A composite is not defined by one particular resin, fiber, or process. The category includes a wide family of engineered materials in which reinforcement carries or redirects load while a surrounding matrix binds the structure together, transfers stress, protects reinforcement, and establishes environmental performance.
Manufacturing methods range from manual fiberglass layup to automated molding, pultrusion, resin infusion, filament winding, compression molding, laminate pressing, CNC machining, waterjet cutting, bonding, drilling, and assembly.
What Are Composite Materials?
A composite is an engineered material made from two or more distinguishable constituents, commonly a reinforcement and a matrix, combined so the finished structure provides mechanical, thermal, electrical, chemical, dimensional, or weight-related properties not achieved as effectively by either constituent alone.
Fiber-reinforced polymers are among the most common industrial composites, but industrial laminates can also combine paper, cotton fabric, glass cloth, aramid, carbon, fillers, resin systems, and other layered reinforcements into rigid stock for machining and fabrication.
Reinforcement, Matrix, and Composite Structure
Each Constituent Has a Different Job
Composite properties depend not only on which materials are used, but also on their orientation, volume, distribution, bonding, thickness, cure, and final geometry.
Continuous fibers generally provide the greatest reinforcement along their aligned directions. Chopped fibers can support more distributed reinforcement and easier molding, while woven fabrics provide reinforcement in multiple directions within a layer.
Fiberglass-Reinforced Composites
Fiberglass combines glass reinforcement with a polymer resin system. It is widely used because glass fibers provide useful strength and stiffness while remaining electrically nonconductive and generally more economical than many advanced reinforcement systems.
Composite Manufacturing Methods
Hand Layup
Reinforcement is positioned in tooling and manually wetted with resin before consolidation and cure.
Spray-Up
Chopped fiber and resin are deposited onto tooling, rolled for consolidation, and cured into the finished laminate.
Vacuum Bagging
Flexible vacuum films apply atmospheric consolidation pressure over a laminate during cure.
Resin Infusion
Dry reinforcement is placed in tooling and resin is drawn through the fiber structure under vacuum.
Pultrusion
Continuous reinforcement is pulled through resin and a heated die to create constant-cross-section structural profiles.
Filament Winding
Resin-impregnated fibers are placed around rotating tooling to build tubes, pressure structures, tanks, and cylindrical products.
Compression Molding
Preforms or molding compounds are compressed between heated mold surfaces to create repeatable composite components.
Laminate Pressing
Reinforced sheets are stacked with resin systems and consolidated under heat and pressure into rigid industrial laminate stock.
CNC Fabrication
Composite panels, laminates, rods, tubes, and profiles are cut, drilled, routed, machined, and assembled after curing.
Layup, Consolidation, and Vacuum Processing
Mold surfaces are cleaned and prepared with release systems, coatings, or surface films as required.
Cloth, mat, tape, core, or prepreg materials are cut into the required ply shapes and orientations.
Reinforcement layers are positioned according to the laminate schedule and structural orientation.
Resin is manually applied, infused, injected, or already present in prepreg reinforcement.
Rollers, vacuum, pressure, matched tooling, or other methods remove air and bring the reinforcement into controlled contact.
Resin polymerizes under controlled time, temperature, and pressure.
The component cools sufficiently before handling or demolding.
The composite is removed from tooling without damaging edges, surfaces, or structural regions.
Excess material is removed and dimensions, laminate quality, surface condition, and final structure are evaluated.
Pultruded Composite Profiles
Pultrusion is a continuous process for manufacturing reinforced profiles with substantially constant cross-sections. Fibers are pulled through resin and then through a heated shaping die where the composite cures into the final profile.
Continuous Reinforced Structural Shapes
Pultrusion places a high percentage of continuous fibers along the length of the profile, making the process particularly useful when axial strength and stiffness are important.
