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Causes and Precautions of Leakage in Die Casts

Source: Junying   Author: Junying   Posted: 2017-03-07 17:15:08   Hits: 37
As we all know, the yield of die casts is directly related to the cost and profit of casting enterprises, casting quality has a great impact on reputation of the enterprise. For many die-casting companies, there might be a leakage problem after manufacturing, and these die casts can not be used without repairing. What causes that? This article will do a detailed analysis.

Defects
There is leakage in the die cast testing and red light of dry pressure testing machine will be on.

The cause of the defect
1. Boost pressure is insufficient.
2. The design of gating system is not good.
(1) It is far from the leaking area, the internal quality is poor.
(2) The metal flow didn't emerge well and causes cold shut.
(3) The cross-sectional area of the inner gate is small, pressurized transmission is not in place, which led to air pore or shrinkage porosity in the far end.
3. Improper alloy selection and poor mobility are not suitable for die-casting manufacturing.
4. Pores, shrinkage porosity and cold shut occur partially due to poor exhaust.
5. The defect of pores and shrinkage porosity which were caused by unreasonable design, uneven or thick wall thickness have seriously influenced tightness.
6. Too much processing destroies the dense oxidation layer of the surface or thins wall thickness, especially on double-sided processing parts. 
7. With too high alloy melting temperature and long holding time, shrinkage porosity and crack easily will easily occur on the wall thickness of die casts.
8. The amount of gas evolution from the coating is huge, which can lead to pores easily.
9. Pressure test equipment failure.
10. The sealing surface is damaged or does not meet the roughness requirements. Such as scratches and indentation on the processing surface. Non-processing seal groove has roughness difference due to cracking.
11. Casting deformation will cause warpage of sealing surface.

Measure for preventing defects
1. The far end of the cast or wall thickness are not even--increase specific pressure.
2. Improving the pouring system reasonably based on the simulation of filling process or actual sample debugging analysis.
3. Choosing good alloys.
4. To analyze if there is air entrapment for the casts partially in the hot die stage. You can add slag strap and exhaust vent.
Find the hot junction by X-ray test. If the hot junction is indeed the leak point, you can consulted with the customer’ engineer to change the structure and reduce the wall thickness. In addition, the secondary extrusion process can be used to solve the leakage at the pyrolysis.
6. Try to avoid processing or adopt machining allowance as small as possible.
7. Use X-ray inspection to check the internal quality of the castings, reduce appropriately the melting temperature;
8. Use X-ray inspection to check the internal quality of the casts and have an impregnation treatment with lower gas evolution.
9. Test the pressure test equipment by qualified castings so as to maintain the equipment.
10. The defect can be found by bulge test. Strengthen protection for the process and repair the mold timely;
11. Defects can be found by flatness check. Control the manufacturing process and the holding time must be sufficient. To prevent extrusion when the equipment is running.