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Fabricating: The manufacture of plastic products by appropriate operations. This includes plastics formed into molded parts, rods, tubes, sheeting, extrusion and other forms by methods including punching, cutting, drilling, tapping, fastening or by using other mechanical devices.

Family mold: A mold that produces non-identical parts simultaneously from multiple cavities.

Fan Gate: A gate used to help reduce stress concentrations in the gate area by spreading the opening over a wider area. Less warping of parts can usually be expected by the use of this type of gate.

Fatigue Strength: The maximum cyclic stress a material can withstand for a given number of cycles before failure occurs.

Fill pattern: the contours of the advance of the material as the cavity fills. (See flow pattern)

Fill pressure: the pressure required to fill the cavity.

Fill Time (also known as Injection): Time required to fill the cavity or mold.

Fill: The packing of the cavity or cavities of the mold as required to give a complete part or parts that are free of flash and porosity.

Filler: A relatively inert substance added to a plastic compound to reduce its cost and/or to improve physical properties, particularly hardness, stiffness and impact strength.

Fines: In the classification of powdered or granular materials such as molding compounds according to particle size, fines are the portion of the material composed of particles which are smaller than a specified size.

Finish: The surface texture and appearance of a finished article.

Finite element analysis: the solution of simultaneous equations for each element with resulting pressure, temperature and elapsed time at each node.

Flame Retardant: Having the ability to resist combustion (A flame retardant plastic is considered to be one that will not continue to burn or glow after the source of ignition has been removed.)

Flash Gate: Wide gate extending from a runner which runs parallel to an edge of a molded part along the parting line of a mold.

Flash: Any excess material that is formed with and attached to the component along a seam or mold parting line.

Flexural Strength: The maximum stress in the outer fiber at the moment of crack or break. In the case of plastics, this value is usually higher than the tensile strength.

Flow Balancing: modifying flow paths, particularly runner sections, so that all flow paths within a mold fill in equal time with equal pressure.

Flow Leader: local increase in thickness to encourage flow in a particular direction.
Flow Marks: Wavy surface appearances on a molded part caused by the improper flow of the melt into the mold.

Flow Pattern: The contour the melt takes sequentially as it fills the cavity.

Flow Rate: the volume of material passing a fixed point per unit time.

Foaming Agent: Any substance which alone or in combination with other substances is capable of producing a cellular structure in a plastic mass.

Fracture: The separation of a body, usually characterized as either brittle or ductile.

Freeze off: the temperature of the material is reduced to the point that it blocks an area it would fill if it were hotter.

Frictional heating: heat generated by the friction of the chains of molecules slipping past each other or over a surface.

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