Many studies have shown that failure following non-proportional load paths cannot be predicted by a linear Forming Limit Curve (FLC), as the deformation history and a change in loading direction influence the formability and failure mode. In this paper, the different failure modes due to different load paths are investigated, for the first time, by conducting Nakajima tests with pre-formed specimens. The main objective of the investigation is to better understand the influence of pre-forming and change in loading direction on the formability. To predict this behaviour, regardless of the failure mode, the Generalized Forming Limit Concept (GFLC) is extended.

To convert electric into kinetic energy within an electrical motor emerging magnetic fields have to be amplified by using electrical steels. The efficiency of this energy conversion is determined by the electrical steel’s magnetic properties. Due to residual stress having a negative effect on an electrical steel’s magnetic behavior, manufacturing processes like stamping that deform the material thereby decrease the electrical motor’s efficiency. This paper presents a novel approach to predict stamping-related increased magnetic property deteriorations from in situ measured values. Using the approach can prevent an excessive efficiency decrease from increasing tool wear by just in time maintenance.

Since an inhomogeneous punch pressure distribution occurs in the Nakajima test, equibiaxial flow curves have been determined solely in the hydraulic bulge test so far. By using an innovative measurement technique, it is possible to determine both the punch pressure and strains that occur in the Nakajima test. In this paper, a calibration and realization strategy is presented that allows to determine accurate equibiaxial flow curves for sheet metal materials using a modified Nakajima test without inverse parameter identification. This setup is suitable to substitute the expensive and time-consuming hydraulic bulge test by a simple and common experimental setup.

During every kind of sheet metal manufacturing process, thermoelectric voltages and currents result from a temperature rise between tool and sheet metal. Their influence on the process and tool wear behavior has been investigated insufficiently so far. Therefore, Seebeck coefficients, representing thermoelectric properties, have been determined for several materials. The correlation between different Seebeck coefficients of tool, respectively, sheet materials and arising thermoelectric currents are exemplarily shown by an instantaneous measurement during blanking. An adequate material selection with regard to thermoelectric properties reduced adhesive wear to 22%. The obtained results improve the fundamental understanding of wear causing interactions.

Shear cutting is an essential part of the sheet metal manufacturing processes. Almost every metal component produced from sheets or stripes is subjected to a shearing process. During shear cutting with an open cutting line, the lateral component of the cutting force enlarges the die clearance according to the tool’s stiffness. As a result, the tool life and part quality are likely to decrease. To date, neither the amount nor the course of the lateral force has been analyzed in detail. Especially the reduced tool stiffness in most measuring concepts, caused by the sensor integration, leads to a die clearance variation which alters the measured results. Thus, an extremely stiff measuring concept was developed and integrated in a shear cutting tool. Therefore, we can assume that the sensor integration does not influence the shear cutting process. This novel concept allows to measure the lateral force separately from the normal component of the cutting force for an open cut. Following, shear cutting experiments were performed utilizing the thermo-mechanically rolled, microalloyed bainitic steel grade SZBS800. Finally, distinctive phases of the measured cutting and lateral force curves are discussed in detail. These results contribute to a better understanding of the shear cutting process and enables designing the tool’s stiffness for an open cut appropriate to the lateral forces.

A temperature rise occurs in the sheet metal and tool parts due to the dissipation of a large part of plastic work during blanking. The resulting temperature in the shearing zone has various impacts on the process. The correlation between the temperature rise and sheet metal behaviour under varying process parameters is investigated. Causal associations can be shown by in-situ measurements of the dynamic temperature development at the cutting edge of the punch and analyses of the sheet metal behaviour. The presented results provide essential knowledge for further experimental, analytical and numerical blanking investigations.

The formability requirements of high-strength steels are increasing as a result of progressive lightweight construction. An innovative two-stage shear cutting process has been developed in order to meet these requirements. It significantly reduces the edge crack sensitivity of the material in the cutting zone. Studying the effect of worn tool elements on process safety is a key focus for the ongoing improvement of this production process. A production-based tool condition was simulated by creating different cutting edge radii on the active tool elements. Collaring tests showed a reduction of residual formability through wear of up to 65% for high-strength heavy plates (plate thickness > 3 mm).

