Process Flow for U.S.-Standard Twelve-Point Bolts

The production process for American-style twelve-point bolts is primarily designed based on their material properties, strength grades, and manufacturing standards. Typically, cold or hot upsetting is used as the core forming process. Combining general bolt manufacturing specifications with the processing characteristics of specific head structures, the mainstream production process is as follows:

I. Preparation and Pre-treatment of Raw Materials

Material Selection
American-style bolts are commonly made from carbon steel (such as 1035, 1045), alloy steel (such as 4140), or stainless steel (such as 304, 316), with the specific material determined by the strength grade (such as Grade 2, Grade 5, Grade 8).

Low-carbon steel is suitable for low-strength bolts.
Medium- and high-carbon steels or alloy steels must undergo tempering treatment to meet high-strength requirements.

Wire Rod Drawing and Spheroidizing Annealing
The raw material is drawn and reduced in diameter to the desired wire gauge, with the reduction rate carefully controlled within the range of 10% to 15% during the process to ensure both surface quality and ductility.
Subsequently, spheroidizing annealing is performed to spheroidize the pearlitic structure, enhancing the material’s cold heading formability and preventing cracking.

II. Forming Process: Cold upsetting is the primary method, with hot upsetting serving as a supplementary process.

Cold Heading
Most U.S.-standard twelve-point bolts are formed using multi-station automatic cold heading machines. The twelve-point head with flange structure can be forged in one step using a specialized die, ensuring continuous distribution of metal fibers along the contour and significantly enhancing tensile strength.
The process includes: material cutting → cold heading forming (pre-heading + final heading) → shank shaping.

Hot Forging
For twelve-point bolts made of large-specification or high-hardness materials, the hot upsetting process may be employed, particularly for products with diameters exceeding Φ20mm. After heating to the austenitizing temperature, the bolts are rapidly upset-forged and then subjected to subsequent heat treatment.