Extending tool life: High-dynamic stiffness nanocomposite coating for improved machining performance

Numerous studies are available regarding the effect of PVD and CVD coatings on cutting tools (inserts), cutting parameter optimization, and the application of the minimum quantity lubrication on the reduction of cutting tool wear and the improvement in surface quality of the machined parts. However, there still exists the deficiency of the comprehensive analysis of improving machining performance by suppressing high frequency vibration (micro-vibration) at the cutting edge due to the random nature of cutting force. The present study aims to mitigate this challenge of suppressing micro-vibration by applying the high dynamic stiffness multilayered Cu: CuCN x nanocomposite coating at the close proximity of cutting edge (in between the cutting insert and shim) by synthesizing the Cu:CuCN x coating on conventional cemented carbide (WC-Co) square shims. The primary objective of this study was to experimentally investigate the effect of Cu:CuCN x coating's morphology on machining performance. Coating morphology was characterized by the total coating thickness and total number of alternative Cu and CuCN x layers in a certain coating thickness. Machining performance was evaluated based on the criteria of cutting tool life and machined part's surface quality. External longitudinal turning operations of SS2541-03 alloy steel (34CrNiMoS6) material with rough cutting parameters and wet condition (using cutting fluid) were adopted for evaluating machining performance. Three different Cu:CuCN x coating series- A, B and C were synthesized by means of a double cathode Reactive High-Power Impulse Magnetron Sputtering (R-HiPIMS) deposition system. Coatings of series-A were deposited on steel disc substrates, and were used to evaluate the Cu:CuCN x nanocomposite coating's mechanical properties as a function of total number of Cu and CuCN x layers in a fixed coating thickness. Mechanical properties of the coatings were investigated by Vickers micro-indentation, and the damping loss factor of the coating was evaluated on the basis of indentation creep measurements under room temperature. Results from the analysis with coating series A demonstrated that the maximum elastic modulus, loss factor and loss modulus values of the coating was obtained when the ratio of total number Cu and CuCN x layers to coating thickness (n/h) is 0.6. However, the hardness, H/E and H 3 /E 2 values were observed to be increasing with increasing number of total layers. The coating with optimum mechanical properties exhibited the highest loss modulus of 2.85 ± 0.03 GPa confirming the high dynamic stiffness of Cu:CuCN x nanocomposite. Coated shims prepared with coating series- B and C were used to evaluate the effect of total number of Cu and CuCN x layers and the effect of total coating thickness on the machining performance, respectively. From the turning tests with conventional shim and coated shims it was evident that the coated shim with 200 μm Cu:CuCN x coating (sample C3) increased the cutting tool life by at least 50 % and reduced the machined workpiece's surface roughness by 15 %. For all turning tests, the thicknesses of coated shims and corresponding conventional uncoated shim were kept constant. The maximum error between the experimental and predicted values of the mechanical properties of coating series-B was found to be less than 10 %Moreover, in case of 200 μm Cu:CuCN x coating containing 150 layers of Cu and CuCN x phases, the coated shim (sample B3) was able to increase the cutting tool life by at least 167 %, and the machined workpiece's average surface roughness was reduced by 10 %. Analysis of the acquired vibration signals during turning tests, indicated that the cutting tool life was prominently affected by the higher frequency vibration (>7000 Hz) at the tool's cutting-edges. It was observed that with the application of 200 μm Cu:CuCN x coating in coated shim, the root mean squared (RMS) vibration energy in overall frequency range (0 to 30,000 Hz) was reduced by 40 %. From material and mechanical characterization, it was postulated that the primary vibration energy dissipation mechanisms of the multilayered nanocomposite coating are the interface frictional energy loss between the alternative Cu and CuCN x layers and the intrinsic damping due to grain boundary sliding in CuCN x layers. • High-dynamic stiffness nanocomposite coatings improve tool life. • Cu:CuCNx coatings enhance machining efficiency and part quality. • HiPIMS technique creates durable, high-performance coatings. • Coatings significantly reduce tool wear and suppress vibrations. • Optimal coating thickness and layers boost damping capacity.