The development of USM was started in 1927. It was accidentally discovered during investigating ultrasonic grinding of abrasive powders.

In many cases, if weld flash must be removed, this can be accomplished on welder as an integrated part of machine cycle. Part geometry and accessibility of flash are two major factors which determine wher on-machine flash removal can be incorporated, and which system can be employed.

Following are advantages of direct drive friction welding over inertia friction welding:
? Lower weld force for solid parts. Larger parts can be welded on same tonnage machine
? Lower weld torque if brake is applied at end of weld cycle. Tooling requirements are, refore, less rigid
? Lower RPM for solid parts
? No flywheel change between setups.

Ultrasonic machining accomplishes material removal through abrading action of grit-loaded slurry which is kept circulated between tool and workpiece. The cutting is actually performed by abrasive particles which are suspended in slurry.

The concentration of abrasive grits in slurry is related as follow
n = (6AC)/ ?d_g²,
where n= number of grits
A= total surface area of tool facing workpiece
C= concentration of abrasive grits in slurry
d_g= diameter of a grit
Thus above relation shows that any increase in ?C? will increase ?n? and hence material removal rate (MRR).

Following are few reasons to consider friction welding over or techniques:
? The machine-controlled process eliminates human error, and weld quality is independent of operator skill.
? It?s ecologically clean?no objectionable smoke, fumes, or gases are generated that need to be exhausted.
? No consumables are required? no flux, filler material, or shielding gases.
? Power requirements are as low as 20% of that required of conventional welding processes.
? Since re is no melting, no solidification defects occur, e.g. gas porosity, segregation or slag inclusions.

The shape of tool (solid or hollow), mechanical properties of materials used in tool making are some of parameters that may affect performance of USM process significantly.

Following are few components which are friction welded by manufacturers of agricultural equipment;
? Hydraulic piston rods
? Track rollers
? Gears
? Bushings
? Axles
Cultivators are heavy duty machines used for soil cultivation.

The abrasive grains are driven by high speed reciprocations across small gap in between tool and work piece, as already discussed. Uniform force is used to gradually feed tool. The impact of abrasive is energy source that is mainly responsible for material removal. Due to impact of abrasives, material removal takes place in form of small particles, which are carried away by abrasives slurry.

USM is used for machining;
? round shaped holes
? square shaped holes
? irregular shaped holes
? surface impressions.