Milan Vucetic

Manufacturing of functional elements by sheet-bulk metal forming processes

Due to increasing economic and ecological restrictions, conventional sheet and bulk forming operations often reach their limits with regard to part weight and functional integration. One solution to meet those challenges is provided by sheet-bulk metal forming (SBMF) processes. SBMF is defined as the application of bulk forming operations on sheet metal. SBMF can be combined with conventional sheet forming operations and offers the opportunity to form highly functional integrated parts out of sheet metal. It contains the benefit of an optimization of the part weight and a shortening of the process chain. Recent research has found different solutions regarding the actual implementation of SBMF in several process variants. In this paper, a categorisation for functional elements on sheet metal parts is proposed. A selection of possible approaches for their manufacturing is presented. The process variants are compared by means of the main process characteristics. By these means, the choice of a suitable option shall be facilitated for practical manufacturing design and for a particular relevant product.

Experimental Test and FEA of a Sheet Metal Forming Process of Composite Material and Steel Foil in Sandwich Design Using LS-DYNA

A structural concept in multi-material design is used in the automotive industry with the aim of achieving significant weight reductions of conventional car bodies. In this respect, the specific use of steel foils and continuous fiber-reinforced thermoplastics represents an interesting material combination for the production of hybrid parts in sandwich design. This contribution deals with the experimental and numerical analysis of a conventional sheet metal forming process using a composite material based on Polyamide 6 (PA6) with unidirectional endless glass fiber reinforcement and HC220Y+ZE steel foil. A unidirectional composite plate is positioned between two steel foils in sandwich design and formed under appropriate temperature conditions. For the numerical analysis of the forming process the software LS-DYNA is used.

FEA-Based Optimisation of a Clinching Process with a Closed Single-Part Die Aimed at Damage Minimization in CR240BH-AlSi10MnMg Joints

The paper presents results of FEA-based optimisation of the tool design of a clinching process with a closed single-part die. The studied materials are the bake-hardening steel CR240BH, 1.5 mm thick, on the punch side and the die-cast aluminium alloy AlSi10MnMg, 2.95 mm thick, on the die side. The optimisation was aimed at suppression of cracks that appear at the bottom of the clinch joint in AlSi10MnMg in the case of using conventional tool designs. By varying geometry parameters of the tools it was possible to reduce crack probability, though along with slightly worse, but still acceptable geometry parameters of the clinch joint.

Numerical and Experimental Investigations of Multistage Sheet-Bulk Metal Forming Process with Compound Press Tools

Sheet-bulk metal forming is a manufacturing technology, which allows to produce a solid metal component out of a flat sheet. This paper focuses on numerical and experimental investigations of a new multistage forming process with compound press tools. The complete process sequence for the production of this solid metal component consists of three forming stages, which include a total of six production techniques. The first forming stage includes deep drawing, simultaneous cutting and following wall upsetting. In the second forming stage, flange forming combined with cup bottom ironing takes place. In the last stage of the process sequence, the component is sized. To investigate and to improve process parameters such as plastic strain distribution, resulting dimensions and process forces, FEA is performed. Based on these results the developed process is designed.

Production of Patient-Individual Hip Cups by Sheet Metal Forming: Simulation-Based Planning and Metal Forming Adapted Design Method

Total hip arthroplasty (THA) is a routine procedure for the treatment of advanced hip joint damage. The long-term result of the prosthesis is mainly determined by migration or aseptic loosening caused by bone remodelling. Especially the migration of the artificial hip cup as a consequence of the remodelling process is a major problem. Patient-specific hip cups can be used to counteract this. However, individual hip cups are currently only implanted for the treatment of great deformations or tumours in the hip joint due to the cost-intensive manufacturing. The aim of this project is the development and establishment of a concept for the economical production of patient-individual prosthetic hip cups out of titanium sheets. This process consists of two steps. First, undersized cups of a universal acetabulum geometry are produced. In the second step a true-to-size enlargement of the produced universal cup prothesis is carried out by means of a modified adaptive rubber-die forming process. The development of this process is accompanied by a simulationbased planning of the production process as well as by a realization of a metal forming adapted design method. For the examination of the feasibility of the concept, CT-data of canine pelvis geoemtries are used because of the large number of CT data, which were aviable for the project. Furthermore it is planned, that the first manufactured prototypes will be tested using canine cadaver. In this study the planning of the manufacturing of the standardized titanium sheet metal components is carried out. For this two methods of producing the standardized hip cup were compared. The first method is a hydraulic forming; the second is a normal pressing process with a bunch die and a binder. Pure titanium was introduced in the simulation, which shows the same mechnical properties like the in prosthetics normally used titanium alloy TiAl6V5. The results of the process simulation of both methods showed that the reducing of the blank thickness is a problem of the manufacturing of the prosthesis. Because of that an adaption of the tool geometry was executed and the influence of the increase of the forming temperature at 200 C was examined. These simulations indicated, that the hydraulic forming seems to be a convenient method to produce the prosthetic acetabulum. The first part of the metal forming adapted design method is the deduction of a universal acetabulum geometry, which has to be designed for the production of the standardized component. This deduction shall be realized by means of a superposition of 3D models of pelvis geometries. For this, two different superposition methods were compared and the Best Fit method was determined as the suitable method. By means of the Best fit method a first universal geometry was created.

