|Aluminum Die Casting Defects|
|1||Short Fill||1.Metal is frozen before the cavity is filled
or by insufficient metal being ladled.
2.Metal can cool down too much in the shot sleeve.
3.Some part of the die may be too cold
|2||Cold Shut||1.Metal is frozen when two metal fronts join
2.Metal may be losing too much heat in the runner and cavity.
|3||Scaling||Layers of metal and oxides can be created by poor shot end
control and /or bad gate and runner design
|4||Blister||Trapped gases are in the casting when the die is opened
when the casting is still weak.
This allows the compressed gas to expend and cause a blister.
|5||Flash||Metal pressure is too high upon the projected surface area
(facing the platens ) of the casting at the end of cavity fill.
This creates a force across the parting line which is too great for the
clamping force of the machine.
The die is then forced apart which allows metal escape.
|6||Cold Flakes||Metal is allowed to cool too much in the shot sleeve.
The solid particles are then injected into the cavity.
These flakes are often clearly visible on the surface of the casting
with the naked eye
|7||Shot Lube Stain||This defect occurs when too much shot (tip) lube is used|
|8||Air Porosity||This defect is caused by trapped air in the casting which can come from
It can be caused by poor shot end control, poor venting and overflow
function or bad gating and runner design.
|9||Drag Marks||Insufficient draft or an undercut causing a casting to be damaged on the
surface when it is ejected.
This effect may be reduced by changing the temperature at which the
casting is ejected. Poor surface finish of the die can be another cause.
|10||Hot Tearling or crackig||This defect is caused by metal shrinking during solidification while under
At the last place to solidify a tear or crack develops which can be seen
at the surface.
|11||Hot Shortness||The composition of the alloy causes the metal to be too weak at high
temperatures (after solidification ).
This then can cause cracks in the surface of the casting to appear in
regions of high stress when the casting is cooling (and contracting ).
NOTE: This defect can occur in conjunction with hot cracking.
|12||Sink||A sink is caused by a shrinkage cavity being near the surface of the casting.
This causes the surface of the casting to collapse into the cavity as
Sinks are caused be the same things as shrinkage porosity as well as
very poor thermal control of the die because hot spots are required for
sinks to form.
|13||Exploded Metal||A combination of porosity and the casting being ejected before it
has solidified completely.
This allows the trapped gases to burst out of the casting along with
any unsolidified metal.
|14||Warpage||A casting can deform after ejection during the time it is cooling down
to room temperature.
The root cause can sometimes be the casting geometry or the alloy
specification. Warping can be minimized by ejecting at a lower
Uneven die temperature is a major cause of this type of defect.
|15||Soldering||Chemical attack and bonding of aluminium to die steel.
This causes aluminium to be torn away from the casting during
ejection soldering can be reduced by a change in alloy and/or
a reduction in die/metal temperature.
|16||Shrinkage Porosity||This defect is caused by metal reducing its volume during solidification
and an inability to feed shrinkage with more metal before solidification.
Hot spots can also cause shrinkage porosity to be concentrated in a
specific zone. See ‘sink’
|17||Heat Checking||This defect is caused by the surface of the tool steel continually
expanding &contracting during use.
Excessively cold dies &die flexing accelerate this effect.
|18||Leaker||Causes of leaks in castings where pressure tightness is required
can be oxide folds and/or inclusions and/or porosity in conjunction
with a surface defect which completes the path for a leak.
A close analysis of the leaking area may reveal which of the many
causes is causing the leak.
|19||Discoloured Surface||Oxide films (dross) and/or residues in the cavity and/or particles
in the metal and/or excess die lube can cause the surface to be discoloured.
Also it can be caused by a part of the die being too cold causing
the casting to have darker regions or ‘smears’ on the surface.
|20||Break Out||Metal flakes(cold flakes) which get caught in the gate during cavity
fill can break out unevenly when the casting is trimmed.
|21||Inclusions||The main causes of this type of defect are dirty/contaminated metal
and/or poor melt banding practice.
|22||Ejector Damage||In broad terms, it can be defined as excessive pressure on the casting
surface by the ejector pin(s) during ejection.
|23||Erosion or cavitation||Erosion is caused by direct molten metal impingment on die steel.
Cavitation type erosion is caused by turbulence which causes
low pressure regions in the flowing metal.
|24||Craked Casting||A crack in the casting can be caused by mechanical damage
when the die is opened or when the casting is ejected.
This classification excludes HOT CRACKING &cracking at the
surface due to SHRINKAGE POROSITY.
Also, this definition excludes HOT SHORTNESS.
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