Spray Forming

The other names for spray forming are spray deposition, in-situ compaction and spray casting. This is a technique of casting near net shape metal components with other homogeneous microstructures through the deposition of some semi-solid sprayed droplets on a shaped substrate. In spray forming method using an induction furnace and alloy is melted after which the molten metal is poured slowly through a conical tundish in the small-bore ceramic nozzle.

Atomisation:

The ideas of gas atomised spray forming is first developed by Professor Singer during 1970s in Swansea University. Here the atomisation is caused by making a high pressure gas to impinge on a stable melt stream. After this process, the resulting droplets are collected which could be used to form a near-dense billet of near-net shape.  The stainless steel cladding of incinerator tubes, the aluminium-titanium, aluminium-silver sputter targets, the aluminium-neodymium, the aluminium-silicon alloys, nickel superalloy rings and discs for aerospace-engines and other high speed steels are the applications that are found in the spray forming.

Molten alloy flow rate:

 The molten alloy flow rate of the gas atomised spray forming (GASF) is about 1-20 kg/min-1. The metal flow rate of about 80kg/min-1 can be achieved by using twin atomizer systems. On a commercial basis some extraordinary steel billets of 1 tonne or more have been used collectively with Al alloy extrusion billets of about 400kg and Ni superalloy ring blanks of about 500 kg.

Advantages of Spray Forming:

There are several advantages offered by the spray forming in some specialized techniques like powder metallurgy and in certain conventional ingot metallurgy. Spray forming is considered to a flexible process which could be effectively used to make some wide range of materials. Some materials Al-5wt% Li alloys or Al-SiC, Al-Al₂O₃ metal matrix composites which are used by this method are difficult to be used by other methods. A fine equiaxed microstructure in the range of about 10-100µm can be achieved by combining the rapid cooling in the spray and there by generation of a large population in the impacting spray.

One important attraction of the spray forming is the gain of the potential economic benefit which is achieved by reducing the number of process step between the finished product and the melt. Strip, ring, tube, clad bar/roll and some other cylindrical extrusion feed stock products are produced using spray forming.

Disadvantages:

The spray forming process has two big disadvantages. One is the low process yield relatively with a typical loss of about thirty percent. The second one is the process control which is a free-forming process with some interdependent variables.

Questions:

• What is Spray forming?
• What are the advantages and disadvantages of Spray forming?