Sheet metal forming processes allow for production of lightweight and durable goods. For this reason, drawing operations have been widely used across the automotive, aviation and construction industries and for production of various components of machines. Despite the popularity of deep-drawing steel sheet metal, non-ferrous materials, such as aluminium, magnesium and titanium are also used for such purposes. Titanium materials seem to be particularly attractive due to a beneficial ratio of strength to density and excellent corrosion resistance in the most of technological environments. However, titanium and its alloys belong to a group of materials with low tribological properties and tendencies for galling and build-up of layers of the deformed material on the tool surface. Therefore, this study will discuss the results of the investigations concerning selection of technological lubricants based on vegetable oils used for the operation of forming of sheet metal made of commercially pure titanium (Grade 2). The focus of the experiment is on lubricants based on vegetable oils i.e. rapeseed oil, sunflower oil and olive oil. The main lubricating additive was boric acid and stearic acid. The study presents the results of the determination of friction coefficient during a strip drawing test.

The paper evaluates the drawability of titanium sheet metal Grade 2, with the focus on friction conditions that are present in the sheet metal forming process. The study aims to present the results of the examinations of the friction coefficient during a strip drawing test. The focus of the experiment was on lubricants based on vegetable oils i.e. rapeseed oil, sunflower oil and olive oil. Boric acid was used to improve the lubricating properties of vegetable oils. The results of numerical simulations of the process of forming a cover with stiffening components made of grade 2 titanium sheet metal was also presented. The numerical simulation was carried out using the FEM method with PAMStamp 2G software. The effect of conditions of friction between the sheet metal and tool parts and pressure force of the blank holder on the forming process were investigated. Numerical calculations were performed with consideration for the phenomenon of material strain hardening and anisotropy of plastic properties of the sheet metal formed. The analysis of the deformations and reduction in wall thickness of the drawn parts can be used for determination of the effect of changes in selected parameters on the process of drawn part forming. The quality of drawn parts was assessed based on the shape inaccuracy determined during simulation of forming. The inaccuracy depended on the conditions of the process and strength properties of the titanium sheet metal.

ExpErImEntal and thEorEtIcal dEtErmInatIon of formIng lImIt curvE DoświaDczalno-teoretyczne wyznaczanie krzywej oDkształceń granicznychThe paper presents a method for determining forming limit curves based on a combination of experiments with finite element analysis. In the experiment a set of 6 samples with different geometries underwent plastic deformation in stretch forming till the appearance of fracture. The heights of the stamped parts at fracture moment were measured. The sheet -metal forming process for each sample was numerically simulated using Finite Element Analysis (FEA). The values of the calculated plastic strains at the moment when the simulated cup reaches the height of the real cup at fracture initiation were marked on the FLC. FLCs for stainless steel sheets: ASM 5504, 5596 and 5599 have been determined. The resultant FLCs are then used in the numerical simulations of sheet -metal forming. A comparison between the strains in the numerically simulated drawnparts and limit strains gives the information if the sheet -metal forming process was designed properly.

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IntroductionIn addition to the existing trend towards the development of lightweight and durable materials used in aviation, there is the desire to design and manufacture aircraft structures of sheet metal. Among the various production techniques, only sheet-metal forming enable the production of thin-walled components with high strength [1][2][3][4]. According to [5,6], the tribological properties of the deformed materials and the friction conditions are important factors determining the results of sheet metal forming, particularly in the deep drawing process. Friction increases the drawing force, and as a result deteriorating energy efficiency of the process. High friction resistance at the blank holder -blank -die interface causes a rise in the drawing force and increases the risk of cracking of the drawn part, which has particular significance in forming sheets of small thickness [7]. Additionally, friction has an impact on the strains distribution in the drawn part as well as on the changes in the thickness of its walls [8].The negative effects of frictional forces are uneven strain, temperature rise in the workpiece -tool interface and lubrication deterioration, which in turn affects the quality of the drawn parts and tool life. The set of tribological processes occurring during formation in the tool contact zone, including mechanical and adhesional friction surface interaction as An important factor in the possibility of obtaining correct drawn parts with the desired functional properties is the friction between the stamped sheet and the tool.The article discusses the impact of technological lubricants developed according to our own formulas, based on vegetable oils, on the stamping process taking into account the strain distributions in the drawn parts. Biodegradable lubricants based on rapeseed oil with an addition of stearic acid or boric acid were used. The results of the friction coefficient in a strip drawing test and the numerical analysis results of the stamping process of a spherical cap from sheet metal: aluminium 2024, commercially pure titanium Grade 2, steel 5604 in dry friction and lubrication conditions, are presented. Strain distributions and changes in the drawn part wall thickness were analysed.