Dimensional accuracy and CT control method of steering joint mold

Dimensional accuracy and CT control method of steering joint mold
The dimensional accuracy of the steering knuckle is usually controlled according to CT6-CT7 levels, and the key to the mold side is shrinkage compensation, sand core positioning, and prediction of heat treatment deformation.
What does CT grade mean
The corresponding dimensional tolerance for CT6 level is about 0.6% of the nominal size, while for CT7 level it is 0.8%. The key mating surfaces of steering knuckles often require stricter requirements.
Taking the 100mm size as an example, the tolerance zone for CT6 grade is about 0.6mm. This accuracy is already a high requirement for castings and requires full process control.
The precision of mold manufacturing should be 2-3 levels higher than the requirements for castings. The mold itself is out of tolerance and cannot be compensated for by subsequent process adjustments.
Shrinkage rate is not a single numerical value
The linear shrinkage rate of aluminum alloy is often taken as 0.8% -1.2%, but the actual shrinkage in the thin-walled and thick walled regions is different. Uniform values can lead to local exceedance.
The contraction of wheel hub type rotating bodies is relatively uniform, while the difference is significant for long arm components such as steering knuckles. The contraction in the long arm direction is obstructed, and the actual value is relatively small.
The method is to set the shrinkage rate for partitioning. Calculate the values of the long arm, ear, and flange regions separately using simulation or trial data.
Sand core positioning determines wall thickness consistency
The inner cavity of the steering knuckle is mostly formed by sand cores, and the deviation of the sand cores can directly cause uneven wall thickness. If the offset is 0.5mm, the thin side may be lower than the minimum wall thickness.
It is recommended to control the clearance between the core head and the core seat at 0.1-0.2mm. If the clearance is too large, the sand core will drift under the filling pressure.
Xinfeng Mold adopts a dual core head positioning and anti rotation structure on the steering knuckle mold, and the wall thickness deviation can be controlled within ± 0.4mm.
Pre compensation for heat treatment deformation
Aluminum alloy steering knuckles are often treated with T6, and uneven cooling after solid solution quenching can cause deformation. The bending deformation of long arm components often reaches 0.2-0.4mm.
The method of pre compensation is to reserve a reverse deformation amount on the mold. The reserved value should be determined based on actual heat treatment data and cannot be based on experience.
The loading method also affects deformation. The deformation direction of vertical furnace and horizontal furnace is different, and the mold compensation should be linked to the heat treatment process.
Selection of detection methods
Three coordinate measurement is suitable for first piece and sampling inspection, and can provide complete dimensional reports. Batch testing often uses specialized inspection tools for higher efficiency.
It is recommended to use 100% inspection tools for key mating surfaces, and conduct 5% sampling inspection for each batch based on the three coordinate system. Combining the two, balancing efficiency and reliability.
CT scanning can detect internal defects and wall thickness distribution, but it is costly and slow in pace. Mostly used for new product development and failure analysis.
Troubleshooting sequence for accuracy loss of control
First, check if the mold, cavity dimensions, and positioning structure are within the design tolerances. The mold is out of tolerance, and all adjustments are temporary.
Further investigation of the process reveals that fluctuations in mold temperature and pouring temperature can alter the amount of shrinkage. If the temperature fluctuation exceeds ± 15 ℃, it is difficult to control the size drift.
Finally, check the heat treatment. The first two items are stable but still drift in size, and the temperature uniformity and loading method of the heat treatment furnace should be rechecked.
Frequently Asked Questions
Q: What is the general CT grade of the steering knuckle?
Answer: Common CT6-CT7 levels, with stricter critical areas.
Question: What is the shrinkage rate?
Answer: 0.8% -1.2%, long arm components need to be partitioned.
Q: How much is the sand core offset control?
Answer: The clearance should be 0.1-0.2mm, and the wall thickness deviation should be within ± 0.4mm.
Question: How much deformation does heat treatment cause?
Answer: Long arm components are commonly 0.2-0.4mm and require pre compensation.
Q: How to check the size in batches?
Answer: 100% inspection tool for key surfaces, 5% for three coordinate sampling.
Q: What should I check for size deviations first?
Answer: First check the mold cavity and positioning, then check the mold temperature.
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