| Aluminium castings | | | | injecting and quick solidification under high pressure |
| Using an aluminium casting to replace an iron | | | | make a fine grain surface, which leads to having |
| casting will result in reducing component weight by | | | | best wear and fatigue properties. Aluminum die |
| half. That is why auto producers are searching the | | | | castings are generally not given heat treatment, |
| areas where they may replace iron parts with | | | | so they cannot be welded. |
| aluminium parts. Most auto manufacturers prefer | | | | Permanent die casting: |
| alloys of aluminium specially the A 300 series | | | | It is also known as gravity die casting and is |
| which have a mix of silicon + a minor amount of | | | | suitable for large scale production. Their maximum |
| magnesium. | | | | weight is 10kg. But where heavy cost machinery |
| The silicon provides fluidity while casting, which | | | | and tools are used the weight of casting may go |
| allows thinner parts to be cast. The magnesium | | | | up to 50kg. Permanent mold casting have low |
| gives strength (via heat treatment). An important | | | | pouring rate but metal molds solidify quickly, |
| feature of aluminium and its alloys is that in | | | | mechanical properties of permanent mould |
| comparison with ferrous alloys which show a | | | | castings may be further bettered by heat |
| unlimited fatigue strength, the fatigue strength of | | | | treatment. |
| aluminium alloys goes down with increase in | | | | Sand casting: |
| number of stress cycles this needs to be taken in | | | | Sand casting is casting of a mold with sand. In |
| account while designing its parts. | | | | normal sand casting, the mould is made around a |
| For getting high quality castings a variety of | | | | design by forcing sand mixed along with a bonding |
| processes are followed. While casting permanent | | | | agent on the design. Then the design is taken out |
| moulds precautions are taken to ensure that it | | | | which leaves a cavity for casting. Melted metal is |
| gets required cooling and vacuum pressure is also | | | | poured into the mould and after its solidification |
| applied to ensure correct flow and lessen porosity. | | | | the mould is broken to remove casting. The most |
| Aluminium is one of the few metals which may | | | | normal bonding agent is a mix of clay and water. |
| be cast by all processes of casting. | | | | Good metal handling practice is needed for getting |
| Die casting: | | | | good castings. |
| Aluminium alloys are more utilized in die casting | | | | Investment castings: |
| than alloys of any metal. In USA alone 2.5 billion | | | | It normally uses plaster moulds and throwaway |
| dollars worth aluminium alloy die castings are | | | | designs of wax or other burnable materials. |
| manufactured every year. Die casting is suitable | | | | Plaster slurry is "invested" all round designs for |
| for production of smaller parts. But when | | | | many castings the designs are melted out as the |
| expensive manufacturing equipment is used the | | | | plaster is baked. By these castings you can make |
| castings weigh 5kg-50kg. Cost effectiveness can | | | | precision parts, the aluminium parts can have walls |
| be obtained only by large scale production. With | | | | as thin 0.40 to 0.75 mm. It is also used to make |
| die casting it is possible to have close tolerance | | | | large number of parts of fine shapes which need |
| and fine finishing surface. Die castings are | | | | no further machining. These parts have low |
| manufactured by injecting melted metal into metal | | | | mechanical properties. |
| moulds under considerable pressure. Quick | | | | |