Die casting is a complex and detailed process, which can be affected by several factors that we can separate into two types: defects caused by the alloy and defects caused during casting. The latter includes difficulties such as problems with filling the mould cavity or others related to solidification.
In this article, we will detail some of the most common casting defects and their underlying causes, as understanding the faults and identifying the reasons for them can significantly improve the integrity and consistency of parts produced by the die casting process.
Porosity due to air or trapped gas
Defects with air during casting are the result of the expansion of air under the skin of the part during solidification. This phenomenon occurs when the walls of the part do not have sufficient tension to retain the air inside the part, so the air rises to the surface and deforms the part. The presence of air or gas in the cavity and high ejection temperatures favour the appearance of this problem.
Flow marks in injection moulding
Flow marks are non-directional lines on the surface of the die cast part that appear when a portion of the liquid metal solidifies prematurely compared to the rest. Early solidification can be related to metal front breakage, too long filling times or inadequate temperatures in the mould. This leads to imperfect joints between the different metal faces.
Oxide slag inclusions or laminations
Flakes are defects manifesting as thin material layers that flake off after mechanical surface treatment, e.g. polishing. What happens in these areas is that they are areas with adhesion problems, the origin of which can be either in the splitting of the metal face, long mould filling times or inadequate temperatures during casting.
Incomplete die fills
Incomplete fills occur when the metal solidifies before the mould cavity is completely filled, resulting in premature solidification of the metal. This premature solidification can result in missing details on the surface area of the casting. Occurs due to long filling times or low mould temperatures.
Inclusions or unwanted particles
Inclusions can be a defect caused by either the previous or current injection. In the case of the previous injection, a metal fragment remains attached, and the fusion with the new metal is incomplete. If, on the other hand, there is a problem with the current injection, a part of the metal solidifies prematurely and is pulled by the metal front into the cavity.
Inclusions can affect the mechanical functions of the metal casting, so it is crucial to find a solution to this defect during casting. Controlling the filling time and temperature and the amount of metal injected or air entrapment are some measures to be taken in cases where inclusions are the defect during die casting.
Jegan, Zamak die casting
Understanding defects in the casting process is critical to implementing effective corrective measures. By addressing these problems, we can significantly improve the integrity and consistency of the parts produced by casting. At Jegan, we have decades of experience in die casting and zamak die casting production, so we know the process, the potential pitfalls and how to resolve them to provide our customers with quality parts.