6. Detailed introduction of permanent mold casting process -3
After the casting process drawing, the metal mold design can be carried out. The design content mainly includes determining the structure, size, core, exhaust system, and ejector mechanism of the metal mould. The designed metal mold should be simple in structure, convenient in processing, reasonable in material selection, safe and reliable
1. Metal-type structural form
The structure of the metal type depends on the shape and size of the casting, the number of parting faces, the type of alloy, and the production volume. By the typed face position, the metal structure has the following forms: 1. The overall metal type, the shape-free non-dissonant face, the structure is simple, but it is only suitable for simple shape, non-dissonant face castings; Horizontal parting metal type, which is suitable for thin-walled wheel-shaped castings. 3. Vertical parting metal type, this kind of metal type is easy to open the gating port and exhaust system, open and close type is convenient, easy to achieve mechanized production; Integrated parting metal type: It consists of two or more parting faces, or even live blocks, and is generally used in the production of complex castings. Easy to operate, widely used in production.
The structure of metal mold depends on the casting shape, size, number of parting surfaces, alloy type, and production batch. Depending on where the parting surface is, the metal structure can take the following forms:
- The whole metal mold has no parting surface and simple structure, but it is only suitable for the castings with the simple shape and no parting surface
- Horizontal Parting Metal Mold for thin wall wheel castings.
- Vertical parting metal mould, which is easy to open and close, and easy to realize mechanized production; it is mainly used to produce simple small castings
- Integrated parting metal mold: it consists of two or more parting surfaces, even live blocks, and is commonly used in the production of complex castings. Easy to operate, widely used in production.
2. Metal Body design
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.
3. Metal core design
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.
4. Metal Exhaust
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
5. Ejection casting mechanism design
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
6. The positioning, guiding and locking mechanism of the metal type
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.
7. Choice of metal profiles
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.