The evolution and future of manufacturing: A review

A review on tailored blanks—Production, applications and evaluation

Hot stamping of ultra-high strength steel parts

A review on functionally graded structures and materials for energy absorption

The paper deals with the testing and modelling of metals response when subjected to sheet forming operations. The focus is both on the modelling of hardening behaviour and yield criteria and on the description of the sheet metal formability limits. Within this scope, the paper provides a critical review of the models available today for predicting the material behaviour at both industrial and scientific level, and the tests needed to identify the models’ material parameters. The most recent advances in the field are also presented and discussed with particular emphasis on the challenges the sheet metal forming community is now facing.

Testing and modelling of material behaviour and formability in sheet metal forming

Time dependent determination of forming limit diagrams

The ISO standard 12004-2:2008E for the determination of forming limit curves based on the section method was approved in 2008. About 4 years of measuring experience in different laboratories has shown advantages and weaknesses of the standard and is leading to some minor changes in the specification. In the years from the development of this standard until today a further technical development of the optical measuring devices occurred, so that it is now possible to determine forming limit curves using the time history of the test. This procedure of determination is referred to a time dependent technique and could be the basis of the ISO 12004 part 2 proposal worked out by the work group Erweiterung FLC ISO 12004 of the German group of the IDDRG. This publication recapitulates existing work which was carried out from the IDDRG work group regarding the determination of forming limit curves for sheet metal materials. On one hand known issues with the current section based approach are discussed and on the other hand it deals with a comparison of different algorithms to determine the FLC from the time history of the Nakajima test using strategies to identify the instant of onset of instable necking. The different time dependent algorithms [ utilised are automatically selecting the area where necking is leading to fracture and then analyze the time history of such points using the first or the second time derivative of the true major strain, or of the true thinning strain using methods like: correlation coefficient (modified method based on [2]), gliding correlation coefficient, linear best fit (modified method based on [3]) and gliding difference of mean to median. The resulting experimental FLC points are compared with the results from the section technique described in ISO 12004 part 2 and with the maximum strain values measured in each test. Further a large number of forming limit curves were determined and used for a comparison of these different methods to define the most promising time dependent algorithm, which was selected as a suggestion for the working group defining the new proposed ISO standard 12004 part 2.

Time Dependent FLC Determination Comparison of Different Algorithms to Detect the Onset of Unstable Necking before Fracture

The layer compression test is used in the field of material characterization to determine the onset of yielding and the hardening behavior of a sheet metal within uniaxial compression loading. For testing anisotropic materials the experimental setup has to be adjusted and the evaluation has to be adapted. This could be achieved with the installation of a second optical strain measurement system to get data of both symmetry axes. In the following paper the experimental procedure with two strain measurement systems and the evaluation methodology regarding the two sets of data will be presented and validated with experimental results. The advantage of the layer compression test is discussed in comparison with the results of a standard tensile test.

A method for the layer compression test considering the anisotropic material behavior

Ti-6Al-4V is one of the most frequently used titanium alloy in aerospace applications such as for load carrying engine structures, due to their high strength to weight ratio in combination with favourable creep resistance at moderate operating temperatures. In the virtual development process of designing suitable thermo-mechanical forming processes for titanium sheet metal components in aero engine applications numerical finite element (FE) simulations are desirable to perform. The benefit is related to the ability of securing forming concepts with respect to shape deviation, thinning and strain localisation. The reliability of the numerical simulations depends on both models and methods used as well as on the accuracy and applicability of the material input data. The material model and related property data need to be consistent with the conditions of the material in the studied thermo-mechanical forming process. In the present work a set of material tests are performed on Ti-6Al-4V at temperatures ranging from room temperature up to 560°C. The purpose is to study the mechanical properties of the specific batch of alloy but foremost to identify necessary material model requirements and generate experimental reference data for model calibration in order to perform FE-analyses of sheet metal forming at elevated temperatures in Ti-6Al-4V.

Andreas Kuppert

Papers

A review on tailored blanks—Production, applications and evaluation

Time dependent determination of forming limit diagrams

Time Dependent FLC Determination Comparison of Different Algorithms to Detect the Onset of Unstable Necking before Fracture

A method for the layer compression test considering the anisotropic material behavior

Thermo-mechanical sheet metal forming of aero engine components in Ti-6Al-4V – PART 1: Material characterisation