Hybrid cylindrical roller thrust bearing washers of type 81212 were manufactured by tailored forming. An AISI 1022M base material, featuring a sufficient strength for structural loads, was cladded with the bearing steel AISI 52100 by plasma transferred arc welding (PTA). Though AISI 52100 is generally regarded as non-weldable, it could be applied as a cladding material by adjusting PTA parameters. The cladded parts were investigated after each individual process step and subsequently tested under rolling contact load. Welding defects that could not be completely eliminated by the subsequent hot forming were characterized by means of scanning acoustic microscopy and micrographs. Below the surface, pores with a typical size of ten µm were found to a depth of about 0.45 mm. In the material transition zone and between individual weld seams, larger voids were observed. Grinding of the surface after heat treatment caused compressive residual stresses near the surface with a relatively small depth. Fatigue tests were carried out on an FE8 test rig. Eighty-two percent of the calculated rating life for conventional bearings was achieved. A high failure slope of the Weibull regression was determined. A relationship between the weld defects and the fatigue behavior is likely.

The present paper describes a new method concerning the production of hybrid bevel gears using the Tailored Forming technology. The main idea of the Tailored Forming involves the creation of bi-metal workpieces using a joining process prior to the forming step and targeted treatment of the resulting joint by thermo-mechanical processing during the subsequent forming at elevated temperatures. This improves the mechanical and geometrical properties of the joining zone. The aim is to produce components with a hybrid material system, where the high-quality and expensive material is located in highly stressed areas only. When used appropriately, it is possible to reduce costs by using fewer high-performance materials than in a component made of a single material. There is also the opportunity to significantly increase performance by combining special load-tailored high-performance materials. The core of the technology consists in the material-locking coating of semi-finished parts by means of plasma-transferred-arc welding (PTA) and subsequent forming. In the presented investigations, steel cylinders made of C22.8 are first coated with the higher-quality heat-treatable steel 41Cr4 using PTA-welding and then hot-formed in a forging process. It could be shown that the applied coating can be formed successfully by hot forging processes without suffering any damage or defects and that the previous weld structure is completely transformed into a homogeneous forming-typical structure. Thus, negative thermal influences of the welding process on the microstructure are completely neutralized.

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 Fe_xAl_y phase in the resulting intermetallic layer.

The production of multi-metal bulk components requires suitable manufacturing technologies. On the example of hybrid bevel gears featuring two different steels at the outer surface and on the inside, the applicability of the novel manufacturing technology of Tailored Forming was investigated. In a first processing step, a semi-finished compound was manufactured by cladding a substrate using a plasma transferred arc welding or a laser hotwire process. The resulting semi-finished workpieces with a metallurgical bond were subsequently near-net shape forged to bevel gears. Using the residual heat after the forging process, a process-integrated heat treatment was carried out directly after forming. For the investigations, the material combinations of 41Cr4 with C22.8 (AISI 5140/AISI 1022M) and X45CrSi9-3 with C22.8 (AISI HNV3/AISI 1022M) were applied. To reveal the influence of the single processing steps on the resulting interface, metallographic examinations, hardness measurements and micro tensile tests were carried out after cladding, forging and process-integrated heat treatment. Due to forging and heat-treatment, recrystallization and grain refinement at the interface and an increase in both, hardness and tensile strength, were observed.

This paper describes two process routes with focus on the die forging of coaxial hybrid workpieces. Using the example of two multi-material demonstrators, a bevel gear and a bearing bushing, two fundamental principles of hybrid-forged components will be presented. A cost-effective construction is realized for the bevel gear by means of a high-strength steel combined with a low-cost steel in the areas where high strength is not required. In contrast, the bearing bushing consisting of a steel-aluminium combination offers new potentials in terms of lightweight construction, saving component weight while featuring equal durability. In addition, forging tooling systems and tailored heating strategies for both demonstrators are presented and discussed.

ESAFORM is an association with the mission to stimulate applied and fundamental research in the field of material forming. Its annual conference, the International ESAFORM Conference on Material Forming, is used to achieve one of the main goals of ESAFORM: to spread scientific and technological information related to material forming within academic and industry. The next conference will be held online on 14-16 April 2021.