Dry machining of silicon-aluminium alloys with CVD diamond brazed and directly coated Si3N4 ceramic tools (original) (raw)
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Dry machining of aluminum–silicon alloy using polished CVD diamond-coated cutting tools inserts
Surface and Coatings Technology, 2006
In this research, we investigated the performance of polished chemical vapor deposited (CVD) diamond tool carbide inserts in comparison with unpolished CVD diamond coated carbide tool inserts in the dry turning of A390 aluminum-silicon hypereutectic alloy. The special emphasis is on exploring the role of machining parameters and cutting tool surface morphology on the aerosol generation. Global demand for high speed machining in combination with environmentally benign methods make diamond coated carbide tools an attractive candidate for dry machining. The results of this research demonstrate that CVD diamond-coated polished tools generate fewer particles, unlike conventional diamond tools (PCD and unpolished CVD), which cause the formation of respirable airborne particles during machining. Further, polished CVD diamond tool inserts improve tool life and reduce the cutting forces. Overall, in an important finding it is shown that polishing of tools provides a better opportunity for an environmentally benign dry machining along with improvement in machining outcome.
Diamond and Related Materials, 2008
Nanostructured diamond films were grown to a thickness of approximately 35 µm by a 30 kW, 915 MHz, microwave plasma-assisted chemical vapor deposition (MPCVD) on chemically treated WC-6 wt.% Co tool inserts. Rockwell indentation tests were performed to evaluate the adhesion of the films and compared to that of traditional microcrystalline diamond. A series of high speed dry turning tests on high-silicon (18 wt.% Si) aluminum alloy A390 under continuous and interrupted modes were performed and comparisons were carried out to investigate the wear behavior on tool inserts that were uncoated, coated with nanostructured diamond, and commercial PCD (polycrystalline diamond cutter) ones. The tests showed that nanostructured diamond coatings demonstrated excellent durability against the highly abrasive A390 aluminum-silicon alloys in high speed dry turning. Ultra fine grain structure of this coating produces workpiece surface finish comparable or even better than PCD tools in the range we studied. Excellent coating adhesion of nanostructured diamond on WC-6% Co substrates leads to reliable wear behavior. For the first time, we evaluated the performance of nanostructured diamond film coated insert under high speed interrupted turning mode. A "self-cleaning" mechanism was observed which can significantly improve the performance of nanostructured diamond films. Micro-Raman spectra were taken on tested tools to study the wear mechanism of the coating.
Diamond and Related Materials, 2006
Very smooth CVD diamond films are used as direct coatings on Si 3 N 4 tool substrates. By adjusting deposition parameters, namely Ar/H 2 and CH 4 /H 2 gas ratios, and substrate temperature, nano-(27 nm) and submicrometric (43 nm) crystallite sized grades were produced in a hot filament reactor. Also, a conventional 5 and 12 μm micrometric grain size types were produced for comparison. Normalized coated inserts were tested for dry turning of WC-25 wt.% Co hardmetal. All the CVD diamond grades endured the hardmetal turning showing slight cratering, having the flank wear as the main wear mode. Their turning performance was distinct, as a consequence of morphology and surface roughness characteristics. Among all the tested tools, the more even surface and the submicrometric grade presented the best behaviour regarding cutting forces, tool wear and workpiece surface finishing. For this coating, the depth-of-cut force attained the lowest value, 150 N, the best combination of wear types (KM = 30 μm, KT = 2 μm and VB = 110 μm) and workpiece surface finishing (Ra = 0.2 μm).
3D characterisation of tool wear whilst diamond turning silicon
Wear, 2007
Nanometrically-smooth infrared silicon optics can be manufactured by the diamond turning process. Due to its relatively low density, silicon is an ideal optical material for weight sensitive infrared (IR) applications. However, rapid diamond tool edge degradation and the effect on the achieved surface have prevented significant exploitation. With the aim of developing a process model to optimise the diamond turning of silicon optics, a series of experimental trials were devised using two ultra-precision diamond turning machines. Single crystal silicon specimens <1, 1, 1> were repeatedly machined using diamond tools of the same specification until the onset of surface brittle fracture. Two cutting fluids were tested. The cutting forces were monitored and the wear morphology of the tool edge was studied by scanning electron microscopy (SEM).
In the present study investigation was done to analyze the tool life by analyzing the change in surface roughness with time during machining of silicon (infrared crystal) at optimized parameters with a single crystal diamond tool. Silicon has low mass density, low cost & low coefficient of thermal expansion. Due to these properties it is used in microelectro, micro-mechanical & weight sensitive infrared applications where surface roughness is a major criteria for the acceptance of the fabricated part. A contact type mechanical profilometer was used to measure the surface roughness of silicon.
