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Wednesday, February 19, 2014

Type of Mandrel in Filament Winding Process

In mandrel design and material selection, the following criteria should be considered:
1. cost
2. mandrel reusability (durability)
3. production quantity
4. mandrel material thermal characteristics
5. mandrel strength/ability to resist deflection during winding and cure
6. final part tolerances required
7. dimensional stability

To ease part removal, mandrels may be constructed from water-soluble materials (sand), plaster, or an assemblage of metal shells that is collapsible or segmented. Tube mandrels constructed with a high-quality surface finish and a slight taper are often used for cylindrical parts.

The mandrel, which determines accurate internal geometry for the component, is generally the only major tool. Low-cost mandrel materials such as cardboard or wood can often be used when winding low-cost routine parts.
For critical parts requiring close tolerances, expensive mandrels designed for long-term use may be required. For high-temperature cure 315°C (600"F), graphite mandrels with low thermal expansion may be advantageous, however some attention should be paid to the potential difficulties of mandrel removal. Gas containment pressure vessels often require metal liners because composites are porous; these metal liners can also serve as mandrels.

Mandrels can be group to four types of mandrels. First is non-removable, which the mandrel remaining as a part of the wound structure. The other three are removable and classified according to the removal technique as:
-entirely removed (for example, tubular mandrels with or without taper and with release agent);
-collapsible (the mandrel is disassembled or removed piece by piece)
-Breakable or soluble (plaster, sand or salts).

The selection of a mandrel involves several trade-offs. These include part size and complexity, size of openings, resin system and its curing cycle and the number of components to be fabricated. The basic requirements for a mandrel, whether it will be removed from the part after winding or remain as a part of the structure, are:
-It must be stiff and strong enough to support its own weight and the weight of the applied composite while resisting the fiber tension pressure from winding and curing.
-It must be dimensionally stable and should have a thermal coefficient of expansion greater than the transverse coefficient of the composite structure.