High pressure die casting
High pressure die casting uses a single plunger and a narrow in-gate, which causes turbulence and high levels of porosity.
The Acurad process (die casting with secondary plunger)
In the Acurad process, the high pressure die casting process is modified. A secondary plunger is used a fraction of a second after the initial plunger has operated, in order to feed the shrinkage porosity. A larger in-gate is designed into the die to reduce turbulence during injection.
- Acurad process uses a modified high pressure die casting machine, as follows.
a. The gate is made as large as possible to prevent turbulence and air entrapment; it is positioned at the lowest point in the die cavity to allow for gravity defects.
b. A secondary plunger delivers a delayed action (time delay 0.015–1.5 s, depending on size of casting) pulse of pressure to feed shrinkage.
c. Dies are water-cooled to optimise directional solidification with automatic die temperature control.
- Total Acurad cycle time is about the same for conventional die casting. The increased fill time is offset by the reduced solidification time.
- Lower pressures are used for Acurad than with die casting:
Acurad 35–100 MPa
die casting 70–140 MPa
- Reduced operating pressures and speeds improve machine downtime and die lives.
- Reduced impact shock pressure reduces the frequency of hydraulic equipment breakdowns.
- There is also less thermal shock to the dies, heat checking of the dies is reduced and erosion at the in-gate is reduced.
- Range of components includes car wheel trims, transmission casings, engine blocks, and motorcycle and bicycle components.
- Mainly used for aluminium die casting alloys. Magnesium- and zinc-based also can be used.
- Difficult-to-cast aluminium alloys can also be used for some components.
- Improvements in tensile strength by up to 30% are claimed. Tensile ductility can be improved from values of 1–3% (for die casting) up to 10% (for Acurad castings), e.g. Al-(6.5-7.3)Si-(0.2-0.45)Mg alloy in T6 heat treated condition, seen below.
- Reduced porosity and air entrapment enables aluminium alloys that would not normally be treated after die casting to be welded and/or heat treated.
- Castings are pressure-tight.
Tensile strength (MPa)
0.2% proof strength (MPa)
- Acurad process enables designers to design for higher allowable stresses.
- Wall section thicknesses can be reduced compared with die casting, with a consequent decrease in the volume of metal required per casting.
- Acurad castings can be used for pressure-tight, weldable and heat treatment applications.
- Castings have smooth surfaces.
- Intricate design details can be cast.
This article is a part of Manupedia, a collection of information about some of the processes used to convert materials into useful objects.