ORIGINAL ARTICLE A flexible sheet-bulk forming demonstrator João P. Magrinho 1 & Maria B. Silva 1 & Paulo A.F. Martins 1 Received: 29 January 2019 /Accepted: 25 March 2019 /Published online: 5 April 2019 # Springer-Verlag London Ltd., part of Springer Nature 2019 Abstract Sheet-bulk forming (SBF) processes based on a combination of deep drawing and upsetting are being increasingly used to produce new sheet metal parts with significant changes in wall thickness to accommodate three-dimensional functional features such as solid bosses, teeth and ribs. The utilisation of sheet-bulk forming processes introduces additional complexity in the design, setup and costs of tooling due to the inherent high forces and complex material flow that easily lead to underfilling and failure in critical die regions. This paper is concerned with these issues and is focused on the development of a sheet-bulk forming demonstrator capable of replicating material flow and failure in sheet thickening, local sheet thickening and sheet injection operating conditions. The demonstrator combines sheet bending and upsetting operations with a flexible design concept based on the utilisation of active modular tool parts to allow different materials, geometries and tool concepts to be tested under laboratory conditions and rapidly transferred to industrial SBF tools. Keywords Sheet-bulk forming . Tool demonstrator . Bending . Upsetting . Experimentation . Finite element method 1 Introduction In the last years, there has been an increasing demand for sheet metal forming parts with three-dimensional functional fea- tures to be produced by a combination of sheet and bulk forming operations. The combination of plane stress states of sheet forming and three-dimensional stress states of bulk forming throughout a production process falls under what is currently designated as ‘sheet-bulk forming’ [1] or ‘plate forg- ing’ [2]. The main advantage of sheet-bulk forming (SBF) over con- ventional sheet forming is the possibility of integrating two or more functional features in a single sheet part to reduce weight, to minimise the number of individual parts in a com- ponent and to reduce the overall costs of assembly and main- tenance. Figure 1 shows two examples taken from the auto- motive industry in which it is possible to identify the different types of material flow that will be considered in this investi- gation; (i) thickening, (ii) local thickening and (iii) injection. These three different types of material flow are the basis for producing sheet metal parts with local functional features placed outside the plane of the blanks from which they were produced, such as solid bosses, teeth and ribs. Figure 1 a shows a belt pulley of an engine accessory with material injection and thickening of the wall cup. Figure 1 b shows a gear drum with thickening of the wall cup plus local- ised thickening in the teeth located along the perimeter. Thickening and local thickening in SBF were first investigated by Maeda and Araki [ 3] who proposed the combined utilisation of deep drawing and upsetting to fabricate drum gears. The upsetting is schematically shown in the leftmost drawing of Figure 1 c and allows integrating teeth or other power and torque actuators in deep drawn or bended sheet parts. Figure 1 c also shows the possible defects arising from SBF, namely the occurrence of folding and buckling in the cup corner and side wall in case of thickening and local thick- ening [4] and the appearance of cracks and flaws in case of injection. Improvements in formability and decrease in the upset compression force, which is generally high in SBF, can be attained from damage analysis [5], multi-objective optimisa- tion [6] and heating the blanks prior to forming [7] at a cost of increasing the process chain runtime. * Paulo A.F. Martins pmartins@tecnico.ulisboa.pt João P. Magrinho joao.magrinho@tecnico.ulisboa.pt Maria B. Silva beatriz.silva@tecnico.ulisboa.pt 1 IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal The International Journal of Advanced Manufacturing Technology (2019) 103:1405–1417 https://doi.org/10.1007/s00170-019-03637-x