Research On A New-type Of High Speed End Milling Cutter Based On The Machining Stability

As an important common and basic technology of advanced manufacturing, highspeed cutting(HSC) is widely used in aerospace, automobile, and mould industries oweto its advantages, such as improving production efficiency and machining precision,reducing cutting force and power consuming, simplifying process flow, shorteningproduction cycle, and et al. However, HSC tool engineering is technical, and comparedto overseas technology, there is a big gap in tool substrate and coat material researchand development, tool manufacturing process and technology, tool safety technology,tool application technology and HSC mechanism research. Because the independentresearch and development capability is weaker, as a result, a majority of HSC tools areimported in our country. With the purpose of improving high speed milling(HSM)stability, dynamic cutting force, cutting chatter, and milling stability and dynamicbalance of end mill with unequal blade spaces are thoroughly researched by means oftheoretical research, simulation and experimental study, and a method to design a newtype of high speed end mill with variable pitch is put forward. The research workincludes four parts as follows:(1) Milling chatter and force in high speed milling processes are studied. Whenresearching milling chatter marks on the machined surface, it is discovered that thechatter frequency calculated from the distance between two vibration marks is nearlythe same with that calculated from the cutting force signal. According to theconclusion, based on the principle that machined surface contour reflects the movingtrack of cutting edge, a new method to study high speed milling chatter is proposed,and the fast tool-off experiment device is designed. At last, on the basis of theinstantaneous rigid force model for micro cutting edge, static and dynamic cuttingforce models for high speed milling processes are established.(2) The cutting stability of end mills with equal pitches and that of end mill withvariable pitches are researched and compared. Based on the force models and dynamicdifferential equation, the limited depth of cut and speed are solved, which lay thetheoretical basis for drawing the stability lobe diagram. By comparing the structureand cutting force spectrum of the two kinds of end mill, it is discovered that thesubstaintial cause for end mill suppressing chatter is that the unequal pitches dispersevibration spectrum by changing the delay time, and destroying chatter generatingconditions. By simulation and experiment, researches on HSM stability of end mill and the law for the difference of pitch to affect milling stability are carried out. The resultsindicate that increasing the difference of pitch can enlarge the stability domain andeffectively suppress the high frequency vibration.(3) In order to reveal the influence of structure parameters on dynamic balance,the dynamic balance for end mill with variable pitches is deeply investigated. Based onthe basic theories of dynamic balance and the geometry characteristics of helical flutes,a mathematical model of mass eccentricity and imbalance value of the high speed endmill with three unequal pitches is established. The3D solid model of the end mill isbuilt in the software UG, and its mass eccentricity value is calculated. Meanwhile, theimbalance value of the end mill is measured by a dynamic balance measuringinstrument, and the reliability of the mathematical model is verified by this dynamicbalance test experiment. According to the mathematical model of eccentricity andimbalance, influencing factors are thoroughly analyzed. It is found that the length ofcutting edge and helical angle have the most influence on mass eccentricity andimbalance value, and they change mass eccentricity and imbalance periodically.(4) The cutting performance of end mills with equal and variable pitches iscomprehensively researched from the aspect of anti-vibration. Considering the abilityin anti-vibration and dynamic balance, the structure optimal design method for the newtype of high speed end mill with variable pitched is proposed. Making high speedmilling aluminum alloy as the experimental condition, and end mill with equal andvariable pitches as the cutting tool, comparative tests of cutting force and vibration arecarried out. The results show that, when the cutting parameters and imbalance are thesame, the new end mill can effectively suppress chatter and enhance resistance tochipping, and especially under the condition of high speed milling thin-walled part ormilling in small cutting depth and big cutting width, the capability of the new end millto suppress vibration is better.