Most of the common structures on parts are obtained by forging (or casting) and machining, so they are called process structures. Knowing the common process structure on a part is the basis for learning a part drawing.
Forging process structure on parts
1, forged rounded corners
In order to facilitate the casting shape, it is prevented from falling sand at the corner of the sand mold when the mold is lifted from the sand mold, and the corner is destroyed when casting, avoiding the defects of forging, looseness and shrinkage at the corner of the casting, so the intersection of adjacent surfaces on the casting The place should be rounded. For compression molded parts, the rounded corners ensure that the material fills the stamp and facilitates the removal of the part from the stamp.
Forged corner radius is generally 0.2-0.4 times the wall thickness, which can be found from relevant standards. The fillet radius of the same casting should be as close as possible or close.
2, the draft angle
In the modeling, in order to facilitate the wooden mold to be pulled out from the sand mold, a certain inclination is often designed on the inner and outer walls of the casting along the direction of the mold, which is called the draft angle (or forging slope). The size of the draft is generally 1:100-1:20. When expressed by angle, the hand-shaped wood looks like 1°-3°, the metal looks like 1°-2°, and the structural shape looks like 0.5°-1 °.
Because there are forged rounded corners at the intersection of the casting surfaces, the intersection line of the surface becomes less obvious. In order to distinguish different surfaces when looking at the picture, the intersection line in the figure still needs to be drawn. This kind of intersection line is usually called transition. line. The transition line is drawn in the same way as the intersecting line without the fillet.
3, casting wall thickness
In order to ensure the forging quality of the castings, it is avoided that the crystallization rate is different due to uneven wall thickness, loosening of the structure outside the wall thickness and shrinkage of the holes, cracks occurring at the thin and thick phases, etc., and the wall thickness of the casting should be uniform or gradually changed to prevent sudden twisting of the wall. Thick and local hypertrophy. The wall thickness change should not be too large, so the transition slope can be set at the intersection of the two walls. The wall thickness may not be noted in the figure, but is written in the technical request.
In order to facilitate molding, sculpt, sand cleaning, removal of the riser and machining, the shape of the casting should be as simple as possible, the shape should be as straight as possible, and the inner wall should reduce the concave and convex structure. If the thickness of the casting is too thick, the forging defects such as cracks and shrinkage cavities may occur, but the thickness of the casting is too thin and the strength of the casting is insufficient. In order to prevent the influence of the thickness on the strength, the reinforcing rib can be used to compensate.