14 major principles of die casting structural design
- Part wall thickness
✅ Appropriate wall thickness —(1) Appropriate wall thickness of parts
The wall thickness of the die-casting part is too thin, making it difficult to fill during die-casting and prone to poor filling. The wall thickness of die-casting parts is too thick and internal parts are prone to appear.
The grains are coarse, causing defects such as shrinkage cavities and pores, and at the same time, depressions occur on the outer surface, which reduces the mechanical properties of the die casting. Thin-walled parts have good density, which relatively improves the strength and pressure resistance of castings. In addition, if the wall thickness is too thick, it will increase the weight of the parts and waste too much metal, resulting in increased costs. Generally speaking, the wall thickness of die casting parts shouldn't exceed 5mm.
If the local area of the part is too thick, a hollow design should be used to make the overall wall thickness of the part uniform. This won't only avoid defects such as shrinkage holes in the wall thickness area, but also reduce the weight of the part, killing two birds with one stone.
💡(2) The wall thickness of the parts is uniform, and there is an even transition where the wall thickness changes.
📏 The wall thickness of each section of the die casting should be uniform or very close to uniform. If it can't be uniform due to functional or other reasons, the ratio of wall thickness to wall thickness shouldn't exceed 3 times. Consideration should be given to increasing the slope to slow down drastic changes in wall thickness, otherwise it will affect the flow of molten metal and produce poor flow channels or wrinkle defects. In addition, due to the different solidification times of thicker and thinner walls, uneven stress will be exerted on the product, which can easily cause cracks and deformation of the parts. If there is a sharp change in wall thickness in the part, consideration should be given to increasing the slope to slow down the change and make the transition uniform.
- Minimum hole of die casting
🔧 Too small holes / deep holes → cast positioning marks then machine (adds cost). Must consider distances between holes, grooves, edges to ensure die-casting mold strength against high-temperature metal impact & thermal stress.
- Avoid excessive thinning of parts of the die-casting mold
⚠️ Thin mold sections = low strength → easily deformed, bent, broken at high temperatures.
- Design of reinforced ribs
🎯 Functions
One is to enhance the strength of the product and prevent parts from deforming. (The way to improve strength isn't to simply increase the wall thickness). The second is to assist the flow channel of molten metal.
✔️ (1) Reinforcement rib size
Stiffener design requirements
- The thickness of the root of the reinforcing rib is generally not greater than the thickness of the wall here.
- The draft angle of the reinforcing rib is 1°∼3°.
- Fillets should be added to the roots of the reinforcing ribs to avoid drastic changes in the cross-section of the part, while assisting the flow of molten metal, reducing stress concentration on the part, and improving the strength of the part. The fillet radius is generally close to the wall thickness of the part.
- The height of the reinforcing rib shall not exceed 5 times the thickness of the reinforcing rib.
- Draft angle
🔹 The three commonly used die-casting alloy materials, aluminum alloy, zinc alloy and magnesium alloy, have different adhesion to the die-casting mold, and the demoulding slopes are:
- The adhesion between aluminum alloy and die-casting mold is the largest, and the draft of the inner surface is generally 1°.
- The adhesion between magnesium alloy and die-casting mold is slightly less than that of aluminum alloy, and the inner surface demoulding slope is generally 0.75°.
- The adhesion between the zinc alloy and the die-casting mold is the smallest, and the draft angle of the inner surface is generally 0.5°.
The draft of the outer surface of the die-casting part can be twice the draft of the inner surface to ensure that the part remains on the punch side when demoulded.
- Rounded corner design
🚫
(1) Avoid external sharp corners
Not only are the external sharp corners prone to poor filling, non-dense metal structure, and low strength because they are too thin, but sharp corners can also easily cause safety problems.
(2) Internal rounded corners design to avoid internal sharp corners
The fillet at the wall-to-wall connection has a great effect on the performance and quality of the part and the life of the mold:
- Assist the flow of molten metal, reduce eddy currents or turbulence, improve filling performance, and facilitate gas discharge.
- Sharp corners can easily cause stress concentration in die castings and lead to crack defects. Even if there is no cracking, stress concentration will cause the part to fail under the influence of force.
The rounded corners of die castings are designed to avoid stress concentration, thereby improving the strength of die castings.
- Improve the service life of die-casting molds.
- When die castings need to be electroplated, rounded corners can obtain uniform coating and prevent sharp corner deposition.
The size of the inner fillet is generally determined by the wall thickness of the part, and the size of the outer fillet radius is the wall thickness of the part plus the inner fillet radius. The fillet radius can't be too large. If the fillet radius is too large and the local area of the part is too thick, defects such as shrinkage cavities, pores, and depressions on the outer surface of the part may easily occur.
