Comparing the advantages and limitations of sand casting, permanent mold casting and die casting; Choose suitable molds for typical castings and explain your considerations.
valve with small-medium size and intricate cavity, 300 pieces: casting process? Why?（中小型阀门，复杂的腔体，300件，该选用哪种工艺啊？沙箱，永久模型还是压铸哇？）