A high-speed stream of abrasive particles carried by a high pressure gas or air is impinged on the surface of workpiece. The metal is removed due to erosion caused by the impact of high-speed abrasive particles as a jet. The gas stream flow through a nozzle at pressures up to 0.7 MPa and a velocity of 300 m/s. The chipping action produced is very effective on hard and brittle materials.
The air or gas is compressed and mixed with abrasive powder in the mixing chamber of nozzle. The jet diameter is 0.12 mm to 1.25 mm. The delivery nozzle is made of sapphire or tungsten carbide. The useful life of nozzle is about 30 hours. The abrasive powder is made of aluminium oxide, silicon carbide and sodium bi-carbonate mixture. The particle sizes vary from 10 to 50 micrometer.
(R.K. Singal, Mridul Signal, Rishi Signal, Fundamentals of Machining and Machine Tools,I.K. International Pub., 2008, p.210-211 )
Electron Beam Welding (07.4.2011; 02:05)
Electron beam welding is a process in which the heat required to produce fusion is obtained from the impact of a high velocity high density stream of electrons on the work piece. Upon impact the kinetic energy of the electrons is converted the thermal energy causing both vapourisation and melting. The vapourisation of the material beneath the beam enables the beam to penetrate into the material to be welded, with the beam and the vapour forming a hole. As the beam moves along the joint, the molten metal flows round the hole leaving the welded joint in the wake of the beam.
The EB welding have depth to width ratio of more than 10:1 due to the extremely high heat concentration. The beam is very narrow, less than 0.25 in. diameter and the welding speed is high. The net heat input is very low.
(V.M.Radhakrishnan, Welding Technology and Design, New Age International Pub., 2005, 2nd Edition, p.30-31 )
Liquid Thermal Polymerization (LTP) (07.4.2011; 12:49)
LTP process is quite similar stereolithograpy in a way that the part is built by solidification of successive layers of liquid polymer. However, polymers used in LTD process are thermosetting polymers instead of photopolymers and hence the solidification is induced by thermal energy rather than light energy. The thermal nature of the process is expected to make the control of the size of the voxels difficult due to dissipation of heat.
(Narendra B. Dahotre, Sandrip P. Harimkar, Laser Fabrication and Machining of Materials, Spr,nger Pub., 2008, p.356)
Beam Interference Solidification (BIS) (07.4.2011; 13:02)
This process is based on the point-by-point solidification of photosensitive polymers (contained in transparent vat) at the intersection of two laser beams having different wavelengths. The first laser excites the liquid polymer to the reversible metastable state which is subsequently polymerized by the radiations from the second laser. The process is associated with various technical limitations such as insufficient absorption of laser intensity at higher depths, shadowing effect of already solidified material, and diffraction of laser lights leading to difficulties in obtaining the precise intersection of the beam.
(Narendra B. Dahotre, Sandrip P. Harimkar, Laser Fabrication and Machining of Materials,Spr,nger Pub., 2008, p.356)
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