ALBERT

Description: Single Point Incremental Forming (SPIF) has great potential as it can be easily implemented and the forming process does not require the use of dies. However, its application to high performance alloys such as Ti6Al4V has not been resolved due to its characteristic low formability. In the literature, studies on the warm SPIF process applied to this alloy report improved formability. However, in some of these studies the procedures used are complex and in others the surface finishes obtained are unsatisfactory. The present study proposes a methodology consisting of a simple heating device which permits working at moderate temperatures and quantifies the benefit of the temperature on the alloy formability, the forces acting during the process, and finally the dimensional precision of the parts produced. Working temperatures in the range of 300–400 °C significantly reduce forces, increase formability of the alloy, and substantially reduce springback. However, the springback values suggest the need for dimensional compensation at the design stage of products.

Description: Titanium is one of the most interesting materials in modern manufacturing thanks to its good mechanical properties and light weight. These features make it very attractive for use in the aeronautical and aerospace industries. Important alloys, such as Ti6Al4V, are extensively used. Nevertheless, titanium alloys present several problems in machining processes. Their machinability is poor, affected by low thermal conductivity, which generates very high cutting temperatures and thermal gradients in the cutting tool. Lubricants and cutting fluids have traditionally been used to solve this problem. However, this option is unsustainable as such lubricants represent a risk to the environment and to the health of the operator due to their different chemical components. Therefore, novel, sustainable and green lubrication techniques are necessary. Dry machining is the most sustainable option. Nevertheless, difficult-to-machine materials like titanium alloys cannot be machined under these conditions, leading to very high cutting temperatures and excessive tool wear. This study is intended to describe, analyse and review the non-traditional lubrication techniques developed in turning, drilling and milling processes since 2015, including minimum quantity of lubricant, cryogenic lubrication, minimum quantity of cooling lubrication or high-pressure coolant. The aim is to provide a general overview of the recent advances in each technique for the main machining processes.

Description: The consideration of anisotropic and asymmetric tension-compression behaviour in some materials has proved to be of great importance for the modelling of plastic behaviours that allow for accurate results in sheet metal forming analysis. However, obtaining this compression behaviour of a sheet metal in the principal plane directions is one of the most complex aspects from an experimental point of view. This complexity is notably increased when this behaviour needs to be analysed under high temperature conditions. This paper presents a compression test system with load application in the in-plane sheet directions which is characterised by a relative technical simplicity allowing its application under temperature conditions of up to 750 °C and different strain-rates. Due to the specific test conditions, namely the high temperature, it is not possible to use the common systems for measuring the strains involved and to obtain the stress-strain curve. Therefore, this paper proposes two methods for this purpose. The first is the performance of interrupted tests and measurement of the central cross sections. The second consists of inverse calibration using finite element simulations. The sensitivity of the proposed test methodology is validated through the characterisation, at room temperature, of the compression and tensile behaviour of six materials with different plastic deformation phenomena. In this way, the asymmetric tension-compression phenomena are accurately identified and high compression strains of around 0.3, higher than those existing in the literature, are investigated. A novel test methodology is thus established that is easily applicable for the mechanical characterisation of sheet metal at high temperature.