New method of producing tailored blanks with constant thickness

The concept of weight-saving in automotive manufacture by using tailored blanks is well established. The methods used to produce extra strength in particular areas of the blank can be based either on increasing material thickness in those areas or keeping the thickness constant but varying the material properties. Typically the first option is used by welding blank patches of different thickness. From the view point of forming blanks into sheet metal products uniform thickness is less problematic and it can be achieved by welding different materials of the same thickness or localised heat treatment. However, these approaches have major limitations: welding introduces discontinuity in material structure and properties while selective heat treatment is difficult to control. A new, original method presented here is based on a local shear deformation of the blank material. The particular process used is incremental equal channel angular pressing. The proposed approach is simulated using finite element modelling and then experimentally verified by producing a constant thickness pure aluminium strip with varying hardness. A discussion of different variants of this approach indicates its potential

Wytwarzanie wielofunkcyjnych blach do tłoczenia za pomocą przyrostowego odkształcania w kanale kątowym : Production of tailored blanks by Incremental ECAP

The paper reviews the current methods of producing tailored blanks (TBs), together with the areas of applications and possible problems. A new method of producing TBs, based on simple shear, has been proposed. It is a variant of the process, which originally has been developed as a means of refining grain structure of metals by Equal Channel Angular Pressing (ECAP). Further development of ECAP towards an incremental version of this process (I-ECAP) enables processing very long billets and varying their thickness. Taking advantage of the latter, two different experimental rigs have been built in order to check feasibility of producing TBs by I-ECAP. TBs produced in this way have been named Tailored Sheared Blanks (TSBs). Finite element simulation of the process realised on one of these rigs provided an insight into the mechanism of changing blank thickness and strain distribution. The proposed method has several advantages such as lack of welding seams, possibility of thinning as well as thickening initial blanks, creation of thickness steps on both sides of the blank and flexible length of thickness transition

Incremental non-equal channel angular pressing - FE simulation

Equal channel angular pressing is the most popular process of severe plastic deformation used to refine grain structure in metals in order to improve their properties. One of the features of severe plastic deformation is lack of change of billet's shape and dimensions. However, for practical reasons, departure from this pure definition might be useful. This paper considers a possibility of changing billet's cross section in the first pass of the incremental version of equal channel angular pressing from round to rectangular to avoid material loss when machining the initial billet. The process has been simulated using a finite element program Abaqus. This simulation showed feasibility of the process and provided information regarding tool geometry and required forces

Modelling microstructure evolution during equal channel angular pressing of magnesium alloys using cellular automata finite element method

Equal channel angular pressing (ECAP) is one of the most popular methods of obtaining ultrafine grained (UFG) metals. However, only relatively short billets can be processed by ECAP due to force limitation. A solution to this problem could be recently developed incremental variant of the process, so called I-ECAP. Since I-ECAP can deal with continuous billets, it can be widely used in industrial practice. Recently, many researchers have put an effort to obtain UFG magnesium alloys which, due to their low density, are very promising materials for weight and energy saving applications. It was reported that microstructure refinement during ECAP is controlled by dynamic recrystallization and the final mean grain size is dependent mainly on processing temperature. In this work, cellular automata finite element (CAFE) method was used to investigate microstructure evolution during four passes of ECAP and its incremental variant I-ECAP. The cellular automata space dynamics is determined by transition rules, whose parameters are strain, strain rate and temperature obtained from FE simulation. An internal state variable model describes total dislocation density evolution and transfers this information to the CA space. The developed CAFE model calculates the mean grain size and generates a digital microstructure prediction after processing, which could be useful to estimate mechanical properties of the produced UFG metal. Fitting and verification of the model was done using the experimental results obtained from I-ECAP of an AZ31B magnesium alloy and the data derived from literature. The CAFE simulation results were verified for the temperature range 200-250 °C and strain rate 0.01-0.5 s-1; good agreement with experimental data was achieved

Wytwarzanie wielofunkcyjnych blach techniką ścinania

Incremental shear has been used to vary blank properties along the sheet plane. The feasibility of the method has been investigated to manufacture so called Tailor Sheared Blanks featuring property distribution of the blank without thickness variation. Mechanical properties resulting from evolution of coarse grain microstructure towards ultra fine grain one can be achieved. Tool configuration, experimental procedure, simulation using finite element method and preliminary trials of producing tailored blanks by incremental shear were described

