Effect of Cutting Conditions on Machinability of Superalloy Inconel 718 During High Speed Turning with Coated and Uncoated PCBN Tools

Inconel 718, an efficient superalloy for energy and aerospace applications, is currently machined with cemented carbide tools at low speed (vc≈60 m/min) due to its unfavorable mechanical and thermal properties. The article presents results of superalloy machinability study with uncoated and coated PCBN tools aiming on increased speed and efficiency. Aspects of tool life, tool wear and surface integrity were studied. It was found that protective function of the coating, increasing tool life up to 20%, is limited to low cutting speed range. EDX and AFM analyses suggested dominance of chemical and abrasive wear mechanisms. Residual stress analysis has shown advantageous compressive surface stresses

Wear mechanisms of silicon carbide-whisker-reinforced alumina (Al2O3-SiCw) cutting tools when high-speed machining aged Alloy 718

The paper is aimed at the identification and characterization of wear mechanisms of SiC whisker-reinforced alumina when turning aged Alloy 718 under different cutting conditions and when machining dry and with coolant. Secondary and backscatter electron microscopy accompanied by focus ion beam milling and EDX techniques were used for analysis of worn-out tools. Notch wear on the major cutting edge was found to consist of two notches: depth-of-cut notch and secondary notch located outside the chip area. The last was found to be governed by adhesion and attrition associated with adverse chip flow conditions. Formation of a minor notch was related to attrition by the defects found on the machined surface. Diffusion of Ni, Fe, and Cr into SiC whiskers was found to degrade them and facilitate adhesion. Chemical wear mechanisms were found to be responsible for degradation and decomposition of whiskers and formation of tribolayer on tool surfaces, which in turn was related to the reduced adhesion of Alloy 718 on the tool. Cracking on the tool rake and localized plastic deformation were found to further accelerate tool deterioration

Tool Life and Wear Modelling in Metal Cutting, Part 2 ─ Based on Combining the Archard and the Colding Equations

In this article an analytical and empirical model for describing tool life and tool wear in metal cutting is presented. The model is based on combining the Colding tool life equation and an extended version of the Archard wear function. It is shown that through the combining of these two models a substantial saving of resources can be achieved in terms of the workpiece material required, as well as the manpower and machine time needed for determining the model constants and the optimum cutting data to be employed

Selecting Cutting Data Tests for Cutting Data Modeling Using the Colding Tool Life Model

An analysis on selecting cutting speed, cutting feed and depth of cut when collecting data for the Colding Tool Life Model based on Woxen's Equivalent Chip Thickness was performed to achieve the lowest possible model error. All possible combinations of a large data set were evaluated with regard to model error. This work shows that an increase of ratio between the highest and lowest cutting speed, feed, depth of cut and tool life within the five included tool life tests increases the likelihood of an accurate model. Further, to ensure an accurate model, it is not enough to have a large ratio of one single parameter, but a large ratio in all parameters is needed. The paper also presents a suggestion on how to select the cutting data points, derived from the best performing tool life models. It is concluded that one should aim to have one pair of cutting data points with equal equivalent chip thickness while varying cutting speed and three more test points with different equivalent chip thickness

Mechanical properties of boron phosphides

International audienceMicrostructure and mechanical properties of bulk polycristalline boron phosphides (cubic BP and rhombohedral B12P2) have been studied by scanning electron microscopy and micro- and nanoindentation. The obtained data on hardness, elastic properties and fracture toughness clearly indicate that both phosphides belong to a family of hard phases and can be considered as prospective binders for diamond and cubic boron nitride

Automated detection of tool wear in machining and characterization of its shape

Flank wear VBmax remains one of the most essential and used metrics for measuring tool wear. VBmax is used to characterize tool wear rate, machinability of materials, the quality of machined surface. While VBmax measures the size of wear scar, the shape of the tool wear remains less used but not the least applicable for such characterization. However, quantification of the wear shape requires a more detailed information about the wear contour. This study develops an Image Processing solution for automated tool wear detection and applies Delaunay triangulation and implenarity parameter for characterizing the shape of the wear scar. Validation of the approach has been performed for machining stainless steel 316L without and with abrasive Al2O3 and SiO2 inclusions. It is shown that VBmax and area parameters of the wear scar are insensitive to wear shape, while implenarity can accurately quantify irregularity, curvature, asymmetry of the scar. The results also show a strong relationship between the tool wear shape, the hardness and size of inclusions in the steel

Cryogenic and hybrid induction-assisted machining strategies as alternatives for conventional machining of refractory tungsten and niobium

Tungsten (W) and niobium (Nb) belong to the refractory metal group and are used as alloying elements in steels and superalloys for high demand products. These metals are also used in a high purity single-phase state for products within nuclear, space, military and research facilities.In the current study, tool wear development and surface quality at different cutting conditions have been evaluated when machining high purity W 99.95% and Nb 99.7% in longitudinal turning. Cryogenic LN2 cooling and hybrid induction-assisted machining strategies were applied in order to alter W and Nb material state with respect to the ductile-to-brittle transformation temperature, and thus to attempt controlling their machinability. These advanced machining strategies were benchmarked against the more conventional machining solutions of dry, flood and high pressure cooling.It was found that the use of LN2 cooling demonstrated the best result in terms of tool life when machining W followed by induction-assisted heating, dry and flood. All machining strategies provided similar surface quality which is related to strong build-up edge formation and respective surface alteration. When machining Nb, high pressure coolant results in best performance in terms of tool life and surface quality, then followed by flood and cryogenic strategies. Overall, substantial improvement of surface quality (Ra = 0.4–0.6 μm) was observed for high cutting speeds vc ≥ 225 m/min

On twinning in ultrahard nanocrystalline cubic boron nitride

International audienceMicrostructure of bulk nanocristalline cubic boron nitride synthesized at 20 GPa and 1770 K has been studied by scanning and high-resolution transmission electron microscopy. The material is characterized by high density of twins with average size of 5.5 nm, and multiple stacking faults within the twin domains that results in the exceptional material hardness