Rheological casting (die casting) is a method of preparing semi-solid slurry from liquid metal and then die casting. The main equipment consists of rheological slurry continuous preparation machine and die casting machine.
The so-called thixotropic casting (die-casting) is a method that the slurry from the slurry continuous preparation device is not directly die-cast, but is first made into ingots, which are melted into a certain size and can be sold as commodities. When users use them, they are first heated and sent to a die casting machine for die casting. The whole system consists of die casting machine, induction furnace and corundum ingot softness instrument.
During the period of 1970, MIT accidentally discovered the possibility of using semi-solidified metal slurry for die casting while studying the fluidity of partially solidified alloys. The main solid particles of this slurry contain coarsened dendrites or spherical agglomerates. They are not connected with each other, and the volume ratio of solid phase can be as high as 80% when cooled in liquid matrix. These solid particles can avoid contact with each other in any long stirring time, thus obtaining semi-solid paste slurry with rheological and thixotropy (its viscosity decreases with the increase of shear rate or time and is reversible). In recent 30 years, reports on patented technologies of rheocasting and thixocasting die-casting have appeared continuously.
Because secondary heating consumes energy, the process is complex, and there are not many kinds of thixotropic metal materials. Therefore, the industrial application of semi-solid metal casting is limited. In recent years, researchers from all over the world have applied the principle of plastic injection molding to the solid metal casting process when studying the new semi-solid metal die casting technology, and formed a new rheological injection molding process (1 theo. Molding) and thixotropic injection molding (1 ~ Ixomolding), integrating the preparation, transportation and molding of semi-solid metal slurry. The storage, transportation and forming control of semi-solid metal slurry have been well solved, which shows a bright prospect for a large number of industrial applications of semi-solid metal casting technology.
(1) Thixotropic Injection Molding
The thixomolding process of semi-solid metal ("rhixomoulding") proposed by Fhixomat Company of the United States adopts the method and principle of plastic injection molding. Magnesium alloy can be transformed into semi-solid slurry with solid content above 60% by feeder, driving and spraying system, shearing screw and heating, and the translation speed of the shearing screw is 380 CRA/ s.
The forming process is as follows: magnesium alloy raw materials made into granules, wastes or fine blocks are added from a hopper; A certain amount of semi-solid metal liquid accumulates at the front end of the spiral; Finally, under the action of the shot cylinder, the semi-solid molten metal is injected into the mold for molding.
(2) Rheological injection molding
Wang et al. of Honel University. ) the first combination sSM. Rheological casting forms a semi-solid metal.
This is a new semi-solid metal forming process called rheoforming.
The working principle of rheological injection molding is that liquid metal enters the mixing drum from the melting and holding furnace by gravity, and then is cooled into semi-solid under the stirring action of the screw (the screw has no downward thrust). After a certain amount of semi-solid metal liquid is accumulated, it is injected and molded by the injection device. All the above processes are carried out under protective gas.
Temperature control accuracy is one of the key factors in semi-solid metal forming.