Causes analysis and improvement methods of cracking in die casting products
Posted on : March 23, 2022 By GREFEE
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What is cracks in die casting products?
The casting body is damaged or disconnected, which forms the filamentous crevices. It has two types, penetrable or non-penetrable with developing tendency.
Cracks have two types, cold cracks and hot cracks. The main difference between them is: the metal in cold cracks is not oxidized yet, while the metal in hot cracks is oxidized already.
（1）improper casting structure, difficult to shrink, too small casting fillet.
（2）The pulling core of slide and eject system is inclinder in working, non-uniform stress.
（3）Mold, especially the core temp is low
（4）Too long mold opening or core pulling time
（5）Improper selection of alloys or too high impurities content causes the plasticity of alloys is decreased.aluminum alloy: high zinc, copper, iron content
（6）the casting structure has too thick and large hot junction area.
（7）too high alloy pouring temp
（8）Mold core is curved or parting surface is damaged or has inverted angled
（9）Cracks happened when trimming the casting system.
How to improve cracks in die casting?
1. Checks the structure of casting and size to see whether the shrinkage ration is proper or not. Modifies the mold,selects appropriate shrinkage ratio. Negotiate with customers to improve the casting structure, reduce the wall thickness differences and increases the fillet.
2. Scratches on the die core or sides in certain directions. Modifies the model to ensure the ejection and mold release.
3. cold shut in the mold core holes. Increases the mold working temp.
4. there may be stains in core hole or sides. shortens the time of mold opening and core pulling.
5. chemical content of alloys analyze to die casting material by spectrum
6. thick and large hot junction surface will have sinks and cracks. Negotiates with customers to change the structure without affecting the function.
7. there has ultra-brightening areas, sticking, or strains on casting surface, sinks on the thick wall. Controls pouring temp within the standardized range.
8. There is serious strains or burrs on the side of the hole or the damaged surface. Replaces the mold core or repair the mold.
9. Main cracks are around the gate. Repairs the sharp edges of trimming die.
Key inspection areas to die casting parts:
The cracks is in the fillet of product, corner, or the positions which has too small R corner.
How does crack affect the product?
The cracks will largely affect the airtightness and mechanical behavior of products.
How to evaluate whether a die casting product with cracks qualified or not?
To check if there are any cracks exited, first is to inspect by visual, or measures after finding or applying fluorescent penetrant.
1.generally, die casting parts with cracks are unqualified.
2. Pulls the mold will lead to cracks, especially be careful with the strains or brightened areas caused by pulling the mold.
3. Slight cracks cannot be identified easily. Uses searchlight and magnifying glass to check the cracking areas.
Improves the problem of cracks in die casting
Based on many years of experience, GREFEE believes that cracks are mainly caused by the too-small corner position R or too small product angle, the splits of insufficient ejection. The insufficient ejection, besides, could be the too high mold-temp, occasionally, or incomplete cooling. The product is not dense and too loose. Another one is material. All of these possible factors could lead to cracks.
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