On the Mechanism of Formation of Back-End Defects in the Extrusion Process

Valberg, Henry; Lefstad, Martin; Costa, André Luiz de Moraes

doi:10.1016/j.promfg.2020.04.207

Cited by 8 publications

(5 citation statements)

References 2 publications

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“…The material is drawn more strongly into the centre due to the locally varying forming speed and forms the funnel shape in the of subsequent material flow. With increased relative forming path s, the effect mentioned becomes stronger, which is why the shape of the joining zone between steel and aluminium is characterised by a steadily increasing joining zone depth H. The occurring defect in the centre of the specimen is caused by the funnel formation, which usually occurs in monolithic semi-finished products due to a lack of subsequent material flow at the end of the forming process [20]. A locally weak bond in the centre of the joined materials before forming is pre-existent, due to low relative friction speeds in the friction welding process.…”

Section: Resultsmentioning

confidence: 99%

Investigation of the joining zone formation of impact extruded hybrid components by varied forming sequence and partial cooling

PIWEK

2023

Materials Research Proceedings

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Abstract. Hybrid material concepts enable the combination of beneficial properties of different materials to extend the limited potential of monolithic components. When it comes to steel and aluminium, a wear-resistant and a lightweight metal are combined to produce a weight-reduced high-performance component with load-adapted areas. A method to create hybrid gear shafts is a novel approach called Tailored Forming. The process chain consists of joining e. g. by friction welding and subsequent impact extrusion under elevated temperature. Before forming, an axial temperature gradient is set in the serial arranged semi-finished products to adjust the different yield stresses of the dissimilar materials through induction heating of the steel part. The subsequent forming is intended to positively influence the joining zone thermo-mechanically and geometrically. However, prior work indicated a limitation of the influence on the joining zone in forward rod extrusion. Therefore, approaches are being researched that enable a stronger formation of the joining zone geometry to influence the resulting bond qualities through surface enlargement. A forward rod extrusion process of friction welded hybrid semi-finished products made of 20MnCr5 (AISI 5120H) combined with EN AW-6082 (AA6082) was carried out experimentally. Complementary to prior investigations, in which mainly the aluminium section was reduced through the die angle followed by the steel, the forming sequence of the materials was reversed to increase the joining zone surface with variation of the forming path. Additionally, a cooling of the aluminium side was realized through an immersion cooling to adjust maximum temperature gradients and further equalize the different yield stresses. Hardness tests, metallographic and SEM images of cross-sections were taken to evaluate the bond quality with regard to the temperature influence, joining zone formation, occurring defects and the resulting intermetallic compound (IMC). Impact extrusion with initially steel formed followed by aluminium resulted in a spherical formation of the joining zone and consequently in greater surface area, but also lead to partial defects in the IMC. The partial cooling of the aluminium allowed higher temperature gradients to be set, thus reducing defects through improved material flow in the joining zone.

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Section: Resultsmentioning

confidence: 99%

Investigation of the joining zone formation of impact extruded hybrid components by varied forming sequence and partial cooling

PIWEK

2023

Materials Research Proceedings

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“…1). In turn, this results in surface defects and a loss of durability in the finished product [3]. In technical literature it's common to distinguish two types of billet skin flow [2,3].…”

Section: Introductionmentioning

confidence: 99%

“…In turn, this results in surface defects and a loss of durability in the finished product [3]. In technical literature it's common to distinguish two types of billet skin flow [2,3]. Flow type 1, also called inward flow, occurs when defective material flows into the tool ports along dead metal zones formed between the container and inlet surface of the tool.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the skin contamination predictability by means of QForm UK extrusion code

KNIAZKIN¹

2023

Materials Research Proceedings

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Abstract. The paper presents an innovative approach implemented in QForm UK Extrusion FEM software to analyse one of the core defects encountered in profile extrusion known as billet skin defect. The validation of the algorithm has been performed based on a number of experimental case studies taken from the literature [1,2]. Additionally, the sensitivity of the accuracy of the results to the variation in initial parameters has been analysed for both types of profile shapes: solid and hollow. Based on this, practical recommendations have been formalised for the successful industrial use of the presented algorithm.

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“…For structural applications, mechanical properties must be consistent throughout the extent of the profile, so that defects deteriorating such properties cannot be tolerated. In particular, the billet skin contamination, also known as back-end defect since occurring at the end of each extruded billet, may compromise mechanical properties [5] and lead to the scraping of material. This defect is related to the outer surface (also called skin) of the billet marked by different properties than those of the inner material, as microstructure and chemical composition.…”

Section: Introductionmentioning

confidence: 99%

FEM Analysis of the Skin Contamination Behavior in the Extrusion of a AA6082 Profile

Negozio

Pelaccia

Donati

et al. 2022

KEM

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In the extrusion of aluminum alloys, the skin contamination lead to the scraping of the profile extent in which this defect occurs. In order to optimize the scraping process, extrusion companies and die makers can either perform time-consuming and expensive analyses to experimentally determine the evolution of the defect or rely on predictive methods. Recently, numerical methods, as the Finite Elements, are increasingly used to predict the evolution of the skin contamination, but their accuracy is still uncertain. In this work, an AA6082 aluminum profile of industrial complexity is analysed and the data collected used to validate an innovative method for the prediction of the skin contamination evolution developed using the commercial FEM code Qform®. In addition, the results are used to assess the prediction accuracy of an industrial empirical formula often used by operators.

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On the Mechanism of Formation of Back-End Defects in the Extrusion Process

Cited by 8 publications

References 2 publications

Investigation of the joining zone formation of impact extruded hybrid components by varied forming sequence and partial cooling

Investigation of the joining zone formation of impact extruded hybrid components by varied forming sequence and partial cooling

Investigation of the skin contamination predictability by means of QForm UK extrusion code

FEM Analysis of the Skin Contamination Behavior in the Extrusion of a AA6082 Profile

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