54
SQUEEZE CASTING
Figure 4.3 Microstructural comparisons between conventional die casting and
squeeze casting. Courtesy of UBE Machinery, Inc.
Gas porosity can also originate from gases dissolved in the liquid metal. Although not a major factor in conventional die cast-
ing due to the extremely high cycle times, the longer solidification durations associated with squeeze casting may allow dissolved
gases to precipitate and form porosity. This source of porosity can be controlled using good melting and holding practices.
4.3 MANAGING SHRINKAGE IN THE DIE
High metal intensification pressures are maintained throughout so- lidification in conventional and vacuum die casting. Unfortunately,
the small gates typically used in conventional die casting freeze quickly. Once solidified, the gates are a barrier that inhibits further
pressurization within the die.
4.3 MANAGING SHRINKAGE IN THE DIE
55
a
b
Figure 4.4 Graphical illustration showing the progression of a die cavity filling
with a atomized filling and b a planar metal front.
56
SQUEEZE CASTING
Due to increased gate areas in comparison to conventional and vacuum die casting, gates typically remain open throughout much
of component solidification when using the squeeze casting process. Pressurized metal is fed to the die cavities, reducing
solidification shrinkage and minimizing the effect of this porosity-forming mechanism.
4.4 ELEMENTS OF SQUEEZE CASTING
MANUFACTURING EQUIPMENT
Both horizontal and vertical conventional die casting machines can be used in conjunction with the squeeze casting process. The
differences in squeeze casting are attributed to the die design and process parameters.
Although squeeze casting has been utilized for many years to manufacture production components, a consistent die design
methodology has not been documented in the technical literature. Squeeze casting die design philosophies are viewed by many pro-
ducers as a trade secret. As such, most producers do not wish to disclose die design methodologies. However, several qualitative
characteristics are known.
In comparison to conventional die casting, squeeze casting dies have larger gate areas. Gates are no less than 3 mm in thickness
to avoid premature solidification during intensification. Some manufacturers utilize classical fan gating such as that used in con-
ventional die casting. Other producers have found large single- point gates ideal.
As squeeze castings have thicker gates, trimming is not a viable option to removing components from their runner systems. Saw-
ing is typically required. Automated sawing systems are available for high volume production. However, automated systems require
customer fixtures. Although sawing may be necessary for remov- ing components from their respective runner systems, trimming
often is not avoided. The removal of overflows and flash is still accomplished using traditional trimming techniques.
As with any die casting process, shot control is essential. Often the shot control systems currently available on conventional die
casting machines may be used with the squeeze casting process. Process parameters, however, must be adjusted to allow for slower
4.5 APPLYING SQUEEZE CASTING
57
Feature CDC Squeeze Metal temperature
Cycle time Number of cavities
Alloy flexibility Shrink porosity
Oxide entrapment Equipment cost
Automation Metal cost
Recycling Mechanical properties
Heat treatable Metal heating
Metal loss
+ = indicates favorable rating -
+ +
+ -
- ++
++ +
+ -
- +
+ -
- +
+ +
+ +
+ +
+ +
+ +
+
Figure 4.5 Comparisons of conventional die casting and squeeze casting.
fill of the die cavity and longer intensification times. Key process characteristics of squeeze casting include metal temperature, melt
cleanliness, cavity pressure, and gate velocities.
2
4.5 APPLYING SQUEEZE CASTING
Squeeze casting is a high integrity die casting process that builds upon conventional die casting practices and is compatible with
aluminum, magnesium, zinc, and copper alloy systems. Cycle times are longer in comparison to conventional die casting due to
longer metal injection durations. Component integrity is improved by minimizing entrapped air and reducing solidification shrinkage.
Most squeeze casting components can be heat treated without blis- tering defects to improve mechanical properties.
Squeeze cast components have many advantages over conven- tional die castings. A qualitative comparison of these two pro-
cesses is shown in Figure 4.5.
3
Conventional die casting is lower
