2. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 1 Lecture 11 & 12 Processing Routes Compression Molding: -One type is matched die molding: useful for complex contour, strict tolerance, relatively small sizes; high volumes(to offset/ justify high cost of tooling) -Uses forms such as mat, chopped fiber molding compounds, fabric prepregs -Product form placed in mold -Top of mold placed in position -Apply heat and pressure with hydraulic plates -A limitation would be the size of the press -Fast and precise production -Very good for sheet molding compound (SMC)

3. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 2 Moldings Preform molding: based on gl/ polyester or vinyl ester, similar to SMC process (form fibers to shape first, then add resin, followed by heat and pressure to cure. Rubber Expansion Molding: - another procedure for applying pressure Uses se up shown Pressure achieved due to thermal expansion of silicon rubber constrained against metal shell – results in high pressure -heat from oven -Limitation include deterioration of rubber after a few cycles.

4. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 3 Filament Windings shaft Filament Winding (one-step process) -very high rate process -Amenable to automated machine control (little labor required) -pressure bottle and cylindrical shapes -rapidly growing variety applications -continuous roving/yarns/strands -Continuous filaments wound a mandrel(tool) Major concerns in filament windings -Resin selection -Viscosity -Need diluent or heat to lower viscosity -Curing requirements Fiber Requirements -high tensile strength -highest mechanical quality -finishes to improve handling

5. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 4 Filament Windings Impregnation methods -Wet winding -Fiber is impregnated immediately -Most common in aerospace -Most economical Prepreg winding - resin and fiber combined in separate step -better control -better wet-out -allows use of resin with viscosities too high for wet winding Wind fibers are n two ways: -planar winding: side by side no cross over -Helical winding: mandrel moves while feeding

6. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 5 Filament Windings Mandrel: can be in sections (removed piece by piece) can be salt or sand (dissolved) -after winding, product is cured on mandrel with heat alone (under tension) -tension can affect void content, resin content, thickness or part.

7. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 6 Filament Windings

8. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 7 Filament Windings Characteristics of filament winding -automation -no prepreg step -low labor cost -high machine cost Tape winding -similar to filament winding except uses prepreg tape -Wrapped around mandrel using rolling machine -Used for golf clubs/pipes/tubes/fishing rods

9. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 8 Filament Windings

10. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 9 Pultrusion Pultrusion: a process for producing continuous length of shapes with a constant cross section by pulling resin-impregnated fibers through a heated die where curing occurs. Characteristics -Pultrusion produces parts with -high fiber volume, high percentage of unidirectional reinforcement. -primarily a method for thermosetting resins -one of few continuous FRP process -Accounts for 3% of total FRP -based on continuous fibers

11. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 10 Pultrusion Process Steps: -String-up of desired fiber pattern -Resin impregnation -Preforming shape around mandrel (if necessary) -Pre-heat (augmented cure) -Cut finished part to length -Speed: 0.5 to 10 ft/min -Throughput: up to 4 lb/min

12. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 11 Pultrusion Resins -polyesters: mostly isophtalics, accounts for most of market -vinyl ester Epoxies(aromatic amine, anhydride cures) Desirable resin characteristics: -low viscosity (300-1200 CPS) -Long pot life (in impregnation bath) -Good wet-out for fiber type used -Fast curing (cure time can limit production rate) -Appropriate cured resin properties -Mechanical (toughness, flexibility) -Chemical resistance -Weather-ability -Fire retardancy

13. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 12 Pultrusion Reinforcements: -unidirectional roving (tows) usually the major type and provides longitudinal stiffness/strength - E-glass Pultrusion roving is most common -Kevlar 49, Graphite

14. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 13 Pultrusion Mats, tapes, fabric, veils, non-woven - must be available in continuous forms - must be strong enough to wiothstand pulling force -E-glass continuous strand mat is most commonly used to provide transverse properties - non-wovens can be used to improve surface quality Desirable characteristics -high yield(100-200 yd/lb) to reduce number of ends which must be handled -fiber finish to reduce “fuzzing”, improve handling and wet-out

15. Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 14 Pultrusion Advantages of Pultrusion: -continuous process -easy to automate, low labor -High output; very long parts are possible -Uses inexpensive forms of reinforcement -Selective placement of reinforcement relatively easy -Low scrap