Control of Thin Wall Filling Cold Insulation Defects in Structural Casting Molds | Flow Control of Aluminum Alloy Wheel Hub Molds
55% of the cold insulation defects in the thin-walled area of structural casting molds are caused by rapid cooling of the aluminum liquid front and insufficient fusion at the filling front.
The thickness of the thin-walled position is less than 2.2mm, and the temperature drop rate at the front edge of the aluminum liquid flow can reach 3.6 ℃/s. Interruptions in the filling process can easily form cold lines.
When the pouring temperature of aluminum liquid is below 695 ℃, the flowability decreases, the fusion strength of the filling end in thin-walled areas decreases, and the cold insulation scrap rate increases by 44%.
When the filling flow rate is lower than 35mm/s, the heat dissipation time at the front of the aluminum liquid becomes longer, the oxide film continues to thicken, and the two aluminum flows converge and cannot be fused.
The distance between the inner pouring channel and the thin-walled far end exceeds 28mm, the flow path is too long, the temperature drop accumulates, and the cold insulation defects are concentrated at the far edge.
The preheating temperature of the mold is below 170 ℃, the cavity wall continues to absorb heat, and the aluminum liquid rapidly loses heat after entering, resulting in a significant narrowing of the thin-walled forming window.
Structural casting molds are commonly used for aluminum alloy shells and brackets of new energy vehicles, and customers have strict requirements for air tightness and mechanical properties. Low pressure die-casting molds (LPDC), counter pressure casting molds (CPC), gravity casting molds, motorcycle wheel hub casting molds, wheel hub differential pressure casting molds, wheel hub low-pressure casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, and low-pressure casting tooling molds have their own adaptation advantages in different product thickness ranges. Zhejiang Xinfeng Machinery has compiled failure cases of thin-walled castings, and many solutions rely solely on increasing the temperature of the aluminum liquid to solve cold insulation. After the temperature exceeds 750 ℃, the amount of aluminum liquid suction increases, and the number of porosity defects begins to increase, which belongs to the category of robbing the east wall to make up for the west wall. The reasonable approach is to shorten the filling path, increase the preheating temperature of the mold, match the appropriate charging speed, and coordinate multiple parameters for adjustment. Many thin-walled structural components require vacuum filling. When the vacuum degree is below 0.06MPa, the gas back pressure inside the mold cavity hinders the flow of aluminum liquid, and the risk of cold insulation increases. The blockage of the vacuum pipeline filter element is an implicit fault, and the filter element needs to be checked every 1100 production cycles. Dust accumulation will reduce the vacuum extraction efficiency. The exhaust groove of thin-walled casting molds must be arranged at the end of the filling process. Holding air at the end will directly block the flow of aluminum liquid, forming intermittent cold insulation. North American auto parts customers often request fluorescent penetrant testing for thin-walled castings, and cold sealing is an unacceptable surface defect with strict testing standards. In the RFQ of Alibaba International Station, there is a significant premium for inquiries about thin-walled aluminum structural component molds, and customers are willing to pay higher fees in exchange for stable process solutions.
FAQ
1. Question: What is the critical wall thickness at which thin-walled castings are prone to cold shut?
Answer: When the wall thickness is less than 2.2mm, the difficulty of cold insulation control significantly increases.
2. Question: What is the lower limit reference for the temperature of thin-walled formed aluminum liquid?
Answer: The temperature of the aluminum liquid should not be lower than 695 ℃ to ensure fluidity.
3. Question: What is the recommended minimum filling flow rate for thin-walled areas?
Answer: The filling flow rate should not be lower than 35mm/s to shorten the leading edge heat dissipation time.
4. Question: What is the minimum temperature reference for mold preheating?
Answer: The preheating temperature of thin-walled forming molds shall not be lower than 170 ℃.
5. Question: What is the minimum vacuum degree reference for vacuum filling?
Answer: The vacuum degree should be maintained as high as possible above 0.06MPa to ensure filling.
6. Question: What is the regular inspection cycle for vacuum filter cartridges?
Answer: Continuously produce about 1100 molds to check the status of the vacuum filter element.
