What are the special requirements for molds for casting spiral wheel hubs

What are the special requirements for molds for casting spiral wheel hubs
The cast wheel hub is first made into a blank by low-pressure casting, and then the wheel rim is heated and spun to reduce thickness. The mold should ensure the wall thickness margin and tissue density of the blank.
The process logic of casting and spinning
Casting and spinning are combined. The spokes maintain their cast shape, while the wheel rims are thinned by spinning, resulting in a weight reduction of up to 10% -15%.
The wall thickness of the rough wheel rim should be thicker than that of the finished product, leaving room for spin thinning. The thinning rate is usually between 30% and 45%.
The thinning rate is too high, which makes it easy to crack during spinning. Too low, the weight loss effect is not significant, but the cost has increased.
Consistency requirements for blank wall thickness
Spinning is sensitive to wall thickness uniformity. If the deviation of the blank wall thickness exceeds 0.5mm, ellipses or uneven wall thickness may appear after spinning.
The wheel rim of the mold requires higher dimensional accuracy, and it is recommended to control it within ± 0.3mm.
Cooling should be uniform. The local temperature of the wheel rim is low, and the plasticity is insufficient during spinning, which makes it easy to wrinkle.
Requirements for organizational density
Spinning will enlarge internal defects. The shrinkage of the blank may expand into cracks after spinning.
The X-ray judgment of the wheel rim should not be lower than level 1-2. The scrap rate of spinning has significantly increased for blanks with insufficient density.
Xinfeng Mold will strengthen the shrinkage design of the wheel rim on the casting wheel hub mold, guiding the hot spot towards the gate direction.
Coordination between mold structure and spinning equipment
The positioning reference of the blank should be consistent with the spinning fixture. The benchmark is not uniform, and the wall thickness deviates after spinning.
The mold needs to reserve a spinning clamping section. The length of the clamping section is usually 20-40mm, and being too long will waste materials.
The demolding slope of the blank should be small. Excessive slope can cause slipping during spinning and clamping.
The impact of heat treatment
T6 treatment is commonly used for casting rotary parts. The deformation after spinning and heat treatment overlap, making size control more difficult.
The solid solution temperature and time should match the microstructure after spinning. Excessive temperature and coarse grain size; Too low, insufficient reinforcement.
Pre compensation should consider both spinning and heat treatment, and cannot be reserved solely based on casting experience.
Cost and Applicability
The equipment investment in the rotary casting production line is higher than that in pure casting. The investment in spinning machines, heating furnaces, and fixtures is often in the tens of millions.
Suitable for mid to high end wheel types with an annual output of over 200000 pieces. When the batch is insufficient, it is difficult to amortize the investment in molds and equipment.
Small batch wheel types in the modification market are more practical through pure casting or forging.
Raw material inspection before spinning
Before spinning, the wall thickness and roundness of the blank should be randomly inspected. The risk of ovality increases significantly after spinning for blanks with a wall thickness deviation exceeding 0.5mm.
Practical tips
The blank before spinning needs to undergo ultrasonic thickness measurement, with a focus on measuring the three sections of the wheel rim. If the wall thickness range exceeds 0.6mm, it will not be put into production.
After spinning, the wheel rims should undergo roundness inspection, and any parts that exceed the tolerance should not be processed by the machine to avoid wasting subsequent working hours.
The inner side of the wheel rim for casting and spinning blanks should have sufficient machining allowance, and uneven wall thickness after spinning can be corrected by machining.
Frequently Asked Questions
Question: How much weight can be reduced by rotary casting?
Answer: Commonly 10% -15%, depending on the thinning rate.
Question: How much allowance is left for the blank wall thickness?
Answer: The thinning rate is 30% -45%, calculated backwards based on the finished product.
Q: What is the requirement for wall thickness deviation?
Answer: It is recommended to be within ± 0.3mm, otherwise the spinning will be elliptical.
Q: What is the required density for the blank?
Answer: It is recommended to have a 1-2 level X-ray of the wheel rim.
Q: What is the suitable batch size for rotary casting?
Answer: More than 200000 pieces are required to be invested before they can be evenly distributed.
Q: Does heat treatment require pre compensation?
Answer: Yes, the deformation caused by spinning and heat treatment needs to be considered together.
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