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Tuesday, August 4, 2009

Composite Fabrication : Filament Winding

FILAMENT WINDING is a process for fabricating a composite structure in which continuous reinforcements (filament, wire, yarn, tape, or other), either previously impregnated with a matrix material or impregnated during winding, are placed over a rotating form or mandrel in a prescribed way to meet certain stress conditions. When the required number of layers is applied, the wound form is cured and the mandrel can be removed or left as part of the structure.

High-speed, precise lay-down of continuous reinforcement in predescribed patterns is the basis of filament winding. The filament-winding machine traverses the wind eye at speeds that are synchronized with the mandrel rotation, controlling the winding angle of the reinforcement and the fiber lay-down rate. The deposition can be controlled either by computer numerically controlled (CNC) machines or by simple mechanically controlled winders; the latter are less convenient, but require a lower capital investment.

Figure below shows the basic six axes of the CNC machines. Usually, the mechanical machines are limited to three axes or less, whereas the CNC machines can accommodate up to seven axes.

Thermoset resins, generally used as binders for reinforcements, can be applied to the dry roving at the time of winding, which is known as wet winding. They may also be applied prior to winding as a tow or tape prepreg and used promptly or refrigerated. Usually the cure of the filament-wound composite is conducted at elevated temperatures without vacuum bagging or autoclave compaction. Mandrel removal, trimming, and other finishing operations complete the process.

Six axes of filament-winding machine motion. Courtesy of McClean Anderson, Inc Axis 1- Spindle/ Mandrel rotation Axis 2-Horizontal Carriage Motion Axis 3-Cross or Radial Carriage Motion Axis 4- Axis 5-Eye Motion Axis 6-Yaw Motion

The mandrel can be cylindrical, spherical, or any other shape as long as it does not have reentrant (concave) curvature—although several manufacturers have been able to incorporate complex reentrant curves in filament wound structures (Fig. 4 and 5). Large or thick-walled structures, particularly structures of revolution such as cylinders or pressure vessels, are most easily wound.

A Complex Winding Pattern


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