Influence of Superimposing of Oscillation on Sheet-Bulk Metal Forming

Due to novel processes like sheet-bulk metal forming, the requirements for sheet metal forming are increased. Sheet-bulk metal forming is a new interconnected process in which the part itself is manufactured by deep drawing and the gearing will be produced with bulk forming in a combined process at room temperature. This process is characterized by a triaxial state of stress and a triaxial dimensional change with true strains up to  = 1-2 by using sheet blanks. Within the use of superimposing of oscillation on a sheet-bulk metal forming process the required forming force can be reduced and the accuracy of dimension of the part can be improved. Within this paper the influence of the superimposing of oscillation on the sheet bulk metal forming will be shown on combined ironing and external extrusion process. For the superimposing of oscillation different excitation frequencies will be analysed. Furthermore the die clearance will be varied to increase the requirements on the process. Finally the influence of the different excitation frequencies and the different die clearances will be summarized in cause and effect relationship diagram.

Material Characterization for Sheet-Bulk Metal Forming

Sheet-bulk metal forming is a novel manufacturing technology, which unites the advantages and design solutions of sheet metal and bulk metal forming. To challenge the high forming force the process is superimposed with an oscillation in the main flow of the process. The paper focuses on the characterization of the material behavior under cyclic load and the effects for the sheet bulk metal forming process.

Development of a Hydraulic Actuator to Superimpose Oscillation in Metal-Forming Presses

A novel principle of a rotary piston valve and a high-frequency cylinder for a hydraulic actuation system are presented. This system will be utilized in metal-forming presses to superimpose a high-frequency oscillation on the movement of the ram. This technique was proven to enhance the forming parts quality, to extend the process limits and to reduce the forming force significantly. The key components of the valve are a stator and a rotary piston with radial drilled holes that is designed to provide a pulsating pressure and mass flow rate at a high frequency. A hydraulic cylinder is connected to the valve and converts the pulsating flow into a dynamic process force. The valve and the cylinder will be mounted on the bolster plate of a metal-forming press. In order to superimpose oscillation in the main forming direction, the cylinder is centered under the punch of the metal-forming tool. Three-dimensional computational fluid dynamics (CFD) simulations have been conducted to evaluate and to optimize the designs of the main components of the system. Hereby the commercial simulation code of ANSYS CFX was employed to determine the properties of the cylinder and the valve. Through its mesh motion technique, this simulation code allows the flow analysis between the rotary and the stationary part of the valve. Furthermore the dynamic characteristics of the system have been investigated under the influence of inertia and the compressibility of oil.

Superimposed Oscillating and Non-Oscillating Ring Compression Tests for Sheet-Bulk Metal Forming Technology

The new manufacturing technology sheet-bulk metal forming (SBMF) combines the sheet metal forming and bulk metal forming techniques. At the Institute of Forming Technology and Machines (IFUM), a new multistage SBMF process is being developed. In order to reduce the friction and improve the dimensional accuracy of the parts, superimposed oscillation is used within the new SBMF process. SBMF processes allow the manufacturing of solid metal components out of flat steel. To analyse the effect of friction on the superimposed oscillating SBMF process more precisely, superimposed oscillating and non-oscillating ring compression tests at room temperature were carried out. Like the semi-finished products for SBMF process the ring specimens were cut out of a sheet plate by water jet cutting. A new tool system with an integrated hydraulic oscillation system was developed for superimposed oscillating compression of the ring specimens. This tool system enables the absorption of the forming force and displacement stroke of the ring specimen during the ring compression test. After the practical experiments, the force profiles of superimposed oscillating and of non-oscillating process were compared. The influence of the frequency on the surface roughness of ring specimens was investigated. Furthermore, the tribological conditions of the superimposed oscillating ring compression test were analyzed.

Evaluation of common tests for fracture characterisation of advanced high-strength sheet steels with the help of the FEA

The paper presents results of evaluation of common tests for fracture characterization of advanced high-strength sheet steels with the help of the FEA. The tests include three in-plane shear tests, two uniaxial tension tests, two plane strain tension tests and two equibiaxial tension tests. Three high-strength steels with different yield loci, strain hardening rates and strengths in three different thicknesses each were used. The evaluation was performed based on the spatial distribution of the equivalent plastic strain and damage variable in the specimen at the moment of crack initiation as well as on the time variation of the stress state at the crack initiation location. For in-plane shear, uniaxial tension and plane strain tension, no test can be unconditionally recommended as disadvantages of all studied tests in these groups cannot be neglected. However, in each of these groups, a test can be chosen, which represents an acceptable compromise between its advantages and disadvantages: the shear test on an IFUM butterfly specimen for in-plane shear, the tensile test on a holed specimen for uniaxial tension and the tensile test on a waisted specimen for plane strain tension. On the contrary, the bulge test on a circular specimen with a punch of O 100 mm can be unconditionally recommended for equibiaxial tension. In the future, optimisation of the studied tests for in-plane shear, uniaxial tension and plane strain tension appears to be necessary.