Cold heading technology and precision method for fasteners

Cold heading technology and precision method for fasteners

Cold heading is a forging method by which metal rods are upset and formed by a die at normal temperature. It is usually used to make screws, bolts, rivets, nuts, etc. Can reduce or replace cutting machining. Forging blank materials can be copper, aluminum, carbon steel, alloy steel, stainless steel and titanium alloy. The cold heading is mostly carried out on the special cold heading machine, which is convenient to realize continuous, multi-station and automatic production. The process of cutting, heading, accumulation, forming, chamfering, rolling, reducing and trimming can be completed in sequence on the cold heading machine.

?

Next, we will briefly introduce how to choose cold heading raw materials：

?

First, the characteristics of cold heading process

(1) According to the theory of metal plasticity, a certain pressure is applied to the metal blank at room temperature to make it produce plastic transformation in the mold cavity according to the specified shape and size. (2) Must choose high-quality metal materials with good plasticity, and its chemical composition and mechanical properties have strict standards. (3) Cold heading bolt and nut forming machinery has multiple models and series of machines, and the equipment has reliable performance, high efficiency and stable quality. (4) The workpiece forming upsetting force is large, and the configuration of power equipment is expensive. (5) The workpiece has better surface quality and higher dimensional accuracy, because there is cold hardening during the upsetting process, the deformation should not be too large. (6) Cold heading process is applicable to large batch and various specifications of the workpiece.?

Second, the reasons affecting the upsetting accuracy

(1) chemical composition of raw materials: pure metal plasticity is better than alloy, impurity elements usually cause brittleness to reduce plasticity, and various alloys have different effects on plasticity.

(2) raw material metallographic structure: the nature, shape, size, quantity and distribution of the heterogeneous structure are different, and the degree of influence on the plasticity is also different. Defects such as grain and segregation, inclusion, bubble and porosity will reduce the plasticity of the metal.

(3) Process deformation temperature: plasticity increases with the increase of temperature, but this increase is not a simple linear rise.

(4) Metal strain rate: The increase of strain rate both reduces the plastic side of the metal and increases the plastic side of the metal. The result of the combined action of these two factors ultimately determines the change of metal plasticity.

(5) Deformation mechanical conditions: compressive strain is conducive to the development of plasticity, while tensile strain is unfavorable to plasticity, plastic processing methods with three-way compressive principal strain diagram and two-way compressive tensile principal strain diagram are very conducive to the development of metal plasticity.

(6) Other problem factors: in the case of discontinuous deformation, the plasticity of the metal can also be improved, especially when the thermal deformation of low-plasticity metal is more obvious.