Manufacture:
- Viable alternative to gravity sand, gravity die and low pressure die casting, for low-medium production numbers.
- Metal melted in a resistance furnace to minimise turbulence, before non-turbulent transfer to holding furnace, where impurities sink or float.
- Metal transferred from centre of holding furnace in a non-turbulent manner by means of an electromagnetic pump, gradually displacing air through the permeable sand mould.
- Moulds produced by zircon sand (ZrO2/silicate) which has a very low coefficient of thermal expansion (<0.2% at casting temperature), leading to high accuracy. Cores and moulds are assembled at room temperature, with accuracies of ±0.5 mm. Patterns are usually cast resin, and hence less expensive than metal tooling.
- Scrap rate is <2%, due mainly to broken cores, and yields in excess of 90% are achieved since only vertical in-gates are used. Almost 100% sand is recycled since degradation is negligible, and loss on ignition is <0.1%.
- Production rates of 1 mould min-1 are possible from a single set of tooling.
- Cheaper than gravity die casting due to less fettling, cleaning, machining and quality assurance.
- Typical products include military and aerospace castings, and cylinder heads, manifolds, etc. for the automotive industry.
Materials:
- At present only aluminium alloys such as LM 25, but process could be used for many other alloys.
- Porosity levels of 0.01–0.001% are possible, compared with 1–2% for conventional methods.
- A cheaper, unmodified, copper-hardened, eutectic silicon alloy has recently been developed. Up to 2% zinc and 0.9% iron can be tolerated in this alloy if used for less exacting applications such as cylinder heads, which do not require elongations in excess of 1%.
- Typical properties for unmodified LM 25 and the eutectic silicon alloy are as follows:
Properties | LM25 (Al-7Si-0.5Mg) | Al-11Si-3Cu | |||||
As cast |
Soln + polymer quench |
Soln, polymer quench and age |
As cast |
Aged only |
Soln, water quench and age |
Soln, air quench and age |
|
UTS (MPa) |
– | – | – |
195 |
210 |
320 |
290 |
0.2% PS (MPa) |
100 |
140 |
285 |
135 |
180 |
300 |
250 |
Elongation (%) |
4 |
10 |
3 |
1.3 |
1.0 |
0.75 |
1.0 |
Hardness (VPN) | – | – | – | 90 | 95 | 120 | 110 |
Design:
- Complex 3D castings from 1 to 50 kg.
- Components can be designed with thinner wall sections due to better dimensional accuracy, leading to a 15% weight saving and reduced machining costs.
- Wall thicknesses are repeatable to within ±0.15 mm, compared with 1–3 mm for die and sand castings.
- Accuracies of 0.1–0.2 mm possible up to 500 mm, with a repeatability of 0.2 mm in 500 mm.
- Threaded inserts can be cast-in.
- Tolerance on hole diameters is approximately ±0.05 mm on a 10 mm diameter.
- Flatnesses of ±0.15 mm possible after heat treatment.
- Typical surface finish 4.6–6.0 µm Ra.
See Also: Gravity die and Low pressure die casting.
This article is a part of Manupedia, a collection of information about some of the processes used to convert materials into useful objects.
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