented carbide were tested against pins of steel to characterize the resistance to sliding wear. From this characterization a mixed grade cemented carbide with 12% cobalt binder and micrometric grain size was chosen due to the best toughness properties shown from characterization. Saw blades work under interrupted cutting conditions so toughness was required as the most important feature. In the second part of this study the cutting geometry of the cemented carbide inserts was optimized via experimental cutting tests and CAE methods. After a set of benchmark cutting tests on an industrial sawing station, the experimental cutting forces were calculated analytically and than used to calibrate a FEM 2D numerical calculation model. Two cutting geometries were then tested among those simulated: -15° and -25° rake angles. Thanks to the use of an hard metal with increased toughness (KIC> 15 MPa), a tool with a rake angle of -15 ° has been designed to guarantee lower cutting forces (less than 90 N in the first cuts), friction and temperature on the surface of the tool’s rake face (Figure 1). By experimental validation of the simulated geometries the cutting model gained predictive power. In the second phase of the work, three CAE - PVD coatings of the Al - Ti - Cr - N system were studied. Two of them were monolayer and one multilayer. The aim of this part of the work was to investigate the mechanical and microstructural properties of the analyzed coatings using different experimental methods to describe their behavior. The coatings were characterized not only from the mechanical point of view (hardness, toughness and adhesion) but also from the morphological (defective), and microstructural point of view. From the tests carried out, a multi-layered coating with improved toughness for use in interrupted cutting was designed

Ultraviolet–Visible-Near InfraRed spectroscopy for assessing metal powder cross-contamination: A multivariate approach for a quantitative analysis

The last few years have seen an increasing use of spherical metals powders to produce bulk parts through metal forming technologies like Additive Manufacturing and Metal Injection Molding. This, coupled with the wide availability of metal powders, leads to a critical issue: contamination across different systems in different process steps. Consequently, it is necessary to find a new, fast, and reliable analysis sensible to tiny traces of contamination. This work evaluates the applicability of Ultraviolet–Visible-Near InfraRed (UV–Vis-NIR) spectroscopy, a technique providing information on powders’ reflectance, for studying contaminated powders. This work focuses on assessing 3 binary systems obtained from the cross-contamination of 3 components (A92618, C10200 and S31603) in a low contamination range (from 0.5 vol% to vol. 6%) and in a high contamination range (25 vol% and vol.50%). After the UV–Vis-NIR analysis, multivariate analysis has been used to obtain quantitative results. Results show that, as the contamination level increases in the binary system, the shape of spectra changes and becomes progressively more similar to the contaminant one. The chemometric analysis allows the detection of the contaminant type and its concentration percentage in the contaminated powder

Effetto di affinante e modificante sulla microstruttura delle leghe Al-Si da colata = Effect of refining and modification on the microstructure of Al-Si casting alloys

La necessità di ridurre le emissioni di CO2 ha spinto i produttori di veicoli verso l’adozione di materiali in grado di garantire una riduzione del peso quanto più possibile consistente. Per questa ragione, oltre che per le buone proprietà meccaniche specifiche, le leghe alluminio-silicio trovano vasta applicazione nel settore dell’autoveicolo. Sebbene le leghe Al-Si siano leghe note e oggetto di numerosissimi studi, un ulteriore passo in avanti può coinvolgere la valutazione degli effetti degli additivi modificanti ed affinanti sulla microstruttura della lega e sulla forma delle fasi intermetalliche. In questo lavoro, dei getti in lega EN AC 45300 (AlSi5Cu1Mg), verranno analizzati nello stato as-cast e in seguito a trattamento termico T6, con e senza l’adozione di agenti affinanti e modificanti, con l’obiettivo di studiare le evoluzioni che avvengono nelle microstrutture in termini di morfologia delle fasi intermetalliche

Perfluoropolyether-Based Micellar Aggregates Coatings for Corrosion Resistance Enhancement of Copper-Based Alloys

In this paper, a perfluoropolyether (PFPE) micellar solution was effectively deposited on metallic substrates using a dip-coating process to enhance brass and nickel aluminum bronze (NAB) corrosion resistance. Particular attention was paid to the aesthetic results as well. Enabling the metallic substrates hydrophobic to facilitate water and moisture removal was the key concept of this work. The corrosion resistance of the as-received and coated metals was investigated via a salt spray chamber test. The study focused on the characterization of the polymeric coating via dynamic light scattering and wettability tests, while the substrates were assessed with traditional metallographic techniques. The preparation of the polymeric solution was important in determining the final corrosion resistance of the two substrates. Noteworthy was the effectiveness of the PFPE-based coating when it was applied to the brass rather than the NAB. Moreover, the polymer concentration of the dip-coating polymeric emulsion was the most significant factor to obtaining adequate protection: higher polymer concentrations resulted in a decrease in corrosion resistance

Design and Manufacturing of a Nd-Doped Phosphate Glass-Based Jewel

This paper reports the results of the designing, manufacturing and characterization of a jewel obtained by means of coupling the dogmas of industrial design to the analytical engineering approach. The key role in the design of the jewel was played by an in-house synthesized Neodymium (Nd)-doped phosphate glass, selected due to its easy handling and capability to change color according to the incident light wavelength. The glass core was covered by a metal alloy to mitigate its relatively high fragility and sensitivity to thermal shock and, at the same time, to highlight and preserve its beauty. The selection of the proper metal alloy, having thermo-mechanical properties compatible with those exhibited by the glass, was carried out by means of Ashby’s maps, a powerful tool commonly adopted in the field of industrial design

A numerical modeling framework for predicting the effects of operational parameters on particle size distribution in the gas atomization process for Nickel-Silicon alloys

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Case Study of the Tensile Fracture Investigation of Additive Manufactured Austenitic Stainless Steels Treated at Cryogenic Conditions

Additive manufacturing is a key enabling technology in the manufacture of highly complex shapes, having very few geometric limitations compared to traditional manufacturing processes. The present paper aims at investigating mechanical properties at cryogenic temperatures for a 316L austenitic stainless steel, due to the wide possible cryogenic applications such as liquid gas confinement or superconductors. The starting powders have been processed by laser powder bed fusion (LPBF) and tested in the as-built conditions and after stress relieving treatments. Mechanical properties at 298, 77 and 4.2 K from tensile testing are presented together with fracture surfaces investigated by field emission scanning electron microscopy. The results show that high tensile strength at cryogenic temperature is characteristic for all samples, with ultimate tensile strength as high as 1246 MPa at 4.2 K and 55% maximum total elongation at 77 K. This study can constitute a solid basis for investigating 316L components by LPBF for specific applications in cryogenic conditions

Case Study of the Tensile Fracture Investigation of Additive Manufactured Austenitic Stainless Steels Treated at Cryogenic Conditions

Additive manufacturing is a key enabling technology in the manufacture of highly complex shapes, having very few geometric limitations compared to traditional manufacturing processes. The present paper aims at investigating mechanical properties at cryogenic temperatures for a 316L austenitic stainless steel, due to the wide possible cryogenic applications such as liquid gas confinement or superconductors. The starting powders have been processed by laser powder bed fusion (LPBF) and tested in the as-built conditions and after stress relieving treatments. Mechanical properties at 298, 77 and 4.2 K from tensile testing are presented together with fracture surfaces investigated by field emission scanning electron microscopy. The results show that high tensile strength at cryogenic temperature is characteristic for all samples, with ultimate tensile strength as high as 1246 MPa at 4.2 K and 55% maximum total elongation at 77 K. This study can constitute a solid basis for investigating 316L components by LPBF for specific applications in cryogenic conditions