Knowledge integration of die casting design

Update:01-07-2019
Summary:

Core Abstract: How to design die-cast parts? First, the […]

Core Abstract: How to design die-cast parts? First, the design of die casting involves four aspects: a, that is, the requirements of pressure casting on the shape and structure of the part; b, the process performance of the die casting; c, the dimensional accuracy and surface requirements of the die casting; d, the die casting parting The determination of the surface; the design of the part of the die casting is an important part of the die casting production technology. The following problems must be considered in the design: the selection of the mold parting surface, the opening of the gate, the selection of the position of the ram, the shrinkage of the casting, the size of the casting Accuracy guarantee, prevention of internal defects of castings, related requirements of casting holes, relevant requirements for shrinkage deformation, and the size of machining allowance.
How to design die-cast parts?

First, the design of die casting involves four aspects:

a, that is, the requirements of the shape and structure of the part by pressure casting; b, the process performance of the die casting; c, the dimensional accuracy and surface requirements of the die casting; d, the determination of the parting surface of the die casting; the part design of the die casting is the die casting production technology In the important part of the design, the following problems must be considered in design: the selection of the mold parting surface, the opening of the gate, the selection of the position of the ejector, the shrinkage of the casting, the dimensional accuracy of the casting, the prevention of the internal defects of the casting, and the relevant Requirements, requirements for shrinkage deformation, and the size of the machining allowance.

Second, the design principles of die castings are:

a, correctly select the material of the die casting;

b. Reasonably determine the dimensional accuracy of the die casting;

c. Try to make the wall thickness evenly distributed;

d. Increase the corner of the craft at each corner to avoid sharp corners.

Third, the classification of die casting:

According to the requirements of use can be divided into two categories, one type of parts subjected to large loads or parts with higher relative motion speed, the items examined have dimensions, surface quality, chemical composition, mechanical properties (tensile strength, elongation) ,hardness);

The other category is other parts, and the items to be inspected are size, surface quality and chemical composition.

When designing die castings, it should also be noted that the parts should meet the process requirements of die casting. The processability of die casting is considered from the position of the parting surface, the position of the top pusher, the relevant requirements of the casting hole, the relevant requirements of the shrinkage deformation, and the size of the machining allowance. Reasonable determination of the parting surface of the die-casting surface not only simplifies the die-casting structure, but also ensures the quality of the casting.

Fourth, the design requirements of die castings:

(1) The shape and structure requirements of the die-casting parts: a. Eliminate the internal undercut; b, avoid or reduce the core-pulling part; c, avoid core crossover; reasonable die-casting structure can not only simplify the die-casting structure, but also reduce the manufacturing cost. It also improves the quality of castings.

(2) Wall thickness requirements for casting design: The wall thickness of the die casting (usually called wall thickness) is a special factor in the die casting process. The wall thickness is closely related to the whole process specification, such as the calculation of filling time and the gate. Speed ​​selection, solidification time calculation, mold temperature gradient analysis, pressure (final specific pressure), mold retention time, casting temperature and operating efficiency; The mechanical properties of the parts are obviously reduced, the thin-walled castings have good compactness, and the strength and pressure resistance of the castings are relatively improved. b. The wall thickness of the castings should not be too thin. Too thin will cause poor filling of the aluminum liquid, and the molding is difficult, so that the aluminum alloy is not welded. Well, the surface of the casting is prone to defects such as cold insulation, and it brings difficulties to the die-casting process; as the thickness of the die-casting part increases, the defects such as internal pores and shrinkage cavities increase, so that the casting has sufficient strength and rigidity, The wall thickness of the casting should be minimized and the thickness of the section should be kept uniform. In order to avoid defects such as shrinkage, the thick wall of the casting should be thickened (reduced) and the ribs should be increased; for large areas Plate type thick-wall castings, set ribs to reduce the wall thickness of castings; According to the surface area of ​​die-casting parts, the reasonable wall thickness of aluminum alloy die-casting parts is as follows: Surface area of ​​die-casting parts/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.

(3) Requirements for casting design ribs:

The role of the rib is to reduce the strength and rigidity of the part after the wall thickness is reduced, to prevent the shrinkage deformation of the casting, and to prevent deformation when the workpiece is ejected from the mold, and to act as an auxiliary circuit (passage of metal flow) during filling. The thickness of the die-casting rib should be less than the thickness of the wall where it is located, generally taking 2/3~3/4 of the thickness of the place.

(4) Fillet requirements for casting design:

Where the wall-to-wall connection of the die-casting part, whether it is a right angle, an acute angle or an obtuse angle, a blind hole and a root of the groove, it should be designed to be rounded, and the rounded connection is not used only when it is expected to be determined as a parting surface. The rest of the parts must be rounded, the rounded corners should not be too large or too small, too small die castings are prone to cracks, too large and easy to produce loose shrinkage holes, die castings are generally taken: 1/2 wall thickness ≤ R ≤ wall Thick; the role of rounding is to help the flow of metal, reduce eddy currents or turbulence; avoid stress concentration on the part due to the presence of rounded corners, causing cracking; when parts are to be plated or coated, rounded corners are available Uniform coating prevents deposits at sharp corners; it can extend the service life of die-casting molds without causing cornering or cracking due to the presence of sharp corners of the mold cavity.

(5) Casting slope requirements for die casting design:

The slope function is to reduce the friction between the casting and the mold cavity, easy to take out the casting; to ensure that the surface of the casting is not pulled; to extend the service life of the die-casting mold, the minimum casting inclination of the aluminum alloy die-casting is as follows: the minimum casting inclination of the aluminum alloy die-casting The inner surface of the outer surface has a core hole (single side) of 1° 1°30′2°.

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