TE671 Textile Composites Manufacturing Process

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Manufacturing Processes of Textile Composites :

Manufacturing Processes of Textile Composites By: Dr. Mumtaz Hasan Malik

Manufacturing Processes :

Manufacturing Processes Open Moulding Closed Moulding Filament Winding Pultrusion

OPEN MOULDING PROCESS:

OPEN MOULDING PROCESS

Introduction :

Introduction Only one mould surface is made, which is either positive or negative. (Fig. 3.1) Large components and structures can be produced by this method. Mostly glass fibres are used as reinforcing agents and thermosetting resins such as epoxy and polyester are used as matrix material.

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Desired thickness of composite is achieved by applying matrix resins and reinforcement fibres (woven roving or yarns mats) layer by layer. Laying processes can be alternated by the use of prepregs , which are linear or planar fibrous structure coated with a predetermined quantity of an uncured catalyzed resin matrix After lay-up, curing treatment is carried out Open mould process is cost effective.

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Larger and complex structures cab be produced. Better design flexibility. However, only one surface of the composite is smooth. Labor intensive process and more skill required, automation held reduce their problems Longer running time.

Classification of Open Mould Process :

Classification of Open Mould Process Based on resin and reinforcement application method or curing method. Two or more processes are continued to take advantages of each method. Hands layup Spray-up Bag moulding Autoclave moulding

Hand Lay-up Process :

Hand Lay-up Process First used in the middle of 20 th century to manufacture boat hulls. Layers of resin and reinforcement are applied manually on the mould one by one to obtain the desired thickness. Cleaning, gel coating, laying up, curing, and part removal are included in the manufacturing procedure (Fig. 3.2)

Automation in Lay-up:

Automation in Lay-up Automated tape-laying machines. Rolls of fibrous structure mounted on machine are passed through catalyzed matrix resin for fibre wetting. Wetted fibres are passed through adjustable rollers which maintain the thickness of laminates.

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Then material is placed on the mould . Rate of automated tape laying machine depends on laminate thickness, looseness/tightness of fibre structure and resin type used. Automated machines give controlled fibre: resin ratio Machines are available in various sizes, from a small to large model used for making boat hulls.

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Automated tape-laying machines are suitable for simple and large geometries. The main application area is the air craft body parts.

Spray-up Process:

Spray-up Process It is an alternative method of laying-up in open mould process. It helps to automate matrix and fibre application thereby reduce the time period as compared to hand lay-up process. Chopped fibres along with matrix resins are sprayed on to an open mould surface until the desire thickness is achieved.

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Spray up may also be used for applying gel coat to the mould surface before hand lay-up and spray process. Equipment for spray-up process include: a spray gun, a glass fibre chopper attachment and a pumping system. Main types of Spray guns are: internal airmix , air less internal mix, external airmix and external airless mix.

Vacuum Bag Moulding:

Vacuum Bag Moulding Laminated components are covered by flexible, non-adhering polymer sheet (PVA, PA). Sealing of edges of covered mould . Applying pressure by plastic bag to laminated components during curing by creating vacuum.

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Process provides higher V f and better adhesion between layers compared to layup process without bag moulding . To accelerated curing, heating is applied. Pressure applied limited to 98 kPa Fig. 3.4 a)

Pressure Bag Moulding:

Pressure Bag Moulding Positive air pressure is supplied by blowing air to inflate an elastomeric bag covering laminate on open mould surface. Pressure can be applied upto 300 kPa (Fig.3.4 b).

Curing:

Curing Thermoset matrix resins require curing to harden. Hardening of matrix resins take place due to extensive crosslinking of polymeric structure. Cross linking in curing process is influenced by time, temperature and pressure. Heating is done in ovens, by infrared radiations or in autoclaves.

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A curing oven is a large metal, thermally insulated, air-circulating contain with large doors at one or both ends. Standard size is 3m high, 4m wide and 9m long. Infrared heating is used when laminates on open moulds are large In autoclave curing, heat is applied in an enclosed chamber, both under temperature and pressure control.

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An autoclave is a thermally insulated large hot air insulating cylindrical metal pressure vessel. Pressure is applied with air and/or CO 2 or Nitrogen gas. A typical size of autoclave is 4m in diameter and 17m long.

Autoclave Moulding Process :

Autoclave Moulding Process Autoclave consists of the following parts: A pressure vessel. A heating source gas or electrical upto 700 o C. A fan to circulate gas uniformly in the vessel. A system to pressure vessel, nitrogen, CO 2, or air upto 15MPa. A system to create vacuum to laminates covered by a vacuum bag. A system to control operating parameters. A system to load moulds into autoclave.

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Prepregs are used for autoclave moulding Prepregs typically contains 42% by weight of resin Curing without any loss of resin makes V f 50 %. Loss of resin during curing increases V f . Excess resin flowing removes entrapped air and residual solvents from prepregs and reduces voides in laminates.

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Recently, 34 weight percent is applied during prepregs manufacturing and only 1–2 weight percent resin loss during moulding is allowed. Prepregs are brought from freezer to clean room (class 100,000 or 400,000) Plies are cut from prepregs role into desired shape, size and orientation .

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Cut parts are laid up in proper orientation. Components of vacuum bag lay-up are shown in Fig. 3.9. Roles of typical vacuum bag materials are given in the table.

Curing Process :

Curing Process Loading of laid-up moulds into autoclaves. Running of a cure cycle, developed through various studies. At the start application of vacuum to remove air, volatiles etc. Heating starts at a specified heat rate. Resin viscosity first decrease, then attains a minimum and then increases rapidly as crosslinking (curing reaction) begins and completes (Fig. 310)

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Resin flow by face bleeding (normal to top laminate face) is preferred over edge bleeding (flow through edges of part). Cure temperature and pressure are selected to meet the following requirements: Uniform curing of resin and achieving specific degree of cure in the shortest possible time. Temperature should not exceed the prescribed limit Cure pressure should remove excess resin completely before viscosity increase.

Tooling:

Tooling Provides contour configuration to the composite part. Transfers heat to the part lay-up. Typical composite tooling materials are given in Table 3.5.

Applications:

Applications Automotive Aerospace Marine Architectural structures Skis, golf clubs, tennis rackets

Merits and Demerits :

Merits and Demerits Autoclave moulding is used for quality composites especially for aerospace industry. Good dimensional stability and variable thickness can be produced. Pressurization, controlled heating and cooling and vacuum is expensive. Time consuming operation. Labour intensive. Expensive material Auxiliary materials are single-use item

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