Making of Bolts and Nuts

Industrial fasteners (bolts, screws, and nuts) require high-speed precision manufacturing to ensure dimensional accuracy, high fatigue strength, and structural reliability. High-strength bolts are manufactured through cold heading (cold forging) rather than machining, preserving uninterrupted grain flow along the bolt head and shank for superior shear and fatigue resistance.

Key Steps in Fastener Manufacturing:

Wire Drawing & Spheroidizing: Coiled alloy steel wire rod is uncoiled, acid-pickled, and drawn through carbide dies to exact diameter.
Cold Heading: High-speed multi-station cold formers cut wire blanks and strike the head with progressive punch dies.
Thread Rolling: Threads are rolled between hardened reciprocating flat dies or cylindrical rotational dies under high compressive force, inducing beneficial compressive residual stresses.
Heat Treatment (Quench & Temper): Bolts are heated in a controlled atmosphere furnace, oil-quenched, and tempered to achieve target hardness and toughness (e.g., ISO Class 8.8, 10.9).
Surface Finishing & Quality Inspection: Parts receive protective coatings (zinc electroplating, black oxide, or hot-dip galvanizing) followed by optical sorting and proof load testing.

Watch the detailed manufacturing and quality testing process in the video below:

Check this discovery video on manufacturing of bolts and nuts. From cold forging, to testing were shown.