Industrial Laminates
Industrial laminates are commonly supplied as rigid sheet, plate, rod, tube, or specialty shapes made by combining reinforcement with thermosetting resin under controlled heat and pressure.
| Laminate Type | Reinforcement | Common Characteristics |
|---|---|---|
| Paper Phenolic | Paper | Electrical insulation, machinability, economical rigid stock, and general industrial use. |
| Cotton Fabric Phenolic | Woven cotton fabric | Toughness, wear performance, machining capability, mechanical strength, and bearing behavior. |
| Glass Epoxy | Glass cloth | High mechanical strength, electrical insulation, dimensional stability, and moisture resistance. |
| Glass Silicone | Glass reinforcement | Useful electrical and thermal properties for elevated-temperature service. |
| Specialty Laminates | Engineered reinforcement systems | May be selected for arc resistance, thermal performance, electrical insulation, wear, or specialty environments. |
Laminates can be machined into electrical insulators, terminal boards, spacers, gears, wear components, fixtures, structural panels, supports, bushings, switchgear parts, and other industrial components.
Common Composite Reinforcements and Resin Systems
| Material | Role | General Characteristics |
|---|---|---|
| Glass Fiber | Reinforcement | Strength, stiffness, electrical insulation, corrosion resistance, and broad industrial availability. |
| Carbon Fiber | Reinforcement | High stiffness-to-weight ratio, low density, and strong directional mechanical performance. |
| Aramid Fiber | Reinforcement | Toughness, impact resistance, low weight, and useful tensile performance. |
| Polyester Resin | Matrix | Widely used in fiberglass products with practical processing and broad general-purpose performance. |
| Vinyl Ester Resin | Matrix | Useful corrosion resistance, toughness, and chemical-service performance. |
| Epoxy Resin | Matrix | Strong adhesion, mechanical properties, low cure shrinkage, and broad structural usefulness. |
| Phenolic Resin | Matrix | Useful fire, electrical, thermal, and industrial laminate characteristics. |
| Core Materials | Structural Core | Foam, honeycomb, balsa, and other cores increase section thickness while limiting weight. |
Products Made From Composites and Industrial Laminates
Composite Machining and Fabrication
Cured composites and laminates are often cut and machined after molding. Drilling, sawing, milling, routing, turning, waterjet cutting, sanding, grinding, and edge finishing can create final dimensions and assembly features.
CNC Routing
Routing creates edge profiles, cutouts, pockets, holes, slots, and large panel geometry.
CNC Milling
Machining can create controlled pockets, faces, holes, grooves, and assembly geometry.
Drilling
Holes require suitable tools, support, and cutting parameters to limit splintering and delamination.
Waterjet Cutting
Waterjet can profile selected composite sheets while limiting conventional cutting heat.
Sanding & Grinding
Abrasive finishing removes flash, smooths edges, and prepares surfaces for bonding or coating.
Assembly
Composite parts can be bonded or mechanically joined with inserts, fasteners, brackets, metal hardware, and other components.
Composite machining can generate abrasive dust and exposed fibers. Tooling, dust collection, worker protection, edge sealing, and contamination control should match the material and process.
Design for Composite Manufacturing
Continuous reinforcement is most effective when its orientation matches the primary structural load paths.
Abrupt laminate thickness changes can create stress concentration and manufacturing complexity.
Reinforcement and fabrics do not conform easily around extremely sharp internal corners.
Molded composite geometry should include appropriate draft, splits, removable tooling, or flexible release strategy.
Hole locations and fasteners should account for possible splitting, crushing, delamination, and bearing loads.
Machining can expose reinforcement, so sealing or coating may be needed in moisture or chemical environments.
Adhesive joints should provide adequate overlap, surface area, preparation, access, and load distribution.
Threaded inserts and metal hardware should distribute load rather than concentrate it into weak laminate regions.
Composite properties can vary significantly with direction, unlike many homogeneous isotropic materials.
Resin system, reinforcement, coatings, and joint materials should match moisture, UV, temperature, chemical, electrical, and fire requirements.
