Gerhard Hirt

RWTH Aachen University · Institute of Metal Forming

Damage that exists in the form of microvoids in a material can be influenced by various process parameters during forming. Depending on these parameters, the static recrystallization (SRX) occurring during the holding time between two hot forming steps can also lead to a reduction in damage. Therefore, this work aims to investigate the influence of...

Due to the current changes in mobility, lightweight design concepts continue to be of particular interest to the automotive industry. One form is the multi-material design, in which the advantageous properties of different materials are combined in one component. In this work, a component made of a steel sheet with stiffening structures of cast alu...

Nowadays, the requirements on metallic materials have become more comprehensive, which gradually exceed the capability of monolithic metals. One of the solutions is the composite metal, where different properties of the constituents are integrated as one. In industrial practice, hot roll bonding has been frequently employed to produce laminated com...

Friction is part of almost any forming process, thus, friction modelling is mandatory for process modelling. Since frictional stresses are difficult to measure, typically laboratory experiments are used, where a dimension sensitive to frictional stresses is measured instead. The conical tube-upsetting test, an advancement of ring compression test,...

The damage introduced into components during forming operations is often critical for the component performance in service. Because these performance properties depend strongly on the local stress state, it is important to consider this while evaluating material or components produced under specific processing chains. In this paper, we present an a...

For the press hardening process an Al-Si coating is usually applied on the surface of typical boron-manganese steels (22MnB5), to form a diffusion layer for protection against scaling. However, the diffusion layer requires long heating times and is environmentally questionable. This paper describes a new approach to substitute the Al-Si coating by...

Non-grain-oriented (NO) electrical steels are soft magnetic materials that are commonly used in electrical drives and machines. The magnetic properties of NO electrical steels are influenced by the alloying components (Si + Al), sheet thickness, grain size, and crystallographic texture. Compared to the conventional production of NO electrical steel...

The ring rolling process offers the possibility of producing seamless rings. For certain applications, it would be advantageous for cost reasons to produce rings with different materials at the area of the inner and outer circumference. Composite ring rolling, the combination of ring rolling and roll bonding, enables the production of such rings. I...

Press hardening of manganese-boron steels is one of the most widely used production processes for high-strength automotive components. The low residual formability of these parts is a decisive disadvantage. The low formability originates from a strong, but brittle martensitic microstructure transformed during quenching in the press-hardening tool....

Decision support systems can provide real-time process information and correlations, which in turn assists process experts in making decisions and thus further increase productivity. This also applies to well-established and already highly automated processes in continuous production employed in various industrial sectors. Continuous production ref...

In industrial production, customers’ requirements are rising regarding various aspects. Products have to be produced more economical, more flexible, faster, and with much higher quality requirements. Furthermore, especially for traditional mass production processes, shorter product cycles increase the demand in rapid production and process developm...

Modern hot sheet metal forming processes offer the opportunity, especially in the automotive sector, to meet current demands for ultra-lightweight design. Due to the increased formability at the high process temperatures, high-strength aluminium alloys are increasingly coming into the focus of the industry. However, the complex thermo-mechanical in...

Today’s industrial world is characterized by ever-shortening product development cycles and increasing degrees of product individualization which demand tools and enablers for accelerated prototyping. In addition, the existing uncertainty in the product development cycle should be reduced by involving stakeholders as early as possible. However, sho...

In this chapter, the focus lies on a predictive description of the material response to the thermomechanical loads within different process steps by means of physical and data-driven models. The modeling approaches are demonstrated in examples of innovative production technologies for components of a drive chain: Fine blanking of parts; powder meta...

The surface roughness including average roughness (Ra) and peak number (RPc) after skin-pass rolling influences the strip’s product properties, such as its friction coefficient in the subsequent sheet metal forming process. In order to both ensure an optimal tribological behavior and fulfill the process requirements of the following forming steps,...

