The complexity and the need to take care of each stage of the die casting process make it a process in which it is essential to detect defects and their causes. As we have discussed in previous articles, casting defects caused by the alloy and casting defects originate during the casting process. This time, we will focus on some of the defects during casting. In addition to air, flux marks, flakes, incomplete fillings and inclusions, there is also the possibility of finding defects such as depressions, welds, flash and ejection, which can be just as critical as those mentioned above and have their specific causes and effects on the quality of the castings.
Depressions: web cracks and sinks
Depressions are the inevitable result of the solidification process. The metal shrinks naturally, but it must occur uniformly throughout the melt. When this is not the case, we speak of a depression. Its origin can be attributed to a short compression period or hot spots in the mould. The higher the temperature, the greater the shrinkage, which can have a significant influence on the occurrence of depressions.
Defect of weld marks in die casting
Under specific conditions of metal velocity and temperature, the impact of the liquid in the cavity can generate an electrochemical reaction that degrades the wall and causes strong metal fouling. This phenomenon is caused by an abnormally high velocity of the liquid metal microdroplets and hot spots in the mould.
Burrs or flash; structural casting defects
Flash, more colloquially known as burr, is formed due to the pressure exerted by the piston during metal injection. The metal is trapped in the mould parts that are not press-fitted and remain outside the cavity. This defect is caused by a lack of sealing between the fixed and movable parts of the injection mould, which allows the metal to escape between them, forming burrs or flashes.
Ejection defect or imbalance of forces
The ejection defect can manifest itself either during the mould opening, during ejection or during the fall of the part. Paying attention to the precise moment it occurs to diagnose its origin is crucial. Identifying at which stage of the casting process the ejection occurs can shed light on possible underlying causes.
The measures to be taken will differ depending on the stage at which the error is detected.
Jegan, die casting of zinc alloys
At Jegan, we understand the importance of identifying and understanding defects in the die casting process to achieve the best possible guarantee in manufacturing parts. Each defect has characteristics and implications within the production cycle, from shrinkage problems and electrochemical reactions to sealing and ejection problems. Knowing their origins and understanding their impact on part quality is the first step towards practical solutions.