The main body of a metal mold is the part forming the mold cavity for forming the shape of the casting. The main structure is related to the casting size, the pouring position in the mold, the parting surface, and the alloy type. In the design, the cavity should be accurate in size, easy to set up the gating system and exhaust system, easy to cast out the mold, have enough strength and stiffness.

Depending on the complexity of the casting and the type of alloy, cores of different materials may be used. Generally casting thin-walled complex parts or a high-melting-point alloy (such as stainless steel, cast iron), the use of sand core, and in the casting of the fusible alloy (such as aluminum, magnesium alloy), most of the use of metalcore. Sand Cores and metal cores may also be used on the same casting.

In the design of the metal mold must be exhaust facilities, exhaust in the following ways:

• Exhaust the air by the clearance of the parting surface or the combination surface of the part in the cavity.

• Open an air vent. That is, in the parting surface or cavity parts of the combined surface, core or ejector surface to do exhaust slot.

• Set vent holes. The exhaust hole is usually arranged at the highest part of the metal mold.

• The exhaust plug is the common exhaust equipment of the metal type

The concave-convex part of the metal mold cavity will hinder the shrinkage of the casting, and there will be resistance when the casting comes out of the mold. In the design of ejector mechanism, the following points should be paid attention to prevent the top damage casting, that is, to prevent the casting from being deformed by the top or from ejector pits on the surface of the casting; to prevent the ejector Rod from being stuck, first of all, the clearance between ejector Rod and ejector rod hole should be appropriate. If the gap is too large easy to drill into the metal, too small may cause the phenomenon of stuck. Experience has shown that d 4 / DC4 level is preferable

When the metal type is closed, the positioning of the two halves is required to be accurate, and generally, two methods are used, namely, positioning of the positioning pin and positioning of the “stop”. For the top and bottom parting, when the parting surface is round, “stop” positioning can be adopted, while for the rectangular parting surface, positioning pins are mostly used. The locating pin should be located in the contour of the parting surface. When the size of the metal mould is large and its weight is large, it should be easy to open and close the mold.

From the analysis of the failure causes of the metal mold, it can be seen that the following requirements should be eliminated for the manufacture of the metal mold materials: good heat resistance and thermal conductivity, no deformation and no damage when repeatedly heated, and certain strength, toughness and wear resistance, good machinability.

Cast iron is the most commonly used material for metal molds. Its processing performance is good, cheap, the general factory can be made, and it is heat-resistant, wear-resistant, is a more suitable metal material. Carbon and low-alloy steels are used only when high requirements are required.

It has been noticed abroad that the aluminum alloy is used to make a metal mould, the surface of aluminum mould can be anodized, and a layer of oxide film composed of Al2O3 and Al2O3 H2o is obtained, which has a high melting point and hardness, heat resistance and wear resistance. It has been reported that this aluminum mold, if water-cooled, can be used not only to cast aluminum and copper but also to cast Ferrous.