Ultra-high-strength-steel parts produced by press hardening are widely used in the automotive sector for lightweight construction and passenger safety applications. Medium-manganese-steels (MMnS) are currently investigated as an alternative to boron-manganese steels. Their favorable mechanical properties of high strength and high ductility after qu...

Rolling is a well-established forming process employed in many industrial sectors. Although highly optimized, process disruptions can still lead to undesired final mechanical properties. This paper demonstrates advances in pass schedule design based on reinforcement learning and analytical rolling models to guarantee sound product quality. Integrat...

About 95% of all steel products are rolled at least once during their production. Thus, any further improvement of the already highly optimized rolling process, for example reduction of energy consumption, has a significant impact. Currently, most rolling processes are designed by experts based on their knowledge and heuristics using fast analytica...

In the original publication [...]

In article 2200327, Gouverneur, Bailly, and Hirtcover, show an ingot made of AISI4140 with artificially introduced voids, forged on the Institute for Metal Forming (IBF) forging press. This setup validates the shear model for void closure in open‐die forging developed in this article.

The increasing need for high performance materials for lightweight construc-tions results in a rising demand for compound materials. Electric vehicles re-quire innovative materials to face the challenges of the increasingly wide-spread production of batteries. Aluminium copper compounds present an an-swer to these new challenges as they combine the...

Um den steigenden Anforderungen der Stahloberflächen beim Kaltwalzen nachzukommen, werden neue modellbasierte und datengestützte Rege-lungskonzepte benötigt. Hierzu werden zwei nichtlineare, online-lernfähige Prozessmodelle eingeführt, die die Gerüstauffederung und das Abprägever-halten der rauen Arbeitswalzen beschreiben sollen. In einem abschließ...

The rolling process induces a heterogeneous deformation over the rolling stock height. The causes are the frictional shear stress between the contacting surfaces and the roll gap geometry. They induce a complex material flow within the rolling stock describable by the shear evolution. The shear evolution has a significant impact on rolling values l...

Bond formation plays a major role in the production of metallic composites, e.g. in roll bonding, composite ring rolling, and the permanent closure of voids by metal forming at elevated temperatures. At the same time the determination of the corresponding bonding strength is quite challenging due to various influencing factors. These factors includ...

New rapid gas-based hot sheet metal forming processes are being invented to manufacture geometrically complex automotive components from lightweight high-strength aluminum alloys. The complexity of the forming processes necessitates a computationally economic yet sufficiently accurate modelling and simulationSimulation methodology to ensure a succe...

In addition to achieving a specific target geometry and good material properties, one of the main goals of open‐die forging is to eliminate internal casting‐related voids, as they can lead to critical failure of the component during application. Models designed to predict void closure often use simplifying assumptions, so that they have limited val...

Der Einsatz von Stahl im Bauwesen war über viele Jahre von engen Vorgaben hinsichtlich der einsetzbaren Halbzeuge geprägt und verlieh Stahlkonstruktionen häufig den Charakter von „Baukastensystemen“. Die Modernisierung der Bearbeitungsmethoden veränderte diese Gegebenheiten. Im digitalen Zeitalter ist es nunmehr möglich, nicht nur aufseiten der Pro...

Eigenspannungen können erhebliche Auswirkungen auf die Struktur eines Bauteils haben, obwohl sie oft unbemerkt bleiben. Eigenspannungen lassen sich nutzen, um besondere rohrförmige Strukturbauteilen zu entwerfen; die so genannten bistabilen Rohre. Solche leichten Bauteile haben zwei stabile Geometrien und können dadurch kompakt und ohne Gehäuse in...

In order to meet the continuously increasing environmental concerns, automotive lightweight concepts of replacing steels with high strength aluminium alloys are one promising solution. Therefore, complex automotive structural components manufactured with new processes like rapid gas-based hot sheet metal forming can become a key factor from a formi...

