Fundamental study of central crack mechanism and criterion in cross wedge rolling

Cross wedge rolling (CWR), a novel metal forming process for manufacturing axisymmetric stepped shafts, is widely applied in transport industries. Central crack, the cavity formed in the product centre, is a critical problem, preventing its development in safety-critical industries. However, the understanding of the central crack mechanism is insufficient, and there is not yet a robust fracture criterion to predict its occurrence. This study aims to establish a fundamental understanding of the central crack mechanism and build a robust physically-based fracture criterion. An innovative CWR physical model with plasticine billets was built in house, which allowed the dies to be rapidly 3D printed and the workpiece with specific mechanical properties to be efficiently manufactured. The effects of the stress variables and initial material properties (ductility) on central cracking were investigated by varying the die geometries and billet material compositions, respectively. It is found that the maximum shear stress plays a dominant role in the central crack formation, and with the increase of the material ductility, the central crack transitions from brittle fracture to ductile fracture. A robust physically-based damage model set was proposed, along with a novel material constant calibration method. The reliability of the proposed model was validated quantitively by 60 groups of CWR tests with different materials and die geometries. The proposed calibration method will significantly benefit the industry due to the extremely simplified die geometries. To further understand the central crack mechanism in the practical industry, the microstructural characteristics (e.g., inclusion, grain size and phase composition) of two high-strength steel CWR billets (with/without high possibility to crack) were quantitatively analysed and compared. It is found that central cracking can be effectively avoided by controlling the inclusion content in the CWR billets.Open Acces

Numerical simulations of screw spike, worm and gear rolling

Cross wedge rolling (CWR) is a very efficient technological process which has a favourable effect on properties of rolled products. At the same time, however, this forming technique causes complex non-linear problems resulting from variable contact conditions in the deformation zone. During the rolling process either adhesion or surface slip on the rolling contact surface may occur. The situation is further complicated by complexly-shaped wedge tools with thread-forming grooves. Those problems notwithstanding, the cross wedge rolling process can be examined effectively with the aid of computer simulations which precede both laboratory and industrial tests. Lublin University of Technology has developed and implemented a novel method of screw spike rolling as well as it has conducted computer simulations and model tests of rolling semi-finished gears. Even though the rolling tests have been carried out on semi-finished gears, it is expected that significant material savings can be yielded in the process of producing finished products. Given the rolling tests conducted on other products, it can be assumed that the quality of produced gears thus can be also improved, in contrast to gears produced by means of metal machining methods. Apart from screw spikes, hot cross wedge rolling also allows to produce coarse-pitch gears, which is not possible in a cold cross wedge rolling operation.Поперечно-клиновая прокатка (ПКП) является высокопроизводительным процессом получения изделий высокого качества. В то же время процесс формообразования является сложной нелинейной задачей вследствие различных условий на контактной зоне деформации. В течение процесса прокатки может происходить как прилипание, так и скольжение на контактной поверхности. Положение усложняется в дальнейшем сложной формой клиновидного инструмента для формовки винтового профиля. Несмотря на это процесс ПКП может быть эффективно осуществлен с использованием компьютерного моделирования, предшествующего как лабораторной, так и производственной проверке. В Люблинском технологическом университете разработан и осуществлен новый метод прокатки винтов для крепления рельс к шпалам согласно с результатами компьютерного моделирования, а также модельное тестирование прокатки заготовок шестерен. Полученные результаты позволят повысить качество изделий и сократить расход материала по сравнению с методами изготовления изделий механической обработкой. Горячая КПК позволит получать зубчатые колеса большого модуля, которые невозможно получить при холодной прокатке

Numerical simulation and experimental validation of the cladding material distribution of hybrid semi-finished products produced by deposition welding and cross-wedge rolling

