Plasticity of workpieces processed by deforming broaching with through deformations

Abstract

One of the essential parameters of the parts quality processed by deforming broaching is the surface plasticity, which depends on many factors and the technological aspects of the process. To create opportunities for technological control of the resource of used plasticity, it is necessary to evaluate the effect of deforming broaching modes on the plasticity resource of the workpiece. This work modeled the stress-strain state of an axisymmetric workpiece made of plastic metal under deforming broaching. The creation of finite-element models of the process made it possible to study the change in the parameters of the stress-strain state of the machined workpiece on its inner and outer surfaces. When analyzing the peculiarities of the change in the stress-strain state in the deformation cell, two zones of local plastic deformation appeared at the beginning of the contact zone and its end. The change in the plasticity increment along the deformation cell during the deformation of a thick-walled part also had two sharp peaks corresponding to the junction of the contact zone with the non-contact zone. It was proven that the size of the local plastic deformation zone depends on the workpiece thickness. The stress state in the contact zone and non-contact zones, as well as the influence of deforming broaching modes and workpiece thickness on the parameters of the stress-strain state and the deformation history of a material particle on the outer and inner surfaces of the workpiece, were investigated. When studying the features of the workpiece deformation by a group of deforming elements, it was found that the accumulated deformation and the resource of the used plasticity on the inner surface depend on the total deformation and the number of deforming elements. A new deformation scheme with consistent use of the plasticity resource on the outer and inner surfaces of the workpiece was developed. This allowed for designing a deforming broach with a group arrangement of deforming elements. The developed design ensured minimal use of the plasticity resource on the inner and outer surfaces. The conditions for the fracture (micro-peeling) appearance at the inner surface were identified. The obtained regularities made it possible to control the quality parameters based on the resource of the used plasticity of the surface layer of the inner and outer surfaces of the part during its deforming broaching. These studies also made it possible to refine the technology for restoring worn piston pins, which includes deforming broaching and subsequent chemical and thermal treatment, the duration of which was reduced by 20 %. The introduction of this technology at one enterprise alone saved 4.5 tons of 12HN3A steel when restoring 1000 piston pins of 10D100 diesel engines.