What types of casting defects can be induced by improper design of exhaust slots in casting molds

What types of casting defects can be induced by improper design of exhaust slots in casting molds
The exhaust groove is the basic structure of LPDC, gravity, and CPC molds. The problem of air entrapment caused by poor exhaust is very common in overseas orders.
If the depth of the exhaust groove exceeds 0.15mm, aluminum liquid is prone to enter the groove and seal the channel, resulting in exhaust failure after hundreds of continuous production cycles.
The depth of the exhaust groove is less than 0.06mm, resulting in high gas discharge resistance and preventing timely escape of gas at the filling front, forming subcutaneous pores.
The intersection of the wheel hub and spoke, as well as the thin-walled corner of the chassis support, are high-risk areas for gas accumulation, and the density of the exhaust groove layout needs to be doubled.
Gravity casting molds have fast filling speed and strong turbulence, and the total cross-sectional area of the exhaust groove needs to reach 12% -18% of the gate cross-sectional area.
LPDC bottom injection type has a smooth flow and lower exhaust pressure. The total cross-sectional area of the exhaust groove can be taken as 8% -12% of the gate cross-sectional area.
The CPC back pressure mold cavity has back pressure inside, and the cross-sectional area of the exhaust groove needs to be increased by about 20% on the basis of LPDC.
Xinfeng Machinery relies on CAE flow field simulation to locate the convergence position of the filling front and arrange exhaust slots in a directional manner to avoid blind slotting.
Many novice designers only provide exhaust on the parting surface, and the hidden gas accumulation points at the blind core and top pin positions are easily overlooked.
The gap between the top pin and the gap itself can assist in exhaust, with a gap control of 0.03-0.05mm, balancing exhaust and preventing aluminum liquid from entering.
It is recommended to extend the end of the exhaust groove to the outside of the mold and set up a gas collection groove to prevent gas from flowing back and re entering the mold cavity.
Foundries in Türkiye and Southeast Asia produce continuously, and the exhaust slot is easy to be blocked by aluminum accumulation. Generally, it needs to be cleaned every 800 – 1200 mold times.
When cleaning the exhaust groove, the polishing depth should not exceed the original design depth. Increasing the groove depth may result in aluminum burrs.
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Pore defects are often misjudged as poor degassing of aluminum liquid, and despite repeated adjustments to the refining process, the defects cannot be eradicated.
Prioritizing the verification of exhaust layout and adjusting aluminum refining parameters is the correct sequence for defect investigation.
The exhaust at the thick and large hot section position cannot rely on the main exhaust groove, and needs to be synchronized with the release of gas from the cold material package and slag collection package.
The precision requirements for mold exhaust groove machining are high, and the consistency of electrical discharge machining is better than milling, making it suitable for batch stable production.
When overseas customers perform casting flaw detection, subcutaneous porosity is a high-frequency rejection item, and the exhaust design directly determines the pass rate of the flaw detection.

## FAQ

Q: What is the recommended depth range for regular exhaust ducts?
A：0.06–0.15mm， Adjust according to the type of process.
Q: What is the ratio of exhaust cross-sectional area for gravity molds?
A: The total exhaust area is taken as 12% -18% of the gate cross-sectional area.
Q: What is the ratio of exhaust cross-sectional area for LPDC molds?
A: The total exhaust area is taken as 8% -12% of the gate cross-sectional area.
Q: How much should the exhaust area of CPC mold be increased?
A: Compared to regular LPDC, the exhaust area increases by about 20%.
Q: How much is the clearance control for the top pin assisted exhaust?
A：0.03–0.05mm， Balancing exhaust and anti runaway aluminum.
Q: How often is the exhaust duct cleaned?
A: It is recommended to clean the 800-1200 cycles of continuous production conditions.
Q: What are the problems with deepening the polishing of the exhaust groove?
A: Aluminum liquid enters, causing burrs on the casting and rapid exhaust failure.
Q: Which one should be prioritized for checking porosity defects?
A: Prioritize checking the exhaust layout before adjusting the aluminum liquid refining process.