Manufacturing Review
Enormous developmental work has been made in synthesis of metastable diamond by hot filament chemical vapor deposition (HFCVD) method. In this paper, micro-crystalline diamond (MCD) was deposited on WC–6 wt.% Co cutting tool inserts by HFCVD technique. The MCD coated tool was characterized by the scanning electron microscope (SEM), X-ray diffraction (XRD) and micro Raman spectroscopy (μ-RS). A comparison was made among the MCD tool, uncoated tungsten carbide (WC) tool and polycrystalline diamond (PCD) tool during the dry turning of rolled aluminum. The various major tests were conducted such as surface roughness, cutting force and tool wear, which were taken into consideration to establish a proper comparison among the advanced cutting tools. Surface roughness was measured during machining by Talysurf. The tool wear was studied by SEM after machining. The cutting forces were measured by Kistler 3D-dynamometer during the machining process. The test results indicate that, the CVD coat...
Machining hardmetal with CVD diamond direct coated ceramic tools: effect of tool edge geometry
Diamond and Related Materials, 2005
A new challenge for chemical vapour deposited (CVD) diamond tools is the machining of hardmetal, one of the most difficult tasks a tool has to accomplish due to the extreme hardness of the workpiece. The development of cutting tool inserts made via direct diamond deposition on silicon nitride ceramic substrates for machining WC-Co materials was recently pointed as an alternative to the conventional brazed CVD diamond tips. In the present work, silicon nitride round inserts having different edge geometry, namely sharp, honed and chamfered edges, were produced by pressureless sintering. Turning of hardmetal containing 25 wt.% Co was conducted in a numerically controlled lathe with 15 Am thick CVD diamond coatings. The effects of depth of cut (0.1 to 0.3 mm), feed rate (0.03 to 0.3 mmd rev À1 ) and wear on the cutting forces were monitored online using a dynamometer and were related to the surface finishing of the workpiece. Honed tools were more prone to diamond film delamination from the cutting edge than the chamfer or sharp edge ones. Adequate finishing quality (Rab0.2 Am) can be achieved with the sharp edge tools while machining tolerances are respected. D
Single Point Diamond Turning of CVD Coated Silicon Carbide
Manufacturing Science and Engineering, Parts A and B, 2006
Scratching experiments, using diamond styli and single point diamond tools, were performed to simulate Single Point Diamond Turning (SPDT). The results of these experiments were used to determine if a ductile response is possible, and then to determine the critical depth of cut or penetration depth for the ductile to brittle transition (DBT). The depths of the scratches produced at different loads were measured and correlated to the ductile and brittle response of the material. The DBT depth for Chemically Vapor Deposited (CVD) coated Silicon Carbide (SiC) samples was determined. The analysis for the critical depth (DBT) did confirm the possibility for SPDT of CVD coated SiC in the ductile regime. These results were further used for SPDT of CVD SiC.
This paper investigates the effects of different surface pretreatments on the adhesion and performance of CVD diamond coated WC–Co turning inserts for the dry machining of high silicon aluminum alloys. Different interfacial characteristics between the diamond coatings and the modified WC–Co substrate were obtained by the use of two different chemical etchings and a CrN/Cr interlayer, with the aim to produce an adherent diamond coating by increasing the interlocking effect of the diamond film, and halting the catalytic effect of the cobalt present on the cemented carbide tool. A systematic study is analyzed in terms of the initial cutting tool surface modifications, the deposition and characterization of microcrystalline diamond coatings deposited by HFCVD synthesis, the estimation of the resulting diamond adhesion by Rockwell indentations and Raman spectroscopy, and finally, the evaluation of the dry machining performance of the diamond coated tools on A390 aluminum alloys. The experiments show that chemical etching methods exceed the effect of the CrN/Cr interlayer in increasing the diamond coating adhesion under dry cutting operations. This work provided new insights about optimizing the surface characteristics of cemented carbides to produce adherent diamond coatings in the dry cutting manufacturing chain of high silicon aluminum alloys.
Surface and Coatings Technology, 2007
A diamond-like carbon (DLC) thin film was deposited on cemented carbide cutting tool substrate by PECVD technique. In the first part of this research work a DLC thin film characterization was carried out. It was determined the following important characteristics: hydrogen content, nanohardness, Young modulus, friction coefficient and thickness of DLC coating. The DLC hydrogen content was situated between 10 and 20 at.% while the friction coefficient was 0.2. The DLC nanohardness and Young modulus were respectively 21 GPa and 205 GPa. The coating thickness was approximately 2.5 μm. The R a roughness of the DLC coated surface was around 0.037 μm while the R a roughness of the uncoated surface was around 0.030 μm. In the second part of this work cutting and feeding forces were evaluated when turning Al-Si alloys, using DLC coated and uncoated cemented carbide cutting tools. For the machining forces evaluation, a cutting speed of 450 m/min and cutting depth of 0.5 mm was used. The silicon content in the aluminum alloys was 12 wt.% and 16 wt.%. The feeding force was found to be higher when turning the aluminum alloy with 16 wt.% of silicon. The use of DLC coated cemented carbides tools reduces the feeding component of the machining forces, despite the silicon content in the aluminum alloy. However, the cutting force is not significantly affected either by the presence of a DLC thin film or by the silicon content in the aluminum alloy.