Challenges in the Forging of Steel-Aluminum Bearing Bushings

Abstract

The current study introduces a method for manufacturing steel–aluminum bearing bushings by compound forging. To study the process, cylindrical bimetal workpieces consisting of steel AISI 4820 (1.7147, 20MnCr5) in the internal diameter and aluminum 6082 (3.2315, AlSi1MgMn) in the external diameter were used. The forming of compounds consisting of dissimilar materials is challenging due to their different thermophysical and mechanical properties. The specific heating concept discussed in this article was developed in order to achieve sufficient formability for both materials simultaneously. By means of tailored heating, the bimetal workpieces were successfully formed to a bearing bushing geometry using two different strategies with different heating durations. A metallurgical bond without any forging defects, e.g., gaps and cracks, was observed in areas of high deformation. The steel–aluminum interface was subsequently examined by optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that the examined forming process, which utilized steel–aluminum workpieces having no metallurgical bond prior to forming, led to the formation of insular intermetallic phases along the joining zone with a maximum thickness of approximately 5–7 µm. The results of the EDS analysis indicated a prevailing FexAly phase in the resulting intermetallic layer.

Numerical Process Design for the Production of a Load-Adapted Hybrid Bearing Bushing

“…Furthermore, material properties such as the maximum tolerable tensile stress are strongly temperature-dependent. In [6] experimental closed-die forging tests were carried out using pre-joined semi-finished products consisting of the steel 20MnCr5 (AISI 5120) and the aluminium alloy EN AW-6082 to produce a hybrid bearing bushing. For some parts, tangential cracks were observed, which were caused by high tangential strains during the forging process.…”

Ejector pin-related high-cycle fatigue fracture of the critical die corner during automatic multistage cold forging of an automotive wheel nut

“…Besides the primary role of the ejector pin, it enhances the shape accuracy of the forging because a substantial draft is no longer needed to ensure the release of the forgings from the die insert [ 8 ]. The ejector pin is also used to form the shape onto the bottom side of the forging [ 9 ] or support large force in manufacturing hollow parts [ 10 ]. The ejector pin may apply counterpressure to prevent the material's fracture during forward extrusion [ [11] , [12] , [13] ].…”

Non-destructive Evaluation of Workpiece Properties along the Hybrid Bearing Bushing Process Chain

“…This prefabricated semi-finished product is then formed into the desired component by deep drawing. By contrast, within the Collaborative Research Centre (CRC) 1153, aluminum and steel are combined in the first production step to produce loadadjusted hybrid solid components with wear-resistant functional surfaces (Ref 9,10). This new approach allows for a greater degree of control over the evolution of the interfacing microstructure along the whole process chain.…”