Filament winding turns continuous reinforcement into hollow composite structures by placing fibers along controlled paths over a rotating tool. The vocabulary connects three decisions: what material is deposited, where it is placed, and how the finished laminate is verified. Pipes, tanks, poles and pressure vessels share much of this language, although their manufacturing constraints differ.

1. From fiber package to mandrel

Mandrel — The forming tool that supports deposition and establishes the inner geometry. It may be removable, collapsible or sacrificial.

Liner — An inner barrier that can remain in the product. A liner is not automatically a load-bearing structural layer.

Creel, tensioner and delivery eye — The creel holds fiber packages, the tensioner regulates their pull, and the delivery eye guides the band toward the surface. [1]

In wet winding, dry reinforcement receives liquid resin during production. Towpreg uses reinforcement supplied with resin already incorporated. Thermoplastic winding requires a suitable heating and consolidation strategy rather than a thermoset cure reaction. Process selection changes handling, storage and thermal requirements. [2, 3]

2. Reinforcement and resin terminology

Filament, strand, roving and tow — A filament is an individual fiber. Larger bundles are described as strands, rovings or tows, depending on the reinforcement and supplier terminology.

Tex and K count — Tex expresses linear mass in grams per 1,000 m. Carbon tow designations such as 12K indicate approximately 12,000 filaments; they do not specify bundle width.

Band width — The deposited reinforcement width, measured perpendicular to its direction. Several bundles can form one band. [1]

Matrix — The continuous resin phase surrounding the reinforcement; its processing window and cured properties affect manufacturing and service behavior.

Impregnation and wet-out — Impregnation introduces resin into the reinforcement. Wet-out describes how effectively resin wets the fibers. A glossy exterior alone does not prove complete internal impregnation.

Pot life and gel time — Pot life is the usable working interval under stated conditions. Gel time marks development of a gel network. Neither term means the laminate has reached its final properties.

Cure cycle and post-cure — The prescribed thermal schedule develops a thermoset matrix. A subsequent post-cure may be specified to achieve the required property level. Follow the resin supplier’s validated schedule.

3. Winding angle: always declare the reference

Here, 0° is axial and 90° is circumferential. The signs +α and −α distinguish opposite slopes in a declared coordinate system. They do not, by themselves, command clockwise or counterclockwise spindle rotation. A drawing, simulation and CNC program must use compatible references. [1]

4. Hoop, helical and polar winding

Hoop winding places fibers nearly circumferentially and is effective for carrying hoop load. A small axial advance distributes adjacent turns along a cylinder. Helical winding combines rotation with longitudinal motion, producing inclined paths. Opposite traverses can create crossing fiber directions. Polar winding routes reinforcement over the ends and around polar openings; its feasibility depends on the part geometry and machine arrangement. [2]

Dome and boss — The dome is the curved end region of a vessel. The boss is an end fitting associated with an opening and the surrounding wound structure.

Geodesic path — A surface path that is locally straight within the surface geometry. On a general curved surface, it need not resemble a straight line in a side view.

Non-geodesic path — A path that departs from a geodesic and may require lateral restraint from friction or other process mechanisms. A plotted path is not proof that the fiber will remain in position.

5. Motion, pitch and speed

For an ideal cylinder with constant diameter D, no slip and steady deposition, the surface geometry gives:

tan(α) = πDn / vₐ and p = vₐ / n

Here n is spindle speed in revolutions per minute, vₐ is axial deposition speed in mm/min, D is in mm, and p is axial advance per revolution in mm/rev. Thus tan(α) = πD/p. These relations describe the cylindrical deposition path; they do not model dome motion or turnarounds.

Worked example: D = 200 mm, n = 10 rpm and α = 60° give vₐ ≈ 3,628 mm/min and p ≈ 362.8 mm/rev. If diameter grows while the speed ratio stays fixed, the angle changes. A controller may therefore update motion as the laminate builds.

6. Passes, circuits and pattern closure

A revolution is one spindle turn. A pass usually means a traverse in one direction. A circuit commonly includes an outward and return traverse. “Cycle” is less consistent: a machine supplier may use it for a circuit, a repeat or another programmed operation. Record the definition beside the count rather than assuming that one cycle equals one revolution.

Pattern closure occurs when the deposited path sequence returns to its repeating relationship. Closure and full coverage are different checks: a repeating pattern can still contain gaps. Indexing is the controlled circumferential shift between successive path placements. Turnaround is the end region in which traverse direction reverses; local angle, speed and buildup can differ from the central cylinder.

Coverage — The extent to which deposited bands cover the intended surface. Coverage should be checked over the useful length and end regions.

Ply or layer — A structural or manufacturing grouping of reinforcement. State whether one layer means one orientation, a ±α pair, or a complete coverage sequence.

Laminate and stacking sequence — The full layered construction and the order of its orientations. For example, [ +55 / −55 / 90 ] lists three orientations; thickness and repetition still need definition.

Balanced and symmetric — A balanced laminate pairs matching +α and −α contributions. A symmetric laminate mirrors its construction about the mid-plane. One property does not imply the other.

7. Useful length and trim allowance

The useful length is the portion retained in the finished component. Trim allowance is extra material removed after manufacture. Keep both distinct from total carriage travel, which can include lead-in, turnaround and clearance movements.

8. Quality terms that matter on the shop floor

Fiber volume fraction, Vᶠ — The fiber volume divided by total composite volume. It differs from fiber mass fraction; converting between them requires constituent densities and a consistent treatment of voids.

Void content — The fraction of internal empty volume. It requires an appropriate measurement method; visual surface inspection alone cannot establish it.

Resin-rich region and dry area — A resin-rich region has relatively little reinforcement. A dry area has inadequate resin impregnation. Their acceptance depends on the product requirements.

Fiber waviness and slippage — Waviness is deviation from the intended fiber alignment. Slippage is movement of reinforcement away from its intended deposited position.

Delamination — Separation between laminate layers. It is distinct from a surface scratch or a gap between adjacent bands.

Tension and compaction — Tension is tensile force applied to the reinforcement. Compaction describes consolidation of the deposited material. Tension influences consolidation, but the relationship also depends on curvature, angle and material behavior. [2]

9. Writing an unambiguous winding specification

A usable recipe identifies the part geometry, material system, angle reference, deposited band width, tension basis, speed limits, sequence, count definitions, end treatment, cure schedule and inspection criteria. Axis names such as X, Y, Z and A depend on the machine: define their physical functions rather than treating a letter as a universal filament-winding convention.

Example wording: “Wind the cylindrical section at ±60° relative to the mandrel axis. One circuit means one outward and one return traverse. Apply the specified number of circuits and verify coverage over the useful length. Record deposited band width, tension per bundle and actual diameter. Use the approved turnaround and cure recipes.” Numerical values and acceptance limits must be added for the particular part.

References and further reading

[1] Cadfil. Filament Winding Glossary. https://www.cadfil.com/help/html/glossary.htm

[2] University of Plymouth, MATS347. Filament winding and pultrusion. https://ecm-academics.plymouth.ac.uk/jsummerscales/MATS347/MATS347C9%20FWpult.htm

[3] Polar Technology. Filament Winding. https://www.polartechnology.co.uk/capabilities/filament-winding/

All figures are original explanatory schematics. The worked numerical example is illustrative.