Due to the development of corrosion-resistant lightweight, todays automotive manufacturers typically use zinc coated sheet metals in the forming process. However, zinc abrasion in industrial presses decreases the process stability and often causes interruption of the whole process. The application of high strength steels leads to a significant increase of the temperature due to the plastic work. So far a detailed, quantitative analysis of the relation between temperature and zinc abrasion is not available. Therefore, this paper examines the impact of the temperature on abrasion behaviour in sheet metal processes. To achieve this, a progressive die was built. The deep drawing stage of this tool is connected to a cooling / heating system in order to obtain a constant temperature during the forming process. A variety of different galvanized sheet metals compared to commonly used tool materials has been tested. For each combination of materials five experiments at different temperatures were performed to determine the effect of the temperature on the zinc abrasion. Applying the method of total reflection x-ray fluorescence (TXRF) the quantity of zinc abrasion was measured. A relation between low temperatures and reduced zinc abrasion can be clearly observed. Industrial experiments revealed that temperature exerts a high influence on the zinc abrasion. The new insights into the impact of the temperature show a significant way to lower the zinc abrasion and therefore increase the process stability in deep drawing processes.

Round point clinching with rotational tool movement is a novel technique to join endless sheets of same or different metals in a quick and economic way. The main challenges are the asymmetry of the resulting clinch points as well as the non-perpendicular impact and retraction of the tools. To address these challenges, the material flow during the joint formation is closely examined. For this purpose an experimentally validated simulation strategy was developed. The influence of the process parameters on the material flow was then analyzed using this simulation model. Based on these crucial insights, an optimization approach is presented.

A thermal process window to form a stable metallurgical compound of AlSn6Cu and Al99.5 was obtained by initial experiments. A special mould system for a horizontal continuous composite casting process was developed, supported by finite element simulations. Preliminary 2D models were used to identify the main process variables influencing the temperature in the region where the compound is formed between the two layers. The thickness ratio of the layers and the initial temperature of the AlSn6Cu substrate strip were found to be the most important parameters. The special bilayer mould system was manufactured and implemented into an existing continuous casting device upgraded by a second furnace to hold the additional pure aluminium. A stable casting process was achieved. The quality of the manufactured compound was assessed by metallographic specimens cut from the obtained bilayers. Based on temperature measurements, a full 3D finite element model was developed to gain a more realistic description of the temperature and fluid flow conditions in the composite casting, especially in the margin regions.

Composite castings exhibit high residual stresses, mainly because of different thermal expansion of the used materials. Similar to the in-cast cylinder liners in a motor block, a composite specimen, consisting of a steel insert and an aluminum cast surrounding, was analyzed by neutron diffraction. The temperature- and time-dependent change of lattice spacing and thus the strain evolution was investigated by in-situ experiments directly after casting and during the cooling of the part. Different cooling conditions were investigated using two different molds, namely a sand and a permanent (steel) mold, optimized for in-situ neutron diffraction.

The edge cracking sensitivity of AHSS and UHSS is quite challenging in the cold forming process. Expanding cut holes during flanging operations is rather common in automotive components. During these flanging operations the pierced hole is stretched that its diameter is increased. These flanging operations stretch material that has already been subjected to large amounts of plastic deformation, therefore forming problems may occur. An innovative cutting process decreases micro cracks in the cutting surface and facilitates the subsequent cold forming process. That cutting process consists of two stages, which produces close dimensional tolerance and smooth edges. As a result the hole expanding ratio was increased by nearly 100% when using thick high strength steels for suspension components

Austempered ductile iron (ADI) alloyed with 0.42% Mn and 0.72% Cu was heat treated in a mirror furnace and the phase transitions were studied in-situ by neutron diffraction. The heat treatment consisted of austenitisation at 920 degrees C and isothermal austempering at 400 degrees C, 350 degrees C and 300 degrees C, respectively. Due to the growth of ferrite platelets, the austenite content decreases rapidly at all temperatures within the first 15-20 min and reaches a stable plateau after 35 min (400 degrees C) to 80 min (300 degrees C).The carbon content of the residual austenite, which was monitored and characterised by the change of the lattice parameter, increases up to 1.6 wt.% caused by redistribution from the newly formed ferrite. While at higher austempering temperatures this takes place almost parallel to the phase transformation, at 300 degrees C the redistribution of carbon to austenite lags behind considerably.Furthermore the neutron data revealed an austenite peak asymmetry during austempering which is attributed to successive phase transformation. It results temporarily in two fractions of austenite, an initial low-carbon and an enriched high-carbon modification. (C) 2013 Elsevier Inc. All rights reserved.

