Die-casting Intros


►Surface Defects


There are many types of surface defects occuring during the production. We enumerate

some certain most frequently shown defects and roughly describe what are some

factors causing these defects.


♦1 Flow defects including cold flow / cold shot / non-fill / flow marks

Flow defects result from how metal flows to and within the die. The alloy does not have

enough heat energy to remain completely liquid during the fill time.

These defects are usually surface blemishes that range widely

in severity, from a deep crease to a barely discernible line.


♦2 Soldering

Soldering is the fusion of aluminum in the die casting alloy with iron from steel surface

of die cavity. Typically, the die cavity has an oxidized coating on it.

The coating protects the cavity surface from the aluminum.

If the alloy impinges on a portion of the die or on a core pin to the extent

that a hot spot develops, the aluminum will break down the oxidized interface

between the die surface and the casting.


♦3 Blisters

Blisters are bubble like bumps on the casting. Gases trapped in the casting near

the casting surface cause them. These gases are under very high pressure. After all,

the process uses high metal pressure or intensification at the end of the shot in order

to compress the trapped gases. When the casting is ejected and the casting surface over

the blister is not strong enough to withstand the gas pressure of the blister, the surface

yields and the blister forms.