Thin walled filling and deformation control of motorcycle wheel hub molds

Thin walled filling and deformation control of motorcycle wheel hub molds
The wall thickness of the motorcycle wheel hub is 2.5-4mm. The mold should be filled with aluminum liquid within 1.5 seconds and the ellipticity should be pressed within 0.3mm.
The window of thin-walled filling is very narrow
The rim with a wall thickness of 3mm has a rapid cooling of the aluminum liquid front during the filling process. If it is not filled for more than 1.5 seconds, the front temperature may fall below the liquid phase line.
The pouring temperature is usually taken as 680-720 ℃, and the mold temperature is controlled at 280-350 ℃. When the temperature is low, the far end of the wheel rim is prone to insufficient watering.
It is recommended to control the sprue speed between 0.3-0.6m/s. If the speed is too high, it will cause air entrainment, and if it is too low, it will not be fully charged. This range needs to be determined based on actual measurements of the wheel type.
Uneven deformation from three directions
The first issue is uneven cooling. When the wheel rim is thin and the wheel hub is thick, and the solidification sequence is reversed, the shrinkage stress will pull the wheel rim into an ellipse.
The second issue is uneven force distribution during ejection. When the number of top rods is less than 6, thin-walled wheel rims are prone to plastic deformation at the moment of ejection.
The third issue is insufficient stress relief. Castings that have not undergone aging treatment before machining will experience secondary dimensional drift due to stress release after cutting.
Countermeasures for mold structure
The wheel rim adopts an embedded structure, which can be replaced separately after wear. The fitting tolerance of the insert is taken as H7/m6 to avoid loosening in the hot state.
Cold points are arranged in the transition zone between the spokes and the hub. Cooling rods with a diameter of 6-10mm are inserted into the hot joint, which can shorten the local solidification time by 20% -30%.
Xinfeng Mold divides the motorcycle wheel hub mold into 4-6 cooling zones, each with independent temperature control, to correct ovality deviation.
Detection and correction of ellipticity
Ellipticity detection is usually completed on specialized gauges, taking 6-8 points on the inner edge of the wheel rim, and the difference between the maximum and minimum diameters is called ellipticity.
The common control target in the industry is within 0.3mm, and high-precision vehicle models require 0.2mm. Exceeding 0.5mm will affect tire assembly and dynamic balance.
The corrective measures include adjusting the flow rate in the cooling zone, modifying the layout of the top rod, and adding a shaping process in the machining process. The first two items have lower costs.
Batch characteristics of motorcycle wheels
The annual production of a single model often ranges from 50000 to 300000 pieces, far higher than that of modified car wheels. The requirement for mold lifespan is correspondingly higher, usually aiming for over 50000 mold cycles.
The two wheeler market is price sensitive, and the sensitivity of mold pricing is also high. The price range for a single set of molds is mostly between 80000 and 200000 yuan.
The Southeast Asian and Indian markets are mainly dominated by small and medium-sized displacement models, with fast updates in wheel types. The convenience of mold changeover is sometimes more important than the lifespan.
Common Misconceptions
The first misconception is to make the wall thickness thicker to ensure filling. An increase in wall thickness will lead to an increase in weight and a decrease in heat dissipation, which is opposite to the direction of lightweighting.
The second misconception is to only change the process without changing the mold. The filling problem of thin-walled parts is often related to the position of the gate and exhaust, and it is difficult to cure it solely by adjusting the pressure.
Misconception three is to ignore machining allowance. Leaving a large margin for thin-walled parts can cause cutting forces to compress and deform the workpiece, which in turn cannot guarantee the size.
Frequently Asked Questions
Q: How thin can the wall thickness of motorcycle wheel hub molds be made?
Answer: Conventional 2.5-4mm, below 2.5mm, simulation verification is required.
Question: What is the charging time controlled for?
Answer: It is recommended to wait for 0.8-1.5 seconds, depending on the wheel type and gate.
Q: What is the standard for ellipticity?
Answer: Conventional models are within 0.3mm, while high-precision models are within 0.2mm.
Q: What is the required lifespan for the mold?
Answer: For mass-produced models, it is recommended to have at least 50000 mold cycles.
Q: How much does a set of molds cost?
Answer: The common range is 80000 to 200000 yuan, depending on the number of cavities and configuration.
Q: Can deformation be solved by adjusting the process?
Answer: When caused by cooling and ejection, the mold structure needs to be changed.
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