Refractory linings are, in addition to loads due to corrosion and creep processes, particularly affected by thermomechanical stresses caused by the restricted thermal expansion of the lining. These stresses can occur within individual components as well as in bricks and can lead to plastic deformation, cracks and material failure. Thus, comprehensi...

Non-oriented (NO) electrical steel sheets find their application in rotating electrical machines, ranging from generators for wind turbines to motors for the transportation sector and small motors for kitchen appliances. With the current trend of moving away from fossil fuel-based energy conversion towards an electricity-based one, these machines b...

Non-oriented electrical steel sheets are applied as a core material in rotors and stators of electric machines in order to guide and magnify their magnetic flux density. Their contouring is often realized in a blanking process step, which results in plastic deformation of the cut edges and thus deteriorates the magnetic properties of the base mater...

The magnetic properties of non-oriented electrical steel, widely used in electric machines, are closely related to the grain size and texture of the material. How to control the evolution of grain size and texture through processing in order to improve the magnetic properties is the research focus of this article. Therefore, the complete process ch...

A tailor-made microstructure, especially regarding grain size and texture, improves the magnetic properties of non-oriented electrical steels. One way to adjust the microstructure is to control the production and processing in great detail. Simulation and modeling approaches can help to evaluate the impact of different process parameters and finall...

Due to the nonlinear material behavior and contradicting application requirements, the selection of a specific electrical steel grade for a highly efficient electrical machine during its design stage is challenging. With sufficient knowledge of the correlations between material and magnetic properties and capable material models, a material design...

To produce cold-rolled steel strips with specific mechanical properties and surface roughness typically temper rolling is adopted. In most cases, a uniform roughness pattern on the strip surface is mandatory. Due to the wear of the textured work rolls, their surface roughness (Ra) continuously reduces during the process, which should be accounted f...

Iron–silicon alloys with up to 6.5 wt.% Si offer an improvement of soft magnetic properties in electrical steels compared to conventional electrical steel grades. However, steels with high Si contents are very brittle and cannot be produced by cold rolling. In addition to solid solution hardening, it is assumed that the B2- and DO3-superlattice str...

Zusammenfassung Bistabile Bleche verfügen aufgrund der über Umformprozesse eingebrachten Eigenspannungen über zwei stabile Strukturen: Im Transportzustand können sie platzsparend transportiert werden, bevor sie am Einsatzort in eine gestreckte Form entfaltet werden. Die gestreckte Form weißt eine größere Stabilität auf, wenn sie vollständig geschlo...

Austenitic high manganese steels exhibit outstanding mechanical properties, such as high energy absorption, owing to various deformation-mechanisms such as dislocation slip, twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP). Here, we show a novel thermomechanical treatment to manufacture a high manganese steel Fe–18Mn-...

The ferrite fraction and phase distribution of duplex steels depend strongly on the temperature evolution during hot deformation and are correlated to different mechanical behaviors during hot deformation as well as cold deformation. Therefore, the control of microstructure evolution during hot forming is relevant for target-oriented material desig...

Bistable metal sheets with a coiled transport geometry and an unfolded profile as second stable state, are of great interest as lightweight components. It is well known that a specific distribution of residual stresses is necessary to enable bistable properties. With the help of numerical FE models, the optimal process parameters for production of...

Bistable fully closed shells can serve as long supporting structures that can be folded into a compact transport geometry and unfolded at the construction place. Bistability is achieved by introducing a specific distribution of residual stresses through the thickness of the shell, e.g., by incremental die-bending. In order to find a suitable bendin...

In order to not only produce an open-die forged part with the desired final geometry but to also maintain economic production, precise process planning is necessary. However, due to the incremental forming of the billet, often with several hundred strokes, the process design is arbitrarily complicated and, even today, often only based on experience...

Gaseous medium is being used for sheet metal forming at elevated temperatures, especially for lightweighting purposes. These processes enable forming of high strength alloys of a wide range of thickness due to low material flow stress as well as improved formability. In these processes, the resulting component properties are an interplay of numerou...

