Research On Cutting Force And Surface Roughness Of High-speed Ball-end Milling

1.IntroductionThe technology of High-Speed Machining is famous for its high speed, high processing precision and high surface quality. The ball milling cutters are widely applied in the aerospace, automobile and mold industries. Ball milling cutter adapts many kinds of free curved surface. Cutting tool path computation is also quite simple. The cutting process path is easy to control. The interference is easy to examine. Therefore, the ball milling cutters are widely applied in 3-axis digital machines to process free curved surface. But in the High-Speed Machining, there are a series of problems about the rule of cutting force and surface quality. This paper, in the direction of the High-Speed Machining development, aiming at the characteristics of complex curved surface of high strength aluminum alloy LY12, with the high-speed cutting theory and the modern analysis method, does research on cutting force and surface roughness during high-speed ball-end milling.2. Modelling of Cutting Force during High-Speed Ball-End MillingThis paper adopts the method between theoretical analysis and the experimental study, has established the model of cutting force during High-Speed ball-end milling. From analysis of the path in the foundation, these equations are established:The sketch of cutting area computation of ball milling cutter is shown as follow.The cutting area is:The High-Speed Milling pressure can reduce along with the cutting speed increase and can arrive at the minimum value. When the cutting speed continues the increase, it meets the micro increase. The rule can be obtained by the means of experimental study. The cutting force will decompose and transform to the rectangular coordinate system:During High-Speed Machining, the rule of cutting force periodic variation has the close relation with the length of cutter edge line in the work. Correspondingly, the integral area varies in the formula. 3. Experimental Study of Cutting Force during High-Speed Ball-End MillingThe mean value of cutting force is gotten in the experiment. The coefficient of High-Speed Milling pressure can be calculated from the formula, F_t = p×A_cav=p×a_p×a_e×f_z×n_z/(π×d) . Thus under the existing experimental condition, the rule curve of"v - p"of aluminum alloy LY12 is simulated. In order to much more approach the rule of"v ? p", the data obtained in the experiment pass through simulation twice. Finally the curve of"v - p"is obtained , like chart 2. Its equation is: p = 342. 9687×v^0.2425(N/mm²)The curvilinear figure of the ball milling force is obtained from the formula (11):From the fig.3, these are concluded: The simulation curve andthe actual value tally very much well in the size and the change tendency; the theoretical formula may reflect in well the rule of cutting force during High-Speed ball-end milling. From (a)(b)of figure 3, these are concluded: The actual value of cutting force component displayed a bigger change in X direction and the Y direction on cyclical two wave ridges and wave troughs, which reasons are as follow: The cutter exists bias, which causes the cutting parameter to be different during High-Speed Machining, and the cutter edge that produces the small wave ridge is near to the host axle; the cutter exists certain attrition, which make difference between two cutter edges, and cutting area is smaller than the theory during High-speed Machining.4. Experimental Study of Surface Roughness during High-Speed Ball-End MillingIn recent years, along with the high speed precision machining technology development, great feed and light cutting has gradually substituted for the traditional machining. During the high speed precision machining, the surface quality has the tendency to reduce. At the same time, when the cutting depth is not deep, the cutting tool distorts is not big. Thus, the geometry factor becomes the primary factor to influence the surface roughness.(1) Smaller good spacing is, smaller the volume in the the transition surface is removed also. Corresponding, the surface roughness is smaller. But the good spacing is not too smaller to affect the processing efficiency.(2) The feed per tooth reduces, which will make the surface roughness to reduce. At the same time, the upright direction also reduce the surface roughness.(3) During the machining, the increase of f ,the reducing of n ,and the less of tooth can all increase f_z. Those factors can affect the surface roughness indirectly by affecting f z.Speaking of High-Speed Machining, f zand a eare two primary factors affecting the surface roughness. Other factors affect the surface roughness indirectly by affecting them.5. ConclusionThis paper does research on the AL-alloy LY12 deformation rule, cutting force and surface roughness during High-Speed ball-end Machining, based on the analysis of the domestic and foreign study and application. In this case, the cutting force model is established by means of microelements. Periodic variation rule during High-Speed Machining is studied. Through experimental study, the function between the milling speed and milling pressure is established. The experimental study indicated: the milling pressure will reduce with the milling speed increasing when aluminum alloy LY12 is machined above the speed of 377 m/s; the cutting force components are big in the direction of feed and its upright direction. The ball milling cutter theoretical formula is validated through the experiment. Along with the main axle rotational speed enhancement, the cutting force gradually reduces, which is increased by the increasing of f , a ea p. Many factors affecting the surface roughness are analysed. The experimental study indicated: f zand a eare two primary factors affecting the surface roughness. Other factors affect the surface roughness indirectly by affecting them.