Sheet-bulk Metal Forming Processes Research Articles

Investigation of the Influence of a Superimposed Oscillated Forming Process on Forming Characteristics

The increasing demand for resource-efficient production methods is driving the development of new technologies. Sheet bulk metal forming (SBMF) offers the possibility to combine sheet metal and bulk forming operations. This allows the production of complex functional components with secondary forming elements from sheet metal. Compared to other production techniques such as machining, a more efficient use of material can be achieved. Further advantages are a near net shape production and increased strain hardening. SBMF processes are limited by forming technology boundaries. These include high forming forces, incomplete mould fillings and limited surface qualities. In this research, the possibility of enhancing the material flow, improving surface quality and reducing the tool loads in SBMF-processes is investigated by using a superimposed oscillation. The focus here is on achieving a high surface quality of components produced by forming technology and an enhanced material flow during forming. For this purpose, a forming process for ironing an axial gear geometry is superimposed with an oscillation in the main force flow.

Influence of Tailored Surfaces and Superimposed-Oscillation on Sheet-Bulk Metal Forming Operations

Producing complex sheet metal components in fewer process steps motivated the development of the innovative forming process called sheet-bulk metal forming (SBMF). In this process, sheet metal forming and bulk-metal forming are combined to create a unique forming process in which a component with external and internal gearing is produced in three production steps. However, the high degrees of deformation that occur using high-strength steels and the number of different process steps result in high process forces, strongly limiting the service life of tools. To reduce the forming force during SBMF processes, tool and process modifications were investigated. Therefore, plane-strain compression tests were conducted to examine the influence of a CrAlN PVD coating and tailored surfaces produced by high-feed milling (HF) of tool-active elements on the material flow of the specimens. In addition to the tool-sided modifications, the influence of an oscillation overlay during the forming process was investigated. Based on the results of the compression tests, the surfaces of the active tool elements of the SBMF process were modified in order to transfer the basic experimental results to the production of a functional component. The friction is thus adapted locally in the SBMF process.

Comparison of extrusion processes in sheet-bulk metal forming for production of filigree functional elements

Increasing demands on forming processes with regard to the functional integration of components and lightweight construction pose a challenge to conventional processes. The application of bulk forming operations on sheet metal semi-finished products, also called sheet-bulk metal forming (SBMF), is a suitable approach to meet these challenges. Insufficient die filling and high tool loads are limiting factors in SBMF processes. In order to overcome these limitations in the future, it is necessary to provide appropriate measures. The basis for this is a comprehensive understanding of the manufacturing process for lock and gear toothing by extrusion on sheet metal. This paper identifies requirements for extrusion processes and establishes two corresponding processes. In addition to carrying out experimental investigations, numerical models are developed and validated with the aid of forming tests. In combination with experimental analysis, the simulation models are then used to investigate similarities and differences between both processes. During the processing of the steel 1.0338 (DC04), the investigations showcase a process class specific material flow, demanding tool loads and challenges in the production of filigree functional elements.

Tribological measures for controlling material flow in sheet-bulk metal forming

Sheet-bulk metal forming (SBMF) is characterized by successive and/or simultaneous occurrence of quite different load conditions regarding stress and strain states. These conditions significantly influence the material flow and thus the geometrical accuracy of the components. To improve the product quality a control of the material flow is required. An appropriate approach is given by locally adapted tribological conditions due to surface modifications of tool and workpiece, so-called tailored surfaces. Within the present study different methods to adapt the surfaces are presented and investigated with respect to their tribological effectiveness in SBMF. In a first step, requirements regarding necessary adaptions of the friction values for two SBMF processes are numerically defined. Based on the requirements different tailored surfaces are presented and analyzed regarding their tribological influence. Finally, the potential of surface modifications to improve SBMF processes is shown.

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.

Applicability of Blasted Blanks for Adaption of Tribological Conditions in Sheet-bulk Metal Forming

Manufacturing by sheet-bulk metal forming (SBMF) leads to varying stress and strain states that significantly influence the geometrical component accuracy. To improve the product quality, control of the material flow is needed. A suitable approach is given by adapting the surface properties of tool and/or workpiece and the associated tribological conditions. The study investigates blasted blanks as a method to achieve suitable frictional behavior. The influence of different grit sizes and pressures during abrasive blasting on the surface integrity was analyzed. Based on these results, the tribological behavior of the blasted blanks was evaluated using a pin extrusion test. Finally, functional cause-effect relationships to identify the mechanism of blasted blanks regarding a control of the material flow during SBMF processes were derived. The results revealed that a pressure increase and growing grit sizes lead to an enhanced material removal rate during blasting and thus a roughening of the surface. The strengthening increases with increasing blasting pressures and grit size. The surface integrity significantly influences the frictional behavior and thus the material flow. Thus, blasted blanks with rough surfaces and a high strengthening in the near surface area positively affect the material flow what improves the process results of SBMF processes.

