Design difficulties of molds for large-sized wheel hubs over 20 inches

Design difficulties of molds for large-sized wheel hubs over 20 inches
The weight of a single 20-22 inch wheel hub is 12-16kg, and the mold needs to simultaneously address rigidity, thermal balance, and machine matching.
The clamping force and pressure caused by the projected area
For every 2 inches increase in hub diameter, the projected area of the mold increases by approximately 20%. When the clamping force is insufficient, the parting surface will open and produce burrs.
The projected area of the mold for a 20 inch wheel hub is usually 0.25-0.3 square meters. According to the required locking force per unit area, the tonnage of the machine needs to be adjusted accordingly.
When selecting a machine, one should not only consider the tonnage, but also the size of the pressure plate and the distance between the pull rods. The mold cannot fit in, and no matter how large the tonnage is, it cannot be produced.
Template rigidity is the first hurdle of large size
After the diameter of the mold exceeds 550mm, the middle of the template is prone to elastic deflection. If the deflection exceeds 0.05mm, there will be a unilateral deviation in the thickness of the wheel rim wall.
The common solution is to thicken the template and arrange cross shaped bars. When the thickness of the template is increased from 80mm to 120mm, the deflection can be reduced by about 40%.
Xinfeng Mold will perform finite element stiffness verification on large-sized wheel hub molds, controlling the maximum deflection within 0.03mm before proceeding with processing.
Establishing thermal equilibrium is more difficult
A larger diameter means a longer circumference of the wheel rim, increasing the flow of aluminum liquid from the sprue to the far end. The temperature difference between the beginning and end can reach 40-60 ℃.
Waterways must be divided into zones. Wheels larger than 20 inches usually require 8-12 independent circuits to compress the surface temperature difference of the mold cavity to within 15 ℃.
Excessive partitioning also brings debugging complexity. It is recommended to install independent flow meters in each area and label the target flow rate on the nameplate to reduce on-site trial and error.
Lifting and changeover issues caused by weight
The weight of a single set of large-sized molds often reaches 6-10 tons, exceeding the normal driving capacity. Replacement requires specialized lifting equipment and floor load-bearing calculation.
When the mold is flipped, the center of gravity deviates significantly, and an unreasonable design of the lifting point can lead to tilting. Suggest setting up 4 symmetrical lifting ears and marking the center of gravity on the drawing.
The changeover time will also be extended. The replacement of large-sized molds usually takes 3-5 hours, which is twice as long as conventional sizes.
Details of machine adaptation
The capacity of the insulation furnace should be matched. After the weight of a single piece increases, the turnover of aluminum liquid in the furnace accelerates, and the fluctuation of liquid level will affect the filling pressure.
The diameter of the liquid lifting tube needs to be increased accordingly, otherwise the filling time will be too long. For every 10mm increase in pipe diameter, the filling flow rate increases by approximately 20%.
The stroke of the pressure plate and the height of the mold should have sufficient margin. The clamping stroke of large-sized molds is longer, and insufficient machine stroke will result in the inability to open the mold.
Common Misconceptions
The first misconception is to enlarge the design based on the experience of small-sized molds. Geometric similarity does not equal thermal similarity, and the cooling scheme must be recalculated.
The second misconception is to ignore transportation restrictions. Molds with a diameter exceeding 2.4 meters cannot be loaded in regular containers and require a frame box.
Misconception three is equating large size with high rigidity. The larger the size, the lower the stiffness per unit weight, making the arrangement of reinforcing bars more critical.
Frequently Asked Questions
Q: How much does a 20 inch wheel hub mold weigh?
Answer: Commonly 6-10 tons, depending on the number of chambers and structure.
Question: How much is the deflection control of the template?
Answer: It is recommended to be within 0.03mm, and exceeding 0.05mm will affect the wall thickness.
Q: How many sets of waterways are needed?
Answer: Usually 8-12 independent circuits are available for sizes over 20 inches.
Q: How long does it take to change the model?
Answer: Large molds often take 3-5 hours.
Q: Can regular containers be loaded?
Answer: If the diameter exceeds 2.4 meters, a frame box or an open top box is required.
Q: How to choose the tonnage of the machine?
Answer: Calculated based on the projected area and unit locking force, leaving a 20% margin.
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