Abstract: By means of system identification, three types of mechanical models of sand molds at room temperature were developed in this paper:(1)cohesive model σ=K0+K1b; (2)adhesive model σ=K”0+K”1b+K”2b,(K =K”1/K”2＜10）; (3)mixed model σ=K”0+K”1b+K”2b,( K =K”1/K” ≥10).The precision of the models was within 0.2.The conclusions of system identification of models are as follows: (1) Silica bonded sand molds can be expressed as cohesive models, and the most effective method to improve the mechanical properties of them is the modification of the binders. (2) Clay-bonded sand molds can be expressed as mixed models, and the most effective method to improve the mechanical properties of them is in conjunction with other binders. (3) Resin-bonded sand molds can be expressed as adhesive models, and the most effective method to improve the mechanical properties of them is to increase the adhesive force between resin and sand grain .In addition, the addition of silage increased the adhesive force between sand grain and resin ,changed the models of sand molds from adhesive ones to cohesive and mixed ones ,and as a result, the mechanical properties of molds were greatly improved.

Key words: 力学模型, 砂型, 系统辨识, TIG welding, Atomic tracer method, Optical reflection principle, weld pool flow behavior