A new test for determining the mechanical and fracture behavior of materials in sheet-bulk metal forming

This paper presents a new experimental test for determining the stress–strain curve and the fracture toughness of sheets to be used in sheet-bulk metal forming (SBMF) applications. The test is based on the utilization of double-notched specimens loaded in shear and combines the plane stress loading conditions of sheet metal forming with the three-dimensional plastic flow conditions of bulk metal forming, which are commonly found in SBMF processes. The methodology to obtain the stress–strain curve involves calculation of the shear stresses and strains along the two symmetric plastic shear zones of the test specimens up to point where cracks start to propagate along the ligaments that connect each pair of opposite notches. The determination of fracture toughness involves characterization of the evolution of load with displacement for a number of test cases performed with specimens having different ligaments between the two symmetric opposite notches. The work is performed on aluminium alloy EN AW 5754 H111 sheets with 5 mm thickness and the results obtained by means of the new proposed test are compared against those from conventional mechanical and fracture characterization tests.

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.

Analysis of Effectiveness of Locally Adapted Tribological Conditions for Improving Product Quality in Sheet-Bulk Metal Forming

Due to current ecological and economic developments there is a growing demand for functional components with complex and closely tolerated geometrical features. Conventional sheet and bulk metal forming operations leads to products which are often limited in their geometrical and functional variety. A promising approach is the process-class sheet-bulk metal forming (SBMF). SBMF is characterised by the application of bulk and sheet forming operations on sheet metals [1]. This combination leads to locally and temporally varying load conditions regarding stress as well as strain states. In order to get high quality parts, controlling the material flow is of major importance. Modified Surfaces, so-called tailored surfaces represent an innovative approach to control the material flow. The objective of the current study is the experimental investigation of the effectiveness of locally adapted tribological conditions using workpiece-and tool-sided tailored surfaces within SBMF processes. The study has shown that the local adaption of workpiece and tool surface increased the heights of functional elements. Thus, using locally adapted tribological conditions leads to an improvement of the quality of the produced gearing components. In a further step the influence of surface modifications on the surface properties of the manufactured components are analysed. Additionally, investigations regarding the wear behaviour of tool-sided surface adaptions lead to the assumption, that the effectiveness of tailored surfaces is reduced during the operating time of the tools.

Influence of Surface Modifications on Friction, Using High-Feed Milling and Wear Resistant PVD-Coating for Sheet-Metal Forming Tools

Increasing technological requirements, as well as the demand for an efficient production demands high performance materials and enhanced manufacturing processes. The development of a new manufacturing process, sheet-bulk metal forming (SBMF), is one approach to produce lightweight forming parts with an increased number of functional properties while, at the same time, combining the advantages of sheet and bulk metal forming. For SBMF processes, the specific adjustment of the friction between tool and workpiece for a specifically designed material flow, which is called tailored friction, is of great importance. The reduction of friction is essential in order to ensure a homogeneous forming zone. However, a higher friction can be used to control the material flow to increase the local thickness of the work piece for additional functional integration. This paper shows the development of surface structures for SBMF tools by means of high-feed milling. Process parameters like the tilt angle or the feed are varied to influence the surface parameters of the structures, which results in different tribological properties of the forming tool. The structured surfaces are subsequently coated with a wear resistant CrAlN coating, processed by a magnetron-sputtering process (PVD) to enhance the lifetime and performance of the forming tool. Finally, a ring compressing test is used to investigate the tribological behavior of the coated structures.

High-feed milling of tailored surfaces for sheet-bulk metal forming tools

The increasingly investigated and applied production process sheet-bulk metal forming (SBMF) has novel requirements for the forming tools, e.g., the need of an adaptive material flow at different areas of the tool for an adequate form filling. One new method to realize different, defined tribological conditions are tailored surfaces (TS). During the design of forming tools, it is imperative to have profound knowledge about the tribology between the tool and the workpiece. This article introduces structuring with high-feed milling tools as one possibility for influencing the material flow during forming processes and presents a ring-compression test for the quantification of the tribological conditions, which is adapted for SBMF. On the basis of various machined structures, surface parameters are analyzed to identify a correlation with the friction coefficient to gain knowledge about the mechanisms of TS and to be able to choose structures according to the needs of SBMF processes.