The service life of rolling contacts is dependent on many factors. The choice of materials in particular has a major influence on when, for example, a ball bearing may fail. Within an exemplary process chain for the production of hybrid high-performance components through tailored forming, hybrid solid components made of at least two different steel alloys are investigated. The aim is to create parts that have improved properties compared to monolithic parts of the same geometry. In order to achieve this, several materials are joined prior to a forming operation. In this work, hybrid shafts created by either plasma (PTA) or laser metal deposition (LMD-W) welding are formed via cross-wedge rolling (CWR) to investigate the resulting thickness of the material deposited in the area of the bearing seat. Additionally, finite element analysis (FEA) simulations of the CWR process are compared with experimental CWR results to validate the coating thickness estimation done via simulation. This allows for more accurate predictions of the cladding material geometry after CWR, and the desired welding seam geometry can be selected by calculating the cladding thickness via CWR simulation. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Study of stress-strain state billets when rolling in a continuous mill of hot-rolled thin stripes using MSC super forge

The article proposes a new design of a continuous mill. To study the stress-strain state during rolling of thin slabs on the proposed mill, a three-dimensional geometric and simulation model of the rolling process was developed using MSC SUPER FORGE. Based on the obtained results of numerical modeling, the distributions of equivalent strains in a thin slab when rolling in 1 mill stand, the distribution of equivalent stresses in a thin slab when rolling in 1 mill stand, the distribution of the temperature field in a thin slab when rolling in 1 mill stand

Hybrid Bulk Metal Components

In recent years, the requirements for technical components have steadily been increasing. This development is intensified by the desire for products with a lower weight, smaller size, and extended functionality, but also with a higher resistance against specific stresses. Mono-material components, which are produced by established processes, feature limited properties according to their respective material characteristics. Thus, a significant increase in production quality and efficiency can only be reached by combining different materials in a hybrid metal component. In this way, components with tailored properties can be manufactured that meet the locally varying requirements. Through the local use of different materials within a component, for example, the weight or the use of expensive alloying elements can be reduced. The aim of this Special Issue is to cover the recent progress and new developments regarding all aspects of hybrid bulk metal components. This includes fundamental questions regarding the joining, forming, finishing, simulation, and testing of hybrid metal parts

Odabrane nove tehnologije i zadaci istraživanja u oblikovanju deformiranjem materijala

The article gives a review of selected new technologies of materials forming. That is selected 10 procedures, first, high pressure torsion processing, at the end, metal injection molding. All the new procedures have good performance and in the future for expect more the application in industry.Članak daje osvrt odabranih novih tehnologija u oblikovanju deformiranjem materijala. To je odabranih 10 postupaka, prvi, visokotlačna torziona obradba i na kraju, lijevačko injektiranje metala. Svi novi postupci imaju dobre karakteristike i u budućnosti za očekivati veću primjenu u undustriji

Book of abstracts of the 14th International Symposium of Croatian Metallurgical Society - SHMD \u272020, Materials and metallurgy

Book of abstracts of the 14th International Symposium of Croatian Metallurgical Society - SHMD \u272020, Materials and metallurgy held in Šibenik, Croatia, June 21-26, 2020. Abstracts are organized in four sections: Materials - section A; Process metallurgy - Section B; Plastic processing - Section C and Metallurgy and related topics - Section D

Hot forging for producing railway wagon bogie adapter

Hot forging forming of railway wagon bogie adapter is a new railway wagon bogie adapter processing technology. In this paper, a hot forging die for railway wagon bogie adapter was designed, and the forming quality were analyzed by using DEFORM-3D software. Then, the feasibility of the process was verified by experiments. It was found that using this mold can eliminate the defects such as loose as-cast in metal smelting process, optimize the microstructure, forging products with good density, product quality and other characteristics of stability

Hot forging for producing railway wagon bogie adapter

Hot forging forming of railway wagon bogie adapter is a new railway wagon bogie adapter processing technology. In this paper, a hot forging die for railway wagon bogie adapter was designed, and the forming quality were analyzed by using DEFORM-3D software. Then, the feasibility of the process was verified by experiments. It was found that using this mold can eliminate the defects such as loose as-cast in metal smelting process, optimize the microstructure, forging products with good density, product quality and other characteristics of stability