Linsheng Electromechanical Co , Ltd. – How To Control: Gun Drill Chip
Linsheng Electrical Co , Ltd. said: The gun drill has the characteristics of wide processing range, good surface quality and high processing efficiency. It can be used to machine deep holes with 0.5-40mm aperture, depth to diameter ratio up to 200, and surface precision of carbide drill. Can reach H8 level. However, when processing difficult-to-machine materials such as titanium alloys and precipitation-hardened stainless steels, problems such as high strength, high hardness, poor thermal conductivity, and elastoplasticity of the materials have problems such as poor surface quality and reduced tool life. The related research results show that the tool geometry optimization, tool coating and process parameter optimization can significantly improve the drilling quality, drilling accuracy and tool life of the gun.
Next, Linsheng Electrical Co , Ltd. analyzes the control factors of the gun drilling process from three aspects:
(1) Study on the stability of the cutting process
The stability of the cutting process has a significant impact on the quality of the deep hole machining of the gun drill, and is one of the main causes of the failure of the gun drill. The machining stability at the entrance of the gun drill is poor, so the pre-drilled hole or the guide sleeve should be drilled at the entrance of the gun drill. The gun drill inlet is divided into two stages: the cutting edge cutting phase and the guiding surface entering the workpiece material phase by the guiding sleeve. In the first stage, as the cutting edge cuts into the workpiece, the length of the cutting edge participating in the cutting increases, the cutting force increases steadily, and the cutting process stability at this stage is better. In the second stage, the inner and outer cutting edges all participate in the cutting. Since the diameter of the drilling hole is small during the first stage of cutting, the tangential force of the drilling continues to increase, but the axial force remains substantially unchanged. When the guide strip enters the workpiece, the diameter of the drill hole is enlarged, the axial force is significantly increased, and the tangential force is gradually reduced. The main phenomenon of the gun drill entrance process is the violent fluctuation of the tangential force and the radial force, . The change in cutting force is one of the main reasons for tool failure (usually manifested as fatigue fracture of the shank and breakage of the drill bit). The main reason for the instability of the bit cutting process is that the gap between the guide sleeve and the drill bit is too large and the design of the gun drill guide bar is unreasonable.
(2) Gun drill chip breaking mechanism and chip removal process
Whether the gun drill can be normally chipped and chipped is one of the decisive factors that determine whether the gun drill can be cut normally. Due to the small chip evacuation space during deep hole machining, there are strict requirements on chip size and shape. Whether the chips can be discharged smoothly depends on the chip, curl and break, corresponding to the width, shape and length of the chips. The chip breaking mechanism of cutting is mainly divided into two types: geometric chip breaking and mechanical chip breaking. Geometric chip breaking mainly refers to the change of cutting parameters, the chip thickness is regularly changed to zero and chip breaking. The mechanical chip breaking mainly refers to the external environment formed by changing the chip to generate a new mechanical mechanism, so that the internal stress of the chip exceeds its Break at the stress limit. The chip breaking method applied to the gun drill mainly includes vibration drilling, adding a chip breaking table in the front surface of the gun drill and changing the geometric angle of the gun drill.
(3) Research on cutting force and cutting temperature
Cutting force is an important basis for calculating cutting power, machine tool and tool selection, and affects the quality of cutting surface, tool wear and cutting heat. It is one of the important factors in cutting process control. The main factors affecting the cutting force of the gun drill are the tool geometry, workpiece material and machining process parameters. When the tool and workpiece material are fixed, the process parameters are the main factors affecting the cutting force of the gun drill. Wang Haiqin carried out the cutting test of 50B material in cemented carbide gun drilling, and obtained the influence of process parameters on axial force and torque. The test results show that the axial force and torque of the gun drill decrease with the increase of the cutting speed, and increase with the increase of the feed speed, and the trend is obvious. For the same material, the cutting force remains basically the same under the same process parameters, but the cutting force changes significantly when drilling different layers of material.
In addition to cutting forces, the cutting temperature is an important factor that must be considered in the gun drilling process. Excessive cutting temperatures can alter material properties and increase tool wear. However, accurate measurement of the cutting temperature is difficult. T. Ueda of Kanazawa University in Japan measured the temperature during the drilling of the twist drill by colorimetry, and obtained the temperature distribution of the twist drill and the influence of the cutting speed and the feed rate on the cutting temperature, and passed the oil mist. Lubrication reduces the drilling temperature by 20%-25%. Although the experimental study of cutting temperature is difficult, in recent years, with the advancement of computer simulation technology, the research on drilling temperature is more convenient. Jia Yongpeng and so on through the Deform-3D gun drilling process simulation, the cutting edge temperature distribution of the ductile cast iron was obtained, and the variation of cutting temperature under different cutting parameters was obtained: cutting temperature with cutting speed and feed rate Increase and increase. Although the simulation results of the computer can qualitatively reflect the variation of the cutting temperature with the process parameters, it is necessary to perform a large number of engineering tests to correct the simulation model to accurately predict the cutting temperature.
The cutting force and cutting temperature of the gun drill are important indicators of the stability of the gun drill cutting process. However, the measuring equipment for cutting force and cutting temperature is complicated and has a limited application range, which is difficult to use in actual production. Moreover, for a large amount of cutting of expensive and difficult-to-machine materials such as titanium alloys, the test cost is often unacceptable. Therefore, forecasting cutting force and cutting temperature through low-cost computer simulation technology is the main research direction of future gun drilling.