High-speed Milling Force Model Based On Material Properties Of Difficult-to-machine Materials

Difficult-to-machine materials such as nickel-base superalloy and titanium alloy have been widely used in machining the key hot-end components in aerospace, nuclear power, shipping, automotive industries because of the good mechanical properties. During the high-speed milling of such components, the milling force is an important procedure parameter, because it is of the cutter parameters, workpiece material properties, cutting parameters, and will influence the machining quality, efficiency and stability directly. Therefore, simulating machining process, making milling force prediction and revising the improper cutting process parameters and paths for the area with too strong or violent vibrational cutting forces in time before the machining process is important to enhance efficiency and reduce cost. In respect of the previous milling force predition methods, there usually are of various defects such as poor universality,complex calculation procedure or low precision. In addition, the cutting mechanism in high speed milling difficult-to-machine material is different from that in conventional milling. Hence, it is necessary to propose a new milling force predition method suitable for high-speed milling, which is also of wide universality and high precision.In this paper, the primary end point is to exactly predictthe milling force prediction on different difficult-to-machine materials, investigating the relationship interactions between milling force and the cutting tools geometric parameter, cutting parameters and the surface features. Through investigating the relationship between milling force and the yield strength, the heat conductivity and the plasticity of the material which are the most important factors to influence cutting force, and its interactions with the cutting tools geometric parameter, cutting parameters and the surface features, a new milling force prediction model has been developed to predict cutting forces both in ball end milling and flat end milling The main research contents of this paper are as follows:First of all, the milling force modeling theory which is appropriate for the feature of the difficult-to-machine material high-speed milling is investigate to upgrading modeling ideas and flowchart. Based on differential thought, the milling cutter is discretized as axial differential cutting element, and each discrete element is view as a separate entity, there is no interaction between adjacent elements. Then some intense research on the cutting mechanism is carried out upon the rake face of cutting edge. Furthermore, differential scheme is used to split the entire milling process into a combination of a series of static cutting states. The coordinate system including cutter coordinate system, local coordinate system, machine coordinate system and workpiece coordinate system is established to investage the geometrical characteristic of ball end mill and flat end mill, the mapping relation between different coordinate systems under cutter moving states and the way that acting force on rake face mapped to the only measurable workpiece coordinate system.Based on the analysis of the acting form of the load and the vector transformation law of each discrete element during the cutting process, for the cutting edge of ball end mill and the flank edge of the flat end mill, their cutting process is explained by oblique cutting mechanism due to their fixed or varying helical angle, and orthogonal cutting mechanism for the bottom edge of the flat end mill. The reciprocal effect of workpiece material parameters and the cutting parameters on the load of the discrete elemnt is investaged by the study on the inner mechanism of metal cutting process and the combination of mechanistic approach and unified mechanics of cutting approach. Based on the mechanical comprehensive analysis and the conbination of empirical relationship, the calculation algorithm between acting force on rake face and the input elements is established. The calculation method for the undeformed chip thickness in ball end milling is regulated, which takes the axial feed of cutting tool into consideration. In addition, this paper puts forward a constant coefficients calibration method in light of special requirements, which uses the single-disk average cutting force per revolution values. After all of these work been done, two different milling force prediction model are respectively established for ball end milling and flat end milling process.Eventually, a series of plane and sculptured surface machining experiments were carried out both on Inconel 718 and TC4 to verify the prediction accuracy of the model proposed in this paper. The milling process is simulated by a segment program and calculated by Matlab to predict the real-time load status of the cutter, and then, the predicted cutting force values are compared with the oness measured by dynamometer during the machining process. The good matchings of predicted and experimental results confirm the effectiveness of the presented method. On this basis and combined with the actual project's requirement, a series of suggestions about prediction accuracy improvement are proposed. All above lay a solid foundation for the further research, meanwhile has a certain practical significance for the practical processing and production.