The process which forms axisymmetric parts over a mandrel by the use of various tools and rollers is known as spinning. Forming clay on a potter’s wheel is similar to this process.

Conventional spinning:

Conventional spinning process
Fig.1 Conventional spinning process

Conventional spinning is a process in which a circular blank of preformed or flat sheet metal is connected to a mandrel.
The mandrel rotates and a tool is used to deform the circular blank in the desired shape.
Manual or computer controlled (for higher production rates) mechanisms are used to operate the tool.
Skilled manpower is required for this process as a sequence of passes are involved into this.
Conical and curvilinear shapes are suitable to be produced by this process, which otherwise would be difficult or uneconomical to manufacture.
Part diameters range up to 6 m.
High strength or low ductile materials require spinning at elevated temperatures but most of the spinning process takes place at room temperatures.

Shear spinning:

Shear spinning process
Fig. 2 Shear spinning process

Shear spinning is also known as power spinning, flow turning, hydro spinning, and
spin forging.
This process reduces the sheet’s thickness while maintaining its maximum (blank) diameter.
Two rollers are preferable in order to balance the forces acting on the mandrel but a single forming roller can also be used.
Typical parts made are rocket motor casings and missile nose cones.
Shear spinning has the capability to produce parts upto 3m in diameter.
This operation wastes little material, and it can be completed in a relatively short time in some cases in as little as a few seconds.
Various shapes can be produced by simple tooling.
The maximum reduction in thickness to which a part can be subjected by spinning without fracture is known as spinnability of a metal.
Spinnability is mainly involved in tensile reduction of area of the material similar to that of bending.
Thus, a metal’s thickness can be reduced by 80% in just one spinning pass if it has a tensile reduction of area of 50% or higher
This operation is carried out at elevated temperatures for metals with low ductility.

Tube spinning:

Tube spinning process
Fig. 3 Tube spinning process

In tube spinning, solid or round mandrel with rollers are used to reduce the thickness of hollow or cylindrical blanks.
A longer tube is produced due to reduction in thickness.
This operation is capable of producing external and internal profiles from cylindrical blanks with constant wall thickness.
The parts may be spun forward or backward; this nomenclature is similar to that of direct and indirect extrusion.
As in shear spinning, the maximum thickness reduction per pass in tube spinning is related to the tensile reduction of area of the material.
Tube spinning is used to produce rocket, missile, and jet-engine parts, pressure
vessels, and automotive components, such as car and truck Wheels.

Incremental forming:

Incremental forming
Fig. 4 Incremental forming

Incremental forming is a term applied to a class of processes that are related to conventional metal spinning.
No special tooling or mandrel is used.
The final part shape is determined by the motion of rod.
The tool path across the part profile determines the strain distribution along the workpiece.
Proper lubrication is essential for this process.
CNC incremental forming uses a CNC machine tool that is programmed to follow contours at different depths across the sheet-metal surface.
In this arrangement, the blank is clamped and is stationary, and the tool rotates to assist forming.
Low tooling costs and high flexibility in the shapes are the biggest advantages of this process.
CNC incremental forming has been used for rapid prototyping of sheet-metal parts.
Low production rates and limitations on materials that can be formed are the biggest drawbacks of this process.

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