The cold heading nut forming process is a machining method that utilizes plastic deformation of metal under external force. With the aid of dies, the metal volume is redistributed and transferred to form required parts or blanks. It is mainly used to manufacture bolts, nuts, nails, rivets, steel balls and other components. Forging blanks can be made of copper, aluminum, carbon steel, alloy steel, stainless steel, titanium alloy and so on. On cold heading machines, coil or bar stock goes through roller feeding, sequential material transfer, cutoff, ball pressing, angle forming, piercing and other operations, with multiple processes completed in one machine. Below is a brief introduction by Yida Borun Petrochemical on selecting raw materials for cold heading processes.

I. Selection of Cold Heading Machine Equipment

(1) Equipped with variable frequency speed regulation assembly to realize stepless speed adjustment within a certain range. (2) The machine body is cast from alloy-enhanced nodular cast iron, featuring high tensile strength and good wear resistance. (3) Adopts a two-stage gear transmission system with high transmission efficiency and large transmission torque. (4) Fitted with a pneumatic clutch brake to reduce power consumption of the motor. (5) The cutting system uses a guide plate to drive the cutter rod. Reciprocating motion of the guide plate delivers cutting force in a straight line, offering large, stable cutting force and good dynamic balance. (6) Multi-station cold heading machines use open-close clamps to transfer workpieces. The clamp system can flip or translate, facilitating the arrangement of forming processes. (7) High-wear-resistant alloy copper bushes are used for connections between crankshaft and machine body as well as impact connecting rods, boasting large bearing capacity, long service life and low maintenance cost. (8) Equipped with fault detectors and safety protection devices. The machine will stop automatically upon failure to provide maximum protection for equipment and tooling. (9) Thrust assemblies are installed on the feeding box to improve feeding accuracy. (10) The lubrication system features a simple and efficient oil circuit design. On the basis of circulating filtration, it can effectively protect punches and workpieces.

II. Selection of Workpiece Raw Materials

(1) Raw materials must undergo spheroidizing annealing, and their metallographic structure shall be spherical pearlite. (2) To minimize cracking tendency of materials and extend die service life, cold drawn materials shall have the lowest possible hardness for improved plasticity. (3) The dimensional accuracy of raw materials is generally determined according to specific product requirements and process conditions. For multi-station cold heading machines, the dimensional accuracy requirements for diameter reduction and heavy reduction are relatively loose. (4) The surface of raw materials shall have a matte, non-glossy lubricating film. No scratches, folds, cracks, galling, rust, oxide scale, pits or blemishes are permitted on the surface. (5) The total thickness of the decarburized layer in the radial direction of raw materials shall not exceed 1% of the raw material diameter. (6) To guarantee cutting quality during cold forming, the material is required to have a relatively hard outer surface and softer core. (7) Raw materials shall pass cold heading tests. Cold work hardening increases deformation resistance. Materials are expected to have the lowest possible sensitivity to cold work hardening.

III. Selection of Cold Heading Forming Oil

(1) It has excellent extreme-pressure lubricating performance, low-temperature performance, extreme-pressure anti-wear property, rust resistance and high-temperature oxidation stability. It improves the precision and surface finish of machined parts, prevents die seizure, meets multi-station forming requirements for standard and non-standard fasteners, and is fully capable of cold heading stainless steel workpieces. (2) It can minimize oil fume and mist, meeting stringent requirements for nut machining on multi-die presses with heavy reduction dies. (3) It delivers good processing performance for products with large deformation, such as hollow and high-strength bolts, sleeves, stainless steel hollow and semi-hollow rivets and other formed components. (4) It can effectively protect punches and dies, extend service life and reduce overall costs. (5) It provides good heat dissipation and prevents excessive local temperature rise of workpieces and dies during cold forming. (6) It features outstanding high-temperature resistance, low sludge formation, low odor and low smoke, protecting the working environment. (7) It offers moderate rust prevention to meet inter-process rust protection requirements during production. (8) It is suitable for demanding cold heading forming of stainless steel and large-deformation carbon steel.

The above covers the selection of raw materials, cold heading machine equipment and cold heading forming oil for cold heading nut processes. Using raw materials that meet process requirements can effectively avoid workpiece quality defects. Yida Borun’s special cold heading forming oil for nuts is compounded with self-developed high-performance sulfurized lard and sulfurized fatty acid esters as main agents. It is suitable for processing various types of automotive nut fasteners under high extreme-pressure and large-deformation conditions via cold and hot working methods. Widely used for cold heading forming of hard-to-machine materials including stainless steel and high alloy steel in automotive, shipbuilding, aerospace and other industries, it provides superior extreme-pressure anti-wear performance, avoids workpiece galling, effectively extends punch die life, and has received consistent recognition from fastener enterprises at home and abroad in practical applications.