Precautions for designing die casting parts

If you want to master the precautions for designing die casting parts, you need to start from the design basis of die casting, which is easier to understand.

The design of die castings involves four aspects

a. That is, the requirements of die casting for the shape and structure of parts;

b. Process performance of die castings;

c. Dimensional accuracy and surface requirements of die castings; d. Determination of parting surface of die casting;

The part design of die casting is an important part of die casting production technology. The following problems must be considered in the design: the selection of die parting surface, the opening of gate, the selection of ejector position, the shrinkage of casting, the guarantee of dimensional accuracy of casting, the prevention of internal defects of casting, the relevant requirements of casting hole, the relevant requirements of shrinkage deformation and the size of machining allowance;

The design principles of die castings

a. Correctly select the materials of die castings,

b. reasonably determine the dimensional accuracy of die castings;

c. Try to make the wall thickness evenly distributed;

d. Add process corners at each corner to avoid sharp corners.

 

Classification of die castings

According to the use requirements, it can be divided into two categories. One is the parts with large load or high relative movement speed. The inspection items include size, surface quality, chemical composition and mechanical properties (tensile strength, elongation and hardness); The other is other parts. The inspection items include size, surface quality and chemical composition. When designing die-casting parts, it should also be noted that the parts should meet the process requirements of die-casting. The process of die casting is considered from the position of parting surface, the position of top push rod, the relevant requirements of casting hole, the relevant requirements of shrinkage deformation and the size of machining allowance. Reasonably determining the parting surface of the die-casting surface can not only simplify the structure of the die-casting mold, but also ensure the quality of the casting. Requirements for die casting parts design.

Design requirements for die castings

Shape and structure requirements of die castings

a. eliminate internal side concave;

b. Avoid or reduce core pulling parts;

c. Avoid core cross; Reasonable die casting structure can not only simplify the structure of die casting mold, reduce manufacturing cost, but also improve casting quality,

Wall thickness requirements for casting design

the wall thickness of die castings (usually called wall thickness) is a factor of special significance in the die casting process. The wall thickness is closely related to the whole process specification, such as the calculation of filling time, the selection of inner gate speed, the calculation of solidification time, the analysis of mold temperature gradient, the role of pressure (final specific pressure), the length of mold retention time Casting ejection temperature and operation efficiency;

a. The mechanical properties of die castings will be significantly reduced if the wall thickness of parts is too thick. The compactness of thin-walled castings is good, which relatively improves the strength and pressure resistance of castings;

b. The wall thickness of the casting shall not be too thin, which will lead to poor filling of liquid aluminum, difficult forming, poor fusion of aluminum alloy, cold insulation and other defects on the surface of the casting, and bring difficulties to the die-casting process; With the increase of wall thickness, the defects such as internal air holes and shrinkage cavities of die castings increase. Therefore, on the premise of ensuring that the castings have sufficient strength and stiffness, the wall thickness of the castings should be reduced as much as possible and the thickness of the section should be uniform. In order to avoid shrinkage porosity and other defects, the thickness of the thick wall of the castings should be reduced (material reduction) and ribs should be added; For large-area flat plate thick wall castings, ribs are set to reduce the wall thickness of the castings; According to the surface area of die castings, the reasonable wall thickness of aluminum alloy die castings is as follows: die casting surface area / mm2 wall thickness s / mm ≤ 25 1.0 ~ 3.0 ＞ 25 ~ 100 1.5 ~ 4.5 ＞ 100 ~ 400 2.5 ~ 5.0 ＞ 400 3.5 ~ 6.0

Requirements for design reinforcement of castings

The function of the rib is to improve the strength and rigidity of the parts after the wall thickness is thinned, prevent the shrinkage deformation of the casting, and avoid the deformation of the workpiece when it is ejected from the mold. During filling, it is used to act as an auxiliary circuit (metal flow path). The thickness of the rib of the die casting part shall be less than the thickness of the wall, generally 2 / 3 ~ 3 / 4 of the thickness of the part;

Fillet requirements for casting design

All wall to wall connections on die castings, regardless of right angles, acute angles or obtuse angles, the root of blind holes and grooves, shall be designed as rounded corners. Rounded corners shall not be used for connection only when it is expected to be determined as the parting surface. Other parts must generally be rounded corners. The rounded corners shall not be too large or too small. Too small die castings are prone to cracks and too large die castings are prone to loose shrinkage holes, Generally, the fillet of die casting parts is taken as: 1 / 2 wall thickness ≤ R ≤ wall thickness; The function of fillet is to help metal flow and reduce eddy current or turbulence; Avoid cracking due to stress concentration caused by rounded corners on parts; When parts are to be electroplated or coated, the fillet can obtain uniform coating to prevent deposition at sharp corners; It can prolong the service life of the die casting die, and will not cause angle collapse or cracking due to the existence of sharp corners in the die cavity;

Casting slope requirements for die casting design

The function of inclination is to reduce the friction between the casting and the mold cavity, and it is easy to take out the casting; Ensure that the casting surface is not damaged; To prolong the service life of die casting die, the minimum casting inclination of aluminum alloy die castings is generally as follows: the minimum casting inclination of aluminum alloy die castings is 1 ° 1 ° 30 ′ 2 ° on the outer surface and the core hole on the inner surface (one side)