Now more and more die-casting parts are used in mobile phones, and structural design of die-casting parts is the first step in die-casting work. Rationality of design and adaptability of process will affect smooth progress of follow-up work, such as selection of parting surface, opening of gate, layout of ejection mechanism, structure of mold and difficulty of manufacturing, law of solidification and shrinkage of alloy, accuracy of casting, defect types, etc., will all be based on pros and cons of die casting itself. Quality of structural design will directly affect production yield and cost. This article will introduce relevant requirements for structural design of die casting.

 

a. That is, requirements of die casting for 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 castings;
Design of die casting parts is an important part of die casting production technology. Following issues must be considered in design: selection of mold parting surface, opening of gate, selection of ejector pin position, shrinkage of castings, guarantee of dimensional accuracy of castings, prevention of internal defects of castings, related requirements of casting holes, related requirements of shrinkage and deformation, and size of machining allowance;

a. Correctly select material of die casting;
b. Reasonably determine dimensional accuracy of die castings;
c. Try to make wall thickness evenly distributed;
d. Add craft corners at each corner to avoid sharp corners

1) Try to eliminate internal undercut of casting to make mold structure simple.
2) Make wall thickness of casting as uniform as possible, use ribs to reduce wall thickness and reduce defects such as pores, shrinkage cavities, and deformation of casting.
3) Eliminate deep holes and deep cavities on castings as much as possible. Because small core is easy to bend and break, deep cavity is poorly filled and exhausted.
4) Designed castings should be easy to demold and core-pulling.
5) Uniformity of thickness is necessary.
6) Avoid sharp corners.
7) Pay attention to draft angle.
8) Pay attention to tolerance mark of product.
9) Neither too thick nor too thin.
10) Avoid dead angle chamfering (as little as possible).
11) Consider difficulty of post-processing.
12) Minimize voids in product.
13) Avoid peninsula-style partially weak shapes.
14) Too long forming holes, or too long forming columns are not suitable

a. Eliminate internal undercuts; simplify mold structure, temperature of die-casting mold is relatively high, internal structural parts are easy to expand and cause jamming;
b. Avoid or reduce core-pulling parts;
c. Avoid core crossing; a reasonable die casting structure can not only simplify structure of die casting mold, reduce manufacturing costs, but also improve quality of castings.

Wall thickness of die castings has a great influence on quality of castings. When wall of casting is too thin, metal welding is not good, which affects strength of casting, and at the same time brings difficulty in forming; if wall thickness is too large or seriously uneven, shrinkage and cracks are easy to occur. As wall thickness increases, defects such as pores and shrinkage porosity inside casting also increase, which also reduces strength of casting. Therefore, under condition of ensuring sufficient strength and rigidity of casting, its wall thickness should be reduced as much as possible, and wall thickness should be kept uniform. Wall thickness of die casting is generally 2.5 ~ 4mm, and parts with a wall thickness exceeding 6mm are not suitable for die casting. Recommended minimum wall thicknesses and normal wall thicknesses are given in table below.

 

Intersection of each part of die casting should have rounded corners (except for parting surface), so that flow of metal is smooth when filling, gas is easy to discharge, and cracks caused by sharp corners can be avoided. For die-casting parts that need to be electroplated and painted, rounded corners can be plated evenly and prevent paint accumulation at sharp corners.
Fillet radius R of die castings should generally not be less than 1 mm, and minimum fillet radius is 0.5 mm, see table below.

When designing die castings, there should be a structural slope on structure. When there is no structural slope, there must be a demoulding process slope where necessary. Direction of slope must be consistent with demoulding direction of casting. Recommended draft angles are shown in Table 4.

Function of reinforcing rib is to increase strength and rigidity of part after wall thickness is reduced, reduce shrinkage deformation of casting, and avoid deformation of workpiece when it is ejected from the mold. It is used to act as an auxiliary circuit (path of metal flow) when filling. ;
Thickness of die-casting ribs should be smaller than thickness of wall, generally 2/3~3/4 of thickness of place. Setting of ribs can increase strength and rigidity of parts, and at the same time improve manufacturability of die-casting. But pay attention to a few points:
① Distribution should be uniform and symmetrical;
② Root connected with casting should have rounded corners;
③ Avoid multi-rib crossing;
④ Width of rib should not exceed thickness of wall to which it is connected. When wall thickness is less than 1.5mm, reinforcing ribs should not be used;
⑤ Demoulding slope of reinforcing rib should be greater than casting slope allowed by inner cavity of casting.
Size of generally used reinforcing ribs is selected from table below:

Ratio of maximum wall thickness to minimum wall thickness should not be greater than 3:1 (wall thickness should be designed to be uniform to ensure sufficient strength and rigidity).

1) Casting hole
Minimum size and depth of holes that can be die-cast in die-casting parts are restricted by distribution position of cores that form holes in cavity. Thin cores tend to bend or break when withdrawn, so minimum hole size and depth are limited. Its depth should have a certain slope to facilitate core pulling.
Hole diameter and hole depth of die castings can be directly pressed out for holes with low requirements, as shown in table below.

For bottom holes for self-tapping screws in die-casting parts, see Table 6 for recommended bottom hole diameters.

2) Minimum distance from casting hole to edge
In order to ensure that casting has a good forming condition, a certain wall thickness should be maintained from casting hole to edge of casting, see figure below

 

b≥(1/4～1/3)t When t<4.5, b≥1.5mm
3) Rectangular holes and slots
Design of rectangular holes and grooves on die-casting parts is recommended in following table
 

1) If it is cast by die-casting, it should be embossed. Relief height is greater than 0.3m to adapt to characteristics of mold manufacturing.
2) Adopt new technology that is becoming popular at present: "transfer color film", which can transfer colorful text, logos, and pattern color film to surface of die-casting parts.
3) After die-casting casting, laser is used to print text, logos and patterns on the surface of casting, and very fine text can be printed. Example: Parallel grain (straight grain) is 0.7MM in height, 1MM in spacing, and 60.5 in angle. Outer diameter Φ34.5mm, a total of 104 teeth.