1. As the casting solidifies faster in the metal mold than in the sand mold, and the metal mold has no allowance, the casting stress generated in the metal mold casting is more inclined to crack than that in the sand mold casting, and it is also easy to produce defects such as insufficient pouring, cold insulation and white opening (for the casting). Usually:

(1) the following structural problems should be paid attention to in the prevention of cracks in metal mold casting:

A the requirements of uniform wall thickness, moderate transition and connection between walls, and appropriate rounded corners should be stricter than those of sand mold casting;

B. The vertically connected walls shall be changed to be obliquely connected;

C. The structurally weak parts shall be reinforced with ribs and boss to prevent casting cracks;

D. Protrusions such as boss, rib and flange that hinder free shrinkage of casting should be minimized;

The effect of reinforcing rib on casting shrinkage should also be considered when placing reinforcing rib on the casting.

(2) the following structural problems should be paid attention to in order to prevent metal mold casting from undercasting and cold isolation:

A the wall thickness of the casting should be moderate and not too thin, especially when the casting contour size is large;

B should avoid large horizontal plane, because it makes the metal liquid rise slowly during casting, and the surface in contact with air is large and easy to be oxidized. At the same time, due to the rapid heat dissipation of the metal mold, the metal liquid loses its fluidity quickly, which is likely to cause defects such as insufficient casting, cold insulation and slag inclusion.

The shape of C castings should be streamlined as far as possible to avoid sharp edges and sharp changes in connection and other structural shapes, so as to facilitate the flow of liquid metal.

2 in the design of complex metal mold castings, if the production process has greater difficulties, should not affect the conditions of use of the casting, as far as possible to make the shape of the casting simple, strong structure change, in order to remove the casting from the metal mold.

3 in the design of the basic structural units of metal mold casting and the selection of its parameters, it is usually necessary to pay attention to:

(1) due to the rapid heat dissipation of metal mold, the minimum wall thickness of metal mold casting should be larger than that of sand mold casting;

(2) the thickness of casting inner wall and inner rib should be generally 0.6 ~ 0.7 of the thickness of the outer wall connecting the casting; otherwise, as the inner wall (rib) cools slowly, it is easy to generate cracks at the junction of inner and outer walls during casting shrinkage;

(3) in order to prevent white holes in gray cast iron, except for technological measures, the wall thickness must not be too thin (some data point out that, when the wall thickness is more than 15mm, the corner of the casting with metal mold must be rounded, for aluminum alloy, magnesium alloy metal mold casting casting casting rounded Angle should not be less than 3 ~ 4m;

(4) as there is no sex metal mold and core, and take out for ease of casting, metal mold casting casting foundry slope should be the appropriate larger than that of sand mold casting, thrown commonly 30% ~ 30%, it should be pointed out: casting Angle size except associated with types of alloy, the height of the wall, also related to the position of the casting surface, and in the casting cooling contraction with has a tendency to leave the surface of the metal mold casting surface can be smaller slope design, and when the casting contraction tends to pressure on the metal mold casting surface should be given a larger Angle.