The analysis of the mechanism of cutting tool wear in high speed machining of cast aluminum alloys is conducted in this research work. The result of analysis indicates that the interaction between the hard silicon constituencies of the alloy and the surface of the cutting tool is the most detrimental to tool life. The wear of the cutting tool in such interactions, governed by fatigue wear mechanism, is directly proportional to silicon content of the alloy, silicon grain size and to the tool’s loading conditions. In order to predict the tool wear in machining aluminum cast alloys, a new wear model is developed. The fracture mechanics approach in wear rate estimation is implemented in this model. As an input data for the tool wear modeling, the normal and tangential stresses, acting on the flank of cutting tool are used. The fracture mechanics analysis of the subsurface crack propagation in the cobalt binder of cemented carbide cutting tool material is performed using a finite element (FE) model of the tool-workpiece sliding contact. The real microstructure of cemented carbide is incorporated in the FE model of tool-workpiece contact, and elastic-plastic properties of cobalt, defined by continuum theory of crystal plasticity are introduced in the model by UMAT subroutine of the ABAQUS® FE software. The crack propagation rate, determined from FE modeling, is used then in the model of cutting tool wear, developed in this work. This model is capable to predict the wear rate of cutting tool, base on the microstructural characteristics of the cutting tool and workpiece material and the tool’s loading conditions. The model can be used for cutting tool life assessment and management in high speed machining of Al-Si alloys in an industrial setting.
The utilization of cast aluminum alloys in automotive industry continues to rise because of consumer demand for a future generation of vehicles that will offer excellent fuel efficiency and emissions reduction, without compromising safety, performance, or comfort. Unlike wrought aluminum alloys, the cutting speed for cast aluminum alloys is considerably restricted due to the detrimental effect of the alloy’s silicon constituencies on tool life. In the present study, a new wear model is developed for tool-life management and enhancement, in a high-speed machining environment. The fracture-mechanics-based model requires normal and tangential stresses, acting on the flank of the cutting tool, as input data. Analysis of the subsurface crack propagation in the cobalt binder of cemented carbide cutting tool material is performed using a finite element (FE) model of the tool-workpiece sliding contact. The real microstructure of cemented carbide is incorporated into the FE model, and elastic-plastic properties of cobalt, defined by continuum theory of crystal plasticity are introduced. The estimation of the crack propagation rate is then used to predict the wear rate of the cutting tool. The model allows the microstructural characteristics of the cutting tool and workpiece material, as well as the tool’s loading conditions to be taken into consideration. Analysis of the results indicates that the interaction between the alloy’s hard silicon particles and the surface of the cutting tool is most detrimental to tool life. The fatigue wear of the cutting tool is shown to be directly proportional to the silicon content of the alloy, silicon grain size, and to the tool’s loading conditions.
The disadvantages of conventional metalworking fluids such as disposal problems, health problems and economic factors have led to the development of strategies to reduce their amount in metalworking. Recently, Minimum Quantity Lubrication (MQL) technology was developed and it seems to be a suitable alternative for economically and environmentally compatible production. It combines the functionality of lubrication with an extremely low consumption of lubricant and has a potential to replace metalworking fluids application in machining operations. The MQL lubricants are formulated with two major groups of additives; anti-wear (AW) additives and extreme pressure (EP) additives. When such lubricants are applied to the cutting zone, protective layers are formed on the interacting surfaces of the workpiece and the cutting tool. These layers prevent direct contact between the tool and chip surfaces, and, therefore reduce friction forces and tool wear. In order to utilize MQL to its full potential, it is essential to select appropriate lubricant composition for particular work material and machining parameters. The experimental study of different compositions of MQL lubricants is reported. The effectiveness of the lubricants are determined in terms of their ability to protect the cutting tool in high speed machining of cast aluminum alloys, which are widely used in automotive industry. The main objective of this research is to quantitatively evaluate the ability of lubricant’s additive composition to reduce the tool wear. This is reached through the comparison between the tool wear rate measured during the machining of aluminum cast alloy with the application of MQL, and the tool wear rate obtained in dry machining of the same alloy. Two kinds of the lubricants are evaluated; vegetable and synthetic. The content of AW and EP additives in each kind of lubricant was varied on three levels in order to capture the effect of the lubricant’s composition on tool wear. The result of the MQL lubricants evaluation is discussed and the recommendations for optimal lubricant composition are made.
Background. Aluminum alloys are extensively used in the automotive industry and their utilization continues to rise because of the environmental, safety and driving performance advantages. Experimental study has been carried out in this work to establish the effect of cutting conditions (speed, feed, and depth of cut) on the cutting forces and time variation of carbide tool wear data in high-speed machining (face milling) of Al–Si cast alloys that are commonly used in the automotive industry. Method and Approach. The experimental setup and force measurement system are described. The cutting test results are used to calibrate and validate the fracture mechanics-based tool wear model developed in part 1 of this work. The model calibration is conducted for two combinations of cutting speed and a feed rate, which represent a lower and upper limit of the range of cutting conditions. The calibrated model is then validated for a wide range of cutting conditions. This validation is performed by comparing the experimental tool wear data with the tool wear predicted by calibrated cutting tool wear model. Results and Conclusions. The maximum prediction error was found to be 14.5%, demonstrating the accuracy of the object oriented finite element (OOFE) modeling of the crack propagation process in the cobalt binder. It also demonstrates its capability in capturing the physics of the wear process. This is attributed to the fact that the OOF model incorporates the real microstructure of the tool material. The model can be readily extended to any microstructure of Al–Si workpiece and carbide cutting tool material.
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