Tailored sheared blanks produced by incremental ECAP

Incremental equal channel angular pressing (I-ECAP) is a process used for production of continuous ultrafine grained bars, plates and sheets. Normally the thickness of the processed billet is kept unchanged in consecutive passes to enable repetitive insertion into the same die. This is achieved by controlling the bottom dead centre of the reciprocating punch. However, if a final product requires being thinner and therefore longer, the bottom position of the punch can be lowered before the last pass. Going further, the bottom position of the punch can be changed during the process, which opens up a possibility to vary billet thickness along its length. Such a product, especially sheet, can serve as a preform for further metal forming operations and is known as tailored blank. This paper will show examples of varying thickness sheets produced by different configurations of I-ECAP. Experimental and finite element results will be presented

Determination of friction factor by ring compression testing and FE analysis

The goal of this study was to examine performance of various lubricants for aluminium alloy AA5083. Conventional ring compression tests were conducted at 200 °C. Samples were compressed to 50% of the initial height with a constant ram velocity 0.5 mm/s using a servo-controlled hydraulic press. The optimization procedure was implemented in self-developed software to identify friction factors from experiments. The application launches remotely finite element (FE) simulations of ring compression with a changing friction factor until a difference between experiment and numerical prediction of the internal diameter of the sample is smaller than 0.5%. FE simulations were run using Forge3 commercial software. The obtained friction factor quantitatively describes performance of a lubricant and can be used as an input parameter in FE simulation of other processes. It was shown that application of calcium aluminate conversion coating as pre-lubrication surface treatment reduced friction factor from 0.28 to 0.18 for MoS2 paste. It was also revealed that commercially available graphite-based lubricant with an addition of calcium fluoride applied on conversion coating of calcium aluminate had even lower friction factor of 0.1

Microstructure and mechanical properties of friction stir welded joints made from ultrafine grained aluminium 1050

In order to obtain ultrafine grained structure, commercially pure aluminium (Al 1050) plates were subjected up to 8 passes of Incremental Equal Channel Angular Pressing (IECAP) following route C. Plates in different stages of IECAP were joined using Friction Stir Welding (FSW). All welded samples were investigated to determine their mechanical properties and structure evolution in the joint zone. The joining process reduced mechanical strength of material in the nugget zone, which was explained by the grain growth resulting from temperature rise during FSW. Nevertheless, the obtained results are promising in comparison to other methods of joining aluminium

In situ analysis of the influence of twinning on the strain hardening rate and fracture mechanism in AZ31B magnesium alloy

The influence of twinning on the strain hardening rate and fracture mechanism in AZ31B magnesium alloy was studied in this work by in situ microstructural analysis during tensile testing in a chamber of scanning electron microscope. Three types of samples used in this study were obtained by (1) extrusion (as-supplied), (2) I-ECAP and (3) I-ECAP followed by side upsetting. Microstructures, textures and mechanical properties were examined after each processing step. An analytical equation was used to describe flow stress curves of the samples which exhibited various modes of deformation (1) only by slip, (2) dominated by tensile twinning followed by slip and (3) dominated by contraction twinning followed by slip. It was shown that tensile twinning increases strain hardening rate, while the opposite is observed for contraction twinning. The effective Schmid factors for slip in volumes deformed by tensile and contraction twinning were determined in this work using modelling approach as 0.215 and 0.45, respectively. Contraction twinning was also revealed to be responsible for an earlier fracture of the extruded sample subjected to tension, since microcracking was shown explicitly to be initiated within twins

Incremental ECAP as a method to produce ultrafine grained aluminium plates

In this work, we propose a new approach to producing ultrafine grained plates using a modified ECAP method, namely incremental ECAP. Unlike conventional ECAP, incremental ECAP works step by step whereby deformation and feeding are performed with two different tools acting asynchronously. Incremental processing reduces forces and allows to process relatively large billets. The major advantage of this technique is that the specimens are in the form of plates with a rectangular shape, which makes them suitable for further processing, e.g. via deep drawing. This paper reports a study on microstructure development, mechanical properties and their anisotropy in aluminium plates processed by means of incremental ECAP. Eight passes applied (with the accumulated strain of 9.2) with the rotation about the Z axis brought about the reduction in the grain size down to 600 nm with the 80% fraction of high angle grain boundaries and a very homogenous equiaxial microstructure. This, in turn, resulted in a significant increase in mechanical strength with the ultimate tensile strength reaching 200 MPa and, more importantly, very low anisotropy with respect to the rolling direction