Risk classification of strain and deformation caused by insufficient demolding slope of aluminum casting molds | Reference for draft design of gravity casting molds
The design of the demolding slope is too small, which is the main cause of 47% of the side wall scratches, deformations, and top white defects in castings.
The aluminum alloy has smooth side walls without skin patterns, and the demolding slope is less than 0.8 °. When opening the mold, the casting tightly holds the mold cavity, and the probability of surface strain increases significantly.
The surface has areas with fine cast grain and sandblasted grain, with a slope of less than 1.5 °, and the grain is hooked, continuously tearing off the surface of the casting.
The hub spoke area with thick and large shrinkage and high tightening force, with a slope of less than 1.2 °, is prone to demolding deformation and poor top marks.
After nitriding the surface of the mold cavity, the roughness Ra0.4 or less, the friction coefficient decreases, and the slope can be taken as the lower limit; If Ra>1.6, the slope must be enlarged.
When the release agent film is unstable and the spraying is insufficient, even if the slope meets the standard, local strains may still occur, and the process and structure need to be matched.
Low pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), differential pressure casting molds for wheel hubs, low-pressure casting molds for wheel hubs, motorcycle wheel hub casting molds, gravity casting molds, structural component casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, low-pressure casting tooling molds. Many customers forcibly compress the draft angle for product appearance dimensions, which poses production risks. Zhejiang Xinfeng Machinery compares a large number of drawings, and overseas customers often require the minimum slope. During the design phase, an evaluation of the clamping force must be done, and it cannot be simply based on experience. The clamping force of deep cavity structural components is much greater than that of shallow wheel hub cavities, and it is recommended that the inclination of deep tube structural components should not be less than 1.8 °. When the local position cannot have a large slope, priority should be given to the embedded core pulling structure instead of forcibly reducing the slope; The core pulling mechanism increases costs, but avoids mass production damage and scrap. Once a strain appears, polishing the cavity and adding release agent can only provide temporary relief and cannot cure it. The best solution is to lock in the slope during the initial drawing review. The thicker the casting wall thickness, the greater the cooling shrinkage force, and the slope value increases synchronously with the wall thickness. Many domestic drawings ignore the additional requirements of skin texture on slope, and are forced to change the mold after being delivered to overseas customers for trial molding, which prolongs the delivery time.
FAQ
1. Question: What is the minimum draft angle for smooth textured aluminum castings?
Answer: Priority should not be less than 0.8 °.
2. Question: What is the recommended slope for leather grain/sandblasted surfaces?
Answer: The slope of the leather texture area should be ≥ 1.5 ° to prevent material scratching.
3. Question: What is the bottom line of the inclination in the thick area of the wheel hub and spoke?
Answer: The spoke wrap has a high tightening force, and the inclination should be ≥ 1.2 ° as much as possible.
4. Question: Can polishing the cavity significantly reduce the slope?
Answer: Nitriding polishing can have a lower limit, but it cannot be lower than the safety threshold.
5. Question: What is the recommended slope for deep cavity structural components?
Answer: It is recommended that the slope of deep tube structural components be ≥ 1.8 °.
6. Question: Is the slope insufficient for temporary handling?
Answer: Polishing and optimizing release agents only provide temporary relief, and curing requires changing the mold or adding core pulling.