Improvement of component performance by controlling the damage state after metal forming enables a reduction in sheet thickness and, consequently, in component weight and material cost. To establish methods for controlling damage in finished parts, the entire process chain from steelmaking and casting through hot and cold rolling to deep drawing mu...

In forming simulations, flow curves are cardinal inputs to predict features, such as forming forces and material flow. The laboratory-scale experiments to determine them, like compression or tensile tests, are affected by deformation heating, restricting direct flow curve determination. In principle, the current analytical and inverse methods deter...

Bistable fully closed shells can serve as long supporting structures that can be folded into a compact transport geometry and unfolded at the construction place. Bistability is achieved by introducing a specific distribution of residual stresses through the thickness of the shell, e.g. by incremental die-bending. In order to find a suitable bending...

Although great improvements have been made in cold rolling over recent years, roughness and related properties such as the strip’s tribology and paintability have not been mastered yet. In order to obtain a predefined surface quality, a layered control loop is implemented in context of a cold rolling mill to track a given roughness reference. Feedb...

Zunehmend steigende Anforderungen an die Effizienz und Leistung elektrischer Maschinen für den Einsatz in Fahrzeugen machen neue Herstellungsverfahren für Statorwicklungen notwendig. Daher wurde in Zusammenarbeit mit der RWTH Aachen University sowie den beiden Firmen Schaeffler und Breuckmann ein serientaugliches Herstellungsverfahren entwickelt, m...

Flow curves characterize plastic flow in materials and their accurate description is necessary to reproduce any forming process in simulations. For flow curve determination, laboratory uniaxial compression or tensile tests are conducted to record force-displacement during deformation. Flow stress is then calculated as the ratio of force to cross-se...

Many metal forming processes involve several steps, which influence the shape and properties of the final component. The previous manufacturing process of the semi-finished component influences the properties of extruded components. The authors analyze the evolution of damage and voids in the sequence of caliber rolling to cold forward rod extrusio...

In the production industry, the digital transformation enables a significant optimization potential. The concept of reinforcement learning offers a suitable approach to train agents on learning control strategies, further advancing automation. While applications training directly on real-world processes are rare due to economical and safety constra...

In der Thermoprozesstechnik treten Oberflächenkontakte zwischen Festkörpern an vielen Stellen auf und führen zu zusätzlichen Wärmewiderständen. Die Kenntnis dieser Widerstände kann relevant für die Prozessmodellierung oder die Auslegung von Anlagen sein. Im Rahmen der Industriellen Gemeinschaftsforschung wurde ein Versuchsstand zur Bestimmung von K...

Roller leveling is a widely used production process to eliminate the coil set from metal strips. Therefore, this process aims mainly on removing the sheet curvature, while the created residual stresses are not systematically adjusted. Nonetheless, a straight strip can possess a disadvantageous residual stress distribution leading to a curvature whe...

Incremental sheet forming (ISF) is a flexible sheet metal forming process to realize products within short time from design to the first produced part. Although fundamental research on ISF has been carried out around the world, ISF still misses commonly required tolerances for industrial application. In this study, the influences of tool path as we...

Steel sheets are manufactured from slabs produced in continuous casting, which inevitably results in a porous initial microstructure. These pores are nuclei for ductile damage and need to be closed during rolling in regard of the strict performance requirements of todays advanced high strength steels. Due to the beneficial shape factor of the roll...

Understanding the interdependencies of the processing steps of high silicon containing non-oriented (NO) electrical steel is a key factor for improving its final magnetic properties. Moreover, every process step in the production has a significant impact on the properties. Steels with a high silicon content are ferritic (α-Fe). Accordingly, the mic...

In modern process design of metallic components, the influence of the metal forming process on the component properties can be taken into account. However, damage occurring concurrent to forming cannot be accounted for yet. Due to the complex multi-scale, multi-mechanism nature of damage, it is very challenging to predict its evolution through any...