1. The research on the source of cutting force, cutting resultant force and its decomposition, and cutting power cutting force is of great significance for further understanding cutting mechanism, calculating power consumption, designing tools, machine tools and fixtures, formulating reasonable cutting parameters and optimizing tool geometric parameters. When metal is cut, the cutting force that deforms the processed material into chips is called cutting force.
Cutting force comes from three aspects:
Overcome the resistance of elastic deformation of the processed material; Overcome the resistance of plastic deformation of the processed material; Overcome the friction between the chip and the rake face and the friction between the transition surface of the tool side and the machining surface. The source of cutting force The sum of the above forces forms the resultant force Fr (F in the national standard) acting on the tool. For practical application, Fr can be decomposed into three vertical components: Fx (Ff), Fy (Fp) and Fz (Fc).
When turning: FZ- cutting force or tangential force. It is tangent to the transition surface and perpendicular to the base surface. Fz is necessary to calculate the strength of turning tool, design machine tool parts and determine machine tool power. FX- feed force, axial force or feed force. It is a force on the base surface, parallel to the axis of the workpiece and opposite to the feed direction. Fx is necessary for designing feed mechanism and calculating feed power of turning tool. Fy-resistance to cutting depth, or back force, radial force and cutting force. It is a force perpendicular to the axis of the workpiece on the base surface. Fy is used to determine the deflection of the workpiece, and the strength of lathe parts and turning tools is related to the machining accuracy of the workpiece. It is related to the vibration of the workpiece during cutting. The power consumed by the resultant force and component of cutting force in the cutting process is called cutting power Pm(Po national standard). The cutting power is the sum of the power consumed by the forces Fz and Fx, and no power is consumed because there is no displacement in the Fy direction. So PM = (FZV+FxNWF/1000) ×10-3, where: PM- cutting power (kW); FZ- cutting force (n); V- cutting speed (m/s); FX- feed force (n); NW-rotational speed of the workpiece (rpm/s); F- feed speed (mm/s). The second term on the right of the equal sign in the formula is the power consumed by the feed movement, which is generally very small compared with the power consumed by F (
Second, the measurement of cutting force and computer-aided testing of cutting force In production practice, the size of cutting force is generally calculated by the empirical formula established by experimental results. When we need to know the cutting force under a certain cutting condition more accurately, we need to actually measure it. With the modernization of testing means, the measuring method of cutting force has made great progress, and it has been able to accurately measure cutting force on many occasions. The measurement of cutting force has become an effective means to study cutting force.
At present, the measuring methods of cutting force mainly include:
After measuring the power PE consumed by the machine tool motor in the cutting process with a power meter, the cutting power Pm can be calculated as follows: PM = PE η m When the cutting speed V is known, the cutting force F can be calculated by using PM. This method can only roughly estimate the cutting force and is not accurate enough. When it is necessary to know the cutting force accurately, it is usually measured directly by dynamometer.
Measuring cutting force with dynamometer The measuring principle of dynamometer is to read the values of Fz, Fx and Fy by using the deformation produced by cutting force on the elastic element of dynamometer or the charge produced by piezoelectric crystal after conversion. In automatic production, the cutting process can also be optimized and monitored by using the signal generated by the force sensing device. According to the working principle of dynamometer, it can be divided into mechanical dynamometer, hydraulic dynamometer and electric dynamometer. At present, resistance strain dynamometer and piezoelectric dynamometer are commonly used.
Computer aided testing of cutting force. Empirical formula and estimation of cutting force At present, people have accumulated a lot of experimental data of cutting force and established empirical formulas that can be directly used in general machining methods, such as turning, hole machining and milling.
Commonly used empirical formulas can be divided into two categories: one is exponential formula, and the other is calculated according to unit cutting force. Practice has proved that there are many factors affecting cutting force, mainly including workpiece material, cutting amount, tool geometric parameters, tool material, tool wear state and cutting fluid.