Two basic types of load for the tool active elements can be distinguished for the shear cutting process of sheet metal. For high strength, brittle materials, the stamping punch will be exposed to distinctive oscillating axial dynamic loads as a result of abrupt released potential energy, from the tool active elements, the blanking tool and the stamping press, caused by a sudden cracking of the sheet. In contrast, when shear cutting ductile materials, sheet metal will be drawn into the die clearance and the resulting friction between the punch and the cut surface can cause high forces when pulling the punch out of the hole. When using punches featuring a complex cutting peripheral form, - not available as a standard part - it is necessary to decide between head and shank of the punch manufactured out of one part or a shaft without head, which is usually cheaper and can be manufactured by electro-erosive wire-cutting. In the second case, a linking element must be accepted, transferring the load transmission between shaft and tool. This linking element, realized by a form lock or traction, can be the reason for premature failure of the punch. The two described cases of load, in combination with lacking knowledge of the real load on the link as well as eligibility of different punch linking types for each case of loading, cause unnecessary cost in tool manufacturing by oversizing or punch fracture. For this, solid punches as well as joined punches with dowelled or screwed heads have been compared in systematic tests. Brazed and bonded punch heads have been involved in the test series as cost-efficient alternatives to custom punches. Collaterally, characteristic values have been determined for each type of punch in static and dynamic measurements. Especially impact absorption and stiffness of the connection represent non-destructive measureable values allowing a comparison of stamping punches in terms of their dynamic fatigue limit.

It is necessary to describe properly anisotropic material behavior for realistic numerical analyses of sheet metal forming processes. The implementation of many yield criteria in finite element analysis is very complicated. Various material tests are also required to determine yield function coefficients. Stress ratios and anisotropy coefficients are not constant during forming processes due to deformation induced anisotropy. This paper introduces a yield function using strain dependent plastic strain ratios and stress ratios. The main advantage is to fully utilize the data of uniaxial tensile tests. The described material behavior shows a significantly improved agreement with experimental data.

Driving, an incremental forming method, can be carried out on driving machines. In a past project, this traditionally manual manufacturing method was automated through performing manual manipulations and manufacturing identical parts by robot handling. An advancement of this automation scheme is to define a set of standard sheet metal parts and derive a manufacturing strategy by combining tracked strategies for these standard parts. In this paper, we present a method to derive manufacturing strategies for geometric variations of standard sheet metal parts. In addition, a model describing the relation between geometric and process parameters is built to improve transformed manufacturing strategies.

Blanking is one of the most widely used manufacturing technologies in sheet metalprocessing, because nearly each sheet must be trimmed out of a semi-finished part or has to beblanked after a forming process to get the precast part in the manufacturing chain. In general, a highquantity of blanked parts should be manufactured without reworking the tool. Therefore a capableprocess is indispensable to avoid inadequate part quality or premature failure of the tool because ofwear. The blanking process is affected by tool parameters, the press and the material properties ofthe blanked part.However, another important factor is the occurring temperature in the shearing zone of the sheetmetal due to the dissipation of nearly 95% of the plastic work during blanking and, in addition,frictional heating. This temperature impacts the blanking process features such as tool-wear andresulting cut edge quality. It has been presumed to be negligible by a lot of authors yet. In contrastsome publications with experimental and analytical research assume that the temperature reachesvalues up to 1000°C. Therefore, this report outlines a thermoelectric method to measure theresulting temperature distribution during the blanking process on the cutting edge of the blankingpunch. The feasibility of the investigated measurement concept is shown on a concrete example.

Kurzfassung Das Clinchen mit runden Stempeln und Matrizen zählt zu den wirtschaftlichsten Fügeverfahren für Blechwerkstoffe. Um die Taktzeit zu verringern und das Clinchen damit auch für das Fügen von Endlosprofilen im Durchlaufverfahren einsetzen zu können, bieten sich rotierende Werkzeugaktivelementen an. In diesem Beitrag wird die simulationsunterstütze Entwicklung eines Verfahrens zum Rundpunkt-Clinchen mit rotierenden Werkzeugen beschrieben.