Draft for Seminar

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DRAFT FOR SEMINAR

Processing of structural composites

Aamir

1.Manufacturing process selection techniques/criteria

2.Processing needs

3.Processing techniques per thermoset e

thermoplastic

Forming Processes for Thermosetting matrix composites:

Hand layup and sprayup techniques.

Filament winding.

Pultrusion.

Resin transfer moulding.

Autoclave moulding.

Ehsan

Forming Processes for Thermoplastic matrix composites:

Injection moulding.

Film stacking.

Diaphragm forming.

Thermoplastic tape laying.

4.Applications

5.Example of aerospace industry

•

Main parts and the processing techniques used



6.Conclusion

• In the RTM process, dry (i.e. non-impregnated ) reinforcement is pre-

shaped and oriented into skeleton of the actual part known as the preformwhich is inserted into a matched die mold.

• The heated mold is closed and the liquid resin is injected

• The part is cured in mold.

The mold is opened and part is removed from mold

Resin Transfer Moulding

Close mold low pressure process.

A dry preform is placed in a matched metal die.

A vaccum pulls the Low – viscosity resin through a flow medium that helps

impregnate the preform.

Resin may also be forced by means of a pump.

6.1 IntroductionEvery material possesses unique physical, mechanical, and processing characteristicsand therefore a suitable manufacturing technique must be utilizedto transform the material to the final shape. One transforming method maybe best suited for one material and may not be an effective choice for anothermaterial. For example, wood is very easy to machine and therefore machiningis quite heavily utilized for transforming a wooden block to its finalshape. Ceramic parts are difficult to machine and therefore are usually madefrom powder using hot press techniques. In metals, machining of the blankor sheet to the desired shape using a lathe or CNC machine is very common.

In metals, standard sizes of blanks, rods, and sheets are machined and thenwelded or fastened to obtain the final part. In composites, machining of standard-sized sheets or blanks is not common and is avoided because it



cuts the fibers and creates discontinuity in the fibers. Exposed and discontinuousfibers decrease the performance of the composites. Moreover, theease of composites processing facilitates obtaining near-net-shape parts.Composites do not have high pressure and temperature requirements forpart processing as compared to the processing of metal parts using extrusion,roll forming, or casting. Because of this, composite parts are easily transformed

to near-net-shape parts using simple and low-cost tooling. In certainapplications such as making boat hulls, composite parts are made at roomtemperature with little pressure. This lower-energy requirement in the processingof composites as compared to metals offers various new opportunitiesfor transforming the raw material to near-net-shape parts. There are two major benefits in producing near-net- or net-shape parts.First, it minimizes the machining requirement and thus the cost of machining.Second, it minimizes the scrap and thus provides material savings. Thereare cases when machining of the composites is required to make holes or tocreate special features. The machining of composites requires a differentapproach than machining of metals; this is discussed in Chapter 10.© 2002 by CRC Press LLC

Composite production techniques utilize various types of composite raw

materials, including fibers, resins, mats, fabrics, prepregs, and molding compounds,for the fabrication of composite parts. Each manufacturing techniquerequires different types of material systems, different processingconditions, and different tools for part fabrication. Figure 1.5 in Chapter 1shows a list of the various types of most commonly used composites manufacturingtechniques and Figure 2.1 in Chapter 2 shows the type of rawmaterials used in those manufacturing techniques. Each technique has itsown advantages and disadvantages in terms of processing, part size, partshapes, part cost, etc. Part production success relies on the correct selectionof a manufacturing technique as well as judicious selection of processingparameters. The main focus of this chapter is to describe emerging andcommercially available manufacturing techniques in the field of thermosetandthermoplastic-based composite materials. Various composites manufacturing

techniques are discussed in terms of their limitations, advantages,methods of applying heat and pressure, type of raw materials used, andother important parameters. The basic knowledge of these processes willhelp in selecting the right process for an application. Section 6.2 brieflydescribes the manufacturing process selection criteria.

6.2 Manufacturing Process Selection CriteriaIt is a monumental challenge for design and manufacturing engineers toselect the right manufacturing process for the production of a part, the reasonbeing that design and manufacturing engineers have so many choices interms of raw materials and processing techniques to fabricate the part. Thissection briefly discusses the criteria for selecting a process. Selection of aprocess depends on the application need. The criteria for selecting a processdepend on the production rate, cost, strength, and size and shape requirements

of the part, as described below.6.2.1 Production Rate/SpeedDepending on the application and market needs, the rate of production isdifferent. For example, the automobile market requires a high rate of production,for example, 10,000 units per year (40 per day) to 5,000,000 per year(20,000 per day). In the aerospace market, production requirements are usuallyin the range of 10 to 100 per year. Similarly, there are composites manufacturingtechniques that are suitable for low-volume and high-volumeproduction environments. For example, hand lay-up and wet lay-up processescannot be used for high-volume production, whereas compression molding(SMC) and injection molding are used to meet high-volume production needs.© 2002 by CRC Press LLC

6.2.2 Cost

Most consumer and automobile markets are cost sensitive and cannot affordhigher production costs. Factors influencing cost are tooling, labor, raw materials,



process cycle time, and assembly time. There are some compositeprocessing techniques that are good at producing low-cost parts, while othersare cost prohibitive. Determining the cost of a product is not an easy taskand requires a thorough understanding of cost estimating techniques. Thecost of a product is significantly affected by production volume needs aswell. For example, compression molding (SMC) is selected over stamping

of steel for the fabrication of automotive body panels when the productionvolume is less than 150,000 per year. For higher volume rates, steel stampingis preferred. Various cost-estimating techniques, as well as various parametersthat affect the final cost of the products, are discussed in Chapter 11.6.2.3 PerformanceEach composite process utilizes different starting materials and therefore thefinal properties of the part are different. The strength of the composite partstrongly depends on fiber type, fiber length, fiber orientation, and fibercontent (60 to 70% is strongest, as a rule). For example, continuous fibercomposites provide much higher stiffness and strength than shorter fibercomposites. Depending on the application need, a suitable raw material andthus a suitable composite manufacturing technique are selected.6.2.4 Size

The size of the structure is also a deciding factor in screening manufacturingprocesses. The automobile market typically requires smaller-sized componentscompared to the aerospace and marine industries. For small- tomedium-sized components, closed moldings are preferred; whereas for largestructures such as a boat hull, an open molding process is used. Table 6.1reveals the suitability of composites manufacturing techniques in terms of product size.

6.2.5 Shape The shape of a product also plays a deciding role in the selection of aproduction technique. For example, filament winding is most suitable forthe manufacture of pressure vessels and cylindrical shapes. Pultrusion isvery economical in producing long parts with uniform cross-section, suchas circular and rectangular. Table 6.1 characterizes each manufacturing method based on the abovefactors. The cost category of the part is shown when the manufacturingequipment is running at full capacity.

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