The feed rate in milling, drilling and tapping is a parameter that reflects the speed of the machining process and is also an important basis for evaluating the machining efficiency of the machine tool. The principle is to machine a certain amount of material in unit time. Through the previously described mathematical models, this paper discusses the cutting force, temperature, chip morphology and other parameters in the cutting process, and determines the reasonable feed rate.
In the milling process, the total cutting force is composed of radial force Ff and cutting speed force Ft. The cutting force Ff Generally speaking, it is determined by the parameters of the cutter, such as rake angle, helix angle and space angle, etc., and approach angle is the most important. Ff can also be obtained through the expression Ff=(Sf*Sz*B*Tf), where Sf is the feed rate per unit length, Sz is the depth of cut, B is the width of cut, and Tf is the torque force. While the cutting speed force generally increases with the cutting speed, Ff tends to be constant when the above parameters are unchanged.
In the drilling process, the total cutting force consists of torque force Ft and thrust force Fm. The thrust force is generated because of the plastic deformation of material and the friction between the cutter and the material, both of which can be calculated. Under the condition of constant parameters, when the cutting speed V is accelerated, the friction force Ff gradually increases and reaches a fixed value. The torque force mainly increases with the increase of the feed rate and the final cutting force is the vector sum of the thrust force and torque force.
In tapping process, the main force is the torque force Ft. The torque force is primarily proportional to the pitch diameter of the tapped holes, and decreases its value when the pitch diameter decreases. In general, the cutting force is not affected by the cutting speed, and the cutting speed can be converted directly into the feed rate when the cutting speed is constant.
The reasonable feed rate should be determined by considering the influence of cutting speed, load force, temperature and chip morphology. When dealing with soft material, high cutting speed and reasonable feed rate should be used to get a good chip to prevent cutting process jammed. When dealing with hard material, low cutting speed and small feed rate should be used to avoid cutting process breakage. In addition, if the feed rate is higher than the reasonable value, the cutting temperature will rise and the chip morphology will be rough. On the contrary, if the feed rate is lower, the cutting temperature and chip morphology will be better.
In summary, the reasonable feed rate of milling, drilling and tapping depends on the material being machined, the cutting tool and other cutting parameters. The cutting force, temperature, chip morphology and other parameters in the cutting process have great influence on the feed rate. Through correct calculation and control of the feed rate, machining accuracy and machining efficiency can be improved.