Bonding and Mechanical Joining
Composite assemblies can be joined with adhesives, bolts, screws, rivets, inserts, clips, brackets, and hybrid joints. The preferred method depends on laminate thickness, load, serviceability, environment, access, and whether drilling through reinforcement is acceptable.
| Method | Strength | Key Considerations |
|---|---|---|
| Adhesive Bonding | Distributes load across a larger area | Surface preparation, adhesive compatibility, cure, overlap, environment |
| Bolted Joint | Serviceable and mechanically defined | Hole quality, bearing stress, washers, inserts, laminate crushing |
| Threaded Insert | Provides repeated fastening interface | Insert retention, local reinforcement, pullout resistance |
| Hybrid Joint | Combines adhesive and mechanical retention | Load sharing, assembly sequence, cure, inspection |
Common Composite Manufacturing Defects
Composite Inspection and Testing
Composite quality often requires both dimensional and structural evaluation. A part can meet its exterior dimensions while containing voids, delamination, poor fiber placement, incomplete cure, or improperly bonded internal regions.
Characteristics Commonly Evaluated
Inspection methods can include visual examination, dimensional measurement, ultrasonic testing, tap testing, radiography where suitable, thermal methods, coupon testing, destructive sectioning, microscopy, hardness or cure checks, and mechanical testing.
What Drives Composite Manufacturing Cost?
Glass, carbon, aramid, specialty fabrics, roving, mat, and core materials can vary substantially in cost.
Polyester, vinyl ester, epoxy, phenolic, specialty additives, fire-retardant systems, and corrosion-resistant formulations affect material cost.
Mold size, surface finish, temperature capability, vacuum systems, matched tooling, and expected production life drive upfront expense.
Manual ply cutting, orientation, wet-out, rolling, vacuum setup, and inspection can create significant recurring labor.
Room-temperature, heated, press, oven, or other cure cycles influence production throughput.
Complex ply schedules and local reinforcements increase planning, cutting, placement, and traceability requirements.
Drilling, routing, milling, trimming, dust control, specialized tools, and edge finishing add downstream cost.
Nondestructive inspection, coupon testing, material certification, mechanical testing, and documentation increase quality cost.
Related Composite Manufacturing Resources
Composite components often require machining, fabrication, bonding, fastening, sealing, inspection, and contract production after the primary laminate or molding process is complete.
Composite, Machining & Fabrication Research
These manufacturing references correspond with secondary operations and related production methods commonly used with composite structures.
How to Select a Composite or Laminate Supplier
Composite suppliers should be evaluated against reinforcement, resin system, process, part size, structural requirements, environmental exposure, dimensional needs, machining, bonding, inspection, and expected production volume.
Confirm experience with hand layup, infusion, vacuum bagging, pultrusion, filament winding, compression molding, laminate pressing, or the required process.
Review familiarity with glass, carbon, aramid, polyester, vinyl ester, epoxy, phenolic, cores, and specialty laminate systems.
Tool design, mold construction, vacuum systems, temperature control, maintenance, and engineering changes should be supported.
Structural parts require repeatable ply orientation, reinforcement placement, resin content, and laminate thickness.
CNC routing, drilling, milling, trimming, waterjet cutting, dust collection, and edge finishing may be required.
Adhesive bonding, inserts, mechanical fastening, brackets, and hybrid assembly should match the final structure.
Dimensional measurement, laminate inspection, NDT, coupon testing, material traceability, and mechanical testing may be needed.
Confirm capability for corrosion, UV, electrical, temperature, fire, moisture, and chemical service where applicable.
Composite Performance Comes From the Combination of Materials, Orientation, and Process
Fiberglass, carbon reinforcement, industrial laminates, resin systems, cores, and bonded structures can produce components that are lightweight, corrosion-resistant, electrically insulating, structurally efficient, and highly configurable. Successful composite manufacturing depends on reinforcement selection, fiber orientation, resin compatibility, tooling, consolidation, cure, machining, bonding, inspection, environmental exposure, and the load paths expected in final service.