- Design of pillars
(1) Avoid the pillars being too close to the wall or the pillars being too close (resulting in thin mold walls or thick product walls)
The design of pillars needs to follow the principles of uniform wall thickness and avoiding excessive local wall thickness.
(2) Reduce the height of the pillars as much as possible
The height of the pillars can't be too high, otherwise the strength of the pillars will be low and it will be difficult to fill.
(3) Add reinforcements around the pillars
Adding reinforcing ribs around the pillars can improve the strength of the pillars and assist the filling of the pillars. The design of isolated pillars should be avoided.
(4) Redesign the inclined pillar to simplify the mold structure
When the pillars are inclined, reasonable design optimization can simplify the mold structure and reduce mold costs.
- Characters
🔠 (1) It is better if the characters protrude from the surface of the part
In this case, the mold processing cost is relatively low, and the mold maintenance cost is low.
(2) Relevant dimensions of characters
The size of the characters needs to be able to ensure that the characters can be filled smoothly. The minimum character width W is 0.25mm, the height H is 0.25-0.5mm, and the demoulding slope θ is 10°, as shown in the figure below. At the same time, characters are generally not placed on the side walls. This will cause the characters to be buckled and unable to be demoulded.
- Thread
🧵 (1) Avoid full-thread design for external threads;
(2) Internal threads shouldn't be cast directly;
- Provide convenience for removing flash and gates
✂️ (1) Avoid sharp angles between the part wall and the parting surface
(2) Simplify parts and avoid complex parting surface shapes (making flash removal difficult)
(3) Avoid strict flash and gate removal requirements, reduce processes and reduce costs.
- Tolerance requirements for die castings
🎯 (1) Dimensional tolerance accuracy of die castings
The dimensional tolerance accuracy of die castings is affected by the parting surface and core pulling mechanism.
(2) Minimize the tolerance requirements of die castings while meeting the performance of the parts.
Strict part tolerances will inevitably mean strict mold tolerances, and mold costs will inevitably increase.
Die Casting Mold life can be shortened by excessive tolerance requirements.
In order to maintain tight part dimensional tolerances, die casting molds must be regularly maintained and replaced.
Using more die-cast mold parts and high-frequency die-cast mold dimensional inspection to ensure tight tolerances on parts increases part costs.
Higher defective rate of die castings.
(3) To avoid mechanical processing, try to increase tolerance requirements
Avoiding machining reduces part costs.
(4) Reasonably select the parting surface to improve the dimensional accuracy of important parts
- If concentricity of D1 and D2 is important, select CC as parting line
- If concentricity of D1 and D3 is important, select BB as the parting line
- If you need to ensure that the diameter of D1 is consistent at the left or right end, select AA as the parting line
- Simplify the mold structure and reduce mold costs
🏗️ (1) Avoid undercuts inside parts
Internal undercuts are obtained through side core pulling mechanisms or secondary processing, which will significantly increase the cost of the mold or parts.
Reasonable part design to avoid internal undercuts can reduce the cost of molds or parts
(2) Avoid undercutting on the outside of the part
(3) Avoid obstruction of the core pulling mechanism
(4) Avoid rounded corners on the die-casting parting surface
The parting surface has rounded corners, the die-casting mold is complex, and the mold processing is difficult. The mold strength at the rounded corners is low and the service life is reduced.
(5) Reasonably select the parting surface and simplify the mold structure
The selection of the parting surface should make the mold structure simple, the mold easy to process, and the mold cost low.
If AA is selected as the parting surface, both D1 and D3 need to be core-pulled. The mold structure is complex and the mold cost is high.
If BB or CC is selected as the parting surface, the mold structure will be simple and the mold cost will be low.
- Mechanical processing
⚙️ Avoid machining when possible
Machining of die castings should be avoided as much as possible because:
- Die-casting parts can achieve high dimensional accuracy and appearance surface quality. When designing products, loose dimensional and surface quality requirements can be put forward for die-casting parts to avoid mechanical processing.
- The surface layer of die castings is solid and dense, with high mechanical properties. Mechanical processing may damage the surface dense layer of die castings.
- Sometimes there are pores inside die-casting parts. The pores are exposed after machining, which will affect the application of the parts.
- Machining can significantly increase part costs.
- Use die castings to simplify product structure and reduce product costs
💰
(1) Use die castings instead of machined parts
Taking advantage of the fact that the cost of the die-casting process is lower than that of the machining process, the use of die-casting parts instead of machining parts can significantly reduce the cost of parts under the premise of meeting the strength and dimensional accuracy of the parts.
(2) Use die castings to reduce the number of parts and simplify the product structure
- Use die-casting parts instead of plastic parts
Utilizing the anti-electromagnetic radiation properties of die castings
- Use die castings instead of sheet metal parts and machined parts