What should we pay attention to when selecting cold heading raw materials?
1, Analysis of the characteristics of cold heading process
(1) According to the theory of metal plasticity, a certain pressure is applied to the metal billet at room temperature to cause it to undergo plastic deformation in the mold cavity and form according to the specified shape and size.
(2) It is necessary to choose high-quality metal materials with good plasticity, and their chemical composition and mechanical properties have strict standards.
(3) There are multiple models and series of cold heading bolt and nut forming machinery, with reliable equipment performance, high efficiency, and stable quality.
(4) The forging force of the workpiece is large, and the configuration of power equipment is expensive.
(5) The workpiece has good surface quality and high dimensional accuracy, but due to cold work hardening during the forging process, the deformation should not be too large.
(6) The cold heading process is applicable to workpieces with large quantities and various specifications.
2, Reasons affecting upsetting accuracy
(1) Chemical composition of raw materials: Pure metals have better plasticity than alloys, and impurity elements generally cause brittleness and reduce plasticity. Various alloys have different effects on plasticity.
(2) Metallographic structure of raw materials: The different properties, shapes, sizes, quantities, and distribution states of multiphase structures have varying degrees of influence on plasticity. Defects such as grain size, segregation, inclusions, bubbles, and porosity can reduce the plasticity of metals.
(3) Process deformation temperature: With the increase of temperature, plasticity increases, but this increase is not simply a linear rise.
(4) Metal strain rate: An increase in strain rate has both a decrease in metal plasticity and an increase in metal plasticity. The combined effect of these two factors ultimately determines the change in metal plasticity.
(5) Deformation mechanics conditions: Compressive strain is conducive to the development of plasticity, while tensile strain is detrimental to plasticity. The plastic processing method with triaxial compressive principal stress diagram and biaxial compressive tensile principal strain diagram is extremely conducive to the development of metal plasticity.
(6) Other problem factors: In the case of discontinuous deformation, the plasticity of metals can also be improved, especially when low plasticity metals undergo thermal deformation.