Parameter Analysis of Vibroimpact Machines Dynamics With Variable Mass and Stiffness

Abstract

Vibroimpact machines operate under high repeated loadings. This poses certain requirements with regards to the strength and durability of their components that have to be met by the design. In order to predict the magnitude and time distribution of the acting forces the dynamics of the vibroimpact systems need to be studied. A two-body mechanical system is considered as a model of a shake-out machine designed for Azovmash company and used for extraction of steel casts from the mold. The first body is the suspended frame with the shake-out grid driven by an unbalanced vibrator, while the second one is the cast. Its sand mold is damaged at every impact with the shake-out grid, which results in the gradual loss of mass. The previously developed rigid body dynamics model is extended in order to account for the variable mass factor. Two approaches for the time evolution of the cast mass has been taken. The first one suggests that mass is a predefined linear or piecewise linear function of time. Alternatively the mass is treated as an unknown variable and was determined in the course of solving the equations of motion. A constitutive law for the mass reduction based on the energy dissipated at each impact is proposed. It has been shown that this model results in more adequate description of the shake-out process compared to the fixed-law mass evolution. In addition to the variable mass the influence of stiffness characteristics has been investigated. Nonlinear double springs with variable stiffness and length difference suspending the shake-out platform are considered. The survey on the combined effect of mass and stiffness parameters on the dynamics of the modelled shake-out machine allowed to determine the loads sustained by its structural elements and to make the rational design with the required strength. In particular, it has been shown how to detune the machine from resonance frequencies, in particular from the discovered dangerous subharmonic regimes due to variable mass and stiffness.