Jigang Liu

Research and Development of High Speed Cutting Tribology

Due to large deformation, high pressure and high temperature, the tribological behavior between tool and workpiece in high speed cutting is markedly different from that between mechanical parts. High speed cutting tribology is a interdependent scientific discipline, in which kinematics and friction between tool and workpiece, tool wear and fracture, match of mechanical, physical and chemical properties of materials between tool and workpiece, as well as influences of cutting conditions and external environment (such as air, cutting fluids) on tribology and machined surface are investigated. The discipline of high speed cutting tribology is the science base for tool materials design and predicting the tool life, surface integrity and cutting accuracy for high speed cutting. In this paper, the concept of high speed cutting tribology and its research development and prospect are presented.

The Impact of Tool Materials and Cutting Parameters on Surface Roughness in High-Speed Face-Milling

High speed machining has received important interest because it leads to an increase in productivity and a better workpiece surface quality. Experimental investigation of the impact of tool materials and cutting parameters on surface roughness in high speed machining is presented in this paper. The surface roughness of machined workpiece is measured when high speed face milling of hardened carbon steels and cast iron by using PCBN and ceramic tools at various combinations of cutting speed and feed rate. The experimental results show that the surface roughness tends to decrease with increases of the cutting speed, but further increases of cutting speed cause an increase in surface roughness. Lower surface roughness is obtained by using less feed rate at high cutting speed region, which is as expected the same as at conventional cutting speeds. It is anticipated that the minimum surface roughness could be obtained by selecting the appropriate cutting speed and feed rate for the given material pairs between workpiece and cutting tool. Introduction The surface finish of a component affects the functional requirements and reliability of the component such as its load carrying capacity, friction, wear and lubricants characteristics as well as its corrosion resistance and fatigue life. At conventional cutting speed region, it is well known that cutting speed has no appreciable effect on surface roughness when brittle materials are machined. However, the surface roughness tends to decrease with the increase in cutting speed when cutting of ductile materials. This phenomenon is usually explained relating to the type of chip formation and built-up-edge generated from the machining process [1]. At very low cutting speed, discontinuous chip formation occurs which gives a poor surface finish. As the cutting speed increases, the chip formation becomes less discontinuous and the surface finish improves. With further increases in cutting speed, a continuous chip with built-up-edge occurs so that the surface roughness deteriorates again reaching a peak roughness. Further increase of cutting speed reduces the size of the built-up-edge until a continuous chip is formed and the surface roughness approaches a steady low value. Under high speed cutting conditions, the cutting speeds adopted are higher than those favouring built-up-edge formations, which appear to indicate that a better surface finish would be produced at high cutting speed [2]. However, it has been demonstrated that the segmented chip formation arises in high speed machining process. The cutting force oscillations associated with the unsteady chip segmentation are very of importance to tool wear and surface finish [3]. It seemed to imply that the surface roughness increases when the cutting speed is increased. This phenomenon needs further explanation. Indeed, much research has shown that increases in cutting speed reduce the surface roughness [4-6]. Unfortunately, detailed studies of the critical cutting speed boundaries have not been thoroughly studied from a quantitative point of view for a wide range of tool-workpiece material combinations. In this paper, surface roughness of machined 45# hardened carbon steel and cast iron when face milling with PCBN and ceramic tools was studied through high speed cutting experiments. Experiments Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 462-465 doi:10.4028/www.scientific.net/KEM.259-260.462

Plastic flow modeling of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy at elevated temperatures and high strain rates

The true stress-strain relationships of Ti-5Al-2Sn-2Zr-4Mo-4Cr(TC17) alloy with a wide range of strain rates were investigated by uniaxial quasi-static and dynamic compression tests, respectively. Quasistatic compression tests were carried out with Instron 8874 test machine, while dynamic compression tests were performed with the split Hopkinson pressure bar (SHPB) which was installed with heating device and synchroassembly system. The dynamic mechanical behaviors tests of TC17 were carried out from room temperature to 800 °C at intervals of 200 °C and at high strain rates (5 500–1 9200 s−1). The stress-strain curves considering temperature-strain rate coupling actions were obtained. The Johnson-Cook constitutive model was developed through data fitting of the stress-strain curves. The material constants in the developed constitutive model can be determined using isothermal and adiabatic stress-strain curves at different strain rates. The Johnson-Cook constitutive model provided satisfied prediction of the plastic flow stress for TC17 alloy.

Development of an Intelligent System for Tool Materials Selection in High Speed Machining

Tool materials play one of the pivotal roles in the machining system. Tool materials must be carefully chosen in relation to the workpiece material to be machined, the tool life, the metal removal rate, the machining cost, and the required accuracy and finish. The advantages and decision-making processes of case-based reasoning (CBR) are described. The CBR system for tool material selection in high speed machining (HSM) is developed. The case expression and organization, searching, matching and constraint-based adaptation rules are presented. With combining the case-based reasoning strategy and constraint-based adaptation, the tool material can be properly selected on the basis of previously successful tool materials used in HSM operations, which is helpful to push the wide applications of HSM.

Balancing of Tool/Toolholder Assembly for High-Speed Machining

High-speed machining has become mainstream in machining manufacturing industry. In industries such as moldmaking and aerospace, it has become the norm rather the exception. The centrifugal force increases as the square of the speed. At rotational spindle speeds of 6,000 r/min and higher however, centrifugal force from unbalance becomes a damaging factor and it reduces the life of the spindle and the tool, as well as diminishes the quality of the finished product. Under high rotational speed, good balance becomes issue. High-speed machining experimental results shown that a well-balanced tool/toolholder assembly could obviously improve machining quality, extend tool life and shorten downtime for spindle system maintenance etc.

Development of a Cutting Database System with Prediction and Analysis Functions

Cutting tool and machining parameters selection are central activity in process planning, which was traditionally performed by numerical control programmers or machine tool operators. The surface integrity has great effect on part quality and the sudden tool failure increases the machining costs greatly. The present paper details the development of a cutting database system with surface integrity prediction and tool failure analysis functions (CUT-P&A). The design and implement of this system has been presented. The system includes three main modules: cutting database, premature tool failure analysis and surface integrity prediction. The functions of this system include cutting tool selection and machining parameters recommendation, prediction of surface integrity and premature tool wear analysis. A case has been studied to explain the application of the system. The wide application of this system will be helpful for machining tool programmers, the improvement of machined part quality and the reduction of machine cost.